What are mechanisms that bacteria or pathogens use to cause disease?
Invasion - The process of microorganisms entering body tissue or host cells, surviving & spreading in the body. Toxigenicity - Production of microbial toxins that damage the host but aid in microorganism's survival. Immunopathology - Host's immune response causes damage to the host itself.
Give an example of a bacteria that uses toxigenicity to cause disease.
Clostridium tetani - Causes tetanus by production of tetanospasmin toxin, which causes muscle spasms. Prevents neurons from releasing inhibitory neurotransmitters GABA & glycine by degrading protein synaptobrevin. Results in FAILED INHIBITION of motor reflexes by sensory stimuli. Gram+ rod, anaerobic, spore-forming, found in soil & faeces.
Give an example of a bacteria that uses invasion to cause disease.
Brucella abortus - Causes Brucellosis in cattle by invading host cells. Gram (-), non-spore-forming, facultatively intracellular.
Give an example of a bacteria that uses immunopathology to cause disease.
Mycobacterium bovis or M. tuberculosis - Causes granulomatous response that damages lung tissue. Gram+ rod, aerobic, non-motile; replicates in alveoli of host.
What is pathogenicity?
The ability of an infectious agent to cause disease.
What is virulence?
The measure of a pathogen's ability to cause disease; how pathogenic something is.
What is pathogenesis?
The process of disease progression.
What is an opportunistic pathogen?
A pathogen only capable of causing disease when allowed to do so through particular circumstances of the host.
What is a commensal?
A microorganism that naturally resides on the body, causing no harm. In some cases, when immunity in the host is suppressed or compromised or ends up in the wrong area, a commensal can become pathogenic. Eg., E. coli is a commensal of the colon but becomes pathogenic if it gets into the urinary tract. Eg. Staphylococci is a commensal of the skin but can cause infection if skin is broken.
What is nosocomial infection?
Hospital-acquired infection. Eg., Bacteria tend to become more pathogenic in hospitals where a lot of antibiotics are used, resulting in resistant microorganisms.
What are the differences between Gram (+) & Gram (-) bacteria?
The distinction depends on the microorganism's response to Gram stain with crystal violet. Gram (+) bacteria stain purple because they have a thick peptidoglycan wall that absorbs and reacts with the stain. Gram (-) bacteria stain pink with counterstain because they have outer & inner membranes that sandwich the thin peptidoglycan cell wall, which doesn't pick up the crystal violet.
What are the main mechanisms employed by Gram+ bacterial exotoxins?
1. Digest surroundings / break down host tissue so bacteria can extract needed nutrients for survival and replication. 2. Damage host's immune system using neurotoxin or biological toxin.
Give some examples of exotoxins that are enzymes.
1. Phospholipase 2. Protease 3. Collagenase 4. Hyaluronidase - digests host proteins
Give some examples of Gram+ exotoxins that are neurotoxins/biological toxins and explain how they work.
1. Botulinum - produced by Clostridium botulinum; causes botulism. Prevents vesicles in neuromuscular junction from anchoring to neuron cell-membrane to release acetylcholine. Inhibition of Ach release at synapse results in FLACCID PARALYSIS. 2. Tetanus, aka tetanospasmin: produced by C. tetani; prevents affected neurons from releasing inhibitory neurotransmitters GABA & glycine, so muscles respond to just tiny sensory stimuli, tetanic spasms.
Give some examples of exotoxins that damage the host's immune system.
1. Leucocidins: kill white blood cells such as neutrophils, basophils, eosinophils, monocytes, lymphocytes, etc. These are produced by Staphylococcus & Streptococcus spp. 2. Antichemotaxins: Inhibit chemotaxis of neutrophils to site of infection. Eg., Chemotaxis Inhibiting Protein of S. Aureus (CHIPS) 3. C5a Protease: Cleaves potent neutrophil chemotaxin called C5a, which is produced by complement system. C5a peptidase, produced by Streptococcal progenes, is necessary to minimuse influx of neutrophils.
What are endotoxins and what type of bacteria produce them?
They are lipopolysaccharides (LPS) in the bacterial cell's outer membrane that don't do damage themselves but ignite host immune response (mainly cytokine response). They are kept "within" the bacteria cell membrane & only released after destruction of the bacteria cell wall, e.g. via detergent. The lipid part of cell membrane is the "endotoxin" & the hydrophilic"polysaccharide O side-chain" makes up the "O-antigen". Gram (-) bacteria ONLY are associated with endotoxins.
What mechanisms of pathogenicity do Gram (-) bacteria employ?
1. Adhesion 2. Exotoxins 3. Endotoxins (lipopolysaccharides) 4. Cell-host interaction 5. Capsular polysaccharide 6. Iron acquisition 7. Evasion of host immune system
How do Gram (-) bacteria use adhesion as a mechanism of pathogenicity?
1. Fimbriae, villi-like extensions on cell wall made of pili protein units that act as antigens. Eg., K88 aka F4 help E. Coli stick to mucosal surfaces / enterocytes in colon. P. fimbriae help E. Coli stick to epithelium of urinary tract, causing infection. 2. Filamentous haemagglutinin helps Bordatella bronchisepta to stick to canine ciliated tracheal epithelium, avoiding muco-ciliary escalator. 3. Polar fimbriae help Dichelobacter nodosus to stick to keratinised tissues in hoof of sheep, leading to footrot.
Give examples of exotoxins used by Gram (-) bacteria.
1. Cholera toxin - Activates adenylate cyclase; increased level of intracellular cAMP promote secretion of fluid and electrolytes in intestinal epithelium leading to diarrhea 2. Heat-labile LT toxin - released by E. Coli; similar or identical to cholera toxin 3. Heat-stable ST toxin - released by E. Coli; binding of ST enterotoxins to a guanylate cyclase receptor results in an increase in cyclic GMP (cGMP) that adversely effects electrolyte flux. Promotes secretion of water and electrolytes from intestinal epithelium leading to diarrhea 4. Shiga-like toxin - released by E. coli; cleaves rRNA resulting in inhibition of protein synthesis in susceptible cells. Results in diarrhea & hemorrhagic colitis. 5. Osteolytic toxin of Pasteurella multocida 6. Leucotoxin of Mycobacterium haemolytic 7. Exotoxin A of Pseudomonas aeruginosa 8. Keratinase of Dichelobacter nodosus
What is meant by cell-host interaction employed by Gram (-) bacteria?
Bacteria that are either commensal and/or opportunistic.
What is a Gram (-) bacteria's capsular polysaccaride (capsule) and how does it work?
A thick, mucous-like, layer of polysaccharide. This "capsule" cloaks antigenic proteins on the bacterial surface that would otherwise provoke an immune response - phagocytosis by neutrophils and opsonophagocytosis by macrophages -- & thereby lead to the destruction of the bacteria. Capsular polysaccharides are water soluble, commonly acidic & linear.
What is LPS and what role does Lipid A play in LPS's role as Gram (-) endotoxin?
LPS is a three-part structure in Gram (-) outer membrane. The innermost, hydrophobic portion is Lipid A, which anchors the LPS molecule, comprised of Lipid A, core polysaccharide & O-side chains, aka O-antigen, to the outer membrane. When released from the bacterial cell well, Lipid A activates macrophages and causes IL-1 & TNFalpha release, stimulating a strong immune response. Clinically, the response can range from fever, thrombosis, DIC, leucopenia to complement, hypotension, circulatory collapse, shock & death.
How does iron acquisition aid in a Gram (-) bacteria's pathogenicity?
Since no bacteria can synthesize iron, Gram (-) bacteria scavenge or harvest it to grow using: 1. Siderophores: High-affinity chelating compounds put out by Gram (-) bacteria into environment that scavenge iron & bring back. 2. Transferrin-binding protiens - Proteins that hold iron, like Hb, that bacteria can clutch onto & steal from. Eg. S. aureus possess transferrin-binding proteins in cell wall.
What are three ways in which the cell membrane & capsule of the Gram (-) bacteria help the pathogen evade the host immune system?
1. Evade phagocytosis by innate immune system: use hydrophilic capsule or LPS outer membrane; 2. Resist complement & lysozyme: same non-stabilising capsule & LPS helps avoid opsonisation with C3b (alternative pathway); 3. Use of molecular mimicry to avoid antibody-mediated opsonophagocytosis ie., host recognises surface components as "self antigens", thus no antibody not produced. Eg., K1 antigen (sialic acid) of E. coli, hyaluronic-acid capsule of beta-haemolytic streptococci & K5 antigen (desulfoheparin) of E. coli.
What are some diseases caused by bacterial use of adhesion, ie., fimbriae or filamentous haemagglutinin?
Kennel cough (Bordatella bronchisepta) Pink Eye / New Forest Eye (Moraxella bovis) Diarrhoea (E. coli) Footrot (Dichelobacter nodosus)
How do obligate & facultative intracellular pathogens hide from the host's immune defences?
1. Inhibit phagosome & lysosome fusion (evading macrophages); 2. Lyse phagosomal membranes to escape into cytoplasm 3. Resist killing by lysosomal killing mechanisms
Which of the following are extracellular pathogens? More than one. A. Escherichia coli B. Chlamydia C. Rickettsia D. Streptococci
A & D Chlamydia & Rickettsia are obligate intracelluar bacteria.
Salmonella, Listeria, Mycobacterium and Brucella are: A. Extracellular pathogens B. Obligate intracellular pathogens C. Facultative intracellular pathogens D. None of the above
Fimbriae that bind mannose are non-pathogenic except for assisting in bladder colonisation & infection. True or False?
True. Mannose sugar binds to fimbriae, thus blocking it from binding to enterocytes. But mannose-resistant fimbriae, such as K88 aka F4 on E. coli are highly pathogenic.
Which type of bacteria, Gram (+) or Gram (-), staphylococci or bacilli, can form spores?
Gram (+) bacilli only.
What are the two main genera of Gram (+) bacilli?
Bacillus and Clostridium
Describe Clostridium bacteria.
- Gram (+) bacilli - Spore-forming - Anaerobic - Found in faeces-contaminated soil & sewage - Cause tissue-invading (histotoxic) and enterotoxic syndromes in sheep especially, controlled by toxoid vaccines - Cause botulism & tetanus using neurotoxins - Clostridium perfringens - five types - cause serious enterotoxaemias.
What is special about Clostridium perfringens?
It produces many exotoxins that cause enterotoxaemias in various species, especially ruminants. FIVE TYPES (A-E), all producing alpha-toxin. Type A: Mostly alpha. Causes enteritis in pigs & chickens, gas gangrene in humans. Type B: Mostly beta, some epsilon. Causes LAMB DYSENTERY. Type C: Mainly beta. STRUCK & Necrotic enteritis in lambs & piglets. Type D: Mainly epsilon. PULPY KIDNEY in sheep. TYPE E: Mostly iota, less important. C. perfringens also causes histotoxic infections in which spores germinate in contaminated tissue, which becomes anaerobic, enabling secondary infection.
What is LAMB DYSENTERY & how is it caused?
Enterotoxaemia in sheep caused by Type B Clostridium perfringens (mostly beta toxin, some epsilon), prevalent in Scotland & N. England. Lambs < 2 mo suckle from infected ewe, overgrowth of toxin absorbed, die.
What is STRUCK & how is it caused?
Sheep enterotoxaemia caused by Type C Clostridium perfringens (mostly beta toxin), prevalent all over England. Sheep overeat, β-toxin not INactivated by trypsin because maybe there’s a pancreatic deficiency in the sheep, toxin damages mucosa, absorbed, major organ failure.
What is PULPY KIDNEY & how is it caused?
Sheep enterotoxaemia caused by Type D Clostridium perfringens (mostly epsilon toxin). Lambs transferred from rough pasture onto richer diet, poss. with concentrate, suddenly have overgrowth of bacteria, ε-toxin activated by enzymes, ↑ permeability of small intestine, absorption, ε-toxin affects brain & kidney ↑ capillary permeability, ↑ intracranial pressure, CNS affected. At PM, kidney shows autolytic changes.
How do spores, formed by Gram (+) bacilli, survive in the face of adversity?
They are resistant to: - dessication - cold & freezing - boiling - radiation - UV light - chemicals such as detergents & disinfectants
Name two types of anaerobic, spore-forming, Gram (+) bacteria that release neurological toxins.
Clostridium tetani & Clostridium botulinum
Name an aerobic, spore-forming, Gram (+) bacteria that uses its polysaccharide capsule & toxins to cause death.
Bacillus anthracis -> anthrax
What is the pathogenesis of Bacillus anthracis, which causes anthrax?
Spores in contaminated soil are ingested by mainly ruminants (and also horses) → phagocytosed by neutrophils, eosinophils, macrophages, etc. → germinate in the lymphatics → spread to bloodstream → multiply → septicaemia
How does the bacterial capsule aid in the virulence of Bacillus anthracis?
The poly-γ-D-glutamic acid (PGA) capsule disguises B. anthracis from immune surveillance by preventing C3b (complement) from binding to the surface (thus it’s anti-phagocytic) and allows its unimpeded growth in the host. The capsule stains mauve/pink with polychrome methylene blue stain.
How does the exotoxin aid in the virulence of Bacillus anthracis?
Toxin contains three components that become progressively more toxic as they come together, the most lethal being the triple combination called Holotoxin. When Factor I (oedema factor), Factor II (protective factor) & Factor III (lethal factor) come together, the holotoxin inhibits phagocytosis, becomes toxic to macrophages, causes pulmonary oedema, shock and death.
What is Blackleg or Blackquarter & what causes it?
It's a histotoxic infection in cattle caused by Clostridium chauvoei. Spores lie dormaon in muscle until activated by trauma, which lowers redox of tissues (lower oxygen tension); anaerobic environment leads to outbreak. Runs down fascia, darkish purple, gaseous tissue.
What are the three types of clostridial diseases?
1. Enterotoxaemia eg. Lamb dysentery caused by C. perfringes 2. Histotoxic infection eg. Blackleg caused by C. chauvoei 3. Intoxication eg. Botulism caused by C. botulinum; ingestion of pre-formed toxin
How can clostridial diseases be treated?
1. Clostridial toxoids - deactivated toxin treated with formalin, retain antigenicity but loses toxicity. Eg. Tetanus vaccine, Heptavac for sheep 2. Antiserum for immediate treatment - passive protection from antibody purified from horses; has antibodies in it so doesn't stimulate immune system; faster than vaccine
How can bacillus diseases be treated?
1. Sterne spore vaccine - live, avirulent (non-capulated) strain of B. anthracis (anthrax is notifiable - report to DEFRA)
All Gram (+) bacteria are capable of forming spores. True or false?
False. Only Clostridia & Bacilli, which are Gram (+) bacilli, can form spores. Other Gram (+) bacilli don't form spores. These include: Listeria Corynebacterium Erysipelothrix Rhodococcus Arcanobacterium Actinomyces Nocardia Dermatiphilus Mycobacterium Gram (+) cocci also don't form spores.
Can all Gram (+) bacteria be divided into acid-fast and non-acid-fast?
No. Only non-spore-forming Gram (+) bacilli can be divided into acid-fast and non-acid fast. Only Mycobacterium species, eg. M. bovis, M. tuberculosis & M. paratuberculosis, are classified as acid-fast. This means they carry a waxy layer on their surface that's resistant to many chemicals & don't let stains in. They must be stained with Ziehl-Neelsen, which reacts with mycolic acid in cell wall to stain red. Non-acid-fast stains blue.
Which Gram (+) bacteria is acid-fast?
Mycobacteria spp. including: M. bovis (bovine TB) M. tuberculosis (human TB) M. paratuberculosis (Johnes disease, ruminants) M. avian (avian TB) Mycobacterium is a Gram (+) bacillus, non-spore-forming, acid-fast.
Name four Gram (+) bacillus bacteria that are NOT acid-fast.
1. Listeria 2. Erysipelothrix 3. Actinomyces 4. Arcanobacterium Others include Corynebacterium & Rhodococcus
Name five Gram (+) bacilli that are commensal or opportunistic, and name the diseases they cause.
- Erysipelothrix: Erysipelas in pigs. - Arcanobacterium (Trueperella); Summer mastitis aka "dry cow mastitis"; ovine foot disease - Actinomyces: Lumpy jaw in sheep & cattle (A. bovis); Actinomycosis in dogs; Canine thoracic lesions (A. viscosus) - Corynebacterium: Cystitis, UTI, kidney abscesses - Rhodococcus equi: Chronic suppurative bronchopneumonia in foals
What is Erysipelothrix?
Gram (+) bacilli, non-spore-forming, non-acid-fast commensal bacteria that resides in lymphoid tissue of pigs (also found in turkeys, fish & reptiles). Its capsule resists phagocytosis by white blood cells & it produces neuraminadase toxic enzyme that penetrates & damages tissue. Causes systemic bacterial infection by invading lymphatics; septicaemia results in acute cases. Endocarditis & arthritis in chronic infection in pigs. Characterised by diamond-shaped lesions on skin due to dermal ischaemic infarction. Zoonosis in fish & meat workers = Erysipeloid
What is Arcanobacterium?
Also known as Trueperella, it's a non-motile, small, opportunistic Gram (+) bacilli that resides in the nasopharynx of ruminants, URT & genital tracts of domestic animals & the ruminal wall of cattle. It can cause a wide variety of suppurative infections in farm animals, & is the commonest cause of wounds & abscesses. Causes summer mastitis aka "dry cow mastitis". Uses haemolysin, proteases, DNase, neurominadase. Important species: A. pyogenes
What is Actinomyces?
It's a Gram (+) bacilli, non-acid-fast, FACULTATIVE AEROBE (prefers anaerobic), opportunistic & non-motile, normally reside in oral cavity of cattle. Filamentous & branching under micro. Inoculated into tissues by trauma such as barbed wire, it may set up granulomatous lesions in soft tissue & bone. A. viscosus -> canine thoracic lesions, actinomycosis A. bovis -> lumpy jaw (actinobacillosis) in ruminants
What is Corynebacterium?
Gram (+) bacillus, non-acid-fast, usually commensal, non-motile, found in skin & mucous membrane of animals & humans. In cattle it can cause cystitis, UTI & kidney abscesses. Transmitted via infected urine, sexual contact; adheres to urinary tract using fimbriae & produce potent urease enzyme.
What is Corynebacterium pseudo-tuberculosis?
Like other Corynebacterium species, it is found in skin of ruminants. Microscopically, it resembles "Chinese letters". Unlike other Corynebacterium species, it is facultatively intracellular, and forms nodules that rupture & spread. It uses phospholipase as exotoxin, and causes caseous lymphadenitis in sheep & goats from shearing wounds; and ulcertiave lymphangitis in horses.
What is Rhodococcus?
Gram (+) bacilli, short rods, non-motile, can survive intracellularly & persists in contaminated soil for years. Its natural habitat is the soil and intestines of horses. It can cause chronic suppurative bronchopneumonia in foals (adults are immune), characterised by large pulmonary abscesses.
What is Mycobacterium?
Gram (+) bacillus, round-ended, aerobic, non-spore-forming, non-filamentous, non-branching, some pathogenic. Cause bovine TB, Johnes Disease, avian TB, leprosy (M. leprae) Pathogenesis: Inhalation/ingestion→uptake by macrophages & survival in macrophages → migration to lymph nodes → formation of granulomas → delayed (type IV) hypersensitivity & cell-mediated immune response (destructive to tissues). Transmitted via respiratory route in cattle >6 mo, via alimentary tract in post-natal calves, and congenital route Important species: M. bovis, M. paratuberculosis, M. avium
Name some PATHOGENIC, Gram (+) bacilli bacteria that are non-spore-forming.
- Mycobacterium tuberculosis, M. bovis, M. paratuberculosis. - Nocardia - Dermatophilus congolensis - Listeria monocytogenes, L. ivanovii
What is Listeria?
Gram (+) bacillus, motile, survives intracellularly in epithelial cells by lysing the phagosome that endocytoses it inside the cell, using listeriolysin. Can grow at low temperature (eg in fridge), 4C-45C, pH 5-9. Usually saprophytic; healthy ruminants can be carriers that shed it in milk & faeces. Causes septicaemia, mastitis, meningocephalitis, abortion & CNS disease in cattle & sheep (Listeriosis). Zoonotic in young & elderly who ingest contaminated meat or milk. Pathogenic: L. monocytogenes - found in silage from sheep faeces in cut pasture L. ivanovii
What is Dermatophilus congelensis?
Gram (+) bacillus, pathogenic, non-spore-forming. It's in the actinomycete group so it microscopically resembles filaments, but also has life cycle that includes longitudinal & transverse division & a motile coccoid form that spreads the infection across the skin. Releases adenase & lectinase. Causes Mud Fever (streptothricosis) aka rain scald in horses; pyogenic.
What is Nocardia?
Gram (+) bacillus soil bacterium, non-spore-forming, non-motile, branching, short filamentous. Semi-acid-fast (contains mycolic acid). Often in oral flora. Infection by wound or inhalation, causes chronic, progressive disease: Causes granulomatous lesions because it can survive & grow in macrophages. Nodules form, rupture & spread. Resistant to penicillins that would kill Actinomyces. Important species: N. asteroides
What are two Gram (+) bacillus, non-spore-forming MOTILE bacteria?
1. Listeria - tumbling motility at 18C 2. Dermatophilus congolensis - motile in its coccoid form
What is bovine tuberculosis & what causes it?
Caused by Mycobacterium bovis, a Gram (+), non-spore-forming, non-motile, acid-fast, strictly aerobic bacteria. It's inhaled by cattle over 6 mo (nasal secretions) or ingested from pasture. It survives phagocytosis by macrophages & migrates to lymph nodes, where it causes granulomas, delayed hypersensitivity & destruction of tissues by T-cell response. It changes the cytokine response to favour spread of disease. It's chronic progressive, fatal wasting disease. Shed from respiratory tract & udder by "open case" carriers. It's resistant to drying and antibiotics.
How do you diagnose bovine TB?
Skin test: comparative intradermal tuberculin test. Inject the cow at two sites: PPD (purified protein derivative) from avian TB and bovine TB. Should only be concerned if there's swelling in bovine TB site and not avian TB site. Can also use IF-gamma stimulation test: culture the lymphocytes from blood sample, stimulate with PPD from bovine TB. Degree of simulation is measured by release of IF-gamma. PCR, ELISA, immunofluorescence
What is Johne's disease?
Aka paratuberculosis or MAP, it's a progressive disease of the colon & ileum caused by Mycobacterium paratuberculosis, a Gram (+) bacillus, non-motile, acid-fast, pathogenic, non-spore-forming, strictly aerobic bacteria. It infects very young ruminants, s Patches, leading to epithelioid & giant cells, secondary infection, with thickened & corrugated mucous membrane. Severe diarrhoea, weight loss, oedema & death.
What are the two main genera of Gram (+) cocci?
Staphylococcus & Streptococcus
Which Gram (+) cocci is catalase (+)? Which is catalase (?)
Staphylococcus is catalase (+). Streptococcus is catalase (-).
What is the point of the catalase test? What is catalase?
Use the catalase test after Gram-staining to detect Gram (+) cocci. They will not always be arranged in bunches (staph) or chains (strep), so the catalase test is used as further identification. Catalase is an enzyme produced only by Staphylococcus that decomposes hydrogen peroxide (H202) to water and oxygen, resulting in a "fizzing" effect.
Which Gram (+) cocci is classified as coagulase (+) or coagulase (-)? What does it mean?
Staphylococci. Coagulase (+) staph are virulent & aggressive pathogens. Coag (-) are found on skin in large numbers & harmless.
Streptococci & Streptococci are identified first using Gram stain, then catalase test, then coagulase / DNase test. True or false?
False. Only Staphylococci are subjected to coagulase test and DNase test.
Staphylococcus are Gram (+) cocci, catalase (+), facultative anaerobes and facultatively intracellular. True or false?
Staphylococcus that's coag (+) / DNase (+) is pathogenic. Name two species and the disease they cause.
1. Staphylococcus aureus - bovine mastitis - tick pyaemia (seen in sheep bitten by insect that also introduces bacteria) - cellulitis (when infection runs between muscles & skin) - abscesses & boils 2. Staphylococcus intermedius (dogs) - canine otitis externa - canine pyoderma - post-surgical osteomyelitis
Staphylococci that's coag (-) / DNase (-) is non-pathogenic, found to stick to plastics & cause nosocomial infections. Name two example.
S. saprophiticus & S. epdidermidis These commensals reside on skin or mucous membranes. They adhere to plastic implants & catheters. May be responsible for subclinical mastitis in cows.
What are the three main pathogenic features of virulent staphylococci species?
1. Exotoxins 2. Cell-surface proteins 3. Intracellular survival
Staphylococcus that's coag (-) and DNase (+) is rare but also highly virulent. Name one pathogen & what disease it causes.
Staphylococcus hyicus - attacks skin of pigs: Exudative dermatitis aka "greasy pig disease"
What exotoxins do virulent, coagulase (+) / DNase (+) Staphylococcus produce?
1. Alpha toxin (haemolysin) 2. Beta-toxin (not a haemolysin) 3. TSST-1 (toxic shock syndrome toxin) 4. Leucocidins 5. Protease, Hyaluronidase & Lipase 6. Enterotoxin
Describe the Staphylococci exotoxin, alpha toxin (aka haemolysin).
- haemolytic (β haemolysis - indicated by narrow zone of haemolysis on agar plate) - necrotising - damages cells by causing mast cells & platelets to degranulate, releasing histamine & other damaging factors
Describe the Staphylococci exotoxin, beta toxin (NOT a haemolysin).
- sphingomyelinase that converts sphingomyelin to ceremide, causing cell membranes to be damaged, leaving RBCs fragile - causes wide zone of RBC change on blood agar - contributes to necrosis
Describe the Staphylococci exotoxin, TSST-1 (Toxic Shock Syndrome Toxin)
- TSST-1 is a super-antigen that cross-links/locks together T-cell receptor to MHC II on antigen-presenting cell to induce T-cell response without a need for antigen - activates T-cells non-specifically - causes release of cytokines TNFα & IL-1 that cause fever ↑cardiovascular shock ↑ microthrombus formation in capillaries ↑ destruction of host cells by cytotoxic T-cells ↓ immune response to staph
Describe the Staphylococci exotoxin, Leucocidin
Kills white blood cells.
Describe the Staphylococci exotoxins Protease, Hyalurodinase & Lipase
- similar/same as Gram (+) bacillus enzyme toxins - degrade host tissue & cells, feed bacteria with nutrients
Describe the Staphylococci exotoxin, Enterotoxin
- makes bacteria heat-stable.
Aside from exotoxins, what structural pathogenicity factors do virulent Staphylococci bacteria use?
1. Protein A 2. Capsule 3. Fibrinogen-binding & Fibronectin-binding proteins
Describe the virulent Staphylococci bacteria's structural pathogenicity factor, Protein A.
- surface protein that binds to IgG ↓ complement activation, opsonisation ↓ recognition of bacterial cell as foreign
Describe the virulent Staphylococci bacteria's structural pathogenicity factor, capsule.
- produced while the bacteria is in the host (in vivo) ↓ “surface phagocytosis” (ie. when a phagocyte can trap a bacteria that needn’t be opsonised against a surface like a blood-vessel wall to initiate ingestion) - C3 convertase not stabilised (so no complement, no opsonisation) ↓ phagocytosis in absence of specific antibody
Describe the virulent Staphylococci bacteria's structural pathogenicity factor, fibrinogen-binding protein & fibronectin-binding protein.
- help bacteria stick to damaged tissue at wound by hitching a ride on fibrin-producing fibrinogen, key in forming clots.
Which of the following bacteria can survive inside host cells? (More than one) A. Staphylococcus aureus B. Staphylococcus intermedius C. Streptococcus faecium D. Streptococcus agalactiae E. Streptococcus suis
A, B & C. Only staphylococci are facultatively intracellular, while all streptococci except for Streptococcus suis are obligately extracellular.
What bacteria are classified by Lancefield groupings?
Streptococci. Lancefield classifies strains based on bacterial host & disease specificity.
Streptococci are Gram (+) cocci, catalase (-), aerotolerant although a few strains are obligate anaerobes. True or false?
Aside from Lancefield Groups, Streptococcus are classified according to whether they're: Pyogenic, Viridans, Enterococci or Lactic. What do these mean?
1. Pyogenic - form pus Eg. S. pyogenes 2. Viridans - greening in culture or wound; oral streps are viridans. Eg. S. salivarius, S. sanguis, S. mutans (in dental cavities) 3. Enterococci - faecal Eg., E. faecalis, S. faecium 4. Lactic - found in milk. Eg. S. lactis, S. thermophilus in yoghurt
What are the key pathogenicity factors employed by Streptococci? Ie., those factors mostly used by pyogenic strep?
1. Capsule 2. M Protein 3. Toxins
What is the Streptococcus structural pathogenicity factor, capsule?
Hyaluronic acid capsule -tricks host into thinking bacterial proteins are “self” antigens - evades phagocytosis - produced by S. progenes, S. equi
What is the Streptococcus structural pathogenicity factor, M Protein?
- anti-complement - evades phagocytosis - produced by S. pyogenes & S. equi
What are the Streptococcus exotoxin pathogenicity factors?
1. Proteases, lipases - enzymes 2. Streptolysin O & S - haemolysins 3. Streptokinase - dissolves clots, encouraging spread of infection, produced by S. pyogenes, S. equi & S. canis
Using the Lancefield Groups, A, B, C, D & G, what are the bacterial hosts of these Streptococci pathogens in each group?
Group A: Humans Group B: Bovines Group C: Horses, cows, sheep, goats, pigs Group D: Bovine & Pigs, enterococci. Group G: Dogs
What is the most important strep of Lancefield Group A?
S. pyogenes - causes acute disease in humans. Possesses all of the pathogenicity factors (toxins & structural factors such as M Protein & capsule); pus-forming.
What is an important strep of Lancefield Group B?
Streptococcus agalactiae - lives in bovine milk duct, causes contagious, chronic bovine mastitis.
What are four important streptococci pathogens of Lancefield Group C, the group with the widest host range?
1. S. zooepidemicus - causes horse pneumonia, endometrius, abortion & severe mastitis in cows & goats. 2. S. equimilis - affects piglets, causing suppurative arthritic joints, entry via skin would, umbilicus, tonsil 3. S. dysgalactiae - affects cows & lambs, causing acute mastitis & joint ill, respectively. Alpha-haemolytic with viridans. 4. S. equi - strangles (very severe tonsillitis), respiratory infection in horse. Strongly beta-haemolytic, highly contagious, can lead to rupture of submandibular lymph node.
What are some streptococci pathogens of Lancefield Group D?
1. Enterococcus faecalis & S. faecium - cause UTI 2. S. bovis - causes mastitis 3. S. suis - affects piglets; live in tonsil without symptoms but stress, related to husbandry, induces infection. Piglets catch from sow & can die neonatally from meningitis or become carriers. Might be able to surive as an intracellular pathogen in macrophages.
What is an important strep in Lancefield Group G?
Streptococcus canis - severe form of kennel cough ie., bronchopneumonia.
Which Lancefield Groups can be successfully treated with Penicillin G?
Groups A, C & G: S. pyogenes S. equi S. dysgalactiae S. esquimilis S. zooepidemicus S. canis
Which Lancefield Groups CANNOT be successfully treated with Penicillin G?
Groups B & D: S. agalactiae Enterococcus faecalis S. faecium S. suis
Name five antimicrobials that are effective against Gram (+) cocci bacteria.
Cloxacillin (cidal) Cephalosporin (Cephalexin) (cidal) Macrolides (Erthromycin, Tylosin) (static) Lincosamides (Clindamycin, Lincomycin) (static) Fluoroquinolones (Enrofloxacin) (Cidal)
Describe Enterobacteria in terms of how they react to Gram stain, sugar fermentation of glucose, and oxidase test.
Enterobacteria are Gram (-) bacilli. They always ferment glucose, which means they produce acid, or acid + gas, and are able to reduce nitrates to nitrites. They are always oxidase negative, meaning they do not possess cytochrome C oxidase.
Enterobacteria cannot grow in the presence of bile salts. True or false?
False, enterobacteria such as E. coli, Salmonella, Shigella, Klebsiella, etc. can grow on MacConkey agar, which contains bile salts.
Name two very important genera of enterobacteria.
Salmonella and Escherichia.
Which of the following are enterobacteria along with Salmonella and Escherichia? More than one. A. Shigella B. Campylobacter C. C. jejuni D. Shigella E. Pseudomonas
A & D only. Campylobacter & C. jejuni are curved Gram (-) rods, not enterobacteria, although they have similar effects on the GIT. They are not classified according to glucose fermentation or oxidase. Pseudomonas is a Gram (-) rod but not an enterobacteria.
Enterobacteria prefer oxygen but can survive in anaerobic conditions. True or false?
True. They are facultative anaerobes.
All enterobacteria live in animal intestines, mainly colon. Some are opportunistic like E. Coli. Some are primary, aggressive pathogens, like Salmonella and E. Coli. Which is incidental, and non-specific?
How does E. coli act as both an enteric as well as an extra-enteric pathogen?
E. coli resides normally as commensal in colon of most mammals. As extraintestinal, it can cause UTI, oedema, mastitis in ruminants, pyometra in dogs. It uses O antigens, K antigens, H antigen, siderotrophs, ability to resist complement, its mannose-resistant fimbriae that can bind on mucous membranes & exotoxins haemolysin & CNF-1 & CNF-2. As a primary enteric pathogen, it uses K88 fimbriae, exotoxins aka enterotoxins that reverse sodium pumps, thus reversing sodium & water retention. Toxins include LT & ST.
Salmonella & E. Coli are commensal. True or False?
False. Salmonella isn't commensal. It hides in host in latent state in gall bladder & tissue. It's intracellular, able to enter & survive in macrophages, causing systemic disease. It is actually commensal on reptiles and amphibians but we should know it mainly as a primary intracellular pathogen that is opportunistic.
How do the H-antigens differ in E. Coli & Salmonella?
E. Coli has one, Salmonella has two interchangeable flagellae.
How is salmonella classified by antigen & serovar in the Kauffmann-White scheme?
Know the O antigen is in LPS, & H antigen is flagellae. O antigen determines group, H antigen determines serovar in Kauffmann-White scheme.
Lactose fermenters are all non-pathogenic commensals.
False. Lactose fermentation can't be used effectively to identify which Enterobacteria are pathogenic or harmless. E. coli & Enterobacter, which are pathogenic, can ferment lactose, while Salmonella and Shigella, which causes dysentery, are non-lactose fermenters, along with Proteus, which doesn't cause disease.
What is the biggest single difference in pathogenic mechanism between E. Coli & Salmonella?
Salmonella can enter macrophages & survive & spread in them, causing systemic disease. It can lay dormant in cells in "active carriage" state. Also, Salmonella is cytotoxic for enterocytes.
What are the main pathogenicity factors of E. coli as an extraintestinal pathogen?
1. K antigens in capsule 2. Iron acquisition via siderotrophs 3. Complement resistance 4. Mannose-resistant fimbriae 5. Haemolysin toxin 6. CNF-1 & CNF-2
Salmonella enterica is easily identified on selective medium such as XLD by ?
Black colonies of hydrogen sulphide.
What oxygen environment does Campylobacter prefer?
Microaerophilic: 5-10% oxygen, ideally 7%.
What are some species of campylobacter in humans, birds, pigs & ruminants?
C. jejuni in birds and humans C. coli in pigs C. foetus in cattle & sheep that causes infertility and abortion that's systemic.
What are the pathogenicity factors of campylobacter?
1. Polar flagellae 2. Attachment 3. Toxin production
Where are campylobacter naturally found?
Naturally in mucous membranes of intestinal tracts or genital tracts of chicken, wild birds, cattle, sheep & dogs.
Non-enteric Gram (-) bacilli can only be glucose fermenters that are oxidase negative.
False. Actinobacillus is the only glucose-fermenting, oxidase-negative non-enteric that we are concerned with. Other non-enteric Gram (-) bacilli bacteria are oxidase glucose-fermenting oxidase-positive, as well as non-glucose-fermenting oxidase-positive.
Name some Gram (-) bacilli non-enteric bacteria that are non-glucose-fermenting and oxidase negative?
None - at least we haven't learned any. Pseudomonas, Bordatella, Aeromonas & Brucella are non-glucose-fermenting, oxidase-positive.
Name some Gram (-) bacilli, non-enteric bacteria that are primary pathogens to animals & describe the diseases they cause.
1. Brucella (B. abortus) - bovine enzootic abortion 2. Pasteurella (P. multocida) - also opportunistic, causes fowl cholera, atrophic rhinitis in pigs, haemorrhagic septicaemia in cattle & rabbit snuffles 3. Spirochaetes (Leptospira, Brachyspira, Borellia) - Porcine intestinal spirochaetosis, Borelliosis, transmitted by many ticks & some lice. 4. Chlamydophila (C. abortus) - otherwise opportunistic; enzootic abortion in horses, pigs, rodents & humans 5. Rickettsias - Typhus in humans
Name some Gram (-) bacilli, non-enteric bacteria that are opportunistic and name the secondary infections they cause.
1. Pseudomonas (P. aeruginosa) - chronic otitis externa of dogs, cystic fibrosis & post-surgery wounds & burns 2. Bordatella (B. bronchisepta) - sets in after primary viral infection (distemper, CPIV or mycoplasma), leading to severe kennel cough 2. Pasteurella (P. multocida) - also pathogenic; bovine pneumonia, enzootic pneumonia of pigs, wound infections 3. Mannheimia (M. haemolytica) - bovine respiratory disease complex (BRDC), pneumonic pasteurellosis, follows viral infection (PI-3, IBR, BRSV) 4. Chlamydophila (C. felis) - feline conjunctivitis, rhinitis & respiratory problems
What is a key pathogenic feature of Brucella (B. abortus, B. canis, B. suis, B. obis)?
1. Facultatively intracellular - it can survive inside cells of the spleen, liver & lymphatics 2. Transmitted from mother to placenta causing abortion 3. No exotoxins except for O-side-chain antigen (endotoxin, structural) Brucellosis is notifiable as it causes bovine enzootic abortion. Cows are vaccinated against it.
What are the key pathogenic features & pathogenesis of Pasteurella multocida?
1. Releases exotoxin: osteolytic toxin that destroys turbinate bones, causing atrophic rhinitis in pigs 2. Hyaluronic capsule evades host immune system as it's recognised as "self"
What are the key pathogenic features & pathogenesis of Spirochaetes, esp. Leptospira?
1. Transmitted by contact with urine of infeted animals or contaminated water or soil. 2. Axial filament flagella with inner & other membrane cause bacteria to twist around. 3. Causes leptospirosis, common zoonotic for vets.
What are the key pathogenic features & pathogenesis of Chlamydophila, esp. C. abortus?
1. Transmitted orally & sexually in ruminants 2. Endemic in ruminants 3. Causes enzootic abortion in horses, pigs, rodents, humans
What are the key pathogenic features & pathogenesis of Rickettsias?
1. Transmitted by many ticks, fleas, lice 2. Obligately intracellular 3. Aerobic 4. Causes typhus in humans but treatable with antibiotics.
What are the key pathogenic features & pathogenesis of Pseudomonas, esp. P. aeruginosa?
1. Opportunistic - free-living in soil & water 2. Multiple antibiotic resistance 3. Fimbriae 4. Exotoxin A - inhibits host protein synthesis 5. Exotoxin elastase - destroys elastin in lungs & blood-vessel walls 6. Exotoxins protease, hydrolytic enzymes
What are the key pathogenic features & pathogenesis of Bordatella, esp. B. bronchi septa?
1. Opportunistic 2. Strict aerobe 3. Colonisation of ciliated epithelium of trachea 4. Adhesins 5. Fimbriae 6. Exotoxin leucocidins 7. Exotoxin dermonecrotic toxin 8. Resistant to vaccines
What are the key pathogenic features & pathogenesis of Pasteurella, esp. P. multocida?
1. Opportunistic - found in mouth of many animals; also pathogenic 2. Osteolytic toxin that causes atrophic rhinitis in pigs 3. Hyaluronic capsule that evades immune system
What are the key pathogenic features & pathogenesis of Mannheimia, esp. M. haemolytica?
1. Opportunistic 2. Exotoxin leukotoxin (leucocidins, Lkt) - kills neutrophils & macrophages 3. Causes fibrin buildup 4. Causes influx of inflammatory cells 5. Causes haemorrhage in host tissues
What are the key pathogenic features & pathogenesis of Chlamydophila, esp. C. felis?
1. Opportunistic - in stomach & repro tract of cats 2. Endemic in house cats 3. Obligately intracellular
Name some Gram (-) bacilli, non-enteric bacilli that are either obligately or facultatively intracellular.
1. Brucella (B. abortus) - obligate 2. Chlamydophila (C. felis, C. abortus) - obligate 3. Rickettsias - obligate
If a Gram (-) bacillus, non-enteric bacteria is shown to grow on MacConkey, secretes a greenish pigment and gives off a distinctive odour and is shown to be resistant against many antibiotics except Gentamicin & carbenicillin, what is it likely to be?
Pseudomonas, probably P. aeruginosa. It can grow in the presence of bile salts (MacConkey) but is non-glucose fermenting & oxidase positive. It secretes green pyocyanin & an odour. It has multiple antibiotic resistance.
What is the selective agent in MacConkey medium & what does it say about a bacteria that can grow on it effectively?
Bile salts. It indicates an enteric bacteria, but non-enteric bacteria can also grow on MacConkey, such as Pseudomonas (P. aeruginosa) & Bordatella (B. bronchiseptica).
Aside from bile salts, what is the sugar in MacConkey & what colour would show up if a bacteria could ferment it?
Lactose. Pink or magenta.
What are the main differences between fungi/yeasts & bacteria in terms of: 1. Cell Structure 2. Reproduction 3. Pathogenicity factors
1. Fungi/yeasts are eukaryotic with nucleus surrounded by membrane, & organelles surrounded by membranes. Bacteria are prokaryotic with no nucleus or membrane-bound organelles. Fungi/yeasts have no cell walls while bacteria have thick cell wall (Gram-pos) or thin cell walls (Gram-neg). 2. Fungi/yeasts reproduce by vegetative growth (budding) & production of sexual spores. Bacteria reproduce by binary fission. 3. Yeast & fungi use penetration & pressure on nerves, tissue, walls of blood vessels & bone once they're ingested or inhaled, causing hypersensitivity & inflammatory reax. No toxins produced in body. Bacteria enter via skin, oral-faecal, respiratory & via blood, can enter cells, evade immune system, using capsules, flagellae, endotoxin and exotoxins.
What are the three major yeast diseases in order of most pathogenic to least pathogenic/commensal?
1. Cryptococcosis - caused by Cryptococcus neoformans; very rare & severe; affects CNS or becomes systemic 2. Candidosis (THRUSH) - caused by Candida albicans, C. tropicalis, C. pellicosa; sexually transmitted, also commensal, cutaneous, mucous membranes 3. Malassezia pachydermatitis - caused by M. pachydermatis; very common, commensal on skin, triggers allergic reaction, associated with otitis externa in dogs
What is Cryptococcosis?
A rare, highly pathogenic disease caused by spherical, encapsulated yeast Cryptococcus neoformans. Route of infection is primarily respiratory - from pidgeon droppings Acute, sub-acute or chronic exogenous mycosis (tissue invasion) Capsule leaves big spaces in PM histology. Affects CNS or can become systemic. Cats: detected with nose lesions Cats & Dogs: oral, pulmonary or cutaneous lesions w/ CNS problems Cattle: mastitis Horses: myxoma-like lesions of lung & lip
What is Candidosis?
Common, opportunistic disease aka thrush, caused either by endogenous mycosis of Candida albicans, C. tropical is, C. pellicosa in mucous membrane or exogenously from soil, water, etc. Causes cutaneous and mucous-membrane mycosis - less severe than cryptococcosis. C. albicans is yeast in environment, filamentous in tissue (not not dimorphic). Buds from small base.
What is Malasezzia pachydermatitis?
A mild, superficial skin disease caused by the commensal (lives on skin) yeast M. pachydermatis. Triggers hypersensitivity when in high numbers on skin. Associated with otitis externa in dogs. Buds from large base so looks pretty big under microscope.
Name three fungal diseases caused by filamentous fungus (not yeast).
1. Mucormycosis - alimentary disease caused by mucor (bread) moulds such as Mucor, Rhisopus & Absidia, saprophytes, found in grain, straw; leads to granulomatous or ulcerative lesions that can become systemic; gastritis & rumenitis in calves 2. Aspergillosis - mainly respiratory disease caused by filamentous Aspergillus found everywhere, in hair, straw, foodstuffs; A. fumigates, A. nidulans, A. falvus, A. niger; non-contagious 3. Blastomycosis - Blastomyces dermatidis in wood & soil, inhaled (dimorphic - yeast when pathogenic) 4. Histoplasmosis - Histoplasma capsulatum in soil contaminated with bird or bat droppings, inhaled, becomes systemic (also dimorphic)
What types of stain would you use in PM histopathology if you suspected fungal infection?
1. Grocott silver stain: fungs shows up black or brown against turquoise background. 2. Periodic Acid Schiff (PAS) - fungus stains magenta & mycelium (filamentous fungus) is clearly indicated.
What type of media would you use to grow yeast & fungus?
1. Sabouraud's medium - 1% peptone, 2% glucose, agar & dextrose 2. Malt extract agar Also add antibiotic eg. chloramphenicol
What produces arthrospores?
These are the fragmented hyphae of multinucleated, filamentous fungi such as Microsporum canis. They are asexual spores.
What produces conidiospores?
These are external spores that are specialised for spreading the multinucleated fungus in large numbers, produced by Aspergillus fumigatus, for example.
What produces chlamydospores?
These are the resting form (non-budding) of sexual spores produced by the YEAST Candida albicans.
What produces sporangiospores?
These are spores formed inside specialised structures that release (explode even) into the environment, produced by mucor and similar filamentous fungi such as Rhizopus sp and saprolegniosis, the fish fungus.
What is saprolegniosis?
Filamentous fungal disease on skin or eggs of fish.
What does Aspergillus cause?
Aspergillosis includes: - Mycotic abortion in ruminants - Guttural pouch mycosis in horses - Avian aspergillosis - Pulmonary aspergillosis - Canine nasal aspergillosis
Which filamentous fungus is characterised by sporing heads seen in tissue under microscope?
Why is it important to be able to identify Dermatophytes?
They cause dermatomycosis, aka ringworm. Ringworm is both enzootic and zoophilic (zoonotic). That is, it's contagious between animals and between animals and humans.
What are the two genera of dermatophytes that cause ringworm in animals?
Microsporum spp (M. canis, for example) Trichophyton spp
What are the pathogenic features of dermatophytes?
1. Keratinophilic fungi - digest keratin in nail, horn, hoof, hair & SKIN 2. Contagious 3. M. canis spores are called Macroconidia!!
What are three ways to diagnose ringworm/dermamycosis?
1. Woods Lamp (long-wave UV) - apple green 2. Microscopy from plucked hair or skin scrape: add potassium hydroxide to dissolve keratin; add paraffin; look for refractile, glassy ARTHROSPORES 3. Culture: Sabouraud's medium with chloramphenicol & cycloheximide selective agent, 27 degrees C for 10 days (not convenient)
What's the pathogenesis of ringworm?
1. Arthrospores germinate. Note that these are fragments of mycelium, of M. canis. 2. Infective hyphae grow into skin & down hair follicle. 3. Hyphae grow downwards & penetrate hair shaft. 4. Arthrospores (macroconidia) form around britlle hair shaft as hyphae age. 5. Hair breaks off to infect environment. 6. Hyphae don't penetrate living tissue. 7. Secondary infection can start where ringworm damaged follicle.