Phase 2 - Microbiology (ICS) Flashcards
Define pathogen
Organism that causes or is capable of causing disease
Define commensal
Organism which colonises the host but causes no disease in normal circumstances - e.g. bacteria from throat can cause pneumonia in lungs
Define opportunist pathogen
Microbe that only causes disease if host defences are compromised
Define virulence/pathogenicity
The degree to which a given organism is pathogenic
Define asymptomatic carriage
When a pathogen is carried harmlessly at a tissue site where it causes no disease
Resolving power of naked eye
100μm
Resolving power of light microscope
0.2μm
Typical size of protazoa like entamoeba histolytica
~30μm
Common size of spirochetes like borrellia recurrentis
~15μm
Common size for bacilli like e. coli
~2-3μm
Common size of cocci
~1μm
Which is the biggest virus we learn of
Rotavirus
What is the typical size of viruses
All smaller than 1μm
Bigger viruses ~0.3-0.8μm
Smaller virus <0.1μm
What is the smallest virus we learn of
poliovirus
What is unique about the nature of Chlamydia trachomatis
It is a bacteria but it is an obligate intracellular organism - it’s smaller than rotavirus
Rickettsia and Coxiella are also obligate intracellular bacteria
Define serovar/serotype
a distinct variation within a species of bacteria/viruses/among immune cells of different individuals
Which areas are open to bacterial colonisation
Mucosal surfaces
Bacteria can also get into many organs and cause inflammation
What do the colours of the gram stain signify
Purple - gram positive
Pink/red - gram negative
purPle - Positive; piNk - Negative
Basic shapes of bacteria
Coccus (round berry-like)
diplococcus (2 cocci)
streptococcus (chain of cocci)
staphylococcus (cluster of cocci)
Bacillus (rod)
Chain of rods
Vibrio (curved rod)
Spirochete (spiral rod)
Filamentous/branching bacteria
Typical structures that a bacterium is composed of
Chromosome of circular double ctranded DNA (free in cytoplasm)
Inner membrane
Outer membrane
Pili/fimbriae
Cell wall
Some bacteria also have
- a capsule made from polysaccheride
- flagella
- plasmids, which can be transferred from bacterium to bacterium
On which bacteria are capsules more common and why
On bacteria which get into blood/lungs
It helps protect them against the immune system
What is the purpose of pili/fimbriae
Recepting/sensing the environment
Which stain is commonly used for mycobacteria; what colour does it stain?
Ziehl-Neesen stain - stains red
How does the ziehl-neelsen stain only stain non-gram bacteria? What is the term used for this kind of bacteria?
There is a stage in the Ziehl-Neelsen stain where the bacteria are bathed in alcohol/acid. Regular gram bacteria are decolourised at this stage but certain organisms like mycobacteria resist the acid.
These are called acid/alcohol fast bacteria (AFB or AAFB)
Describe the cell envelope of a gram positive bacterium
Thin cytoplasmic membrane
Thick layer of peptidoglycan with lipoteichoic acid strands within it
Potentially a capsule
Describe from inside to out the cell envelope of a gram negative bacterium
Cytoplasmic membrane:
- Thin inner membrane
- Very thin layer of peptidoglycan
- (piller-like) Lipoproteins within periplasmic space
- Thin outermembrane
Lipopolysaccerides (ENDOTOXIN) - composed of:
- Lipid A
- O antigen
- Terminal sugars
potentially a capsule
What is the peptidoglycan in bacteria
Crosslinked sugers and amino acids
What causes the difference in staining between gram positive and negative bacteria?
Gram positive bacteria are able to resist decolouration (usually a mix of ethanol and acetone) due to their thick peptidoglycan layers
Gram negative have a thin peptidoglycan layer so the stain is easily lost and they have to be counterstained (with safranin or basic fuchsin stain)
What is a spore
Small oval or spherical structures with thick walls which are very resistant to high temperatures, radiation, desiccation and chemical agents. They are involved in reproduction and are used by certain bacteria to defend themselves. They can last for a long time in the environment
What environment can bacteria survive in?
Temperature: <-800C to + 80C
pH: <4 - 9
Water/desiccation: 2 hours - 3 months
Light: could be killed by UV
What environment can spores survive in
Temperature: <-800C to 1200C
pH: <4-9
Water/desiccation: >50 years
Growth rate of bacteria (give doubling time)
Common bacteria like E. coli or S. aureus:
- In a broth or solid media: 20-30 min
Mycobacterium tuberculosis in broth or media:
- 24 hours
Mycobacterium leprae in broth or media:
- 2 weeks
What is typically done now to test for mycobacteria in a culture
Grow too slowly for regular agar plate techniques ao using nucleic acid boosting techniques/PCR can be useful
Types of bacterial toxins
ENDOTOXIN
Component of the outer membrane of GRAM NEGATIVE bacteria, eg lipopolysaccharides
EXOTOXIN
Secreted proteins of Gram positive and Gram negative bacteria
What is an example of a condition caused by bacterial exotoxins
Tetanus - causes simultaneous, prolonged, severe muscle contraction
Differences between Endo- and Exotoxins (bacterial)
Exotoxins are composed of protein, endotoxins are composed of lipopolysacherride.
Exotoxins have specific action while endotoxins are non-specific
exotoxins are labile in heat, endotoxins remain stable
exotoxins have strong antigenicity, endotoxins have weak antigenicity
exotoxins are produced by both gram positive and gram negative; endotoxins are only found on gram negative (LPS)
exotoxins can be converted to toxoid; endotoxins cannot
How many chromosomes do bacteria normally contain
1
typically 2-4 x10^3 kb (kilobase - 1kb= 1000 bases)
How many RNA polymerases do bacteria have
1
What type of ribosomes do bacteria contain
30s/50s
What does much of bacterial antibiotic resistance result from
Point mutations. Commonly:
- base substitution
- deletion
- insertion
How many bases typically in a plasmid
10-60 kb
Name some sections commonly found in a plasmid
- Transfer promotion genes
- plasmid maintenance genes
- antibiotic/virulence determinant genes
How are plasmids typically transferred between bacteria
Bacterial conjugation
How can gene transfer occur in bacteria
- Transformation (gain from environment) eg via plasmid
- Transduction eg via bacteriophage
- Conjugation eg via sex pilus
Where does most bacterial variation come from
Gene transfer - lateral transfer of genes
Name the main obligate intracellular bacteria
Genus Rickettsia:
- R. rickettsii
- R. prowazekii
- R. conorii
- etc.
Genus Chlamydia:
- C. trachomatis
- C. psittaci
- C. pneumoniae
Genus Coxiella:
- C. burnetii
Which notable illness is caused by the Rickettsia genus of bacteria
Rickettsia rickettsii causes:
- scrub typhus/rocky mountain spotted fever
- transferred via tick
Which notable illnesses are caused by the Chlamydia genus
Chlamydia trachomatis can cause:
- the STI
- trachoma (eye infection)
Chlamydia psittaci causes:
- bird related pneumonia (can get from kissing pet parrots)
Chlamydia pneumoniae:
- associated with respiratory tract infections
Name the bacteria that may be cultured on artificial media AND has NO cell wall
Mollicutes:
- Mycoplasma pneumoniae (atypical pneumonia)
- M. hominis (STIs and infertility)
- Ureaplasma urealyticum
Name the bacteria that may be cultures on artificial media AND has a cell wall AND grow as filaments
Genus ACTINOMYCES e.g. A. israelii
Genus NOCARDIA e.g. N. asteroides
Genus STREPTOMYCES (important source of antibiotics)
Name the bacteria that may be cultures on artificial media AND has a cell wall AND grow as single cells AND are cocci AND gram negative
Anaerobic: Genus VEILLONELLA
Aerobic: Genus NEISSERIA
- N. meningitidis
- N. gonorrhoeae
What diseases are caused by the genus Neisseria
N. meningitidis causes:
- meningitis in late teens/early twenties
N. gonorrhoeae causes:
- gonorrhoea (2nd most common bacterial STI)
- has increased bacterial resistance
Name the bacteria that may be cultures on artificial media AND has a cell wall AND grow as single cells AND are cocci AND gram positive
Anaerobic:
- PEPTSTREPTOCOCCUS
- ENTEROCOCCUS (E. faecalis)
Aerobic:
- STAPHYLOCOCCUS
- STREPTOCOCCUS
How can Staphylococcus be further divided up
Coagulase positive:
- S. aureus
(- S. intermedius)
Coagulase negative:
- S. epidermidis
(- all other staph species)
How can Streptococcus be further divided up
Alpha-haemolytic:
- Viridans streptococcus
- S. pneumoniae
- S. sanguis
- S. oralis
etc.
Beta-haemolytic:
- S. pyogenes
- S. agalactiae
etc.
Non-haemolytic:
- S. bovis
What do different haemolytic reactions look like
Alpha-haemolytic partially lyses blood (via production of hydrogen peroxide) so makes the bacterial colonies look green
Beta-haemolytic fully lyses haem (via production of 2 pore-forming toxins) so turns blood agar clear
Non-haemolytic can’t lyse blood (also known as gamma-haemolysis)
What is the Lancefield classification? Give names of relevent bacteria.
It classifies bacteria from group A to group G based on which antibody they have
- S. pyogenes is Lancfield group A
- S. agalactiae is Lancefield group B
- Enterococcus faecalis (a different genus, NOT a strep) is Lancefield group D
Diseases caused by staph
S. aureus - associated with skin infections; also sometimes endocarditis, particularly after dental surgery
S. epidermis is oppertunistic, normally lives on skin but can cause infection if the human is compromised (e.g. due to catheter, plasters etc.)
What diseases are caused by strep
S.pyogenes:
- associated with pus,
- causes scarlet fever
- strep throat
S. pneumonia causes:
- common pneumonia
- meningitis in older people
Alpha-haemolytic strep - esp. viridans
- associated with infective endocarditis
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND acid fast
MYCOBACTERIA:
- M. tuberculosis (TB)
- M. leprae (leprosy)
- M. avium-intracellulare
- M. ulcerans
- M. kansasii
- etc
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram positive
Anaerobic:
- CLOSTRIDIUM
* C. tetani (tetanus)
* C. difficile (diarrhea)
* C.perfringens
* C. botulinum
etc.
- PROPIONIBACTERIUM
* P. acnes
Aerobic:
- CORYNEBACTERIUM
* C. diphtheriae
etc
- LISTERIA
* L. monocytogenes
etc
- BACILLUS
B. anthracis (Anthrax)
B. cereus (food poisoning)
etc
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative
Anaerobic:
- BACTEROIDES
* B. fragilis
Aerobic:
- ‘Coliforms’ (gut bacteria - non-spore forming)
- ‘Pseudomonads’ (belonging to pseudomonas genus)
- ‘Vibrio’ (curved rod)
- ‘Parvobacteria’ (small, fastidious, non-spore forming coccobacilli)
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative AND are coliforms
ESCHERICHIA
- e.g. E. coli
KLEBSIELLA
SALMONELLA
- e.g. S. typhi
SHIGELLA
- e.g. S. sonnei
CITROBACTER
PROTEUS
YERSINIA
- e.g. Yersinia pestis
etc
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative AND are Pseudomonads
PSEUDOMONAS
- e.g. P. aeruginosa
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative AND are vibrio bacteria
VIBRIO
- e.g. V. cholerae
CAMPYLOBACTER
- e.g. C. jejuni
HELICOBACTER
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are bacilli AND gram negative AND are parvobacteria
HAEMOPHILUS
- eg H. influenzae
BRUCELLA
BORDETELLA
- e.g. B. pertusiss
PASTEURELLA
Name the bacteria that may be cultured on artificial media AND has a cell wall AND grow as single cells AND are spirochaetes
LEPTOSPIRA
- e.g. L. icterohaemorrhagiae (Leptospirosis)
TREPONEMA
- e.g. T. pallidum (syphilis)
BORRELIA
- B. burghdorferi (lyme disease)
- B. recurrentis
etc
Which antigenic groups of strep are Beta-haemolytic?
A, B, C, G
How do you differentiate between viridans strep and S. pneumoniae?
Optochin test
- Viridans strep is resistant to optochin; S. pneumonia is sensitive to optochin
- On agar culture - optochin sensitivity looks like an area around the optochin disk that is clear of bacteria
How do you differentiate between S. aureus and other staphylococcus
Coagulase/DNAse test
- S. aureus is coagulase positive (also s. intermedius)
- rest are negative
What is a go-to antibiotic for staph infections
Flucloxacillin
How many species of staph are there
at least 40
What is coagulase? Why might this be produced?
Enzyme produced by bacteria that clots blood plasma
- Fibrin clot formation around bacteria may protect from phagocytosis
Where is the normal habitat of staph
nose and skin
Are coagulase +ve or -ve staph more likely to cause problems
Coagulase +ve
Coagulase -ve species (e.g. S. epidermidis) only important as opportunistic infections
How is staph aureus spread
Aerosol and touch
- some people are carriers/shedders
What are S. aureus’ virulence factors
Pore-forming toxins (in some strains)
- α - haemolysin (low levels: apoptosis, high levels: mass necrosis)
- Panton-Valentine Leucocidin ‘PVL’ (causes hemorrhagic pneumonia)
Proteases
- Exfoliatin (exotoxin - scalded skin syndrome)
Toxic Shock Syndrome toxin (super antigen)
- (stimulates cytokine release)
Protein A
- (surface protein which binds antibodies in wrong orientation)
What is MRSA?
Methicillin (aka flucloxacillin) Resistant S. aureus
- resistant to major antibiotics
- break open beta-lactam ring of certain antibiotics
- resitant to gentamicin, erythromycitetracycline
Types of S. aureus infections
Pyogenic:
- wound infections
- causes:
* abscesses
* Impetigo
* Septicaemia
* Osteomyelitis
* Pneumonia
* Endocarditis
Toxin mediated:
- Scalded skin syndrome
- Toxic shock syndrome
- Food poisoning
Name the main coagulase -ve staph species
- S. epiderimidis
- S. saprophyticus
Characteristics of S. epidermidis
- Oppertunistic infections
- common in immunocompromised and people with prostheses
- Main virulence factor - ability to form persistant biofilms (clusters of bacteria that are attached to a surface and/or to each other and embedded in a self-produced matrix)
Characterictisics of S. saprophyticus
Causes acute cystitis (UTI)
- commonly comes from skin contact in sexual intercourse
Virulence factors:
- haemagglutinin for adhesion
- urease
Is S. pyogenes aerobic or anaerobic?
It’s facultatively anaerobic (can grow anaerobically or aerobically)
Is S. pyogenes penicillic sensitive?
Yes
Where is s. pyogenes most likely to infect?
Throat, skin, post partum infections
What kind of infections are s. agalactiae associated with
Neonatal infections - passed from mother to child
How are Lancefield groups tested? Describe the procedure.
Lancefield microbead agglutination test:
- Antiserum (solution of antibodies) made that recognise each specific group
- The antiserum is tagged to tiny plastic beads
- These are added to a suspension of bacteria
- If the bacterial antigen is complementary to the antiserum, they bind together and cause the beads to clump together
- this is visible to the naked eye
Virulence factors of S. pyogenes
Exported factors:
- Enzymes
* Streptokinase (important)
** breaks down clots
* Hyaluronidase
** spreading
* C5a peptidase
** reduces chemotaxis
- Toxins
* Streptolysins O&S (Important)
** binds cholesterol
* Erythrogenic toxin (Importnat)
** Streptococcal pyrogenic toxin e.g. SPeA – exaggerated response
** Can lead to scarlet fever in children
Surface factors:
- Capsule - hyaluronic acid
- M protein – surface protein (Important)
(encourages complement degradation)
* can cause scarlet fever in children
Infections caused by S. pyogenes
Respiratory
- Tonsillitis & pharyngitis (most common)
- Otitis media
Skin and Soft tissue
- Wound infections
- Impetigo
- cellulitis
- puerperal fever
Scarlet fever
- SPeA and M type
Complications
- rheumatic fever
- glomerulonephritis
Characteristic appearances of S. pneumonia in culture/tests
- “draughtsman” colonies (depressed central part with raised edges)
- α- haemolytic
- Gram positive cocci in pairs
- Optochin sensitive
Where is S. pneumonia often found (non-pathogenically)
Found as a commensal in oro-pharynx of 30% of population
What does S. pneumoniae cause pathogenically
Pneumonia
Otitis medis (middle ear infection)
Sinusitis
Meningitis
What factors predispose to S. pneumoniae infection
- Impaired mucus trapping (e.g. viral infection)
- Hypogammaglobulinaemia (problems making antibodies)
- Asplenia (absence of spleen)
- HIV
S. pneumonia virulence factors
Capsule
- polysaccharide (84 types), antiphagocytic
Inflammatory wall constituents
- teichoic acid (choline)
- peptidoglycan
Cytotoxin
- pneumolysin (pore-forming)
Which vaccines are there for S. pneumoniae infection
- polysaccharide vaccine ‘PPV’ - contains 23 types of pollysaccheride antigens from s. pneumoniae capsule
- conjugate vaccine ‘PCV’ - contains 13 types of pollysaccheride antigens from s. pneumoniae capsule
Who are S. pneumoniae vaccines given to and why
Only at risk people over 2 y/o
The immune response to polysaccheride antigens is poor in the very young
Who is at risk for S. pneumoniae infection
People with:
- sickle cell disease,
- asplenia,
- renal disease,
- immunodeficiency,
- diabetes
- chronic liver disease
How does pneumolysin form pore
Subunits assemble into a ring structure on host cell surface thus forming a pore in the membrane
Characteristics of Viridans group strep
α- haemolytic (or non-haemolytic)
Optochin resistant
What diseases can Viridans group strp cause
- Some cause dental caries & abscesses - typically live in mouth
- Important in infective endocarditits (difficult to diagnose and treat)
- Cause deep organ abscesses (e.g. brain, liver)
Which strep species are typically associated with infective endocarditis? What is a typically presentation of this?
- S. sanguinis
- S. oralis
Very typical for people to get endocarditis after having dental surgery - they get into the blood from the mouth
Most virulent group of Viridans group strep
‘milleri group’
S.intermedius, S.anginosus, S.constellatus
Main aerobic Gram positive bacilli
- Listeria monocytogenes
- Bacillus anthracis
- Corunebacterium diphtheriae
What does listeria monocytogenes cause?
causes listeriosis (starts as type of food poisoning - grows in moist areas)
- usually self-limiting
- can cause issues in immunocompromised people and pregnant women
What does bacillus anthracis cause?
Anthrax
- associated with cattle
- spore forming so can be around for a long time
3 syndromes depending on route of acquisition:
- Cutaneous - blister with black centre (‘eschar’)
- Inhalation - respiratory sepsis
- Ingestion - severe gasteroenteritis
What does corynebacterium diphtheria cause
Diphtheria
- infectin of pharynx
* thick greyish pseudo membrane on tonsils can be a characteristic of it
- involves infection of immune cells
- involves metachromatic granules
Main anaerobic gram positive bacilli
All main are types of CLOSTRIDIA
- C. tetani
- C. botulinum
- C. difficile
What does C. tetani cause? Associated symptoms and characteristics.
Tetanus
- muscle contractions and stiffness progressing from head to body (neck stiffness, sore throat, difficulty opening mouth) - rictus grin
- Get from infected wounds
- Toxin inhibits GABA
What does C. botulinum cause?
Botulism
- paralysis spreading from head to body (from Botulinum toxin)
- from contaminated food or infected wounds
What does C. difficile cause?
Antibiotic associated diarrhea (as it kills off good bacteria and leaves C. difficile able to colonise more of the gut)
- pseudomembranous colitis (destroys coloon)
What are the components of LPS
- Lipid A - the toxic portion that is anchored in the outer leaflet of outer membrane
- Core (C) antigen (AKA core oligosaccheride) - short chain of sugars, some are unique to LPS
- Somatic (O) antigen (O-polysaccheride) - highly antigenic repeating chain of oligosaccherides
Why do mycobacteria or mycoplasmas not stain with Gram stain? Are they considered gram positive or negative?
Mycobacteria outer lipid bilayer is composed of Mycolic acids
Mycoplasmas don’t have peptidoglycan
- They are phylogenetically considered Gram positive
The two types of virulence factors/pathogenicity determinants
Colonisation factors
Toxins (‘effectors’)
Name colonisation factors
Adhesins, invasins, nutrient acquisition, defence against the host
sdfk
What are toxins/’effectors’ released by gram bacteria?
- Usually secreted proteins that cause damage and subversion
- In gram neg bacteria the protein secretion system spans both layers on the cell membrane - proteins are translocated from inside cytoplasm and secreted
Which bacteria are within the Phylum proteobacteria
Enterobacteriaceae or Enterobacteria FAMILY (contains Shigella, salmonella, escherichia etc.)
Vibrio (e.g. vibrio cholerae)
Pseudomonans
Haemophilus (e.g. H influenza)
Legionella (e.g. Legionella pneumophila)
Bordetella (e.g. bordetella pertussis)
Neisseria
Campylobacter
Helicobacter (e.g. Helicobacter pylori)
Characteristics of Enterobacteria
Rods
Most are motile (have peritrichous flagella - flagella over their entire surface, like around the perimeter)
Some species colonise the gut (commensals and pathogenic)
Facultatively anaerobic
Name main members of enterobacteria?
Shigella
Escherichia (esp E. coli)
Salmonella (e.g. S. enterica)
Proteus (e.g. P. mirabilis)
Klebsiella (e.g. K. pneumoniae)
Less relevent according to lecturer:
Serratia (e.g. S. marcenescens)
Yersinia pestis
Enterobacter spp.
Which main enterobacteria are lactose use positive?
E. coli
Klebsiella pneumoniae
Which main enterobacteria are motile
E. coli
Salmonella enterica
Serratia marcensens (is this important??)
Yersinia pestis at 25 degrees C (NOT motile at 37 degrees so NON-MOTILE inside humans)
Proteus mirabilis
Which main enterobacteria are NOT motile?
Shigella flexneri
Klebsiella pneumoniae
Yersinia pestis at 37 degrees C
How do you test Lactose phenotype?
On MacConkey agar
Selective for gram-negative bacteria (contains bile salts and crystal violet)
Contains indicator so Lactose metabolising positive organism colonies turn red
Which antigen is associated with flagella
H antigen
How do you discriminate between similar bacteria like Salmonella and Shigella
Serology
(in this case, no H (flagella) antigen pressent for Shigella)
What is serotyping
Differentiating between specieses/strains by identifying cell surface antigens
What is a serovar
Antigenically distinct varients of a single species
What are the 3 main antigenic determinants for serotyping in gram negative bacteria
K antigen (exopolysaccheride ‘capsulel’)
H antigen (flagella)
O (somatic) antigen (LPS)
What is Escherichia coli normally
Commensal gram -ve bacteria - most abundant facultative anaerobe in gut (10^7-10^8/g faeces)
Has peritrichous flagella
Principal infections caused by pathogenic E. coli
(i) Wound infections (typically post-surgical)
(ii) UTIs (cystitis; 75-80% of female UTIs - faecal source or sexual activity;
* catheterisation - most common type of nosocomial (originating in hospital) infection)
(iii) Gastroenteritis
(iv) Travellers’ diarrhoea
(v) Bacteraemia (can be asymptomatic - sometimes leading to sepsis syndrome)
(vi) Meningitis (infants) - rare in UK
What are the species’ of Shigella
S. dysenteriae,
S. flexneri,
S. boydii,
S. sonnei
What does shigella cause
Shigellosis: severe bloody diarrhoea (bacillary dysentery)
- S. dysenteriae causes most severe form.
BUT - S. sonnei most prevalent in developed world.
Where is Shigella infection often found
Endemic in developing countries where sanitation is poor – mainly in children.
Symptoms of shigellosis
Frequent passage of stools (>30/day)
Small volume, pus and blood, prostrating cramps, pain in straining, fever
Usually self-limiting (in adults)
Pathogenesis of Shigella infection
Acid-tolerant (low infective dose, ~10^2)
Person-to-person, or contaminated water & food
(fresh/raw vegetables used in salads)
Entry through colonic M cells (antigen sampling cells - lie over lymphoid follicles and deliver antigens to underlying immune cells)
Induced uptake
Important virulaence factor: Shiga toxin
Pathology of Shigella
- lands on M cell apical surface
- gets taken to basolateral surface
- phagocytosed by macrophage (but rmains unharmed)
- Shigella induces apoptosis of macrophage
- moves laterally, destroying tissue
- Macrophages also release cytokines to attract polymorphoneuclear leukocytes to the site of in fection causing more tissue damage
What are the 2 specieces of Salmonella
S. enterica (has >2 500 serovars, including Salmonella enterica serovar Typhi)
S. bongori (rare - contact with reptiles)
What does S. enterica cause
salmonellosis (usually from contaminated food/drink)
3 forms:
1. Gastroenteritis/enterocolitis
2. Enteric fever
3. Bacteraemia (bacteria in blood)
Pathogenesis of salmonellosis
Ingestion of contaminated food/water - high I.D. (infective dose)(~10^6) (‘faecal-oral route’)
→ Invasion of gut epithelium (small intestine)
→ Transcytosed to basolateral membrane
→ Enters submucosal macrophages
→ Intracellular survival/replication
In Serovars Enteritidis and Typhimurium:
- intestinal secretion and inflammatoryresponse are LOCALISED
- DO NOT produce toxins
In serovar Typhi:
- Infection is SYSTEMIC due to dissemination within macrophages (macrophages migrate to reticuloendothelial organs via lymph and blood)
- produces TYPHOID TOXIN (has DNAse activity - a genotoxin)
Gastroenteritis/enterocolitis - causes and characteristics
Caused by serovars Enteritidis and Typhimurium
Frequent cause of food poisoning (milk, poultry meat & eggs)
Second highest no. of food-related hospitalisations/deaths (UK)
6-36 hr incubation period, resolves (~7 days)
Localised infection, only occasionally systemic
Enteric fever - causes/characteristics
Typhoid/paratyphoid fever - caused by serovars Typhi and Paratyphi
Linked to poor quality drinking water/poor sanitation
Systemic disease
~20 million cases, ~200,000 deaths/year (globally)
What causes Bacteraemia
Serovars Cholerasuis and Dublin
- it is uncommon
Steps of gastroenteritis pathogenesis
- Bacterial-mediated endocytosis
- Induction of interleukin-8 release →
- Neutrophil recruitment and migration
- Neutrophil-induced tissue injury →
- Fluid and electrolyte loss → diarrhoea
Inflammation/necrosis of gut mucosa
Steps of enteric/typhoid fever pathogenesis
- Bacterial-mediated endocytosis
- Transcytosis to basolateral membrane
- Survival in macrophage (MΦ) → systemic
spread
Initially, little damage to gut mucosa
What % of people become carriers of S. enterica serovar Typhi
~10% are carriers for < or = 3 months (bacteria shed in faeces)
~ 1-4% become chronic carriers (at least a year or more)
Notable characteristic of Proteus mirabilis
Can differentiate into an elongated hyperflagellated
form → gives it surface motility (ability of ‘swarming’) over solid surface
What does Proteus mirabilis cause
Catheter-associated UTIs (~30% of cases)
- can ascend and cause pyelonephritis (kidney infection)
Formation of bladder/kidney stones, can block catheter
- does this by producing urease (increasing urine pH) which forms ammonia and leads to calcium phosphate precipitation
Characteristics of Klebsiella pneumoniae
- environmental (it is an enterobacteria but more common in environment)
- opportunistic, nosocomial infections (neonates, elderly, compromised)
- colonisation of gastrointestinal tract (normal) and oropharynx (less frequently) is often benign
Multi-drug resistant (resistant to carbapenems)
What does Klebsiella pneumoniae cause
UTI, pneumonia (aspiration from oropharynx), surgical wound infections from gut,
bacteraemia → sepsis (high mortality).
Characteristics of Vibrio cholerae
- Facultative anaerobe
- Normally from Saline environments: commensal to planktonic crustaceans such as copepods
→ ingestion by shellfish
→ contamination of drinking water due to
flooding of coastal areas or poor sanitation
(faecal contamination) - characteristic curved rod shape
What does vibrio cholerae cause
Cholera: Most severe diarrhoeal disease
Associated with LPS O1 serotype → epidemics (and occasionally O139 variant)
Characterised by pandemics (7 recorded since 1817)
History of Choleral pandemics
1P-6P, Indian subcontinent;
7P began in Sulawesi (1961) → SE Asia (1963) →
Africa (1970) → Latin America (1991) → Caribbean (2010)
1.4-4.0 million cases/year, 20,000-140,000 associated deaths
General pathology of Cholera (aquisition, incubation, consequence)
Faecal-oral route (not person-to-person) - high infective dose required (not acid resistant)
(faecal contaminated water (poor sanitation)
or undercooked shellfish from risk areas)
↓
Incubation, few hours to 5 days (V.c. multiplies in small intestine)
↓
Voluminous watery stools (‘secretory’ diarrhoea - rice water stool)
Can lose 20 litres fluid/day plus electrolytes
→ dehydration/death (hypovolaemic shock)
→ 50-60% mortality if untreated
No blood, pus or fever (i.e. not dysenteric)
i.e. no invasion or damage to mucosa
What can most cases of Cholera be treated by
Oral re-hydration therapy (ORT)
What is the main virulence factor of V. cholerae
Cholera toxin
Pathogenesis of Cholera (mechanism of cholera toxin)
CT binds to a glycolipid receptor on epithelial cell (B subunits)
A subunit ADP-ribosylates G-protein (Gs) → locked in ‘ON’ state
Uncontrolled cAMP production
Protein kinase A activated
Phosphorylates CFTR (cystic fibrosis transmembrane conductance regulator) anion transporter
CFTR activity modified
(loss of Cl- & Na+ into gut lumen)
→ massive loss of H2O
Characteristics of Pseudomonas aeruginosa
Ubiquitous, free-living (in environment), motile (single polar flagellum), rod-shaped.
Opportunistic (serious cause of nosocomial infections)
Resistant to multiple antibiotics (& disinfectants) - very difficult to treat
Infections caused by P. aeruginosa. Can it cause acute or chronic?
Acute infections:
(i) Localised
- burn/surgical wounds
- UTI (catheters)
- Keratitis (infection of cornea - requires some kind of scratch etc.)
(ii) Systemic (bacteraemic → sepsis - hard to treat)
- affects neutropenic patients - low white blood cell count (leukaemia, chemotherapy, AIDS)
(iii) affects ICU patients (ventilator acquired pneumonia)
- leading cause of nosocomial pneumonia
Chronic infections:
(i) In Cystic fibrosis (CF) patients
Common denominator to all infections - compromised host defences
What happens in cystic fibrosis (general overview)
Defective CFTR (chloride ion transporter)→ thick mucus produced in lungs.
- Lungs prone to microbial infection
Most problematic source of infection for CF patients
P. aeruginosa
Types of P. aeruginosa
P. aeruginosa ‘wild-type’ (non-mucoid)
P. aeruginosa ‘CF’ phenotype (mucoid) = mutants that secrete a thick coating of exopolysaccharide (i.e. hyper-produce capsule): provides additional protection against host defences in the lung
What leads to the progressive lung damage following infection of CF lung by P. aeruginosa
Mainly due to effect of host immune system trying to clear infection
Characteristics of Haemophilius influenzae
Exclusively human parasite (obligate/ no environmental reservoir):
Nasopharyngeal carriage in 25-80% population (non-capsulate strains)
- transient carriage of capsulate strains occurs in 5-10% (more dangerous as they are invasive - can move around body)
Oppertunistic
Who are particularly susceptible to H. influenzae infection
Young children and adult smokers
What infections can Haemofilius influenza cause
- Meningitis* (age <5 yrs), 5-10% of adult cases
∙ Bronchopneumonia
∙ Epiglottitis, sinusitis, otitis media
∙ Bacteraemia (often associated with pharyngitis)
∙ Pneumonia in CF, COPD, HIV patients - infections caused by capsulate strains (invasive) – uncommon in healthy adults
Diagnostic characteristics of H. influenxae
Fastidious
- requires ‘factor X’ (haem) and ‘factor Y’ (NAD)
- requires chocolate agar (lysed/oxidised blood)
Non-motile
Virulence determinants of H. influenzae
(i) Capsule - invasive strains are capsulate (‘encapsulated’)
→ can penetrate nasopharyngeal epithelium
→ resistance to phagocytosis and complement system
- 6 different capsule serotypes (a-f)
(type b strains are the main cause of meningitis)
Commensals and upper respiratory tract pathogens are non-capsulate referred to as ‘non-typeable’ H. influenzae (NTHi)
(ii) LPS (‘endotoxin’) → inflammation
→ complement resistance
Which vaccine has reduced the cause of H. influenza caused meningitis
Hib vaccine (HH. influenza type b)
What does Legionella pneumophila cause, source of acquisition and who does it usually affect
Legionnaires’ disease - severe inflammatory pneumonia (1-3% of all pneumonias)
- 15-20% mortality
Infection from man-made aquatic environments
(air-conditioning cooling towers, shower heads, nebulisers, humidifiers etc.) - never person-to-person transmission
- replicate within freshwater protozoa
- can repliacte in alveolar macrophages too
Affects immunocompromised (elderly, alcoholics, smokers etc.)
What does Bordetella pertussis cause
Pertussis (whooping cough)
Non-specific flu-like symptoms (~7 d), followed by paroxysmal coughing
(https://www.youtube.com/watch?v=l5SHtdczSBc)
(B. parapertussis causes mild pharyngitis)
Characteristics of B. pertussis
Humans - only known reservoir (obligate human pathogen)
Highly contagious (low I.D.) - aerosol transmission
(- produces pertussis toxin and Adenylate cyclase-haemolysin toxin (CyaA))
Non-invasive
Diagnostic characteristics of B. pertussis
Short (sometimes oval) rods (coccobacilli)
Fastidious
Gram negative
Diagnostic characteristics of Neisseria
Non-flagellated diploccoci
Fastidious
Gram -ve
Where can Nessieria be found in the environment
Humans are the only known reservoir
Characteristics of N. meningitidis
Nasopharyngeal carriage in 5-10% population (asymptomatic)
Rises to 20-90% during outbreaks
Person-to-person (aerosol) transmission (universities, barracks, Haj)
Pathogenesis of N. meningitidis
crosses nasopharyngeal epithelium and enters bloodstream
→ low level - bacteraemia (asymptomatic) or high level - septicaemia (sepsis - high mortality if not treated) → meningitis: invasion of the meninges - bacteria enter CSF of subarachnoid space after crossing blood-brain barrier
(second most frequent cause of meningitis in young children)
Virulence determinants of N. meningitidis
(i) Capsule is major virulence determinant (serogroup B - 90% cases)
→ anti-phagocytic
(noncapsulated N.m. only found in nasopharynx - not pathogenic)
(ii) LPS (membrane ‘blebs’)
→ cytokine cascade
→ sepsis
What are non-blanching petechial pr purpuric rashes associated with
Meningococcal sepsis
(capillary damage - bleeding - ecchymosis AKA bruising)
What does N. gonorrhoeae cause
Gonorrhoea - second most common STD worldwide
How is gonorrhoea transmitted
Person-to-person only
How often can N. gonorrhoeae infection be asymptomatic
~10% men, ~50% women
Characteristic infection presentation of gonorrhoea
Urethritis with additional infection of female genitalia.
Serious complications in women - can lead to salpingitis (fallopian tubes) and/or PID (pelvic organs) if infection ascends.
Proctitis, gingivitis, pharyngitis depending on sexual preference
Can transmit as conjunctivits to newborns
Are gonococci capsulated or not
They are non-capsulated
Helicobacter pylori appearance
spiral shape, tuft of polar flagella
Where are H. pylori found in the body
Discovered in gastric mucus (1982) which was previously thought to be sterile
Incidence of H. pylori in global population
Present in ~50% global population, but only
a fraction develop disease
Which diseases are H. pylori associated
Major role in gastritis and peptic ulcer disease (80-90% of ulcers)
Implicated in ~10% cases of gastric adenocarcinoma & mucosa-associated lymphoid tissue lymphoma (linked to production of VacA and CagA toxins)
Name of main bacteria in Phylum bacteroidetes
Bacteroides
Characteristics of Bacteroides
Non-motile rods
Obligate anaerobes
Commensal flora of colon (most abundant organism in gut - 30-40% of total)
Opportunistic
What amount per g of faeces is Bacteroides? Population ratio compared to E. coli?
> 10^10/g faeces (outnumbers E. coli 20:1)
What infections can infections can Bacteroides cause
Infection of tissue injury (surgery, perforated appendix or ulcer)
→ predominantly peritoneal cavity
infections (peritonitis,
intrabdominal abscesses are most
common) can lead to bacteraemia
Most frequent cause of banaerobic infections
Often present in polymicrobial infections with enterobacteria
- presence of facultative anaerobes depletes O2, allowing anaerobes such as Bacteroides to proliferate
Which Bacteroides species is most commonly responsible for infections
B. fragilis
(although it is only 0.5-1.0% of total commensal Bacteroides)
Which genuses are in Phylum Chlamydiae
Chlamydia and Chlamydophila
Characteristics of Chlamydia and Chlamydophila
Very small, non-motile.
Obligate intracellular parasites.
Many species within this group live asymptomatically as endosymbionts in
amoebae, invertebrates and vertebrates.
Cannot culture in bacteriological media - detect by serum Abs (antibodies - tho these could be due to previous infection so anleternate confirmatory test must also be done) or PCR (AKA NAA or NAAT)
Life cycle of Chlamydia and Chlamydophila
2 developmental stages:
(i) Elementary bodies (EBs) - rigid, extracellular form, ~0.3 μm, dormant
infectious enter cell through endocytosis prevent phagosome-lysosome fusion ↓ differentiates into...
(ii) Reticulate bodies (RBs) - fragile, intracellular form, ~1.0 μm, metabolically active
replicative non-infectious acquire nutrients from host cell
How many developmental stages in life cycle of Chlamydia/Chlamydophila
2
- Elementary body stage
- Reticulate body stage
Form/characteristics of Chlamydia/Chlamydophila Elementary bodies
Rigid, dormant extracellular form
~0.3 micrometers
What occurs during the elementary body phase of Chlamydia/Chlamydophila life cyle
Infectious
Enter cell throughendocytosis
prevent phagosome-lysosome fusion (so it can’t be destroyed by host defence of cell)
What happens in reticulate body phase of Chlamydia/Chlamydophila life cycle
Non-infectious
Replication
Acquire nutrients from host cell
Characteristic of Chlamydia/CHlamydophila reticulate body
fragile, metabolically active, intracellular form
pleiomorphic
~1.0 micrometers
Medically important members of genus Chlamydia
C. trachomatis (has 3 biovars):
- trachoma biovar (serotypes A-C)
- gentital tract biovar (serotypes D-K)
- lympho granuloma venereum (LGV) biovar
What disease does the Chlamydia trachomatis biovar trachoma cause
Trachoma → blindness
(eye-to-eye transmission via hands, fomites (innanimate objects like mascara brushes) or flies)
Largest cause of preventable blindness caused by infectius organisms
Easily treated if caught early but often not recognised till later
What does C. trachomatis biovar genital tract cause
Chlamydia STI
- most common STD in UK - infects epithelial cells of mucous membranes of urethra (both sexes) and vagina
- can ascend to uterus and ovaries (PID, infertility)
- usually asymptomatic (i.e. 70-80% cases in women)
Conjunctivitis (hand-to-eye transmission OR mother-to-child during delivery)
What does the lympho granuloma venereum (LGV) biovar of Chlamydia trachomatis cause
LGV (an STD) - invasive urogenital/anorectal infection
- endemic to the tropics, cases rising in Europe/North America
Medically important members of Chlamydophila
C. pneumoniae
C. psittaci
What does C. pneumoniae cause
Resp tract infection (mild/’walking’ pneumonia)
Causes ~10% community acquired pneumonias
What does C. psittaci cause
Psittacosis (severe pneumonia)
Mainly affects bird owners (zoonotic)
Uncommon
Spirochaete physical form
Long, slender, helical, highly flexible
Characteristics of Spirochaetes
Most are free-living and non-pathogenic
Pathogenic varieties difficult to culture
Has a modified outer membrane (Treponema and Borrelia lack LPS, have a different glycolipid instead)
Where is the spirochaete endoflagella located
Between peptidoglycan and outer membrane
Periplasmic flagella
Fixed at each end of bacterium and confers shape
Overlap in centre of bacterium
Characteristics of spirochaete endoflagella function
Propels in corkscrew motion
Swims faster in high viscosity medium (i.e. normal environment of spirochaetes)
‘Hides’ antigenic flagellum
What are the 3 medically important members of Spirochaetes
Borrelia burgdorferi
Leptospira interrogans
Treponema pallidum
What does Borrelia burgdorferi cause
Lyme disease
How is Lyme disease transmitted
Via ticks
B.b. infects small mammels (e.g. rodents)
Tick larvae feeding on the infected animal acquire B.b.
Usually transmitted to humans by tick nymphs (adults easier to spot)
Symptoms of Lyme disease
Bull’s eye rash
Flu-like symptoms (fever, fatigue, headache)
(neurological problems in 10-15% patients, joints → arthritis)
Most symptoms arise as consequence of immune response
How can lyme disease spread within the human body
dissemination via lymphatics/blood to other organs
What does leptospira interrogans cause
Leptospirosis (zoonosis) - rare in UK
Symptoms of leptospirosis:
- Flu-like
- Severe form (Weil’s disease) in 10-15% infected individuals
* jaundice, acute renal and hepatic failure, pulmonary distress, haemorrhage
How is leptospirosis acquired?
Contact of infected animal urine with mucous membrane or abraded skin
What does treponema pallidum cause
Syphilis
How many stages of syphilis (treponema pallidum infection)
3
Primary stage
Secondary stage
Tertiary stage
What occurs in primary stage syphilis (treponema pallidum infection)
Localised genital infection (chancre)
Defined as days-weeks post-infection (i.e it is in the primary stage if it is occuring within days/weeks of being infected)
