Bacteria structure Flashcards
Lipopolysaccharides
- Also known as endotoxins
- Found in the outer membrane of Gram negative bacteria and elicit strong immune responses
- It contributes to the structural integrity of the bacteria
- LPS increases the negative charge of the cell membrane
- It helps with adhesion
- It is composed of 3 parts: O-antigen, Core oligosaccharide and Lipid A
Lipooligosaccharides
- It is the low molecular weight form of LPS
- Glycolipids found in the outermembrane of some types of Gram-negative bacteria including: Neisseria spp. and Haemophilus spp
- They play an important role in the pathogenesis of some bacterial infections as they can act as immunostimulators and immunomodulators
- Virulence factors, help in immune evasion
Exotoxin
- Mostly gram positive bacteria
- Extracellular
- Polypeptide
- Unstable
- Powerful
- Specific
- THe most important Exotoxin is the AB toxin
Endotoxin
- Almost all gram negative bacteria
- It is part of the outer layer of the cell wall
- They are also called LPS
AB toxin
- 2 component protein complexes secreted by pathogenic bacteria
- They can be classified as type III toxins as they interfere with internal cell function
Streptococcus pneumoniae
- Encapsulated gram positive
- Diplococci, lancet shaped, do not form spores and are non-motile
- Comensal bacteria in nasopharynx
- It is spread by respiratory droplets
- IT is the main cause of community acquired pneumonia and meningitis in children and the elderly
- Do not produce the catalase enzyme
VIRULENCE FACTORS
- Key virulence factor is the polysaccharide capsule
It is anti-phagocytic and is the basis for vaccination
- Invasins: pneumolysin (cytotoxin)
- Surface adhesins
-sIgA protease interferes with mucosal immunity
- Teichoic acid
- H2O2 can be cytotoxic to host cells
ADHERENCE
- RgA, pillin tip protein, PsaA
INFECTION
It colonises the air sacs of the lungs
THe body responds by stimulating the inflammatory response causing plasma, blood and white blood cells to fill the alveoli (pneumonia)
TOXINS
- pneumolysin
ANTIBIOTICS
It is susceptible to clindamycin Resistant to penicillin
Invasin
A class of proteins associated with the penetration of bacteria into host cells
Streptococcus pyogenes
Group A Streptococci
- Gram positive bacteria
- Non motile and non sporing cocci
- Commensal as part of the skin microbiota
- It is transmitted by respiratory droplets and from cattle to humans through contaminated food
VIRULENCE FACTORS
It has several virulence factors that enable it to attach to host tissues, evade the immune response and spread by penetrating host tissue layers
- A carbohydrate based bacterial capsule surrounds the bacterium, protecting it from phagocytosis
- M protein, lipoteichoic acid and protein F facilitate attachment to various host cells
- M protein also inhibits opsonisation
- M proteins are unique to each strain
- F proteins
INFECTION
- strep throat
- Scarlett fever
TOXINS
- 4 pyrogenic exotoxins: A, B, C & F trigger inflammatory responses
- Erythrogenic toxin (exotoxin)
ENZYMES
- Streptolysin S and O lyse RBCs
Viridans Streptococci
- Gram positive
- Cocci
- Commensal bacteria in the mouth
- If they are introduced into the bloodstream, they have the potential to cause endocarditis
VIRULENCE
- No noteworthy virulence factors, but they contribute to disease when thre are breaks in mucosal barrires
Enterococcus
- Gram positive
- Cocci
- Faculatiev anaerobic
- Do not form spores
- 2 species are common commensals in the intestines- E.facecalis and E. faecium
INFECTION
UTI’s
Bacteremia
Meningitis
Staphylococcus aureus
- Gram positive cocci
- Commensal in the nasopharynx + skin
- Faculative anaerobe
VIRULENCE FACTORS
- Exotoxins: membrane disrupting toxins
1. Hemolysins, lysis of RBC
2. Enterotoxin
3. Leukocidin, destroys WBCs - Extracellular enzymes
1. Coagulase, conversion of fibrinogen to fibrin = clots plasma and prevents phagocytosis
2. Catalase, converts H202 to H20 and O2
3. Lipase, penetrates fatty tissue
4. Deoxyribonuclease, which breaks down the DNA
ANTIBIOTICS
- Penicillin
RESISTANT
- MRSA
Staphylococcus epidermidis
- Gram positive
- Commensal bacteria in the skin
- It is a concern with people with catheters as it is known to form biofilms
VIRULENCE
- The ability to form biofilms on plastic devices
It produces an extracellular material known as polysaccharide intercellular adhesion, which allows other abcteria to bind to the existing biofilm
Staphylococcus saprophyticus
- A gram positive coccus
- Coagulase negative
- Community acquired UTI
- Commensal in the female genital tract
VIRULENCE FACTORS
- Adherence to urothelial cells by lipoteichoic acid
Micrococcus
- Gram positive cocci
- M. luteus (yellow) and M. roseus (red) produce yellow or pink colonies when grown on mannitol salt agar
- Commensal on skin
- Aeorobic
Bacillus cereus
- B. anthracis
- B. cereus
Bacillus anthracis
- Gram positive bacillus
- Faculatative anaerobe
- Encapsulated
- Forms spores
VIRULENCE FACTORS
- Capsule, inhibits phagocytoss
- Anthrax exotoxin
- Protective antigen
Bacillus cereus
- Gram positive rod
- Motile
- Nonencapsulative
- Faculative anaerobe
- Forms spores that adhere to epithelial cells, virulence factor
INFECTION
- Food poisoning
gastroenteritis, ingestion of spores (diarrhea)
intoxication, ingestion of toxins (vomiting)
TOXINS
- Enterotoxins
- Hemolysins
- Phospholipase C
Hemolysin
Lipids and proteins that cause lysis of red blood cells by destroying their cell membrane
Phospholipase C toxin
It can interact with cell membranes and hydrolyse them leading to cell lysis
Clostridium
- C. perfrigens
- C. difficile
- C. tetani
- C.botulinum
- Gram positive bacilli
- Obligate anaerobes
- Produce endospores with a distinct bowling pin shape
- Inhabit soil
- Commensal of reproductive tract in women
CLOSTRIDIUM PERFRIGENS
- It causes food poisoning and gas gangrene (a-toxin)
VIRULENCE FACTORS
- Type II toxin, disrupts plasma membrane
CLOSTRIDIUM DIFFICILE
- diarrhea
- risk factors= antibiotics, when the antibiotic kills off other competing bacterine in the intestine
- It is spread by bacterial spores in feces
VIRULENCE FACTORS
- enterotoxin
- cytotoxin
CLOSTRIDIUM BOTULINUM
- types A, B and E cause diseases in humans
- Commensal in the large intestine
- Spores enter anaerobic environment and organism produces toxin
- Obligate anaaerobe
VIRULENCE FACTORS
- Produces a neurotoxin called botulinum onlyduring sporulation in an anaerobic environment
- It is associated with canned food
CLOSTRIDIUM TETANI
- Anaerobic
- It is found in spores in the soil
- Produces spores that are heat tolerant
- It usually enters a host through a wound to the skin
VIRULENCE FACTORS
- Toxin, tetanospasmin (neurotoxin) and tetanolysin
Obligate anaerobe
They are poisoned by oxygen
Facultative anaerobes
They can grow with or without oxygen
Mycobacterium
M. tuberculosis
M. leprae
- Aeorobic and nonmotile
- Acid fast
- Capsules and most do not form endospores
- Notoriously difficult to treat, cell wall is neither truly gram positive or negative
- characteristic thick waxy coating prevents its gram stain
MYCOBACTERIUM TUBERCULOSIS
- An obligate pathogenic bacterial species
- Waxy coating on its cell surface due to mycolic acid
- It requires high levels of oxygen
- Humans are the only known reservoirs of M. tuberculosis
- It can be spread through air droplets
- When in the lungs it is phagocytosed by macrophases but they are unable to kill and digest the bacterium
- It secretes proteins that preents the fusipon of the phagosome with the lysosome
VIRULENCE FACTORS
- mycolic acid wax in cell wall
- catalase
MYCOBACTERIUM LEPRAE
- Aerobic bacillus surrounded by the characteristic waxy coating unique to mycobacteria
- Obligate intercellular parasite
- Disease, leprosy
VIRULENCE FACTORS
- A waxy exterior coating formed by the production of mycolic acids
- Catalase
Acid fast stain
Ziehl-Neelson stain
Purpose: to differentiate between acid- fast and non acid- fast bacteria
Some bacteria contain a waxy lipid, mycolic acid, in their cell wall
- Used carbol-fuschin and heat
- Decolourised with an acid alcohol
- Counterstain with methylene blue
Non acid fast= blue
Acid fast= Red
Nocardia
- Gram positive, catalase positive
- Weakly acid fast
- Commensal in mouth
- Infections are acquired by inhalation or by traumatic introduction
- Pathogenic with low virulence
VIRULENCE FACTORS
- Catalase
- Superoxide dismutase
Listeria monocytogenes
- Facultative anaerobe
- Motile
- It can grow and reproduce inside the host’s cells and is one of the most virulent foodborne pathogens
- It causes listeriosis
- It can tolerate low and high temperatures
VIRULENCE FACTORS
- listeriolysin O, LLO
- phospholipase A + B
