MECHANISMS OF BACTERIAL VIRULENCE 2 Flashcards
PATHOGENICITY DEFINITION?
CAPACITY TO INITIATE DISEASE (QUALITATIVE, ALL OR NONE CONCEPT)
WHAT IS VIRULENCE?
CAPACITY TO CAUSE DISEASE AND THE SEVERITY OF THAT DISEASE (QUANTIFIES PATHOGENICITY)
WHAT IS INFECTIVITY?
ABILITY OF A PATHOGEN TO BREAK HOST DEFENSES
WHAT ARE VIRULENCE FACTORS?
PROTEINS ENCODED BY A BACTERIAL ORGANISM THAT ARE ESSENTIAL FOR ITS PATHOGENICITY (HELP ACHIEVE INFECTION)
ROLE OF KOCH’S POSTULATES AND WHEN WERE THEY CREATED?
- TO DETERMINE WHETHER A MICROORGANISM CAUSES A DISEASE
- 19 TH CENTURY
LIST THE KOCH’S POSTULATES?
1) THE SUSPECTED CAUSATIVE AGENT MUST BE ABSENT FROM ALL HEALTHY ORGANISMS BUT PRESENT IN ALL DISEASED ONES
2) IT MUST BE ISOLATED FROM THE DISEASED ORGANISM AND GROWN IN PURE CULTURE
3) THE CULTURED AGENT MUST THE SAME DISEASE WHEN INOCULATED INTO A HEALTHY SUSCEPTIBLE ORGANISM
4) THE SAME CAUSATIVE AGENT MUST THEN BE REISOLATED INOCULATED, DISEASED ORGANISM
LIMITATIONS OF KOCH’S POSTULATES?
- CAUSATIVE AGENTS ARE SOMETIMES PRESENT IN HEALTHY ORGANISMS BUT NEVER CAUSE A DISEASE, WHICH KOCH OVERLOOKED
- NOT ALL PATHOGENS CAN BE GROWN IN PURE CULTURE
- SOME HUMAN DISEASE CAN’T BE RELIABLY REPLICATED IN HUMAN HOSTS, SO THE POSTULATES AREN’T ALWAYS USEFUL
WHAT ARE THE STEPS TO INFECTION?
1) TRANSMISSION (EXPOSURE TO PATHOGENS)
2) ADHERENCE (BINDING TO THE SKIN OR MUCOSA)
3) INVASION (BREAKING THROUGH THE BARRIER)
4) SURVIVAL IN THE HOST (GROWTH ON ORIGINAL AND DISTAL SITES, PRODUCTION OF VIRULENCE FACTORS)
5) TISSUE DAMAGE (TOXICITY AND THE DISEASE)
WHAT ARE BACTERIAL SECRETION SYSTEMS AND HOW MANY TYPES ARE THERE?
- KEY TO PATHOGENICITY
- SYSTEMS WITH THE CAPACITY TO SECRETE MOLECULES AND VIRULENCE FACTORS OUT OF THE BACTERIAL CELL TO THE CONTACT HOST CELL
- TYPES I-IX
WHICH BACTERIAL SECRETION SYSTEMS HAVE THE CAPACITY TO TRANSFER PROTEINS DIRECTLY FROM THE CYTOPLASM TO THE OUTSIDE OF THE BACTERIAL CELL (ONE-STEP MECHANISM)? HOW IS SECRETION DONE BY OTHER SYSTEMS?
I, III, IV, VI AND VII
OTHER SYSTEMS CAN ONLY SECRETE PROTEINS FROM THE PERIPLASM TO THE OUTSIDE SPACE (TWO-STEP ACTIVITY, PROTEINS ARE FIRST TRANSPORTED OUT OF THE INNER CELL MEMBRANE, THEN DEPOSITED IN THE PERIPLASM AND FINALLY THROUGH THE OUTER CELL MEMBRANE INTO THE HOST CELL)
WHICH BACTERIAL TRANSPORT SYSTEMS DELIVER PROTEINS DIRECTLY INTO THE CYTOPLASM OF THE HOST CELL, USING SPECIALISED PILI?
III, IV, VI
WHICH SECRETION SYSTEMS ARE PRESENT IN BOTH G+ AND G- BACTERIA?
I, II, V, VI
TYPE VII SECRETION SYSTEM IS SPECIFIC TO WHICH TYPE OF BACTERIA?
GRAM POSITIVE BACTERIA
TYPES III AND VI SECRETION SYSTEMS ARE EXCLUSIVE TO WHICH TYPE OF BACTERIA?
GRAM NEGATIVE
WHICH TYPE OF SECRETION SYSTEM IS INVOLVED IN FLAGELLA BUILDING?
TYPE III
WHAT IS A RESERVOIR?
THE NATURAL SITE OF A PATHOGEN
WHAT IS MODE OF TRANSMISSION?
THE MECHANISM BY WHICH THE HOST PICKS UP THE PATHOGEN (E.G. DIRECT OR INDIRECT CONTACT, DROPLET, AIRBORNE..)
MOST COMMON ROUTES OF ENTRY FOR A PATHOGEN?
- RESPIRATORY
- GI
- MUCUS MEMBRANE
- SKIN
WHAT IS INITIAL BACTERIAL ATTACHMENT MOST OFTEN MEDIATED BY?
PROTEIN APPENDAGES SUCH AS FIMBRIAE/PILI (SHORT FIBRES, ENABLE BACTERIA TO STICK) AND FLAGELLA (LONGER, USED FOR MOTILITY)
WHAT ARE EXOPOLYSACCHARIDES?
- STRUCTURES THAT HELP MEDIATE BACTERIAL ADHESION
- CONSIST OF MONOSACCHARIDES AND ARE SECRETED BY BACTERIA INTO THEIR ENVIRONMENT
- HYDROPHOBIC STRUCTURES THAT CAN DISPLACE WATER BETWEEN THE BACTERIUM AND THE HOST CELL SURFACE PROMOTING CLOSER CONTACT
DESCRIBE THE ‘ZIPPER MECHANISM’ OF BACTERIAL INVASION?
- BACTERIA EXPRESS PROTEINS THAT BIND WITH HIGH AFFINITY TO HOST CELL ADHESION RECEPTORS (E.G. INTEGRINS, CADHERINS)
- TRIGGERS HOST CELLS INTO ATTEMPTING TO BIND TO ANOTHER CELL, FORM CELL JUNCTIONS AND SPREAD OVER THE BACTERIUM
- THE SMALL SIZE OF THE BACTERIAL CELL RELATIVE TO HOST CELL RESULTS IN THE ENGULFING OF THE BACTERIUM
DESCRIBE THE ‘TRIGGER MECHANISM’ OF BACTERIAL INVASION?
- BACTERIA EXPRESS PROTEINS KNOWN AS EFFECTORS
- INJECTED DIRECTLY INTO THE HOST CELL CYTOPLASM USING TYPE III SECRETION SYSTEM
- ACTIVATE SIGNALLING PATHWAYS LEADING TO CYTOSKELETAL REARRANGEMENTS AND THE FORMATION OF MEMBRANE RUFFLES
- RUFFLES EXTEND AROUND THE BACTERIA AND FUSE AROUND IT
- E.G. SALMONELLA AND SHIGELLA
DESCRIBE THE BACTERIAL SURVIVAL IN THE HOST?
- VACUOLES (WHERE BACTERIA ARE ONCE ENGULFED) ARE HOSTILE ENVIRONMENTS (LOW PH, NUTRIENT DEPRIVED, TARGETED BY HOST DEFENCES)
- THEY NEED TO ESCAPE INTO THE CELL CYTOPLASM WHERE THEY MULTIPLY RAPIDLY BEFORE SPREADING TO ADJACENT CELLS
- BACTERIA SCAVENGE SPECIFIC HOST DERIVED NUTRIENTS LIKE AMINO ACIDS AND IRON (VIA SPECIFIC UPTAKE SYSTEMS)
- BACTERIA NEED TO HIDE FROM AUTOPHAGY
- BACTERIA NEED TO AVOID LYSOSOME KILLING
WHAT ARE SIDEROPHORES?
SPECIFIC BACTERIAL SYSTEMS FOR UPTAKE OF HOST IRON
