pathogenesis of bacterial infection Flashcards
normal flora ( microbiomes as good bugs commensals and microbiota ) are in or on our body and they —— diseases as most of them are —–
- may cause infection if:
1. —- from usual location
2. —– breached
3. host is —-
- don’t cause diseases
- non-pathogenic
- escape
- barrier
- immunospression
—– bacteria has increased ability to invade or damage the host
—- able to cause a disease bc of their presence within the host
these bacteria can live along normal flora without causing any disease in host aka —-
the genetic/biochemical/structural features of pathogens that enable it or enhances the ability to produce disease is known as —-
- virulent bacteria
- primary pathogens
- colonised
- virulent factors
1.opportunitic bacteria have —- intrinsic virulence which usually don’t cause infections in non immunocompromised patients
2. they may cause serious infections in situations as :
- low
- immunocompromised and forge in body
1.why does infection occur ( steps )
2. how pathogens are transmitted
-the organism is virulent –> the size of the inoculum —-> the portal of entry —> survival in the host —> the state of the host
- get in –> attach to cells —> invade immune system —> cause damage to host cells —> get out and spread further
the 5 types of entry :
1. —– as salmonella in food poisoning
2. ——– as tucerculosrosis
3. ——— staphylococcus aurous
4. —— chalamydia
5. —— group b strepcoccous
- ingestion
- inhalation of droplets of aerosols
- penetration/inoculation
- sexual
- vertical
—- of the bacteria to host cell is required to establish a stable population of bacteria within the host and prevents bacterial clearance from mechanical host defences
- adhesion
adhesion occurs through —– mediated process called —- by which they are small bacterial protein ligands which recognise specific receptors on host cells
- receptor / ligand
- adhesins
—– formation protectrs the bacteria and makes eradication difficult with our the removal of prosthesis
- biofilm
to facilitate invasions pathogens can employ biochemical virulence factors called —– these can be:
- invasins
1. proteins
2. damaged host cells and facilitate spread and invasion
3. hylauronidase , kinase , and collagenase
-the presence of bacteria in the host induces — responses to attempt bacterial eradication
-to ensure ongoing survival bacteria have developed numerous mechanisms to prevent immune mediated clearance which are:
- immune
1. prevents phagocytosis which is the ingestion go bacteria by phagocyte immune wbc as neutrophils
2. survival within the phagocytes
3. immune cell destruction
-inhibition of phagocytosis is done by — which is composed of polysarchide which sits outside the cell membrane
- pathogens associated w meningitis and penunomia as: neisseria meningitides , streptococcus penunomia , hemolphilus influenza )
- capsule
survival within phagocytes:
- they escape the —- aka listeria monocytogene
- prevents —— fusion aka mycobacterium tuberculosis
- survival within —– aka staphylococcus aureus
- phagosome
- phagosome / lysozyme fusion
- phagolysosome
some bacteria are able to produce —- that directly target immune cells or prevent their function such as:
1. —- pore forming enzyme which targets phagocytes ( canton - Valentin leucodicin of staphylococcus aureus )
2. —- pore forming enzyme produced by streptococci
3. —- produced by s. aureus , converts fibrongigen to fibrin which promotes clotting , coats bacteria in fibrin which acts as a barrier to immune cells ( can be tested in the lab to help identify S. auerous )
-enzymes
- leucocidins
- streptolysins
- coagulase
bacterial enzymes damage — cells as well as being important in —- evasion. this is done by:
- host cells
- immune
1. invasins
2. toxins
2. superantigens
—- are compounds/chemicals which are toxic to host cells by directly harming host tissue or by interacting with immune cells. the two types are:
- toxins
- endotoxins and exotoxins
1- is integral part of bacterial cell envelop
2.release from bacterial cell due to cell lysis or turnover
3. LPS is prototypical example of gram — bacteria
4. can indue pro inflammatory cascade leading to septic shock
these are all under —– toxins
- gram -ve
- endotoxins
-are polypeptide molecules produced by living and mostly gram +ve bacteria , secreted and released during cell lysis , bacterial replication m or by certain antibiotic use ( b lactam antibiotic )
- many target specific cells to induce toxic effects and can act locally or distally as: cytotoxins , neurotoxins , enterotoxins
- exotoxins
-superantigeen is a type of — which initially was discovered in strain of straph aureus TSST-1
- superantigen can cause —- of immune system mediated via interaction of MHC class II on T cells
- non specific binding at these sites cause polyclonal expansion of T cells leading to a shock syndrome
- exotoxins
- hyper activation
( check slide 39 soooo important !!)
dissemination - how pathogens are spread in the body :
- Spread through tissues or tissue planes
(contiguous) - Spread through the bloodstream
(haematogenous) - Spread through the lymphatic system
- Carriage within macrophages (e.g. Typhoid)
- Ascending/descending spread within a tract
how are pathogens transmitted :
. Person-to-person by direct contact: skin carriage
2. Respiratory: coughing, sneezing
3. Gastrointestinal: diarrhoea
4. Sexually: genital discharge /ulcer
5. Vertically & Perinatally (from mother to newborn)
6. Transmission from the environment e.g. a
contaminated inanimate object (fomite)
host risk factors for infection :
- certain factors will —- the susceptibility of the host in infection
- increases the likelihood of — manifestation of infection
- extremes of —
- diabetes
- Immunosuppression
– Disease induced: cancer / asplenism / HIV/ renal
failure / hepatic failure
– Medications: chemotherapy, steroids, other
immunosuppressive medications
* Major breach in —–
– Recent major surgery
* —— material (portal of entry and biofilm
formation)
– IV lines
– Urinary catheters
– Ventilation
– Prosthetic joints/heart valve
* Anatomical abnormality or malfunction
– Complications post surgery
* Antibiotic therapy
– Clostridium difficile infections post antibiotics
- increase
- severe
- age
-skin/mucosa
-Prosthetic
