1.11. Bacterial Pathogenesis 2 Flashcards
Normal flora
Causes disease in humans as a result of compromised immunity or foreign material
Obligate pathogens
- Must cause disease in humans in order to survive
- Wide range of symptomatology (asymptomatic to severe disease)
- E.g. Smallpox, M.tuberculosis
- Cannot kill all hosts, otherwise it won’t survive
Accidental/incidental Pathogens
- Causing disease offers no advantage, and may in fact be a dead end
- 2 types:
- Reservoir= man, but causes disease in only a few e.g. Streptococcus pyogenes
- Reservoir= nature, cause disease in humans accidentally e.g. Vibrio cholerae
Pathogens in the Environment
- Whatever the environment, pathogen must be able to survive long enough to encounter a susceptible host
- Dynamics of pathogen survival in different environments are relevant to control of infection e.g. Vibrio cholerae-water, Methicillin Resistant Staphylococcus aureus -hospital
list the pathological patterns of infection
- toxin mediated
- acute
- subacute
- chronic
what organisms are involved in toxin mediated pathological patterns of infection
Mainly bacterial
what organisms are involved in acute pathological patterns of infection
Viral and bacterial
what organisms are involved in subacute pathological patterns of infection
Many viruses and several atypical bacteria
what organisms are involved in chronic pathological patterns of infection
Viral, chronic granulomatousbacterial, fungal and parasitic
describe toxin mediated bacterial infections
- Toxin production responsible for most of the features of infection
- Damage usually distant from the site of replication
- Onset of disease usually very rapid-as soon as organism grows and starts producing toxin
- Antibiotics are not effective at treating disease, but may prevent further toxin formation
- In some cases e.g. E.coli O157, antibiotics stimulate further toxin production
describe acute pyogenic bacterial infection
- Pus inducing infections
- Localized or disseminated
- Rapid onset
- Early treatment with antibiotics usually terminates illness
- Some cases immunopathology develops -e.g. Post streptococcal glomerulonephritis
- Most bacteria that cause pyogenic infections also produce toxins
- Thus there may be pyogenic±toxin mediated components to the infection
- E.g. Staphylococcal and Streptococcal infection
- Combination of pathogenic processes attributable to different virulence factors
- Can cause very severe disease
subacute bacterial infections
- Insidious onset
- Less prominent signs of acute infection
- E.g.
- Subacute bacterial endocarditis
- Mycoplasma pneumoniae infection
- Damage often as a result of adaptive immune response rather than the organism itself
Chronic granulomatous bacterial infection
- Over months or years
- Development of a granuloma= form of localised cell-mediated immune response directed against antigens or other foreign bodies that appear to be refractory to elimination from tissues. An accumulation of lymphocytes and macrophages occurs around a central focus
- Organisms grow slowly and can survive in host cells, esp. Macrophages
- Cell mediated immuno-pathology is a key feature
- E.g. Mycobacteria, Brucella
describe the patterns in the presentation and pathology of bacterial infection in toxin mediated disease
- Pathology often distant from site of bacterial growth
- Diphtheria, tetanus
- Protective immunity may be mediated by anti-toxin antibodies alone
- Staphylococcal food poisoning
- Cholera
- Disease may be fully reproduced by administering the toxin alone
- Pseudomembranous colitis
describe the patterns in the presentation and pathology of bacterial infection in acute pyogenic infection
•Generally rapid growing organisms
-Streptococcal pharyngitis
•Interaction with innate immune system and acute inflammation predominates
-Staphylococcal abscess, bacterial meningitis, lobar pneumonia, acute cystitis
•Where immune damage occurs, it is ‘post-infective’
-Post-streptococcal glomerulonephritis
