Gram positive rod Flashcards
characteristics & culture of clostridum species
characteristics: obligate anaerobic gram positive rods, spore-forming, widely found in the soil
culture: needs to be cultured under anaerobic conditions
characteristics & culture of clostridum species
characteristics: obligate anaerobic gram positive rods, spore-forming, widely found in the soil
culture: needs to be cultured under anaerobic conditions
culture of clostridum perfringens
nagler plate (egg yolk media plate, with half the plate precoated with antitoxin to demonstrate that the lipase activity is due to the toxin) tests for alpha-toxin (lecithinase) → positive test means there is an area of opacity
blood agar → double zone of hemolysis (indicates presence of 2 hemolysins, one providing complete and the other providing incomplete hemolysis)
virulence factors of clostridum perfringens
α-toxin (lecithinase - destroys cell membranes which therefore leads to RBC hemolysis)
clinical presentation of clostridum perfringens
gas gangrene (clostridial myonecrosis)
- occurs after spores are introduced into area of tissue which is anaerobic, results in rapid-spreading tissue damage
- gas is usually produced, detected by pressing/feeling crepitus/X-ray
food poisoning (clostridial necrotising enteritis)
- due to ingestion of spores
- spores survive cooking → allows for germination and toxin production in the gut
- slow onset → diarrhoea 12-24h after ingestion -
diagnosis of clostridum perfringens
histology, culture (blood, discharge, tissue)
treatment of clostridum perfringens
gas gangrene: removal of dead tissue, IV penicillin G, clindamycin
food poisoning: rehydration therapy, antibiotics NOT indicated
characteristics and histology of clostridum tetani
characteristic: gram positive, obligate anaerobe, spore-forming
histology: drumstick appearance (long thin rod with large terminal spores)
virulence factors of clostridum tetani
tetanospasmin (very potent neurotoxin which blocks inhibitory stimuli received by lower motor neurons → motor neuron only receives excitatory messages → continuous contractionn)
clinical presentation of clostridum tetani
tetanus (spastic paralysis due to release of toxins)
- local signs: pain & stiffness at the site of infection
- mild symptoms: lockjaw (masseter is affected earlier), risus sardonicus
- serious symptoms: opisthotonus (all back muscles contract, body assumes rigid posture determined by the stronger of each set of antagonistic set of muscles), autonomic disturbance, and eventually CVS derangement
Cross sectional studies
Advantages
- inexpensive, fast, simple
- can study wide range of factors
- provides basis for more extensive studies
Cross sectional studies
Disadvantage
- not good for rare/ acute conditions
- Problem of TEMPORALITY, cannot establish cause-effect relationship
- LENGTH BIAS (timing is ignored. A could cause B, or B could cause A. or neither)
- Study of survivors and survivor factors
disadvantages of cohort studies
- Not feasible when disease is rare
- Not feasible if there is a long latent period between exposure and disease
- Resource intensive for extensive and long term follow up
advantages of cohort studies
- Describe natural history of disease
- Calculate cumulative incidence/incidence rate
- Direct measure of risk
- Temporal sequence can be established
- Several outcomes can be studied
- Least susceptible to bias among observational studies
disadvantages of case-control studies
- Temporal relationship difficult to establish
- Prone to bias (Recall bias & Selection bias)
- Calculates “odds”, does not measure “risk” directly
