7. Bacterial Growth and Identification Flashcards
The name ‘staphylococcus’ comes from where? What does this mean?
- grape in Greek
- under a microscope appears as clumps of round cells, like a bunch of grapes
Where is Staph.aureus found in body?
- nose/anterior nares
- throat/nasopharynx
- skin
How do staph survive in body?
- withstand high concs of salt
- survive in sweaty areas
- provide a means of selectively culturing staph using high salt medium
What kind of bacteria is staph?
Exception?
commensal
- staph. aureus involved in infections and called opportunistic
What kinds of conditions are caused by staph aureus?
- broad range
- toxin-mediated conditions like toxic shock syndrome or food poisoning (preformed enterotoxins)
- localised skin infections like impertigo
- wound infections
- systemic infections like infective endocarditis
MRSA is what?
methicillin resistant staph aureus
Staph is gram …, … positive cocci.
- positive
- catalase
Staph and the oxidase test?
- contain cytochrome oxidase
- a respiratory chain component that’s readily tested by oxidase test
How to distinguish staph aureus from other staph?
- coagulase test
- enzyme coagulase binds fibrinogen in plasma and triggers cascade of reactions leading to blood clotting
- most staph aureus produce coagulase but other staph don’t
- aureus also produces one or more DNase enzymes which can help it escape from host DNA released at sites of infection to trap bacteria
Most oral strep are … as they can cause what?
- pathogenic
- infective endocarditis
When is S. salivarius used for good?
- sold in some areas as probiotic
- these strains produce bacteriocins which are peptide antibiotics to help control pathogenic species
Strains of strep produce what? that is used to identify it
Why?
- urease
- enzyme converts urea into basic (high pH) compound ammonia
- helps protect against dental caries
Even though strep can protect against dental caries, how can it contribute?
- S.salivarius can produce acid from sugars
- means levels of this bacteria can be elevated at site of carious lesions
Strep are gram …, non-motile/motile, what shape?
- postive
- non-motile
- spherical/cocci
Most oral strep produce … on blood agar culture. Why?
- green tinge
- hydrogen peroxide’s effect on iron in RBCs
How to differentiate staph and strep?
- strep form chains
- staph form bunches
Hydrogen peroxide is produced by what bacteria? and isn’t degraded. Why?
- strep
- lacks catalase
If you can’t see the shapes of staph and strep, how to differentiate?
- strep aren’t degraded as don’t have catalase
- staph are catalase-positive
Where are E.Coli found?
- human gut
- animals
Are all E.Coli bad?
- most are harmless
- well established as lab model
- pathogenic strains are just not uncommon
Which strains of E.Coli are harmful?
- 157 version of O-antigen and 7 version of H antigen (flagellar protein)
- cause foodborne outbreaks with diarrhoea and vomiting
- most common cause of UTIs in women