Staphylococcus aureus
- enterotoxin
- Enterotoxin A-F: heat resistant polypeptide (121*C, 20min)
- requirements for the production: Temp 10-45*C, water activity > 0,92
- infective dose: < 0,1 ug toxin –> 10^5 microbe/gram food
Staphylococcus aureus
- culturing media
Giolitti-cantoni broth, Baird-Parker agar,
Staphylococcus aureus
- Giolitti-cantoni broth
- composition: mannitol, LiCl, potassium tellurite
- reaction: potassium tellurite is reduced to metallic tellurium by S.aureus, therefore black compounds is developed
Staphylococcus aureus
- Baird-parker agar
- composition: mannitol, LiCl, potassium tellurite, egg yolk emulsion
- reaction: colonies of Staph. aureus appear as black and shiny whith a fine white rim, surrounded by a clear zone after 18-24hr incubation
Staphylococcus aureus
- confirmation methods
- gram staining, coagulase test, thermostable deoxyribonuclease test
Staphylococcus aureus
- coagulase test
- staph aureus is coagulase +
- the coagulation test is positive in case of S. aureus 99%, while for S. hyicus and S. delphi it is sometimes positive.
- in case of S. epidermidis the test is negative (no coagluation)
Staphylococcus aureus
- Thermostable deoxyribonuclease test
evaluation:
- S. aureus has thermostable DNase enzyme in 100%. it is susceptible to traces of the enzyme (0.005 ug/ml) so the tst can be done from the heat treated food itself, result can be obtained in 4-5hr.
- Positive reaction: pink ring (S.aureus is positve)
Bacillus cereus
- characteristics
- glucose fermentation without gas production
- catalase, lecitinase, phospholipase positive
- nitrate –> nitrite reduction
- b-hemolysis
Bacillus cereus
- MYP agar
MYP agar (mannitol, yolk, polymyxin)
- composition: meat extract, peptone, mannitol, phenol red, egg yolk, polymyxin-B
- evaluation: B.cereus form large, pink color colonies around percipitation zone –> 1day, 37*C
Bacillus cereus
- confirmation
double zone b-hemolysis is een on sheep blood agar –> 1day, 30*C
Enterococcus faecalis
- characteristics
- indicator of fecal contamination and insufficient heat treatment
- most resistant to disinfectants (except for spores=
- glucose fermentation without gas production
- aerotolerant anaerobic
Enterococcus faecalis
- sherman criteria
- can survive: 60*C for 30min (can survive low pasturization)
- can grow in 6,5% salt concentration, pH 9.6, 10-45*C, milk with 0,1% methylene blue, blood agar with 40% bile
Enterococcus faecalis
- media to use
- Slanetz-Bartley agar, Na-azide broth/Raj broth, Litsky-Mallmann broth
Enterococcus faecalis
- Slanetz-Bartley agar
- composition: triphenyl tetrazolium chloride, sodium azide
- evaluation: enterococcus reduces the TTC to red formazan, so the colonies are reddish brown
Enterococcus faecalis
- Na-azide broth, Raj broth
it contains Na-azide for the selectivity and bromothymol blue as indicator
Enterococcus faecalis
- Litsky-Mallman broth
it contains Na-azide for the selectivity and ethylviolet as indicator
Enterococcus faecalis
- confirmation
- gram staining, catalase test, heat resistance examination
Enterococcus faecalis
- catalase test
- it is catalase negative
- inoculation into meat broth
Enterococcus faecalis
- heat resistance examination
- inoculation into meat broth
- evaluation: if the broth is turbid and the microbe is catalase negative, the presence of enterococcus is confirmed
Clostridium perfringens
- culturing
- sulphite-cycloserine agar (SC),
Clostridium perfringens
- confirmation
fluid thioglycolate medium, Lactose-sulphite broth
Clostridium perfringens
- Sulphite-cycloserine agar (SC)
- inhibitor: cycloserine
- reaction: black colonies are formed by FeS production (sulphite reduction)
- cycloserine inhibits other microbes
Clostridium perfringens
- fluid thioglycolate medium
- composition: L-cystin, sodium thioglycolate, resazurine
- reaction: sodium thioglycolate decreases the redox potential (ensures anaerobic conditions), resazurine controls the anaerobic conditions. the agar inhibits the oxygenation of the broth
Clostridium perfringens
- lactose-sulphite broth
- composition: lactose, disodium disulphote, ferric ammonium citrate
- reaction: black iron sulfide precipitate at the bottom of the tube
