Lab stuff Flashcards
(30 cards)
Three main routes for microbe entry
Respiratory
Alimentary/swallowing
Dermal, cuts etc
Colony morphology of Staph aurerus on aerobic blood agar
Opaque, white, slightly domes colonies
Circular, 1-2mm diameter
Narrow zone of haemolysis
Which organisms are catalse positive
Most gram negative
Useful discriminatory test for gram positive
+ve(fizzing/bubbles)
Staphylococci, Corynebacteria, Bacillus
-ve
Streptococci, Lactobacilli, Clostridium
Target of Oxidase test
Detects cytochrome C oxidase
More discriminatory for gram -ve than +ve
Useful for distinuguishing species of Pseudomonas and Vibrio from Enterobacteriaceae
Positive test: Purple within 15 sec
Test for distinguishing Staph aureus from Staph epidermis
The coagulase test
Aureus has ability to coagultae plasma,
epidermis doesn’t
For growth microorganisms require:
- A source of energy
- Carbon, nitrogen, mineral salts and vitamins
- Certain ‘accessory’ growth factors
- Water
E. coli appearance on gram stained slides
Cocci/Bacilli
Arrangement
Gram reaction
Bacilli
Single cells
Negative
P. aeruginosa appearance on gram stained slides
Cocci/Bacilli
Arrangement
Gram reaction
Bacilli
Single cell
Negative
C. perfringens appearance on gram stained slides
Cocci/Bacilli
Arrangement
Gram reaction
Bacilli
Single cells
Positive
B. cereus appearance on gram stained slides
Cocci/Bacilli
Arrangement
Gram reaction
Bacilli
Single cells
positive
S. Typhimurium appearance on gram stained slides
Cocci/Bacilli
Arrangement
Gram reaction
Bacilli
Single cells
Negative
S. Aureus appearance on gram stained slides
Cocci/Bacilli
Arrangement
Gram reaction
Cocci
Clusters
Positive
S. pyogens appearance on gram stained slides
Cocci/Bacilli
Arrangement
Gram reaction
Cocci
Short chains
Positive
Aerobe/Anaerobe?
E. coli
P. Aeurignosa
C. perfrigens
B. cereus
E. coli: Facultive aerobe
P. Aeurignosa: strict aerobe
C. perfrigens: Strict anaerobe
B. cereus: Facultibe aerobe
Use of MacConkeys agar tests…
Gut bacteria able to grow in bile salt levels inhibitory to most bacteria. MacConkeys contains sodium taurochloate.
Also conatins lacose and neutral red.
Both a selective and indicator mediuim:
selective: bile tolerance
indicator: lactose utilisign bacteria turn red, others turn it yellow
Expected colours from E. coli and S. Typhimurium on MacConkey
E. coli: bright pink colonies
ST: Yellow colonies
As E.coli is able to metabolise the lactose
What are the components of COBA
Colistin Oxolinic Acid Blood Agar
- C: Active against gram -ve
- OA: inhibits gram+ve apart from streptococci
I.E. (B-haemolytic) Selective for streptococci
Three types of AB sensitivity testing:
Define antibiotic syngergism
In the synergistic response, the applied antibioticswork together to produce an effect more potent than if eachantibiotic were applied singly
E.G: trimethoprim and sulphamethoxazole bcause the two inhibit two different enzymes in same pathway
Define antibiotic antagonism
Presence of one AB inhibits action of another
E.G. Nitrofurantoin and nalidixic acid
Bacterocidal(penicillin) ABs can be antagonised by bacterostatic ABs(tetracycline)
Timeline in identifying a specimen
Sabourauds agar is used fro isolation of…
Candida albicans
Xylose Lysine Sodium Deoxycholate (XLD) and seline broth for isolation of…
Salmonaella from faeces
Optochin discs used to ID…
Strep. pneumonniae
i.e. pneumococci
