Exercise 9

Question 1

Food-borne infection

Answer 1

Live pathogenic bacteria are contracted by eating raw or undercooked food products

Question 2

Bacterial toxins are present in raw, undercooked or cooked food products.

Answer 2

Food borne intoxication

Question 3

Standard Mathis plate count determines?

Answer 3

Number of mesophilic aerobes

Question 4

Food may be? Of many diseases

Answer 4

Vector

Question 5

Cooking should kill bacteria present, but toxins?

Answer 5

May remain because many are heat-stable

Question 6

Direct detection vs indirect detection

Answer 6

Direct - virtually impossible.

Indirect - reduction whether likely to be present = test for presence of sewage indicator or fecal organisms.

Question 7

E.coli + e.faecalis absent =?

Answer 7

Recent fecal contamination did not occur & pathogens transmitted by this route most likely absent.

Question 8

Intestinal organisms and pathogens tested for ? Or after ?

Answer 8

Directly or after enrichment culture.

Question 9

Initial growth on differential/selective medium =?

Answer 9

Gives presumptive test. Further tests to confirm & complete identification of organism

Question 10

Number of bacteria in original sample calculated by?

Answer 10

Average # of colonies * reciprocal of dilution * 1/vol plated = #viable cells in original

Question 11

Standard plate count assay requires

Answer 11

Aseptic technique and pipetting accuracy

Question 12

Diluted sufficiently to?

Answer 12

30-300 colonies per plate

Question 13

what is pour plate?

Answer 13

bacterial dilution added to empty sterile petri plates + molten agar added to make suspension of bacteria in agar medium.
detection of aerobes + microaerophiles.

Question 14

spread plating - detects?

Answer 14

only aerobes as samples are only grown on surface of the plates.

Question 15

agar in pour plate assay must be?

Answer 15

liquid. not too hot to kill bacteria.

45-47C

Question 16

serial dilution?

Answer 16

1g meat to 99ml buffer. take 1 ml of that, add to 9ml of buffer = 10-3 dilution. take 1ml of 10-3 add to 9ml buffer = 10-4 dilution.

Question 17

tests for e.coli

Answer 17

lactose broth, emb plate, gram stainn

Question 18

tests of e. faecalis

Answer 18

azide dextrose broth, KF plate, gram + and catalase (-)

Question 19

s. aureus

Answer 19

TCS + NaCl’ BAP, G+, Coagulase +

Question 20

what is azide dextrose broth?

Answer 20

selective medium. contains aide (N3-) blocks e- transport along cytochrome chain = inhibits respiring organisms streptococci can grow bc aerotolerant anaerobe.

Question 21

TCS + NaCl

Answer 21

selective medium, high salt concentration, inhibit bacteria through dehydration.
staphylococcus is salt tolerant + maintain cytoplasmic water activity + grow in presence of aCl. accumulate K+ in cytoplasm.

Question 22

lactose broth

Answer 22

differential medium, demonstrates fermentation of lactose.

phenol red turns yellow when exposed to acid. gas trapped in vial too.

Question 23

KF agar

Answer 23

selective for fecal streptococci. azide inhibit aerobic organisms. bromocresol purple turns yellow when acid is produced. reduced TCC = red colour in colonies.

Question 24

BHI broth

Answer 24

elevated temp + rich medium. E. faecalis can grow at high temps. other mesophilic, non-sporing bacteria will be killed.

Question 25

coagulase test

Answer 25

coagulase = exotoxin, extracellular protein released into enviro by pathogenic s. aureus.
virulence factor, enables bacterium to turn fibrinogen to fibrin (clot) immobilize and protective bacteria in infection.

bacteria mix w citrated plasma = produce coagulase if fibrin clot observed.