Bacteroides spp

Question 1

Bacteroides culture conditions

Answer 1

Anaerobic 37C blood agar

Question 2

Anaerobic bacteria

Answer 2

Clostridioides
Bacteroides

Question 3

Anaerobic Gram negative bacillus

Answer 3

Bacteroides

Question 4

Bacteroides colonial morphology

Answer 4

1-3mm, round, shiny grey, no haemolysis

Question 5

Gram stain

Answer 5

Gram negative bacilli
Small slender rods
clusters
sometimes coccobacilli

Question 6

Biochemical tests

Answer 6

KOH positive
Catalase positive
Oxidase Negative

Question 7

Presumptive Bacteroides spp tests

Answer 7

1. Anaerobic growth
2. Metronidazole susceptibility test
3. Anaerobic identification discs - MID8

Question 8

Anaerobic growth + metronidazole susceptibility test procedure

Answer 8

1. Lawn inoculate blood agar purity plate with test organism + PC ( P. aeruginosa) + NC (B. fragilis) and incubate AEROBICALLY overnight at 37C
2. Lawn inoculate blood agar purity plate with test + controls (PC = B. fragilis, NC = P. aeruginosa).
3. Place metronidazole disc on secondary inoculum of test organism.
4. Incubate ANAEROBICALLY for 48hrs using anaerobic jar and AnaeroGen sachet.

Question 9

Anaerobic growth + metronidazole susceptibility test results

Answer 9

Anaerobic organisms only grow anaerobically (no O2) AND anaerobic organisms are SUSCEPTIBLE to metronidazole = produce zone on inhibition of growth around disk.

Question 10

Anaerobic identification discs - MID8 test procedure

Answer 10

1. Suspend test organism in 5ml water = dense suspension
2. Lawn suspension on BA plate
3. Using forceps place MID9 mastring on surface of BA plate.
4. Incubate anaerobically 37C for 48hrs.
5. Measure inhibition zones using digitial calipers.

Question 11

B fragilis MID8 sensitivity results

Answer 11

E + RP sensitive
Resistant to the other 4 (CO, PG, K, VA)

Question 12

MID8 code and corresponding drug
E
RP
CO
PG
K
VA

Answer 12

E = erythromycin
RP = rifampcin
CO = colistin sulphate
PG = penicillin G
K = kanamycin
VA = vancomycin

Question 13

Additional confirmatory tests

Answer 13

Vitek, MALDI-TOF

Question 14

Bacteroides infections

Answer 14

Normal commensal of human colon so it is an endogenous infection which occurs when they gain access to tissue/blood following bowel perforation - surgery/trauma.
Causes ABSCESSES - abdominal or peritoneal

Question 15

Bacteroides treatment

Answer 15

1. AST - AMR is common
2. Metronidazole.