Practical 6: Investigation of Gram Negative anaerobic bacilli Flashcards

1
Q

List the gram negative anaerobic bacilli
(5)

A

Bacteroides

Porphyromonas

Prevotella

Fusobacterium

Pasteurella (practical 5)

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2
Q

How do you differentiate pasteurella from the bacteroidaceae

A

Pasteurella is a coccobacilli while the bacteroidaceae are GNBs

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3
Q

List the genera that make up the family bacteroidaceae
(4)

A

Bacteroides

Poryphyromonas

Prevotella

Fusobacterium

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4
Q

What are the three clinically significant species of bacteroides?

A

B. fragilis

B. oralis

B. ureolyticus

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5
Q

What % of anaerobe cultures are B.fragilis

A

25%

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6
Q

How can you identify bacteroides

A

Pleomorphic bacilli or coccobacilli -> different shapes

Non-endospore forming

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7
Q

How could you identify a bacteroides from a case study?
(3)

A

Bacteroides are opportunistic pathogens

May be seen following surgery e.g. bowel surgery

They may be isolated from abscesses and other legions

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8
Q

How could you identify B. fragilis from a case study?

A

Frequently associated with intra-abdominal and soft tissue infections below the waist or bloodstream infections

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9
Q

What are the five strains of fusobacterium

A

F. nucleatum

F. necrophorum

F. periodonticum

F. mortiferum

F. necrophorum

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10
Q

How can you identify fusobacterium from the case study
(2)

A

Commensals of the respiratory tract and GIT

Colonise mucous membranes of humans and animals

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11
Q

What fusobacterium strains are found in the oral cavity?
(3)

A

F. nucleatum

F. necrophorum

F. periodonticum

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12
Q

What fucobacterium strains are seen in intra-abdominal infections
(3)

A

F. nucleatum

F. mortiferum

Usually both seen together

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13
Q

What fucobacterium strain causes Persistent Sore Throat Syndrome

A

F. necrophorum

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14
Q

What is the only clinically significant strain of pasteurella

A

P. multocida

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15
Q

How could you identify pasteurella from a case study

A

A pet bite with cellulitis and bloody drainage at site of wound

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16
Q

What is the only clinically significant strain of prevotella?

A

Pr. melaninogenica

17
Q

How could you identify Pr. melaninogenica from a case study

A

Indigenous to the oral cavity

18
Q

How do you identify porphyromonas from the ID?

A

Black colonies

Gram negative bacilli

19
Q

What three tests should be carried out on gram-negative bacilli

A

Anaerobic growth

Metronidazole susceptibility

Anaerobic identification discs -> MID8

20
Q

What is the principle behind the anaerobic and metronidazole susceptibility test for anaerobic GNBs
(3)

A

We need to prove that the bacilli are in fact anaerobic

Need to put up an aerobic and anaerobic plate -> the organism must grow on the anaerobic plate

Anaerobic GNBs are susceptible to metronidazole so a disc should be put up on the anaerobic plate to prove its an anaerobic GNB

21
Q

How do you carry out an anaerobic metronidazole susceptibility test for anaerobic GNBs
(4)

A

Ask for x2 blood agar plates and a metronidazole disc and your controls (Bacteroides fragilis + and pseudomonas fragilis -)

Split your plates into three sections for your controls and test

Inoculate both plates

Add metronidazole discs to your test inoculum

22
Q

What is your positive control (anaerobic growth and metronidazole susceptibility)

A

Bacteroides fragilis (anaerobic growth only)

23
Q

What is your negative control (non anaerobic/aerobic growth and metronidazole susceptibility)

A

Pseudomonas aeruginosa (aerobic growth only)

24
Q

What is the MID8 Identification Mastring Test?
(2)

A

Anaerobic Identification Discs

A commercial system for the identification of gram negative anaerobic bacteria based on the susceptibility to six antimicrobials

25
Why can the MID8 Identification Mastring Test not be used for susceptibility testing of the GNBs
Due to the high concentrations of some of the antibiotics used in the MID8
26
What six antimicrobials make up the MID8 ID Mastring test
Erythomycin Eifampicin Colistin sulphate Penicillin Kanamycin Vancomycin
27
How do you carry out an MID8 ID Mastring Test (6)
Ask for MID8 mastring (list antimicrobials), blood agar and a McFarland 0.5 standard Great a dense suspension of organism equivalent to a McFarland 0.5 standard Lawn inoculum Using a sterile forceps press the MID mastring onto the plate Incubate the plate anaerobically at 37 degrees for 48 hours Do the same for your B.fragilis control
28
How should you incubate your MID8 ID mastring test
incubate anaerobically at 37 degrees for 48 hours
29
What is your positive control for MID8 ID mastring test
B. fragilis
30
Why do you use B. fragilis as your positive control for MID8 (6)
Erythromycin Susceptible (occasionally) Rifampicin susceptible Colistin Resistant (occasionally) Penicillin resistant Kenamycin resistant Vancomycin resistant