Practical 6: Investigation of Gram Negative anaerobic bacilli Flashcards
List the gram negative anaerobic bacilli
(5)
Bacteroides
Porphyromonas
Prevotella
Fusobacterium
Pasteurella (practical 5)
How do you differentiate pasteurella from the bacteroidaceae
Pasteurella is a coccobacilli while the bacteroidaceae are GNBs
List the genera that make up the family bacteroidaceae
(4)
Bacteroides
Poryphyromonas
Prevotella
Fusobacterium
What are the three clinically significant species of bacteroides?
B. fragilis
B. oralis
B. ureolyticus
What % of anaerobe cultures are B.fragilis
25%
How can you identify bacteroides
Pleomorphic bacilli or coccobacilli -> different shapes
Non-endospore forming
How could you identify a bacteroides from a case study?
(3)
Bacteroides are opportunistic pathogens
May be seen following surgery e.g. bowel surgery
They may be isolated from abscesses and other legions
How could you identify B. fragilis from a case study?
Frequently associated with intra-abdominal and soft tissue infections below the waist or bloodstream infections
What are the five strains of fusobacterium
F. nucleatum
F. necrophorum
F. periodonticum
F. mortiferum
F. necrophorum
How can you identify fusobacterium from the case study
(2)
Commensals of the respiratory tract and GIT
Colonise mucous membranes of humans and animals
What fusobacterium strains are found in the oral cavity?
(3)
F. nucleatum
F. necrophorum
F. periodonticum
What fucobacterium strains are seen in intra-abdominal infections
(3)
F. nucleatum
F. mortiferum
Usually both seen together
What fucobacterium strain causes Persistent Sore Throat Syndrome
F. necrophorum
What is the only clinically significant strain of pasteurella
P. multocida
How could you identify pasteurella from a case study
A pet bite with cellulitis and bloody drainage at site of wound
What is the only clinically significant strain of prevotella?
Pr. melaninogenica
How could you identify Pr. melaninogenica from a case study
Indigenous to the oral cavity
How do you identify porphyromonas from the ID?
Black colonies
Gram negative bacilli
What three tests should be carried out on gram-negative bacilli
Anaerobic growth
Metronidazole susceptibility
Anaerobic identification discs -> MID8
What is the principle behind the anaerobic and metronidazole susceptibility test for anaerobic GNBs
(3)
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
How do you carry out an anaerobic metronidazole susceptibility test for anaerobic GNBs
(4)
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
What is your positive control (anaerobic growth and metronidazole susceptibility)
Bacteroides fragilis (anaerobic growth only)
What is your negative control (non anaerobic/aerobic growth and metronidazole susceptibility)
Pseudomonas aeruginosa (aerobic growth only)
What is the MID8 Identification Mastring Test?
(2)
Anaerobic Identification Discs
A commercial system for the identification of gram negative anaerobic bacteria based on the susceptibility to six antimicrobials
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
What six antimicrobials make up the MID8 ID Mastring test
Erythomycin
Eifampicin
Colistin sulphate
Penicillin
Kanamycin
Vancomycin
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
How should you incubate your MID8 ID mastring test
incubate anaerobically at 37 degrees for 48 hours
What is your positive control for MID8 ID mastring test
B. fragilis
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
