An internal biomérieux investigation was conducted due to low mic results with b.Fragilis atcc 25285 on etest® metronidazole mzh 256 ww f100 ref 530018.Lots tested: 1002689900, 1003007690, 1003409180, 1003827270.A reference lot was also used for testing.Due to the absence of customer return, testing was only done on retention lots.Customer results: agar : home-made (anaeroplates without antibiotics), oxoid or bd.Results below the range for the strain atcc 25285 e.Coli.Deviations: use of 0.85% nacl for the suspension instead of broth of brucella mh, incubation time of 18 hours.Unconfirmed at 48 hours.Use of mueller hinton.Investigation results: at 24 hours of incubation with lot 1003409180, results of atcc 29741 and atcc 25285 are orl in comparison to the ranges at 48 hours of incubation.Ranges for 24 hours incubation don't exist.Conclusion: following investigation several hypotheses were formulated that could explain the issue observed by the customer old investigation on etest® metronidazole showed results orl for b.Fragilis atcc 25285 after 24 hours incubation.For anaerobe strains: media: brucella agar- 5% blood-vitamin k (mcg/ml)- hemin (5mcg/ml) and not mueller hinton agar.Inoculum suspension should be prepared in brucella broth, mh broth or schaedler broth + vitamin k3.(0.85% nacl should not be used).Qc ranges are validated after 48 hours of incubation, not at 24 hours.In addition, other recommendations for anaerobes were included: for patient strains all "s" results must be confirmed at 48 hours of incubation.Do not vortex.Anaerobiosis must be achieve within 1-2 hours for metronidazole.In conclusion, the results of the microbiological quality control are in accordance with the expected specifications for all batches on e.Coli atcc 25922, b.Thetaiotaomicron atcc 29741 and b.Fragilis atcc 25285 after 48 hours of incubation.
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