質量控制微生物培養基，是否足以遵循NCCLS M22-A2程序？

英文原文：

Quality control for microbiological culture media. Is it enough to follow the NCCLS M22-A2 procedures?

Results from SBA using S. pneumoniae and S. agalactiae, and TM with N. meningitidis or N. gonorrhoeae, showed no marked difference in terms of colony counting, irrespective of medium source.

Chocolate agar, on the other hand, showed a remarkable difference regarding the recovery of H. influenzae (Fig. 1). In-house plates displayed a limited capacity to recover this organism compared to the commercial plates. In fact, only 5 colonies could be obtained were the expected colony count was 4.5 x103 CFU .

The CA plates were also tested using the procedures described in the NCCLS M22-A2 document, which uses a bacterial suspension known to provide 1 to 2 x 104 CFU/plate, showing typical colonies, irrespective of its source. This result is in accordance with the result obtained with our test when 104 CFU of H. influenzae were inoculated on both commercial and in-house chocolate agar plates, if only growth or non-growth would have been recorded.

DISCUSSION

The procedure described in the NCCLS M22-A2 document can be used to check for failure to support growth or yield the expected colony size. Our in-house media were all approved following the M22-A2 guidelines. However, our results demonstrated that some media may have a limited capacity to recover fastidious microorganisms, such as H. influenzae, which is in accordance with previously published data (1).

In summary, we report here on the variability of the growth capacity of some media, particularly to isolate fastidious organisms like H. influenzae. Checking all media with several dilutions of two or more organisms may be unnecessary. We suggest that only those media used to recover fastidious pathogens, that may be present at very low concentration in a critical clinical sample, be tested using the protocol described here. For other less critical media, following the NCCLS M22-A2 guidelines may be adequate.

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