COMPARISON OF COMMERCIAL AND LABORATORY PREPARED CITRATE AGAR AS A DIAGNOSTIC MEDIUM

Abstract

The ability to utilize citrate as sole carbon source using 75 bacterial stock cultures was tested in a citrate medium formulated from basic chemical ingredients in the laboratory. A commercial Simmons citrate medium obtained from Biotec Laboratories (Surrey, United Kingdom) was employed as a control. Both the laboratory-prepared medium and the commercial medium were inoculated simultaneously with each of the 75 bacterial cultures supplied as coded unknowns. Results of citrate utilization were recorded after 24 and 48 hours of incubation at 360C ± IOC. Forty-six (46) strains gave positive citrate utilization results in both the laboratory prepared medium and the commercial Biotec medium after 24 hours of incubation. Nineteen (19) strains gave equivocal or intermediate results in both media after 24 hours of incubation but re-incubation for an additional 24 hours resulted in clearly positive citrate utilization results. Ten (10) strains gave negative results in both media and these results remained negative after re-intubation for an additional 24 hours. There were no discrepant results of citrate utilization and a 100% correlation of test results was obtained. The identities of the test strains were revealed at the end of the study and the citrate utilization test result for each strain was shown to be what was expected of it given its identity and the predictions of diagnostic tables. This blind study indicates the equivalence of a laboratory-prepared citrate medium and the one obtained commercially. However, more extensive studies would need to be carried out to confirm this. Considering the fact that the cost of one unit of a laboratory prepared citrate medium, is far less than that of a commercial medium, it is suggested based on the outcome of this investigation that laboratory preparation of the citrate medium from basic ingredients should be more cost-effective.