Evaluation of a single tube medium, Y-nitrophenyl-phi-D galactopyranoside phenylalanine motility sulphate for screening pathogenic members of the family enterobacteraceae

ABSTRACT

Identification of members of the Enterobacteriaceae requires the application of biochemical tests before serological confirmation. Of the important tests in such a setting are ONPG, phenylalanine deaminase, motility, H2S and indole production. ONPG-PA-M sulfate medium is a semisolid medium in which all these reactions can be detected. The present study evaluated this medium for detecting such reactions in comparison to the diagnostic set in the microbiology lab [TSI, MIO and urease] and the standard API 20-E system for enterobacteria were evaluated. The reactions of 192 gram negative isolates from stool and other clinical specimens [urine, pus and sputum] as well as 63 control strains were compared. All tested strain showed identical reactions in the three sets, except for a missed positive ONPG reaction in the ONPGPA-M sulfate medium [by an atypical E. coli] and two missed H2S production in the TSI that were detected by the single tube medium [one E. coli and one Cit. freundii]. The ONPGPA-M sulfate medium appeared to be a reliable in assessing these reactions and even superior to TSI in detecting H2S, in addition to the cost reduction achieved by performing all these tests in a single tube. Thus, its use in routine microbiology laboratories was recommended