Identification of Proteus morganii and distinction from other Proteus species.

The identification of Proteus morganii in the clinical laboratory is complicated by the differences in incidence of hydrogen sulfide (H2S) production recorded by different sources. Since this quality appeared to be a frequent feature of strains of P. morganii at the author's center, all isolates of this species were studied over a six-month period. During this time, 12 of 21 were found to produce scant H2S in Kligler's iron agar (KIA) and triple-sugar iron (TSI) agar butts. The strains were, in every respect, biotypical, and were easily distinguished from other species of Enterobacteriaceae by biochemical study. They also possessed the features of high resistance to cephalothin and ampicillin and relative sensitivity to tetracycline, unlike strains of Proteus mirabilis. It is concluded that weak H2S production in TSI or KIA medium is a frequent normal characteristic of P. morganii, and its presence should not deter microbiologists from correctly identifying isolates manifesting this quality.