Comparison of Hektoen and Salmonella-Shigella agar on 6033 stools of human origin submitted for routine isolation of Salmonella sp. and Shigella sp.

From 1989 through 1991, 6033 stool specimens from patients at Orleans Hospital (France), were cultured for enteric pathogens. Hektoen agar (HE) was compared with Salmonella-Shigella agar (SS) after direct streaking and after overnight enrichment in Mueller-Kauffmann broth. Yersinia strains were not computed. Seven strains of Salmonella serotype Typhi were isolated, on both media, and excluded from computations for discussed reasons. Out of a total of 9 Shigella strains, HE isolated 9 and SS isolated 7. No statistically significant difference appeared about isolation of non-Typhi Salmonella strains (127 vs 114 from direct streaking, 237 vs 243 after enrichment). Predictive values of suspicious colonies were not statistically different. Numbers of false positives were not different, except for black centred colonies of the direct streaking (231 on HE vs 186 on SS, p less than 0.05). The skill of technologists was not taken into account but was found likely to be more accurate on SS agar. This data suggest that, since the frequency of Shigella sp became much lower, the differential of efficiency of HE vs SS agar is no longer obvious in human medical routine.