IMPROVED XLT4 AGAR - SMALL ADDITION OF PEPTONE TO PROMOTE STRONGER PRODUCTION OF HYDROGEN-SULFIDE BY SALMONELLAE

Xylose lysine tergitol(4) agar (XLT4) is a highly selective plating me dium used for isolating salmonellae. Studies have shown that XLT4 incr eases the recovery of salmonellae found in food, environmental and cli nical samples. Further testing demonstrated that the addition of low c oncentrations of proteose peptone No. 3 (pp3) to XLT4 produced blacker Salmonella colonies in shorter incubation times (increased hydrogen s ulfide production), while still maintaining strong inhibition of compe ting bacteria. The increased black colony formation facilitates prompt recognition of the weaker hydrogen sulfide-producing Salmonella strai ns. Test concentrations of pp3 at 0.5, 1.2 and 1.8 gn were added to XL T4 and compared with plain XLT4 using pure bacterial cultures, In addi tion, these four plating media, plus xylose lysine desoxycholate agar( XLD) were evaluated using nonspiked chicken liver and pork sausage sam ples. The concentration of 1.2 gn of pp3 in XLT4 gave the best overall results. In virtually all cases, the Salmonella colonies were larger and more black than on plain XLT4 without pp3. The improved XLT4 is re commended for more reliable detection of salmonellae from food, enviro nmental and clinical samples.