Serology unit, Animal Health Research Institute, ARC, Dokki, Egypt
Abstract
the general concept that lactose fermenting Salmonella (lac+ Salmonella) are rare may be correct; however, these strains can become endemic in a given geographic area. Failure to detect these strains presents a public health problem.This study report cases of lactose fermenting Salmonella Typhimurium (4 isolates), Salmonella Stratford (2 isolates) isolated from diarrheic calves and S.Blegdam (one isolate) isolated from diseased chicken. The strains are strong lactose fermenter and resemble Escherichia coli on primary plating media and in triple sugar iron agar. The aim of this study was to compare the capacity of 4 different selective media:- Xylose Lysine Deoxycholate agar (XLD), novobiocin – brilliant green – glucose agar (NBG), modified semisolid Rappaport –Vassiliadis agar (MSRV) and Bismuth sulphite agar (BS) to detect the growth of lactose fermenting S. Typhimurium, S. Stratford and S.Blegdam inoculated in milk replacer. They were cultured, in parallel, on these media, both by direct cultivation and after selective enrichment in selenite broth. The performance of BS was the excellent medium of all media used followed by XLD in combination with lysine iron agar (LIA). On MSRV only two strains grew and only one produced swarming. On NBG after 48h in the cases where there was growth, the number of colonies was much lower and the rest were inhibited. Antibiotic sensitivity pattern differed between lactose -positive Salmonella isolates and lactose-negative Salmonella Typhimurium standard strain ATCC 14028. Lactose-positive strains showed a higher degree of resistance than lactose-negative strain. The differences in resistance were seen in the case of erythromycin, chloramphenicol, streptomycin and tetracycline.
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