Multiplex PCR was used to investigate the presence of enterotoxins genes (sea, seb, sec, sed and see) and femA gene (specific for Staphylococcus aureus) in coagulase-positive staphylococci (CPS) isolated from cheese and meat products. From 102 CPS isolates, 91 were positive for femA, 10 for sea, 12 for sed and four for see.

ABSTRACT

Staphylococcus xylosus is a microorganism involved in fermentation of meat products and also a natural producer of extracellular lipases. The aim of the present work was to clone and express in E. coli a lipase from S. xylosus (AF208229). This lipase gene (1084 bp) was amplified from a S. xylosus strain isolated from naturally fermented salami and introduced in pET14b expression vector in order to express the recombinant fusion protein (histidine-tagged lipase) in E. coli. Recombinant histidine-tagged S. xylosus lipase was purified by affinity chromatography in an HPLC system. The histidine-tagged lipase is a monomer in solution, as determined by size-exclusion chromatography. It presents a high lipase activity at pH 9.0 and 42 degrees C for p-nitrophenyl acetate and p-nitrophenyl butyrate, among seven different esters assayed (pNPC(2), pNPC(4), pNPC(10), pNPC(12), pNPC(14), pNPC(16), pNPC(18)). Moreover, the enzyme presented a quite interesting thermal stability, after an incubation period of 10 min at 95 degrees C, 77% of the initial activity was retained.

The occurence of Listeria species in refrigerated chicken carcasses was evaluated, comparing the conventional culture methodology of FDA, modified by the introduction of a secondary enrichment step prior plating, and the Clearview TM rapid method (Oxoid, UK Ltd). Forty-eight refrigerated whole chicken carcasses purchased from supermarkets in Florianópolis, SC, Brazil, were analysed. Listeria species occured in 21 (43.7%) samples. Using the Clearview method, 17 (35.4%) samples were positive for Listeria species. Of these isolates, 11 (23%) were L. monocytogenes, 4 (8.3%) L. innocua, 1 (2.1%) L. welshimeri and 1 (2.1%) L. seeligeri. Using the conventional culture methodology of FDA (with modifications), 14 (29.2%) samples were positive for Listeria species. Among these 7 (14.6%) were L. monocytogenes, 6 (12.5%) L. innocua and 1 (2.1%) L. seeligeri. With the Clearview rapid method plus API Listeria for identification, results were confirmed to Listeria species level within 115-139 h. Using the conventional culture method of FDA (with modifications) plus API Listeria, results were confirmed within 120-160 h. However, the Clearview method could indicate the presence of Listeria organisms in only 43 h. Results given by the methods were in moderate concordance and the differences between them were not significant (C.I. = 95%).