HIGH PREVALENCE OF MULTIPLE RESISTANCE TO ANTIBIOTICS IN 144 LISTERIAISOLATES FROM SPANISH DAIRY AND MEAT-PRODUCTS

The resistance to 12 commonly used antimicrobial agents of 144 foodbor ne isolates belonging to the genus Listeria (23 L. monocytogenes, 54 L . innocua, 66 L. seeligeri, and 1 L. welshimeri) was tested by using t he agar disc-diffusion assay. The Listeria strains were isolated from dairy products (different varieties of unripened fresh and bacteria-ri pened hard cheeses made from ewe's, cow's, and goat's milk) and meat p roducts (longaniza, a type of pork sausage). A total of 84 (93%) and 5 4 (100%) Listeria strains isolated from cheese and pork sausage, respe ctively, were resistant to multiple antimicrobial agents. More than 80 % of the Listeria strains of both food origins were found to be suscep tible to penicillin G and ampicillin, whereas the proportion of isolat es resistant to the cephalosporins cefotaxime and cefoxitin was nearly 100%. The prevalence of resistance was much higher for isolates from pork sausage (73.8% on average) than for isolates from cheese (20.9%). This marked difference was statistically significant (P < 0.05; chi-s quare test) for all antibiotics except ampicillin, cefotaxime, and cef oxitin.