Antimicrobial-resistant Salmonella enterica serovars isolated from chickens in Spain

In order to analyze the antibiotic resistance of Salmonella enterica serovars, a total of 112 Salmonella strains were tested (54 S. enteritidis, 32 S. typhimurium, 11 S. heidelberg, 7 S. infantis, 4 S. virchow and 4 S. hadar). The bacteria were isolated from 691 samples of frozen and fresh chicken meat. Identification of microorganisms and antimicrobial sensitivity testing were undertaken by means of the automated MicroScan AutoScan 4 method (Baxter in Spain). 45.5% of 112 strains tested were susceptible to all antibiotics. The highest percentage of resistance was found to: chloramphenicol (44.6%), ampicillin (34.8%) and tetracycline (33.9%). Multiple resistance was observed in 49 strains (43.7%), whereas single resistance was seen in 12 isolates (10.7%). We found 12 different patterns of resistance in Salmonella enterica serovar enteriditis. Resistance to chloramphenicol was the most common single resistance. The most frequent patterns of multiresistant strains were ampicillin + amoxicillin/clavulanate + cefazolin + imipenem and chloramphenicol + impipenem. In this serotype, 49 isolates belonged to phagetype 4. Salmonella typhimurium showed the highest percentages of resistance to the tested drugs, with six different resistance patterns found. 25 strains out of 32 S. typhimurium isolates belonged to phagotype 120 and 13 of these showed the same resistance pattern: chloramphenicol + tetracycline + ampicillin. The high incidence of antibiotic resistant salmonellae found in chickens in our study suggests the need for public health interventions to decrease selective pressure on bacterial strains by antimicrobial agents.