Risk Characterization of Antibiotic Resistance in Bacteria Isolated from Backyard, Organic, and Regular Commercial Eggs.

This study was conducted to assess the risk due to antimicrobial-resistant strains of Salmonella spp., Listeria monocytogenes, and Escherichia coli isolated from the eggshell and the contents of eggs bought in markets in Valencia (Spain). Thirty-four samples from three different production styles were analyzed: standard ( n = 34), organic ( n = 16), and backyard ( n = 10) eggs. L. monocytogenes was not isolated in any style of production. Only one strain of Salmonella was isolated from standard production, which was resistant to ciprofloxacin and amoxicillin. E. coli strains were resistant in 22% of the isolates from organic production, 12.25% from standard production, and 11.23% from backyard production. In all cases, the highest resistance was observed for amoxicillin-clavulanate. None of the isolates from standard and backyard eggs were resistant to chloramphenicol, ciprofloxacin, gentamycin, and streptomycin, while only ceftriaxone was found to be effective against all E. coli isolates from organic eggs. ß-Lactamase genes blaTEM , blaSHV, and blaCMY-2 and the resistance genes for tetracycline tetA, tetB, and tetC were tested. The most commonly detected antimicrobial resistance genes among the E. coli isolates were tetA (49.30%), blaTEM (47.89%), and tetB (36.62%). Overall, a maximum public health risk is associated with ß-lactam antibiotics.

Antimicrobial resistance of Escherichia coli isolated in newly-hatched chickens and effect of amoxicillin treatment during their growth.

The use of antimicrobials in food animals is the major determinant for the propagation of resistant bacteria in the animal reservoir. However, other factors may also play a part, and in particular vertical spread between the generations has been suggested to be an important transmission pathway. The objective of this paper was to determine the resistance patterns of Escherichia coli isolated from newly-hatched chickens as well as to study the antibiotic pressure effect when amoxicillin was administered during their growing period. With this aim, meconium from 22 one-day-old Ross chickens was analysed. In addition, during their growth period, amoxicillin treatments at days 7, 21 and 35 were carried out. Results showed a high number of E. coli-resistant strains were isolated from the treated one-day-old chickens, and were the highest for ß-lactams group, followed by quinolone and tetracyclines. After treatment with amoxicillin, the highest percentage of resistances were detected for this antibiotic compared to the others analysed, with significant differences in resistance percentages between control and treated broilers detected in relation to ampicillin, cephalothin, streptomycin, kanamycin, gentamicin, chloramphenicol and tetracycline. Differences in resistances to ciprofloxacin and nalidixic acid between control and treated animals were not observed and there was lack of resistance for amikacin and ceftriaxone. These results suggest the possibility of vertical transmission of resistant strains to newly-hatched chicks from parent flocks, and seem to indicate that the treatment with amoxicillin increased the resistance of E. coli to other antibiotics.