Ceftiofur-Resistant Salmonella Strains Isolated from Dairy Farms Represent Multiple Widely Distributed Subtypes That Evolved by Independent Horizontal Gene Transfer

Abstract

Salmonella is the leading cause of known food-borne bacterial infections in the United States, with an incidence rate of approximately 15 cases per 100,000 people. The rise of antimicrobial-resistant Salmonella subtypes, including the appearance of subtypes resistant to ceftriaxone, represents a particular concern. Ceftriaxone is used to treat invasive cases of Salmonella in children and is closely related to ceftiofur, an antibiotic commonly used to treat diseases of cattle. In order to develop a better understanding of the evolution and transmission of ceftiofur resistance in Salmonella, we characterized ceftiofur-resistant and -sensitive Salmonella isolates from seven New York dairy farms. A total of 39 isolates from these seven farms were analyzed for evolutionary relatedness (by DNA sequencing of the Salmonella genes fimA, manB, and mdh), antibiotic resistance profiles, and the presence of bla CMY-2 , a beta-lactamase gene associated with resistance to cephalosporins. Our data indicate that (i) resistance to ceftriaxone and ceftiofur was highly correlated with the presence of bla CMY-2 ; (ii) ceftiofur-resistant Salmonella strains were geographically widespread, as shown by their isolation from farms located throughout New York State; (iii) ceftiofur-resistant Salmonella strains isolated from farms represent multiple distinct subtypes and evolutionary lineages, as determined by serotyping, DNA sequence typing, and antimicrobial-resistance profiles; and (iv) ceftiofur-resistant Salmonella strains evolved by multiple independent acquisitions of an identical bla CMY-2 allele and by clonal spread of ceftiofurresistant subtypes.

Phenotypic and genotypic resistance profile of Salmonella Typhimurium to antimicrobials commonly used in poultry

“…This was also reported by Alcaine et al (2005), who observed that nineteen resistant Salmonella isolates carried the ceftiofur gene BlaCMY. Studies conducted by Frye & Cray (2007) reported that 17% of resistant strains did not have the BlaCMY gene or some other β-lactamase resistant genes detected by PCR, raising a concern that other mechanisms are associated to ceftiofur resistance.…”

Salmonella enterica Serotype 4,5,12:i:−, an Emerging Salmonella Serotype That Represents Multiple Distinct Clones

“…aroC was chosen as an additional gene because it was found to represent the greatest number of different ATs among all isolates in the seven-gene MLST database for Salmonella in July 2007 (http://web.mpiib-berlin.mpg.de/mlst/dbs/Senterica). ATs for fimA, mdh, and manB and three-gene sequence types (STs) were assigned to be consistent with previous studies published by our group (2,3,33). ATs for aroC were also assigned to be consistent with the seven-gene MLST Max Planck Institute database (http://web.mpiib-berlin.mpg.de/mlst/dbs/Senterica).…”

Diversity and antimicrobial resistance of Salmonella strains isolated from different sources in Burkina Faso

“…This finding corroborates with the report of Alcaine et al (2005), where Salmonella Typhi, Agona, Derby, Kiambo, Albany, Newport, Haardy, Enteritidis and Typhimurium isolates have been found to harbor resistant genes for chloramphenicol. There are two mechanisms in which Salmonella resistance to chloramphenicol is conferred: (i) by the plasmid-mediated enzymes called chloramphenicol acetyltransferases (CAT) or nonenzymatic chloramphenicol resistance gene cm1A and (ii) Efflux pump in which the antibiotic is pumped out of the cell.…”