Molecular Characterization of Cephalosporin-Resistant Salmonella enterica Serotype Newport Isolates from Animals in Pennsylvania

Abstract

Multidrug-resistant (MDR) strains of Salmonella enterica serotype Newport have been described for many years. However, the recognition of Newport strains with resistance to cephalosporin antibiotics is more recent. Plasmid-mediated CMY-2 AmpC ␤-lactamases have been identified in Salmonella in the United States, and the bla CMY-2 gene has been shown to be present in Salmonella serotype Newport. This organism is currently undergoing epidemic spread in both animals and humans in the United States, and this is to our knowledge the first description of the molecular epidemiology of this Salmonella strain in animals. Forty-two isolates were included in this study. All isolates were characterized by pulsed-field gel electrophoresis, plasmid analysis, and antibiogram. Four pulsed-field profiles with XbaI were observed. Plasmid analyses showed that although the majority of isolates harbored a single plasmid of 140 kb, this plasmid was not identical in all strains. All isolates showed the presence of the bla CMY gene by PCR. Integrons were detected in 16 of the 42 isolates; a fragment of approximately 1,000 bp, amplified with the intI-F and aadAI-R primers, confirmed the presence of the aadAI gene cassette within an integron in these 16 isolates. The potential for coselection of the bla CMY gene, if located on an MDR replicon, may not be dependent on any particular antibiotic but rather may be the result of more general antimicrobial use. If this replicon is mobile, it is to be expected that similar MDR strains of additional Salmonella serotypes will be recognized in due course.

Characterization ofSalmonella entericaSerotype Newport Isolated from Humans and Food Animals

“…Cattle have been identified as the major reservoir for Salmonella serotype Newport MDRAmpC; however, other animals, such as pigs, horses, dogs, and pigeons, also can be infected with the pathogen, and certain clones of serotype Newport MDR-AmpC have spread among these animals. This spread has been confirmed based on genomic DNA fingerprinting patterns and antimicrobial resistance profiles (16).…”

Emergence of Salmonella epidemics: The problems related to Salmonella enterica serotyp Enteritidis and multiple antibiotic resistance in other major serotypes

“…This multidrug resistance phenotype included resistance to Sm, sulfamethoxazole, Tc, Ap, Cm, and decreased susceptibility to E-S cephalosporins. These resistant strains have also been detected in cattle [128]. An increase in prevalence of E-S cephalosporin-resistant strains could be in part related to the use in food animals of ceftiofur, which is an E-S cephalosporin approved for used in veterinary medicine [151].…”

Frequency and polymorphism of sopE in isolates of Salmonella enterica belonging to the ten most prevalent serotypes in England and Wales

“…All S. Hadar PT2, 5, 22 and 58 strains, but only antimicrobial-resistant strains of PT10, 11 and 18, were positive (Table 2). sopE was more prevalent in MDR S. Newport than in antimicrobial-sensitive strains (Table 2); however, it was not found in bovine and human MDR S. Newport isolates tested (K. L. Hopkins, unpublished observation) that are currently epidemic in the United States (Rankin et al, 2002). Only two S. Java strains and one strain of S. Infantis were sopE-positive, while all strains of S. Braenderup, S. Agona and S. Stanley were negative.…”