Detection of a bla(SHV) extended-spectrum {beta}-lactamase in Salmonella enterica serovar Newport MDR-AmpC.

Salmonella enterica serovar Newport MDR-AmpC expressing TEM-1b and extended-spectrum beta-lactamase SHV-12 was isolated from affected animals during an outbreak of salmonellosis that led to a 3-month closure of one of the largest equine hospitals in the United States.

The role of disinfectant resistance of Salmonella enterica serotype enteritidis in recurring infections in Pennsylvania egg quality assurance program monitored flocks.

The Pennsylvania egg quality assurance program (PEQAP) has made major gains in the reduction of Salmonella enterica serotype enteritidis (S. enteritidis). However, S. enteritidis continues to be a major food safety concern for the commercial egg laying industry. Despite intensive control efforts through PEQAP, some commercial egg layer houses still remain positive for S. enteritidis. The primary objective of this study was to determine whether S. enteritidis isolates obtained from historically environmentally S. enteritidis-positive houses were resistant to commonly used disinfectants. Archived S. enteritidis isolates (environmental, rodent, or egg) were compared with recently obtained isolates from the environment, rodents, or eggs from the same S. enteritidis-positive house. In addition, the isolates were compared with archived isolates from those premises that appeared to have eliminated S. enteritidis from their layer facilities. The official methods of the use-dilution analysis of the Association of Official Analytical Chemists were used to evaluate each disinfectant product. Two phenolic, one quaternary ammonium, and one combination product containing quaternary ammonium and formaldehyde were evaluated, in addition to one sodium hypochlorite detergent. All products diluted according to the manufacturers' recommendations killed the S. enteritidis isolates in this test system. There was no difference in susceptibility or resistance to the disinfectants used between the isolates from those facilities that remained S. enteritidis-positive and those that appeared to have eliminated S. enteritidis from their facility.

Molecular characterization of cephalosporin-resistant Salmonella enterica serotype Newport isolates from animals in Pennsylvania.

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 beta-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.