PREVALENCE AND RESISTANCE OF SALMONELLA NEWPORT 1997 - 2000: A NARMS REPORT

Authors: Cray, Paula; Wallace, Frederick; Gray, Jeffrey; Tankson, Jeanetta; ANANDARAMAN, NEENA - USDA-FSIS; SALAMONE, BEN - USDA-FSIS; DARGATZ, DAVE - USDA-APHIS; HEADRICK, MARCIA - FDA-CVM

Submitted to: National Foundation for Infectious Disease
Publication Type: Abstract Only
Publication Acceptance Date: 4/27/2002
Publication Date: 6/27/2002
Citation: Cray, P.J., Wallace, F.M., Gray, J.T., Tankson, J.D., Anandaraman, N., Salamone, B., Dargatz, D., Headrick, M. 2002. Prevalence and resistance of salmonella newport 1997 - 2000: a narms report. National Foundation for Infectious Disease. S8:36.

Interpretive Summary:

Technical Abstract: Salmonellae are ubiquitous in nature and over 2,000 serotypes have been identified. Of concern is the increasing tendency for isolates to develop multiple resistance to antimicrobials. Interestingly, development of resistance is not uniform among Salmonella serotypes, and when resistance is observed, it may not persist within the serotype. An increased prevalence of Salmonella Newport, particularly MR Newport, has been observed from both human and animal populations. We report on the characterization of S. Newport isolates from the animal arm of the National Antimicrobial Resistance Monitoring System (NARMS) from 1997 - 2000. Salmonella isolates were obtained from diagnostic (clinical submissions to a veterinary diagnostic laboratory) and non-diagnostic (on-farm sampling and raw product collected from federally inspected slaughter and processing plant) sources from cattle, swine, chickens, turkeys, horses, dogs, cats, and exotics. Isolates were tested for susceptibility to a custom made panel of antimicrobials using the SensititreTM System according to manufacturer¿s directions. Isolates were characterized by pulse field gel electrophoresis. Additionally, all isolates were tested for the presence of plasmids which were subsequently characterized. Results: From 1997 through 2000 the total numbers of Salmonella isolates tested were 2392, 3318, 8508, and 7834 for 1997 through 2000, respectively. Of these, the total number of serotypes increased each year (98, 120, 125, and 138 for 1997 through 2000, respectively) as did the total number of S. Newport (18, 42, 134 and 282 for 1997 through 2000, respectively). Isolates were recovered from both diagnostic and non-diagnostic sources. MR among the Newport isolates increased each year and in 2000, 76% (214/282) were resistant to > 5 antimicrobials. A majority of the MR isolates were recovered from cattle (both diagnostic and non-diagnostic sources) and comparison of isolates by PFGE indicated that the strains were nearly indistinguishable. A single large plasmid was found to carry determinants mediating the resistance phenotype expressed by these isolates. Interestingly, restriction digest of several plasmids indicated at least two unique patterns. Recovery of S. Newport has increased within the NARMS program as well as the recovery of MR Newport. Resistance appears to be plasmid mediated. While strains appear to cluster by PFGE, variations within plasmids are observed. Localization of resistance on a plasmid may enable the transfer of MR resistance to other serotypes in lieu of resistance developing as a result of antimicrobial use. Other MR isolates within NARMS are also being characterized to determine if a similar plasmid is harbored within other serotypes. Continued monitoring and surveillance for MR S. Newport, as well as MR plasmids, is warranted.