GENETIC RELATEDNESS OF A RARELY ISOLATED SALMONELLA: SALMONELLA ENTERICA SEROTYPE NIAKHAR FROM NARMS ANIMAL ISOLATES

Authors: Tankson, Jeanetta; Cray, Paula; Jackson, Charlene; HEADRICK, MARCIA - FDA - CVM

Submitted to: Antimicrobial Agents and Chemotherapy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2005
Publication Date: 12/13/2005
Citation: Tankson, J.D., Cray, P.J., Jackson, C.R., Headrick, M. 2005. Genetic relatedness of a rarely isolated Salmonella: Salmonella enterica serotype Niakhar from NARMS animal isolates. Antimicrobial Agents and Chemotherapy. 57:190-198.

Interpretive Summary: Salmonella bacteria are ubiquitous in nature and food borne illness is often caused by ingesting food contaminated with Salmonella. Over 2,400 different strains of Salmonella have been reported and recently, some strains have developed resistance to many of the antibiotics that may be used to treat severe illness. One strain, Salmonella Niakhar, while rarely isolated in the US, appears to have developed resistance to ciprofloxacin, a new antibiotic which is often used to treat severe illness in human. We determined the genetic characteristics of Niakhar isolates submitted to our laboratory as part of the National Antimicrobial Resistance Monitoring System (NARMS). Since 1997, only 5 Niakhar isolates have been submitted to NARMS. Of the 5 isolates, four originated from cattle, including one isolate which was resistant to ciprofloxacin, and 1 was from a dog. Results indicated two of the isolates (from cattle) which were not resistant to any antibiotic, were genetically similar, while the 3 other isolates, including the one isolate which was resistant to ciprofloxacin, were genetically different. The ciprofloxacin resistant isolate originated from a diagnostic submission from a cow that we presume was ill. Further genetic analysis indicated that the ciprofloxacin resistant gene is located on a plasmid, a piece of DNA that can easily move between bacteria which is known to play an essential role in transmitting antibiotic resistance among bacteria. These data underscore the importance of continued monitoring and characterization of antibiotic resistant strains of Salmonella and are useful for physicians and veterinarians who may need to treat ill humans and animals as well as scientists and commodity group specialists as they develop new control measures to ensure that Niakhar does not spread in the US.

Technical Abstract: In the United States, Salmonella enterica serotype Niakhar is infrequently isolated. Between 1997 and 2000, the animal arm of the National Antimicrobial Resistance Monitoring System ¿ Enteric Bacteria (NARMS) assayed a total of 22,383 Salmonella isolates from various animal sources (swine, cattle, chickens, turkeys, cats, horses, exotics, and dogs) for antimicrobial susceptibility. Isolates originated from diagnostic and non-diagnostic submissions. Only 5 (0.02%) of these isolates were identified as S. Niakhar. Of the five, three isolates were isolated in the Midwest from cattle, and two isolates, one from cattle and one from a dog, originated in the Southern United States. Antimicrobial resistance testing indicated that three isolates were pan-susceptible, one isolate was resistant to ampicillin and one isolate was resistant to ampicillin, chloramphenicol, ciprofloxacin, kanamycin, nalidixic acid, streptomycin, sulfamethoxazole, tetracycline, and trimethoprim/sulfamethoxazole. RAPD-PCR analysis, pulsed-field gel electrophoresis (PFGE), and ribotyping indicated that two pan-susceptible isolates were genetically similar, while the three remaining isolates were genetically different. The one S. Niakhar isolate which was multiple resistant harbored a class I integron, intI1, and two large plasmids. This study describes the phenotypic and genotypic characteristics of Salmonella Niakhar and represents the first report of a ciprofloxacin resistant Niakhar from the animal arm of NARMS.