Abstract
To evaluate multidrug-resistant strains of Salmonella enterica Typhimurium, including definitive type 104 (DT104) in the United States, we reviewed data from the National Antimicrobial Resistance Monitoring System (NARMS). In 1997–1998, 25% (703) of 2,767 serotyped Salmonella isolates received at NARMS were S. Typhimurium; antimicrobial susceptibility testing and phage typing were completed for 697. Fifty-eight percent (402) were resistant to >1 antimicrobial agent. Three multidrug-resistant (>5 drugs) strains accounted for 74% (296) of all resistant isolates. Ceftriaxone resistance was present in 3% (8), and nalidixic acid resistance in 1% (4), of these multidrug-resistant strains. By phage typing, 37% (259) of S. Typhimurium isolates were DT104, 30% (209) were of undefined type and 15% (103) were untypable. Fifty percent (202) of resistant (>1 drug) isolates were DT104. Multidrug-resistant S. Typhimurium isolates, particularly DT104, account for a substantial proportion of S. Typhimurium isolates; ceftriaxone resistance is exhibited by some of these strains.
Highlights
To evaluate multidrug-resistant strains of Salmonella enterica serotype Typhimurium, including definitive type 104 (DT104) in the United States, we reviewed data from the National Antimicrobial Resistance Monitoring System (NARMS)
Typhimurium isolates is not routinely done in the United States, 93% of the R-type ACSSuT isolates tested from a national sample of isolates from all state and public health laboratories conducted in 1995 were DT104, which suggests that 9% of all human Salmonella infections in this country in 1995 were caused by S
At Centers for Disease Control and Prevention (CDC), partial range MICs were determined by using broth microdilution (Sensititre, Trek Diagnostics, Westlake, OH) for 16 antimicrobial agents: amikacin, amoxicillin-clavulanic acid (Cl), ampicillin (A), apramycin (Ap), ceftiofur (Cef), ceftriaxone (Cx), cephalothin (Cep), chloramphenicol (C), ciprofloxacin, gentamicin (G), kanamycin (K), nalidixic acid (N), streptomycin (S), sulfamethoxazole (Su), tetracycline (T), and trimethoprim-sulfamethoxazole (Tm)
Summary
In 1996, NARMS was established to prospectively monitor the patterns of antimicrobial-drug resistance among human enteric pathogens, including nontyphoidal Salmonella isolates received at select public health laboratories in the United States [8]. Typhimurium typing phages based on the method of Anderson et al [12] and the interpretive guide supplied by the Public Health Laboratory Service (PHLS) in Colindale, United Kingdom. Isolates that did not have antimicrobial susceptibility test results or phage type results were excluded from analysis. Statistical testing of differences in proportions was conducted using the chi-square test; p values
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