Ceftriaxone-resistant salmonella infection acquired by a child from cattle.

Background: The emergence of resistance to antimicrobial agents within the salmonellae is a worldwide problem that has been associated with the use of antibiotics in livestock. Resistance to ceftriaxone and the fluoroquinolon es, which are used to treat invasive salmonella infections, is rare in the United States. We analyzed the molecular characteristics of a ceftriaxone-r esistant strain of Salmonella enterica serotype typhimurium isolated from a 12-year-old boy with fever, abdominal pain, and diarrhea. Methods: We used pulsed-field gel electrophoresis and analysis of plasmids and beta-lactamases to compare the ceftriaxone-resistant S. enterica seroty pe typhimurium from the child with four isolates of this strain obtained fr om cattle during a local outbreak of salmonellosis. Results: The ceftriaxone-resistant isolate from the child was indistinguish able from one of the isolates from cattle, which was also resistant to ceft riaxone. Both ceftriaxone-resistant isolates were resistant to 13 antimicro bial agents; all but one of the resistance determinants were on a conjugati ve plasmid of 160 kb that encoded the functional group 1 beta-lactamase CMY -2. Both ceftriaxone- resistant isolates were closely related to the three other salmonella isolates obtained from cattle, all of which were susceptib le to ceftriaxone. Conclusions: This study provides additional evidence that antibiotic-resist ant strains of salmonella in the United States evolve primarily in livestoc k. Resistance to ceftriaxone, the drug of choice for invasive salmonella di sease, is a public health concern, especially with respect to children, sin ce fluoroquinolones, which can also be used to treat this disease, are not approved for use in children. (N Engl J Med 2000;342:1242-9.) (C) 2000, Mas sachusetts Medical Society.