Volume 20, Number 5—May 2014
Ciprofloxacin-Resistant Salmonella enterica Serotype Kentucky Sequence Type 198
To the Editor: Mulvey et al. (1) reported the emergence of ciprofloxacin resistance in Salmonella enterica serovar Kentucky of multilocus sequence type 198 (ST198) in Canada (1). Ciprofloxacin resistance in S. enterica ser. Kentucky was reported in 2011 in patients from Europe, most of whom had traveled to Africa and the Middle East (2). Since then, S. enterica ser. Kentucky ST198 with additional resistance to third-generation cephalosporins and carbapenems has been reported from France and Morocco, again associated with travel (3). Poultry has been implicated as the most likely vehicle for infection by this sequence type (2,3). Resistance to third-generation cephalosporins and carbapenems has not been seen in North America; however, the emergence of ciprofloxacin-resistant infections has been observed (1).
In the United States, S. enterica ser. Kentucky is the most common serotype isolated from chickens and the second most common found among retail chicken, but ciprofloxacin resistance has not been documented among these sources (4). We sought to determine if ciprofloxacin- or ceftriaxone-resistant S. enterica ser. Kentucky has emerged in humans in the United States. We examined isolates and data from the National Antimicrobial Resistance Monitoring System to document antimicrobial resistance and sequence type and to assess possible risk factors for acquiring infection.
Participating state and local public health laboratories submit every 20th nontyphoidal Salmonella (NTS) isolate to the Centers for Disease Control and Prevention for susceptibility testing. MICs of >15 antimicrobial agents were determined by using broth microdilution (Sensititer, Cleveland, OH, USA) according to the manufacturer’s instructions. Where available, Clinical and Laboratory Standards Institute performance standards were used for interpretation of MICs; otherwise, interpretations established by the National Antimicrobial Resistance Monitoring System were used (5,6).
During 2009–2012, a total of 21 (0.2%) of the 9,225 NTS isolates tested were S. enterica ser. Kentucky. Six (29%) were resistant to ciprofloxacin; all were susceptible to ceftriaxone (Table) (5). As was observed in Canada, the 6 resistant isolates were >80% similar by pulsed-field gel electrophoresis analysis (XbaI; data not shown), and all 6 were ST198. Although a rare cause of human infection, S. enterica ser. Kentucky represented 23% (6/26) of all ciprofloxacin-resistant NTS detected during 2009–2012.
The median age of the 6 patients with ciprofloxacin-resistant S. enterica ser. Kentucky infections was 32 years (range 9 months–56 years); 5 (83%) were female. Of the 4 patients for whom information was available, 2 were hospitalized, and 1 died. Specimen sources were stool (n = 3) and urine (n = 3). Travel histories were obtained for 5 patients, and all had traveled internationally in the 7 days before specimen submission: 2 were residents of other countries (Saudi Arabia and Ethiopia), and 3 were US residents who had returned from travel to India. By comparison, only 3 of 10 patients with ciprofloxacin-susceptible infections had traveled (p = 0.02).
Resistance to ciprofloxacin in Salmonella is a growing concern because it limits treatment options for invasive disease. We describe ciprofloxacin-resistant S. enterica ser. Kentucky isolated from 6 patients in the United States. The emerging global story of S. enterica ser. Kentucky ST198 demonstrates the need for international integration of surveillance for antimicrobial drug resistance.
- Mulvey MR, Boyd DA, Finley R, Fakharuddin K, Langner S, Allen V, Ciprofloxacin-resistant Salmonella enterica serovar Kentucky in Canada. Emerg Infect Dis. 2013;19:999–1001 .
- Le Hello S, Hendriksen RS, Doublet B, Fisher I, Nielsen EM, Whichard JM, International spread of an epidemic population of Salmonella enterica serotype Kentucky ST198 resistant to ciprofloxacin. J Infect Dis. 2011;204:675–84.
- Le Hello S, Harrios D, Bouchrif B, Sontag L, Elhani D, Guibert V, Highly drug-resistant Salmonella enterica serotype Kentucky ST198-X1: a microbiological study. Lancet Infect Dis. 2013;13:672–9.
- US Food and Drug Administration. National Antimicrobial Resistance Monitoring System retail meat annual report, 2011 [cited 2013 Jul 1]. http://www.fda.gov/AnimalVeterinary/SafetyHealth/AntimicrobialResistance/NationalAntimicrobialResistanceMonitoringSystem/ucm334828.htm
- Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing; Twenty-third informational supplement. CLSI document M100–S23. Wayne (PA): The Institute; 2013.
- Centers for Disease Control and Prevention. National Antimicrobial Resistance Monitoring System human isolates annual report, 2011 [cited 2013 Jul 1]. http://www.cdc.gov/narms/pdf/2011-annual-report-narms-508c.pdf