Cephalosporin and ciprofloxacin resistance in Salmonella, Taiwan

Emerging Infectious Diseases, June, 2005 by Jing-Jou Yan, Chien-Shun Chiou, Tsai-Ling Yang Lauderdale, Shu-Huei Tsai, Jiunn-Jong Wu

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Conclusions

We describe the prevalence of resistance to ciprofloxacin and ESCs among salmonellae isolated from January to May 2004 in Taiwan. We found widespread resistance of Salmonella isolates to both ESCs and ciprofloxacin; high prevalence of resistance to ciprofloxacin, ESCs, and both in S. Choleraesuis; and widespread prevalence of CMY-2 producing Salmonella isolates of various serotypes in Taiwan.

The prevalence of Salmonella isolates resistant to both ceftriaxone and ciprofloxacin may pose a therapeutic problem. CMY-2 is one of the AmpC enzymes, which are usually less active against cefepime and cefpirome than ESBLs (15). Accordingly, we have used cefepime to successfully treat several patients infected with CMY-2-producing and ciprofloxacin-resistant S. Choleraesuis (8). Therefore, AmpC-producing strains should be differentiated from ESBL-producing strains by phenotypic or genotypic methods when ESC-resistant Salmonella strains are isolated in the clinical microbiology laboratory (15).

The ciprofloxacin-resistant rate in S. Choleraesuis in Taiwan has been >60% since 2001; the high prevalence was mainly due to clonal spread of resistant strains (4-6). The ciprofloxacin-resistant rate in S. Choleraesuis in this report (84.4%) was higher than those reported previously ([less than or equal to] 70%) (4-6). [bla.sub.CMY-2] in Salmonella in Taiwan was first reported in 2 S. Typhimurium strains isolated in 2000 (3). The first reported S. Choleraesuis strain with [bla.sub.CMY-2] was a ciprofloxacin-resistant strain isolated in 2002 (7). All our 38 ciprofloxacin-resistant S. Choleraesuis isolates, including 8 ESC-resistant isolates, were genetically related. Moreover, we found possibly unrelated [bla.sub.CMY-2]-positive plasmids (lanes 3, 4, 7, 8, 10, and 11 in Figure 1) among closely related isolates (Figure 2). These data together suggest that the development and rapidly increasing prevalence of ESC and ciprofloxacin resistance in S. Choleraesuis in Taiwan might result from the extremely high prevalence of ciprofloxacin resistance followed by the horizontal transfer of [bla.sub.CMY-2] into ciprofloxacin-resistant epidemic strains rather than from the spread of a clone that had been resistant to ciprofloxacin and ESCs.

All our ciprofloxacin-resistant Salmonella isolates tested had mutations in the QRDRs of gyrA and par, a finding consistent with previously reported results (1,4,5). The rates of ciprofloxacin resistance in the 3 most common serotypes, Enteritidis, Typhimurium, and Stanley, remained very low (0%-0.6%). Six of 11 ciprofloxacin-resistant isolates in the group of uncommon serotypes belonged to serotype Schwarzengrund and accounted for 42.9% of all serotype Schwarzengrund isolates. Thus, the high rate (5.5%) of ciprofloxacin resistance in this group was in part due to the high prevalence of ciprofloxacin resistance in serotype Schwarzengrund.