Session: Poster Session: Trends in Multi-Drug Resistance in Salmonella sp.
Saturday, October 25, 2008: 12:00 AM
Room: Hall C
Background: Non-Typhi Salmonella (NTS) is a leading cause of bacterial foodborne illness in the United States. Antimicrobial agents, such as fluoroquinolones (e.g., ciprofloxacin) and 3rd generation cephalosporins (e.g., ceftriaxone), are essential to treat serious illness. Resistance to nalidixic acid, a quinolone, correlates with decreased susceptibility to ciprofloxacin. Resistance to ceftiofur, a 3rd generation cephalosporin used in food animals in the United States, correlates with decreased susceptibility to ceftriaxone. Methods: In 1996, 14 sites began submitting NTS isolates to the National Antimicrobial Resistance Monitoring System (NARMS) at CDC for susceptibility testing. Participation increased and became nationwide in 2003. Minimum inhibitory concentrations for 15 agents were determined by broth microdilution and interpreted using CLSI criteria. We modeled annual resistance from 1996 to 2006 using logistic regression. Results: From 1996 to 2006, 18,968 NTS isolates were tested. Nalidixic acid resistance in NTS rose from 0.4% (5/1324) in 1996 to 4% (127/2864) in 2006 (OR 95% CI=5.7-34.4). Salmonella serotype Enteritidis accounted for 31% of all nalidixic acid-resistant NTS isolates. Ceftiofur resistance in NTS rose from 0.2% in 1996 to 3% in 2006 (OR 95% CI=6.5-106.8). This increase was mainly driven by the emergence in 1998 of a multidrug resistance pattern (MDR-AmpC) in serotype Newport that included ceftiofur resistance. MDR-AmpC peaked at 25% in 2001 in Newport and was seen in 13 other serotypes. Conclusions: Resistance to nalidixic acid and ceftiofur in NTS has increased since 1996, representing quinolones and 3rd generation cephalosporins, respectively. MDR-AmpC emerged in 1998 in Newport and has been noted in 13 other serotypes. Monitoring to detect emerging multidrug and clinically important resistance, including serotype-specific trends, is important to guide clinical care and public health interventions.
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