Fluoroquinolone Susceptibility Testing of Salmonella enterica: Detection of Acquired Resistance and Selection of Zone Diameter Breakpoints for Levofloxacin and Ofloxacin
ABSTRACT Fluoroquinolones (e.g. ciprofloxacin) have become a mainstay for treating severe Salmonella infections in adults. Fluoroquinolone resistance in Salmonella is mostly due to mutations in the topoisomerase genes, but plasmid-mediated quinolone resistance (PMQR) mechanisms have also been described. In 2012, the Clinical and Laboratory Standards Institute (CLSI) revised the ciprofloxacin interpretive criteria (breakpoints) for disk diffusion and minimum inhibitory concentration (MIC) test methods for Salmonella. In 2013, CLSI published MIC breakpoints for Salmonella to levofloxacin and ofloxacin, but breakpoints for assigning disk diffusion results to susceptible (S), intermediate (I), or resistant (R) categories are still needed. In this study, MICs and inhibition zone diameters for nalidixic acid, ciprofloxacin, levofloxacin and ofloxacin were determined for 100 clinical isolates of non-Typhi Salmonella with or without resistance mechanisms. We confirmed that the new levofloxacin MIC breakpoints resulted in the highest category agreement (94%) when plotted against ciprofloxacin MICs and that the new ofloxacin MIC breakpoints resulted in 92% category agreement between ofloxacin and ciprofloxacin. By applying the new MIC breakpoints in MIC zone scattergrams for levofloxacin and ofloxacin, the following disk diffusion breakpoints generated the least number of errors: S≥28mm, I=19-27mm and R≤18mm for levofloxacin and S≥25mm, I=16-24mm and R≤15mm for ofloxacin. Neither the levofloxacin nor the ofloxacin disk yielded a good separation of isolates with and without resistance mechanisms. Further studies will be needed to develop a disk diffusion assay that efficiently will detect all isolates with acquired resistance to fluoroquinolones.
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ABSTRACT: The influence of qnrA1 on the development of quinolone resistance in Enterobacteriaceae was evaluated by using the mutant prevention concentration parameter. The expression of qnrA1 considerably increased the mutant prevention concentration compared to strains without this gene. In the presence of qnrA1, mutations in gyrA and parC genes were easily selected to produce high levels of quinolone resistance.Antimicrobial Agents and Chemotherapy 06/2007; 51(6):2236-9. DOI:10.1128/AAC.01444-06 · 4.45 Impact Factor
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ABSTRACT: Estimates of foodborne illness can be used to direct food safety policy and interventions. We used data from active and passive surveillance and other sources to estimate that each year 31 major pathogens acquired in the United States caused 9.4 million episodes of foodborne illness (90% credible interval [CrI] 6.6–12.7 million), 55,961 hospitalizations (90% CrI 39,534–75,741), and 1,351 deaths (90% CrI 712–2,268). Most (58%) illnesses were caused by norovirus, followed by nontyphoidal Salmonella spp. (11%), Clostridium perfringens (10%), and Campylobacter spp. (9%). Leading causes of hospitalization were nontyphoidal Salmonella spp. (35%), norovirus (26%), Campylobacter spp. (15%), and Toxoplasma gondii (8%). Leading causes of death were nontyphoidal Salmonella spp. (28%), T. gondii (24%), Listeria monocytogenes (19%), and norovirus (11%). These estimates cannot be compared with prior (1999) estimates to assess trends because different methods were used. Additional data and more refined methods can improve future estimates.Emerging Infectious Diseases 01/2011; 17(1):7-15. DOI:10.3201/eid1701.091101p1 · 7.33 Impact Factor
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ABSTRACT: Patients with typhoid fever due to Salmonella enterica serotype Typhi strains for which fluoroquinolones MICs are elevated yet that are classified as susceptible by the current interpretive criteria of the Clinical and Laboratory Standards Institute may not respond adequately to fluoroquinolone therapy. Patients from seven U.S. states with invasive Salmonella serotype Typhi infection between 1999 and 2002 were enrolled in a multicenter retrospective cohort study. Patients infected with Salmonella serotype Typhi isolates with ciprofloxacin MICs of 0.12 to 1 microg/ml (decreased ciprofloxacin susceptibility but not resistant to ciprofloxacin [DCS]) were compared with patients infected with isolates with ciprofloxacin MICs <0.12 microg/ml for fever clearance time and treatment failure. Of 71 patients, 30 (43%) were female and 24 (34%) were infected with Salmonella serotype Typhi with DCS; the median age was 14 years (range, 1 to 51 years). Twenty-one (88%) of 24 isolates with DCS were resistant to nalidixic acid. The median antimicrobial-related fever clearance times in the DCS and non-DCS groups were 92 h (range, 21 to 373 h) and 72 h (range, 19 to 264 h) (P = 0.010), respectively, and the fluoroquinolone-related fever clearance times in the DCS and non-DCS groups were 90 h (range, 9 to 373 h) and 64 h (range, 34 to 204 h) (P = 0.153), respectively. Four (17%) of 24 patients in the DCS group and 2 (4%) of 46 patients in the non-DCS group (relative risk, 2.5; 95% confidence interval, 1.2 to 5.1) experienced treatment failure. Associations persisted after adjustment for potential confounders. We demonstrate that patients infected with Salmonella serotype Typhi isolates with DCS show evidence of a longer time to fever clearance and more frequent treatment failure. Nalidixic acid screening does not detect all isolates with DCS.Antimicrobial Agents and Chemotherapy 04/2008; 52(4):1278-84. DOI:10.1128/AAC.01509-07 · 4.45 Impact Factor