Fluoroquinolone Susceptibility Testing of Salmonella enterica: Detection of Acquired Resistance and Selection of Zone Diameter Breakpoints for Levofloxacin and Ofloxacin
Journal of clinical microbiology (Impact Factor: 3.99). 01/2014; 52(3). DOI: 10.1128/JCM.02679-13
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: We compared Etest and disk diffusion to broth microdilution for the detection of fluoroquinolone resistance in 135 typhoidal and nontyphoidal serovars of Salmonella. Categorical agreements for the ciprofloxacin and levofloxacin Etests were 89.6 and 83.7%, respectively. Disk diffusion categorical agreements were 88.2 and 93.3%, respectively. Only minor errors were observed.Journal of Clinical Microbiology 10/2014; 53(1). DOI:10.1128/JCM.02715-14 · 3.99 Impact Factor
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ABSTRACT: Invasive Salmonella infections (typhoidal and non-typhoidal) cause a huge burden of illness estimated at nearly 3.4 million cases and over 600,000 deaths annually especially in resource-limited settings. Invasive non-typhoidal Salmonella (iNTS) infections are particularly important in immunosuppressed populations especially in sub-Saharan Africa, causing a mortality of 20-30% in vulnerable children below 5 years of age. In these settings, where routine surveillance for antimicrobial resistance is rare or non-existent, reports of 50-75% multidrug resistance (MDR) in NTS are common, including strains of NTS also resistant to flouroquinolones and 3rd generation cephalosporins. Typhoid (enteric) fever caused by Salmonella Typhi and Salmonella Paratyphi A remains a major public health problem in many parts of Asia and Africa. Currently over a third of isolates in many endemic areas are MDR, and diminished susceptibility or resistance to fluoroquinolones, the drugs of choice for MDR cases over the last decade is an increasing problem. The situation is particularly worrying in resource-limited settings where the few remaining effective antimicrobials are either unavailable or altogether too expensive to be afforded by either the general public or by public health services. Although the prudent use of effective antimicrobials, improved hygiene and sanitation and the discovery of new antimicrobial agents may offer hope for the management of invasive salmonella infections, it is essential to consider other interventions including the wider use of WHO recommended typhoid vaccines and the acceleration of trials for novel iNTS vaccines. The main objective of this review is to describe existing data on the prevalence and epidemiology of antimicrobial resistant invasive Salmonella infections and how this affects the management of these infections, especially in endemic developing countries. Copyright © 2015. Published by Elsevier Ltd.Vaccine 04/2015; 33. DOI:10.1016/j.vaccine.2015.03.102 · 3.62 Impact Factor
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ABSTRACT: Salmonella enterica infections are common causes of bloodstream infection in low-resource areas, where they may be difficult to distinguish from other febrile illnesses and may be associated with a high case fatality ratio. Microbiologic culture of blood or bone marrow remains the mainstay of laboratory diagnosis. Antimicrobial resistance has emerged in Salmonella enterica, initially to the traditional first-line drugs chloramphenicol, ampicillin, and trimethoprim-sulfamethoxazole. Decreased fluoroquinolone susceptibility and then fluoroquinolone resistance have developed in association with chromosomal mutations in the quinolone resistance-determining region of genes encoding DNA gyrase and topoisomerase IV and also by plasmid-mediated resistance mechanisms. Resistance to extended-spectrum cephalosporins has occurred more often in nontyphoidal than in typhoidal Salmonella strains. Azithromycin is effective for the management of uncomplicated typhoid fever and may serve as an alternative oral drug in areas where fluoroquinolone resistance is common. In 2013, CLSI lowered the ciprofloxacin susceptibility breakpoints to account for accumulating clinical, microbiologic, and pharmacokinetic-pharmacodynamic data suggesting that revision was needed for contemporary invasive Salmonella infections. Newly established CLSI guidelines for azithromycin and Salmonella enterica serovar Typhi were published in CLSI document M100 in 2015. Copyright © 2015, American Society for Microbiology. All Rights Reserved.Clinical microbiology reviews 10/2015; 28(4):901-37. DOI:10.1128/CMR.00002-15 · 17.41 Impact Factor
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