Abstract
BackgroundTyphoid fever is an acute, invasive, and potentially fatal systemic infection caused by Salmonella enterica subspecies enterica serotype Typhi (S. Typhi). Drug resistance to antimicrobials such as ciprofloxacin is emerging in developing countries, threatening the efficacy of treatment of patients in endemic regions as well as of travellers returning from these countries.MethodsWe compared the antimicrobial resistance profiles of 192 S. Typhi isolated from patients over a time span of twelve years. Susceptibility testing was done by the disk diffusion method. A representative selection of isolates (n = 41) was screened by PCR for mutations in the quinolone resistance-determining regions (QRDRs) of the gyrA and parC genes and all 192 isolates were screened for plasmid-mediated quinolone resistance (PMQR) genes. Multilocus sequence typing (MLST) was used to investigate the sequence type of isolates from patients with a known history of international travel.ResultsResistance rates for nalidixic acid increased from 20 % to 66.7 % between 2002 and 2013. Resistance to ciprofloxacin was detected in 55.6 % of the isolates by 2013. Ciprofloxacin resistance was predominantly associated with the triple substitutions Ser83 → Phe and Asp87 → Asn in GyrA and Ser80 → Ile in ParC. The plasmid-mediated resistance gene qnrS1 was detected in two isolates. Sequence type ST1 was associated with the Indian subcontinent, while ST2 was distributed internationally. Multidrug resistance was noted for 11.5 % of the isolates.ConclusionsFluoroquinolone resistant S. Typhi constitute a serious public health concern in endemic areas as well as in industrialized countries. Increased surveillance of global patterns of antimicrobial resistance is necessary and the control of resistant strains is of the utmost importance to maintain treatment options.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-015-0948-2) contains supplementary material, which is available to authorized users.
Highlights
Typhoid fever is an acute, invasive, and potentially fatal systemic infection caused by Salmonella enterica subspecies enterica serotype Typhi
Plasmid-mediated quinolone resistance (PMQR) confer a form of reduced susceptibility which is thought to promote the accumulation of the target site mutations [7]
Typhi isolates analysed in this study, together with anamnestic data and any travel information of the patients is given in Additional file 1: Table S1
Summary
Typhoid fever is an acute, invasive, and potentially fatal systemic infection caused by Salmonella enterica subspecies enterica serotype Typhi Typhi) is a human-specific etiological agent of an acute, invasive, and potentially fatal systemic infection known as typhoid fever [1]. Resistance is mainly due to the accumulation of mutations in the quinolone resistance-determining regions (QRDRs) of DNA gyrase and topoisomerase IV genes (target site alterations). Primary mutations in target site genes generate resistance to the quinolone antimicrobial nalidixic acid, making it useful as a surrogate marker of decreased susceptibility to fluoroquinolones [12], as resistance to nalidixic acid correlates with decreased susceptibility to ciprofloxacin and to potential treatment failure [13,14,15]
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