Exposure of Escherichia coli to antibiotic-efflux pump inhibitor combinations in a pharmacokinetic model: impact on bacterial clearance and drug resistance

BACKGROUND

Efflux pump inhibitors (EPIs) offer an attractive therapeutic option when combined with existing classes. However, their optimal dosing strategies are unknown.

METHODS

MICs of ciprofloxacin (CIP)+/-chlorpromazine, phenylalanine-arginine β naphthylamide (PAβN) and a developmental molecule MBX-4191 were determined and the pharmacodynamics (PD) was studied in an in vitro model employing Escherichia coli MG1655 and its isogenic MarR mutant (I1147). Exposure ranging experiments were performed initially then fractionation. Changes in bacterial load and population profiles were assessed. Strains recovered after EPI simulations were studied by WGS.

RESULTS

The CIPMICs for E. coli MG1655 and I1147 were 0.08 and 0.03 mg/L. Chlorpromazine at a concentration of 60 mg/L, PAβN concentrations of 30 mg/L and MBX-4191 concentrations of 0.5-1.0 mg/L reduced CIP MICs for I1147 and enhanced bacterial killing. Using CIP at an AUC of 1.2 mg·h/L, chlorpromazine AUC was best related to reduction in bacterial load at 24 h, however, when the time drug concentration was greater than 25 mg/L (T > 25 mg/L) chlorpromazine was also strongly related to the effect. For PaβN with CIP AUC, 0.6 mg·h/L PaβN AUC was best related to a reduction in bacterial load. MBX-4191T > 0.5-0.75 mg·h/L was best related to reduction in bacterial load. Changes in population profiles were not seen in experiments of ciprofloxacin + EPIs. WGS of recovered strains from simulations with all three EPIs showed mutations in gyrA, gyrB or marR.

CONCLUSIONS

AUC was the pharmacodynamic driver for chlorpromazine and PAβN while T > threshold was the driver for MBX-4191 and important in the activity of chlorpromazine and PAβN. Changes in population profiles did not occur with combinations of ciprofloxacin + EPIs, however, mutations in gyrA, gyrB and marR were detected.

Synergistic antibacterial activity of carvacrol loaded chitosan nanoparticles with Topoisomerase inhibitors and genotoxicity evaluation

The increasing prevalence of antibiotic resistant bacteria is a significant healthcare crisis with substantial socioeconomic impact on global community. The development of new antibiotics is both costly and time-consuming prompting the exploration of alternative solutions such as nanotechnology which represents opportunities for targeted drug delivery and reduced MIC. However, concerns have arisen regarding genotoxic effects of nanoparticles on human health necessitating an evaluation of nanoparticle induced DNA damage. This study aimed to investigate the antibacterial potential of already prepared, characterized chitosan nanoparticles loaded with carvacrol and their potential synergism with Topoisomerase II inhibitors against S. aureus, E. coli and S. typhi using agar well diffusion, microdilution and checkerboard method. Genotoxicity was assessed through comet assay. Results showed that both alone and drug combinations of varying concentrations exhibited greater zones of inhibition at higher concentrations. Carvacrol nanoparticles combined with ciprofloxacin and doxorubicin significantly reduced MIC compared to the drugs used alone. The MIC50 values for ciprofloxacin were 35.8 µg/ml, 48.74 µg/ml, 35.57 µg/ml while doxorubicin showed MIC50 values of 20.79 µg/ml, 34.35 µg/ml, 25.32 µg/ml against S. aureus, E. coli and S. typhi respectively. The FICI of ciprofloxacin and doxorubicin with carvacrol nanoparticles found ≤ 0.5 Such as 0.44, 0.44,0.48 for ciprofloxacin and 0.45, 0.45, 0.46 for doxorubicin against S. aureus, E. coli and S. typhi respectively revealed the synergistic effect. The analysis of comet assay output images showed alteration of DNA at high concentrations. Our results suggested that carvacrol nanoparticles in combination with Topoisomerase inhibitors may prevent and control the emergence of resistant bacteria with reduced dose.

Hotspots sequences of gyrA, gyrB, parC, and parE genes encoded for fluoroquinolones resistance from local Salmonella Typhi strains in Jakarta

Background

Infection of Salmonella enterica subsp. enterica serovar Typhi is the primary etiology of typhoid fever globally and is common in many developing countries, especially those with dense populations and poor environmental sanitation. Antibiotic fluoroquinolones were used for the treatment in the 1980s due to the resistance to the first-line antibiotics. However, many cases of treatment failure of fluoroquinolones in typhoidal patients have been reported from numerous countries in Asia, Europe, Africa, and America. Mutations in quinolone resistance determining regions (QRDR) genes, gyrA, gyrB, parC, and parE, are found in fluoroquinolone-resistant Salmonella Typhi. Contrast reports came from the S. Typhi isolates in Indonesia, mainly Jakarta and the surroundings, obtained from patients with typhoid fever, with good sensitivity to the fluoroquinolones, i.e., nalidixic acid, ciprofloxacin, moxifloxacin, and levofloxacin. The present study, therefore, aimed to identify the hotspot sequences of gyrA, gyrB, parC, and parE genes of the local S. Typhi strains based on their susceptibility to fluoroquinolones from patients with typhoid fever in Jakarta and its satellite cities.

Results

A total of 28 isolates were identified as S. Typhi. All isolates were susceptible to nalidixic acid, levofloxacin, and moxifloxacin. Twenty-seven isolates (96.4%) were susceptible to ciprofloxacin, with one isolate (3.6%) being intermediate. The hotspot sequences of gyrA, gyrB, parC, and parE genes from all isolates were identical to the fluoroquinolone-sensitive reference sequence Salmonella enterica subsp. enterica serovar Typhi Ty2 (NCBI GenBank AE014613.1), including the isolate with intermediate susceptibility. The mutation was not found, and amino acid deduced from all hotspots in susceptible and intermediate isolates showed no replacement in all reported codons.

Conclusions

This study showed that the local S. Typhi strains from Jakarta and surroundings were susceptible to fluoroquinolones (nalidixic acid, ciprofloxacin, levofloxacin, and moxifloxacin), and the hotspot sequences of the gyrA, gyrB, parC, and parE genes were all identical to the reference sequence. Thus, the hotspot sequences of the gyrA, gyrB, parC, and parE genes seemingly were conserved in Jakarta’s local S. Typhi strains and could be considered wild type. The phenotypic susceptibility was consistent with the genotypic characteristic without non-synonymous mutations associated with drug resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02666-z.

Mutational Diversity in the Quinolone Resistance-Determining Regions of Type-II Topoisomerases of Salmonella Serovars

Quinolone resistance in bacterial pathogens has primarily been associated with mutations in the quinolone resistance-determining regions (QRDRs) of bacterial type-II topoisomerases, which are DNA gyrase and topoisomerase IV. Depending on the position and type of the mutation (s) in the QRDRs, bacteria either become partially or completely resistant to quinolone. QRDR mutations have been identified and characterized in Salmonella enterica isolates from around the globe, particularly during the last decade, and efforts have been made to understand the propensity of different serovars to carry such mutations. Because there is currently no thorough analysis of the available literature on QRDR mutations in different Salmonella serovars, this review aims to provide a comprehensive picture of the mutational diversity in QRDRs of Salmonella serovars, summarizing the literature related to both typhoidal and non-typhoidal Salmonella serovars with a special emphasis on recent findings. This review will also discuss plasmid-mediated quinolone-resistance determinants with respect to their additive or synergistic contributions with QRDR mutations in imparting elevated quinolone resistance. Finally, the review will assess the contribution of membrane transporter-mediated quinolone efflux to quinolone resistance in strains carrying QRDR mutations. This information should be helpful to guide the routine surveillance of foodborne Salmonella serovars, especially with respect to their spread across countries, as well as to improve laboratory diagnosis of quinolone-resistant Salmonella strains.

The molecular basis of extensively drug-resistant Salmonella Typhi isolates from pediatric septicemia patients

Sepsis is a syndromic response to infections and is becoming an emerging threat to the public health sector, particularly in developing countries. Salmonella Typhi (S. Typhi), the cause of typhoid fever, is one primary cause of pediatric sepsis in typhoid endemic areas. Extensively drug-resistant (XDR) S. Typhi is more common among pediatric patients, which is responsible for over 90% of the reported XDR typhoid cases, but the majority of antibiotic resistance studies available have been carried out using S. Typhi isolates from adult patients. Here, we characterized antibiotic-resistance profiles of XDR S. Typhi isolates from a medium size cohort of pediatric typhoid patients (n = 45, 68.89% male and 31.11% female) and determined antibiotic-resistance-related gene signatures associated with common treatment options to typhoid fever patients of 18 XDR S. Typhi representing all 45 isolates. Their ages were 1–13 years old: toddlers aging 1–2 years old (n = 9, 20%), pre-schoolers aging 3–5 years old (n = 17, 37.78%), school-age children aging 6–12 years old (n = 17, 37.78%), and adolescents aging 13–18 years old (n = 2, 4.44%). Through analyzing bla_TEM1, dhfR7, sul1, and catA1genes for multidrug-resistance, qnrS, gyrA, gyrB, parC, and parE for fluoroquinolone-resistance, bla_CTX-M-15 for XDR, and macAB and acrAB efflux pump system-associated genes, we showed the phenotype of the XDR S. Typhi isolates matches with their genotypes featured by the acquisitions of the genes bla_TEM1, dhfR7, sul1, catA1, qnrS, and bla_CTX-M-15 and a point mutation on gyrA. This study informs the molecular basis of antibiotic-resistance among recent S. Typhi isolates from pediatric septicemia patients, therefore providing insights into the development of molecular detection methods and treatment strategies for XDR S. Typhi.

Multiple introductions of multidrug-resistant typhoid associated with acute infection and asymptomatic carriage, Kenya

Background:

Understanding the dynamics of infection and carriage of typhoid in endemic settings is critical to finding solutions to prevention and control.

Methods:

In a 3-year case-control study, we investigated typhoid among children aged <16 years (4670 febrile cases and 8549 age matched controls) living in an informal settlement, Nairobi, Kenya.

Results:

148 S. Typhi isolates from cases and 95 from controls (stool culture) were identified; a carriage frequency of 1 %. Whole-genome sequencing showed 97% of cases and 88% of controls were genotype 4.3.1 (Haplotype 58), with the majority of each (76% and 88%) being multidrug-resistant strains in three sublineages of the H58 genotype (East Africa 1 (EA1), EA2, and EA3), with sequences from cases and carriers intermingled.

Conclusions:

The high rate of multidrug-resistant H58 S. Typhi, and the close phylogenetic relationships between cases and controls, provides evidence for the role of carriers as a reservoir for the community spread of typhoid in this setting.

Funding:

National Institutes of Health (R01AI099525); Wellcome Trust (106158/Z/14/Z); European Commission (TyphiNET No 845681); National Institute for Health Research (NIHR); Bill and Melinda Gates Foundation (OPP1175797).

Validation of Pefloxacin for detection of fluoroquinolone (FQ) resistance among Salmonella Typhi with special reference to GyrB mutations

Introduction. Fluoroquinolone (FQ) resistant Salmonella are classified as high priority pathogens by WHO. FQ resistance among Salmonella Typhi has emerged rapidly and is predominantly mediated by mutations in the topoisomerase genes gyrA, and parC. Mutations in GyrA result in classical FQ resistance (DCS-NAR) i.e. decreased susceptibility to ciprofloxacin (MIC of 0.12 to 0.5 µg ml^-1) (DCS) and resistance to nalidixic acid (NAR). Previously a nalidixic acid disc test was proposed for detection of DCS. Recently isolates with non-classical FQ resistance caused by plasmid-mediated quinolone resistance (PMQR) and mutations in GyrB have emerged. These mechanisms also result in DCS but are nalidixic acid susceptible (NAS) and thus pose diagnostic challenges. CLSI and EUCAST have recommended use of 5 µg pefloxacin discs for detection of DCS in Salmonella.Hypothesis. The CLSI and EUCAST recommendations for use of 5 µg pefloxacin for detection of DCS has not been validated on typhoidal Salmonella and resistance mediated by GyrB mutation in Salmonella species.Aim. The aim of the present study was to validate the performance of the 5 µg pefloxacin discs to detect isolates of S. Typhi with DCS with special reference to GyrB mutations.Methodology. A total of 180 clinical isolates of Salmonella Typhi (2005-2014) were investigated for genetic mechanisms of resistance. Zone diameters for nalidixic acid (30μg), ciprofloxacin (5μg) and pefloxacin (5µg) and minimum inhibitory concentration (MIC) for ciprofloxacin were determined using CLSI guidelines. Performance of the three discs was evaluated to detect FQ resistance in S. Typhi.Results. Topoisomerase mutations in GyrB +/ ParC and GyrB were detected in 112 and 34 isolates respectively. Different mutations have a varied effect on the MIC for ciprofloxacin. The current breakpoints for susceptible (≤0.06 µg ml^-1) and non-susceptible (≥0.125 µg ml^-1), failed to detect all isolates with a resistance mechanism. Performance of both ciprofloxacin and pefloxacin discs were excellent compared to nalidixic acid in differentiating isolates with non-classical resistance mediated by GyrB from wild-type.Conclusion. The pefloxacin disc can be used to detect FQ resistance among S. Typhi. This is the first report of validation of pefloxacin for detection of FQ resistance in S. Typhi mediated by GyrB mutation.

Changes in antimicrobial resistance and molecular attributes of Salmonellae causing enteric fever in Kolkata, India, 2014-2018

Globally, enteric fever caused by Salmonella Typhi (S. Typhi, ST) and S. Paratyphi A (SPA) remain one of the major diseases of public health importance. In this study, a total of 457 (380 ST, 77 SPA) blood isolates were collected from three tertiary care hospitals in Kolkata during 2014-18. Additionally, 66 (3.4%) ST and 5 (0.25%) SPA were recovered from blood culture of 1962 patients attending OPD of one pediatric hospital during 2016-18. The study isolates were tested for antimicrobial resistance (AMR) profiles; AMR genes; molecular sub-types by PFGE, MLVA and CRISPR. Among the total 446 ST and 82 SPA isolates, fluoroquinolone (FQ) resistance was very common in both serovars. Ciprofloxacin resistance of 24.9% and 9.8% & ofloxacin resistance of 20.9% and 87.8% were found in ST and SPA respectively. Majority (>70%) of the isolates showed decreased susceptibility to ciprofloxacin (DCS). A single point mutation in gyrA gene (S83F) was responsible for causing DCS in 37.5% (n = 42/112) ST and 63% (n = 46/73) SPA isolates. Multidrug resistance (MDR) was found only in 3.4% ST isolates and encoded the genes bla_TEM-1, catA, sul, strA-strB, class 1 integron with dfrA7. All MDR ST (n = 15) possessed non-conjugative non-IncHI1 (180 kb) plasmid except one having conjugative IncHI1 (230 kb) plasmid and one without plasmid. The MDR genes were integrated near chromosomal cyaA gene site in ST with/without the presence of plasmid (nonIncH1). Almost 65.7% resistant ST belonged to H58 haplotype. PFGE showed clonally related isolates with 81% similarity in ST and 87% in SPA. Similarly, CRISPR typing showed less diversity among the isolates. However, the isolates (ST and SPA) were found to be more diverse by MLVA typing (D value 0.987 and 0.938). The study reports decrease in MDR and increase in FQ resistance among typhoidal Salmonella isolates over the years giving interesting information for enteric fever treatment.

Characterization of Salmonella enterica isolates causing bacteremia in Lima, Peru, using multiple typing methods

In this study, different molecular typing tools were applied to characterize 95 Salmonella enterica blood isolates collected between 2008 and 2013 from patients at nine public hospitals in Lima, Peru. Combined results of multiplex PCR serotyping, two- and seven-loci multilocus sequence typing (MLST) schemes, serotyping, IS200 amplification and RAPD fingerprints, showed that these infections were caused by eight different serovars: Enteritidis, Typhimurium, Typhi, Choleraesuis, Dublin, Paratyphi A, Paratyphi B and Infantis. Among these, Enteritidis, Typhimurium and Typhi were the most prevalent, representing 45, 36 and 11% of the isolates, respectively. Most isolates (74%) were not resistant to ten primarily used antimicrobial drugs; however, 37% of the strains showed intermediate susceptibility to ciprofloxacin (ISC). Antimicrobial resistance integrons were carried by one Dublin (dfra1 and aadA1) and two Infantis (aadA1) isolates. The two Infantis isolates were multidrug resistant and harbored a large megaplasmid. Amplification of spvC and spvRA regions showed that all Enteritidis (n = 42), Typhimurium (n = 34), Choleraesuis (n = 3) and Dublin (n = 1) isolates carried the Salmonella virulence plasmid (pSV). We conclude that the classic serotyping method can be substituted by the multiplex PCR and, when necessary, sequencing of only one or two loci of the MLST scheme is a valuable tool to confirm the results. The effectiveness and feasibility of different typing tools is discussed.

Renaissance of Conventional First-Line Antibiotics in Salmonella enterica Clinical Isolates: Assessment of MICs for Therapeutic Antimicrobials in Enteric Fever Cases from Nepal

Enteric fever caused by Salmonella enterica is a life-threatening systemic illness of gastrointestinal tract especially in tropical countries. Antimicrobial therapy is generally indicated but resistance towards commonly used antibiotics has limited their therapeutic usefulness. Therefore, we aimed to determine the antimicrobial susceptibility pattern by minimum inhibitory concentration method of common therapeutic regimens against Salmonella enterica from enteric fever clinical cases. Salmonella enterica clinical isolates recovered from the patients with suspected enteric fever whose blood samples were submitted to microbiology laboratory of Manmohan Memorial Community Hospital, Kathmandu, from March 2016 to August 2016, were studied. These isolates were subjected to antimicrobial susceptibility testing against common therapeutic antimicrobials by Kirby-Bauer disk diffusion method. The minimum inhibitory concentration of ciprofloxacin, azithromycin, chloramphenicol, and cefixime was determined by Agar dilution method based on the latest CLSI protocol. A total of 88 isolates of Salmonella enterica were recovered from blood samples of enteric fever cases. Out of them, 74 (84.09%) were Salmonella Typhi and 14 (15.91%) were Salmonella Paratyphi A. On Kirby-Bauer disk diffusion antimicrobial susceptibility testing, entire isolates were susceptible to cotrimoxazole, cefixime, ceftriaxone, azithromycin, and chloramphenicol. Sixty-four (72.7%) Salmonella enterica isolates were nalidixic acid resistant and nonsusceptible to ciprofloxacin and levofloxacin. On MIC determination, four Salmonella isolates were ciprofloxacin resistant with MIC 1 µg/ml and two isolates were ciprofloxacin intermediate with MIC 0.5 µg/ml. The MIC range of azithromycin was from 0.125 µg/ml to 2.0 µg/ml, whereas that for chloramphenicol was 2.0 µg/ml–8.0 µg/ml and for cefixime was 0.0075–0.5 µg/ml, respectively. Despite global surge of antimicrobial resistance among Salmonella enterica clinical isolates, the level of drug resistance in our study was not so high. However, higher level of NARST strains limits therapeutic use of fluoroquinolones and necessitates the routine monitoring of such resistance determinants in order to effectively and rationally manage enteric fever cases.

Antimicrobial resistance and molecular subtypes of Salmonella enterica serovar Typhi isolates from Kolkata, India over a 15 years period 1998-2012

Typhoid fever, caused by Salmonella enterica serovar Typhi (S. Typhi), remains an unresolved public health problem in India. Emergence of antimicrobial resistant strains poses a great concern for typhoid treatment and influences reshaping of current S. Typhi population. We included representative S. Typhi strains (n=164) from retrospective studies, both community and hospital based, conducted at National Institute of Cholera and Enteric Diseases, Kolkata during 15 years period (1998-2012) to analyze their antimicrobial resistance (AMR) profiles, mechanism of AMR and molecular subtypes of the strains. More than 60% of the S. Typhi isolates were obtained from community based studies. During the study period, steady decline (46.4%-15.6%) in isolation of multidrug-resistant (MDR, resistant to ampicillin, chloramphenicol and co-trimoxazole) S. Typhi was noticed with parallel increase of nalidixic acid-resistant (NAL^R) strains (60.7%-93.8%) and ciprofloxacin resistant (CIP^R) strains (0%-25%). Of 53 MDR strains, 46 (86.8%) were NAL^R showing decreased ciprofloxacin susceptible (DCS) (MIC for ciprofloxacin 0.12-0.5μg/ml) phenotype. Conjugative IncHI1 (230kb) and non-conjugative non-IncHI1 (180kb) plasmids were found in 23 (43.4%) and 14 (26.4%) MDR strains respectively, plasmid was absent in 16 (30.2%) MDR strains. MDR strains with or without plasmid shared the same set of resistance genes (bla_TEM-1, catA1, sul1, sul2, strA and strB) and class 1 integron possessing dfrA7 gene cassette. Two S. Typhi strains harbored 50kb transferrable plasmids carrying dfrA15 and aadA1 gene cassettes in class 1 integron. The majority of the strains (135/164, 82.3%) belonged to H58 haplotype. Among the MDR isolates, fluoroquinolone resistant or combined resistant isolates (n=147), 127 (86.4%) were H58 and 20 (13.6%) belonged to non-H58. NAL^RS. Typhi strains with decreased susceptibility or resistance to ciprofloxacin had point mutation(s) in quinolone resistance-determining region of gyrA and parC genes. Pulsed-field gel electrophoresis showed more diversity among NAL^RS. Typhi than MDR strains. Results of this study generated information useful for better understanding of the disease epidemiology and its control in endemic settings.

Prevalence of Plasmid-Mediated Quinolone Resistance Genes in Clinical Enterobacteria from Argentina

This first nationwide study was conducted to analyze the prevalence of plasmid-mediated quinolone resistance (PMQR) genes in phenotypically unselected (consecutive) clinical enterobacteria. We studied 1,058 isolates that had been consecutively collected in 66 hospitals of the WHONET-Argentina Resistance Surveillance Network. Overall, 26% of isolates were nonsusceptible to at least one of the three quinolones tested (nalidixic acid, ciprofloxacin, and levofloxacin). The overall prevalence of PMQR genes was 8.1% (4.6% for aac(6')-Ib-cr; 3.9% for qnr genes; and 0.4% for oqxA and oqxB, which were not previously reported in enterobacteria other than Klebsiella spp. from Argentina). The PMQR prevalence was highly variable among the enterobacterial species or when the different genes were considered. The prevalent PMQR genes were located in class 1 integrons [qnrB2, qnrB10, and aac(6')-Ib-cr]; in the ColE1-type plasmid pPAB19-1 or Tn2012-like transposons (qnrB19); and in Tn6238 or bracketed by IS26 and bla_OXA-1 [aac(6')-Ib-cr]. The mutations associated with quinolone resistance that were located in the quinolone resistance-determining region (QRDR mutations) of gyrA, parC, and gyrB were also investigated. The occurrence of QRDR mutations was significantly associated with the presence of PMQR genes: At least one QRDR mutation was present in 82% of the PMQR-harboring isolates but in only 23% of those without PMQR genes (p < 0.0001, Fisher's Test). To the best of our knowledge, this is the first report on the prevalence of PMQR genes in consecutive clinical enterobacteria where all the genes currently known have been screened.

Revisit of fluoroquinolone and azithromycin susceptibility breakpoints for Salmonella enterica serovar Typhi

In recent years, increase in occurrence of fluoroquinolone (FQ)-resistant S almonella Typhi isolates has caused considerable inconvenience in selecting appropriate antimicrobials for treatment of typhoid. The World Health Organization (WHO) recommends azithromycin for the empirical treatment option of uncomplicated typhoid. The CLSI updated the breakpoints of disc diffusion (DD) and MIC results of FQs and azithromycin for Salmonella Typhi in 2015, but DD breakpoints of ofloxacin and levofloxacin were not included. In this study, the inhibition zone diameters and MICs of nalidixic acid, ciprofloxacin, ofloxacin, levofloxacin and azithromycin were determined in Salmonella Typhi Kolkata isolates (n =146) over a 16-year period (1998 to 2013) and the data were compared with the available CLSI breakpoints. Very major error and major error (ME) of FQs were not observed in the study isolates, but the minor error of ciprofloxacin (15.8 %) and ME of azithromycin (3.5 %) exceeded the acceptable limit. A positive correlation between MICs of FQ and mutations in the quinolone-resistance-determining region (QRDR) showed the reliability of MIC results to determine FQ susceptibility of Salmonella Typhi (n =74). Isolates showing decreased ciprofloxacin susceptibility (MIC 0.125-0.5 µg  ml-1) were likely to have at least one mutation in the QRDR region. The results on DD breakpoints of ofloxacin (resistant, ≤15 mm; intermediate, 16-24 mm, and susceptible, ≥25 mm) and levofloxacin (resistant, ≤18 mm; intermediate, 19-27 mm, and susceptible, ≥28 mm) corroborated those of earlier studies. In view of the emerging FQ- and azithromycin-resistant Salmonella Typhi isolates, DD and MIC breakpoints of those antimicrobials should be revisited routinely.

Typhoid fever

Control of typhoid fever relies on clinical information, diagnosis, and an understanding for the epidemiology of the disease. Despite the breadth of work done so far, much is not known about the biology of this human-adapted bacterial pathogen and the complexity of the disease in endemic areas, especially those in Africa. The main barriers to control are vaccines that are not immunogenic in very young children and the development of multidrug resistance, which threatens efficacy of antimicrobial chemotherapy. Clinicians, microbiologists, and epidemiologists worldwide need to be familiar with shifting trends in enteric fever. This knowledge is crucial, both to control the disease and to manage cases. Additionally, salmonella serovars that cause human infection can change over time and location. In areas of Asia, multidrug-resistant Salmonella enterica serovar Typhi (S Typhi) has been the main cause of enteric fever, but now S Typhi is being displaced by infections with drug-resistant S enterica serovar Paratyphi A. New conjugate vaccines are imminent and new treatments have been promised, but the engagement of local medical and public health institutions in endemic areas is needed to allow surveillance and to implement control measures.

Characterization of non-classical quinolone resistance in Salmonella enterica serovar Typhi: Report of a novel mutation in gyrB gene and diagnostic challenges

Objective

To establish the relative importance of Salmonella enterica serovar Typhi with non-classical quinolone resistance.

Methods

Eight hundred and ninety-one isolates of S. Typhi, isolated between 2004 and 2011, were tested for antibiotic susceptibility determination using disc diffusion and E-test. The mechanisms of fluoroquinolone resistance were studied in a sub-set of the NAL^S (nalidixic acid susceptible) isolates by wave nucleic acid fragment analysis of PCR products from gyrA, gyrB, parC and parE and from the plasmid borne determinants: qnrA,B,S; aac(6′)-Ib-cr and qepA. To assess genetic relatedness multi-locus variable number tandem repeat analysis was carried out using five loci.

Results

Eighty isolates with a nalidixic acid MIC of <32 mg/L (NAL^S) and a ciprofloxacin MIC of >0.064 mg/L CIP^I (ciprofloxacin reduced susceptibility) were found. In 36 NAL^S CIP^I isolates two distinct genotypes were identified when compared with 16 susceptible controls: Group B (n = 34), mutation in gyrB at codon 464, NAL MIC of 3–12 mg/L and CIP MIC of 0.064–0.5 mg/L.; and Group C, mutation in gyrA at codon 83 (n = 2) NAL MIC of 16 mg/L and CIP MIC of 0.25–0.38 mg/L. Group B isolates were found in different strain backgrounds as defined by MLVA.

Conclusion

The use of nalidixic acid to screen for reduced susceptibility to fluoroquinolones in S. Typhi misses CIP^I-NAL^S isolates, an established phenotype in India.

Lack of efflux mediated quinolone resistance in Salmonella enterica serovars Typhi and Paratyphi A

Salmonella enterica serovars Typhi and Paratyphi A isolates from human patients in France displaying different levels of resistance to quinolones or fluoroquinolones were studied for resistance mechanisms to these antimicrobial agents. All resistant isolates carried either single or multiple target gene mutations (i.e., in gyrA, gyrB, or parC) correlating with the resistance levels observed. Active efflux, through upregulation of multipartite efflux systems, has also been previously reported as contributing mechanism for other serovars. Therefore, we investigated also the occurrence of non-target gene mutations in regulatory regions affecting efflux pump expression. However, no mutation was detected in these regions in both Typhi and Paratyphi isolates of this study. Besides, no overexpression of the major efflux systems was observed for these isolates. Nevertheless, a large deletion of 2334 bp was identified in the acrS-acrE region of all S. Typhi strains but which did not affect the resistance phenotype. As being specific to S. Typhi, this deletion could be used for specific molecular detection purposes. In conclusion, the different levels of quinolone or FQ resistance in both S. Typhi and S. Paratyphi A seem to rely only on target modifications.

Intermediate susceptibility to ciprofloxacin among Salmonella enterica serovar Typhi isolates in Lima, Peru

Thirty-three Salmonella enterica serovar Typhi blood isolates from Lima, Peru (2008 to 2012), were fully susceptible to trimethoprim-sulfamethoxazole, chloramphenicol, ceftriaxone, and tetracycline; 8/33 (24.2%) showed intermediate susceptibility to ciprofloxacin carrying mutations in the quinolone resistance-determining region of the gyrA gene (Ser83-Phe and Asp87-Asn) and in the gyrB gene (Ser464-Phe).

In vitro susceptibility testing of fluoroquinolone activity against Salmonella: recent changes to CLSI standards

Fluoroquinolone (FQ) resistance in Salmonella enterica is a significant clinical concern. Recognition of resistance by the clinical laboratory is complicated by the multiple FQ resistance mechanisms found in Salmonella. The Clinical Laboratory Standards Institute (CLSI) recently addressed this issue by revising the ciprofloxacin break points for Salmonella species. It is critical for clinicians and laboratory workers to be aware of the multiple technical issues surrounding these revised break points. In this article, we review FQ resistance mechanisms in Salmonella, their clinical significance, and data supporting the revised ciprofloxacin break points. We encourage clinical laboratories to adopt the revised CLSI ciprofloxacin break points for all Salmonella isolates in which susceptibility testing is indicated and discuss the technical issues for laboratories using commercial antimicrobial susceptibility systems.