Nalidixic Acid Susceptibility Research Articles

Occurrence of Campylobacter spp. and Phenotypic Antimicrobial Resistance Profiles of Campylobacter jejuni in Slaughtered Broiler Chickens in North-Western Romania

Campylobacteriosis is recognized as one of the most common food-borne zoonoses, with worldwide distribution, having undercooked poultry meat and other cross-contaminated foodstuffs as the main sources of human infections. The current study aimed to provide data on the occurrence of the thermophilic Campylobacter spp. in seven broiler chicken flocks, from three north-western Transylvanian counties of Romania, as well as to determine the antimicrobial resistance profile of the isolated C. jejuni strains. A total of 324 fresh cecal samples were collected during the slaughtering process, and screened for the presence of Campylobacter spp., using routine microbiological and molecular diagnostic tools. Overall, 85.2% (276/324; 95% CI 80.9-88.6) of the tested samples expressed positive results for Campylobacter spp., with dominant occurrence of C. coli towards C. jejuni (63.4% vs. 36.6%). From the six tested antimicrobials, the 101 isolated C. jejuni strains were resistant against ciprofloxacin (79.2%), nalidixic acid (78.2%), tetracycline (49.5%), and streptomycin (7.9%), but total susceptibility was noticed against erythromycin and gentamicin. Seven (6.9%) isolates exhibited multidrug resistance. The study results emphasize the role of broiler chicken as reservoir of Campylobacter infections for humans, as well as strengthen the necessity of the prudent using of antimicrobials in the poultry industry.

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.

Antibiotic Susceptibility Pattern of Nalidixic Acid Resistant Salmonella Isolates in Shree Birendra Hospital Chhauni

Objectives: This study was aimed to know the prevalence of Nalidixic acid resistant Salmonella isolates and their antibiotic susceptibility pattern.Methods: A total of 4619 febrile patients suspecting the cases of typhoid fever by clinician, attending at Shree Birendra hospital during May- November 2013 were subjected to culture. Blood sample (5ml) was collected from the suspected cases and inoculated immediately into 45ml of Brain heart infusion broth (BHI) and further processed for the identification of Salmonella Typhi and S. Paratyphi. Antimicrobial susceptibility pattern of S. Typhi and S. Paratyphi isolates were determined by the modified Kirby-Bauer disc diffusion method.Results: Out of 4619 blood sample, 8.7% (n= 403) sample were culture positive. Among culture positive, 66.3%(n=267) cases were S. Typhi, 26.1% (n=105) cases were S. Paratyphi and 7.7% (n=31) were other than Salmonella isolates respectively. Out of 372 Salmonella isolates, most of the S. Typhi isolates i.e. 95.51%(n=255) and S. Paratyphi isolates i.e. 97.14%(n=102) are highly resistant to nalidixic acid. Most of these isolates were also found resistant to ciprofloxacin and ofloxacin.Conclusion: Therefore, screening of nalidixic acid susceptibility might be done prior to prescribe the drug for the treatment of enteric fever.

Nalidixic acid surrogate test for susceptibility to ciprofloxacin in Salmonella. Revisiting the question.

We investigated the reliability of nalidixic acid (NA) susceptibility as a marker of ciprofloxacin susceptibility in Salmonella, analysing 302 stool isolates. NC53 of the MicroScan system was used for NA susceptibility tests and the E-test was used for ciprofloxacin susceptibility tests. Among the isolates, 178 (58.9 %) were serogroup B, 74 (24.5 %) were serogroup D, 27 (8.9 %) were serogroup C and 23 (7.6 %) were from other minor serogroups. Globally, susceptibility to NA correctly predicted the susceptibility of Salmonella to ciprofloxacin, with a sensitivity of 81.5 %, a specificity of 97.6 %, and positive and negative predictive values of 88 and 96 %, respectively. However, there were differences among the serogroups in terms of sensitivity (P<0.001) and positive predictive values (P=0.013). NA is a reliable marker for serogroup D, but not for serogroups B or C. According to these findings, NA susceptibility measured with the MicroScan system can be used as a marker of ciprofloxacin resistance in some serogroups in our setting.

Relationship between the Susceptibility of Salmonella.Typhi to Ciprofloxacin, Ofloxacin and their respective Susceptibility To Nalidixic Acid

Background: Typhoid fever is an important cause of morbidity and mortality in many parts of the world including Pakistan. Resistance to the first line anti typhoid drugs viz chloramphenicol, cotrimoxazole and ampicillin has aggravated this situation. Quinolones are currently used as the first line antityphoid drugs, instead. Fluoroquinolones are currently recommended for patients infected with Typhi. The fluoroquinolones have shown good in vitro as well as clinical activity against Typhi infections.Materials and Methods: It was a comparative cross-sectional conducted at Department of Microbiology UHS, Lahore, Pakistan within one year (January 2011-December 2011). A total of 100 clinical isolates of Typhi were evaluated. ATCC 9150 Paratyphi A was used as a standarad strain. The bacterial isolates were preserved in microbanks (Pro-Lab Diagnostics, UK) and stored at-70˚C during a period of (2007- 2011). Data was analysed through SPSS version 22.Results: Of the 100 isolates, 45 strains were showing MIC ≤ 1µg/ml which means that they were susceptible while 55 strains were intermediate having MIC 2µg/ml. No strain was however, found resistant to ciprofloxacin according as per the CLSI 2011. As per the CLSI 2012 revised ciprofloxacin break points for disc diffusion and MIC for salmonella species. According to CLSI 2012 interpretive criteria, on disk diffusion testing 13 isolates were sensitive, 13 were resistant and 74 were intermediate to ciprofloxacin. On MIC, 55 strains were resistant showing MIC ≥1µg/ml and 45 isolates were intermediate showing MIC 0.125-0.5µg/ml. No isolate was found sensitive to ciprofloxacin according to CLSI 2012 interpretive criteria.Conclusion: In conclusion, the present study showed the value of nalidixic acid susceptibility as an indirect but a certain marker of ciprofloxacin susceptibility. Nalidixic acid resistant showed increased minimum inhibitory concentration (MIC) by agar dilution method.

High prevalence of fluoroquinolone resistance amongst commensal flora of antibiotic naïve neonates: a study from India.

The emergence of resistance amongst commensal flora is a serious threat to the community. However, there is paucity of data regarding antibiotic resistance in commensals in the absence of antibiotic pressure. Altogether, 100 vaginally delivered antibiotic naïve exclusively breastfed neonates were selected. Stool samples collected on day (D)1, D21 and D60 of birth were cultured. Enterobacteriaceae isolates were screened for nalidixic acid (NA) and ciprofloxacin susceptibility as per CLSI guidelines. In 28 randomly selected neonates, isolates (n=92) resistant to NA and ciprofloxacin were characterized for the presence of plasmid-mediated quinolone resistance (PMQR) genes (qnrA, qnrB and qnrS, qepAand aac(6')-Ib-cr) and mutations in the quinolone resistance determining region (QRDR) of gyrA and parC genes by specific primers and confirmed by sequencing. A total of 343 Enterobacteriaceae were isolated from 100 neonates. On D1, 58 % of neonates were colonized with at least one Enterobacteriaceae predominantly E. coli. Overall resistance to NA was 60 % but ciprofloxacin resistance increased significantly from 15 % (14/96) on D1 to 38 % (50/132) on D60 (P-value <0.001). The predominant mechanism of fluoroquinolone resistance was mutation in gyrA (n=49) with or without PMQR. PMQR carrying isolates increased more than fivefold from D1 to D60. A high level of fluoroquinolone resistance in gut flora of antibiotic naïve and exclusively breastfed neonates suggests a rampant rise of resistance in the community. The source of resistance genes on D1 is probably maternal flora acquired at birth. High load of PMQR genes in commensal flora are a potential source of spread to pathogenic organisms.

Characterisation of Antimicrobial Resistance in Salmonellae during 2014–2015 from Four Centres Across India: An ICMR Antimicrobial Resistance Surveillance Network Report

Purpose: The main purpose of this study was to establish ‘Antimicrobial Resistance Surveillance Network’ in India and to monitor the antimicrobial susceptibility profile of clinical isolates to establish a national network across the country for monitoring antimicrobial resistance in Salmonella. MaterialsandMethods: This study was conducted at All India Institute of Medical Sciences, nodal centre with clinical isolates of Salmonellae collected from four centres across India, which included Christian Medical College, Vellore; Postgraduate Institute of Medical Education and Research, Chandigarh and Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry. Total 20% of the selected strains from each centre were characterised for molecular studies which included molecular mechanism of fluoroquinolones resistance and multiple locus sequence type. Results: A total of 622 Salmonellae were received from all centres during January 2014 to December 2015. Out of these 622 isolates, 380 were Salmonella Typhi, 162 were Salmonella Paratyphi A and 7 were S. Paratyphi B isolated from blood and 73 were other Salmonella serotypes. Multiple drug resistance (resistant to ampicillin, chloramphenicol and co-trimoxazole) was less than 3% in S. Typhi. In S. Paratyphi A, chloramphenicol and co-trimoxazole susceptibility was 100% and 99%, respectively, whereas ampicillin susceptibility was 86% (139/161). Ciprofloxacin and nalidixic acid susceptibility was 15% (24/162) and 1% (2/162) from all centres. S. Paratyphi B was isolated from 7 patients. All isolates were third-generation cephalosporin sensitive. The most common mutations found were at codon 83 and at codon 87. We did not find any mutation in acrR gene. Efflux pump and qnr genes were not found in any isolate tested. All 86 S. Typhi isolates clustered into two sequence types - ST1 and ST2. Out of these 86 isolates, 70 S. Typhi were ST1 and 16 were ST2. All S. Paratyphi A was clustered in ST85 and ST129 on the basis of mutation in sucA gene. Out of 27 S. Paratyphi A, 13 were grouped into ST85 and 14 were grouped into ST129. Conclusions: Enteric fever is one such infection which poses challenges in antimicrobial resistance. Hence, continuous surveillance is important to track bacterial resistance and to treat infections in a cost-effective manner.

Identification of a Plasmid-Mediated Quinolone Resistance Gene in Salmonella Isolates from Texas Dairy Farm Environmental Samples.

A recent increase in plasmid-mediated quinolone resistance (PMQR) has been detected among Salmonella isolated from humans in the United States, and it is necessary to determine the sources of human infection. We had previously isolated Salmonella from dairy farm environmental samples collected in Texas, and isolates were tested for anti-microbial susceptibility. Two isolates, serotyped as Salmonella Muenster, showed the discordant pattern of nalidixic acid susceptibility and intermediate susceptibility to ciprofloxacin. For this project, whole-genome sequencing of both isolates was performed to detect genes associated with quinolone resistance. The plasmid-mediated qnrB19 gene and IncR plasmid type were identified in both isolates. To our knowledge, this is the first report of PMQR in Salmonella isolated from food animals or agricultural environments in the United States.

Six-year susceptibility trends and effect of revised Clinical Laboratory Standards Institute breakpoints on ciprofloxacin susceptibility reporting in typhoidal Salmonellae in a tertiary care paediatric hospital in Northern India

The antimicrobial trends over 6 years were studied, and the effect of revised Clinical Laboratory Standards Institute (CLSI) breakpoints (2012) for ciprofloxacin susceptibility reporting in typhoidal Salmonellae was determined. A total of 874 (95.4%) isolates were nalidixic acid-resistant (NAR). Using the CLSI 2011 guidelines (M100-S21), 585 (66.9%) isolates were ciprofloxacin susceptible. The susceptibility reduced to 11 (1.25%) isolates when interpreted using 2012 guidelines (M100-S22). Among the forty nalidixic acid susceptible (NAS) Salmonellae, susceptibility to ciprofloxacin decreased from 37 isolates (M100-S21) to 12 isolates (M100-S22). The 25 cases which appeared resistant with newer guidelines had a minimum inhibitory concentration (MIC) range between 0.125 and 0.5 μg/ml. MIC50 for the third generation cephalosporins varied between 0.125 and 0.5 μg/ml over 6 years whereas MIC90 varied with a broader range of 0.19–1 μg/ml. The gap between NAR and ciprofloxacin-resistant strains identified using 2011 guidelines has been reduced; however, it remains to be seen whether additional NAS, ciprofloxacin-resistant isolates are truly resistant to ciprofloxacin by other mechanisms of resistance.

Nalidixic Acid Susceptibility Test for Screening Salmonella Isolates of Reduced Susceptibility/Higher Minimum Inhibitory Concentration to Ciprofloxacin

Enteric fever is the major diagnosis among febrile patients in Nepal with yearly increase in nalidixic acid resistance and reduced ciprofloxacin susceptibility among Salmonella isolates. This study was carried out to evaluate the validity of nalidixic acid resistance as an indicator of reduced susceptibility of Salmonella isolates to ciprofloxacin. In this study, 999 blood specimens collected from suspected enteric fever patients visiting B&amp;B Hospital were processed by standard microbiological techniques. Isolates were identified by biochemical tests and serotyping. Antibiotic susceptibility test was performed by Kirby Bauer disc diffusion method and CLSI recommended interpretive criteria. MIC of ciprofloxacin was determined by agar dilution method. Isolation rate of Salmonella species was 6.21%. Among 62 Salmonella isolates, 51 were S. typhi, 10 were S. paratyphi A and one isolate was S. paratyphi B. Only one isolate of S. typhi was multi-drug resistant. Resistance to ceftriaxone, cefixime and azithromycin was nil. On disc diffusion test, 55 isolates were resistant to nalidixic acid. Fifty-seven isolates were found to have increased (&gt;0.125mg/ml) MIC of ciprofloxacin with the clinical and laboratory standards institute breakpoints. Nalidixic acid resistance showed a predictive value of 100% for ciprofloxacin resistance. Screening with nalidixic acid disc had a sensitivity of 100% and a specificity of 71.43% for the determination of decreased ciprofloxacin susceptibility. Before using ciprofloxacin for the treatment of enteric fever, appropriate identification of Salmonella isolates with reduced ciprofloxacin susceptibility is essential to limit the possible treatment failure and further development of highly resistant strains.DOI: http://dx.doi.org/njst.v15i2.12122Nepal Journal of Science and Technology Vol. 15, No.2 (2014) 97-104

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

ObjectiveTo establish the relative importance of Salmonella enterica serovar Typhi with non-classical quinolone resistance. MethodsEight 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 NALS (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. ResultsEighty isolates with a nalidixic acid MIC of <32mg/L (NALS) and a ciprofloxacin MIC of >0.064mg/L CIPI (ciprofloxacin reduced susceptibility) were found. In 36 NALS CIPI 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 3–12mg/L and CIP MIC of 0.064–0.5mg/L.; and Group C, mutation in gyrA at codon 83 (n=2) NAL MIC of 16mg/L and CIP MIC of 0.25–0.38mg/L. Group B isolates were found in different strain backgrounds as defined by MLVA. ConclusionThe use of nalidixic acid to screen for reduced susceptibility to fluoroquinolones in S. Typhi misses CIPI-NALS isolates, an established phenotype in India.

English

CONTEXT: Enteric fever prevails to be a considerable health issue worldwide. Ciprofloxacin became the mainstay of its therapy after multidrug resistant salmonellae emerged. Treatment failure was soon recorded with ciprofloxacin, the index being in-vitro resistance to nalidixic acid. Chloramphenicol sensitive strains have resurfaced. Resistance to alternatives- macrolides is cropping up though not documented widely. These variations in addition to the fact that India is witnessing escalating resistance to antibiotics, stress the significance of continual surveillance of salmonellae resistance. INTENT: The study undertaken intends to document the current deviations in the antibiogram of the Salmonella isolates from blood culture, with a perspective of evaluating ciprofloxacin susceptibility and macrolide resistance, further considering, if there is a need to modify the antibiotic strategies for this condition. METHODOLOGY: The isolates from blood cultures from January 2012 to September 2013 obtained using commercial BACTEC 9120 system, sub-cultured and processed for determining salmonellae serotypes were further subjected to drug susceptibility testing for patterning their resistance. MICs to ciprofloxacin of nalidixic acid resistant (NAR) isolates were recognized. RESULTS: Salmonella was isolated from 114 out of 8210 blood culture specimens received. There were 74 Salmonella Typhi isolates, 39 Salmonella Paratyphi A and 1 Salmonella Paratyphi B. Highest resistance of salmonellae (85.96%) was exhibited to nalidixic acid and highest susceptibility (100%) to ceftriaxone. Decreased ciprofloxacin susceptibility-DCS (MIC of 0.125-1μg/ml) was noticed in around 90% of NAR salmonellae. Isolates demonstrated sizable resistance (42.10%) to azithromycin. Only three strains were multidrug resistant. INTERPRETATION AND CONCLUSION: Routine screening of nalidixic acid sensitivity should be encouraged as a means to predict decreased fluoroquinolone susceptibility, thereby preventing therapeutic failure. In order to avert the profound impact of antimicrobial resistance and to define the best possible therapy, periodic monitoring of Salmonella antibiogram is of prime value. The upsurge of occurrence of ciprofloxacin resistance, impending resistance to macrolide- azithromycin, re-emergence of chloramphenicol sensitive strains is of particular concern and necessitates a change towards 'evidence-based' treatment and rationalization of existing empirical therapy of enteric fever shifting the vital focus towards antibiotic recycling.

Antibiogram of Salmonella Isolates from Blood with an Emphasis on Nalidixic Acid and Chloramphenicol Susceptibility in a Tertiary Care Hospital in Coastal Karnataka: A Prospective Study

Background:Enteric fever is caused by the serotypes Salmonella Typhi, Salmonella Paratyphi A, Salmonella Paratyphi B and Salmonella Paratyphi C. After emergence of multidrug resistant Salmonellae Ciprofloxacin, a fluorquinolone antibiotic was the first-line therapy. Treatment failure was observed with Ciprofloxacin soon and such strains showed in-vitro resistance to Nalidixic acid. Recent reports suggest re-emergence of Chloramphenicol sensitive strains and increasing Nalidixic acid resistance. This study is aimed at detecting the current trend in the antibiogram of Salmonella isolates from blood culture in coastal Karnataka, with an emphasis on antibiotic susceptibility of Nalidixic acid and Chloramphenicol and evaluate, if there is a need to modify the strategies in the antibiotic therapy for enteric fever.Materials and Methods:Blood samples received for culture in the laboratory between June 2009 and August 2011 was cultured in Brain Heart infusion broth, bile broth or in a commercial BACTEC culture media. The growth from blood cultures were processed for identification and antibiotic susceptibility as per standard methods. Antibiotic susceptibility for Ampicillin, Trimethoprim-sulphamethoxazole, Chloramphenicol, Ciprofloxacin, Ceftriaxone and Nalidixic acid were noted.Results:Out of 9053 blood culture specimens received, Salmonella was isolated from 103 specimens. There were 85 Salmonella Typhi isolates, 16 Salmonella Paratyphi A and two Salmonella Paratyphi B. Salmonella Typhi and Salmonella Paratyphi A showed the highest resistance to Nalidixic acid. Salmonella Typhi showed highest susceptibility to Ceftriaxone and Salmonella Paratyphi A to trimethoprim-sulphamethoxazole and Chloramphenicol. Two isolates were multidrug resistant. One Salmonella Paratyphi A was resistant to Ceftriaxone.Conclusion:Routine screening of Nalidixic acid susceptibility is practical to predict fluorquinolone resistance in Salmonella and preventing therapeutic failure while treating with it. It is worthwhile to consider replacing fluorquinolones with Chloramphenicol or Ceftriaxone as the first line of therapy for enteric fever. Periodic analysis of Salmonella antibiogram should be done to formulate the best possible treatment strategies.

Clonal expansion and genetic diversity of nalidixic acid-resistant Salmonella enterica serotype Paratyphi A

The aim of this study was to understand the clonal expansion and genetic diversity of nalidixic acid -resistant (NAR) Salmonella enterica serotype Paratyphi A (SPA) from Yuxi city, China. Antimicrobial susceptibility testing was performed with 3980 SPA isolates from Yuxi city of China between 1999 and 2007. The incidence of resistance to nalidixic acid (NA) of 1999 and 2000 were 25.0 and 82.2%, respectively. More than 95.0% of the isolates obtained from 2001 to 2007 were resistant to NA. Amplification by PCR and sequencing of the genes within the quinolone resistance-determining region with subsets of 15 NAR strains revealed that the mechanisms of NA resistance resulted from single point mutations in the gyrA gene leading to the Ser83Phe substitution. Subtyping of 120 NAR isolates from seven counties and one Nalidixic acid-susceptible (NAS) isolate were studied using pulsed-field gel electrophoresis (PFGE) analysis, followed by digestion of chromosomal DNA with restriction endonucleases SpeI and XbaI. PFGE patterns were analyzed by cluster analysis. SpeI and XbaI digestion of 121 isolates generated five and four different PFGE patterns with predominance of the SpeI01 and SpeI02 (or the XbaI01) epidemic patterns, respectively. The incidence of resistance to NA of the isolates increased during the study period. NAS isolates predominated in 1999 but was replaced by NAR isolates after 2000. PFGE patterns SpeI01 and SpeI02 (or XbaI01), the main clones of the epidemics, are highly prevalent in Yuxi. Key words: Paratyphoid fever, Salmonella enterica serotype Paratyphi, antimicrobial susceptibility, resistance to nalidixic acid, PFGE, clonal expansion.

Clonal expansion and genetic diversity of nalidixic acid-resistant Salmonella enterica serotype Paratyphi A

The aim of this study was to understand the clonal expansion and genetic diversity of nalidixic acid -resistant (NAR) Salmonella enterica serotype Paratyphi A (SPA) from Yuxi city, China. Antimicrobial susceptibility testing was performed with 3980 SPA isolates from Yuxi city of China between 1999 and 2007. The incidence of resistance to nalidixic acid (NA) of 1999 and 2000 were 25.0 and 82.2%, respectively. More than 95.0% of the isolates obtained from 2001 to 2007 were resistant to NA. Amplification by PCR and sequencing of the genes within the quinolone resistance-determining region with subsets of 15 NAR strains revealed that the mechanisms of NA resistance resulted from single point mutations in the gyrA gene leading to the Ser83Phe substitution. Subtyping of 120 NAR isolates from seven counties and one Nalidixic acid-susceptible (NAS) isolate were studied using pulsed-field gel electrophoresis (PFGE) analysis, followed by digestion of chromosomal DNA with restriction endonucleases SpeI and XbaI. PFGE patterns were analyzed by cluster analysis. SpeI and XbaI digestion of 121 isolates generated five and four different PFGE patterns with predominance of the SpeI01 and SpeI02 (or the XbaI01) epidemic patterns, respectively. The incidence of resistance to NA of the isolates increased during the study period. NAS isolates predominated in 1999 but was replaced by NAR isolates after 2000. PFGE patterns SpeI01 and SpeI02 (or XbaI01), the main clones of the epidemics, are highly prevalent in Yuxi. Key words: Paratyphoid fever, Salmonella enterica serotype Paratyphi, antimicrobial susceptibility, resistance to nalidixic acid, PFGE, clonal expansion.

Salmonella isolates’ serotypes and susceptibility to commonly used drugs at a tertiary care hospital in Riyadh, Saudi Arabia

Resistance of Salmonella to therapeutic agents currently being used for treatment of Salmonella infections is emerging as a global problem. This study aimed to assess the prevalence of Salmonella serotypes and their susceptibility patterns to commonly used drugs for treatment of Salmonella infections including quinolones. Correlation between nalidixic acid susceptibility of these isolates and their ciprofloxacin minimum inhibitory concentrations was also sought. Salmonella isolates (n=213) were collected between January 2007 and May 2009 at King Khalid University Hospital in Riyadh, Saudi Arabia. The isolates were serotyped and their susceptibilities to commonly used first-line anti-Salmonella drugs (ampicillin, ceftriaxone, trimethoprim/sulfamethoxazole, nalidixic acid and ciprofloxacin) were determined using the automated Microscan system, the Kirby-Bauer disk diffusion method, and E-test. The most frequently detected serotype was D1 (37%) followed by the serotypes, B (24%) and C1 (11%). Non-typable Salmonella isolates detected using available conventional Salmonella anti-sera were (11%). Overall resistance rates to nalidixic acid, ampicillin, trimethoprim/sulfamethoxazole and ceftriaxone were 99/213 (46%), 43/213 (20%), 34/213 (16%) and 7/213 (3%), respectively. Of the total isolates, 117 (55%) had a ciprofloxacin MIC of <0.125 µg/ml and among these 105 (90%) were susceptible to nalidixic acid. The remaining 96 (45%) isolates had a ciprofloxacin MIC of ≥ 0.125 µg/ml and among them, 83 (86.5%) were resistant to nalidixic acid. The majority of Salmonella isolates in this study were non-typhi serotypes. Significantly higher proportions of Salmonellae were resistant to nalidixic acid and ciprofloxacin and a vast majority of nalidixic acid resistant organisms exhibited decreased susceptibility to ciprofloxacin.

Nalidixic Acid Resistance and Clonal Expansion of &lt;i&gt;Salmonella enterica &lt;/i&gt;Serotype Paratyphi a Isolates in Yuxi City, China

The aim of our study was to understand the nalidixic acid resistance and clonal expansion of Salmonella enterica serotype Paratyphi A (SPA) recovered from patients with paratyphoid fever A in Yuxi City from 1999 to 2008. A typing method is needed to determine the epidemic clones of the isolates. Antimicrobial susceptibility testing was performed with 4 060 SPA isolates. 186 isolates were typed by pulsed-field gel electrophoresis (PFGE) with SpeI, and the MICs for nalidixic acid, ciprofloxacin, levofloxacin, ofloxacin, norfloxacin, and gatifloxacin were determined. The incidence of resistance to nalidixic acid of the isolates increased from 12.5% in 1999, 82.2% in 2000, 93.0% in 2001, to100% in 2008. Nalidixic acid-susceptible (NAS) isolates predominated in 1999 but was replaced by nalidixic acid-resistant (NAR) isolates after 2000. The frequencies of intermediary and susceptibility (Kirby-Bauer disc diffusion technique) to ciprofloxacin were 17.0% and 83.0% before 2005, 65.3% and 34.7% in 2008, respectively. A group of 166 NAR and 20 NAS isolates of SPA were randomly selected. SpeI digestion of 186 isolates gave nine different PFGE patterns with predominance of the SpeI01 and SpeI02 epidemic patterns. All NAR isolates studied had a reduced susceptibility to fluoroquinolone, the MICs were higher than that for 20 NAS isolates.We validate the use of the nalidixic acid screening test in the detection of decreased fluoroquinolone susceptibility in SPA. PFGE patterns SpeI01 and SpeI02, the main clones of the epidemics, are highly prevalent and NAR isolates in Yuxi. Recommendation for the emergency treatments of outbreaks and epidemics caused by a fully fluoroquinolone-resistant strain can be made. PFGE with SpeI is a useful technique to differentiate SPA.

Salmonella enterica serovar Typhi de sensibilité diminuée à la ciprofloxacine

The use of fluoroquinolone (FQ) as first line therapy for typhoid fever should be reconsidered because of the emergence of Salmonella Typhi and Paratyphi A strains with decreased susceptibility to FQ, mainly from Asia. Relapse can occur when ciprofloxacin MIC is over 0.12 mg/l, as illustrated by our case report. Azithromycin can be used successfully for patients infected with reduced ciprofloxacin susceptibility isolates. Literature review led us to suggest a new therapeutic strategy for uncomplicated typhoid fever, the antibiotic was chosen according to nalidixic acid susceptibility and ciprofloxacin MIC of the strain. High-dose intravenous ceftriaxone (4 g per day) is always efficient in first line therapy. Depending on FQ susceptibility testing results, it is relayed by oral therapy with a FQ (ciprofloxacin 500 mg bid for 7 days) if the isolate has maintained susceptibility, or azithromycin (1 g first day and 500 mg per day, 7 days) if the isolate is resistant to nalidixic acid or has a ciprofloxacin MIC superior to 0.12 mg/l.

An imported enteric fever caused by a quinolone-resistantSalmonella typhi

Recent reports indicate that nalidixic acid susceptibility correlates well with the clinical outcome of patients with Salmonella Typhi infection treated with quinolones. We report a case of enteric fever caused by S Typhi in which the isolate was resistant to nalidixic acid, but showed in vitro susceptibility to ciprofloxacin. Following treatment with ciprofloxacin, the clinical outcome was not satisfactory and the patient had a relapse. However, after using a higher dose of ciprofloxacin, the patient was cured. We recommend that all Salmonella systemic infections resistant to nalidixic acid with in vitro but decreased susceptibility to fluoroquinolones be treated with other antibiotics like third-generation cephalosporins or azithromycin. These patients should be closely followed up and observed for further relapse.

High Level of Resistance to nalidixic acid in Salmonella enterica serovar Typhi in Central India

Fluoroquinolones are the drugs of choice for the treatment of typhoid fever. But the recent increase in minimum inhibitory concentration (MIC) values of ciprofloxacin in Salmonella Typhi may result in delayed response and serious complications. Nalidixic acid resistance has been used as an indirect evidence of increased minimum inhibitory concentration for ciprofloxacin in Salmonella Typhi. We evaluated the isolates received at the National Salmonella and Escherichia Centre for nalidixic acid and ciprofloxacin susceptibility using standard methods. Minimum inhibitory concentrations have also been evaluated. Ninety-six percent of the isolates were found to be nalidixic acid resistant while all isolates were found to be ciprofloxacin sensitive. The difference between minimum inhibitory concentration values of ciprofloxacin for nalidixic acid resistant and nalidixic acid sensitive isolates was found to be statistically significant. The study may be helpful in revising treatment strategies for the infections caused by nalidixic acid resistant Salmonella Typhi in the country.