Detection of Shigella gyrA mutations and correlations between gyrA mutations and quinolones resistance

118 clinical strains of Shigella were serotyped, in which 116 strains were tested to be S. flexneri. The susceptibilities of the S .flexneri strains to quinolones were measured by the disk-diffusion method. It was found that most S .flexneri strains were susceptible to norfloxacin and ciprofloxacin, but resistant to nalidixic acid. To study the correlation between gyrA mutations and quinolones resistance, a fragment within the gyrA gene was amplified by PCR. The SSCP （Single-Strand Conformation Polymorphism） analysis was applied to detect mutations in PCR products of different strains. The mutations were then confirmed by DNA sequencing. Altogether, two types of mutation were revealed, in which one type was single mutation （ C42-T）, and the other was double mutations （ C42-T and A54- G）. By statistical analysis, C42-T （encoding Ser83-keu substitution） was shown to have correlation with nalidixic-acid resistance in the clinical strains of Shigella, while A54-G （encoding Asp87-Gly substitution） was shown to have correlations with both norfloxacin resistance and ciprofloxacin resistance.

Molecular characterization of antimicrobial multi-drug resistance in non-typhoidal Salmonellae from chicken and clam in Mangalore, India

Salmonella enterica has been documented as one of the leading causes of salmonellosis throughout the world and is most commonly associated with the consumption of contaminated food products. Thus, this research was aimed at studying the antimicrobial susceptibility pattern and detection of quinolone resistance in Salmonella spp isolated from food of animal origin. Thirty-six Salmonella isolates comprising 8 from poultry and 28 from seafood（clams） were identified, serotyped and characterized for their antimicrobial susceptibility against 10 different antibiotics. Plasmid DNA was isolated from all the isolates by alkaline lysis, quinolone resistant non-typhoidal S. Weltevreden were examined for mutation in the DNA gyrase coding gene. Among the 36 Salmonella isolates, 20 were S. weltevreden（8 from poultry and 12 from seafood） and 16 were S. Typhimurium（from seafood）. All the isolates showed multiple resistance to nalidixic acid, tetracycline, co-trimoxazole and nitrofurantoin, but, interestingly, the isolates were 100% susceptible to ampicillin, chloramphenicol and gentamicin. Resistant isolates from the study carried the genes responsible for resistance to respective antibiotics. The strain S130 isolated in the study showed single point mutation,Asp87Gly, at position 87 in quinolone resistance determining region. It revealed mutation in quinolone resistance determining region as a cause for quinolone resistance in non-typhoidal Salmonellae. The occurrence of genes accountable for plasmid mediated resistance to quinolones（viz., qnrA, qnrB and qnrS） in plasmid of non-typhoidal Salmonellae isolates provides evidence for plasmid mediated quinolone resistance.

Emerging bedaquiline resistance:A threat to the global fight against drug-resistant tuberculosis

Bedaquiline resistance is increasingly observed in the treatment of rifampicin-resistant tuberculosis(TB),yet standardized regimens for managing bedaquiline-resistant TB are lacking.Studies indicate a high proportion of bedaquiline-resistant cases have previously been treated for TB,and often involve strains resistant to quinolones.Regular monitoring of the culture status in patients receiving bedaquiline resistance treatment is advised.Methods such as experimental evolution,protein modeling,genome sequencing,and phenotypic analysis have been instrumental in identifying the mechanisms of bedaquiline resistance.Specifically,variants in the Rv0678 transcriptional repressor of the MmpS5-MmpL5 efflux system are linked to this type of resistance.Bayesian probability estimates show promise in determining the genotypic–phenotypic association for bedaquiline resistance,suggesting potential utility in clinical practice.Future research should explore the practical application of Bayesian probabilities in managing bedaquiline resistance.Sequencing-based technologies are anticipated to play a vital role in the early detection and management of drug-resistant TB strains.

Genotypic Diversity and Characterization of Quinolone Resistant Determinants from Enterobacteriaceae in Yaoundé, Cameroon

Background: Enterobacteriaceae causes many types of infections which are often treated with quinolones and fluoroquinolone (Q/FQ). The resistance mechanisms to Q/FQ are usually associated with mutations in the quinolone resistance determining region which alter the conformation of target amino acid residues within the protein and in the qnr genes. This study aimed at determining the antimicrobial resistant profile of a sample of Enterobacteriaceae from Cameroon and the genetic diversity in quinolone-resistant isolates in view of implementing a better management, treatment, control and prevention of the transmission of these resistant strains. Methods: Identification and antimicrobial susceptibility testing was done using VITEK 2. The detection of plamid-mediated quinolone resistance (PMQR) genes was carried out using the conventional PCR method. Sequencing was done using the Applied Biosystem 3500 genetic analyser. DNA fingerprint was obtained using Pulsed-Field Gel electrophoresis. Results: Among 440 Enterobacteriaceae, the most prevalent genera were: Escherichia 178/440 (39.5%);Klebsiella 148/440 (33.6%);Enterobacter 35/440 (8%);Pantoea 28/440 (6.4%);Proteus 14/440 (3.2%) Salmonella 13/440 (3%). Ampicillin resistance showed the highest prevalence with 371/440 (81%) and Imipenem the lowest resistance 9/440 (2.1%). The ciprofloxacin resistance rate was 161/440 (36.6%). The detected plasmid mediated quinolone resistance (PMQR) genes were: qnrA, 2/161 (1.2%);qnrB, 31/161 (19.3%);qnrS, 13/161 (8.1%): Aac (6')Ib-cr, 84/161 (52.2%) and qepA, 3/161 (1.9%). There were several mutations in the parC gene of Klebsiella leading to S80D and S80N substitutions. Two pairs of Klebsiella peumoniae strains were phenotypically and genotypically identical with 100% similarity in the dendrogramme. Conclusion: This study showed that quinolone resistance was high. The PMQR genes contributing to this resistance were diverse. This high PMQR indicates that there has been an unknown circulation of these genes in our community. To avoid the rapid dissemination of these PMQR genes continuous surveillance of antimicrobial resistance should be carried out not only in humans but also in animals to monitor the evolution of these genes.

Intercontinental spread and clonal expansion of ColRNA1 plasmid-bearing Salmonella Corvallis ST1541 strains:a genomic epidemiological study

Salmonella Corvallis ST1541 has recently emerged as a globally disseminated pathogenic strain that often causes severe food-borne infections.Unlike most pandemic serotypes of Salmonella,the ST1541 strains harbored ColRNA1 plasmids that contain qnr-like determinants known to be responsible for the increasing incidence of ciprofloxacin-resistant food-borne Salmonella infections.In this study,we conducted a genomic analysis of a global collection of 388 S.Corvallis ST1541 strains collected within a twenty-year period.We investigated the genetic characteristics of plasmid-mediated quinolone resistance(PMQR)plasmids harbored by these S.Corvallis strains,established a mini-mum spanning tree(MST)to determine the temporal and spatial distribution of the top 10 MST clusters,inferred a time-phylogenies for the major sub-lineages and traced the routes of international dissemination of this serotype strains.Bayesian algorithm predicted that UK might be the origin of S.Corvallis strains currently prevalent in various countries.This idea is supported by the observation of the emergence of intercontinental-disseminated clonal strains and extensive transmission of the extensive-drug resistance(XDR)-encoding plasmid pSA663.This study there-fore provides valuable insight into the evolution of globally transmitted S.Corvallis strains and suggests a need to strengthen cooperation between different countries to control the dissemination of these drug-resistant bacteria.