Frequency of Mutations in Quinolone Resistance-Determining Regions and Plasmid-Mediated Quinolone Resistance in Shigella Isolates Recovered from Pediatric Patients in Tehran, Iran: An Overlooked Problem

Dissemination of Multiple Drug-Resistant Shigella flexneri 2a Isolates Among Pediatric Outpatients in Urumqi, China

Multiple drug-resistant (MDR) Shigella isolates have been reported worldwide. Between May 2017 and September 2018, 55 Shigella flexneri 2a isolates were collected from 3322 stool samples of 0-10-year-old outpatients with diarrhea at the Children's Hospital of Urumqi, China. All isolates were characterized using serotyping, antimicrobial susceptibility testing, and whole-genome sequencing. A total of 54 of 55 (98.2%) isolates exhibited MDR phenotypes and had accumulated multiple resistance determinants, particularly of fluoroquinolones and cephalosporins preferred for shigellosis treatment: point mutations in quinolone resistance-determining regions (QRDRs) of topoisomerases (GyrA (S83L, D87N) and ParC (S80I) [n = 9]; GyrA (S83L) and ParC (S80I) [n = 45]) and acquisition of qnrS1 (n = 3) and bla_CTX-M (n = 8). Over 70% of isolates acquired two point mutations of GyrA (S83L) and ParC (S80I) in QRDRs and 11 highly resistant isolates accumulated three point mutations in QRDRs or acquired qnrS1. Four S. flexneri 2a isolates from three single-nucleotide polymorphism clusters exhibited coresistance to ciprofloxacin, cefotaxime, or azithromycin (AZM), which are used as first- and second-line shigellosis treatment antimicrobials in clinics. Our data indicated that fluoroquinolones should be terminated in shigellosis treatment for outpatients in Urumqi. The transferable antimicrobial resistance determinants have been identified for third-generation cephalosporins and AZM. Novel strategies are urgently required for developing empirical medication to reduce the antimicrobial selective pressure and prevent dissemination of MDR S. flexneri 2a isolates.

Shigella: Antibiotic-Resistance Mechanisms And New Horizons For Treatment

Shigella spp. are a common cause of diarrheal disease and have remained an important pathogen responsible for increased rates of morbidity and mortality caused by dysentery each year around the globe. Antibiotic treatment of Shigella infections plays an essential role in reducing prevalence and death rates of the disease. However, treatment of these infections remains a challenge, due to the global rise in broad-spectrum resistance to many antibiotics. Drug resistance in Shigella spp. can result from many mechanisms, such as decrease in cellular permeability, extrusion of drugs by active efflux pumps, and overexpression of drug-modifying and -inactivating enzymes or target modification by mutation. Therefore, there is an increasing need for identification and evolution of alternative therapeutic strategies presenting innovative avenues against Shigella infections, as well as paying further attention to this infection. The current review focuses on various antibiotic-resistance mechanisms of Shigella spp. with a particular emphasis on epidemiology and new mechanisms of resistance and their acquisition, and also discusses the status of novel strategies for treatment of Shigella infection and vaccine candidates currently under evaluation in preclinical or clinical phases.

Alternations in DNA gyrase genes in low-level fluoroquinolone-resistant Moraxella catarrhalis strains isolated in Poland

PURPOSE

The purpose of this study was to investigate the molecular mechanisms of fluoroquinolone resistance in Moraxella catarrhalis clinical strains isolated in Lublin, Poland.

MATERIALS AND METHODS

A total of 150 non-duplicate clinical strains of M. catarrhalis were obtained from individuals with signs of upper respiratory tract infection. Bacterial identification was corroborated on the basis of phenotypic and biochemical characteristics as well as with the use of molecular tests. The antimicrobial susceptibility of M. catarrhalis isolates was determined using the disk diffusion method and Etest. Mutations in the gyrase (gyrA and gyrB) and topoisomerase (parC and parE) genes were determined by polymerase chain reaction and sequencing.

RESULTS

It was observed that 16.7% of the studied isolates were drug resistant. Resistance to tetracycline was detected for 12% of the strains. Resistance to nalidixic acid, moxifloxacin, and levofloxacin was exhibited by 2.7% of the strains; 1.3% of the strains were resistant to trimethoprim/sulfamethoxazole and 0.7% to erythromycin. Minimum inhibitory concentration values of the four strains demonstrating fluoroquinolone resistance were: 6-12 mg/L for nalidixic acid, 1-1.5 mg/L for levofloxacin, 1 mg/L for moxifloxacin, and 0.25-0.5 mg/L for ciprofloxacin. The research resulted in the detection of mutations in 4 strains, in gyrase gyrA and gyrB genes. In gyrA gene, there occurred mutation G412C as well as four silent transition mutations. Within gyrB gene, there occurred mutation, substitution A1481G, as well as two identical silent mutations.

CONCLUSION

Our findings reveal that resistance to fluoroquinolones in M. catarrhalis is connected with amino acid substitutions in gyrA and gyrB genes. To our knowledge, this work is the first description of fluoroquinolone-resistant clinical strains of M. catarrhalis with described mutations in gyrA and gyrB genes isolated in Poland and in Europe.

Detection of Plasmid-Mediated qnr Genes Among the Clinical Quinolone-Resistant Escherichia coli Strains Isolated in Tehran, Iran

Background

Escherichia coli is one of the most important bacterial agents to cause urinary tract infections. Inappropriate and unnecessary administration of antibiotics has led to an increase in the appearance of multidrug-resistant E. coli isolates, limiting treatment options. The increase in a number of resistant strains of bacteria is a major concern of health authorities worldwide.

Objective

The purpose of this study was to determine the presence of the qnr genes among E. coli isolated from UTIs of patients in Baqiyatallah hospital in Tehran province, Iran.

Method

Clinical urine samples of patients with suspected urinary tract infection were collected by standard methods in sterile disposable containers. After analysis of urine, microscopic observations and culture analysis, the bacterial genome was extracted by boiling method. PCR for detection of qnr genes including qnrA, qnrB and qnrS was done by specific primers, then PCR products were run using gel electrophoresis and visualized by gel documentation system.

Results

In the present study among the 95 isolates, 60 strains were resistant to nalidixic acid. PCR showed that 92 strains were positive for qnrS. The qnrA and qnrB genes were not found among the clinical isolates.

Conclusion

Our finding indicates a high level of resistance against nalidixic acid among E. coli isolates recovered from the patients with UTI. Also, the high frequency of qnrS imposes the importance of survey of molecular and genetic analysis of mechanisms of quinolone resistance in E. coli strains.