Mechanism of resistance and genetic relatedness among fluoroquinolone resistant Escherichia coli causing urinary tract infections.

INTRODUCTION : Resistance to antimicrobials among bacterial pathogens is a rapidly emerging global problem. Antimicrobial resistance (AMR) is not just a problem in the hospital setting but has already spread to the community. Multidrug resistance has become a reality in the management of many important infections. This limits the choice of therapy, increases mortality, morbidity and the cost. Although the exact magnitude of economic burden and social issues related to AMR are not known, especially from developing countries, it is also likely to be significant. Hence it becomes important to understand the issues related to emergence and spread of AMR in bacteria. Therefore it was considered important to understand the mechanisms of fluoroquinolone resistance and its association with resistance to other antimicrobials in current use. A study was therefore undertaken for this purpose and also to understand the clonal spread of fluoroquinolone resistant (FQR) E.coli in our hospital and in the community. AIMS AND OBJECTIVES: Aim: To describe possible mechanisms for fluoroquinolone résistance (FQR), to document The susceptibility patterns of FQR E.coli causing Urinary tract infections (UTI) and to Ascertain whether these organisms belong to a single clone. Objectives: 1) To determine the prevalence of efflux pump mediated FQR among E.coli causing UTI. 2) To determine the prevalence of high-level resistance to nalidixic acid among FQR E.coli as a phenotypic marker of gyr A mutations. 3) To type FQR E.coli using Random Amplified Polymorphic DNA pattern. 4) To determine the prevalence of resistance to other antimicrobials like aminoglycosides and cephalosporins among the FQR E.coli. 5) To determine the prevalence of extended spectrum beta lactamase (ESBL) production Among FQR E.coli. MATERIALS AND METHODS : E.coli isolated from routine urine cultures were further evaluated to understand more details about Fluoroquinolone resistance (FQR), like its association with other antimicrobial resistance (AMR) and the possible mechanisms involved in causing FQR. The clonal relatedness of the isolates were also studied. A sample size of 120 strains was chosen for RAPD typing, which included a minimum sample size of 30 strains in each category. A sample size of 30 would give us enough information to conclude whether the strains belonged to single or multiple clones. It would also enable us to obtain information on the predominant genotypes in the hospital setting and in the community. This method of an acceptable sample size in each category was followed since there was no data on the clonal characteristics of FQR E.coli from India. RESULTS : Three hundred and forty three strains of E.coli resistant to norfloxacin isolated from urine samples were used for the study. All the strains were resistant to nalidixic acid and all except two were resistant to ciprofloxacin. CONCLUSION : The study was done to determine the mechanisms of fluoroquinolone resistance (FQR) among the E.coli causing urinary tract infections (UTI), its association with other antimicrobial resistance and genetic relatedness among them. The summary of the findings are as follows, 1) Antimicrobial resistance was significantly more among FQR E.coli when compared to fluoroquinolone susceptible E.coli. 2) A significantly high number of FQR E.coli produced ESBL when compared to fluoroquinolone susceptible isolates. 3) Multidrug resistance i.e. resistance to three or more groups of antimicrobials was significantly high among FQR E.coli. This might limit the choice of therapy and lead to therapeutic failures in the management of important infections. Further studies are required to understand why FQR, which is chromosomally mediated is significantly associated with plasmid mediated resistance like ESBL production. 4) All the FQR E.coli had the phenotypic evidence of mutations in the genes encoding for the target enzymes like gyrA. Similar evidence was also found among 90% of fluoroquinolone susceptible E.coli, which were resistant to nalidixic acid. Limiting the use of fluoroquinolones in the treatment of infections caused by nalidixic resistant E.coli is necessary to prevent further evolution of resistant strains. 5) In addition to target alterations 40% of FQR E.coli had up-regulated efflux pumps contributing to resistance. 6) A significant number of the efflux positive isolates were multidrug resistant compared to efflux negative isolates. However 71% of efflux negative strains also exhibited MDR suggesting that factors other than efflux play a role in MDR. 7) Up regulated efflux was significantly associated with nitrofurantoin resistance and also with cephalosporin resistance when compared to efflux negative FQR E.coli