Uropatogena Escherichia coli : povezanost otpornosti na kinolone s prisutnošću činitelja virulencije

Urinary tract infecions are among most frequent human infections and Escherichia coli is their main cause. Uncontrolled use of quinolones leads to resistance to this group of antibiotic. Quinolone-resistance mechanisms include modification of drug target molecule, increased activity of the eflux pump and changing of cell membrane permeability due to decreased activity of porins. Aim of this study was to get an insight of characteristics of quinolone-resistant E. coli, taking into cosnsideration the molecular mechanisms of resistance, presence of virulence factors and resistance to other antibiotics, as well as to a determine difference in characteristics of strains that are quinolone-susceptible. Another aim was to determine how much the laboratory-induced quinolone-resistance in previously susceptible strains was changing the other strain characteristics. During one year period all quinolone-resistant E. coli strains were isolated from urine samples obtained from out-patients with symptoms of urinary tract infections in the Split and Dalmatia County. Control group was formed by taking the next isolated quinolone-susceptible strain of E. coli for each quinolone-resistant strain. In the group where the strains of quinolone resistant E. coli were isolated, there wasa higher percentageof males than in control group, but this difference was not significant. It was observed that resistance rate of E. coli to ciprofloxacin increases with age of patients and resistant strains were more frequently isolated in elder patients. Strains resistant to quinolones show higher resistance to other antibiotics. Among the quinolone-resistant strains the resistance rate to amoxicillin was 96.55%, to cotrimoxazole 67.82%, and to gentamicin 29.89%, in contrast to sensitive strains where the resistance rate to amoxicillin was 54.02%, to cotrimoxazole 28.74% and to gentamicin 24.14%. Virulence factors were found significantly less frequently in quinolone-resistant strains (fim gene in 21.84%, pap gene in 20.69%, cnf1 gene in 1.15% and hemolysis in 2.30%) than in quinolone-sensitive strains (fim gene in 90,80%, pap gene in 50.57%, cnf1 gene in 12.64% and hemolysis in 52.87%). Among quinolone-resistant E. coli isolates, there were no strains with plasmid quinolone-resistance genes (qnrA, qnrB and qnrS). Mutations in the gyrA gene at positions 83 and 87 were present in 90.80% strains of quinolones resistant E. coli. Sequencing of gyrA gen in quinolones resistant E. coli strains showed that the most common mutation were at position 83 (serine → leucine) and at position 87 (aspartic acid → asparagine). In one tested strain extremely rare mutation at position 106 (glycine → arginine) was detected, which has long been thought to be formed only after the induction of quinolone-resistance in experimental conditions. Induction of quinolone-resistance was successful in two E. coli strains. After the induction, strains kept the secretion of hemolysin. In one strain, the fim gene remained present after induction, while in the other its expression was reduced. The strains have no pap and cnf1 genes neither before nor after the induction of quinolone-resistance. Strains with induced resistance to quinolones have gained increased resistance to third generation cephalosporins ceftazidime, cefotaxime and ceftriaxone, as well as to gentamicin, while one strain acquired resistance to cefipime. Both strains with induced quinolone-resistance have gained two points mutation in the gyrA gene (replacement of serine at position 83 with leucine and replacement of aspartic acid at position 87 with asparagine)