Urinary Tract Physiological Conditions Promote Ciprofloxacin Resistance in Low-Level-Quinolone-Resistant Escherichia coli

Abstract

Escherichia coli isolates carrying chromosomally encoded low-level-quinolone-resistant (LLQR) determinants are frequently found in urinary tract infections (UTIs). LLQR mutations are considered the first step in the evolutionary pathway producing high-level fluoroquinolone resistance. Therefore, their evolution and dissemination might influence the outcome of fluoroquinolone treatments of UTI. Previous studies support the notion that low urine pH decreases susceptibility to ciprofloxacin (CIP) in E. coli. However, the effect of the urinary tract physiological parameters on the activity of ciprofloxacin against LLQR E. coli strains has received little attention. We have studied the activity of ciprofloxacin under physiological urinary tract conditions against a set of well-characterized isogenic E. coli derivatives carrying the most prevalent chromosomal mutations (⌬marR, gyrA-S83L, gyrA-D87N, and parC-S80R and some combinations). The results presented here demonstrate that all the LLQR strains studied became resistant to ciprofloxacin (according to CLSI guidelines) under physiological conditions whereas the control strain lacking LLQR mutations did not. Moreover, the survival of some LLQR E. coli variants increased up to 100-fold after challenge with a high concentration of ciprofloxacin under UTI conditions compared to the results seen with Mueller-Hinton broth. These selective conditions could explain the high prevalence of LLQR mutations in E. coli. Furthermore, our data strongly suggest that recommended methods for MIC determination produce poor estimations of CIP activity against LLQR E. coli in UTIs.C iprofloxacin (CIP) is one of the agents commonly utilized for treatment of urinary tract infections (UTIs) (1-3). It is used as an appropriate therapy in patients with UTI not requiring hospitalization in areas where the prevalence of resistance is under 10%. In addition, it is considered an effective treatment in the prevention of UTI in kidney transplant recipients (4, 5). However, during recent years a clear increase in resistance to fluoroquinolones (FQ) has been described worldwide (6, 7).The predominant causative agent of community-acquired UTI, Escherichia coli, acquires resistance mainly through chromosomal mutations in the genes encoding subunits of the DNA gyrase (gyrA and gyrB genes) and topoisomerase IV (parC and parE genes) or in regulatory genes affecting permeability or efflux (8). Some of these mutations lead to generation of low-level-quinolone-resistant (LLQR) E. coli mutants, with a CIP MIC that is higher than the epidemiological cutoff value but still below the resistance breakpoint for most FQs. A high (from 17% to 39%, depending on the study) prevalence of LLQR E. coli in UTIs has been previously described (8,9). However, the causes of this prevalence are unclear, as the high CIP levels found in the bladder after treatment should be sufficient to eradicate any susceptible bacteria.It has been stated that small increases in MIC values produced by LLQR mutations have a profound impact on t...

Plasmidic qnr Genes Confer Clinical Resistance to Ciprofloxacin under Urinary Tract Physiological Conditions

“…These results demonstrate that urinary tract physiological conditions considerably affect the susceptibility of the isogenic and clinical Qnr strains, making all of them resistant to CIP in urine at pH 5. It should be noted here that the urine of more than 60% of the UTI patients had a pH of Յ6 (12). With the aim of testing how survival of Qnr strains under CIP treatment could be affected by urinary tract physiological conditions, we also determined the survival rates of isogenic strains in the presence of the maximum concentration of CIP attained in the bladder (ϳ1,000 g/ml) during the first 6 h of treatment, according to previous pharmacokinetic and pharmacodynamic (PK/PD) studies (26).…”

“…Therefore, low-level quinolone-resistant Escherichia coli mutants have been traditionally considered to be susceptible according to standard susceptibility testing. However, we recently found that growth under physiological urinary tract conditions (i.e., growth in urine, at low pH values, and under anaerobiosis) conferred clinical levels of resistance to the fluoroquinolone ciprofloxacin (CIP) (12). This situation may provide a selective scenario for the evolution of high-level quinolone resistance and could lead to therapeutic failure in patients with urinary tract infection (UTI).…”

“…To reproduce UTI physiological conditions (urine, different pH values, and anaerobiosis), MICs in urine were also determined at pH values of 5, 6, and 7, and plates were incubated under aerobic conditions and under anaerobic conditions. Urine was obtained as previously described (12). MICs of CIP were determined in triplicate for each strain.…”

Genome-wide screening and characterization of genes involved in response to high dose of ciprofloxacin in Escherichia coli

“…The increasing ability of cipro oxacin-resistance or tolerance may lead to high clinical failure rate of bacterial infections and increasing prevalence of infections by antibiotic-resistant bacteria [4,5]. The canonical mechanisms of cipro oxacin-resistance include genetic mutations of gyrA and parC or horizontal dissemination of antibiotic resistance genes which protects or modi es the targets the uoroquinolone [6].…”

Comparación entre ciprofloxacina y antibióticos de otros grupos farmacológicos para el tratamiento de infecciones del tracto urinario

“…En el caso de la Escherichia coli, en la que se ha encontrado una mutación cromosómica denominada "low-level quinolone resistant (LLQR), es considerada el primer paso en la evolución a la alta resistencia a este tipo de fármaco. 7 Ahora bien, debe entenderse que el antibiótico no induce la resistencia, solamente la selecciona a través del proceso de selección natural, por lo que sobrevivirán aquellas variantes capaces de resistir las concentraciones del fármaco. 8 Debido a las ventajas que ofrecen las quinolonas, son las más elegidas para su uso clínico y; no obstante, debe evitarse el abuso o uso incorrecto de este medicamento ya que el uso irracional de antibióticos puede desembocar en la aparición de cepas resistentes con el riesgo sanitario de agotar las opciones para tratar las infecciones.…”