Antimicrobial resistance and extended spectrum beta-lactamases in urinary tract infections: A serious problem in Northern Mexico Resistencia antibiótica y agentes beta-lactamasa de espectro extendido en las infecciones del tracto urinario: un problema grave en el norte de México

Objective: To describe the causal agents, prevalence of antimicrobial resistance, and risk factors associated with extended spectrum beta-lactamase (ESBL)-producing agents in urinary tract infections (UTIs). Materials and methods: A retrospective study was conducted at a tertiary care hospital in Monterrey, Mexico. Inclusion criteria were patients that clinically presented with a UTI and had a positive urine culture, within the time frame of March to October 2017. The association with ESBL-producing agents was determined through the X2 test for categorical variables. Statistical significance was set at a p <0.05, utilizing SPSS version 20.0 software. Results: A total of 353 positive urine cultures were confirmed. ESBL production was found in 21.5% of the strains. There was a high level of resistance (>50%) to amoxicillin-clavulanate, ciprofloxacin, levofloxacin, fosfomycin, and trimethoprim-sulfamethoxazole and moderate resistance (10-50%) to gentamicin and ceftriaxone. Amikacin, ertapenem, nitrofurantoin, and colistin had the lowest resistance rates (<10%). The ESBL-producing agents were associated with complicated UTI (p≤0.0001). The comorbidities associated with ESBL-positive UTIs were diabetes mellitus (p=0.02) and immunodeficiency (p=0.008), as was having undergone radiotherapy (p=0.025) and previous antibiotic use (p≤0.001). Limitations: The clonal relationship of isolates, especially of E. coli, was not analyzed. We could not establish whether there was a high level of genetic diversity between the isolates or whether independent acquisition or cross-transmission occurred. Value: We evaluated the epidemiologic characteristics of the ESBL-producing agents in UTIs at a Mexican tertiary care hospital. Conclusions: One out of every five UTIs was caused by ESBLs in our study population. There was a high level of resistance to the antibiotics used as first-line empiric therapy in the patients studied.


Introduction
Urinary tract infections (UTIs) are among the most prevalent community-acquired and hospital-acquired infections. (1) An estimated 1 million cases of nosocomial UTIs occur in the United States annually, accounting for considerable morbidity and healthcare costs. (2) In

Materiales y métodos:
Realizamos una cohorte retrospectiva en un hospital de III Nivel en Monterrey, México. Se incluyeron pacientes con clínica de ITU de marzo a octubre del 2017 con urocultivo positivo. Se determinó la asociación con agentes productores de BLEE, utilizando la prueba Χ2 para variables categóricas y la prueba T para variables con-   (1,4) The most common agent causing UTIs is Escherichia coli (E. coli). (1,4) However, complicated UTIs are caused by a greater variety of agents with higher antibiotic resistance rates, and a higher frequency of failure to empiric treatment. (5,6) In recent years, increased drug resistance has been reported worldwide, including the emergence of extended spectrum β-lactamase (ESBL)-producing agents in Enterobacteriaceae, mainly E. coli and Klebsiella pneumoniae. (7,8) ESBLs confer resistance to penicillins, cephalosporins, and aztreonam. (9,10) Few studies have reported the risk factors associated with UTIs caused by ESBL-producing E. coli, such as diabetes, recurrent UTIs, urinary catheterization, genitourinary pathology, previous bacterial infection, intravenous antibiotic treatment, hospitalization, and previous antibiotic therapy. (11)(12)(13) The prevalence of ESBL-producing bacteria in UTIs is heterogeneous and dependent on geographic region. (14) Therefore, the aim of the present study was to determine the etiologic agents, antimicrobial resistance rates (including ESBL-producing bacteria), and risk factors associated with ESBL-positive UTIs at a tertiary care hospital in Northern Mexico.

Antimicrobial susceptibility and ESBL determination
Species identification of urine isolates was performed using MALDI-TOF mass spectrometry (Microflex, Bruker Daltonics). Drug resistance of E. coli isolates was determined by the microdilution plate method for all drugs except fosfomycin, which was established through the agar dilution method. The results were interpreted according to the Clinical and Laboratory Standards Institute (CLSI) criteria. (15) The antibiotics tested were amikacin, gentamicin, amoxicillin-clavulanic acid, aztreonam, ceftriaxone, ertapenem, ciprofloxacin, levofloxacin, nitrofurantoin, fosfomycin, trimethoprim-sulfamethoxazole, and colistin. Carbapenem-resistant isolates were screened to detect carbapenemase production using the CarbaNP test. (15) The production of ESBL in E. coli and Klebsiella spp. isolates was performed using the double-disc test, according to the CLSI. (15) Revista Mexicana de URología ISSN: 2007-4085, Vol. 80, núm. 2, marzo-abril 2020:pp. 1-12.

Statistical analysis
Categorical variables were expressed in frequencies and percentages. Numerical variables were expressed as a mean and standard deviation. Clinical and demographic characteristics were analyzed using the χ2 test for the categori-

Discussion
In the present study, we evaluated the epidemiologic characteristics of ESBL-producing agents in UTIs, acquired either in the hospital or the community, in patients at a tertiary care hospital. One-fifth of the UTIs were caused by ESBL-producing strains (21.5%), which is a higher incidence of ESBL-producing agents in UTIs, compared with the results of other published studies. (11,13,16,17) Nevertheless, previous studies in Mexico have reported alarmingly high incidences of UTIs caused by ESBL-producing E. coli in the community (56.5%) and in complicated infections (59.8%). (18,19) Infections caused by ESBL-producing bacteria were more frequent in the community than in our hospital setting (76.3% and 23.7%, respectively).
Even though low resistance rates of uropathogens to fosfomycin are still being reported worldwide, (25) decreasing susceptibility of ESBL-producing E. coli to fosfomycin has been described and limited data has been reported in Latin American countries. (26,27)  99.4%, and 92.2%, respectively). The use of those antibiotics is a good option for the empiric treatment of UTIs in the Mexican population. (24) Our study has several limitations. The clonal relationship of isolates, especially of E.
coli, was not analyzed. Therefore, we could not establish whether there was a high level of genetic diversity between the isolates or whether independent acquisition or cross-transmission occurred. Given the unusually high resistance to fosfomycin detected in the E. coli isolates, further analyses should be performed to characterize those strains and the mechanism of resistance, e.g. the search for fosfomycin-associated genes.

Conclusion
The emergence of ESBL-producing bacteria in UTIs is a serious health problem, in both our community and our hospital settings. Approximately one out of every five UTIs was caused by ESBLs in our study population. An alarmingly high resistance to antibiotics recommended as first-line empiric therapy in UTIs (fosfomycin, fluoroquinolones, and trimethoprim-sulfamethoxazole) was recognized. Consequently, international guidelines are not suitable for our population, limiting our therapeutic options.
The results of our study highlight the need for developing specific guidelines, based on our local susceptibility patterns in geographic regions where elevated antimicrobial resistance may influence therapeutic decisions.