Abstract
Urinary tract infections (UTIs) are some of the most common infections affecting humans worldwide. Occurrence of atypical, lactose non-fermenting, biochemically “inactive” strains of E. coli in clinical material has been described in the literature, which may cause a significant diagnostic challenge. The present retrospective microbiological study was carried out using isolates and data collected between January 1, 2013, and December 31, 2017, at the Institute of Clinical Microbiology. n = 24,285 positive urine samples were noted during the study period, out of which, samples positive for either lac + and lac- E. coli were included in the analysis. E. coli represented n = 7075 (55.8% ± 4.6%) of outpatient and n = 4916 (42.4% ± 3.6%) of inpatient isolates. n = 401 (3.3%; 80.2 ± 14.6/year) lac- E. coli isolates were identified from urinary tract infections. The ratio of lac- E. coli isolates was significantly higher in outpatient samples (262 vs. 139). Resistance levels of lac- isolates for antibiotics commonly used for treating UTIs were significantly higher for both inpatient and outpatient isolates: norfloxacin, ciprofloxacin, fosfomycin and nitrofurantoin. It is essential to pay attention to the presence of lac- strains, and their omission from clinical material during diagnostic procedures may have significant consequences for epidemiological studies and therapy.
Highlights
Urinary tract infections (UTIs) are some of the most common infections affecting humans worldwide; based on their prevalence, they are the third most common infectious pathologies (Flores-Mireles et al 2015; Behzadi and Behzadi 2016)
E. coli is a commensal microorganism abundantly found in the gastrointestinal tract; if these bacteria breach into other anatomical regions, they act as opportunistic pathogens, owing to the plethora of virulence factors they possess (Gajdács et al 2019d; Behzadi 2019; Hozzari et al 2020; Jahandeh et al 2015)
The pathogenic role of E. coli was noted by several reports from international organizations: The World Health Organization has designated it to the priority-pathogen list, while the Infectious Disease Society of America (IDSA) included it among the “ESKAPE” pathogens, pertaining to bacteria causing the highest levels of morbidity and mortality worldwide (Rajendran et al 2019; Gajdács 2019)
Summary
Urinary tract infections (UTIs) are some of the most common infections affecting humans worldwide; based on their prevalence, they are the third most common (following respiratory tract infections and gastrointestinal infections) infectious pathologies (Flores-Mireles et al 2015; Behzadi and Behzadi 2016). The occurrence of atypical, lactose non-fermenting (due to deficiency in the levels of lactose permease, encoded by lacY gene), often non-motile, biochemically “inactive” strains of E. coli in clinical material has been described in the literature, predominantly in the context of diarrheal (shigellosis-like) illnesses (Nicoletti et al 1988; Rychert and Stephenson 1986; Bajpai et al 2016) These non-fermenting atypical variants (lac-) may cause a significant diagnostic challenge; in addition, the few reports available on the prevalence of these isolates have highlighted the potential of these strains to harbor various virulence- and antibiotic-resistance determinants, clinically differentiating them from lac + strains (Chang et al 2014). An Australian study by Platell et al highlighted that the lac- O75 clonal group of E. coli (a serotype that has been frequently associated with causing bacteremia and UTIs) had extensive levels of fluoroquinolone resistance (Platell et al 2012)
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