Caracterização de corinebactérias isoladas de infecções urinárias e investigação de mecanismos de virulência de Corynebacterium mycetoides

Abstract

Corynebacterium species have been increasingly related to cases of invasive infections, including immunocompromised individuals. However, this group of microorganisms remains frequently misidentified and/or dismissed as contaminants, partially due to the fact that many new taxa of coryneform bacteria have been described. Moreover, limited culture-based assays and identification methods typically utilized in microbiology laboratories contribute to this problem. Urinary tract infections (UTI) are considered the second most common bacterial infection. A wide range of factors may increase susceptibility to UTI, including age, gender and renal insufficiency. In the present study were described microbiological and epidemiological aspects of 69 strains of Corynebacterium spp. previously isolated from urine samples of UTI patients attended in a Brazilian university hospital. Additionally, we firstly verified the pathogenic potential to the human urinary tract of Corynebacterium mycetoides. Corinebacterial strains were identified by conventional phenotypic methods. Bacterial susceptibility to 14 antimicrobial agents was verified by the disk diffusion method. Results indicated that cases of ITU related to corynebacteria were mostly observed among outpatients (82.61%) attended in the kidney transplant (50.72%) and urology units (23.19%). Microorganisms were mostly observed among females (71.04%) and 41 to 60 year-old age group (55.07%). Corynebacterium spp., corresponding to >103 UFC/ml, were isolated from monomicrobial (41%) and polymicrobial (60%) infectious episodes, with coagulase-negative staphylococci (including 23.53% multidrug resistant - MDR strains) being isolated most frequently (41.46%). Classical phenotypic analyses identified Corynebacterium striatum/amycolatum/xerosis/minutissimum complex in most (n=40; 57.97%) opportunities, in addition to C. propinquun (n=02), C. afermentans (n=08), C. jeikeium (n=01), C. coyleae (n=01), C. glucuronolyticum (n=01), C. urealyticum (n=01), CDC Grupo G (n=01) and Corynebacterium sp. (n=14). Corynebacterial urine isolates were mostly identified as MDR. Due to variability of phenotypic profiles, a range of urine isolates were unable to be identified to species level, requiring more sophisticated techniques. The 2450 strain isolated from patient previously submitted to renal transplantation that presented atypical colony morphology (non-hemolytic, shiny and yellowish colonies), initially identified as Corynebacterium sp., was also analyzed by API Coryne, RapID CB and BBL Crystal, mass spectrometry and genotyping assays. MALDI-TOF and 16S rRNA and rpoB gene sequencing were effective in identifying it as C. mycetoides. Virulence potential of C. mycetoides was demonstrated by the expression of MDR profile, biofilm formation on catheters surfaces and cytotoxicity effects on Caenorhabditis elegans. C. mycetoides was also able to adhere to and survive within kidney epithelial (Vero) cells. In conclusion, varied corinebacterial species, including C. mycetoides should be included among uropathogens. Recent advances in molecular biology may facilitate the identification of new etiologic agents for UTI. The need for accurate and updated population surveillance data is apparent, particularly in light of concerns regarding antimicrobial resistance.