In vitro Studies of Non-Diphtheriae Corynebacterium Isolates on Antimicrobial Susceptibilities, Drug Resistance Mechanisms, and Biofilm Formation Capabilities

OBJECTIVE: This study aimed to investigate the antimicrobial susceptibilities, drug resistance mechanisms, and biofilm formation capacities of non-diphtheriae Corynebacterium strains isolated from sterile midstream urine of hospitalized patients with clinical urinary tract infections (UTIs). METHODS: A total of 45 non-diphtheriae Corynebacterium isolates were recovered from sterile midstream urine. The available data of 45 patients were collected. Minimum inhibitory concentrations (MICs) of 10 commonly used antibiotics were determined. Meanwhile, the molecular resistance mechanisms of each agent were performed through PCR with specific primers. Moreover, the biofilm formation capability of each isolate on abiotic surfaces was detected with the MTT method. RESULTS: In this study, the most prevalent three species were C. striatum (15/45, 33.3%), C. glucuronolyticum (9/45, 20.0%) and C. urealyticum (8/45, 17.8%). These three species also accounted for most renal and ureteral calculi cases. Male patients older than 50 years, especially those with underlying diseases, were more susceptible to non-diphtheriae Corynebacterium infection. All the 45 isolates were 100% susceptible to vancomycin and linezolid, but highly resistant to macrolide–lincosamide–streptogramin B (MLSB), fluoroquinolones, tetracyclines and β-lactams with corresponding mechanisms. The detection rate of multidrug–resistant (MDR) non-diphtheriae Corynebacterium is 91.1%. All isolates are able to form biofilm on abiotic surfaces, except those of C. urealyticum, C. tuberculostearicum and C. jeikeium. Isolates of C. glucuronolyticum and C. Striatum possessed the strongest biofilm formation capacity. C. amycolatum could form biofilm, but varied greatly among different isolates. CONCLUSION: C. striatum, C. glucuronolyticum and C. urealyticum were the most prevalent species relevant to UTIs. The high occurrence of MDR isolates and high diversities in resistance profiles, and the distinctive abilities of biofilm formation highlighted the urgency for identification to species level. We should pay more attention to the drug resistance profiles of non-diphtheriae Corynebacterium, which would help improve empirical antibiotic therapy and reduce drug resistance transmission.