Antimicrobial Susceptibility and Characterization of Resistance Mechanisms ofCorynebacteriumurealyticumClinical Isolates

Corynebacterium urealyticumis a non-diphtherial urease-producing clinically relevant corynebacterial, most frequently involved in urinary tract infections. Most of theC. urealyticumclinical isolates are frequently resistant to several antibiotics. We investigated the susceptibility of 40C. urealyticumisolated in our institution during the period 2005-2017 to eight compounds representative of the main clinically relevant classes of antimicrobial agents. Antimicrobial susceptibility was determined by the Epsilometer test. Resistance genes were searched by PCR. All strains were susceptible to vancomycin whereas linezolid and rifampicin also showed good activity (MICs90= 1 and 0.4 mg/L, respectively). Almost all isolates (39/40, 97.5%) were multidrug resistant. The highest resistance rate was observed for ampicillin (100%), followed by erythromycin (95%) and levofloxacin (95%). Ampicillin resistance was associated with the presence of theblaAgene, encoding a class A beta-lactamase. The two rifampicin-resistant strains showed point mutations driving amino acid replacements in conserved residues of RNA polymerase subunit beta (RpoB). Tetracycline resistance was due to an efflux-mediated mechanism. Thirty-nine PFGE patterns were identified among the 40C. urealyticum, indicating that they were not clonally related, but producing sporadic infections. These findings raise the need of maintaining surveillance strategies among this multidrug resistant pathogen.