Identification, research of antibiotic resistance pattern and biofilm formation of non-diphtheria coryneform bacteria isolated from clinical specimens

Bacteria belonging to the genus Corynebacterium are divided into two as Corynebacterium diphtheriae and non-diphtheric coryneform bacteria (NDC). Non- diphtheric coryneform bacteria (NDC), which were considered laboratory contaminants in previous years, have been shown in recent studies to be important causative agents of nosocomial infections and that these bacteria are resistant to many antimicrobial agents. The increasing incidence of NDCs in serious infections makes it necessary to recognize them as potential pathogens. In this study, it was aimed to determine the species level identification and antibiotic susceptibility tests, antibiotic resistance patterns, molecular epidemiology and biofilm formation of NDCs isolated from various clinical samples sent from clinical units to Pamukkale University Medical Faculty Research and Application Hospital Medical Microbiology Laboratory between December 2020 and January 2023. All isolates were identified to species level by MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization Time Of Flight Mass Spectrometry). 94,3% of the isolates were identified as C. striatum and 5,7% as C. afermentans. 15% of the isolates were isolated from blood, 5% from intra-catheter blood, 34,3% from wound, 32,9% from tracheal aspirate (TA), 7,9% from sputum, 2,9% from abscess material and 2,1% from pleural fluid samples. The most frequently isolated clinical sample was wound (34,3%), the second most frequently isolated clinical sample was tracheal aspirate (32,9%), while the least frequently isolated clinical sample was pleural fluid sample with 2,1%. Antimicrobial susceptibilities were determined by the Kirby-Bauer disk diffusion method and evaluated according to the criteria of EUCAST (The European Committee on Antimicrobial Susceptibility Testing) guidelines. All of the isolates were susceptible to vancomycin and linezolid, while all of them were resistant to ciprofloxacin. The isolates were resistant to penicillin (98,6%), clindamycin (96,4%), rifampicin and tetracycline (99,3%), gentamicin (88,6%) and erythromycin (75,7%), respectively. Drug-resistant genes were investigated by PCR (Polymerase Chain Reaction). The presence of bla gene was detected in 94,3% of the isolates, ampC gene in 95%, ermX gene in 95,7%, aac(3)-XI gene in 90%, aphA1 gene in 92,1%, gyrA gene in 97,9% and tetA gene in 32,9%. The ermB and tetB genes were not detected in any of the isolates. Gentamicin resistance rate was significantly higher in isolates with positive aac(3)-XI and aphA1 genes (p<0.05). Erythromycin and clindamycin resistance rates were significantly higher in ermX gene positive isolates (p<0.05). No significant difference was found between tetA gene positivity and tetracycline resistance rate in isolates (p>0.05). No significant difference was found between bla/ampC gene positivity and penicillin resistance rate (p>0.05). Biofilm formation of the isolates were detected semi-quantitatively by microtiter plate method. Biofilm formation was detected in 26,4% of the isolates. No statistically significant difference was found between Corynebacterium species and biofilm formation (p>0.05). The clonal relationship of 140 strains in the study were investigated by PFGE (Pulsed Field Gel Electrophoresis) method. XbaI digestion of the 140 Corynebacterium isolates revealed 46 distinct PFGE patterns. 13 of these patterns include only one strain. The remaining 33 patterns include cluster-forming strains, with cluster width ranging from 2-12. The clustering rate was found to be 90,7. The largest cluster is the cluster coded A, which includes 12 isolates.It is thought that the treatment strategy of nosocomial infections due to these microorganisms will be difficult because the isolates in our study have multidrug resistance and have high antimicrobial resistance rates. Therefore, it is important to carry out active surveillance studies considering that these microorganisms may be nosocomial infection agents.