Distribution of Aminoglycoside Resistance Genes in Coagulase-Negative Staphylococci Isolated From Hospitalized Patients

Background: The incidence of coagulase-negative staphylococci (CNS) isolates, as causes of hospital-acquired infections, is increasing annually and it is a truly global challenge. Objectives: The current study aimed at assessing aminoglycoside resistance genes among CNS isolated from hospitalized patients and investigating the prevalence of methicillin and aminoglycoside resistance genes using molecular methods. Methods: A total of 103 species of coagulase negative staphylococci were isolated from clinical specimens from August 2013 to November 2014. All the specimens were identified using conventional microbiological methods including colony morphology, Gram staining, catalase, and slide and tube coagulase. The isolates were subjected to the API-20 Staph identification kit. Antibiotic susceptibility tests were performed using Kirby-Bauer disc diffusion method. The methicillin and aminoglycoside resistant genes among coagulase negative staphylococci were detected by polymerase chain reaction (PCR) and sequencing methods. Results: The most frequent clinically isolated coagulase negative staphylococci species were Staphylococcus hominis and S. haemolyticus (51.9%), S. epidermidis (21.7%), S. lugdunensis (9.8%), S. intermedius (4.9%), S. saprophyticus and S. simulans (3.9%), S. warneri (2.9%), as well as S. chromogenes, S. sciuri, S. caprae, S. schleiferi, and S. xylosus (0.98%). The overall rate of methicillin resistance among CNS species in the present study was 89 (86.4%). The resistance of CNS isolates against tested antibiotics was as follows: 74 (71.8%) to cefoxitin, 54 (52.4%) to kanamycin, 51 (49.5%) to gentamicin, 45 (43.7%) to tobramycin, and 30 (29.1%) to amikacin. The prevalence of aminoglycoside resistance genes such as ant (4’)-Ia, aac (6’)/aph (2") and aph (3’)-IIIa were 89 (86.4%), 87(84.5%), and 68(66%), respectively. Conclusions: The presence of antibiotic resistance among coagulase negative Staphylococcus species, which cause nosocomial infections, has increased. Therefore, identification of coagulase negative staphylococci within 24 hours after development of enzymatic tests would be very useful in any clinical microbiology laboratory for effective treatment. Resistance to antibiotics, including aminoglycosides, develops quickly in CNS species where these antimicrobial agents are widely used. Thus, a better understanding of antibiotic resistance of CNS species is essential to eliminate antibiotic resistance in hospitals and society.