Phenotypic identification and species characterization of clinically significant coagulase-negative staphylococci isolates at Bouaké University Hospital, Côte d’Ivoire

Background: Coagulase-negative staphylococci (CoNS) are now recognized as important agents of nosocomial infections, particularly in immunocompromised patients in the healthcare settings, due to their ability to form biofilms and their high resistance to methicillin. The aim of this study is to identify and characterize different species of CoNS isolated at the Bacteriology-Virology Laboratory of the Bouaké University Hospital, Côte d’Ivoire. Methodology: This was a laboratory-based study conducted at the Bacteriology-Virology Laboratory of the Bouaké University Hospital (CHUB) over a two-month period (November to December 2021). Coagulase negative staphylococci isolated from biological samples of hospitalized patients in the routine laboratory were first re-identified by Gram staining and conventional biochemical tests (catalase, coagulase) and further characterized into species using the API® Staph gallery (BioMérieux, France). Antibiotic susceptibility of the isolates was determined by the Kirby-Bauer disc diffusion method. Results: A total of 100 CoNS were isolated from samples received from various departments of the CHUB during the period of the study. The main CoNS species identified among these were Staphylococcus xylosus (n=30), Staphylococcus haemolyticus (n=20), Staphylococcus epidermidis (n=18), Staphylococcus lentus (n=12), Staphylococcus saprophyticus (n=7), Staphylococcus capitis (n=4), and Staphylococcus chromogenes (n=3). The proportion of CoNS isolates resistant to penicillin was 91.0%, tetracycline 72.0%, cotrimoxazole 67.0%, cefoxitin 65.0%, kanamycin 61.0%, tobramycin 54.0%, levofloxacin 53.0%, and gentamicin 50.0%. The most frequent species, S. haemolyticus (100%) and S. xylosus (60.0%) were resistant to methicillin. Kanamycin, tobramycin and gentamicin (KTG) aminoglycoside resistance phenotypes were seen in 95.0% of S. haemolyticus and 86.0% of S. saprophyticus isolates. The constitutive MLSB resistance phenotype was seen in 13.0% of S. xylosus and 11.0% of S. epidermidis. Conclusion: A variety of CoNS species were isolated in this study, with S. xylosus and S. haemolyticus being the most frequently identified species. Methicillin resistance rate was 100.0% for S. haemolyticus isolates which are likely involved in serious, potentially fatal nosocomial infections.