Biochemical Characterization and Antibiotic Susceptibility of Coagulase Negative Staphylococci Isolates from Exudates and Body Fluids

ABSTRACT

Coagulase negative Staphylococci (CoNS) are increasingly being recognized as significant nosocomial pathogens, partly due to the growing appreciation of this group of organisms as opportunistic pathogens or due to increase in the use of transient or permanent medical devices in seriously ill and immunocompromised patients. Aims and Objectives 1) Isolation of CoNS from exudates and body fluids. 2) Biochemical characterization of CoNS. 3) Antibiotic susceptibility pattern of CoNS. Method 180CoNS isolated from various exudates and body fluids such as pus, wound swabs, endotracheal secretions, sputum, branchialaspitate, and central lining tube were collected. All the CoNS isolates were processed in the Microbiology Laboratory and identified by colony morphology, gram staining, catalase, slide, tube coagulase test, anaerobic acid from mannitol, and deoxyribonuclease. Bacitracin (0.04 U) and furazolidone (100 μg) susceptibilities were done to exclude Micrococcus and Stomatococcus spp. The following biochemical tests were done for the speciation of the CoNS urease test, phosphatase test, polymyxin B disc test, novobiocin disk test, ornithine decorboxylase test, mannitol to acid, Voges-Proskauertest, mannose fermentation, trehalose fermentation and antibiotic susceptibility testing. Result Out of 180 isolates, 78 are Staphylococcus epidermidis (43.3%), 63 are Staphylococcus hemolyticus (35%), 21 are Staphylococcus hominis (11.6%), and 18 are Staphylococcus lugdunensis (10.0%). Maximum number of CoNS were isolated from pus specimens (58.33%), followed by wound swabs (18.33%). A total of 164out of 180 strains were negative for both bound and free coagulase. A total of 60 strains were bound coagulase slow positive and free coagulase negative. S. epidermidis was the most frequent isolate and 68 S. epidermidis isolates were identified if ornithine decorboxylase was considered positive, while negative 10 S. epidermidis isolates required inclusion of trehalose and mannitol for speciation. Antibiotic susceptibility testing showed maximum resistance to penicillin (78.3) followed by chloramphenicol (41.6%). No resistance to vancomycin was seen. Conclusion: The study revealed S. epidermidis is the predominant CoNS from endotracheal secretions and also pus samples. S. hemolyticus was isolated from pus and central lining tubes, S. hominis and S. lugdunensis were isolated mainly from wound swabs. The present study suggests if coagulase-ve Staphylococci are repeatedly isolated from patients with infection they should be taken seriously and ABST done on these isolates for proper diagnosis and treatment especially in nosocomial infections.