Biochemical characterization and antibiotic susceptibility of coagulase negative staphylococci isolates from exudates and body fluids

Nagaraju Vanaparthi, Ravishankar reddy Anukolu, Saileela K, Praful S Patil, Vijay Kumar A.N.


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 & Objectives : 1. Isolation of CoNS  from exudates and body fluids. 2. Biochemical  characterization of CoNS  3. Antibiotic susceptibility pattern of CoNS. Method: 180 CoNS isolated from various exudates and body fluids such as Pus, Wound Swabs, Endotrachial Secretions, Sputum, Branchial Aspitate, 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, 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-proskauer test, Mannose fermentation, Trehalose fermentationand Antibiotic susceptibility testing.Result: Out of 180 isolates, 78 are S.epidermidis (43.3%), 63 are S.hemolyticus (35%), 21 are S.hominis (11.6%), 18 are S.lugdunensis (10.0%). Maximum number of CoNS were isolated from pus specimens (58.33%), followed by wound swabs (18.33%). 164 out of 180 strains were negative for both bound and free coagulase. 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 ten 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.

Keywords: Coagulase negative staphylococci,  Antibiotic susceptibility, Clinical isolates of Exudates and body fluids, Biochemical Chemical characterization

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