Isolation and characterization of coagulase–negative Staphylococci from clinical specimens in Lagos, Nigeria

Abstract

Coagulase negative staphylococci (CoNS) live naturally on the skin and mucous membranes of humans.  In many cases these are picked up from the skin during specimen collection and are not involved in any disease process, while in some cases they have been shown to cause infection.  The purpose of this study was to determine the occurrence and possible involvement of CoNS in infections from various clinical specimens in Lagos and characterize the CoNS isolates obtained using both conventional biochemical methods and API staph-Ident Systems (ID32 STAPH).  A total of 745 gram-positive catalase positive clustering cocci were obtained over 18-month period from Microbiology laboratories of Lagos University Teaching Hospital (LUTH) and General Hospital Ikeja (GHI) Lagos.  A total of 244 isolates of CoNS were obtained of which 241 isolates were characterized to species level, while 3 were unclassified Staphylococcus epidermidis was the most commonly isolated species from all the specimens.  It accounted for (44.7%) of all the CoNS isolates.  Other CoNS were identified as follows: S. saprophyticus (14.8%), S. capitis (11.1%), S. haemolyticus (9.8%), S simulans (9.8%) S. warneri (2.9%), S. xylosus (2.4%), S. hominis (2.1%) S. lugdunensis (0.8%) and S. cohnii (0.4%). Comparing the conventional methods with the rapid commercial API kit (ID 32 STAPH), there was 98.8% specificity for the kit and 95.9% specificity for the former while there was no significant difference at p=1.  From this study, strains of coagulase-negative staphylococci have been associated with a number of human infections in the environment and as such are no longer to be regarded as commensals or contaminants.