A study on Staphylococcus aureus strains submitted to a reference laboratory

Abstract

Background & objectives: Staphylococcus aureus is regarded as one of the most devastating human pathogens. Recently there have been reports of increasing incidence of S. aureus strains resistant to methicillin (MRSA). A surveillance study was undertaken to record the occurrence of MRSA and to study the prevalence of various phage groups in India.

Methods: A total of 7574 strains of S. aureus received during 1992-98 at the National Staphylococcal Phage Typing Centre, New Delhi were tested for methicillin resistance and susceptibility to phages of the International basic set. The occurrence of various phage groups between MRSA and MSSA (methicillin sensitive S. aureus) was compared. Results were analyzed according to the geographical origin and source of isolation of the strains.

Results: The dominant phage group from different parts of the country was phage group III. Prevalence of phage group III among the MRSA and MSSA isolates was 62.32 and 33.95 per cent respectively. The highest isolation of phage group III strains was from nasal carriers (45.94%), phage group II strains from skin (8.74%), phage group I strains from blood (19.44%) and nontypable strains from the environment (80.68%). An increase in the occurrence of MRSA has been noticed from 9.83 per cent in 1992 to 45.44 per cent in 1998.

Interpretation & conclusion: S. aureus strains of phage group III are prevalent in India. The increase in occurrence of MRSA indicates an alarming spread of these organisms. A constant monitoring is important to take appropriate and timely measures to control their spread.