Comparison of expression of virulence genes among invasive and colonizing methicillin-resistant Staphylococcus aureus clinical isolates

Abstract number: P1975

Abu Othman A., O'Neill E., Humphreys H., Hughes D.

Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) can mediate infection by the expression of a wide array of virulence factors, encoded by various virulence genes to facilitate invasion and tissue damage. Some virulence markers have been reported to be associated more with invasive MRSA isolates than with colonising isolates. We compared the expression of virulence genes among 20 colonising and 20 invasive (bloodstream) isolates of MRSA.

Methods: The invasive and colonizing (e.g. nasal carriage) isolates were collected in Beaumont Hospital, Dublin, Ireland between 2001–2006. We determined the expression levels of the virulence genes hlg, cna, sea and the accessory gene regulator agr, in isolates grown in the presence of human serum (to mimic the in vivo environment) using reverse transcriptase real-time PCR (RT-PCR).

Results: There was considerable variation in the expression of virulence genes among both groups of isolates. Transcription of hlg was up-regulated greater than 2 fold in 60% of invasive isolates compared to 35% of colonizing isolates (P value = 0.0193), cna transcription was up-regulated in 63% of invasive isolates compared to 100% of colonizing isolates (P value = 0.0110). Sea transcription was down-regulated in 100% of invasive isolates and 85% of colonizing isolates (P value = 0.0074). Transcription of RNAIII, the effecter gene of the agr regulation system was up-regulated greater than 2 fold in 40% of invasive isolates and 25% of colonizing isolates but this was not statistically significant. The transcription of RNAIII was not accompanied by a reduction in transcription of cna or increased transcription of hlg and sea.

Conclusions: The pattern of expression of specific virulence associated genes in invasive versus colonising isolates differs, which may contribute to the pathogenicity of MRSA. However, some virulence genes are preferentially up-regulated in colonizing isolates suggesting that colonising isolates have the capacity to promote host damage in certain settings. Therefore bacterial virulence is only one factor in invasive infection and other factors, e.g. the host immune response also contribute to infection.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
Back to top