SIRU typing of Staphylococcus aureus: the value of a new typing method

ITQB PhD Seminars

Title: Staphylococcal interspersed repeat unit (SIRU) typing of Staphylococcus aureus: the value of a new typing method

Speaker: Teresa Conceição

Laboratory: Molecular Genetics, ITQB

Abstract

Staphylococcus aureus is a gram positive bacterium and one of the major human pathogens associated with both hospital- and community-acquired infections. The effective control of S. aureus infections and clonal spread depends on accurate and precise typing of isolates that are critical for the establishment of outbreak control measures and surveillance programs. Although a large number of molecular typing methods have been described as valuable tools for the classification and discrimination of isolates, its validation and appropriate application must be ascertained.
The Staphylococcal Interspersed Repeated Units (SIRU) method is a multilocus variable-number of tandem repeats analysis (MLVA) based method developed for S. aureus in order to overcome some drawbacks of other widespread typing strategies. SIRU typing relies on the PCR amplification of seven loci of repetitive DNA, and further determination of the number of repeated units of the targeted SIRU. Each strain is characterized by a sequence of seven numbers corresponding to the number of repeats of each locus.
In the present work we evaluated SIRU typing in a very diverse collection of 104 S. aureus isolates previously characterized by well-established molecular methods, namely PFGE, MLST, spa typing and SCCmec typing. Performance and convenience criteria were evaluated. In addition, the quantitative level of congruence between the different methods was assessed by calculating the Adjusted Rand and Wallace coefficients.
The SIRU method showed a high discriminatory power (99.23%) which translated by the Simpson’s Index of Diversity, was similar to that of PFGE subtype (SID = 99.85%) and slightly higher than that of spa typing (SID = 97.61%). The congruence of the different methods showed that in the present collection, two strains with the same SIRU profile have 100% probability of belonging to the same clonal complex, 90% of sharing the same spa type, and 83% of being classified in a same sequence type.
As a PCR-based method, the SIRU method has proven to be relatively fast, accessible and not expensive, which combined to its high discriminatory power makes it useful and reliable in short-term epidemiological investigations of S. aureus. Moreover, its congruence with MLST results makes it also potentially valuable for evolutionary studies.

Short CV
Since January 2006 - PhD student at the Laboratory of Molecular Genetics, ITQB, under the supervision of Professor Hermínia de Lencastre and Marta Aires de Sousa, PhD.
September 2004-December 2005 – Research student at the Laboratory of Molecular Genetics, ITQB, under the supervision of Professor Hermínia de Lencastre and Marta Aires de Sousa, PhD.
1996-2002 – Degree (“Licenciatura”) in Biology and Microbial Genetics, Faculdade de Ciências da Universidade de Lisboa.