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Open Access Research article

Prevalence of Staphylococcus aureus protein A (spa) mutants in the community and hospitals in Oxfordshire

Antonina A Votintseva1*, Rowena Fung13, Ruth R Miller14, Kyle Knox8, Heather Godwin27, David H Wyllie15, Rory Bowden6, Derrick W Crook12 and A Sarah Walker12

Author Affiliations

1 Nuffield Department of Clinical Medicine, University of Oxford, John Radcliffe Hospital, Level 7, Room 7724, Oxford OX3 9DU, United Kingdom

2 National Institute for Health Research (NIHR) Oxford Biomedical Research Centre, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom

3 Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom

4 School of Population and Public Health, University of British Columbia, British Columbia Centre for Disease Control, 655 West 12th Avenue, Vancouver, BC V5Z 4R4, Canada

5 The Jenner Institute, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, United Kingdom

6 Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, United Kingdom

7 Gasteroenterology Research Office, Great Ormond Street Hospital for Children NHS Foundation Trust, Great Ormond Street, London WC1N 3JH, United Kingdom

8 Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford OX1 2ET, United Kingdom

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BMC Microbiology 2014, 14:63  doi:10.1186/1471-2180-14-63

Published: 12 March 2014

Abstract

Background

Staphylococcal protein A (spa) is an important virulence factor which enables Staphylococcus aureus to evade host immune responses. Genotypes known as “spa-types”, based on highly variable Xr region sequences of the spa-gene, are frequently used to classify strains. A weakness of current spa-typing primers is that rearrangements in the IgG-binding region of the gene cause 1-2% of strains to be designated as “non-typeable”.

Results

We developed an improved primer which enabled sequencing of all strains, containing any type of genetic rearrangement, in a large study among community carriers and hospital inpatients in Oxfordshire, UK (6110 isolates). We identified eight novel spa-gene variants, plus one previously described. Three of these rearrangements would be designated “non-typeable” using current spa-typing methods; they occurred in 1.8% (72/3905) asymptomatically carried and 0.6% (14/2205) inpatient S. aureus strains. Some individuals were simultaneously colonized by both formerly non-typeable and typeable strains; previously such patients would have been identified as carrying only currently typeable strains, underestimating mixed carriage prevalence and diversity. Formerly non-typeable strains were found in more spa-types associated with multilocus sequence type ST398 (35%), common among livestock, compared to other groups with any non-typeable strains (1-4%), suggesting particular spa-types may have been under-represented in previous human studies.

Conclusions

This improved method allows us to spa-type previously non-typeable strains with rearrangements in the spa-gene and to resolve cases of mixed colonization with deletions in one or more strains, thus accounting for hidden diversity of S. aureus in both community and hospital environments.

Keywords:
Staphylococcus aureus; Spa-typing; Spa-gene; Deletions; Non-typeable isolates; Community and hospital strains