Open Access Highly Accessed 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



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”.


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.


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.

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