The carriage population of Staphylococcus aureus from Mali is composed of a combination of pandemic clones and the divergent genotype ST 152

Abstract number: P648

Ruimy R., Maiga A., Arman-lefevre L., Maiga I., Diallo A., Koumare A., Koumare S., Wattara K., Andremont A., Feil E.J.

Objectives: To characterise a sample of Staphylococcus aureus isolates from asymptomatic carriage in Mali, Africa, and to compare the results to the known diversity of the carriage population in order to evaluate the role of microepidemic and pandemic clonal spread in shaping S. aureus population structure.

Methods: Nasal swab was performed in 448 patients admitted for emergency surgery to a single hospital point G in Bamako. S. aureus isolates were characterised by multilocus sequence typing and the results compared against the entire MLST data set and a previous study of carriage isolates from the UK. We used a combination of eBURST and phylogenetic approaches to analyse the data.

Results: Prevalence of nasal S. aureus carriage was 19.6% (n = 88). Carriers differed from non carriers for gender (51% vs 35%) and for mean age (41 vs 51.6) (p < 0.05) but not for chronic health status and previous hospitalisation. Only one isolate was meticillin resistant. Of the 87 meticillin susceptible isolate, 97% were resistant to penicillin, 6% to erythromycin and 74% to tetracycline. The 88 isolates characterised by MLST were found to correspond to 20 STs. Eighteen of these STs were present in the MLST database and two STs were new. No new alleles were detected. Seven of the 20 STs (ST5, ST8, ST15, ST30, ST88, ST152, ST291) were found in at least 4 strains, 4 of the STs (ST1, ST101, ST120, ST852) were found in 2 or 3 strains, and 9 of the STs corresponded to only a single isolate. We note the presence of many of the commonly recorded S. aureus clonal complexes in the Malian carriage population (CC15 (28%), CC8 (8%), CC5 (7%), CC30 (4.5%), CC88 (4.5%), CC45 (3%), CC121 (2%)) but also a high frequency (~24%) of the previously rare genotype ST 152.

Conclusion: Our results confirm the pandemic spread of many S. aureus clonal complexes, an observation which challenges purely neutral hypotheses regarding their origin and maintenance. In contrast, the high prevalence of ST 152 demonstrates that microepidemic transmission may also be important, and that much of the diversity of S. aureus population remains to be uncovered.