Molecular Investigations On A Chimeric Strain Ofstaphylococcus Aureussequence Type 80

A PVL-positive, methicillin-susceptibleStaphylococcus aureuswas cultured from pus from cervical lymphadenitis of a patient of East-African origin. Microarray hybridisation assigned the isolate to clonal complex (CC) 80 but revealed unusual features, including the presence of the ORF-CM14 enterotoxin homologue and of an ACME-III element as well as the absence ofetDandedinB. The isolate was subjected to both, Illumina and Nanopore sequencing allowing characterisation of deviating regions within the strain ' s genome. Atypical features of this strain were attributable to the presence of two genomic regions that originated from otherS.aureuslineages and that comprised, respectively, 3% and 1.4% of the genome. One deviating region extended fromwalJtosirB. It comprised ORF-CM14 and the ACME-III element. A homologous but larger fragment was also found in an atypicalS.aureusCC1/ST567 strain whose lineage might have served as donor of this genomic region. This region itself is a chimera comprising fragments from CC1 as well as fragments of unknown origin. The other deviating region comprised the region fromhtsBtoecfA2,i.e., another 3% of the genome. It was very similar to CC1 sequences. Either this suggests an incorporation of CC1 DNA into the study strain, or alternatively a recombination event affecting "canonical" CC80. Thus, the study strain bears witness of several recombination events affecting supposedly core genomic genes. Although the exact mechanism is not yet clear, such chimerism seems to be an additional pathway in the evolution ofS.aureus. This could facilitate also a transmission of virulence and resistance factors and therefore offer an additional evolutionary advantage.