Diversity of accessory genome of human and livestock-associated ST398 methicillin resistant Staphylococcus aureus strains

Background: Molecular typing of methicillin-resistant Staphylococcus aureus (MRSA) has documented the diversity of the genetic background of strains associated with healthcare (HA-MRSA), community (CA-MRSA) and livestock (LA-MRSA). The accessory and core-variable genomes of those strains however remain largely unknown. Objective: To compare the genetic background and accessory and core variable gene content of ST398 LA-MRSA strains with those of HA-and CA-MRSA strains from the same region. Methods: Representative strains of HA- (n= 21), CA- (n= 13) and ST398 LA-MRSA (n= 18) were selected from Belgian National Reference Laboratory collections. The accessory and core-variable genomes of these strains were characterized by a DNA-microarray composed of oligonucleotide probes targeting ∼400 resistance, adhesion and virulence associated genes. Results: ST398 strains displayed very homogenous hybridization profiles irrespective of their host origin. This ST398 genomic profile was moderately related to that of certain human HA- or CA-lineages but distinctively lacked several virulence- and colonization-associated genes implicated in carriage in humans, such as proteases and adhesins. No enterotoxin gene was found among ST398 strains. Differences were observed in the mobile resistance gene content of ST398 strains, including antibiotic resistance determinants. Conclusion: LA-MRSA strains represent a homogenous lineage distinct from co-local HA- and CA-MRSA strains, especially in its accessory genome content characterized by a lack of human-associated virulence and adhesion determinants. The absence of detectable enterotoxin gene among ST398 LA-MRSA strains from a wide host range is reassuring regarding their foodborne pathogenic potential. © 2010 Elsevier B.V.