Naturally agr-negative livestock-associated MRSA exhibits high adhesive capacity to human and porcine cells

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) of CC398 have emerged as important colonizers of livestock, can cause human infections and evolve rapidly. A recent study reporting a new dominant spa type among MRSA from Finish fattening pigs (CC398/t2741) identified a strain lacking the global virulence regulator gene agr and the adhesion gene fnbB. The aim of this study was to characterize the phenotype of this agr/fnbB-negative livestock-associated MRSA and to provide data on its genetic background. Thus, growth curves, hemolysis patterns, adhesion assays on human keratinocyte and porcine nasal mucosa cell lines and whole genome sequencing were performed. The agr-negative strain adhered significantly better to human and porcine host cells than two agr-positive control pig strains (1. CC398/t274; same herd / 2. CC398/t034; another herd). For the agr-positive porcine MRSA strains, cytotoxic effects on porcine mucosal cells were observed. The strong adhesive capacity of the naturally agr-negative MRSA in combination with diminished cytotoxic effects is likely favorable for inducing persistent colonization in pigs. Independent of the host cell type, similar adhesive capacities of the naturally agr-negative porcine MRSA and the human MRSA (an isogenic Δagr knockout mutant strain) were shown. These results indicate that loss of agr in the livestock-associated MRSA strain investigated in this study may have increased its potential to be transmitted to and amongst humans.