Amphixenosic aspects of Staphylococcus aureus infections in Man and Animals: veterinary and public health perspectives

From a veterinary and public health perspective, Staphylococcus aureus (SA) is a major concern. As opportunistic pathogen responsible for severe nosocomial and community-associated infections of humans, it is one of the most important pathogenic Staphylococcus species in veterinary medicine, especially where animal-derived food products intersect humans. According to the mode of transmission, SA infection between hosts is classified as “direct zoonoses”; actually, the correct definition of SA infections between humans and animals is “amphixenoses” or infections maintained in both man and lower vertebrate animals and transmitted in either direction. SA presents a high genetic plasticity. In the last years, in addition to the genetic lineages associated to the hospital or community in humans, other lineages have emerged in the animal–human interface. Moreover, SA can harbor a wide variety of resistance genes, at least 60 different resistance genes that confer resistance to virtually all classes of antimicrobial agents approved for use in humans and animals. Multidrug-resistant strains, in particular MRSA, have become established as a veterinary pathogens in pets and horses; in livestock, MRSA presents a concern for public health as a reservoir that can infect humans and as a source of transferrable resistance genes. In addition to, SA has been also recognized as intracellular pathogen and biofilm producer. This property potentially contributes to bacterial persistence, protection from antibiotics, and evasion of immune defenses. Based on this evidence, animal-adapted SA lineages exhibiting resistance to antibiotics must be considered a major threat to public health.