Human Colonization and Infection by Staphylococcus pseudintermedius: An Emerging and Underestimated Zoonotic Pathogen

Abstract

S. pseudintermedius is a known resident of the skin and mucous membranes and a constituent of the normal microbiota of dogs. It has also been recognized as an opportunistic and zoonotic pathogen that is able to colonize humans and cause severe diseases, especially in immunocompromised hosts. Most importantly, methicillin-resistant S. pseudintermedius (MRSP), which is intrinsically multidrug-resistant, has emerged with serious public health consequences. The epidemiological situation is further exacerbated with reports of its zoonotic transmission and human infections which have been mostly attributed to the increasing frequency of dog ownership and close contact between dogs and humans. Evidence on the zoonotic transmission of MRSP from pet dogs to humans (such as dog owners, small-animal veterinarians, and other people in close proximity to dogs) is limited, especially due to the misidentification of S. pseudintermedius as S. aureus. Despite this fact, reports on the increasing emergence and spread of MRSP in humans have been increasing steadily over the years since its first documented report in 2006 in Belgium. The emergence of MRSP strains has further compromised treatment outcomes in both veterinary and human medicine as these strains are resistant to beta-lactam antimicrobials usually prescribed as first line treatment. Frustratingly, the limited awareness and surveillance of the zoonotic transmission of S. pseudintermedius have underestimated their extent of transmission, prevalence, epidemiology, and public health significance. In order to fill this gap of information, this review focused on detailed reports on zoonotic transmission, human colonization, and infections by S. pseudintermedius, their pathogenic features, antimicrobial resistance profiles, epidemiology, risk factors, and treatment. In writing this review, we searched Web of Science, PubMed, and SCOPUS databases using the keyword "Staphylococcus pseudintermedius AND humans". A phylogenetic tree to determine the genetic relatedness/diversity of publicly available genomes of S. pseudintermedius was also constructed.

Keywords: human infections; multidrug resistance; staphylococci; zoonotic transmission.

Figure 1

Colony morphology of S. pseudintermedius and its differentiation from S. aureus. (a) Creamy grey-to-white colonies of S. pseudintermedius on Columbia sheep blood agar. (b) S. aureus growth on Columbia sheep blood agar. (c) Mixed culture of Staphylococci on CHROMagar Staph aureus^TM (Oxoid, UK). Tiny blue colonies are S. pseudintermedius, while pink to mauve colonies are S. aureus.

Figure 1

Colony morphology of S. pseudintermedius and its differentiation from S. aureus. (a) Creamy grey-to-white colonies of S. pseudintermedius on Columbia sheep blood agar. (b) S. aureus growth on Columbia sheep blood agar. (c) Mixed culture of Staphylococci on CHROMagar Staph aureus^TM (Oxoid, UK). Tiny blue colonies are S. pseudintermedius, while pink to mauve colonies are S. aureus.

Figure 2

Strains of 147 S. pseudintermedius isolated from humans and animals worldwide. Reference genomes, S. pseudintermedius SP_11304_3A and S. aureus NCTC 8325, were also included. The color of the strain’s name represents the hosts, the color of the nodes indicates the country of isolation, and the node shape indicates the year of isolation. Estimated confidence is shown on each internal branch of the tree. * is just a form of emphasis on Node shape based on years. It was not used to represent the collection year type.

Figure 3

World map showing countries with S. pseudintermedius reports, their MLSTs, and hosts. The information included in the map was based on selected criteria of the phylogenetic tree. Countries with S. pseudintermedius reports are shown in blue. : human, : horse, : cat, and : dog.