Bacteria are grossly categorized into gram positive and gram negative based on certain cellular characteristics. A common commensal of the gram positive group is the Staphylococcus genus. Present in all bodily systems, predominantly the skin, these are part of the normal flora of living beings. Staphylococcus pseudintermedius (SP) is one such commensal of dogs, found in the nares, perioral, perianal and inguinal regions.It has been reported across the globe from 61.4% in Norway ¹to 59% in India². It has been recently reclassified as part of Staphylococcus intermedius group (SIG) of organisms.

SP has been identified in pyoderma, otitis, surgical wounds and urogenital tract infections. The commensal nature, causes flaring up of secondary infections especially in immune-compromised cases like demodicosis. It has been reported in skin affections in a wide range of animals like horses, cattle, dogs, cats, rats, swine and certain wild animals. The main highlight is its identification in the human host.

In man, it has been reported in healthy individuals working closely with animals, like veterinarians, health care professionals, companion animal owners. It has also been known to cause nosocomial infections due to urine catheters and surgical wounds. The spread of SP to man is suspected to be of zoonotic origin, although the hazardous potential of the pathogen remains unexplored. Another prime reason this bacteria is of importance is due to the presence of methicillin resistant strains, that is MRSP. Such resistant isolates has proved diagnostic and therapeutic challenge for the practicing veterinarians.

Characteristics

SP is a gram positive, catalase positive, slide coagulase negative but tube coagulase positive organism.S. intermedius and S. delphini are the two other members of SIG. S. intermedius is canine specific pathogen, whereas S. delphini is found in dolphins. Differentiation using biochemical and molecular techniques can accurately determine SIG members.S. intermedius can be distinguished on the basis of absence of arginine dihydrolase production and positive acid production from β gentobiose and D mannitol, from the other two species. Thermonuclease gene is the most reliable method to detect SP ³.

Virulence factors

SP has an abundant pathogenic potential, due to its many virulence factors such as host cell adherence to fibro keratin, fibronectin and corneocyte, toxin production (leukotoxins, haemolysins, exfoliative toxin, enterotoxins, protein antigens) and enzymes  (coagulase, protease, thermonuclease). These factors are coded by specific genes in SP genome. Identification of such genes is of prime importance to understand host pathogen interactions. The biofilm forming ability of SP contributes to its persistence on the skin.

MRSP

Methicillin resistant Staphylococcus pseudintermedius (MRSP) is an SP isolate that has developed resistance to penicillin class of antibiotics, especially methicillin. Multidrug resistance has also been reported. MRSP has been confirmed from many hospital acquired infections in man. SP being a commensal pathogen, resistant isolates of it, pose a threat to animals as well as humans. MRSP in animals is homologous to MRSA in humans.

Diagnosis

Diagnosis based on clinical symptoms takes expertise, whereas, phenotypic identification through colony characteristics or biochemical methods is inaccurate. Molecular detection is commonly practiced, through Polymerase chain reaction. Thermonuclease (nuc) gene based multiplex PCR has revealed a sensitivity of 99.8% and a specificity of 100 % ⁴. PCR based Restriction fragment based polymorphism (PCR-RFLP)and MALDI-TOF MS has also proven successful in detection.

Identifying the strain of bacteria specific to a region is achieved by typing. Agr , SCCmec, MLST and Spa typing are commonly used to identify the clonal type of SP. Identification of such types will enable one to practice appropriate control methods; analyzing antibiotic susceptibility patterns, genome characteristics and phenotypic data.

Conclusion

SP is a commensal pathogen of dogs, known to cause skin and systemic infections in a wide range of hosts. Diagnosis and detection is optimum by molecular methods. Extensive research is required to enhance data on host- pathogen interactions, as well as SP as an organism.

Abbreviations

SP ; Staphylococcus pseudintermedius, MRSP ; Methicillin resistant Staphylococcus pseudintermedius, MRSA ; Methicillin resistant Staphylococcus aureus, SIG : Staphylococcus intermedius group, PCR ; polymerase chain reaction, PCR-RFLP ; PCR- Restricted fragment length assay, MLST ; Multilocus sequence typing, Agr ; Acessory gene regulator, Spa ; Staphylococcus protein antigen, MALDI – TOF MS ; Matrix assisted laser desroption/ionization – time of flight mass spectroscopy, SCCmec ; Staphylococcal cassette chromosome methicillin resistance

References

1. Norström, M., Sunde, M., Tharaldsen, H., Mørk, T., Bergsjø, B. and Kruse, H., 2009. Antimicrobial resistance in Staphylococcus pseudintermedius in the Norwegian dog population. Microbial Drug Resistance, 15(1):55-59.
2. Chitra, M.A., Jayanthy, C. and Nagarajan, B., 2015. Detection and sequence analysis of accessory gene regulator genes of Staphylococcus pseudintermedius isolates. Veterinary world, 8(7):902.
3. Sasaki, T., Kikuchi, K., Tanaka, Y., Takahashi, N., Kamata, S. and Hiramatsu, K., 2007. Reclassification of phenotypically identified Staphylococcus intermedius strains. Journal of clinical microbiology, 45(9):2770-2778.
4. Sasaki, T., Tsubakishita, S., Tanaka, Y., Sakusabe, A., Ohtsuka, M., Hirotaki, S., Kawakami, T., Fukata, T. and Hiramatsu, K., 2010. Multiplex-PCR method for species identification of coagulase-positive staphylococci. Journal of clinical microbiology, 48(3):765-769.