Staphylococcus hyicus

History and taxonomy The first known description of exudative epidermitis in pigs was in 1842 and the causative agent was later identified as Micrococcus hyicus in 1953. Based on phenotypic similarities, M. hyicus was moved to the Staphylococcus genus in 1965. Other bacteria closely related to S. hyicus include S. schleiferi, S. intermedius, S. pseudintermedius, and S. felis. Morphological characteristics Staphylococcus hyicus, like other members of the Staphylococcus genus, is a gram-positive coccus that forms clusters. It is facultatively anaerobic. S. hyicus colonies normally do not show hemolysis on blood agar however they do show a characteristic small zone of hemolysis on chocolate agar. or thermonuclease (nuc) gene. The complete genome (2,472,129 base pairs) of S. hyicus ATCC 11249T was also sequenced and annotated in 2015. == Virulence and antimicrobial resistance ==

Virulence Division of S. hyicus into virulent and avirulent strains is based on the production of an exfoliative toxin (virulence factor), which produces the clinical presentation of exudative epidermitis, as these toxins specifically target the stratum granulosum and stratum spinosum. S. hyicus exfoliative toxin (SHET) producing strains are further divided into plasmid carrying (SHETB) and plasmidless (SHETA). It was found that genes encoding four different exfoliative toxins (ExhA, ExhB, ExhC and ExhD) were homologous to SHETB. These exotoxins are similar to the exfoliative toxin (ETA, ETB, ETD) that Staphylococcus aureus produces. The mechanism of action is via serine protease-like exfoliative toxins. S. hyicus has demonstrated resistance to penicillin, streptomycin, tetracycline, trimethoprim, erythromycin, sulfonamides, lincomycin and chloramphenicol. Further, it has been suggested that resistance may be passed between staphylococcal species especially when treating pigs prophylactically. Other implicated plasmid resistance genes are tet(L) for tetracyclines, erm(C) for macrolides, lincosamides and streptogramins and the pS194-like str gene is for chloramphenicol and streptomycin resistance. Genetic elements for resistance to methicillin and zinc have been reported, therefore susceptibility testing is recommended before treatment. == Disease in all species ==

Staphylococcus hyicus is most noted for causing disease in pigs but has been shown to cause problems in other species as well. Swine Staphylococcus hyicus is the causative agent of exudative epidermitis in piglets. The morbidity varies greatly but can be up to 80% in some instances. The bacteria can normally be present on the skin, in the nose as well as the vagina and prepuce. Cattle The bacterial species has been isolated from milk in dairy herds and is one of the more uncommon causes of contagious mastitis in the Staphylococcus species. This bacteria can also cause a skin disease in cattle which leads to a mange-like syndrome most common in young adult cattle. This bacteria has also been cultured from chicken meat labelled for human consumption, and could be a cause of Staphylococcus food poisoning. In one study the strains of S. hyicus found in retailed chicken meat were resistant to every antibiotic tested. Humans Humans being affected by S. hyicus is rare and for this reason is not considered a common zoonosis. There is a higher risk of people being infected if they work in close contact with infected pigs frequently, such as one case reported in a farmer with a previously infected foot causing bacteremia. Another notable case is a man who was diagnosed with a case of infectious spondylodiscitis. A culture of his infected bone and blood was confirmed to have S. hyicus present, suggesting it was the causative agent. This case is concerning because he was considered immunocompetent, which is often not the case for rare bacterial infections. There have been very few human cases found other than these rare instances, and it is not currently considered a risk to human health. == Role of Staphylococcus hyicus in exudative epidermitis (greasy pig disease) ==

Epidemiological background Endemic infection with S. hyicus is a common finding worldwide; however the development of exudative epidermitis is based on opportunity and the age of the pigs involved Exfoliative toxins will cleave swine desmoglein-1 (Dsg1); therefore, creating an opportunity for epidermal bacterial invasion with the splitting of the stratum spinosum and stratum granulosum. With bacterial invasion, 1 to 2 cm (diameter) brown lesions will begin to appear within the 24 to 48 hour range; and lesions will first appear cranially before progressing posteriorly as crusting ulcers with possible formation of suppurative folliculitis. However, in younger animals that may die within 3 to 5 days, crusting ulcers may only be situated in the cranial region due to lack of time to progress. Often the young piglets severely affected by S. hyicus causing exudative epidermitis die from dehydration characterized by a loss of protein serum and electrolytes. Besides the characteristic brown lesions of the dermis, ulcerative lesions can form in the mucosa of the mouth and on the tongue. Additionally, peripheral lymph nodes will swell, and internal organs such as the kidney and lungs may become distended. Areas of the body affected • Head, neck, feet, general body, mouth and tongue • Kidneys and ureters may become distended with mucus and debris collection; additionally lungs may accumulate congestion during the disease process Diagnosis Exudative epidermitis is often fatal in piglets especially those within the 1 to 5 week-old range as they are most at risk for the development of the acute disease form. As animals age the likelihood of developing the acute disease form lessens therefore mortality decreases; however, producers may note a reduction in feed conversion and weight gain post-disease recovery. Diagnosis of exudative epidermitis is often made based on the characteristic brown lesions that progress to crusting ulcers along with the other clinical signs mentioned above. == Prevention of disease ==

Vaccine A vaccine can be used for prevention of infection with S. hyicus. The vaccine is made using the genes that encode exfoliative toxin type B (ExhB) from S. hyicus strains. Since there is no commercial vaccine available yet, the vaccine used is an autogenous vaccine with the strain of S. hyicus that is currently affecting the herd of pigs to ensure immunity is developed to the strain within the barn. Vaccination reduces the chance that pigs will die from the disease and can help reduce the use of antimicrobials to treat exudative epidermitis. Vaccinated sows can pass on antibodies to the piglets so that the piglets have some passive immunity to S. hyicus. Management of pigs Staphylococcus hyicus can enter the skin of pigs through any cut. Managing the pigs so they are unable to bite each other or ensuring the flooring is soft can decrease infection. The barn should be disinfected and cleaned regularly to ensure bacteria cannot grow as easily. Any new sows entering the barn should be washed to reduce contamination. When the first signs of disease are noticed, changing the bedding or moving the pigs to a new stall can reduce contamination. Using sterile needles for injections and controlling mange may also decrease infection. Exudative epidermitis is contagious between pigs and quick isolation can reduce the chance of the disease spreading. Ensuring biosecurity of the farm and isolating any new pigs before introducing them to the herd can reduce transmission. For young piglets, reducing the chance of chilling can impact how sick the piglets will get. Keeping the barn dry and clean as well as ensuring there is adequate ventilation and humidity can decrease the amount of S. hyicus that can grow in the barn and possibly infect pigs. == Treatment ==

Treatments for exudative epidermitis include antibiotics given topically or injected, disinfectants, and topical oils which can relieve symptoms. With antibiotic resistance increasing in all bacteria, sending samples to a diagnostic lab for susceptibility testing is important for choosing the right antibiotic in that case. Ensuring bacteria do not develop resistance to many antimicrobials is important for both animal and human health. This is especially true in food animals, such as pigs, because resistant bacteria responsible for many common foodborne illnesses in people may be linked to animal antimicrobial resistance. == References ==