D365 - Staphylococcus aureus

Description:

Staphylococci are facultatively anaerobic, gram-positive cocci. Their principal habitats are the skin and some mucous membranes of mammals and birds. Staphylococci are classified into 28 species and several subspecies. All species of staphylococci isolated from normal animals are potentially pathogenic. Humans are the natural hosts for Staphylococcus aureus, which colonizes the nasal passages of up to 40% of healthy adults and rarely other body sites in the absence of dermatoses. S. aureus comprises less than 10% of clinical isolates from normal dogs and cats and apparently is not indigenous or site specific in these hosts. Coagulase-positive staphylococci are most frequently isolated from pyogenic infections of dogs and, less commonly, cats. As significant pathogens, they can affect every organ system independently or concurrently, but are most common in abscesses and infection of the skin, eyes, ears, respiratory and genitourinary tracts, skeleton and joints. S. aureus infection typically occurs in epithelium damaged by traumatic injury (e.g. incisions, wounds), infections (e.g. demodicosis, dermatophytosis), or clinical conditions (e.g. seborrhoea, thyroid dysfunction). Immunocompromised hosts are most susceptible to clinical illness as a result of infection.
S. aureus infection has also be observed in birds where clinical infection is usually in the form of bacterial skin infections. Like in cats and dogs, infection requires a break in the normal defence barriers, such as damaged skin or mucous membranes, or a severely compromised immune system.

Diagnosis:

Usually, the etiological diagnosis of S. aureus is dependent on isolation of the bacterium from the focus of infection or in blood cultures. In some cases, access to the focus may be difficult or dangerous or cultural confirmation may be hampered by ongoing antimicrobial therapy. Also, superficial contamination by other organisms can be problematic. Staphylococci may die before culture since they require a fairly stringent set of conditions for survival. Under optimal conditions (4oC [39.2oF]), clinical specimens survive for up to 48 hours. Serologic assays, especially for antibodies reactive with teichoic acid or nucleases, are used as clinical aids in the diagnosis and management of bacteremia, endocarditis, and other deep recurrent staphylococcal infections in people. However, the results obtained from these tests, as well as the tests themselves remain controversial and will not likely be adapted for clinical use in animal infections. Furthermore, these tests are of limited value because of insufficient diagnostic sensitivity and specificity. Fortunately, a PCR-based assay is now available for the detection of S. aureus in a sample. This assay utilizes the most recent advances in DNA technology by selectively detecting specific genes unique to S. aureus, thus avoiding contamination by other organisms. This test offers veterinarians a sensitive, specific, and rapid diagnostic tool that can definitely confirm the presence of S. aureus in a sample.

Treatment:

S. aureus are rarely resistant to first-generation cephalosporins, beta-lacatmase-resistant synthetic penicillins, gentamicin, tobramycin, enrofloxacin, bacitracin, and polymyxin B. These should be the drugs of choice when diagnostic results are not available and S. aureus infection is suspected.

Sample:

1. Whole blood (3 ml) in a lavender (EDTA) top tube for cats and dogs. Whole blood (0.1 – 0.3 ml) in a lavender (EDTA) top tube for birds.

Special Handling:

Store sample at 4°C until pick up or shipment.

Test Code:

D365