Immunohistochemistry has been available for many years, but is becoming much more widely used with advances in automated staining processes, available antibodies, and knowledge. The principle behind the technique is relatively simple: all cells have antigens, and the distribution of antigens is tissue-dependent.

Staphylococci are Gram-positive, facultative anaerobic cocci. The genus is subdivided into many different species and most of them are host adapted. For the most part, staphylococci are skin commensals of healthy individuals where they can be carried transiently or permanently and only cause disease when there is a breech of epithelial integrity. The most common clinical presentations are skin abscesses. The species of staphylococci most frequently isolated from both healthy and sick dogs and cats is Staphylococcus intermedius (SI). Staphylococcus aureus (SA), although isolated from animal infections, is not as common as SI. The susceptibility profiles of both staphylococci species is changing, with clear increases in the number of isolates that are multidrug resistant (MDR).

Johne’s disease (JD), caused by Mycobacterium avium subspecies paratuberculosis (MAP), is an economically important disease of ruminants. The disease is characterized by chronic, progressive granulomatous enteritis and affects a wide variety of hosts including cattle, sheep, goats, llamas, alpacas, bison and deer. The U.S. dairy cattle industry estimates an annual economic loss of $220 million due to JD. The presence of MAP in milk, its resistance to pasteurization temperatures, and its possible association with Crohn’s disease in humans suggest a significant public health risk.