Staphylococcus spp. infections

Staphylococcus spp., are Gram-positive bacteria, some of which cause suppurative disease processes in animals and humans. Of the over 40 species recognized at present (Table 1) ^{9, 15} only four (Staphylococcus aureus, S. epidermidis, S. pseudintermedius and S. hyicus) are significant in livestock. These cause various suppurative infections, especially abscesses, mastitis and pyoderma (Table 2). They occur as part of the normal microbial flora on the skin and mucous membranes of healthy humans and animals, and, to a lesser extent, in the environment.

The causation of lesions in the skin and mucous membranes by Staphylococcus depends on a number of factors, such as trauma, the immune status of the animal, disturbance of the normal microflora and whether or not the particular Staphylococcus strain produces certain toxins and enzymes.

Micrococcus spp. are common in the environment and on skin but they are not regarded as pathogenic and are distinguished from Staphylococcus spp. only in that they are strict aerobes. Planococcus spp. are found only in marine habitats, and in clams, shrimps and prawns.¹⁷

Stomatococcus, previously thought to have belonged to the family Micococcae, is now known to belong to Rothia. ⁴ Staphylococcus spp. are Gram-positive cocci (0,8 to 1,0 µm in diameter), non-motile, facultatively anaerobic, and catalase-positive, and in pus they form clusters like bunches of grapes.

Table 1 Currently recognized Staphylococcus spp

Table 2 Most common diseases caused by Staphylococcus spp. in livestock

Table 3 Characteristics that differentiate the pathogenic Staphylococcus spp.¹⁶

+ 90 per cent or more strains positive

− 90 per cent or more strains negative

d 11–89 per cent of strains positive

w weak reaction

They grow well on conventional culture media such as blood tryptose agar or nutrient agar, forming white to yellowish-orange, butyrous colonies, the colour being due to the production of a carotenoid pigment. The colonies of some species, especially S. aureus, may be surrounded by a zone of haemolysis, due to the effect of haemolysins, such as alpha and delta haemolysins, produced by them. The individual species of Staphylococcus are biochemically distinct (Table 3) and ferment sugars with the formation of acid but not gas.

Staphylococcus organisms are among the most resistant of the non-sporing bacteria to dehydration, are relatively heat-resistant (they are destroyed by a temperature of 60 °C maintained for 30 minutes), tolerate common disinfectants better than most other bacteria, and are generally resistant to many of the commonly used antimicrobial drugs.²⁰

Staphylococcus, depending on the species, may be ubiquitous or may occupy very specific ecological niches. An example is S. epidermidis, which inhabits the skin of mammals, especially humans and domestic animals.

Its preferred site is the skin close to natural openings, where it is well placed to opportunistically infect adjacent organs such as the udder or to cause wound infections. In contrast, S. saccharolyticus is only found on the skin of the human forehead and S. auricularis in the external auditory meatus of humans, while S. gallinarum occurs on the skin of poultry, and S. lentus on the skin of goats and sheep.¹⁶

Phage-typing and biochemical differences are used to differentiate between biotypes of S. aureus, ^{5, 14, 21, 28} of which four are now recognized. These are S. aureus biovar A (human), biovar B (porcine), biovar C (bovine and ovine) and biovar...