Staphylococci are found worldwide in all species of animals and are spread between species, including animal to humans and vice versa. The majority of humans and animals are carriers of staphylococci. Staphylococcus aureus is found with a high prevalence in most colonies of laboratory rodents2 as well as in most humans, while in wild mice, S. aureus is rather uncommon. Other types of Staphylococci common in laboratory rats and mice include S. haemolyticus, S. xylosus, S. sciuri, and S. cohnii.83 The bacteria may be transmitted among hosts in various direct or indirect ways, including passive carriers among animal technicians. Staphylococcal disease in immune-competent animals is mainly secondary, e.g., due to trauma, stress, or the equivalent, and is characterized by pyogenic processes, such as abscesses in bite or surgical wounds, pneumonia in rodents kept in poorly ventilated units, and dermatitis in gerbils kept in too humid bedding. In immune-deficient animals, S. aureus may be a primary disease-causing agent, e.g., in the nude mouse, in which it causes multiple abscessation. Also, coagulase negative Staphylococci may cause disease in laboratory animals, e.g., S. xylosus is known to cause intestinal disease in mice,84 dermatitis in gerbils,85 and pneumonia in immune-suppressed rats.86 Interference with research is mainly due to the activation of latent infection by stress or immunosuppression, but also the presence of abscesses in immune-deficient animals, typically nude mice, may be hazardous to research.

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