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Microbiological culture is a commonly used test that, with the exception of dermatophytosis cultures, generally requires the use of diagnostic laboratory services (see Chapter 20 on Dermatophytosis for more information about the performance and interpretation of ringworm cultures). Almost any bodily fluid, excretion, or tissue can be submitted for culture to determine whether or not infectious organisms are present (most commonly bacterial or fungal agents). In contrast to molecular assays, a culture can identify live pathogens, the species of organism(s) present and, when antimicrobial sensitivity is evaluated, which pharmaceutical treatments are likely to be effective and at what dosages. Repeat cultures can be used to evaluate a patient's response to a treatment course and to determine when an infection has been resolved. Unless sampling from a contaminated area such as a wound or a sample of skin or hair (e.g. ringworm cultures), samples must be collected and handled using aseptic techniques in order to provide meaningful results. Fecal samples submitted for culture should include specific differential diagnoses to direct the microbiologist. Similarly, when fastidious microorganisms not easily cultured on standard media are suspected (e.g. Mycoplasma spp., anaerobes, spirochetes, Mycobacterium spp.), the laboratory should be consulted for recommendations on sample collection, preparation, storage, and transportation. Additionally, if the animal is receiving antimicrobial therapy at the time of sample collection, this must be taken into account for proper interpretation of results. Common indications for culturing include UTIs, non‐healing or contaminated wounds, and severe, chronic, or non‐responsive diseases of the respiratory, GI, and dermatologic systems.

Virus isolation is a specialized type of microbiological culture that relies on the need for viruses to replicate in living tissue. Most commonly, laboratory cell cultures are inoculated with test samples, incubated, and evaluated for structural changes due to viral infection (i.e. cytopathic effect). Once an active virus is cultivated, identification can be confirmed through the use of the serological methods described above. Common samples for virus isolation include tissue (belonging to viral target organs), anticoagulated whole blood, respiratory secretions, and urine. Samples should be kept in sterile containers, refrigerated, and arrive at the diagnostic laboratory within 24 hours. In addition to its utility for the identification of novel organisms and to monitor the microevolution of certain viruses (e.g. influenza), virus isolation is commonly used for confirmation of infection with adenoviruses, FeLV, and parvoviruses. Virus isolation of these pathogens may take between one and 4 weeks, limiting the usefulness of this modality in urgent clinical cases.