Microbiological Testing

The shipment of biological specimens must comply with the protocols established by the courier or transport service used. In some cases, air transport requires compliance with the International Air Transport Association (IATA) regulations for dangerous goods.

Any specific infectious agent clinically suspected must be noted on the submission form; some organisms have specific growth requirements (for example, anaerobic culture, special media) that may not be routinely used in laboratories unless the pathogen has been cited as a differential diagnosis.

Laboratory techniques and capabilities for microbiological tests vary; however, most tests are based on the growth or visualisation of intact viable organisms or on the detection of the nucleic acids and proteins of these pathogens. Therefore, unfixed samples (tissues, fluids, etc.) must be collected aseptically and shipped promptly to avoid degradation.

If there is a possibility of performing a microbial culture of a fluid sample such as urine or a cavitary effusion, a separate aliquot of the fluid must be sent in a sterile container without additives. Tubes containing EDTA or other preservatives are usually ideal for cytological evaluation but unacceptable for culture.

If PCR assays are to be performed, it is especially important to avoid cross-contamination between several animals in one shipment; this principle applies to tissues, fluids and even dissection instruments.

In addition, swabs for PCR analysis must not be placed in agar- or charcoal-based transport media, and calcium alginate swabs should be avoided. Instead, sterile cotton- or polyester-tipped applicators should be sent in a tube, either dry (without transport medium.

The requirements for the PCR assay can vary greatly depending on the specific PCR test, so it is strongly recommended to consult the receiving laboratory before obtaining the sample.

Some testing protocols may allow the pooling of organ samples from a single individual; however, in general it is preferable for each tissue to be collected in separate, clearly labelled sterile bags or tubes for shipment. Intestinal samples must never be mixed in one container with other tissue samples.

Tissues and fluids for most microbiological assays can be frozen before shipment, but freezing is usually not advisable if the samples can be refrigerated and delivered directly to the laboratory within 24 hours of collection.

Exceptions to this rule include the analysis of certain toxins, such as those of Clostridium perfringens and C botulinum, in which toxin degradation must be avoided by immediate freezing after collection. A suitable refrigerant must be provided so that the samples remain refrigerated (or frozen) until they reach the laboratory.

Faecal samples for parasitological tests must be sent refrigerated in properly sealed containers. Freezing may have little impact on routine flotation or sedimentation tests, but it will rule out the possibility of the Baermann analysis for nematode larvae. Ectoparasites or nematodes sent for identification must be submitted in vials containing 70% alcohol.