Texas Equine Veterinary Association

www.texasequineva.com • 24 Many test methods may be utilized to identify the presence of a virus. For example, direct methods such as electron microscopy, direct fluorescent antibody testing, virus isolation (either cell culture or eggs), and RT-PCR/PCR can be used to identify the presence of a virus; indirect methods involve antibody testing, ideally convalescent antibody testing and are used to indicate recent exposure to the virus of interest if direct detection is no longer optimal. Q: What is the best way to submit samples for bacteriology? In general, it is preferable to keep samples chilled (but not frozen) once collected and while being shipped. Shipping overnight is also highly recommended, the longer a sample sits before testing the more opportunity for opportunistic bacteria to grow and complicate the identification of a potential pathogen Swabs submitted in transport media are preferred and all of the commercially supplied transport media are good for bacterial culture. Amies and Stuart's media are the most common and are interchangeable. Unless the test is a regulated test which requires the use of a specific transport medium (e.g. Amies with charcoal for Contagious Equine Metritis or InPouch for Tritrichomonas foetus), any of the commercially available media should work. They all provide moisture and pH balancing in a sterile environment. However, not all transport swabs can be used for both culture and PCR testing. When choosing a single type of transport swab to keep on hand, it is best to pick one that contains a "sponge" in the casing and not a gel, which allows flexibility with testing (i.e. gel interferes with PCR testing). When using guarded swabs to collect uterine cultures, it is preferable to send them in transport medium. Simply discard the swab that is included in the transport swab collection system and insert the guarded swab, cutting it off (with sterile scissors) even with the top of the casing and replace the end cap. If the transport medium is not available, it is acceptable to send the swab in a red top tube; however, this is not optimal. Fastidious organisms may not survive and a negative culture may be a "false" negative. Punch biopsies, scabs, tissue samples, and fluids may be submitted in sterile red-top tubes without additives (i.e., no saline added). If the samples will be held, for example over the weekend, before shipping, very small specimens may be wrapped in sterile gauze that has been moistened with sterile saline, and then placed in a sterile tube or specimen cup to prevent drying out. Different test methods may be used to identify potential pathogens and the best method depends on the situation. For example, for regulatory or export samples, the method may be specified by the governing body or importing country. For general diagnostics, it depends on the goal. If looking for a quick "yes" or "no" for the presence (alive or dead) of an organism, PCR may be the best method. If additional testing (e.g., susceptibility, typing, autogenous bacterin preparation, etc.) is desired, then a culture is the best method. Both culture and PCR are excellent tools in the arsenal of diagnostics. Additional considerations, avoid sealing transport swabs or tubes with scotch (clear) tape, the process required to remove this may compromise the sample thereby negatively affecting the testing. Use sterile, leak-proof containers when submitting fluids (e.g., urine, tracheal wash, etc.); do not fill casings with fluids. Casings are not designed to transport fluids and will leak, resulting in loss of and contamination of the sample. We hope that these "helpful hints" have been, well, helpful. If this has generated questions we are always happy to talk with you so please feel free to give us a call (979.845.3414) or check us out at tvmdl.tamu.edu. Our goal is to provide you with the best possible diagnostic service to assist you in the treatment of your patients. We hope you consider TVMDL an extension of your practice. Figure legend: Isolated Streptococcus equi subsp. equi colonies on 5 % sheep blood agar plate. Figure legend: Isolated Klebsiella pneumoniae colonies on tergitol agar plate.

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