Detecting Mycoplasma Mastitis
Signs of Mycoplasma Mastitis
Table 1: Several key procedures at the farm, during sample transportation, and at the diagnostic laboratory before agar inoculation will assure the highest achievable sensitivity and specificity of mycoplasma detection techniques.
Cows chronically-infected with Mycoplasma bovis may show a tannish-colored secretion with sandy or flaky sediments that resembles cooked cereal in a whey-like fluid. Mycoplasma mastitis usually becomes chronic because these bacteria are resistant to the majority of antibiotics currently available in food animals. The reason is that mycoplasmas lack a cell wall and therefore are resistant to antimicrobials that target this structure such as penicillin.
In the case of subclinical mastitis, cases are characterized by progressive hardening and reduction in the size of the affected quarter. In some cases, multiple abscesses within the affected quarter may be found and this characteristic may cause intermittent shedding of mycoplasmas in milk from the affected quarter. In herds with high SCC, mycoplasmas should be considered as one of the possible causes of subclinical mastitis.
Mycoplasma Mastitis Herd Outbreaks
In the case of an open herd, milk from new animals should always be tested for mycoplasma growth before commingling with the herd. Routine bulk tank milk sampling should usually precede individual sampling. Depending on the size of the lactating herd and Mycoplasma prevalence in the dairy operation, these samples should be repeated at least once a month for small herds, and weekly, for large herds.
Aseptic milk sample collection, usually following udder preparation and sanitizing the teat end with alcohol pads,is important to minimize contamination with bacteria from the environment. Good milk sampling procedures alone will increase mycoplasma recovery; this is because environmental bacteria growth will acidify milk and impair mycoplasma growth.
The amount of time between sample collection and culturing should be kept to a minimum. Since immediate culturing is far from practical in commercial herds, it is very likely that samples will require some type of storage. If the time period from sample collection until laboratory processing is less than 72 hr, milk samples should be refrigerated at 36-41 ºF.
On the other hand, if the storage time is longer than 72 hr, samples should be frozen at -68 ºF. In this case, addition of a cryoprotectant, either gyclerol 10 to 30% volume to volume, or dimethyl sulfoxide (DMSO) 10% volume will improve mycoplasma recovery.
Use of the Non-culture Based Mycoplasma Tests
In the case of mycoplasma mastitis outbreaks, PCR testing could be used for screening milk samples from cow groups, thus reducing processing time. Positive PCR results should be interpreted carefully, and ideally confirmed by culture, because of the possibility of false positives.
During a mycoplasma mastitis outbreak, identification of mycoplasma positive cows should be accompanied by a complete critical analysis of milking routines, lactating herd teat condition, milking equipment performance, maternity pen management, protocols for new cow and heifer management, etc. Mycoplasma is prevalent in many Michigan dairy herds, therefore good preventive procedures are essential to minimize the risk of mycoplasma mastitis outbreaks.
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