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Bovine Diagnostics

Misdiagnosis of Mycoplasma spp.

Mycoplasma species are delicate pathogens that grow very slowly. When using culture for diagnostic testing, they require a specific growth medium, such as modified Hayflick agar. That growth medium has the potential to grow several organisms. Acholeplasma laidlawii grow easily on the modified Hayflick agar and are often mistaken for Mycoplasma species in culture, which can result in misdiagnosis.

A positive diagnosis on culture typically requires more testing, which wastes valuable time when you have sick cows. If veterinarians request PCR testing be used upfront rather than culture, it’s possible to save a step later in the process. This can gain valuable time later if Mycoplasma bovis is spreading throughout your dairy herd.

Overview of Acholeplasma laidlawii

Acholeplasma laidlawii is a common, isolate obtained from tank milk or direct from cow samples that is generally viewed as non-pathogenic. As an environmental contaminant, it grows on culture media but there is minimal evidence that it could play a pathogenic role in mastitis.

Difficulty of Culturing Mycoplasma

Experts agree that Mycoplasma is very difficult to handle, culture and diagnose. As a slow growing pathogen, testing for M. bovis using culture can take up to 10 days for results to be read. When the diagnostician views the culture plate, it may be overgrown with other faster growing bacteria, like Acholeplasma laidlawii, making it difficult to recognize which has grown. Both Acholeplasma and Mycoplasma have a “fried egg” appearance, so differentiation by culture alone is not possible and can result in false positive Mycoplasma diagnosis.

There are also reports that Acholeplasma laidlawii can be present in the broth powders used to make bacterial culture plates, increasing its opportunity for growth as a contaminant. A. laidlawii not only survives but flourishes for prolonged time frames at room temperature or in refrigeration which increases the chance of a false positive diagnosis for Mycoplasma spp.

With PCR, farmers usually have results from their veterinarian in one day, so they can take fast action.

Colonies of <em>Acholeplasma laidlawii</em> after 4 days of incubation on NPR agar. Note the colony appearance (“fried egg”), which is typical for many Mollicutes.

Colonies of Acholeplasma laidlawii after 4 days of incubation on NPR agar. Note the colony appearance (“fried egg”), which is typical for many Mollicutes.
Credit: www.vetbact.org and Stefan Jernstedt (SVA) and Karl-Erik Johansson (BVF, SLU and SVA)

Colonies of <em><em>Mycoplasma</em> bovis</em> after 5 days of incubation on NPR agar. Note the colony appearance (“fried egg”), which is typical for many Mollicutes.

Colonies of Mycoplasma bovis after 5 days of incubation on NPR agar. Note the colony appearance (“fried egg”), which is typical for many Mollicutes.
Credit: www.vetbact.org and Virginia Melys (SVA) and Karl-Erik Johansson (BVF, SLU and SVA)

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