What Really Makes Mastitis Types Different?

Gram positive, Gram negative, mycoplasma – you’ve heard the different categories of mastitis many times, but what really makes them different? The basic difference is their cell structure.
calendar icon 17 October 2019
clock icon 2 minute read

This article is authored by Calvin Gunter, Thermo Fisher Scientific Animal Health product management

Gram positive mastitis bacteria have a thick cell wall. The cell wall’s membrane is highly selective about how and what move in and out. Gram negative mastitis bacteria have a thin cell wall with two membranes that are somewhat selective, and the outer membrane protects the cell wall.

“Penicillin antibiotics need to attack the cell wall in order to be effective. For Gram negative infections, the penicillin-type antibiotics, also called beta lactams, cannot get to the cell wall,” described Dr. Larry Fox, professor at Washington State University. “As a result, Gram positives tend to be more susceptible to penicillin antibiotics; Gram negatives are more resistant.”

Similar to Gram negative bacteria, Mycoplasma do not have a cell wall; they only have a cell membrane, making them much more resistant to antibiotics because there's no cell wall to attack. Mycoplasma is very slow growing, which gives it an advantage because some antibiotics focus on the metabolism and reproduction aspects of the cells. Slow growing bacteria are not reproducing or metabolizing as fast, making them more resistant to antibiotics.

Cows with a Gram negative infection tend to get systemically sick and would be considered a “hotter,” more acute case of mastitis. Gram positive mastitis infections tend to show abnormal milk and elevated somatic cell count. Mycoplasma symptoms are somewhere in between, and typically multiple quarters of the animal are infected.

When it comes to antibiotic treatment, Dr. Fox recommends treating Gram positive infections, but says antibiotics are not a solution for Mycoplasma or Gram negative infections. When antibiotics aren’t used, some advocate for frequent milk out, which is designed to evacuate the toxins causing the clinical signs of mastitis from the mammary gland.

Closely monitor your bulk tank diagnostic test results to identify problem areas, and then work with your herd veterinarian to develop a mastitis control program that fits your specific operation.

Find out more at Bovine Diagnostics in the Knowledge Centre


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