Ask the Vet

Mastitis pathogens: Part 2

This month I’ll continue discussing bacteria that cause mastitis. As you may remember, we covered the Gram-positive bacteria last month, so this month we’ll cover the Gram-negative bacteria, which are usually referred to as coliforms. Gram-negatives are common in a cow’s intestinal tract. Because of this, they are everywhere in the cow’s environment. Infections by this family of bacteria can range from mild to very severe.

There is probably not a farmer out there who hasn’t experienced the devastating effects of a severe coliform infection in his or her herd. Common signs of acute infections are high temperature, depression, dehydration, weakness, severe swelling of the infected quarter and watery milk. As the bacteria die, they release an endotoxin that causes many of these symptoms.

Severe coliform infections can be devastating to the cow’s milk production for the current lactation and future lactations. Let’s review the more common Gram-negative bacteria.

Escherichia coli (E. coli): Infections in the cow range from mild to extremely severe, and can even result in death. The source point of infections is any environment that has come in contact with manure.

Antibiotic therapy in the quarter does not work very well. Supportive care with fluids and anti-inflammatory medications are the therapy of choice. Vaccines commonly referred to as the J-5 vaccines target the cell wall of the bacteria and help alleviate the severe sickness. Since these vaccines are commonly used, we do not have to treat nearly as many sick cows anymore.

Klebsiella species: These bacteria cause severe mastitis that is unresponsive to antibiotics. The source point of the infection is the environment. The major environmental source is bedding material, with sawdust being the most common. High numbers of Klebsiella in recycled sand and manure solids used for bedding also have been reported.

Mastitis from Klebsiella tends to be more severe and chronic than that caused by E. coli. It does not seem to respond to the same J-5 vaccines that help E. coli infections.

Enterobacter aerogenes: The source point is manure-contaminated environments.

These bacteria cause many of the same symptoms as the other coliforms. Response to antibiotics is poor. Basic control involves keeping cows clean and dry.

Serratia species: The source point of this infection is soil, water or even teat dip. Nolvasan-based teat dips that become contaminated have been implicated in several outbreaks of Serratia mastitis.

Basic control is good environmental sanitation. Treatment response is very poor, and animals often get culled once they contract Serratia.

Pasteurella species: These bacteria infrequently cause mastitis. The origin is thought to be from the respiratory tract, so the spread of infection could be cow to cow.

This mastitis responds poorly to treatment. If several cows become infected, the producer should look for a common source of the infection.

Pseudomonas aeruginosa: These bacteria infrequently cause mastitis. The source point of infection can be any part of the environment, but it is most commonly water, contaminated teat dips or common infusion products.

Infections tend to be severe, with treatment outcomes poor. These bacteria are resistant to certain sanitizers and antibiotics.

Proteus species: The source point of these infections is the soil, so they spread from environment to cow.

This infection is very rare as a pure culture, so if it does come back from the lab, do a resample of the infected quarter. Treatment is unsuccessful.

From this list you can see a common theme: Coliforms can cause severe mastitis with poor outcomes to antibiotic therapy. Financial losses can be large with a high number of mastitis cases. Clean environments and strict attention to udder hygiene are key to controlling infection rates. It is best to work closely with your veterinarian to develop treatment protocols and control programs for coliform mastitis.

Monty Belmer, DVM, is a veterinarian with the Waupun Vet Service in Waupun. To Ask the Vet, e-mail your questions to:, or mail them to: Wisconsin Agriculturist, 102 E. Jefferson St., P.O. Box 236, Brandon, WI 53919.

This article published in the April, 2010 edition of WISCONSIN AGRICULTURIST.

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