ANSWER TO QUESTION OF THE WEEK! This mastitis pathogen is SERRATIA. As a non-coliform gram-negative bacteria, like Pseudomonas, Serratia colonies on MacConkey agar are clear/translucent. However on blood agar the appearance of Serratia is very distinct from that of Pseudomonas. Serratia colonies on blood agar are white, rounded, and non-hemolytic, while Pseudomonas colonies are gray, flat, and beta-hemolytic (a zone of clearing surrounds the colonies). Identification can be confirmed by catalase & oxidase tests. Serratia is a vigorous catalase reactor and is oxidase-negative, while Pseudomonas is a weak catalase reactor and is oxidase-positive. Pseudomonas typically produces a characteristic odor similar to artificial grape flavoring. Both Serratia and Pseudomonas cause chronic mastitis infections that do not respond to treatment. Both of these bacteria form stable biofilms which can protect them from disinfectants, and they are notorious for thriving in water storage tanks/cisterns and parlor water hoses. Avoid spraying water while cows are in the parlor. If several mastitis cases culture these bacteria, consider culturing water sources to see if they are contaminated.
Posted on: Thu, 18 Dec 2014 21:01:24 +0000
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