Evaluation of a coagulase-negative variant of Staphylococcus aureus as a cause of intramammary infections in a herd of dairy cattle.
A coagulase-negative variant of Staphylococcus aureus was identified in a herd of 250 lactating dairy cows. During testing of the entire herd, this strain of S aureus was isolated from aseptically collected milk samples of 25 cows. Cows with intramammary infections attributable to coagulase-negative S aureus had an increased somatic cell count in their milk, which was indicative of mastitis infection. Speciation of the Staphylococcus organisms was made, using a series of biochemical tests. A strain of a coagulase-positive S aureus also caused intramammary infections in the herd and shared identical biochemical characteristics with the coagulase-negative strain. Moreover, both strains could not be typed by the use of the International Set of Bovine Phages. Analysis of these findings indicated that a coagulase-negative variant of S aureus can cause intramammary infections in cattle, coagulase-negative variants of S aureus that cause mastitis can be more prevalent in herds than coagulase-positive variants, and clinicians should avoid misclassifying coagulase-negative S aureus as organisms that are clinically unimportant.
Fox
L K
LK
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman 99164, USA.
Besser
T E
TE
Jackson
S M
SM
D000818:Animals; D001434:Bacteriophage Typing / Q000662:veterinary; D002417:Cattle; D002452:Cell Count / Q000662:veterinary; D003030:Coagulase; D005260:Female; D008414:Mastitis, Bovine / Q000382:microbiology*; D008892:Milk / Q000166:cytology / Q000382:microbiology; D011933:Reagent Kits, Diagnostic / Q000662:veterinary; D013203:Staphylococcal Infections / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000145:classification / Q000201:enzymology / Q000302:isolation & purification*
D003030:Coagulase; D011933:Reagent Kits, Diagnostic