Moraxella bovoculi is a recently identified species of Moraxella first characterized in 2007. 10 The original 18 characterized isolates were cultured from the ulcerated eyes of calves with infectious bovine keratoconjunctivitis (IBK; "pinkeye") in northern California during summer of 2002. 10 At the present time, it is not known if M. bovoculi plays a primary or secondary role in the pathogenesis of IBK; to date, no published reports have demonstrated Koch's postulates for M. bovoculi and IBK. Nevertheless, M. bovoculi can be isolated with or without Moraxella bovis from eyes of cattle with IBK.7 In 2 recent reports, M. bovoculi was isolated from an affected dairy cow and a dairy bull calf during outbreaks of conjunctivitis in adult dairy cows and dairy beef calves, respectively.
4,15Moraxella bovoculi possesses an RTX (Repeats in the Structural ToXin) operon that encodes an RTX toxin designated MbvA that has 83% deduced amino acid sequence identity to MbxA, the M. bovis cytotoxin.6 Rabbit antisera against the carboxy terminus of MbvA neutralizes hemolytic activity of M. bovoculi. The presence of this cytotoxin would support a putative role for M. bovoculi in the pathogenesis of IBK especially as previous research showed that corneal lesions similar to IBK could be reproduced with purified M. bovis hemolysin (cytotoxin).
11To date, the results of vaccine studies with M. bovoculi antigens have not indicated benefit from the use of such antigens in vaccines to prevent IBK. Vaccination of 1 at-risk beef herd with an autogenous M. bovoculi bacterin did not reduce IBK cumulative incidence.14 In another study, a recombinant M. bovoculi cytotoxin subunit vaccine did not reduce the cumulative proportion of corneal ulcerations associated with IBK.9 Nevertheless, there are anecdotal reports that vaccination of cattle with M. bovoculi bacterin has helped to reduce IBK in herds from which M. bovoculi was isolated. Such reports suggest that this organism plays an important, however, as yet undefined, role in the pathogenesis of IBK. Abstract. Infectious bovine keratoconjunctivitis (IBK) has been associated with ocular infections by Moraxella bovis, the established etiologic agent of IBK, and more recently, Moraxella bovoculi, a recently described species of Moraxella. To assist in designing rational treatment regimens for M. bovoculi infections associated with IBK, the in vitro susceptibilities of 57 M. bovoculi field isolates cultured from eyes of cattle with IBK in California from 2002 through 2007 were determined. The minimum inhibitory concentration required to inhibit the growth of 90% of organisms (MIC 90 ) of the following 18 antibiotics tested in the present study were: danofloxacin and enrofloxacin: ≤0.12 µg/ml; ampicillin and ceftiofur: ≤0.25 µg/ ml; penicillin: 0.25 µg/ml; gentamicin: ≤1 µg/ml; chlortetracycline, oxytetracycline, and tiamulin: 1 µg/ml; florfenicol: 0.5 µg/ ml; trimethoprim-sulfamethoxazole: ≤2/38 µg/ml; clindamycin: 2 µg/ml; neomycin and tilmicosin: ≤4 µg/ml; tulathromycin: 4 µg/ml; spectinom...