Cytopathic effects of Moraxella bovis on cultured bovine neutrophils and corneal epithelial cells.

The effects of Moraxella bovis on the morphologic features of purified bovine neutrophils and bovine corneal epithelial cells were examined, using transmission and scanning electron microscopy and light microscopy. Within 2 minutes after incubation of bovine neutrophils with living M bovis, electron microscopic cellular changes included vacuolation, swelling, and loss of microplicae. Most of the neutrophils were lysed by 10 minutes of incubation. Human neutrophils phagocytosed the M bovis and remained intact, even after 30 minutes of incubation with the bacteria. Living M bovis killed bovine corneal epithelial cells in vitro. Sterile filtrates prepared from 6-hour shaker cultures of M bovis also killed bovine corneal epithelial cells, but the cytotoxic activity was less than that produced by the living bacteria. Cellular changes were first observed in specimens collected 1 hour after corneal cell monolayers were inoculated with sterile culture filtrates. The changes in these cells included pit-like lesions on the cellular surface, cellular separation, and vacuolation.

Effects of Moraxella bovis and culture filtrates on 51Cr-labeled bovine neutrophils.

The cytotoxicity of Moraxella bovis whole cells and culture filtrates was studied, using 51Cr-labeled bovine and human blood neutrophils. The cytotoxicity of living M bovis was directly related to the concentration of bacteria in the neutrophil cultures, and was maximal at an approximate neutrophil to bacteria ratio of 1:10. Cytotoxicity was maximal by 30 minutes after living bacteria were added to the suspension of the 51Cr-labeled neutrophils. Expression of the cytotoxicity was dependent on the presence of Ca2+ in the media, and was independent of the presence of Mg2+. Cytotoxic activity was eliminated by inactivating M bovis in buffers containing formalin or sodium azide. Hemolytic and nonhemolytic isolates of M bovis were examined for cytotoxic activity. All 7 of the hemolytic isolates were cytotoxic for bovine neutrophils, but all 4 of the nonhemolytic isolates were devoid of cytotoxic activity. None of the 11 isolates were cytotoxic for human neutrophils. Sterile filtrates from 6-hour shaker cultures of a hemolytic M bovis isolate were cytotoxic for bovine neutrophils. Cytotoxicity of the filtrate was eliminated by heating, incubation with trypsin, or addition of EDTA to the media. Bacterial homogenates or sterile filtrates prepared from statistically incubated cultures of M bovis were not toxic for bovine neutrophils.

Topically applied furazolidone or parenterally administered oxytetracycline for the treatment of infectious bovine keratoconjunctivitis.

The effectiveness of topically applied furazolidone (FZ) or parenterally administered oxytetracycline (OTC) for treatment of infectious bovine keratoconjunctivitis was determined in a field study. Between June 13 and Aug 6, 1985, a study was conducted on a ranch in northern California. Eyes of Hereford calves (n = 103) were examined 3 times each week for 7 weeks. After daily examinations on June 13 and 14, calves were allotted randomly to 3 groups. On June 17, calves (that had corneal ulcers) of groups 1 (n = 35) and 2 (n = 35) were treated with OTC and FZ, respectively. Treatments were administered again only if new ulcers were observed, if an existing ulcer worsened, or if a healed ulcer recurred. Calves of group 3 remained untreated (controls). Corneal ulcers developed in 35 of the FZ-treated calves, in 33 of the OTC-treated calves, and in 33 of the untreated calves. Corneal perforations were observed in 3 untreated and 2 FZ-treated calves but were not observed in any OTC-treated calves. Panophthalmitis developed in one eye of an untreated calf. Corneal ulcers in the OTC-treated calves were smaller and healed more rapidly than did corneal ulcers in calves of the other groups. By the 22nd day of the study (July 3), the number of OTC-treated calves with corneal ulcers was less than that of the other 2 groups. Calves of the OTC treatment group had the fewest multiple corneal ulcer recurrences, but calves of all 3 groups had a similar number of single corneal ulcer recurrences.(ABSTRACT TRUNCATED AT 250 WORDS)

Light and electron microscopic changes in corneas of healthy and immunomodulated calves infected with Moraxella bovis.

Thirty-nine Holstein calves (50 to 100 kg and 2 to 3 months old) were randomly assigned to 4 groups. Calves in group I (n = 12) were inoculated with Moraxella bovis and were euthanatized 24 hours (6 calves) or 8 days after inoculation (6 calves). Group-II calves (n = 12) were treated with hydroxyurea for 6 days, and then 6 of these calves were inoculated with M bovis. The daily hydroxyurea treatments continued for 14 days, and then all calves in group II were euthanatized. Group-III calves (n = 9) were administered dexamethasone parenterally, beginning 24 hours before inoculation with M bovis, and then daily thereafter, until they were euthanatized at either 24 hours (n = 5) or 8 days (n = 4). Group-IV calves (n = 6) were inoculated with M bovis, and euthanatized 12 hours later. Tears were collected from all calves that had been inoculated more than 24 hours earlier. The concentration of myeloperoxidase and collagenase was determined for each sample. After the calves were euthanatized, the corneas were dissected free, fixed, and examined by use of scanning or transmission electron microscopy, or light microscopy. Microscopic corneal erosions were detected 12 hours after inoculation. These lesions were not accompanied by inflammatory cell infiltration and were detected by use of scanning electron microscopy. Inflammatory cells were first observed in the corneal lesions in specimens collected 24 hours after inoculation. Bacteria that resembled M bovis morphologically were seen in several locations in these lesions. By 8 days, corneas of the group-I calves had the least number of intracorneal bacteria, compared with the corneas from other groups. The number of calves that developed corneal ulcers by 8 days was similar in all groups. The corneal ulcers of the hydroxyurea-treated calves were shallower, but appeared larger in surface area than those of the controls. By 8 days after inoculation, the corneal ulcers of the dexamethasone-treated calves had less corneal neovascularization and opacification than did the controls. Corneal perforations developed in 2 eyes of the dexamethasone-treated calves, but did not develop in any eyes of the controls. Microscopically, a larger number of M bovis were observed in corneas of dexamethasone-treated calves than in corneas of calves from other groups. Collagenase was not detected in any tear samples. The concentration of myeloperoxidase in tear samples were significantly (P less than 0.05) higher in the prehydroxyurea-treatment samples than in the posttreatment samples from corresponding calves.