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  • Author or Editor: Robert H. Whitlock x
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Abstract

Objective—To evaluate the in vitro susceptibility of various field isolates of Mycobacterium avium subsp paratuberculosis (MAP) to gallium nitrate.

Sample—10 isolates of MAP, including 4 isolated from cattle, 2 isolated from bison, 1 isolated from an alpaca, and 3 isolated from humans.

Procedures—The in vitro susceptibility to gallium nitrate was tested by use of broth culture with detection of MAP growth by means of a nonradiometric automated detection method. For each MAP isolate, a series of 7 dilutions of gallium nitrate (concentrations ranging from 200 to 1,000μM) were tested. Gallium nitrate was considered to have caused 90% and 99% inhibition of the MAP growth when the time to detection for culture of the MAP stock solution and a specific concentration of gallium nitrate was delayed and was similar to that obtained for culture of the MAP stock solution (without the addition of gallium nitrate) diluted 1:10 and 1:100, respectively.

Results—Gallium nitrate inhibited MAP growth in all 10 isolates. The susceptibility to gallium nitrate was variable among isolates, and all isolates of MAP were inhibited in a dose-dependent manner. Overall, the concentration that resulted in 90% inhibition ranged from < 200μM for the most susceptible isolates to 743μM for the least susceptible isolates.

Conclusions and Clinical Relevance—Gallium nitrate had activity against all 10 isolates of MAP tested in vitro and could potentially be used as a prophylactic agent to aid in the control of MAP infections during the neonatal period.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate the effect of vaccination of calves with a killed Mycobacterium avium subsp paratuberculosis (MAP) vaccine on colonization of tissues following oral MAP exposure.

Animals—12 healthy Holstein calves.

Procedures—At 14 days after birth, calves received the MAP vaccine (1.0 mL, SC) or saline (0.9% NaCl) solution (1.0 mL, SC [control treatment]). Each calf received 1.2 × 109 CFUs of live MAP orally 21 and 22 days after vaccination. Prior to vaccination and at subsequent intervals, a blood sample was collected for ELISA detection of antibodies against MAP and for whole blood, antigen-specific, interferon (IFN)-γ–release assay. Nine weeks after MAP challenge, calves were euthanized and various tissue samples were collected for mycobacterial culture. Interferon-γ production in prescapular lymph node cells was measured following in vitro stimulation with MAP antigens.

Results—Calves were seronegative for anti-MAP antibodies at all times. Compared with the findings in control calves, antigen-specific IFN-γ production in circulating lymphocytes and prescapular lymph node cells from vaccinated calves was significantly higher. Culture of tissues from vaccinated calves yielded significantly fewer CFUs of MAP (2,417 CFUs/g), compared with tissues from control calves (15,709 CFUs/g). Furthermore, significantly fewer tissue samples from vaccinated calves yielded MAP in culture (21.8 tissues/calf), compared with findings in control calves (27.6 tissues/calf).

Conclusions and Clinical Relevance—Inoculation of calves with a killed MAP vaccine was associated with reduced colonization of intestinal tissues following experimental exposure to MAP. Use of the vaccine could potentially reduce transmission of MAP to calves in infected herds.

Full access
in American Journal of Veterinary Research