Objective—To compare sensitivity of several methods
of bacteriologic culture of pooled bovine fecal
samples for detection of Mycobacterium paratuberculosis
and evaluate homogeneity in number of
M paratuberculosisin pooled fecal samples.
Sample Population—Feces from 10 dairy cows that
shed M paratuberculosis at various concentrations
and 1 dairy cow known to be free of infection with
Procedure—5 fecal pooling methods, 2 culture methods,
and 2 pool sizes were evaluated. Each pooled
sample contained 1 infected sample and 4 or 9 uninfected
Results—Sensitivity of detection of M paratuberculosis was
greater with smaller pool size (5 vs 10 samples/
pool). Detection sensitivity was also associated
with concentration of bacteria in the infected sample.
Results indicated that, compared with concurrent
bacterial culture of individual infected samples, 37 to
44% of pooled samples with low bacterial concentrations
yielded positive culture results and 94% of
pooled samples with high bacterial concentrations
yielded positive results.
Conclusions and Clinical Relevance—Bacteriologic
culture of pooled fecal samples may provide a valid
and cost-effective method of detecting M paratuberculosis
infection in cattle herds. (Am J Vet Res
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.
Objective—To evaluate sensitivity of microbial culture
of pooled fecal samples for detection of
Mycobacterium avium subsp paratuberculosis (MAP)
in large dairy herds and assess the use of the method
for estimation of MAP prevalence.
Animals—1,740 lactating cows from 29 dairy herds
Procedure—Serum from each cow was tested by
use of a commercial ELISA kit. Individual fecal samples
were cultured and used to create pooled fecal
samples (10 randomly selected fecal samples/pool; 6
pooled samples/herd). Sensitivity of MAP detection
was compared between Herrold's egg yolk (HEY) agar
and a new liquid culture method. Bayesian methods
were used to estimate true prevalence of MAP-infected
cows and herd sensitivity.
Results—Estimated sensitivity for pooled fecal
samples among all herds was 0.69 (25 culture-positive
pools/36 pools that were MAP positive).
Sensitivity increased as the number of culture-positive
samples in a pool increased. The HEY agar
method detected more infected cows than the liquid
culture method but had lower sensitivity for
pooled fecal samples. Prevalence of MAP-infected
cows was estimated to be 4% (95% probability
interval, 2% to 6%) on the basis of culture of
pooled fecal samples. Herd-level sensitivity estimate
ranged from 90% to 100% and was dependent
on prevalence in the population and the sensitivity
for culture of pooled fecal samples.
Conclusions and Clinical Relevance—Use of pooled
fecal samples from 10 cows was a cost-effective tool
for herd screening and may provide a good estimate
of the percentage of MAP-infected cows in dairy
herds with a low prevalence of MAP. (Am J Vet Res