Rj. Whittington et al., Evaluation of modified BACTEC 12B radiometric medium and solid media for culture of Mycobacterium avium subsp. paratuberculosis from sheep, J CLIN MICR, 37(4), 1999, pp. 1077-1083
Definitive diagnosis of Johne's disease in ruminants depends on confirming
the presence of the causative bacterium, Mycobacterium avium subsp, paratub
erculosis, in tissues of the host. This is readily achieved in most ruminan
t species by culture. However, culture of clinical specimens from sheep in
many countries has been unrewarding. Such a culture from sheep was achieved
recently in Australia by using a radiometric culture medium. The aims of t
he present study were to evaluate the culture of M. avium subsp, paratuberc
ulosis from sheep by using modified BACTEC 12B radiometric medium, to deter
mine the sensitivity of culture in relation to histopathology, and to evalu
ate a range of solid media. Culture of M. avium subsp. paratuberculosis fro
m sheep with Johne's disease is a sensitive method of diagnosis: intestinal
tissues from all 43 animals with multibacillary disease and all 22 animals
with paucibacillary disease were culture positive, while 98% of feces from
53 animals with multibacillary disease and 48% of feces from 31 animals wi
th paucibacillary disease were culture positive. Of sheep without histologi
cal evidence of Johne's disease from infected flocks, intestinal tissue fro
m 32% of 41 were culture positive, while feces from 17% of 41 were culture
positive. Consequently, culture is recommended as the "gold standard" test
for detection of ovine Johne's disease. Of the wide range of solid media th
at were evaluated, only modified Middlebrook 7H10 and 7H11 agars, which wer
e very similar in composition to modified BACTEC 12B medium, yielded growth
of ovine strains of M. avium subsp, paratuberculosis, The sensitivity of d
etection of M. avium subsp, paratuberculosis on solid media was slightly lo
wer than that in modified BACTEC 12B radiometric medium. Both egg yolk and
mycobactin J were essential additives for growth of ovine strains of M. avi
um subsp, paratuberculosis in both liquid and solid media.