Modifications of Dubos's media for the cultivation of Mycobacterium johnei

Factors affecting isolation and identification of Mycobacterium avium subsp. paratuberculosis from fecal and tissue samples in a liquid culture system

Culture of Mycobacterium avium subsp. paratuberculosis is the definitive diagnostic test for Johne's disease, a chronic granulomatous enteropathy of animals. Compared to solid media, the identification of all strains of the organism in liquid media can be more difficult because the appearance of colonies and mycobactin dependence are not observable, and the growth of other organisms needs to be distinguished, commonly by PCR. Factors affecting the isolation rate of S strains and the contamination rate in modified Middlebrook 7H9 broth (Bactec 12B) and 7H10 agar were studied using 11,598 fecal samples and 2,577 tissue samples from sheep from 1,421 farms over 10 years. Minimization of contamination in Bactec cultures required the avoidance of the carryover of fecal particles from the first sedimentation step in the double-incubation centrifugation method, and contamination was reduced significantly by incubating the sample in a solution containing vancomycin, amphotericin B, and nalidixic acid for 3 days compared to 2 days. The growth of irrelevant microorganisms confounded the identification of M. avium subsp. paratuberculosis in liquid culture by inhibiting IS900 PCR and in solid medium culture by inhibiting the growth of M. avium subsp. paratuberculosis or obscuring colonies. The contamination of samples was clustered in certain laboratory submissions and was reduced by including ampicillin in Bactec medium without affecting the odds of isolation of M. avium subsp. paratuberculosis. The long-term contamination rate for fecal cultures was about 7%, and that for tissue cultures was <0.2%. Liquid medium was more sensitive than solid medium culture for M. avium subsp. paratuberculosis. The applicability of these findings for C strains is discussed.

USE OF ARTHROBACTER TERREGENS FOR BIOASSAY OF MYCOBACTIN

Reich, Claude V. (Johns Hopkins-Leonard Wood Memorial Leprosy Research Laboratory, Johns Hopkins University, Baltimore, Md.), and John H. Hanks. Use of Arthrobacter terregens for bioassay of mycobactin. J. Bacteriol. 87:1317-1320. 1964.-Arthrobacter terregens was used to assay mycobactin, a growth factor for Mycobacterium paratuberculosis. Within 7 days, A. terregens gave a linear photometric growth response to mycobactin in the range of 0.05 to 0.2 mug/ml. Preparations found to be active (or inactive) by this assay produced corresponding effects on the growth of M. paratuberculosis after 6 weeks to 4 months. Mycobactin was produced routinely from pellicles of M. phlei on a peptone-glycerol-beef heart infusion medium, and was extracted from both cells and medium by organic solvents. The mycobactin content per cell rose rapidly after the third day and attained a maximum at 4 to 6 days. The decline to less than one-half this value by the tenth day was associated with excretion into the medium. Production on synthetic media occurred after increasing the usual levels of asparagine. The demonstrated effects of crude mycobactin on the donor strain were (i) to catalyze the onset of growth and (ii) to reverse the effect of conditions which cause the formation of abnormal cells.

The efficacy of mesenteric lymph node biopsy in the eradication of paratuberculosis from an infected dairy farm

Lymph node biopsy was performed on animals older than nine months on a dairy farm which carried 223 animals and was severely affected by paratuberculosis. Biopsies were examined histologically and bacteriologically for the presence of M. paratuberculosis infection. In this way paratuberculosis infection was diagnosed in 29 animals, in which other diagnostic methods (serum complement fixation test, intradermal johnin test and microscopic examination of the faeces) produced negative results. The value of lymph node biopsy is the early detection of infected animals. In the two years after the biopsies, no further cases of clinical paratuberculosis were detected on the affected farm, although infection with M. paratuberculosis persisted.

Isolation of Mycobacterium paratuberculosis from intestinal mucosa and mesenteric lymph nodes of goats by use of selective Dubos medium

To isolate Mycobacterium paratuberculosis from contaminated material, a selective medium, selective Dubos medium (SDubos), was developed by supplementing conventional Dubos medium (CDubos) with carbenicillin, polymyxin, trimethoprim, and amphotericin B. The intestine and mesenteric lymph nodes of 1,501 goats were cultured in parallel on SDubos and CDubos after decontamination with oxalic acid. The contamination rate was reduced more than 150 times by the use of SDubos. The number of positive specimens (18, or 1.2%), i.e., those which revealed growth of M. paratuberculosis, was too small to evaluate the number of specimens which could have been missed due to contamination on CDubos. However, the number of specimens positive on SDubos (16, or 89%) showed that the antibiotics used were not harmful to M. paratuberculosis.