Dynamics of relationship between the presence of Coxiella burnetii DNA, antibodies, and intrinsic variables in cow milk and bulk tank milk from Danish dairy cattle.

Milk samples of 12 Danish dairy herds were collected 3 times during an 11-mo period and tested for Coxiella burnetii DNA by real-time PCR, detecting the IS1111 element, and for the presence of antibodies against the bacterium by ELISA. On average, 25% of 1,514 samples were seropositive and 32% were positive for C. burnetii DNA. Among the 485 DNA-positive samples, quantification cycle values ranging from 15.8 to 37.8 were found. Test sensitivity did not increase after DNA extraction from the cream fraction compared with full milk. The relationship between antibody levels and bacterial shedding was investigated among 166 cows from 9 herds. The prevalence levels of C. burnetii DNA and antibodies in the herds were found to be rather stable for 6 of the herds. The test results were highly influenced by results obtained 3 to 7 mo earlier. A significant association between the antibody titer and the DNA shedding level at the same and the preceding visit was found. In addition, a significant association between the antibody titer and the antibody titers 3 to 11 mo earlier was found. A multivariable analysis identified a significant increase in C. burnetii DNA shedding with increasing parity and increasing protein concentration in milk. The antibody levels in bulk tank milk and prevalence levels of C. burnetii DNA and antibodies in individual cow milk samples were correlated. A significant correlation was also found between the quantification cycle values of the cow samples (weighted according to milk yield) and the C. burnetii concentration in bulk tank milk.

Comparison of contamination and growth of Mycobacterium avium subsp. paratuberculosis on two different media.

AIMS: The purpose of the study was to compare the growth of Mycobacterium avium subsp. paratuberculosis (Map) and the degree of contamination on Herrold's egg yolk medium (HEYM) and modified Löwenstein-Jensen medium (LJ). METHODS AND RESULTS: Culture of 2513 faecal samples from dairy cows was performed on each of the two media. The media were read after 5, 8 and 12 weeks of incubation. Overall, the proportion of contaminated samples was significantly higher on LJ (14.2%) than on HEYM (13.2%) after 12 weeks but the degree of contamination was slightly less on LJ. After 8 weeks of incubation, only 1.0% of the samples were Map positive in LJ with 4.9% on HEYM. After 12 weeks of incubation, 3.3% of the samples were Map positive in LJ whereas 6.9% were positive in HEYM. All suspect and culture positive samples were confirmed by IS900 PCR. CONCLUSIONS: HEYM supported growth of Map significantly better and faster than LJ, however it could not be determined conclusively which of the two media that provided the highest degree of decontamination when the incubation time was also included. SIGNIFICANCE AND IMPACT OF THE STUDY: HEYM should be the primary medium rather than LJ for detection of Map in cattle.

Analysis of repeated tests for interferon-gamma (IFN-gamma) response and faecal excretion for diagnosis of subclinical paratuberculosis in Danish cattle.

A total of 315 cattle were tested for infection with Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) at three consecutive samplings, using the interferon-gamma (IFN-gamma) test on whole blood and bacteriological culture of faecal samples. Of 205 cattle from 10 infected herds 99 (48%) were positive in the IFN-gamma test on at least one sampling using "IDEXX-criteria" for interpretation, and of 110 cattle from five non-infected herds three (3%) were positive. Forty-four animals from infected and one from non-infected herds tested positive at all three samplings. Although support for the specificity of the IFN-gamma test was provided by these results, they also indicate problems with false positives. Approximately half of the positive animals did not give the same result at all three samplings, indicating that repeated testing increases the chance of detecting reactors. Changing, or fluctuating, IFN-gamma test results occurred most frequently in animals younger than 1 year, indicating that the IFN-gamma test should be applied only to animals 1 year and older. M. paratuberculosis was isolated from 16 (4%) of 371 cattle, all from infected herds. Fifteen culture-positive cattle tested positive at least once in the IFN-gamma test. It was not possible to predict from the IFN-gamma test result the number of animals that would eventually develop disease. However, the test may be useful to detect animals that have been exposed to M. paratuberculosis earlier in their lives, and the testing of young cattle could be included in a control program to check for the effectiveness of preventing transmission of infection to calves and to identify animals at risk of developing disease later in their lives.

[Inhibition of Proteus sp. by Nalidixic acid]. / Nalidixinsyre som Proteus sp. vaeksthaemmer

The investigation comprised 192-positive and Gram-negative strains of bacteria, including 111 Proteus sp. The degree of resistance of these strains to nalidixic-acid was investigated on blood agar with 25 mug, 40 mug, and 50 mug nalidixin-acid per ml medium. None of the Proteus strains were able to grow on medium with 50 mug nalidixic-acid per ml, whereas Streptococcus sp., Corynebacterium pyogenes, Peptococcus indolicus, Pseudomonas aeruginosa, and beta-toxic staphylococci all were found resistant to this concentration (Tables I and II), and could be reisolated in pure culture after having grown together with a Proteus strain on such medium (Table III). Blood agar with 50 mug nalidixic-acid per ml is therefore suitable for isolation of the above mentioned Gram-positive bacteria and Pseudomonas aeruginosa from Proteus contaminated material.