Introduction

Testing of beef herds in Texas for paratuberculosis has identified herds with high proportions of seropositive results. In some of these herds, several atypical mycobacteria were isolated from fecal samples. The objective of this study was to investigate the association between atypical mycobacteria in the environment and 1) herds with high or low seroprevalence to Mycobacterium avium subsp. paratuberculosis (M. ptb.) as well as 2) chemical characteristics of the environment.

Methods

Six beef cattle herds with a high seroprevalence for M. ptb. and three closely located herds without a previously high seroprevalence were identified in 2003. In 2004, between six and 13 environmental samples were sampled from these nine farms. Environmental samples were collected from water and soil. Soil samples were cultured using the BACTEC® system for mycobacteria. Acid fast organisms were tested with IS900 PCR, and mycolic acid analyses using HPLC was used to characterize IS900 negative mycobacteria. The Wilcoxon test was used compare the proportion of environmental mycobacteria positive samples for the two herd types and the t-test was used to compare chemical characteristics and isolation of atypical environmental mycobacteria.

Results

Atypical mycobacteria isolated from soil and water included non-identifiable mycobacteria (n=3) M. scrofulaceum (n=2), M. avium complex (n=2), M. avium-intracellulare-scrofulaceum complex (n=2), M. terrae complex (n=1), M. gordonae (n=1), M. abscessus (n=1), M. asiaticum (n=1). Overall, 17.5% and 0.03% of samples were positive for atypical mycobacteria for herds with high and low M. ptb. seroprevalence (P=0.24). Isolation of atypical mycobacteria from soil was positively associated with high iron content (P<0.001), low pH (P<0.001), low Calcium (P=0.008), and high Manganese (P=0.004). In water, isolation of atypical mycobacteria was positively associated with high Manganese (P<0.001), high Potassium (P=0.002), and low pH (P=0.034).

Conclusions

Environmental atypical mycobacteria may be ingested by cattle and possibly cause cross reactions on antibody tests for M. ptb.