Research Sheds Light on Mycobacterium Pathogenicity

NORWAY - Tone Bjordal Johansen of the National Veterinary Institute and colleagues have published a paper in BMC Microbiology. Nine of the 97 isolates examined, all of porcine origin, formed biofilm. The authors conclude that the bacterium's ability to form biofilm relates to its infectious potential.

12 August 2009

3 minute read

Europe

Background

Mycobacterium avium includes the subspecies avium, silvaticum, paratuberculosis and hominissuis, explain Johansen and co-authors. The former, M. avium subsp. avium has been found to cause tuberculosis in captive and free-living birds, while M. avium subsp. hominissuis is an opportunistic environmental pathogen for humans and swine, and occasionally also for other mammals. The most common forms of disease in humans are pulmonary disease, lymphadenitis and disseminated infection, while pigs usually develop localised lymph node lesions.

The aim of this study was to examine isolates of M. avium subsp. avium and M. avium subsp. hominissuis of different origin for biofilm formation and to look for correlations between biofilm formation and RFLP-types, and to standardise the method to test for biofilm formation.

In order to determine the best screening method, a panel of 14 isolates of M. avium subsp. avium and M. avium subsp. hominissuis, were tested for their ability to form biofilm in microtitre plates under different conditions.

Subsequently, 83 additional isolates from humans, swine and birds were tested for biofilm formation.

The isolates were tested for the presence of selected genes involved in the synthesis of glycopeptidolipids (GPLs) in the cell wall of M. avium, which is believed to be important for biofilm formation. Colony morphology and hsp65 sequvar were also determined.

Results

Nine isolates from swine produced biofilm. There was a significant higher frequency of porcine isolates forming biofilm compared to human isolates. All isolates were previously characterised by IS1311- and IS1245-RFLP typing. The ability to form biofilm did not correlate with the RFLP-type, hsp65 sequevar, colony morphology or the presence of gene sequences related to GPL synthesis.

Conclusions

The observed differences in biofilm-forming abilities between porcine and human isolates raises questions regarding the importance of biofilm formation for infectious potential. The optimised method worked well for screening of multiple isolates.

Reference

Johansen, T.B., A. Agdestein, I. Olsen, S.F. Nilsen, G. Holstad and B. Djønne. 2009. Biofilm formation by Mycobacterium avium isolates originating from humans, swine and birds. BMC Microbiology 2009, 9:159. doi:10.1186/1471-2180-9-159.