Growth of mycobacterium avium in dual species biofilms with Pseudomonas aeruginosa

Abstract

Interest in the growth of M. avium in biofilms has increased in the last few years. Research has shown that M. avium cells in biofilms are more resistant to disinfectants than their planktonic counterparts. Although M. avium has been detected in biofilms in in situ and laboratory models, information available on M. avium is limited compared to biofilm model species such as Pseudomonas aeruginosa, Escherichia coli, Staphylococcus and Streptococcus. The main objective of the present research was to study the growth of M. avium in biofilms in the presence of P. aeruginosa. Biofilms were grown in sterile tap water on stainless steel coupons in batch mode. Two kinds of reactors were used; mason jars and a recirculation system. Each experiment lasted from 27 to 35 days depending upon the nature of the experiment. The two strains were inoculated in isolation (monospecies) and also in combination (dual species).

When inoculated simultaneously, in jar reactor experiments, M. avium density was found lower in dual species than in monospecies biofilms and the difference was statistically significant. However the growth of P. aeruginosa in monospecies did not differ significantly from the dual species biofilms. P. aeruginosa reduced the growth of M. avium. In sequential inoculation experiments an established biofilm of P. aeruginosa did not prevent biofilm formation by M. avium. The growth of M. avium and P. aeruginosa was similar whether they were inoculated as base or invading species. The density of P. aeruginosa remained higher than the density of M. avium in the dual species biofilm, likely due to the higher growth rate of P. aeruginosa compared to that of M. avium. It is important to understand their growth in mixed species biofilms, in order to begin to develop effective methods to both monitor and eventually control this opportunistic pathogen.