Bacteriófagos aplicados ao controle microbiano em sistemas de resfriamento industriais

Abstract

Bacteriophages (phages), viruses that infect bacteria, have been widely used as microbial control agents in different sectors due to their ability to reduce or eliminate bacterial populations. In this study, we explored the application of bacteriophages isolated from a cooling system to control bacteria also isolated from the same system. To this end, we used two benchtop bioreactors, which have continuous flow, controlled temperature at 37°C and fed with synthetic water with a composition similar to that of an industrial cooling system. The phages were characterized regarding host spectrum, multiplicity of infection (MOI), bacteriolytic activity, infectivity in different pH conditions (6.5; 7; 7.5; 8 and 8.5) and temperature (30.35, 40 and 45°C) through tests carried out in a Varioskan type Elisa reader, in addition to tests carried out in 250 mL bottles and morphological characterization via transmission electron microscopy (TEM), followed by the extraction of viral genetic material for subsequent characterization genomics. The results demonstrated that all 34 phages analyzed showed polyvalence. Of these, 10 phages were characterized as tailed phages through TEM morphology analysis. Three phages were evaluated at three different MOIs (1,10 and 100), where MOI100 was more effective for phages B1 and 12.1.2 and MOI 1 for phage18.1.4. In infectivity tests in liquid media, 3 bacteriophages were tested in 12 bacteria. In this experiment, 6 bacterial species were identified (Sphingopyxis macrogoltabida, Bacillus. pumilus, Acinetobacter sp., Pseudomonas aeruginosa, Serratia marcescens and Stenotrophomonas maltophilia) that showed greater reductions in density when treated by 6 phages (12.1.2; P2, 12.2.2, 12.3.3, 18.1.4 and B1). Infectivity experiments in different pH and temperature ranges showed that lytic activities were greater at pH between 6.5 and 7.5 and between 30 and 45°C. In experiments evaluating the effectiveness of phage therapy in reactors, they were inoculated with a mixture of 3 or 6 bacterial species and corresponding phages, tested in the infectivity test in liquid medium. The results regarding bacterial density monitoring demonstrated that in the experiments treated with phages there was bacterial control in the sessile form (maximum reduction of 100 times) and planktonic form (maximum control of 10 times), in which the control rates of bacteria in biofilm were shown to be most promising.