Laboratory evaluation of Lactobacillus johnsonii CRL1647 metabolites for biological control of Musca domestica

Abstract

The house fly, Musca domestica L. (Diptera: Muscidae), is a key problem in animal producing and rearing areas. Currently, the use and abuse of chemical pest-control compounds has generated resistance in M. domestica and, hence, new approaches are required. In this work, the potential entomopathogenic activity of Lactobacillus johnsonii Fujisawa et al. CRL1647 was evaluated against M. domestica, under laboratory conditions. Bioassays were done for three consecutive years using bacterial cell suspensions (CS) and cell-free supernatants (CFS) under controlled conditions (27 ± 1 °C, 57 ± 2% r.h., and L12:D12 photoperiod). Both the CS and CFS displayed high levels of larvicidal (96%) and pupicidal (97%) activities. Chemical characterization of the CFS revealed that the bioactive metabolites are acidic compounds, not affected by thermal treatment or by trypsin. Organic acids were identified and quantified by high-performance liquid chromatography (HPLC); only lactic acid (129.7 ± 1.0 mM), acetic acid (37.3 ± 0.8 mM), and phenyllactic acid (0.3 ± 0.1 mM) were detected. A significant decrease in fecundity of the house flies was observed in females from larvae fed on CFS; male fertility was not affected. Interestingly, only the mixture of organic acids exerted the biological effects. These results suggest that the metabolites synthesized by L. johnsonii CRL1647 can be used in a novel biocontrol strategy against house flies.