Biological properties and structural characterization of a novel rhamnolipid like-biosurfactants produced by Lactobacillus casei subsp. casei TM1B.

Biosurfactants are microbial surface-active compounds with antimicrobial and antioxidant activities that display a range of physiological functions. In this study, a strain isolated from a Cameroonian fermented milk "pendidam" and identified as Lactobacillus casei subsp. casei TM1B was used for biosurfactants production. The biosurfactants produced by L. casei TM1B with molasses as the substrate had a good surface (40.77 mN/m) and emulsifying (84.50%) activities. The scavenging of the ABTS+• radical (IC50 value of 0.60 ± 0.03 mg/mL) by the biosurfactants was found to be higher than that of DPPH• radical (IC50 value of 0.97 ± 0.13 mg/mL). The maximum chelating activity of biosurfactants (82.29%) was observed at 3.5 mg/mL. The biologically active compound of the biosurfactants produced by L. casei TM1B was identified as 2,5-O-methylrhamnofuranosyl-palmitate, a novel rhamnolipid-like biosurfactant by using chemical, Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, and NMR analysis. The biosurfactants were bactericidal against several Gram-negative and Gram-positive pathogens (minimum inhibitory concentration values ranged from 3.22 to 12.83 mg/mL), and scanning electron microscope analysis revealed bacterial cell walls and membranes as main targets.

Assessment of the Presence of Total Aflatoxins and Aflatoxin B1 in Fish Farmed in Two Cameroonian Localities.

This work aimed at assessing the presence of total aflatoxins (AFs) and aflatoxin B1 (AFB1) in fish farmed in two Cameroonian localities and the possible origin of that contamination through analysis of fish feeds as well as water and mud collected from the fish farming ponds. Four fish species (kanga, tilapia, catfish, and carp) were collected from two fish farming sites (Mfou and Batié). Mud and water from the farming ponds of the different species and the fish feeds used in these sites were also collected. The samples (34) were analyzed for their levels of AFs and AFB1 using the competitive ELISA method. The results obtained showed that all fish tissue contained AFs and AFB1. A level of AFs higher than the threshold value recommended by the FDA (20 ppb) was observed in catfish (31.38 ± 0.29 ppb). AFs and AFB1 were presented in fish feeds as well as in muds collected from the farming ponds. Catfish was the fish species which mostly bioaccumulated aflatoxins in their tissue. This study presents the state of art on the mycotoxin contamination of fish farmed in some Cameroonian localities and suggests that attention should be paid to the quality of ingredients used to feed fish.