In this study, seven bacteriocinogenic and non-bacteriocinogenic LAB strains previously isolated from the intestines of Nile tilapia and common carp and that showed potent antibacterial activity against host-derived and non-host-derived fish pathogens were assayed for their probiotic and safety properties so as to select promising candidates for in vivo application as probiotic in aquaculture. All the strains were investigated for acid and bile tolerances, transit tolerance in simulated gastrointestinal conditions, for cell surface characteristics including hydrophobicity, co-aggregation and auto-aggregation, and for bile salt hydrolase activity. Moreover, haemolytic, gelatinase and biogenic amine-producing abilities were investigated for safety assessment. The strains were found to be tolerant at low pH (two strains at pH 2.0 and all the strains at pH 3.0). All of them could also survive in the presence of bile salts (0.3% oxgall) and in simulated gastric and intestinal juices conditions. Besides, three of them were found to harbour the gtf gene involved in pH and bile salt survival. The strains also showed remarkable cell surface characteristics, and 57.14% exhibited the ability to deconjugate bile salts. When assayed for their safety properties, the strains prove to be free from haemolytic activity, gelatinase activity and they could neither produce biogenic amines nor harbour the hdc gene. They did not also show antibiotic resistance, thus confirming to be safe for application as probiotics. Among them, Lactobacillus brevis 1BT and Lactobacillus plantarum 1KMT exhibited the best probiotic potentials, making them the most promising candidates.

The present study aimed to evaluate the bacterial load of water, Nile Tilapia and common Carp intestines from earthen ponds, isolate lactic acid bacteria (LAB) and assess their antimicrobial activity against fish spoilage and pathogenic bacteria. Following enumeration and isolation of microorganisms the antimicrobial activity of the LAB isolates was evaluated. Taxonomic identification of selected antagonistic LAB strains was assessed, followed by partial characterisation of their antimicrobial metabolites. Results showed that high counts (>4 log c.f.u ml or 8 log c.f.u g) of total aerobic bacteria were recorded in pond waters and fish intestines. The microbiota were also found to be dominated by Salmonella spp., Vibrio spp., Staphylococcus spp. and Escherichia coli. LAB isolates (5.60%) exhibited potent direct and extracellular antimicrobial activity against the host-derived and non host-derived spoilage and pathogenic bacteria. These antagonistic isolates were identified and Lactococcus lactis subsp. lactis was found as the predominant (42.85%) specie. The strains displayed the ability to produce lactic, acetic, butyric, propionic and valeric acids. Bacteriocin-like inhibitory substances with activity against Gram-positive and Gram-negative (Vibrio spp. and Pseudomonas aeruginosa) bacteria were produced by three L. lactis subsp. lactis strains. In this study, the LAB from the microbiota of fish and pond water showed potent antimicrobial activity against fish spoilage or pathogenic bacteria from the same host or ecological niche. The studied Cameroonian aquatic niche is an ideal source of antagonistic LAB that could be appropriate as new fish biopreservatives or disease control agents in aquaculture under tropical conditions in particular or worldwide in general.

Twenty-one Lactobacillus isolates from “Sha’a” (a maize – based fermented beverage) and “Kossam” (traditionally fermented cow milk) were selected in accordance with their antagonistic activities and tested for their bacteriocinogenic potential as well as safety properties. These isolates were preliminarily identified as Lactobacillus plantarum (62%), Lactobacillus rhamnosus (24%), Lactobacillus fermentum (10%) and Lactobacillus coprophilus (4%) based on phenotypic characteristics and rep-PCR genomic fingerprinting. Twelve (57.1%) out of the 21 strains tested were found to be bacteriocin producers, as revealed by the sensitivity of their antimicrobial substances to proteolytic enzymes (Trypsin, Proteinase K) and inhibition of other Lactobacillus spp. These bacteriocinogenic strains showed no positive haemolytic and gelatinase activities and proved to be sensitive to penicillin G, ampicillin, tetracycline, erythromycin, amoxicillin, chloramphenicol, co-trimoxazole and doxycyclin, but resistant to ciprofloxacin and gentamicin. The bacteriocins showed a broad inhibitory activity against Gram-positive and Gram-negative pathogenic bacteria, several of which are classified as especially dangerous by the World Health Organization, as well as Multidrug-resistant strains. These include Staphylococcus aureus, Salmonella enterica subsp. enterica serovare Typhi, Bacillus cereus, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Shigella flexneri. These Lactobacillus strains are promising candidates for use as protective cultures in food fermentation.

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This study was conducted to evaluate the biopreservative potential of Lactobacillus plantarum Lp6SH (Lp6SH), Lactobacillus rhamnosus Yoba (LrYoba) and their cell‐free supernatants (CFS) on whole captured tropical pink shrimps (Penaeus duorarum notialis) during storage at 4°C for 8 days. Shrimps were inoculated with strains Lp6SH, LrYoba, their supernatants, sodium metabisulfite (2%) and stored at 4 ° C for 8 days. Sensory evaluation, physicochemical, and microbiological analyses were performed daily. Lp6SH, CFS of Lp6SH, and CFS of LrYoba were able to prolong the sensory shelf life up to 8 days. The total volatile basic nitrogen (TVBN) concentration was lower than the acceptable value at the end of the storage period. All the treatments reduced the number of total aerobic bacteria and fungi, and maintained the coliforms count for 2 days. Strain Lp6SH reduced the number of Staphylococci for 4 days. Based on the threshold values, the microbiological shelf life of shrimps was between 2 and 6 days at 4°C. L. plantarum Lp6SH and the CFS of L. rhamnosus Yoba could be used as natural preservatives to replace the use of sodium bisulfate in prolonging the microbiological and sensory shelf life of captured whole shrimps. Practical applications Microbial spoilage of raw fresh shrimps and black spots formation constitute substantial economic losses as well as serious public health problem. Due to the harmful effects of chemical preservatives, attention is paid nowadays to the search for fresh shrimp preservation methods that could obviate the use of chemicals and prevent blackspot formation. In this respect, the results of this study supported that Lactobacillus plantarum Lp6SH strain and the cell‐free supernatant of Lactobacillus rhamnosus Yoba are suitable biopreservatives that could be used to increase the safety, prevent melanosis, and extend the sensory shelf life of captured whole shrimps stored under refrigeration. After studies for their application at large scale, the fishermen and food industries can use the bacterial suspension and the cell‐free supernatant as spray or immersion solutions for the treatment of shrimps (or other seafood) prior to freezing.

The objective of this study was the evaluation of safety, adhesion and antioxidant properties of five L. plantarum strains isolated from the digestive tract of honey bees. The set of variables generated from this study was submitted to a normalized Pearson (n) Principal Component Analysis (PCA). The five L. plantarum strains showed no gelatinase activity and were checked to be non-hemolytic. They were susceptible to chloramphenicol, amoxicillin, penicillin G and tetracycline. The MICs were ranged between 1-4 µg/ml for erythromycin and resistance was observed among 80% of strains (L. plantarum H15, H21, H24, and H28). A significantly high percentage of hydrophobicity in n-hexane was observed with L. plantarum H47 (71.99±1.39) followed by L. plantarum H28 (65.68±1.49) while the highest value in the presence of chloroform, belonging L. plantarum H24 and L. plantarum H28 (28.39±0.88 and 23.58±0.68 respectively). Both the Intact Cells (ICs) and Cell-Free Supernatants (CFSs) of L. plantarum H24 strain displayed the higher percentage (p 0.05) of DPPH radical scavenging activity (76.58±0.55% and 59.13±4.01% respectively). With the HRS activity, ICs of L. plantarum H24 strain exhibited the highest (p > 0.05) activity (73.37±0.62%) whereas, the CFS of L. plantarum H47 was the best (29.49±1.28%, p > 0.05). In allpurpose, based on PCA, L. plantarum H28, and L. plantarum H24 seem to be quite promising as they possessed the best properties tested. Accordingly, they can be chosen as representative of the potential probiotic strains.