Acid stress responses of Lactobacillus amylovorus and Candida kefyr isolated from fermented sorghum gruel and their application in food fermentation.

Exposure of lactic acid bacteria (LAB) and yeasts to adverse fluctuations during fermentation causes stress; consequently, microbes develop adaptive responses. In this study, we investigated the physiological and proteomic responses of LAB and yeast to acid stress and their application in food fermentation. The physiological and proteomic responses of Lactobacillus amylovorus LS07 and Candida kefyr YS12 to acid stress were measured using turbidimetry, SDS-PAGE, and LC-MS/MS. The technique previously reported by the Association of Official Analytical Chemists (AOAC) was employed to evaluate the physicochemical and organoleptic properties of sorghum gruel fermented using LAB and yeast alone and in combination as starter cultures and spontaneous fermentation as a control. The growth of L. amylovorus LS07 was optimal at pH 1.0, and that of C. kefyr YSI2 was optimal at pH 4. An increased intensity of 30S ribosomal protein S2 (L. amylovorus LS07) and 6-phosphogluconate dehydrogenase (C. kefyr YS12) was observed at pH 1 and 4, respectively, suggesting increased microbial metabolism, thereby reducing the stress. Sorghum gruel produced with combined starters had the highest crude protein (10.94%), iron content (0.0085%), and organoleptic acceptability (7.29), which was significantly different from the products produced with the single starters and the control. The combined starter (L. amylovorus LS07 and C. kefyr YSI2) adapted to stress yielded foods with improved sensory properties, minerals, and reduced anti-nutrient contents.

Antimicrobial resistance in coagulase-negative staphylococci from Nigerian traditional fermented foods.

BACKGROUND: Coagulase-negative staphylococci have become increasingly recognized as the etiological agent of some infections. A significant characteristic of coagulase-negative staphylococci especially strains isolated from animals and clinical samples is their resistance to routinely used antibiotics although, resistant strains isolated from fermented foods have not been fully reported. METHODS: A total of two hundred and fifty-five CoNS isolates were subjected to antimicrobial susceptibility test using the disc diffusion technique. The minimum inhibitory concentration of the isolates to the tested antibiotics was determined using the microbroth dilution method. Methicillin resistant strains were confirmed by detection of methicillin resistant genes (mecA) and also employing cefoxitin screening test. RESULTS: The isolates were confirmed to be methicillin resistant by the detection of mecA genes and the cefoxitin screening test. The isolates demonstrated appreciable resistance to ampicillin (86.7%), sulfomethoxazole-trimethoprim (74.9%), amoxicillin-clavulanic acid (52.5%) and oxacillin (35.7%). Methicillin resistance was exhibited by 13 out of the 255 isolates although no mecA gene was detected. It was also observed that the methicillin resistant isolates were prevalent in these traditional foods; iru, kindirmo, nono and wara. CONCLUSION: This study has ameliorated the incidence of multiple antibiotic resistant coagulase-negative staphylococci in Nigerian fermented foods and if not tackled adequately might lead to horizontal transfer of antibiotic resistance from food to man.

Virulence and toxigenicity of coagulase-negative staphylococci in Nigerian traditional fermented foods.

The incidence of coagulase-negative staphylococci (CoNS) may render food unsafe, as the clinical isolates have been reported to exude virulent traits. A total of 255 CoNS isolates from 6 traditional fermented foods (nono, kunu, wara, iru, ogi, and kindirmo) from North Central Nigeria, identified as Staphylococcus epidermidis, Staphylococcus simulans, Staphylococcus xylosus, Staphylococcus kloosii, and Staphylococcus caprae, were investigated for virulence traits. The strains were examined for biofilm formation and production of hyaluronidase, DNase, TNase, haemolysins, and superantigenic toxins (SEA, SEB, SEC, SED, and TSST-1) using standard and genotypic methods. The analysis of virulence factors revealed the production of slime in 200 isolates (78.4%); α-haemolysin in 136 (53.3%); ß-haemolysin in 43 (16.9%); DNase in 199 (78.0%); TNase in 29 (11.4%); hyaluronidase in 125 (49.0%); TSST-1 in 119 (46.7%); and enterotoxin-producing isolates SEA, SEB, SEC, and SED in 61 (23.9%), 19 (7.5%), 9 (3.5%), and 8 (3.1%), respectively. PCR analysis detected tsst-1, sea, seb, and sec genes. The ability of these microorganisms to exhibit virulence evokes the potential to cause disease especially under determinate conditions or in immune-compromised patients. The occurrence of CoNS in food should not be ignored nor their pathogenic potential considered as insignificant, rather safety measures should be taken to reduce or totally eliminate their occurrence in foods.

Antibacterial activities of lactic acid bacteria isolated from selected vegetables grown in nigeria: a preliminary report

Members of lactic acid bacteria (LAB) are known probiotics and have been reported to have antimicrobial properties. Although various researchers have documented the isolation of these bacteria from fruits and vegetables; studies on LAB associated with lettuce; cucumber and cabbage are limited and non-existing in Nigeria. This study was designed to assess lettuce; cucumber and cabbage as potential sources of LAB and investigate the actions of their bacterial cell supernatants (BCS) on some pathogenic bacteria. Using standard microbiological methods; isolated LAB were identified to species level with API 50 CH kits (Biomerieux; France). Cell free supernatants (CFS) from de Man Rogosa Sharpe (MRS) broth cultures of the LAB strains were used to challenge Pseudomonas aeruginosa ATCC 27853; Enterococcus faecalis ATCC 29212; Escherichia coli ATCC 12900 and Proteus penneri ATCC 13315 by agar well diffusion method. The control consisted of the sterile MRS broth subjected to the same growth conditions as LAB broth cultures. A total of four lactic acid bacteria were isolated as follows: Pediococcus pentosaceus 2 from cucumber; Lactobacillus cellobiosus from cabbage; Lactobacillus salivarius and Lactobacillus plantarum 1 from lettuce. Pediococcus pentosaceus 2 and L. salivarius showed inhibitory effects on all the standard strains tested while L. plantarum 1 showed no inhibitory activity against E. faecalis and E. coli. Lactobacillus cellobiosus showed inhibition against all except P. penneri. Although; the molecular characterisation and probiotic potentials of these LAB strains are being investigated in an on-going study; we presumed these vegetables are prospective sources of the bacteria in Nigeria and therefore the need to extensively investigate the vegetables and other related vegetables becomes imperative

Antagonistic activity of bacteriocin produced by Lactobacillus species from ogi, an indigenous fermented food.

Seven Lactobacillus species each with one or more strains were isolated from various fermented cereal gruel's (ogi). They were identified as L. plantarum (3 strains), L. delbrueckii (1 strain), L. brevis (2 strains), L. reuteri (2 strains), L. casei (1 strain), L. fermentum (1 strain) and L. acidophilus (1 strain). Bacteriocin production was observed in cell-free supernatants of 8 of these strains with L. fermentum, L. delbrueckii and L. reuteri strains (white maize ogi) being negative. The bacteriocin produced by the eight strains inhibited the growth of various target organisms with the inhibition strongly noticed using Enterococcus faecalis as indicator. While catalase treatment, pH changes and heat treatment up to 80 degrees C had no effect on the activity of bacteriocin from these isolates, treatment with trypsin and proteinase K resulted in complete loss of inhibitory activity of the bacteriocins. A reduction in the inhibitory activity of the bacteriocins was also found to occur with increasing concentrations of glucose or peptone in the cultivation medium.