Paula Fajardo Bernárdez

Antimicrobial activities of the bacteriocin-like substances produced by lactic acid bacteria isolated from Moroccan dromedary milk

A total of 450 different colonies, isolated from 25 samples of dromedary milk collected from Laâyoune region of Morocco, were tested for antimicrobial compounds production. Out of these, 30 were determined to be lactic acid bacteria (LAB) and able to inhibit the growth of the indicator strain Listeria innocua CECT 4030. Seven isolates were selected by the large and clear zones of inhibition when tested by the agar well diffusion assay. They were classified by phenotypic and biochemical analysis as two Enterococcus durans (E204 and E214), two Lactococcus lactis (R75 and R76), one Enterococcus faecium R111, one Lactococcus cremoris R112 and one Enterococcus avium R122. Their antimicrobial compounds were detected in cell-free culture supernatant fluids under conditions that eliminate acid and hydrogen peroxide inhibition. The antimicrobial activity was altered after treatment with trypsin, -chymotrypsin, pepsin or papain which confirms the proteinaceous nature of the inhibition. It was heat stable even at autoclaving temperature (121°C for 15 min) and also active over a wide pH range (2 to 10). This fact suggests that bacteriocin-like produced by the seven LAB strains may find application as biopreservatives in food products. Key words: Dromedary milk, lactic acid bacteria, bacteriocin-like substances, antimicrobial activity.

Fed‐batch pediocin production by Pediococcus acidilactici NRRL B‐5627 on whey

Cell growth and pediocin production by Pediococcus acidilactici NRRL B‐5627 on whey were compared by using batch fermentation and re‐alkalized fed‐batch fermentation. The batch fermentations were performed on DWG [DW (diluted whey) supplemented with 1% (w/v) glucose], DWYE [DW supplemented with 2% (w/v) yeast extract] and DWGYE (DW supplemented with 1% glucose plus 2% yeast extract) media. The fed‐batch culture on DWYE medium was fed with a mixture of concentrated whey (48 g of total sugars/l) supplemented with 2% yeast extract and 400 g/l concentrated glucose. The re‐alkalized fed‐batch culture was characterized by higher biomass (6.57 g/l) and pediocin [517.6 BU (bacteriocin activity units)/ml] concentrations compared with the batch processes on MRS (de Man, Rogosa and Sharpe) broth (1.76 g/l and 493.2 BU/ml), DW (0.17 g/l and 57.7 BU/ml), DWG (0.14 g/l and 53.6 BU/ml), DWYE (1.43 g/l and 187.6 BU/ml) and DWGYE (1.28 g/l and 167.3 BU/ml) media. A mixed acid fermentation was observed during the growth of P. acidilactici NRRL B‐5627 in the fed‐batch culture on DWYE medium, and other products (acetic acid and ethanol) in addition to lactic acid accumulated in the medium. Mathematical models were set up to describe fed‐batch production of biomass and pediocin by P. acidilactici. The models developed offer a better fit and a more realistic description of the experimental biomass and pediocin production data when compared with the logistic and Luedeking and Piret [(1959) J. Biochem. Microbiol. Technol. Eng. 1, 431–459] model.

Performance and intestinal coliform counts in weaned piglets fed a probiotic culture (Lactobacillus casei subsp. casei CECT 4043) or an antibiotic.

The production of biomass and antibacterial extracellular products by Lactobacillus casei subsp. casei CECT 4043 was followed in both batch and in realkalized fed-batch cultures. Enhanced concentrations of biomass and antibacterial extracellular products were obtained with the use of the latter fermentation technique in comparison with the batch mode. The culture obtained by fed-batch fermentation was mixed with skim milk and used to prepare a probiotic feed for weaned piglets. To test the effect of the potentially probiotic culture of L. casei on body weight gain, feed intake, feed conversion efficiency, and on fecal coliform counts of piglets, two groups of animals received either feed supplemented with the probiotic preparation or avilamycin for 28 days. The control group was fed nonsupplemented feed. At the end of the administration period (day 28), the groups receiving probiotic and avilamycin exhibited the highest average body weight gain values, although the mean feed intake and feed conversion efficiency values were not different among the groups (P > 0.05). For the entire experimental period (42 days), the control group exhibited the lowest feed intake value, the probiotic group exhibited the highest feed conversion efficiency value, and the antibiotic group exhibited the highest body weight gain (P 0.05). Fecal coliform values decreased (although not significantly) by day 28 in the three groups. However, the mean counts returned to pretreatment levels by day 42 in all groups.

Growth of Enterococcus durans E204 producing bacteriocin-like substance in MRS Broth: Description of the growth and quantification of the bacteriocin-like substance

Bacteriocin-like substance E204 is an antimicrobial compound produced by Enterococcus durans E204 isolated from camel milk of Morocco that shows a broad spectrum of inhibitory activity against taxonomically related microorganisms. It is sensitive to digestive proteases. In the first study, de Man, Regosa and Sharpe (MRS) broth was inoculated by E204 strain, incubated for 30°C at 200 rpm and monitored by checking dry cell weight, nutrients consumption, lactic acid and bacteriocin-like productions. The maximum biomass (2.3 g/l) and antimicrobial activity (32 AUml -1 ) were obtained at 12 h of incubation. No increase in the production of bacteriocin-like was recorded after the exponential phase. In the other hand, the quantification of the antimicrobial activity was carried out by a photometric assay on culture tubes based on the determination of the ID50 dose causing 50% growth inhibition of Enterococcus faecium 410 CECT in 6 h of incubation. The highest bacteriocin-like titre (279.71 BUml -1 ) was obtained at acidic pH (3.5) and at 70°C after 10 min of incubation. Key words : Enterococcus durans, bacteriocin-like, MRS broth, nutrients consumption, quantification.