Objective:To investigate the antibacterial effect of selected lactic acid bacteria (LAB) biofilms on the planktonic and biofilm population of methicillin-resistant Staphylococcus aureus (MRSA) (S547).Methods:In this study,biofilm-forming LAB were isolated from tairu and kefir.Isolate Y1 and isolate KF were selected based on their prominent inhibition against test pathogens (using spot-on-agar method and agar-well-diffusion assay) and efficient biofilm production (using tissue culture plate method).They were then identified as Lactobacillus casei (L.casei) Y1 and Lactobacillus plantarum (L.plantarum) KF,respectively using 16S rDNA gene sequencing.The influence of incubation time,temperature and aeration on the biofilm production of L.casei Y1 and L.plantarum KF was also investigated using tissue culture plate method.The inhibitory activity of both the selected LAB biofilms was evaluated against MRSA (Institute for Medical Research code:S547) using L.plantarum ATCC 8014 as the reference strain.Results:L.casei Y1 showed the highest reduction of MRSA biofilms,by 3.53 log at 48 h while L.plantarum KF records the highest reduction of 2.64 log at 36 h.In inhibiting planktonic population of MRSA ($547),both L.casei Y1 and L.plantarum KF biofilms recorded their maximum reduction of 4.13 log and 3.41 log at 24 h,respectively.Despite their inhibitory effects being time-dependent,both LAB biofilms exhibited good potential in controlling the biofilm and planktonic population of MRSA (S547).Conclusions:The results from this study could highlight the importance of analysing biofilms of LAB to enhance their antibacterial efficacy.Preferably,these protective biofilms of LAB could also be a better alternative to control the formation of biofilms by pathogens such as MRSA.

Aims: Postbiotic metabolites are metabolic compounds produced by probiotic lactic acid bacteria. These compounds produced by Lactobacillus sp. have been shown to be effective substitutes for in-feed antibiotic in livestock due to their broad inhibitory activity. Therefore, the aim of this study was to determine the effects of various carbon and nitrogen sources on the bacteriocin-inhibitory activity of postbiotic metabolites produced by Lactobacillus plantarum I-UL4. Methodology and results: The effects of various combinations of carbon and nitrogen sources on the bacteriocininhibitory activity (expressed as modified bacteriocin activity, MAU/mL) of postbiotic metabolites produced by L. plantarum I-UL4 were determined in basal media without micronutrients. The combination of glucose (20 g/L) and yeast extract (22 g/L) gave the best bacteriocin-inhibitory activity as compared to other combinations. Maximum bacteriocininhibitory activity of 1440 MAU/mL was achieved when 36.20 g/L of yeast extract was added as the sole nitrogen source in modified de Man, Rogosa and Sharpe (MRS) medium. The glucose concentration was further optimised to enhance the bacteriocin-inhibitory activity of the postbiotic metabolites. Lower bacteriocin-inhibitory activity was observed at 5, 10, 15 and 40 g/L in comparison to 20 g/L of glucose. Conclusion, significance and impact of study: Maximum bacteriocin-inhibitory activity of postbiotic metabolites was achieved at 1440 MAU/mL when 20 g/L of glucose and 36.20 g/L of yeast extract were added as the sole carbon and nitrogen sources respectively in the modified MRS medium. Optimisation of other micronutrients present in MRS media is necessary to further enhance the bacteriocin-inhibitory activity of postbiotic metabolites produced by L. plantarum IUL4.
Lactobacillus

Objective To investigate the antibacterial effect of selected lactic acid bacteria (LAB) biofilms on the planktonic and biofilm population of methicillin-resistant Staphylococcus aureus (MRSA) (S547). Methods In this study, biofilm-forming LAB were isolated from tairu and kefir. Isolate Y1 and isolate KF were selected based on their prominent inhibition against test pathogens (using spot-on-agar method and agar-well-diffusion assay) and efficient biofilm production (using tissue culture plate method). They were then identified as Lactobacillus casei (L. casei) Y1 and Lactobacillus plantarum (L. plantarum) KF, respectively using 16S rDNA gene sequencing. The influence of incubation time, temperature and aeration on the biofilm production of L. casei Y1 and L. plantarum KF was also investigated using tissue culture plate method. The inhibitory activity of both the selected LAB biofilms was evaluated against MRSA (Institute for Medical Research code: S547) using L. plantarum ATCC 8014 as the reference strain. Results L. casei Y1 showed the highest reduction of MRSA biofilms, by 3.53 log at 48 h while L. plantarum KF records the highest reduction of 2.64 log at 36 h. In inhibiting planktonic population of MRSA (S547), both L. casei Y1 and L. plantarum KF biofilms recorded their maximum reduction of 4.13 log and 3.41 log at 24 h, respectively. Despite their inhibitory effects being time-dependent, both LAB biofilms exhibited good potential in controlling the biofilm and planktonic population of MRSA (S547). Conclusions The results from this study could highlight the importance of analysing biofilms of LAB to enhance their antibacterial efficacy. Preferably, these protective biofilms of LAB could also be a better alternative to control the formation of biofilms by pathogens such as MRSA.