Abstract
Problem statement: This study reports the isolation of lactic acid bacteria from 13 honey samples produced in Malaysia, Libya and Saudi Arabia and their antibacterial activity against three Gram negative pathogenic bacteria. Approach: A modified MRS agar with 0.8% CaCO3 and MRS with 1% glucose was found to facilitate isolation of LAB compared to MRS, tomato juice agar and modified tomato juice agar. 32 isolates were confirmed LAB by catalase test and Gram staining. Six isolates were screened for antibacterial activity and identified as strains of Lactobacillus acidophilus 1 by API CH50. Results: All the isolates showed very good inhibitory activity against target Gram negative bacteria as indicated by the diameter of inhibition zone: Salmonella Typhimurium (23-30 mm), Escherichia coli (7-18 mm) and Enterobacter aerogenes (10-18 mm) after 24 h incubation at 30°C. Supernatants of L. acidophilus 1 strains showed good antibacterial activity against all target bacteria. Heating the supernatants at 90 and 121°C for 1 h enhanced the antibacterial activity against all target bacteria except supernatants H006-A and H010-G against S. Typhimurium. Antibacterial activity of supernatants were maintained after pH adjustment to 3, but at pH5 supernatants H006-A, H008-D and H010-G lost the activity against S. Typhimurium and E. coli within 48 h of incubation while at pH 6 all supernatants lost activity except against E. aerogenes. Enzymes treatments of supernatants with RNase II and Proteinase K for 1 h inhibited all target bacteria except supernatants H008-D, H008-E and H006-A which were relatively sensitive to both enzymes against S. Typhimurium and E. coli. Conclusion/Recommendations: In conclusion, honey from different sources contains strains of L. acidophilus 1 that produced compounds with good antibacterial activity which may be responsible for the antibacterial properties of honey.
Highlights
Honey is well known for its health benefits and it has been used as traditional medicine for many years (Dobrowolski et al, 1991; Bankova, 2005)
The results demonstrate that the antibacterial activity of L. acidophilus strains vary with targeted bacteria and the antibacterial compounds produced by these Lactic Acid Bacteria (LAB) strains
Resistance to all the antibiotic s especially to bactracin, cephalothin, penicillin G, vancomycin and strepromycin; E. coli ATCC25922 was sensitive to tetracycline, naladixic acid and choloramphinicol but very resistant to bactotracin, penicillin G and pH sensitivity of LAB supernatant: Adjusting LAB supernatants to pH 3 resulted in good inhibitory activity against all target Gram negative bacteria especially E. aerogenes (Table 7) within 48 h incubation compared to control
Summary
Honey is well known for its health benefits and it has been used as traditional medicine for many years (Dobrowolski et al, 1991; Bankova, 2005). Effect of heat treatment LAB supernatant on antimicrobial activity: The supernatant of LAB isolates was heat treated at 90 and 121°C for 1 h and tested against the target bacteria using microtiter plate as described above. The supernatant was tested against target bacteria in microtiter plates followed by incubation at 30°C for 48 h and bacterial growth was monitored at 24 h interval as described above. Overnight cultures of the isolates were grown on Determination of antibacterial activity of LAB supernatant using microtiter plates: Cell free supernatant of LAB was obtained from centrifugation (6500× g for 15 min) and filtration of overnight MRS broth inoculated with LAB isolates incubated at 30°C 24 h anaerobically.
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