Antibacterial effects of proteases on different strains of Escherichia coli and Listeria monocytogenes

Escherichia coli O157:H7 and Listeria monocytogenes are pathogens that have received special attention by federal agencies, food safety researchers and food industries due to their economic and human health impact. To reduce the presence of these pathogens, alternative interventions have been studied. However, increasing consumer\u27s demand for natural ingredients has made the investigations of effectiveness of natural antimicrobials necessary. In this study, in vitro antimicrobial activity of bromelain and papain against E. coli JM109 and L. monocytogenes was investigated. Furthermore, actinidin and papain were evaluated to reduce populations of L. monocytogenes strain and three mixed strains of E. coli O157:H7 in cooked meat media and on beef when held at three different temperatures. In vitro, bromelain levels of 4 mg/ml and 1 mg/ml were the most effective concentrations tested against E. coli JM 109 and L. monocytogenes, respectively, at 25 and 35 °C, reducing the populations by (3.37, 5.02) and (5.7, 4.1 ) log CFU/ml after 48 h, respectively. While papain levels of (0.0625 mg/ml) and (0.5 mg/ml) were the most effective concentration tested at 25 and 35°C against E. coli and L. monocytogenes, respectively, reducing populations by (4.94, 5.64) and (6.58, 5.78) log CFU/ml after 48h, respectively. While significant enzyme effects on bacterial populations in cooked meat media were found in this study, significant differences (P ≤ 0.05) were sometimes ≤ 1‐log unit, which are not typically considered of practical significance. However, due to the highly controlled nature of the study and that meat broth media exposes enzymes and bacteria to concentrated amounts of meat protein, the results may indicate positive results are possible when enzymes are applied to foods surfaces. In cooked meat media, at 25 and 35°C, for all actinidin and papain concentrations there were not significant reductions found in E. coli O157:H7 and L. monocytogenes populations for any time-temperature combination. Moreover, there was bacterial growth from 1 to 3 h for 25 and 35°C. The bacterial growth at 35 °C was significantly higher than that at 25 °C. At 5°C, actinidin and papain did not significantly reduce the populations of E. coli O157:H7 and L. monocytogenes except for actinidin at 50 mg/ml on L. monocytogenes at 24 h. Also, no difference was found between bacterial populations at 6 and 24 h for both pathogens except for L. monocytogenes at 24 h where there was bacterial growth for both papain levels tested. On beef, the average reduction of E. coli O157:H7 was ≥ that of L. monocytogenes and higher concentrations of either proteases yielded greater reduction in bacterial populations. For instance, actinidin at 700 mg/ml significantly (p ≤ 0.05) reduced the population of L. monocytogenes by 1.49 log cfu/ml after 3 h at 25 & 35°C, and by 1.45 log cfu/ml after 24 h at 5°C. Also, the same actinidin concentration significantly (p ≤ 0.05) reduced the populations of three mixed strains of E. coli O157:H7 by (1.81 log cfu/ml) after 3 h at 25 & 35°C, and by (1.94 log cfu/ml) after 24 h at 5 °C. While papain at 10 mg/ml reduced the population of L. monocytogenes by 0.56 log cfu/ml after 3 h at 25 & 35°C and by (0.46 log cfu/ml) after 24 h at 5°C. Also, the same papain concentration significantly (p ≤ 0.05) reduced the populations of three mixed strains of E. coli O157:H7 by 1.48 log cfu/ml after 3 h at 25 & 35°C, and by 1.57 log cfu/ml after 24 h at 5 °C. These findings suggest that, in addition to improving the sensory attributes of beef, proteases can enhance meat safety and shelf life when stored at suitable temperatures. The findings also propose a promising approach in developing antimicrobial systems for beef products. If these enzymes are combined with current antimicrobial technologies, higher pathogen reductions may be achieved if present

Antibacterial effects of natural tenderizing enzymes on different strains of Escherichia coli O157:H7 and Listeria monocytogenes on beef

This study determined the efficacy of actinidin and papain on reducing Listeria monocytogenes and three mixed strains of Escherichia coli O157:H7 populations on beef. The average reduction of E. coli O157:H7 was greater than that of L. monocytogenes and higher concentrations of either protease yielded greater reduction in bacterial populations. For instance, actinidin at 700 mg/ml significantly (p ≤ 0.05) reduced the population of L. monocytogenes by 1.49 log cfu/ml meat rinse after 3 h at 25 & 35 °C, and by 1.45 log cfu/ml rinse after 24 h at 5 °C, while the same actinidin concentration significantly reduced the populations of three mixed strains of E. coli O157:H7 by 1.81 log cfu/ml rinse after 3. h at 25 & 35 °C, and 1.94. log cfu/ml rinse after 24 h at 5 °C. These findings suggest that, in addition to improving the sensory attributes of beef, proteolytic enzymes can enhance meat safety when stored at suitable temperatures

Antimicrobial effects of natural tenderizing enzymes on different strains of Escherichia coli O157:H7 and Listeria monocytogenes on Beef

Tenderization of beef meat is widely done for increasing consumer acceptance and enhancing shelf life. This study was conducted on meat surface to determine the efficacy of proteolytic enzymes (papain and Actinidin), meat tenderizer enzymes, on the survivability of multiple strains of E. coli O157:H7 and L. monocytogenes. Two overnight cultures of three strains of E. coli O157:H7 and L. monocytogenes were separately suspended in 1% peptone water and were individually inoculated into beef meat surface (ca. 106 CFU/ml). After 5 minutes attachment time different enzyme concentrations were added. Treated samples were then kept for 3 h at 25°C and 35°C and for 24 h at 5°C. Actinidin concentration (700 mg/ml) tested at 25°C against E. coli O157:H7 and L. monocytogenes was the most effective concentrations tested reducing populations by 2.4 and 1.41 log CFU/ml after 3 h, respectively. Papain concentration of (10 mg/ml) was the most effective concentrations tested at 25°C against E. coli O157:H7 and L. monocytogenes reducing populations by 1.8 and 0.8 log CFU/ml after 3 h, respectively. These findings suggest that, in addition to the potential for improving the sensory attributes of beef meat, tenderization can enhance their safety and shelf life

Extent of pathogenic and spoilage microorganisms in whole muscle meat, meat products and seafood sold in Libyan market

Background: Whole muscle meat, meat products, and seafood contain different nutrients in adequate quantity providing a better environment for presence and replication of different microorganisms. There are underreporting and inaccurate estimation of foodborne diseases due to the lack of effective surveillance systems in Libya. Aim: To determine the extent of microbiological contamination of whole muscle meat, meat products and seafood. Methods: A total number of 731 samples of retail meat were collected from different stores in four cities in Libya. Samples were analyzed for aerobic plate count (APC), and subjected to microbiological enumeration and isolation techniques, followed by molecular identification by PCR and partially sequencing of 16S rDNA. Results: The results showed contamination of samples with enteric and spoilage bacteria. Fifteen genera of spoilage bacteria yielded 149 isolates were detected and identified by PCR and partially sequencing of 16S rDNA as: Proteus spp., Provedencia spp., Raouttella ornithinolytical, Citrobacter spp., Enterobacter spp., Morganella morgi, Shewanella algea, Rhodobacter capsulatus, Listonella pelagia, Kluyvera spp., Pectobacterium spp., Brenneria spp., Klebsiella spp., Acintobacter radioresistens, and Pantoea spp. While for pathogenic bacteria, 143 isolates distributed among nine genera were identified by PCR and partially sequencing of 16S rDNA as: Bacillus spp., Escherichia spp., Shigella spp., Enterococci spp., Cronobacter spp., Staphylococci spp., Salmonella spp., Aeromonas spp., and Vibrio spp.. Many isolated bacteria are zoonotic bacteria with high importance for public health. Conclusion: Excessive handling and processing of meat and meat products seems to be one of the poorest microbiological quality. These findings ought to be helpful in risk assessments and quality assurance of meat in order to improve food safety