Occurrence of emerging food-borne pathogens in common fast foods and inactivation of pathogens with essential oil

Abstract

The present investigation can be classified into four major parts. The first part is the isolation and presumptive identification of Escherichia coli, Staphylococcus aureus and Bacillus cereus from fast food samples collected from various parts of Dhaka city of Bangladesh. This was done following the criteria put forth in Bergey’s manual of Determinative Bacteriology, 9 th edition. The second part is the detection of antibacterial activity of cinnamaldehyde against three food borne pathogens individually and combined by the disc diffusion method. The third part is to determine the effect of pH and temperature on antibacterial activity of cinnamaldehyde against three food borne pathogens. The fourth and the final part is inactivation of isolated organism applied in ground chicken meat with cinnamaldehyde. For isolation of Escherichia coli, Bacillus cereus and Staphylococcus aureus from food samples three types of selective media was used such as Sorbitol MacConkey agar (SMA), Bacillus cereus selective agar base medium supplemented with egg yolk emulsion, Polymyxin B sulphate, and Mannitol salt agar (MSA), From the selective medium, the selected colonies were isolated and then sub cultured to maintain pure culture. From the collected food samples, 14 Escherichia coli, 09 Bacillus cereus and 17 Staphylococcus aureus were subjected to cultural, morphological, and microscopic and biochemical study for their presumptive identification. Antibacterial activity of cinnamaldehyde, carvacrol and euginol was tested against Escherichia coli, Bacillus cereus and Staphylococcus aureus using disc diffusion method. Screening of cinnamaldehyde, carvacrol and euginol extracts showed antibacterial activity against the isolated organisms studied. The MIC values of cinnamaldehyde, carvacrol and euginol were determined by broth dilution method at 37 °C and pH 7. MIC values of cinnamaldehyde, carvacrol and euginol against the test bacteria ranged from 2.5 to 10%. The effect of temperature and pH on the antibacterial activity of cinnamaldehyde against Escherichia coli, Bacillus cereus and Staphylococcus aureus were determined. Cinnamaldehyde showed antibacterial activity after treatment at 100° C for 30 min treatment suggesting that a high temperature does not affect the activity but only reduced the activity insignificantly as showed by decreased zone diameter. The highest antibacterial activity was found at pH 7 for cinnamaldehyde against the test organisms. Cinnamaldehyde at each concentration of 2.5% (MIC level), 7.5% (three times of MIC) and 12.5% (five times of MIC) was applied separately in ground chicken meat inoculated with Escherichia coli, Bacillus cereus and Staphylococcus aureus and kept at -18° C for 10 days. The result showed that only a few log reduction of Escherichia coli, Bacillus cereus and Staphylococcus aureus was found in selective media used in case of MIC level of cinnamaldehyde (2.5%). 3 times (7.5%) and 5 times (12.5%) MIC level of cinnamaldehyde employed resulted 7 log reduction of Escherichia coli, Bacillus cereus and Staphylococcus aureus, respectively, growing on selective media after 24 hours of exposure. Therefore, cinnamldehyde could be useful to control Escherichia coli, Bacillus cereus and Staphylococcus aureus in ground chicken meat. From this experimental finding it was apparent that essential oils from herbs, sharps, trees and spices, especially cinnamldehyde from cinnamon could be fruitfully used to control food borne pathogens in various foods and food commodities.