Evaluation the antibacterial effect of hydroalcoholic coffee extract on L. monocytogenes isolated from milk and milk products

Abstract

Listeria spp . is a very resilient bacteria that can persist hostile dairy-processing environments and consequently, food safety challenges appear here with respect to control its growth. L. monocytogenes is the most important species that cause a great concern in both food processing and public health. Therefore, this study was performed to investigate the incidence of Listeria spp. in 450 samples of raw milk, pasteurized milk, flavored milk, dominate cheese, kareish cheese, small scale ice cream, large scale ice cream, small scale yoghurt, and large scale yoghurt (50 each) were collected from dairy farms, local dairy shops and street vendors in Qena city, Egypt. Listeria spp. were isolated from 27 (6%) out of the total samples examined. They were recovered from the tested market raw milk, kareish cheese, small scale ice cream and domiati cheese samples with percentages of 20, 16, 14% and 4%, respectively. However, Listeria spp. was absent in other analyzed samples. The most prevalent species was L. monocytogenes 10 (2.22%), followed by L. grayii 9 (2%), L. welshimeri 4 (0.89%) and L. innocua 3 (0.67%) with an overall 5.7% verified by PCR. Eight out of 10 L. monocytogenes isolates were confirmed by the presence of the 16S rRNA gene that implies a risk of food-borne listeriosis among dairy product consumers. Furthermore, a unique approach was used for the assessment of antibacterial activity of different concentrations of gentamicin as a reference antibiotic standard and hydroalcoholic coffee extract (H. A. coffee extract) (1, 3, 10 and 30 µg/ml) against local isolated L. monocytogenes strain in vitro using a microplate in ELISA reader is provided in the current work. The most Potent antimicrobial activity of gentamicin and H. A. coffee extract was obtained at 30 µg/ml against the isolated L. monocytogenes strain. At which not exhibit listeria growth up to 98.3 % and 96.1 %, respectively. H. A. coffee extract was screened using gas chromatography–mass spectrometry (GC-Mass). This analysis showed that the antibacterial impact of H. A. coffee extract against L. monocytogenes is attributed to the active components (caffeine and eugenol).