الفهرس 
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Abstract
Milk and dairy products are generally very rich in nutrients which provide the human body with a wide range of important and vital nutrients and compounds. Beside that provide an ideal environment for the growth of many microorganisms. milk contamination by microorganisms can take place during milking, handling, storage, and other pre-processing activities. Listeria monocytogenes is an example that causes a serious food-borne illness called Listeriosis with a high fatality rate at an average of 20 to 30% annually. The outbreak of listeriosis is mainly due to the consumption of raw milk or products from unpasteurized milk.
The aim of the present study was to determine the occurrence of Listeria monocytogenes in milk and dairy products in Alexandria in relation to hygienic condition of selling places.
To fulfill this aim a total of 500 samples of milk and milk products were collected during the period from April 2017 to January 2019 including 150 milk samples, 140 cheese samples, 126 yogurt samples and 84 ice cream samples. Samples were collected from 288 selling places including; 11 hypermarkets, 76 supermarkets, 41dairy products shops, 49 groceries and 88 street vendors, located in east, middle and west districts in Alexandria.
The detection of Listeria monocytogenes based on the principles of the official standard of ISO 11290 2:1998 Amendment 1:2004. The hygienic condition of selling places and the hygienic practices of food handlers were assessed, using a structured checklist. The results of the present study revealed that:
1. Hygienic Requirements
The median percent score of hygienic condition of selling places was 71.43(57.14) and the median percent score of hygienic practices of food handlers was 71.43(28.57), with highly significant difference between them.
The mean of percent score of hygienic condition of selling places was 56.68 ± 29.03, and the mean percent score of the hygienic practices of food handlers was 70.96 ± 16.59, with highly significant difference between them.
42.0 % of the selling places and food handlers had good hygienic condition of selling and good hygienic practices of food handlers, 27.8% were fair and 30.2 % were poor.
1.1. Hygienic condition of selling places
The median percent score of hygienic condition of selling places was 71.43(57.14) and the mean of percent score of hygienic condition of selling places was 56.68 ± 29.03. Control of contamination had the highest median percentage score [71.43 (53.60)].followed by construction [68.75 (73.43)], location [63.12 (50.00)] then cold storage [33.33 (66.67)], with highly significance variation between them.
44.4% of the selling places had good hygienic condition, 24.3% were fair and 31.3 % were poor.
45.1% of selling places had good contamination control, 44.1% had good location , 29.5% had good construction, and 21.9% had good cold storage. On the other hand, 54.2% of selling places had poor cold storage, 29.9 % of selling places had poor
construction, 24.7% had poor contamination control and 20.5 % had poor location. There was a highly significant differences between them according to a Friedman test, (p-value < 0.05, C.I. =95%).
There were highly significant differences in the levels of hygienic condition, as well as location, construction, control of contamination and cold storage according to the type of selling place and type of product.
Districts had a highly significant difference on the level of construction. On the contrary, districts had no significant difference on the level of hygienic condition, location, control of contamination and cold storage.
1.2. Hygienic practices of food handlers
The median percent score of hygienic practices of food handlers was 71.43(28.57) and the mean percent score of the hygienic practices of food handlers was 70.96 ± 16.59.
Health represents the highest median percent score[100.00(50.00)], followed by cleanliness [80.00 (20.00)] then habits [71.43 (28.57)], with highly significance variation between them
Health represents the highest mean percent score[86.28±24.22], followed by habits [71.73±16.35] then cleanliness (63.75±24.59), with highly significance variation between them
Only 45.8% of food handlers had good hygienic practices, 46.2% were fair and 8.0% were poor.
74.3% of food handlers had good health, 52.8% of food handlers showed good cleanliness and only 29.2% showed good habits, with highly significant differences between them.
There were highly significant differences in the levels of hygienic practices of food handlers, as well as their health , cleanliness and habits according to the type of selling place and type of product.
Districts had a significant difference on the level of hygienic practices of food handlers, as well as their health and cleanliness. On the contrary, districts had no significant difference on the level of habits of food handlers.2. Microbiological quality of milk and dairy products A total of 236 samples (47.2%) showed a microbial growth on Brilliance listeria agar medium. The majority of them 70(74.5%) were from raw milk samples and only one sample from each pasteurized (3.7%) or sterilized (3.8%) milk samples. No growth was observed for powdered milk and feta cheese samples.
Most contaminated samples were from east district (56.5%) followed by west district (44%) and then in middle district (41.6%). The highest incidence of contaminated samples were from ice cream shops 75.0%, followed by dairy shops (50.9%), groceries (48.0%), supermarkets (45.8%), street vendors(40.6%), then hypermarkets (16.7%).
The median microbial count of milk and dairy products samples on Brilliance listeria agar medium was 3.04(1.09)/ Log10CFUmL -1, and ranged between a minimum of 1.78(0) Log10CFUmL-1 in pasteurized milk and a maximum of 3.46(1.13) Log10CFUmL-1 in soft cheese, with highly significant differences between different types of milk and milk products.
The median of microbial count of milk samples was 3.23(1.17) Log10CFUmL -1, and ranged between 3.23 (1.11) Log10CFUmL-1 in raw milk and 1.78(1.78) Log10CFUmL-1 in pasteurized milk, with no- significant variation between them.
The median microbial count of cheese samples on Brilliance listeria agar was 3.23(1.03) Log10CFUmL -1, and ranged between a maximum of 3.47(1.12) Log10CFUmL -1 in soft cheese and a minimum of 2.24(0.48) Log10CFUmL -1in cheddar cheese, with no- significant variation between them. That median of microbial count of ice-cream samples was 2.86 (0.71) Log10CFUmL-1, and in yoghurt samples it was 2.74(0.84) Log10CFUmL -1).
Out of the 236 suspected bacterial colonies grown on Brilliance listeria agar medium, 221 samples were gram positive.
A total of 46 samples out of the 221 gram positive species were subjected to confirmatory biochemical tests. All the 46 samples were catalase positive, gram positive cocci with no motility, 33(71.8%) showed hemolysis, only 7(15.2%) were positive to rhamnose while 31(67.4%) of samples were xylose negative.
No listeria monocytogenes or any of listeria spp. were confirmed.
According to MALDI-TOF Biotyper, out of 71 samples of milk and milk products suspected positive samples. The identified microorganisms with MALDI-TOF Biotyper, were as follows: Staphylococcus spp. were identified in 23 samples (35.4%) mostly from raw milk (9 samples ,13.8%) ), Enterococcus spp were identified in 15 samples (23.1%), Kucaria kristinae were identified in 12 samples (18.5%), A.woluwensis were identified in 5 samples (7.7%), C.cellulans were identified in 3samples (4.6%), Curtobacterium albidum were identified in 2 samples
Summary
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(3.1%), and once (1.5%) for A.bremensis, Lactobacillus equi, Macrococcus caseolyticus, Microbacterium barkeri and Paenibacillus massiliensis. The resistance rates of Enterococcus isolates to the tested antimicrobials reported by VITEK system were as follows; quinupristin/dalfopristin (30.0%), benzylpenicillin,, erthromycin , vancomycin , tetracycline (20.0%) for each and oxacillin (10%). Meanwhile 80.0% of isolates were intermediate susceptible to StreptomycinHigh Level (synergy). Moreover all strains were 100% susceptible to for ciprofloxacin, levofloxacin, linezolid, tigecycline and nitrofurantoin. The resistance rates of Staphylococcus spp to the tested antimicrobials reported by VITEK system were as follows: The highest resistance was observed with erthromycin ( 4 samples,100%). Meanwhile all of the isolates were 100% susceptible to the other antibiotics including; azithromucin, vancomycin, linozolide, doxycycline and gentamicin. No isolate showed an intermediate susceptibility.
The resistance rates of isolates other than Staphylococcus and Enterococcus spp to the tested antimicrobials reported by VITEK system showed that all isolates of Cellulosimicrobium cellulans, Kocuria Kristinae and Macrococcus caseolyticus were susceptible to all studied antibiotic except for non-tested, ampicillin, genamicin and streptomycin. No isolates were resistant or even had intermediate susceptibility. The highest resistance rates of Staphylococcus spp to the tested antimicrobials determined by kerby-Beur Disk Diffusion was for penicillin (6 isolates (54.5%) ). Meanwhile, all isolates were 100% susceptible to each of azithromucin, clindamycin vancomycin, linozolide, doxycycline , rifampin, chloramphenicol, ciprofloxacin, levofloxacin, ofloxacin and gentamicin followed by Cefoxitin and Levofloxacin (90.9%) each.
All Enterococcus spp isolates showed intermediate susceptibility to erythromycin 4 (100%) determined by kerby-Beur Disk Diffusion; while chloramphenicol and ciprofloxacin showed intermediate susceptibility(50.0%). Mmoreover all isolates (100%) were susceptible to penicillin, vancomycin, teicoplanin, levofloxacin, ampicillin and streptomycin (HLAR).
The antimicrobial susceptibility profiles of some isolates other than Enterococcus and Staphylococcus species determined by Kurby beur disc diffusion method showed that; 2 isolates (33.3%) were resistant to cefoxitin and penicillin and only one isolate(16.7%) was resistant for each of clindamycin , doxycycline , gentamicin , tobramycin and ampicillin .All isolates (100%) were susceptible to erythromycin , vancomycin , teicoplanin and linozolide . Meanwhile only one isolate (16.7) showed intermediate susceptibility for each clindamycin, ciprofloxacin, levofloxacin, Quinopristin-dalfopristin and Streptomycin (HLAR).