الفهرس 
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Abstract
Animal feed is highly susceptible to the introduction of bacteria throughout the entire production process. In this study, a total of 2948 samples collected from (2100 pet food, 100 pets’ fecal swabs of diseased and apparently healthy dogs and cats, 227 feed additives, 367 fish meal, 29 wastes of poultry slaughter house meal, 47 calves milk replacer, 41 beet gain, 37 bone meal) were submitted to the serology unit, Animal Health Research Institute (AHRI), Dokki, Giza, Egypt from 2017 to 2020. Only 1570 Out of 2948 examined pet animal and animal feedstuff samples (53.3%) were positive to the isolated Gram-negative bacteria,the incidence of isolated Gram negative bacteria among the collected sample types were identified biochemically to E coli, Salmonella sp., Proteus sp, Klebsiella sp., Yersinia enterocolitica, Pseudomonas sp, Citrobacter sp, Enterobater cloacae, Aeromonas hydrophila. E coli isolates were the highest isolated Gram negative bacteria. The antimicrobial sensitivity test revealed that 80% of Salmonellae were resistant to Cefotaxime and Colistin sulphate while 50%, 30%, and 20% of isolates were resistant to Gentamicin, Tetracycline, and Cefepime respectively, while 40% of Salmonellae were resistant to Chloramphenicol, Enrofloxacin, and Amoxicillin-clavulanate. Also 60% of Salmonellae showed resistance to Trimethoprim sulfamethoxazole and Ciprofloxacin. Detection of Extended-spectrum ß-lactamase resistance genes (blaTEM, blaSHV, and blaCTX-M) in Pets using Polymerase chain reaction (PCR) showed the presence of blaTEM and blaSHV genes in all tested isolates in 12 samples out of 12 (100%) and has shown that the ratio of blaCTX-M is 5 out of 12samples (41.6 %).It is desirable for laboratories to maintain bacterial strains in culture for extended periods of time for research purposes. Moreover, evaluation of the survival rate of these species of microorganisms after different preservation time (3, 6, 9 and 12 months) on soft agar, PBS with glycerol and cryopreservation in preservation temperature (4, -20 and -80°C) showed that the lowest survival rate after preservation on soft agar tubes preserved in 4°C, followed by preservation on phosphate buffer saline with glycerol preserved in -20°C, while the recovery rate after cryopreservation in -80°C were 100% for all isolates. The method described for preservation of Gram negative bacteria was a simple and economically useful for laboratories not equipped with the lyophilizer or ultra-low freezer.