دراسة تاثير تركيز الملح ودرجة الحرارة على حيوية جرثومة الزائفة الزنجارية المعزولة من منتجات الحليب واالحوم في محافظة كربلاء

Study the effect of salt concentration and temperature on viability Pseudomonas aerogenoza isolated from Milk and Meat product in karbala City.

Summary
Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen widely distributed in the environment, including water, soil, and food products. Its presence in milk and meat poses significant public health risks due to its ability tocause sever infections, especially in immunocompromised individuals. This bacterium is known for its high resistance to antibiotics, heat, and disinfectants, making it a persistent contaminant in food processing and storage.
The contamination of dairy and meat products with P. aeruginosa can occur at various stages, including the period of milking, slaughtering, processing, and improper storage. Consumption of contaminated food may lead to gastrointestinal infections, septicemia, and other systemic illnesses. Moreover, some strains produce heat-stable toxins and biofilms, further increasing their threat to food safety. The study involved collecting 625 samples distributed across the holy city of Karbala, include 125 samples taken from each of the following areas: city center, Ain Al-Tamr, Al-Hindia, Al-Husseiniya, and Al-Hur. The samples were distributed as follows: 25 raw milk samples, 25 samples of cream, 25 of butter, 25 of meat, and 25 of ground meat collected from local markets.
After incubation and bacterial isolation using standard and specialized culture media, Pseudomonas bacteria were identified and confirmed using the VITEK system (and another method, if specified). Subsequently, an experiment was conducted to test the bacteria’s heat resistance, which included exposure to four different temperatures (7°C, 21°C, 37°C and 45°C) for periods of 3 days and 7 days. Additionally, the bacteria were exposed to varying salt concentrations (2%, 5%, 7%and 10%) for the same durations. All samples were cultured on blood agar and incubated at 37°C for 24 hours. The isolated Pseudomonas aeruginosa colonies exhibited as Round, mucoid, smooth colonies with β-hemolysis, Yellow-green colonies on Cetrimide Agar, Flat, colorless colonies on MacConkey agar, emitting a grape-like odor, Blue-green pigment (pyocyanin) production on King’s A agar. All Pseudomonas isolates from different sources tested Positive for catalase and oxidase, Kligler’s Iron Agar (KIA) results: Alkaline/no change (red), no H₂S production, no gas formation, Simmons citrate test Positive (utilized citrate as a carbon source), Methyl Red (MR) and Voges-Proskauer (VP): Negative, Urease activity: Negative in all isolates. The phenotypically confirmed Pseudomonas aeruginosa isolates were subjected to antimicrobial susceptibility testing using the VITEK-2 automated system (BioMérieux, France) following the manufacturer’s protocol.
Molecular Identification of Pseudomonas aeruginosa by PCR Detection of Virulence genes via exoA and lasB genes, all Pseudomonas aeruginosa isolates were subjected to PCR-based molecular assays to detect key virulence genes.Detection of the exoA Gene (Exotoxin A),PCR amplification followed by agarose gel electrophoresis revealed a 347 bp DNA band, confirming the presence of the exoA gene. Detection of the lasB Gene (Elastase)Similarly, PCR and electrophoresis identified a 226 bp DNA band, verifying the lasB gene.These findings confirm the molecular identification of P. aeruginosa in the tested isolates, supporting their pathogenic potential due to the presence of critical virulence factors.
Summarizes the occurrence of Pseudomonas aeruginosa in dairy and meat products collected from five different regions, 25 samples were examined from five categories: raw milk, minced meat, non-minced meat, butter, and cheese — resulting in a total of 125 samples per region and 625 samples overall. The highest contamination rate was observed in raw milk, with 52 out of 125 samples (41.6%) testing positive for P. aeruginosa. The prevalence in other products was lower: 17 positive samples (13.6%) from minced meat, 10 (8%) from non-minced meat, and 25 (20%) from cheese. Notably, none of the butter samples showed any contamination across all regions. Regionally, Al-Hur recorded the highest number of positive cases (23 out of 125; 21.6%), followed closely by the City Center and Ain-Altumor (22 positive cases each, 17.6%). Al-Hussenyia and Alhindyia showed slightly lower contamination levels, with 19 (15.2%) and 18 (14.4%) positive samples respectively.
The results of the physical tests showed that 37°C is the optimal temperature for bacterial growth and restricted growth at 7°C and 21°C during early incubation followed by complete suppression after 7 days. It was found that temperature has a significant effect on bacterial survival and at a temperature of 45 ℃, no bacterial growth was observed. All samples showed noticeable bacterial growth only when exposed to a salt concentration of 2% sodium chloride, while all concentrations of 5% sodium chloride showed very little bacterial growth. At salt concentrations of 7% and 10%, no bacterial growth was observed. In Conclusion: the study found that milk and its derivatives are more contaminated with bacteria than minced and non minced meat. The study also concludes that bacteria are sensitive to temperature and salt content, with higher tolerance in low-salt environments and moderate temperature