Lake Manzala is considered one of the most important coastal Lakes in Egypt. This study revealed the highly polluted condition of water and fish samples taken from three of the more important sites (Kapoty, Bashtier and Mataryia areas), representative to human activity and different ecosystems in the Lake water environment. Total suspended solids (TSS), ammonia and nitrates, of the samples taken showed figures exceeding the national and international standards. The samples from the study yielded high levels of bacterial content, which were found through plate counts and by using different growth media such as agar and endo agar. Total viable bacteria (TVB) reached more than 104 cfu/ml in water samples and 105 cfu/g in fish samples, particularly in Kapoty and Mataryia areas. Faecal coliform counts reached 102 cfu/ml in water samples and 103 cfu/g in fish samples. Statistical analysis revealed a positive correlation between Aeromonasspp. counts and some minerals, such as chlorides, calcium and magnesium (r = 0.9, 0.8, and 0.6 respectively; p > 0.001), which revealed the interactions and adaptability of such organisms to environmental factors. A total of 88 isolates fromAeromonas differential agar were identified using the API 20E system; 17% of these isolates were Aeromnas hydrophila, and most of these strains were resistant to three or more antibiotics including pencillinG, ampicillin and chloramphenicol. Isolation of plasmid DNA from these strains of A. hydrophila, showed that most harboured plasmids ranging from less than 2.2 - 4 KbP. Such findings could explain the adaptability and multi-drug resistance of such bacterial pathogens, which may have an impact on the course of infection and active causal agents of diarrhoeal diseases in this important coastal area of Egypt on the Mediterranean Sea.
Key words: Aeromonas hydrophila, multi-drug resistance, plasmid DNA, Lake Manzala.
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