Seasonal variations in microbial and physicochemical parameters of Nile river water in Giza, Egypt: comparison of IDEXX and conventional methods

The Nile River is an essential water source for millions of Egyptians, but it is increasingly threatened by microbial and chemical contamination linked to urbanization and seasonal changes. This study investigated seasonal variations in microbial pollution and physicochemical characteristics of Nile water at four sites in Giza Governorate using culture-based methods and the IDEXX Colilert-18 system. The highest total coliform counts occurred in summer, reaching 21,462 MPN/100 ml (IDEXX) and 17,748 CFU/100 ml (traditional methods). Fecal coliforms ranged from 995 CFU/100 ml in summer to 463 CFU/100 ml in winter, while fecal Streptococcus peaked in autumn. Pseudomonas aeruginosa was slightly elevated in summer (1,140 CFU/100 ml), and traces of Salmonella and Staphylococcus were also detected. IDEXX consistently yielded 8–10% higher counts than traditional methods, reflecting greater sensitivity. Seasonal fluctuations were also observed in physicochemical parameters, including temperature (18.6–31.6 °C), pH (8.02–8.26), turbidity (3.89–5.74 NTU), total dissolved solids (205–279 mg/L), and electrical conductivity (310–435 µS/cm). Biological and chemical oxygen demands were highest in summer. Significant correlations (p < 0.05) were found between microbial counts and factors such as temperature and turbidity. These findings highlight elevated contamination risks during summer and underscore the enhanced detection ability of IDEXX. Significant correlations (p < 0.05, ANOVA) were found between microbial counts and temperature, turbidity, and BOD levels. These results emphasize the need for enhanced surveillance to protect public health, particularly during the summer when contamination risk peaks.