AEROMONAS SPECIES IN STABILIZATION PONDS IN THE ARID REGION OF MARRAKESH, MOROCCO, AND RELATION TO FECAL-POLLUTION AND CLIMATIC FACTORS

During the period 12 July 1985 to 23 December 1987, water samples were collected in two-week intervals for estimates of Aeromonas species in a waste treatment system located in the arid region of Marrakech, Morocco. Fecal coliforms, temperature, and chemical oxygen demand were measured simultaneously with Aeromonas species densities. Statistical methods were utilized to analyze the significance of average differences and temporal patterns of Aeromonas species numbers. Removal of Aeromonas in the whole system did not exceed 1.14 log. Aeromonas densities showed significantly higher resistance to the treatment process when compared with fecal coliforms; however, abundance of the two groups presented a similar seasonal change. The highest numbers occurred during the cold months, while the lowest appeared in the warm months. Statistical time-series analyses of the densities data showed the seasonal and cyclic distribution of Aeromonas in this treatment plant. These temporal changes were simultaneously observed in all the stations investigated and were negatively correlated with water temperature values. Aeromonas populations were dominated by A. caviae and A. hydrophila in the inlet samples. These two species were rapidly eliminated in the treatment plant. The temporal distribution of A. caviae was similar to the change in densities of Aeromonas and fecal coliforms. The seasonal fluctuations of abundance of Aeromonas were probably related to this species, which dominated in the winter samples but dropped during the summer. Meanwhile, A. sobria dominated all the final effluent samples. This greater survival of A. sobria and its known pathogenicity may limit the re-use of treated water for irrigation of fodder plants.