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Colistin is a polymyxin antibiotic that has been used in veterinary medicine for decades, as a treatment for enterobacterial digestive infections as well as a prophylactic treatment and growth promoter in livestock animals, leading to the emergence and spread of colistin-resistant Gram-negative bacteria and to a great public health concern, considering that colistin is one of the last-resort antibiotics against multidrug-resistant deadly infections in clinical practice. Previous studies performed on livestock animals in Tunisia using culture-dependent methods highlighted the presence of colistin-resistant Gram-negative bacteria. In the present survey, DNA extracted from cloacal swabs from 195 broiler chickens from six farms in Tunisia was tested via molecular methods for the ten mobilized colistin resistance (mcr) genes known so far. Of the 195 animals tested, 81 (41.5%) were mcr-1 positive. All the farms tested were positive, with a prevalence ranging from 13% to 93%. These results confirm the spread of colistin resistance in livestock animals in Tunisia and suggest that the investigation of antibiotic resistance genes by culture-independent methods could be a useful means of conducting epidemiological studies on the spread of antimicrobial resistance.

The Ichkeul Lake ecosystem, Northern of Tunisia, has been registered as a biosphere reserve in 1977 (MAB-UNESCO Convention), a UNESCO World Heritage site in 1979, and a RAMSAR site in 1980. Damming and global warming drought drastically diminished the fresh water supply to this lake. This leads to water level and salinity fluctuation throughout the year. Consequently, the water clarity of this shallow wind-stressed lake was altered and if this siltation continues to increase, will seriously affects the hydromorphology and ecology of this wetland. Therefore, to study the hydrodynamic water circulation in the lake and the transport of the Total Suspend Matter (TSM), hydrodynamic and transport models were calibrated and applied to this environment. Numerical model predictions based on water level, temperature and salinity sensitivity to the bed roughness show that the Delft 3D-Flow model reproduced well the measured data with RMSE < 0.027 for water level. Keywords: Delft3D-FLOW, Hydrodynamic circulation, Ichkeul Lake, Sedimentary material, TSM, Water clarity