Antibiorésistance et risque sanitaire lié à la bactérie Pseudomonas aeruginosa isolée de quelques systèmes aquatiques dans les villes de Douala et Yaoundé (Cameroun)

Abstract

Data on antibiotic resistance of bacteria isolated from natural water sources in Cameroon are rare. This resistance, however, increases the risk of morbidity and mortality during a waterborne infection since the therapeutic options are reduced. The aim of this study was to contribute to the development of risk management strategies that are related to the presence of resistant bacteria in groundwater in the urban areas of Douala and Yaoundé. In each of these urban cities, 14 wells and 2 hospital effluents were analyzed. These analyses included the isolation and identification of P. aeruginosa cells by the filtration method, their resistance to antibiotics by the diffusion disk method and the examination of some abiotic factors of the environment (physicochemical, hydrological and weather). The multi-factor ANOVA test was used to prioritize the impact of abiotic factors on changes in cell abundances. It appears that groundwater of Douala and Yaoundé are slightly acidic (pH <7) with high electrical conductivity values of 500μS / cm and 700μS / cm in Douala and Yaoundé respectively. This reflects an average mineralization rate of groundwater. Oxygenation of these waters did not exceed 6.5 mg / L on average. These cities have high organic matter loads (2.9 to 7.2 mg / L) which are above those often encountered in oligotrophic ecosystems. Bacteria colonies count have revealed monthly variations in cell abundances ranging from 1 to 218 CFU / 100 mL in the wells of Douala and from 1 to 210 CFU / 100 mL in those of Yaoundé. Considering the cell abundance, the health risk associated with P. aeruginosa would be higher during dermal contamination than during an oral contamination, which requires higher abundances of about 1010 CFU. However, because of the temporal fluctuations in cell densities observed in wells, this health risk was non permanent. The fluctuations were mainly influenced by electrical conductivity, CO2 and dissolved O2. These three parameters would exert more influence on the enzymatic activity and metabolism of P. aeruginosa. Isolated strains of P. aeruginosa from the wells generally expressed resistance to antibiotics against which they are normally sensitive. This was the case for ofloxacin (30%, n = 312), piperacillin (22%, n = 312), ticarcillin (15.84%, n = 312), ceftazidime (14.15%, n = 311) and gentamicin (11.22%, n = 311). The appearance of these resistant strains is a major concern because of its significant reduction in the treatment options for waterborne infection. In order to determine the origin of these resistances, wells were divided into two main groups. Those close to hospitals (PPH) and those far from hospitals (PEH). Similarly, the susceptibility to antibiotics of P. aeruginosa strains isolated from hospital effluents was evaluated in both cities. The multiple regression test was applied to evaluate the variance (%) of antibiotic diameter inhibitions as influenced by physicochemical factors of the well. Hospital effluents of both cities, present a resistance prevalence that was greater than 50% as obtained with ticarcillin, ofloxacin, cefepime, piperacillin, ticarcillin / clavulanate, amikacin and gentamicin. The multidrug resistance index (MRA) established on a scale of 0 to 1 varied from 0.57 to 0.74 and from 0.74 to 0.83 in Yaoundé and Douala respectively. In the PPH, the MRA index fluctuated between 0.47 and 0.68 and between 0.48 and 0.79 for wells in Yaoundé and Douala respectively. Its values were lower in PEH, ranging from 0.1 to 0.47 in Yaoundé and 0.2 to 0.48 in Douala. Comparatively, the prevalence of resistant strains was significantly high in PPH than in PEH. This was explained by the vulnerability of PPH to hospital effluents that contains resistant bacteria. In wells of the two cities, less than 5% of the resistances obtained can be explained by the variations of abiotic factors of the medium. It is indeed established that environmental stress triggers in P. aeruginosa, molecular adaptation mechanisms which leads to antibiotics resistance mechanisms. This weak relationship could be related to the magnitudes of abiotic factors, which would be less stressful for P. aeruginosa and slightly affect its susceptibility to antibiotics. This partly explains the low prevalence of resistance observed in PEH. Among the parameters, only the pH seems to have had a significant impact on the resistance, which could be due to the acidic stress generated by this factor in groundwater. At the end of this study, it was realized that, groundwater of Douala and Yaoundé are contaminated with antibiotic resistant P. aeruginosa. This resistance could be transferred to human and populations upon consumption of the water if not treated. In addition to controlling the proper use of antibiotics in hospitals, the control of water acidity is recommended in the monitoring and limitation processes of resistance in natural waters.