Different bacterial strains identified
Of the 222 water samples collected, 265 bacterial strains were isolated, the majority of which were strains of Coagulase Negative Staphylococcus (CNS) with 37.74% (n = 100), followed by strains of Klebsiella pneumoniae (21.89%; n = 58), Escherichia coli (10.57%; n = 28), Aeromonas spp. (06.42%; n = 17) and Proteus mirabilis (06.04%; n = 16). Regarding hospital wastewater samples, the most isolated bacterial species were Klebsiella pneumoniae (28%), Aeromonas spp. (24%) and Escherichia coli (24%). A predominance of strains of Aeromonas spp. (33.33%) and CNS (30.30%) was observed in the groundwater samples. As for the samples of drinking water in sachets taken from producers, a predominance was observed for strains of CNS (45.80%), followed by strains of K. pneumoniae (26.72%) and E. coli (13.74%). The same remark was made for drinking water samples taken from street vendors, a predominance of CNS strains (31.58%), followed by Proteus mirabilis (21.05%) and K. pneumoniae (13.16%) strains (Table 3).
Resistance of Gram-negative bacilli strains to the antibiotics used
The test of antibiotic resistance showed that all isolated gram-negative bacilli strains are multidrug resistant with resistance of almost all strains to amoxicillin, ampicillin and amoxicillin + clavulanic acid. Moderate resistance was noted to ceftriaxone and very low resistance to imipenem (Figure 1). However, we noted that all strains of K. pneumoniae isolated from groundwater were sensitive to amikacin, nalidixic acid and gentamicin. While the strains of Aeromonas spp. isolated from the same samples were only sensitive to amikacin. As for the P. aeruginosa strains isolated from the same samples, they were sensitive to imipenem, amikacin and gentamicin (Figure 1A). The strains isolated from the samples of hospital wastewater showed very strong resistance to the antibiotics used. Thus, the strains of K. pneumoniae showed strong resistance to amoxicillin (100%) and ampicillin (100%) and moderate resistance to omoxicillin + clavulanic acid (50%). All strains of Aeromonas spp. showed complete resistance to amoxicillin, ampicillin, amoxicillin + clavulanic acid and nalidixic acid and 50% resistance to ceftriaxone, imipenem, amikacin and gentamicin. As for the E. coli strains, they were all resistant to amoxicillin, ampicillin, amoxicillin + clavulanic acid and ceftriaxone (Figure 1B). The resistance of strains isolated from drinking water in sachets collected from producers showed that all strains of Shigella spp. isolated were resistant to all antibiotics tested except amikacin. Strains of Enterobacter spp. isolated from the same samples also showed complete resistance to amoxicillin, ampicillin, amoxicillin + clavulanic acid, ceftriaxone and gentamicin. Strains of K. pneumoniae, on the other hand, showed strong resistance to amoxicillin (100%), ampicillin (100%) and amoxicillin + clavulanic acid (60%), and low resistance to ceftriaxone (40%) and imipenem (20%) (Figure 1C). All the strains isolated from drinking water in sachets collected from street vendors showed total resistance to amoxicillin, ampicillin and amoxicillin + clavulanic acid, except for the strains of Enterobacter spp. which showed resistance of 66.67% to amoxicillin + clavulanic acid and strains of Serratia spp which showed low resistance of 33.33% to amoxicillin, ampicillin and amoxicillin + clavulanic acid (Figure 1D).
Resistance genes detected in Gram-negative bacilli
Of the 15 resistance genes sought in the genome of Gram-negative bacilli strains, only 8 were detected, namely the TEM, SHV, CTX-M15, VIM, NDM, SUL1, SUL2 and AADA genes. Thus, in all 23 strains of Gram-negative bacilli, the SHV gene was detected with a frequency of 56.52% (n = 13), followed by the SUL2 gene (52.17%; n = 12), AADA gene (39.13%; n = 9) and VIM gene (13.04%; n = 3). The SHV, CTX-M15, VIM, SUL2 and AADA genes were detected at the same frequency of 15.79% (n = 3) on all 19 strains of Gram-negative bacteria isolated from hospital wastewater. Among the 71 Gram negative bacilli strains isolated from sachet drinking water collected from producers, the most detected gene is SUL2 with a frequency of 26.76 % (n = 19), followed by the AADA gene (18.31 %; n = 13), SHV gene (14.08 %; n = 10), VIM gene (08.45 %; n = 6), NDM and TEM genes (04.23 %; n = 3). As for the strains (n = 76) isolated from sachet drinking water collected from street vendors, the most detected gene was SHV (32.69 %; n = 17), followed by the SUL1 gene (28.85 %; n = 15), SUL2 gene (23.08 %, n = 12), TEM gene (19.23 %; n = 10), AADA gene (9.62 %; n = 5), CTX-M15 (5, 77 %; n = 3) and NDM gene (3.85 %; n = 2) (Figure 2).
Table 4 shows the association of resistance profiles and resistance genes of the bacterial strains (Gram-negative bacilli) isolated according to the different types of samples. Thus, out of the 58 strains of K. pneumoniae isolated in this study, 4 resistance profiles were established. These 4 profiles are associated with 5 resistance genes (SUL1, SUL2, AADA, SHV and VIM). Of the 28 strains of E. coli isolated in our study, 3 resistance profiles were established and then associated differently with 3 resistance genes (CTX-M15, TEM and SHV). Only one resistance profile was not associated with any resistance gene. This strain was isolated from drinking water in sachets collected from producers. 5 resistance profiles were established after the susceptibility test of the strains of Aeromonas spp. antibiotics. These 5 profiles were associated with 4 resistance genes (SHV, VIM, AADA and SUL2). However, 3 strains of Aeromonas spp. isolated from hospital wastewater and having the same resistance profile were not associated with any resistance gene. Regarding the P. aeruginosa strains isolated in this study, 3 resistance profiles were established with an association of 5 resistance genes (TEM, SHV, SUL1, SUL2, AADA) (Table 4).
Resistance of Gram-positive cocci strains to the antibiotics used
All Gram-positive cocci strains isolated in this study are all coagulase-negative staphylococcus (CNS). A total of 100 strains of CNS were isolated (Table 3). The susceptibility test of the CNS strains to the antibiotics used showed that all the CNS strains isolated from hospital wastewater were resistant to all antibiotics tested except fosfomycin and erythromicin. Strains isolated from groundwater showed high resistance to amoxicillin (100%), oxacillin (100%) and cefoxitin (80%) and low resistance to vancomycin (40%), fosfomycin (20 %) and clindamycin (20%). As for the strains isolated from drinking water in sachets collected from producers, the highest resistance is to amoxicillin (72.73%), oxacillin (72.73%) and cefoxitin (63, 64%). While, the resistance of strains from drinking water in sachets collected from street vendors is much higher to amoxicillin (72.73%), oxacillin (54.55%), and fosfomycin (54.55%) (Figure 3).
Resistance genes detected in coagulase-negative staphylococcus (CNS) strains
Three resistance genes (Mec A, Van A and Van B) were detected in the genome of the CNS strains isolated during this study. The Mec A gene was detected in all strains isolated from groundwater (100%) and hospital wastewater (100%). This same gene was detected at 71.67% and at 41.67% in strains isolated respectively from drinking water in sachets collected from producers and street vendors. As for the Van A gene, it was detected in strains isolated from drinking water in sachets collected from producers and street vendors with frequencies of 33.33% and 8.33% respectively. Whereas, the Van B gene was detected only in the strains isolated from drinking water in sachets collected from producers with a frequency of 33.33% (Figure 4).
Out of the 100 CNS strains, we were able to establish with the results of the susceptibility test of these strains to the antibiotics used, 17 different resistance profiles. These resistance profiles were associated with the resistance genes Mec A, Van A and Van B. All this according to the types of samples analyzed (Table 5).