Seven social housing sites were selected based on specific criteria, including ease of access, population density, type of sanitation system, configuration of latrine pits, mode of effluent discharge into the environment, and spatial distribution. These criteria were applied to ensure the representativeness of various wastewater management practices and discharge conditions observed throughout the city’s social housing network. Wastewater samples were collected from seven designated points: MDG, RPE, BIY, Cverte, MSI, MSII, and MFD. Those geographic coordinates are given in Table 1 .

The samples for the bacteriological analysis were collected in sterile glass bottles of 500 mL. Samples for physicochemical analyses were collected bubble-free by a diver in 250 ml double-capped polyethylene bottles following the techniques recommended by Rodier et al. [10] . At the level of each sampling station, the physico-chemical analysis focused on 12 variables. Physico-chemical parameters (water Temperature (˚C), pH, electrical conductivity of the water (μS/cm), salinity (ppm), suspended solids (mg/L), total dissolved solid (ppm), water colour (Pt.Co), turbidity (FAU), nitrates (mg/L), nitrates (mg/L), orthophosphates (mg/L ${\text{PO}}_4^{3-}$) and ammonium ions (mg/L ${\text{NH}}_4^{+}$) were measured by colorimetry and/or spectrophotometry according to the techniques described by some authors [10] [11] . The various samples were then transported to the laboratory in a refrigerated chamber to undergo the various analyses and tests required. Bacteriological analysis begins within 4 hours of sampling.

The isolation of bacteria from the genus Vibrio was conducted through the utilisation of the surface spreading method. A volume of 100 μL of each sample was collected using a sterile micropipette and deposited onto the surface of Thiosulfate Citrate Bile Salts (TCBS) agar that had previously been poured into sterile Petri dishes (90 mm in diameter). The inoculum was distributed uniformly across the surface using a sterile rake or spreader until complete absorption was achieved. Subsequently, the plates were subjected to an incubation process at a temperature of 37˚C for a duration of 24 hours. The identification of Vibrio species commenced with a search for motility type and Gram staining. Gram staining is a method of staining bacteria that provides information on the morphology and structure of the bacteria wall. The colour, size and shape of colonies on TCBS agar were used as parameters. The process of classical biochemical identification has facilitated the identification of enzymes including oxidase, lysine decarboxylase, ornithine decarboxylase, urease, tryptophanase and β-galactosidase [12] . A suspension in sterile distilled water was prepared from a colony of the pure culture on an alkaline nutrient agar. The bacterial suspension was distributed in the capsules of the API 20E system (BioMérieux, France). After 24 hours of incubation at 37˚C, the metabolites formed were visualised by colour reactions or the addition of reagents. The APIDENT 2.0 software was used to numerically determine the corresponding bacterial species. The identification rate was maintained at least at 98%. Isolated bacteria were enumerated using an OSI brand colony counter. Bacterial abundances are expressed in decimal logarithmic units of colony forming units (CFU) per mL of water sample.

We used agar diffusion to carry out the antibiograms [13] . It was based on the presence or absence of an inhibition zone around an antibiotic-impregnated blotting paper (agar) disc. Antimicrobial susceptibility testing was performed on pure strains in accordance with the recommendations of the Antibiogram Committee of the French Society of Microbiology [14] . The antibiotics used belonged to several families. They were in the form of a disc of blotting paper, 6 mm in diameter, impregnated with well-determined quantities of active substances and rigorously controlled for the diffusion method. Table 2 lists the antibiotics used, their groups and their characteristics. The test results were only validated in those cases where the diameters of the inhibition zones of the control strains were within the performance ranges. Inhibition zone diameters of bacteria isolates were measured and then compared to National Committee of Clinical Laboratory Standards [15] . The sensitive (S) category means that the strain is susceptible to the antibiotic treatment given at the normal dose. In the intermediate category (I), the success of the therapy is not predictable. If the antibiotic is used at a higher dose than usual, the treatment will be effective. Intermediate means moderately susceptible or moderately resistant. The resistant (R) category means that there is a high probability of treatment failure regardless of the type of antibiotic treatment, or that the strain will not be affected regardless of the type of treatment. Monthly changes in physicochemical parameters at the different sampling sites and the prevalence of resistant (R), intermediate (I) or sensitive (S) strains to each antibiotic were plotted using Microsoft Excel.

The Principal Component Analysis (PCA) performed on the physico-chemical and bacteriological parameters facilitated the characterisation of the distinct groups that were formed. The purpose of PCA was to extract the primary information representative of the typical characteristics of the water environment from a database and to represent it as a new set of independent principal component variables [17] .

Bacteriological analysis helped to identify five species belonging to the genus Vibrio. These are: V. cholerae, V. alginolyticus, V. parahaemolyticus, V. vulnificus and V. mimicus. The biochemical profiles of the strains studied, and the different species identified are shown in Table 3 . The cultural characteristics of the different Vibrio species listed were yellow and flat colonies of 2 mm in diameter for the presumptive of V. cholerae, then yellow and large colonies (5 mm in diameter) presumptive of V. alginolyticus, large and green colonies (5 mm in diameter) presumptive of V. parahaemolyticus, small and green colonies (2 mm in diameter) presumptive of V. vulnificus and finally those which were medium and green colonies (3 mm in diameter) presumptive of V. mimicus. Table 3 shows the biochemical profiles of the strains studied, as well as these different species identified.

Continued

MYC = medium yellow colony; LYC = large yellow colony; LGC = large green colony; SGC = small green colony; MGC = medium green colony; +: Positive for 90 to 100 % of strains ; −: Negative for 90 to 100% of strains ; +/−: variable.

Several species of the genus Vibrio have been isolated and identified from water samples collected at all sampling stations. These are V. parahaemolyticus , V. alginolyticus , V. cholerae , V. mimicus and V. vulnificus. These species, known for their role in infectious diarrhea in humans, especially Vibrio cholerae and Vibrio parahaemolyticus, have been regularly isolated from the wastewaters of social housing networks (SIC camps). Some studies carried out in the aquatic environment of the central and coastal regions of Cameroon [18] - [20] have identified strains belonging to Vibrio species similar to those found in our study. The spatio-temporal variations in the abundance of bacterial germs are presented in Figure 1 and Figure 2 . The abundances of V. cholerae cells, expressed in decimal logarithmic units (CFU/ mL), ranged from 0 to 3.20 log CFU/mL. Undetectable bacterial load (0 log CFU/mL) was observed mainly during the month of February at all sampling points. The highest value (3.20 log CFU/mL) was noted at point BIY ( Figure 1 ). Concentrations of V. alginolyticus ranged from 0 to 3 log CFU/mL. Undetectable bacterial load (0 log CFU/mL) was observed mainly at the Cverte and MSII points in March, April and May. The highest value (3 log CFU/mL) in the month of April at the MFD point ( Figure 1 ). V. parahaemolyticus concentrations ranged from 0 to 4.40 log CFU/mL. Undetectable bacterial load (0 log CFU/mL) was observed in March at point MDG, in April at points RPE, MSI and MSII and in May at points MDG, MSI and MSII. The highest value (4.40 CFU/mL) was in February at point BIY ( Figure 1 ).

Concentrations of V. vulnificus ranged from 0 to 2 log CFU/mL. Undetectable bacterial load (0 log CFU/mL) was observed mainly at the MDG, BIY, Cverte and MSI points throughout the study period. The highest value (2 log CFU/mL) in March at the MFD point ( Figure 2 ). And the densities of V. mimicus varied from 0 to 2 log CFU/mL. Undetectable bacterial load (0 log CFU/mL) was observed mainly at the MDG, BIY, Cverte and MSI points throughout the study period. The highest (2 log CFU/mL) in March at the RPE point ( Figure 2 ).

As illustrated in Figure 3 , the recovery frequency of bacteria isolated during the course of the study is demonstrated. Of the species identified, Vibrio parahaemolyticus was the most prevalent, accounting for 91% of the total. This was followed by Vibrio cholerae (6%), Vibrio alginolyticus (3%), Vibrio vulnificus (0%) and Vibrio mimicus (0%) ( Figure 3 ). It has been asserted by certain authors that the aforementioned species, which are distinguished by their role in the causation of infectious diarrhoea in humans, most notably Vibrio cholerae and Vibrio parahaemolyticus, have been frequently isolated with spatial and temporal occurrence rates of 100% each [6] .

In the context of the dry season, strains of V. parahaemolyticus and V. cholerae exhibited the highest levels of resistance to six antibiotics that were subjected to testing. These were V. parahaemolyticus resistance to amoxicillin/clavulanic acid, cefotaxime, colistin, azithromycin, nalidixic acid and doxycycline, and V. cholerae resistance to amoxicillin/clavulanic acid, cefotaxime, colistin, azithromycin, nalidixic acid and doxycycline. The V. alginolyticus species was resistant to two antibiotics: colistin and ciprofloxacin. In general, V. parahaemolyticus and V. cholerae were resistant to beta-lactams, polymyxins, macrolides, quinolones and partially to cyclins. V. alginolyticus was resistant to polymyxins and quinolones ( Figure 4 ). During the

same season, V. mimicus strains showed maximum resistance (i.e., 100%) to three antibiotics tested: amoxicillin-clavulanic acid, colistin and ceftazidime. V. vulnificus strains were resistant to five antibiotics: amoxicillin-clavulanic acid, cefotaxime, colistin, nalidixic acid and doxycycline ( Figure 5 ).

During the rainy season, strains of V. parahaemolyticus and V. alginolyticus species showed maximum levels of resistance to seven of the same antibiotics tested: amoxicillin-clavulanic acid, cefotaxime, ceftazidime, colistin, ciprofloxacin, nalidixic acid and doxycycline. Whereas V. cholerae species were resistant to two antibiotics: amoxicillin-clavulanic acid and colistin. In general, V. parahaemolyticus and V. alginolyticus were resistant to beta-lactams, polymyxins, macrolides, quinolones and cyclins. V. cholerae, on the other hand, was resistant to beta-lactams and polymyxins ( Figure 6 ).

Overall, V. cholerae showed the highest resistance rate in the dry season (60%) and the lowest in the wet season (20%), and V. alginolyticus showed the highest resistance rate in the wet season (70%) and the lowest in the dry season (20%). Table 4 below shows the overall percentage of resistance, susceptibility and intermediary of the strains tested for susceptibility according to season.

Antibiotic susceptibility testing of isolates revealed multiresistant strains depending on the antibiotic used. V. cholerae was the most resistant species, followed by V. vulnificus in the dry season, while V. alginolyticus was the most resistant of six species in the wet season, with resistance rates above 50%.

Furthermore, certain bacterial species of the Vibrio genus demonstrated sensitivities that were contingent on the presence of the antibiotic. In the dry season, V. alginolyticus (70%) demonstrated the highest level of sensitivity, followed by V. parahaemolyticus (60%). Conversely, in the rainy season, V. cholerae (70%) and V. parahaemolyticus (53%) exhibited the highest levels of sensitivity, with resistance rates exceeding 50%. With regard to resistance, the use of antibiotics in both human and veterinary medicine exerts selection pressure on commensal or pathogenic bacteria of humans or animals that can spread to the natural environment (continental and coastal waters or soil via livestock effluent or domestic wastewater). This has the potential to result in the emergence and subsequent dissemination of genetic determinants of antibiotic resistance to other environmental microbial communities [21] . This spread is facilitated by the common phylogeny within the bacterial world. According to some authors, Vibrio resistance is due to multiple mechanisms, including transferable plasmid and chromosomal resistance [22] . Indeed, the documented resistance exhibited by Vibrio strains to beta-lactam antibiotics is attributable to a plasmid that carries genes which also encode for a multitude of other antibiotics [23] [24] . As a result, transferable genetic elements within Vibrionaceae often lead to the acquisition of multidrug resistance, justified by their genetic proximity [25] [26] . What’s more, the penicillinase phenotype is easily detected by beta-lactam resistance [21] . This explains, on the one hand, the resistance of V. cholerae and V. vulnificus to amoxicillin + clavulanic acid and cefotaxime, and the resistance of V. alginolyticus to these same antibiotics in addition to ceftazidime. On the other hand, Vibrio resistance could be explained by the formation of biofilms in the piping of the sanitary sewage systems in Yaoundé’s SIC camps. Indeed, undecontaminated wastewater, stagnant water or water from industry is generally water containing bacteria and is generally a reservoir for microbial proliferation and biofilm development.

Still on the subject of bacterial susceptibility, Vibrio are usually sensitive to beta-lactams, aminoglycosides, quinolones, tetracyclines, chloramphenicol, sulfonamides, trimethoprim, furans, nalidixic acid and fluoroquinolones [21] . Other studies have confirmed that Vibrio cholerae is sensitive to beta-lactam antibiotics (amoxicillin, amoxicillin-clavulanic acid, and cefotaxime), aminoglycosides (gentamicin), tetracyclines (doxycycline), fluoroquinolones (ciprofloxacin), and quinolones (nalidixic acid). These findings are consistent with the results of the present study, which showed that V. parahaemolyticus are sensitive to ceftazidime, amoxicillin-clavulanic acid, gentamicin, chloramphenicol, cefotaxime, ciprofloxacin, nalidixic acid, and doxycycline, while V. alginolyticus is more sensitive to ceftazidime, amoxicillin-clavulanic acid, gentamicin, chloramphenicol, cefotaxime, and doxycycline [18] . Furthermore, the study also revealed that V. parahaemolyticus and V. cholerae are sensitive to ceftazidime, amoxicillin-clavulanic acid, gentamicin, chloramphenicol, cefotaxime, ciprofloxacin, and doxycycline.

The mean values physico-chemical variables of the effluent over the course of the study are shown in Figure 7 . The average water temperature is 25.6 ˚C (±1.7 ˚C), with values ranging from 22.2 ˚C to 26.9 ˚C depending on the site. This moderate variation likely reflects differences in exposure or depth. The highest value was recorded at the MFD sampling point during the short rainy season and the lowest value at the RPE sampling point during the same season ( Figure 7(A) ). Studies have shown that some pathogens grow extremely well at a mesophilic temperature range of 15˚C - 45˚C for most strains [27] [28] . The pH is generally alkaline, with an average of 7.73 (±0.43), ranging from 7.21 to 8.23. These values indicate a slightly basic environment, compatible with a good ecological status for most aquatic organisms. The highest value was recorded at point MDG during the long dry season and the lowest value was recorded at point MSII during the same season ( Figure 7(A) ). This alkalinity of water is due to the nature of the chemical substances present in the grey water of the SIC camps. The pH measured is ideal for growth of bacteria belonging to the Vibrionaceae family. According to some authors pH values between 6 and 8.5 are favourable for the expression of the biological potential of several groups of bacteria [29] .

Turbidity shows strong disparities: the average is 1015.8 FAU (±872.2), ranging from 226.5 to 2589 FAU. The highest value was recorded at sampling site MFD. As for the water color, the mean values ranged from 597.8 to 5657.8 Pt.Co, with the MFD site having the highest value ( Figure 7(B) ). These values are obtained at the MFD during the long rainy season.

The mean values of total suspended solids recorded during the study period ranged from 121 mg/L to 1609 mg/L. The Total dissolved solids values (TDS) varied between 295 and 1080 ppm with an average of 582 mg/L (±250.7). The highest value was recorded at point BIY during the long dry season and the lowest value at point MSI during the short rainy season ( Figure 7(C) ).

The electrical conductivity values varied between 590.3 and 2163 µS/cm. The highest value was recorded at the BIY point during the long dry season and the lowest value was recorded at the MSI point during the short rainy season. The electrical conductivity values varied considerably. The values obtained indicate that these waters are highly mineralised. In fact, minerals are important factors for bacterial growth. The high pH and electrical conductivity would favour the growth and spread of these bacteria, especially as their values coincide with the dry season, when epidemics are also documented [30] .

Salinity values ranged from 0.025 to 0.12 ppm with an average of 0.053 ppm. The highest value was recorded at point BIY during the long dry season and the lowest at point MSI during the short rainy season ( Figure 7(D) ). In addition, regions exposed to relatively high temperatures experience water losses through evapotranspiration, which indirectly affects the salinity of their waters. Identifying interactions between temperature and salinity may explain some of the variability in Vibrio distribution. Indeed, significant differences in Vibrio growth rates due to salinity were only observed at low temperatures [31] . The values for nitrate and nitrite ions are between 11.90 - 98.33 mg/L and 0.35 - 2.55 mg/L respectively. The highest values were recorded at point Cverte during the long dry season regarding nitrate and nitrite ions and the lowest values were recorded at point MS1 for nitrate ions and at a point MDG for nitrite ions during the short rainy season ( Figure 7(E) ). Ammoniacal nitrogen values ranged from 6.48 to 15.39 mg/L, with a mean value of 11.56 ± 0.68 mg/L. The highest value was recorded at the MS2 point during the long dry season and the lowest value at the MDG point during the rainy season. The values of the phosphate ions reached 6294.67 mg/L at the point of RPE during the long dry season ( Figure 7(F) ). Studies have shown that microbial diversity varies following changes in water chemistry that are caused by phosphate enrichment [32] .

A grouping of the parameters into 2 kernels is shown by the PCA applied to the different biological and physico-chemical variables. Most of the total variance is provided by the first two factorial axes F1 (51.89%) and F2 (17.79%), which explain 69.69% of the total inertia ( Figure 8 ). The factorial map shows a distribution of the seven sampling points with respect to their physicochemical and bacteriological characteristics. On the F1-F2 plane, active variables are grouped according to their correlations. Electrical conductivity, salinity, and total dissolved solids (TDS) are strongly associated and aligned along the positive side of F1, suggesting that they co-vary across certain stations. Conversely, variables such as turbidity, suspended solids (SS), water color, ammonium ( ${\text{NH}}_4^{+}$), nitrate ( ${\text{NO}}_3^{-}$), and phosphate ( ${\text{PO}}_4^{3-}$) are grouped toward the negative side of F1, forming a second cluster indicative of organic and nutrient-rich conditions. This opposition on axis F1 thus reflects a physicochemical gradient separating mineralized or saline waters from more organically polluted ones.

The Vibrio species show ecological associations aligned with this gradient. Vibrio parahaemolyticus, V. vulnificus, and V. alginolyticus are positioned on the positive side of F1, close to salinity and conductivity vectors, suggesting a preference for saline environments. In contrast, V. cholerae and V. mimicus appear on the negative side of F1, aligned with nutrient-rich and turbid conditions. These associations are consistent with established ecological patterns: halophilic species like V. alginolyticus and V. vulnificus are typically linked to higher salinity, while V. cholerae and V. mimicus are known to thrive in freshwater or wastewater environments rich in organic matter.

The spatial distribution of the sampling stations further supports this interpretation. Stations MSI, MSII, and MFD are located on the positive side of F1, associated with higher salinity and conductivity, and correlate with halophilic Vibrio species. In contrast, stations MDG, RPE, BIY, and Cverte fall on the negative side of F1, characterized by higher levels of nutrients and suspended matter, and show a greater presence of V. cholerae and V. mimicus. This separation may reflect the distinct environmental conditions associated with the two wastewater networks (labeled N1 and N2), each exhibiting specific physicochemical and microbial profiles. Principal component analysis suggests that physico-chemical and biological variables interact in a complex way, reflecting the complex processes that occur in the natural environment [6] .

The results of the correlations between the abiotic and bacteriological variables show that among the physicochemical parameters analyzed, certain variables significantly influenced the population and distribution of bacteria throughout the study. This would result in the fact that bacteria react differently to chemical compounds. Indeed, the influence of chemical compounds on the microflora of the soil and subsoil varies depending on the ability of the bacterial species to degrade this chemical compound, either to neutralize its toxicity or to make the nutrients available. and the energy source, which are necessary for its biosynthesis. Environmental factors that positively correlate recovery rates of Vibrio isolates from waters include temperature, electrical conductivity, and air flow, although bacterial strains can be actively disseminated during flooding [21] .