The ability of strains of faecal bacteria (
Diarrheal diseases are among the major causes of mortality in developing countries. Most cases of diarrhea (88%) are attributable to unsafe water and inadequate sanitation and hygiene [
Groundwater from wells, springs, and boreholes is largely consumed due to limited tap water supply in Cameroon. These water sources have poor hygienic quality due to their proximity to latrines. Protection and upgrading of wells were recommended for safe drinking and domestic water sources [
Because faecal bacteria are distributed widely in point-of-use water sampled from storage vessels among well water consumers in Garoua [
Household water treatment results in clean water and one usually devoid of coliforms. Filtration with small-pores filters and boiling have been shown to be effective at removing many microbes and suspended solids [
However, unhygienic handling of water during transport or within home can contaminate even previously safe water [
Nola et al. [
Stored water is one of the most important types of water supplies for domestic purposes in Cameroon. The majority of studies undertaken on water in Cameroon has focused on surface and groundwater quality with little work being devoted to point-of-use water quality assessment.
Information about survival/growth capacity of pathogenic bacteria in treated well water stored under local climatic condition is necessary to advice consumers about correct handling of well-treated well water at home.
This research aimed at evaluating survival and growth of some faecal and pathogenic bacteria in autoclaved and/or filtered well water used for drinking purposes in Garoua region. Our study explored the evolution of the abundances of some faecal bacteria in the well water, treated by autoclaving and/or filtration, during its storage in household conditions.
The study was carried out in Garoua (north Cameroon). This region is located at latitude 9°18′N and longitude 13°24′E. The Garoua region is made up of heterogenic soils [
Two well water points (W1, W2) were selected based on their highest importance as a drinking water supply, significant difference between their mineralization levels [
Four water samples (
At each site (W1, W2), water samples were collected in 500 mL sterile glass bottles, respectively, coded in three replicates and in corresponding 100 mL clean polyethylene bottles. Samples collected in polyethylene bottles were used for physicochemical analysis at the sample site. Those collected in glass bottles were destined for bacteriological analyses and experiments in laboratory.
The main physicochemical parameters considered were temperature, total dissolved solids (TDS), pH, electrical conductivity (EC), and salinity. These parameters were chosen in accordance with their general importance on bacterial metabolism and the availability of our laboratory equipments. Physicochemical analyses were made directly in the field using the techniques described by Rodier [
Heterotrophic bacteria were enumerated using the spread plate method with Plate Count Agar (Bio-Rad, France), incubated at 37°C for 72 hours. Membrane filtration was used to enumerate qualitative microbial indicators (total coliforms, faecal coliforms,
For each sample site, one of the 3-bottled samples replicates was analyzed for heterotrophic bacteria and qualitative microbial indicators as previously indicated. The second was autoclaved at 121°C for 15 min to destroy biological and heat sensitive antimicrobial agents. The third replicate was filtered and divided into two water samples: one was autoclaved, to destroy biological and heat sensitive antimicrobial agents that might pass through the 0.2
Three bacterial species were used for their importance to the environment and public health:
For the preparation of bacterial stocks, a colony forming unit (CFU) of each strain from standard agar medium was inoculated into 100 mL of nutrient broth for 24 h at 37°C. The strain of
Cells were then harvested by centrifugation at 3000 g for 10 min at ambient temperature and washed twice with sterile NaCl solution (8.5 g/L).
The washed cells were suspended in autoclaved filtered water from each well (W1 and W2). From these new solutions, inoculations in three flasks (filtered-nonautoclaved water, filtered-autoclaved water, and unfiltered-autoclaved water) were performed for each well. Based on our preliminary study, cell concentration was adjusted at 103 CFU/mL. Only one bacteria strain was added in each solution in the flask. Flasks were then incubated without shaking, in the dark, at room temperature (
Bacterial abundances were determined immediately after inoculation, at regular intervals (one day) up to three days by the spread plate procedure. Samples were serially diluted in a 0.85% (w/v) NaCl solution. The strain of
Bacterial abundances are expressed as colony forming unit (CFU) per volume of water. The number of colony forming units (CFU) is multiplied by the dilution factor and expressed in CFU/mL of water.
The values
The results of the physicochemical analysis show that water samples range from acidic to basic with low to high mineralization. The TDS and salinity of water samples also varied with water source.
The well W2 had the highest pH value, a relatively higher salinity, TDS, and also the highest electrical conductivity (Table
Mean (and standard deviation) values of some physicochemical parameters taken from wells and microcosms water samples.
Parameters | Wells | |||||||
---|---|---|---|---|---|---|---|---|
W1 | W2 | |||||||
Raw water | Unfiltered-autoclaved | Filtered-nonautoclaved | Filtered-autoclaved | Raw water | Unfiltered-autoclaved | Filtered-nonautoclaved | Filtered-autoclaved | |
pH (CU) | 6.85 (0.26) | 7.32 (0.12) | 7.20 (0.15) | 7.18 (0.17) | 7.52 (0.15) | 7.68 (0.11) | 7.71 (0.09) | 7.78 (0.13) |
Conductivity |
626 (49.94) | 567 (15.20) | 510 (16.30) | 491 (17.00) | 1154 (96.77) | 1164 (21.00) | 1142 (18.00) | 1129 (32.00) |
TDS (mg/L) | 435 (36.39) | 395 (17.00) | 364 (33.25) | 343 (34.25) | 819 (65.25) | 800 (31.00) | 797 (21.00) | 768 (25.00) |
Salinity (ppm) | 315 (24.85) | 282 (15.20) | 267 (11.00) | 244 (17.00) | 586 (45.40) | 582 (43.00) | 563 (39.70) | 557 (31.90) |
Sample size (
Although water samples of different microcosms did not have the same physicochemical characteristics as the well they have been taken from, they followed the tendency of the parent points. Filtration and autoclaving both reduced the conductivity, TDS, and salinity levels of the well water samples. These treatments enhanced the water pH.
Abundances of each bacterial group isolated from sampled wells are presented in Table
Averages (and standard deviation) values of bacteriological parameters analyzed in each point of well water.
Sampling site | Bacterial abundances (CFU/100 mL) | ||||
---|---|---|---|---|---|
HPC | Total coliforms | Faecal coliforms |
|
Faecal streptococci | |
W1 | 3.45 |
1.83 |
9.33 |
3.53 |
3.57 |
W2 | 7.03 |
3.06 |
2.56 |
2.93 |
3.67 |
Sample size (
The test bacteria were added at concentration 3 Log10CFU/mL. The viable counts of the six test bacteria increased after one day in unfiltered-autoclaved water, but the decrease depended on the organism and the water sample in which they were examined. The population of
Survival curves of bacterial strains in well W1 water, unfiltered-autoclaved (a1); filtered-nonautoclaved (a2); filtered-autoclaved (a3), and well W2 water, unfiltered-autoclaved (b1); filtered-nonautoclaved (b2); filtered-autoclaved (b3).
Using filtered-nonautoclaved water from well W1,
Of the six bacteria tested,
Comparing the raw and treated well water samples, it seems that treatment leads to a decrease in the concentrations of the major elements. For instance, salinity and electrical conductivity reached respective minimum levels of 244 ppm and 491
Boiling and/or filtering water is advised until disinfection and retesting to confirm that the contamination has been eliminated.
Treatment of well water by filtration and/or boiling is often presented as an adequate solution to compensate the lack of drinking water in poor communities in developing countries [
During three days of water storage, faecal bacteria survive in different microcosms to varying degrees. The dynamics of bacterial abundances, in most cases, can be divided into two phases: a phase of relative stability or low decrease in bacterial abundances, followed by a phase of relative growth or bacterial inhibition (Figure
The second phase is similar to bacterial latency or accelerated development of cells and is visible on the 2nd or 3rd day, reflecting the depletion of nutrients in the environment or good bacterial adaptation to new environmental conditions. Overall, the bacterial latency seems to depend on the origin and type of water as well as the bacterial strain. Microorganisms rapidly develop mechanisms to adapt to changes in their environmental conditions [
The filtered-nonautoclaved water is less favourable to bacterial survival/growth than filtered-autoclaved water. The filtration through the 0.2
Although no disinfectant has been added to the treated water, abundances of bacterial pathogens decreased during storage of household water out of reach of any source of secondary contamination (insects, dust, dirty hands, and soiled containers) [
The survival of
Bacterial strains of
The well water provided at source is unsafe for consumption with regard to microbial indicators. The absence of these bacteria in autoclaved and/or filtered well water indicates that filtration and boiling can be recommended if properly carried out. However, the survival and/or growth of some pathogenic bacteria in autoclaved and/or filtered well water, during storage at home, suggest the importance of water treatment and safe storage at household level. According to our results and taking into account the economical context of the region which is too poor, it is recommended that rather than discouraging the use of traditional latrines, users should be made aware of the importance of discarding them from water sources and maintaining them hygienically.
The authors declare that they have no conflict of interests that could inappropriately influence this work.
The authors thank the