In developing countries increase in human population and industrialization has exerted an enormous pressure on the provision of safe drinking water. Provision of high quality water as well as protecting and conserving scarce water resources is therefore one of the greatest challenges currently facing national and regional governments
. We report here the factors affecting the bacteriological quality of well water in New Bell and Bepanda in Douala, Cameroon. This information will strengthen efforts in the provision of safe water to inhabitants of study sites.
Total viable bacterial counts (0–4.25 × 104 CFU/mL), total coliform counts (0–1.4 × 104 CFU/mL), fecal coliform (0–9.0 × 103 CFU/mL) and Vibrio counts (0–8.0 × 103 CFU/mL) were high throughout the period of study (Table
1). Of the 150 wells sampled, one well (in Bepanda) recorded no bacterial contamination (0 CFU/mL) throughout the study period. In New Bell, bacterial counts of 0 CFU/mL were obtained from one well only during the dry season. These wells recording 0 CFU/ml were disinfected by chlorination and used as a source of drinking water. In New Bell, chlorination was abandoned during the rainy season and bacterial contamination was detected in water. Samples from other wells were heavily contaminated and did not meet the WHO
 standards that stated that coliforms or fecal coliform must not be detectable in any 100 mL of drinking water. TVBC exceeded the EPA
 limit of 1.0 × 102 CFU/mL. These findings are worrisome. Uses of well water reported included laundry and washing of kitchen utencils (100%), cooking (73%) and washing of fruits and vegetables (50.4%) (Additional file
1). These could predispose to waterborne infections. High counts of indicator bacteria suggest heavy pollution of water with fecal matter. Recent studies in other developing countries
[24, 25] have also reported high TVBC, total coliform and fecal coliforms in ground water. Significant differences (P < 0.05) in bacterial counts were observed between seasons, with higher counts recorded in the rainy season than in the dry season (Table
2). The city of Douala is poorly drained. During heavy rains, most parts of the study area are flooded and this could result in well contamination. Rainfall and flooding events have been shown to negatively impact well water quality
 resulting in outbreaks of waterborne diseases as flood water carry microbial contaminants into unprotected water sources. Inhabitants dispose domestic waste in pits (29.3%), public vats (64.2%) and in the open (6.5%). Public vats at times are not regularly emptied when full. Under such circumstances, continuous dumping of wastes results in overflow to the surrounding. During heavy rains, these wastes could be washed into water sources contributing to pollution. A strong positive correlation occurred between fecal colifoms and total colifom counts (+0.635), but correlation between total coliforms and TVBC (+0.468), fecal coliform counts and Vibrio counts (+0.433) though positive was weaker. This finding suggests that these organisms could have originated from same or similar sources of contamination.
Well characteristics including construction and site management have been shown to be the most important factors responsible for well vulnerability to contamination
. We evaluated the relationship between well characteristics and bacteriological quality of well water. Total viable bacterial counts (Table
3), total coliform counts (Table
4), fecal coliform counts (Table
5) and Vibrio counts (Table
6) were higher in open wells than in wells with a lid. High bacterial counts also occurred in wells irrespective of height of casing above ground (Tables
6). A weak negative correlation occurred between well casing elevation and TVBC (−0.003) and also with Vibrio counts (−0.023). This shows that increasing well height will result in only a minor decrease in these counts. However, a weak positive correlation was observed between elevation and total coliform counts (+0.041) (Table
4) and also with fecal coliform counts (+0.036) (Table
5). This was not significant (P>0.05). Thus counts of these bacteria in well water will increase only slightly with increase in well height. Bacterial counts decreased with increase in well distance from sanitary structure (Tables
6). A negative correlation was seen between well distance and TVBC (−0.119), total coliform counts (−0.154), fecal coliforms (−0.131) and, Vibrio counts (−0.121) confirming the fact that increasing the distance between wells and sanitary structure would reduce water contamination. Although respondents demonstrated a good knowledge of waterborne diseases (100%), well water contamination and possible sources of contamination (76.5%) (Additional file
1), an indication of the success of the sensitization campaigns by the Ministry of Public Health, wells were not protected. Majority of wells were not constructed following recommended guidelines of 0.6 m well casing above ground
 and a lateral separation distance of at least 30 m from sanitary facility
. Eighty-two (54.7%) wells were not covered, 52% had well casing <0.6 m above ground and 96% wells were located at a distance <15 m from sanitary structure (Additional file
1). These factors may increase the risk of contamination and account for our observations. Findings of our study show that even protected wells were still exposed to contamination. Covered wells with casing raised above 0.6 m which were poorly maintained, located near sanitary structures were subject to contamination. This may explain our finding of no significant difference in counts between covered and open wells and between wells with different casing elevations. Use of pit latrines (93%) is common in study sites. The distance between wells and sanitary structure ranged from 1 to 17.4 m. Overcrowding in study sites leaves inhabitants with limited distance between wells and sanitary structures. The close proximity of wells to sanitary infrastructure (mean distance of 7.4 m and 7.6 m in Bepanda and New Bell respectively) in addition to the presence of cracks in most casings could facilitate seepage from pit latrines contaminating well water. Wells in study sites are shallow
 and could also be easily contaminated through seepage from latrines through the sandy, porous soil in Douala. However, to confirm this, studies focusing only on protected wells need to be carried out. Thus, poor town planning, indiscriminate well siting, poor maintenance and construction of wells may account for the poor water quality in study sites. Muruka et al.
 detected an indirect association between well distance from pit latrines and fecal contaminants, with a decrease of 3.38 fecal coliforms/100 mL counts for every 1 m increase in distance. Asheesh
 did not find any association between dug-well bacteriological quality and distance to the nearest pit latrines contradicting our findings. However, similar to our findings, Adetunji and Odetokun
 reported a negative correlation between well distance and aerobic bacterial counts. Thus, as long as these wells and sanitary structures are in close proximity, the potential health hazard posed by highly polluted water cannot be overemphasized especially as 73% of respondents reported to have been victims of waterborne disease.
Inhabitants (100%) used the bucket and rope method to lift water from wells. This method is cheaper but could introduce contaminants into water. The use of a submersible pump is recommended but is unaffordable due to restricted financial resources of inhabitants. Although wells were disinfected, 88.5% of respondents used table salt as disinfectant and frequency of disinfection was irregular (Additional file
1). This is inappropriate and explains the heavy microbial contamination recorded in wells. Well characteristics and hygiene and sanitary practices in study sites were similar, hence there were no significant differences in bacteriological quality of water between sites.
Bacteria isolated included both pathogenic and potentially pathogenic species. Overall S. aureus (17.8%), E. coli (12.6%) and A. hydrophila (10.4%) predominated. There was variation in predominant isolates with site (Table
7). S. aureus, a normal flora of the skin, is a well recognized pathogen. It has been associated with a large number of infections including food intoxication, community acquired urinary tract infections
, conjunctivitis, scalded skin syndrome, toxic shock, respiratory infections and skin infections. E. coli (12.6%) the second predominant isolate is a major public health concern as it not only indicates recent contamination with fecal matter and the possible presence of intestinal pathogens but due to the fact that certain pathogenic strains of the organism such as the enteropathogenic O157:H7 responsible for several out breaks of bloody diarrhea
 have been detected in water. A. hydrophila (10.4%) is an opportunistic pathogen particularly in immunocompromised individuals. They cause non-gastrointestinal infections in humans and have been isolated from drinking water even after chlorination
. Its presence in our samples as one of the predominant isolates is thus a cause for concern. Other enteric organisms isolated included Citrobacter fruendii (9.4%), Enterobacter aerogenes (7.6%), Klebsiella pneumoniae (7.2%) and Salmonella spp (4.5%). Their isolation further confirms the contamination of water with fecal material and the possible presence of other waterborne enteric pathogens such as viruses and protozoa not included in our study. These enteric isolates are also of public health importance as they have been associated with several infections. Pseudomonas aeruginosa (9.1%) is an opportunistic pathogen responsible for a wide range of acute and chronic infections
 when introduced into areas devoid of normal defenses. It is a major cause of bacteremia, soft tissue infections, conjunctivitis, infections of burns and wounds, cystic fibrosis, endocarditis and otitis media
Four species of Vibrio were isolated from samples: Vibrio mimicus (4.8%), V. fluvialis (4.1%) V. vulnificus (3.6%) and V. cholerae (2.01%) (Table
7) all of which have been shown to cause infections in man and aquatic organisms. V. mimicus is closely related to V. cholerae in terms of pathogenesis of infections. Pathogenic strains cause cholera-like diarrhea in man
 as well as infections in fish
 and have been reported to express same virulence factors as V. cholerae. V. fluvialis is an important cause of cholera-like bloody diarrhea in humans and is commonly found in areas with poor sanitation
. V. vulnificus has been shown to cause gastroenteritis and is the leading cause of reported death resulting from seafood consumption
. Serological typing of V. cholerae isolates showed that they belonged to the non-O1 serogroup. Although not responsible for epidemic cholera, the presence of the non-O1 serogroup in well water cannot be overlooked as they have been associated with diarrheal disease
. Certain strains have been shown to contain virulence factors present in O1 strain
. Furthermore, non-O1 serogroup have been reported to undergo serogroup conversion resulting in emergence of new strains with pathogenic potential
. Recent studies carried out in our study area
 have reported the co-existence of O1 and non-O1 strains in well water.
It is generally believed that groundwater is relatively free of microorganisms and thus fit for consumption. However, findings from present study show that water from dug wells in New Bell and Bepanda contain high numbers of pathogenic enteric bacteria. Ndjama et al. reported a high prevalence of waterborne diseases in other parts of Douala. Our findings together with the report of Ndjama et al. demonstrate that waterborne diseases could be a significant health challenge in Douala. However, to determine the role of our isolates in causing diarrheal disease, their enterotoxin production potential has to be investigated. Although the Ministry of Public Health carries out sensitization campaigns on well disinfection particularly during cholera outbreaks, findings from our study show an urgent need for a regular and sustained disinfection programme in study sites.
Ciprofloxacin (96.2%) was the most effective antibiotic among those tested. Other potent antibiotics included gentamicin (88.5%), tetracycline (76.9%), ceftriaxone (76.9%), chloramphenicol (70%) and doxycycline (63.1%) (Table
8). Ciprofloxacin and gentamicin are relatively expensive drugs. In addition, gentamicin is formulated as injection. These factors discourage procurement and misuse of these drugs. Drug misuse particularly through automedication is a serious public health concern in Cameroon. Susceptibility to ampicillin (19.2%), cotrimoxazole (34.6%) and to a lesser extend doxycycline (63.1%) was low. These drugs were heavily used for treatment and prophylaxis during past cholera outbreaks in Douala
[45, 46] and could have resulted in selection of resistant bacteria. Considering that resistance markers have the potential of spreading across bacteria species, these organisms might have acquired resistance by various mechanisms. Forty-four (33.8%) isolates were multidrug resistant (Table
9) with twenty (20) showing resistance to five or more drugs. All (100%) P. aeruginosa, Salmonella spp, and E. coli tested were multi-drug resistant. Occurrence of multi-drug resistant bacteria in wells thus constitutes a health threat.
Ciprofloxacin recorded the lowest MIC values (0.117- 0.938 μg/ml) on all the isolates tested and among all the drugs (Table
10). With the exception of the staphylococci, which showed intermediate susceptibility to tetracycline and gentamicin (susceptibility break point = 8.0 μg/ml respectively), MIC determination confirmed isolates to be sensitive to antibiotics. These drugs are therefore of great value in eradication of waterborne infections in study sites. We did not use a control strain in antibiotic susceptibility testing. This constitutes a limitation to our study.
Observing that all multidrug resistant isolates were resistant to ampicillin and/or ceftriaxone, we tested isolates for extended spectrum beta-lactamase (ESBL) production potential as a possible mechanism of resistance to β-lactams. ESBL production was observed in all Salmonella species, Citrobacter fruendii and E. coli Talble 11. (This greatly limits:in treatment of infections caused by these pathogens. Our findings show that well water could play an important role in the dissemination of these ESBL producing organisms.