Bacteriological and physico-chemical assessment of wastewater in different region of Tunisia: impact on human health

<p>Abstract</p> <p>Background</p> <p>In many parts of the world, health problems and diseases have often been caused by discharging untreated or inadequately treated wastewater. In this study, we aimed to control physico-chemical parameters in wastewater samples. Also, microbiological analyses were done to reveal <it>Salmonella </it>strains and each <it>Escherichia coli </it>(<it>E.coli</it>) pathotype.</p> <p>Findings</p> <p>Sixty wastewater samples were collected from fifteen different regions of Tunisia. All physico-chemical parameters (pH, residual free chlorine, total suspended solids, biological oxygen demand, and chemical oxygen demand) were evaluated.</p> <p>For microbiological analyses, samples were filtered to concentrate bacteria. DNA was extracted by boiling and subjected to polymerase chain reaction (PCR) using different pairs of primers.</p> <p>The mean pH values recorded for the sampling point were above the WHO pH tolerance limit. The total suspended solids (TSS) concentrations varied between 240 mg/L and 733 mg/L in entrance points and between 13 mg/L and 76 mg/L in exit points. In entrance points, the studied wastewater has an average COD concentration that varied between 795 mg/mL to 1420 mg/mL. Whereas, BOD concentration of the wastewater ranged between 270 mg/L to 610 mg/L. In exit points, COD concentration varied between 59 mg/L and 141 mg/L, whereas BOD concentration ranged from 15 mg/L to 87 mg/L.</p> <p>The bacteriological control of wastewaters showed that, in entrance points, <it>Escherichia coli </it>(<it>E.coli</it>) was detected at the rate of 76.6%. Three <it>E.coli </it>pathotypes were found: ETEC (53.3%), EAEC (16.6%) and EIEC (6.6%).</p> <p>Concerning the ETEC isolated strains, 8 of 16 (50%) have only the heat-labile toxin gene, 5 of 16 (31.2%) present only the heat-stable toxin gene and 3 of 16 (18.7%) of strains possess both heat-labile toxin gene and heat-stable toxin gene. In exist point, the same pathotypes were found but all detected ETEC strains present only the "est" gene.</p> <p>Concerning <it>Salmonella </it>isolated strains; percentages of 66.6% and 20% were found in entrance and exit points respectively.</p> <p>Conclusions</p> <p>Wastewaters contain a large amount of pathogenic bacteria that present a real impact on human health. Assessment wastewater treatment stations have to consider in account enterobacterial pathogens as potential pathogens that should be correctly controlled.</p

Detection and quantification of Hepatitis A and E vírus in wastewater from Tunisia <br />

Enteric viruses contaminating the environment represent a danger for public health. They are present quite frequently in wastewater and transmitted to humans by the fecal-oral route. The aim of our study was to detect hepatitis A and E viruses (HAV and HEV) in wastewater samples collected from 6 different Tunisian sewage treatment plants during thirteen months. A total of 325 samples were analyzed by real time reverse transcriptase-polymerase chain reaction (RT-qPCR). Results showed the presence of HAV contamination in 36% of the samples. Msaken (58.9%) and SidiBouzid (51.85%) regions showed the highest contamination, followed by Ouerdanine (35.2%), Kasserine (38.9%), Sbitla (23.6%) and El Jem (7.7%) regions. Contamination with HEV was significantly lower (4.9%), being detected HEV positive samples in SidiBouzid (9.25%), El Jem (5.76%), Kasserine (3.7%), Ouerdanine (3.7%), Sbitla (3.63%) and Msaken (3.6%) regions. On the another hand, our research found that, in entry points, 54% of wastewater samples were contaminated with HAV, whereas, in exit points a percentage of 17.9% was found. HAV values were also analyzed by plant showing percentages of positive samples in entry points between 15.38% and 85.18%, while in exit points values ranged from 3.57% to 57.14%. HAV was detected in exit points of all plants except El Jem region. Concerning HEV, the average percentage of contaminated wastewater at entry was 6.75% which was reduced until 3.1% at exit. By plant, HEV positive samples were detected only in three plants, Kasserine, El Jem and Sidi Bouzid at rates of 3.7% 3.84% and 11.11%, respectively. These results support previous findings on the stability of enteric viruses in wastewater and the inefficiency of the procedures employed in the sewage treatment plants. On the other hand, molecular procedures proved to be very sensitive to detect viral genomes in this type of samples. In conclusion, wastewater treatments employed in Tunisian plants can reduce the number of viral particles of hepatitis A and E but do not remove all of them, which constitute a potential risk for human health