Drug resistance in Salmonella strains isolated from domestic wastewater before and after treatment in stabilization ponds in an arid region (Marrakech,Morocco)

Some 118 Salmonella strains isolated before and after treatment in stabilization ponds were tested for antimicrobial resistance. In the treatment plant, which decreases the abundance of Salmonella by 99%, a significantly lower level of antibiotic resistance (P<0.01) was identified at the system's inflow point (19%) than at its outflow (29%). The serotypes most frequently identified as having multiple antibiotic resistance were Salmonella paratyphi B and S. typhimurium. High tetracycline resistance was observed at all sampling points, followed by resistance to ampicillin and streptomycin. Antibiotic resistance can be transferred from Salmonella to other members of the Enterobacteriaceae family, such as Escherichia coli K12; transfer frequencies in nutrient broth and filtered sewage water were 4.5×10^-4 and 7×10^-7, respectively.The authors are with the Université CADI AYYAD, Faculté des Sciences—Semlalia, Département de Biologie, Laboratoire de Microbiologie, Bd Le Prince My Abdallah, BP. S.15, Marrakech, Morocco.     

Abundance and antibiotic resistance of non-O1 Vibrio cholerae strains in domestic wastewater before and after treatment in stabilization ponds in an arid region (Marrakesh, Morocco)

Abstract: The abundance and antibiotic resistance of non-O1 Vibrio cholerae strains were studied in wastewater before and after treatment in stabilization ponds in an arid Mediterranean climate. The seasonal abundance of non-O1 Vibrio cholerae was the inverse of those of fecal coliforms, with high densities in hot periods and low densities in cold periods. Although the stabilization pond presents a good efficiency in removing fecal coliforms (97.97%), this treatment system did not produce any significant reduction in non-O1 V. cholerae abundances between the inflow and outflow stations. Among the 240 non-O1 V. cholerae strains isolated before and after treatment in the stabilization ponds, 89 (37.1%) isolates were resistant to at least one of 14 tested antibiotics. The levels of antibiotic resistance at the inflow and outflow points of the system were respectively 40 and 34%. High ampicillin, amoxicillin and mezlocillin resistance was observed at all sampling points, followed by resistance to cefalexin, cefoperazone and amikacin. Antibiotic resistance can be transferred from non-O1 V. cholerae to other members of the Enterobacteriaceae family such as Escherichia coli K12. Transfer frequencies in nutrient broth and filtered wastewater were 3 × 10⁻⁵ and 2 × 10⁻⁸, respectively.     

Aeromonas species in stabilization ponds in the arid region of Marrakesh,Morocco, and relation to fecal-pollution and climatic factors

During the period 12 July 1985 to 23 December 1987, water samples were collected in two-week intervals for estimates ofAeromonas species in a waste treatment system located in the arid region of Marrakech, Morocco. Fecal coliforms, temperature, and chemical oxygen demand were measured simultaneously withAeromonas species densities. Statistical methods were utilized to analyze the significance of average differences and temporal patterns ofAeromonas species numbers. Removal ofAeromonas in the whole system did not exceed 1.14 log.Aeromonas densities showed significantly higher resistance to the treatment process when compared with fecal coliforms; however, abundance of the two groups presented a similar seasonal change. The highest numbers occurred during the cold months, while the lowest appeared in the warm months. Statistical time-series analyses of the densities data showed the seasonal and cyclic distribution ofAeromonas in this treatment plant. These temporal changes were simultaneously observed in all the stations investigated and were negatively correlated with water temperature values. Aeromonas populations were dominated byA. caviae andA. hydrophila in the inlet samples. These two species were rapidly eliminated in the treatment plant. The temporal distribution ofA. caviae was similar to the change in densities ofAeromonas and fecal coliforms. The seasonal fluctuations of abundance ofAeromonas were probably related to this species, which dominated in the winter samples but dropped during the summer. Meanwhile,A. sobria dominated all the final effluent samples. This greater survival ofA. sobria and its known pathogenicity may limit the re-use of treated water for irrigation of fodder plants.     

Antimicrobial susceptibility of non-O1 Vibrio cholerae isolated from wastewater stabilization ponds in Marrakesh,Morocco

The 365 strains of Vibrio cholerae, isolated in Marrakesh from raw sewage and stabilization pond effluent, were all identified as non-O1 Vibrio cholerae. When tested for their susceptibilities to ampicillin, amoxicillin, cephalothin, streptomycin, novobiocin, chloramphenicol, nalidixic acid and trimethoprim-sulphamethoxazole, 13% of the strains from raw sewage and 20% of those from stabilization pond effluent were found to be resistant to one or more of the antibiotics. There were no significant differences, in terms of drug resistance, between isolates from the new sewage and those from the ponds' effluent.The authors are with the Université Cadi Ayyad, Faculté des Sciences Semialia, Département de Biologie, Laboratoire de Microbiologie, BP S/15, Marrakesh, Morocco     

Seasonal incidence of and antibiotic resistance among Aeromonas species isolated from domestic wastewater before and after treatment in stabilization ponds

The efficiency of stabilization pond treatment of domestic wastewater in removing culturable cells of motile Aeromonas and its influence on the incidence of resistance to seven antibiotics were investigated in this study. Removal efficiency was higher (P < 0.001) in the warm months (98.8%) than in the cold months (97%). Among the 264 isolates, 163 were Aeromonas caviae, 24 were A. hydrophila, and 54 were A. sobria. Twenty-three isolates could not be identified to the species level. In the influent, A. caviae dominated in both cold and warm months. In the water samples originating from the influent, A. sobria was present at higher percentages in the warm period. All the isolates were resistant to amoxicillin and most of them (73%) exhibited resistance to cephalothin. Of the three species tested, A. sobria was more susceptible to antibiotics than either A. caviae or A. hydrophila. The most striking difference among the species was seen in resistance to cephalothin. There were 91 % of A. caviae strains and 96% of A. hydrophila isolates that were resistant to cephalothin. However, only 9% of A. sobria strains exhibited resistance to this drug. The high incidence of resistance in raw sewage was connected with a high proportion of A. caviae, whereas in the water samples collected from the effluent during the warm months, a high proportion of A. sobria decreased the total amount of multiple-resistant bacteria. Results demonstrated the need for identification to the species level.Offprint requests to: L. Hassani.     

Cadmium tolerance and antibiotic resistance in Escherichia coli isolated from waste stabilization ponds

The incidence pattern of cadmium tolerance and antibiotics resistance by Escherichia coli was examined periodically from the samples of water, sludge and intestine of fish raised in waste stabilization ponds in a sewage treatment plant. Samples of water and sludge were collected from all the selected ponds and were monitored for total counts of fecal coliform (FC), total coliform (TC) and the population of Escherichia coli, which was also obtained from the intestine of fishes. Total counts of both FC and TC as well as counts of E. coli were markedly reduced from the facultative pond to the last maturation pond. Tolerance limit to cadmium by E. coli tended to decline as the distance of the sewage effluent from the source increased; the effective lethal concentration of cadmium ranged from 0.1 mM in split chamber to 0.05 mM in first maturation pond. E. coli isolated from water, sludge and fish gut were sensitive to seven out of ten antibiotics tested. It appears that holistic functions mediated through the mutualistic growth of micro algae and heterotrophic bacteria in the waste stabilization ponds were responsible for the promotion of water quality and significant reduction of coliform along the sewage effluent gradient.     

Antibiotic-resistant Escherichia coli in wastewaters, surface waters, and oysters from an urban riverine system

The antibiotic resistance (AR) patterns of 462 Escherichia coli isolates from wastewater, surface waters, and oysters were determined. Rates of AR and multiple-AR among isolates from surface water sites adjacent to wastewater treatment plant (WWTP) discharge sites were significantly higher (P < 0.05) than those among other isolates, whereas the rate of AR among isolates from oysters exposed to WWTP discharges was low (<10%).     

A review of the sustainable value of effluents and sludges from wastewater stabilization ponds

Sludges and liquids from wastewater stabilization ponds are cost effective by-products useful for agriculture, aquaculture and for manufacturing building materials. They represent valuable sustainable resources as raw materials to support fisheries for human consumption, to produce animal feed derived from single cell algal proteins and aquatic weeds. Biogas from waste fermentation represents a significant tertiary product.Stabilization ponds are dynamic, low-cost waste recycling ecosystems comprising complex communities of algae, virus, protozoa, rotifers, insects, crustaceans and fungi. These organisms interact and modify the organic content of the waste to produce effluents which need little further investment in treatment.The economic, societal and sustainable value of stabilization ponds is governed by the management regime and the use for which the sludge and effluent is intended. Fish, ducks, prawn and algal protein production rely upon adequately treated effluent. This is particularly valuable for irrigation in arid and semi-arid climates, where natural waters are insufficient and nutrient depleted. Oxidation ponds provide sustainable mechanisms for dealing with sewage and for reducing the risk of infection from parasites and the effects of toxins. The resulting sludges can be used as fertilizer or be composted with local vegetation. Aerobic and anaerobic digestion, lime treatment and pasteurisation are used to improve sludge acceptability and utility to enhance its value as a sustainable resource.     

Characterization of Escherichia coli populations from gulls, landfill trash, and wastewater using ribotyping

Due to their opportunistic and gregarious nature, gulls may be important reservoirs and vectors for anthropogenically derived fecal pathogens in coastal areas. We used ribotyping, a genotypic bacterial source tracking method, to compare populations of Escherichia coli among herring gulls Larus argentatus, great black-backed gulls L. marinus, wastewater, and landfill trash in New Hampshire and Maine, USA. Concentrations of E. coli in gull feces varied widely among individuals, but were generally high (6.0 x 10(1) to 2.5 x 10(9) g(-1) wet weight). Of 39 E. coli isolates from L. argentatus, 67% had banding patterns that were > or = 90% similar to those from wastewater and trash, whereas only 39% of 36 L. marinus isolates exhibited > or = 90% similarity to these sources. Strains of E. coli from gulls matched (> or = 90% similarity) more strains from wastewater (39% matching) than from trash (15% matching). E. coli isolates from L. marinus feces exhibited a greater diversity of banding patterns than did isolates from L. argentatus. There were more unique E. coli banding patterns in trash samples than in wastewater, and higher diversity indices in the former compared to the latter. These findings suggest that both species of gulls, especially L. argentatus, obtain fecal bacteria from wastewater and landfill trash, which they may transport to recreational beaches and waters. Our results also indicate that E. coli populations may vary widely between gull species, and between the anthropogenic habitats that they frequent, i.e. landfills and wastewater treatment facilities.     

Bioaccumulation of mercury from wastewater by genetically engineered Escherichia coli

Genetically engineered E. coli, which express both a Hg2+ transport system and metallothionein, were tested for their ability to remove mercury from wastewater. The wastewater contained more than ten different ions, including 2.58 mg/l mercury, and its pH was 9.6. Mercury uptake was faster from the wastewater than from distilled water, probably because of the higher ionic strength, as the high pH had little effect on mercury accumulation. EDTA also stimulated mercury uptake rather than inhibiting it. A hollow-fiber bioreactor was used to retain induced cells for continuous mercury uptake. The cells removed more than 99% of the mercury in the wastewater and the final amount of mercury accumulated was 26.8 mg/g cell dry weight, while none of the other ions were removed from the water. These results indicated that the induced cells had a high affinity and specificity for mercury.     

The survival of Escherichia coli, faecal coliforms and enterobacteriaceae in general in soil treated with sludge from wastewater treatment plants

We monitored the effect of the application of treated sludge on the behaviour of enterobacteriaceae (mainly faecal coliforms and especially Escherichia coli) in the soil, and studied their evolution over time after application. Three different sludges were used: two from a municipal sewage plant, one of them had been subjected to anaerobic digestion and heat drying, and the other to anaerobic digestion and mechanical dehydration, and one from a dairy waste treatment to aerobic digestion and gravity thickening. Two types of tests were carried out: type O, in the open air, with no possibility of controlling humidity or temperature; and type L, under laboratory conditions, with controlled temperature and humidity. Sludge tests were also run on unscreened soil previously treated with chemical fertilizer. After 80 days of experimentation the populations of faecal coliforms and E. coli had decreased considerably or were undetectable in assays carried out on the soil/sludge mixtures, under both open-air and laboratory conditions, but that, over the same period, in the mixtures containing chemical fertilizer (calcium ammonium nitrate) there had been a considerable increase in the micro-organism populations studied.     

Odorous swine wastewater treatment by purple non-sulfur bacteria, Rhodopseudomonas palustris, isolated from eutrophicated ponds

Three strains of phototrophic, purple, non-sulfur bacteria, isolated from eutrophic ponds, were used to treat odorous swine wastewater. One isolate, Rhodopseudomonas palustris, when cultured in swine wastewater without supplementation for 7 d, removed odorous organic acids (170 mg l(-1)), COD (10,000 mg l(-1)) and phosphate (180 mg l(-1)).     

Induction and stabilization of synchrony in the cell division of Escherichia coli

Escherichia coli strains B5 and B/r/1 were grown under conditions of periodic glucose starvation in a minimal medium. Such conditions of growth give rise to two synchronous populations that are out of phase regarding their time of division, one dividing shortly after a new supply of fresh medium and the other at a later stage of the feeding cycle. Preferential selection of one of the two populations using heat treatment resulted in a homogeneous synchronized culture that exhibited in a non-limiting medium a high degree of synchrony that was long lasting. Synchrony and its persistence could survive preservation of such a synchronized culture by freeze drying. An explanation of the synchrony persistence was put forward and the practical implications of these findings were discussed.     

Electrostatics of ion stabilization in a ClC chloride channel homologue from Escherichia coli

The structural determinants of electrostatics of ion stabilization within EcClC, a ClC-type chloride channel homologue from Escherichia coli, are studied using a continuum dielectric approximation. Specifically, the ion occupancy is investigated in the wild-type protein and a mutant thereof, and the contribution to the electrostatic binding free energy of local and non-local interactions is characterized at the single-residue level. This analysis shows that, in spite of the desolvation cost and the strong ion-ion repulsion, all previously reported binding sites can be occupied simultaneously. The stabilizing effect of the protein arises from hydrogen bonding as well as from longer-range favorable interactions, such as with the strictly conserved Lys131 side-chain. The latter is involved in the stabilization of the conserved GSGIP motif that delimits two of the binding sites. Interestingly, an additional low-affinity binding site, mediated by a structurally analogous motif including the side-chain of Arg340, can be identified on the extracellular side of the permeation pathway. Finally, it is shown that, in contrast to K-channels, and in analogy to the SBP/PBP sulfate/phosphate-binding proteins, the contribution of helix macrodipoles to chloride binding in EcClC is only marginal.     

Evaluation of photoreactivation of Escherichia coli and Enterococci after UV disinfection of municipal wastewater

Because chlorine disinfection is not permitted in the province of Quebec, wastewater disinfection by ultraviolet (UV) light has been used for years in wastewater treatment plants. Thermotolerant coliforms discharge criteria are set for each plant and are adjusted by a factor of 1 log to compensate for photoreactivation in UV-disinfected effluents. The current study evaluated levels of Escherichia coli and enterococci photoreactivation from disinfected wastewater under varying temperature, visible light, and type of UV lamps. Escherichia coli photoreactivation increased significantly after exposure to 5600 lx compared with 1600 lx of visible light. This increase was significantly higher in warm water (25 degrees C) than cold water (4 degrees C). The level of photoreactivation of E. coli was also higher after wastewater disinfection by low-pressure UV lamps as opposed to medium-pressure UV lamps. Enterococci, however, were not photoreactivated under any test conditions. This result suggests that enterococci could be a better indicator than thermotolerant coliforms or E. coli. The use of enterococci would also eliminate the requirement to set different discharge criteria based on disinfection type (UV or chemical) and would also provide a better assessment of treatment efficiency for more resistant microorganisms.     

Identification and characterization of a critical region in the glycogen synthase from Escherichia coli

The cysteine-specific reagent 5,5'-dithiobis(2-nitrobenzoic acid) inactivates the Escherichia coli glycogen synthase (Holmes, E., and Preiss, J. (1982) Arch. Biochem. Biophys. 216, 736-740). To find the responsible residue, all cysteines, Cys(7), Cys(379), and Cys(408), were substituted combinatorially by Ser. 5,5'-Dithiobis(2-nitrobenzoic acid) modified and inactivated the enzyme if and only if Cys(379) was present and it was prevented by the substrate ADP-glucose (ADP-Glc). Mutations C379S and C379A increased the S(0.5) for ADP-Glc 40- and 77-fold, whereas the specific activity was decreased 5.8- and 4.3-fold, respectively. Studies of inhibition by glucose 1-phosphate and AMP indicated that Cys(379) was involved in the interaction of the enzyme with the phosphoglucose moiety of ADP-Glc. Other mutations, C379T, C379D, and C379L, indicated that this site is intolerant for bulkier side chains. Because Cys(379) is in a conserved region, other residues were scanned by mutagenesis. Replacement of Glu(377) by Ala and Gln decreased V(max) more than 10,000-fold without affecting the apparent affinity for ADP-Glc and glycogen binding. Mutation of Glu(377) by Asp decreased V(max) only 57-fold indicating that the negative charge of Glu(377) is essential for catalysis. The activity of the mutation E377C, on an enzyme form without other Cys, was chemically restored by carboxymethylation. Other conserved residues in the region, Ser(374) and Gln(383), were analyzed by mutagenesis but found not essential. Comparison with the crystal structure of other glycosyltransferases suggests that this conserved region is a loop that is part of the active site. The results of this work indicate that this region is critical for catalysis and substrate binding.