Haemolysin occurrence among Aeromonas hydrophila, Aeromonas caviae and Aeromonas sobria strains isolated from different aquatic ecosystems.

A total of 909 Aeromonas spp. isolates from different aquatic ecosystems were tested for haemolysin production by both sheep and horse blood agar-plate assays and by rabbit erythrocytes in broth assay. A comparison of these different methods was undertaken in order to appreciate their capacity to evaluate the haemolytic activity of Aeromonas spp. isolated from aquatic ecosystems. The haemolytic activity was associated particularly with A. hydrophila and A. sobria (about 95% of strains), whereas A. caviae did not produce haemolysin (about 95% of strains). A method suitable for use in routine diagnostic microbiology laboratories is proposed for quantifying both groups of A. hydrophila/A. sobria and A. caviae in environmental water.

Epidemiological significance of microbiological pollution criteria for river recreational waters.

A retrospective follow-up study was conducted during the summer of 1986 in the French Ardèche basin in order to assess the relationship between swimming-related morbidity and the bacteriological quality of the recreational water. 5737 tourists in eight holiday camps were questioned as to the occurrence of illness and their bathing habits during the week preceding the interviews. The rate-ratio contrasting swimmers and non-swimmers for total morbidity is 2.1 (1.8-2.4) = 95% confidence interval); gastrointestinal illness is the major type of morbidity and differs significantly between the two groups (RR = 2.4 (1.9-3.0) for total gastrointestinal cases; RR = 2.3 (1.7-3.2) for 'objective' gastrointestinal cases). Faecal streptococci (FS) are best correlated to gastrointestinal morbidity, using direct linear regression models. Faecal coliforms (FC) are not as good predictors of the risk. The concentration of faecal streptococci above which the 'objective' gastrointestinal morbidity among bathers is significantly greater than among non-bathers is 20 FS/100 ml. Swimmers suffer skin ailments much more frequently than non-swimmers (RR = 3.7 (2.4-5.7]; although the relationship may be artefactual, this type of morbidity is well correlated with the concentration of faecal coliforms, aeromonas and pseudomonas. This study provides epidemiological data on which to base microbiological standards for river recreational waters dependent on what might be considered as an 'acceptable' risk.

Physiological changes of Salmonella typhimurium cells under osmotic and starvation conditions by image analysis.

The effects of starvation and salinity on the physiology of Salmonella typhimurium were investigated in a microcosm study. The physiological changes were monitored by using fluorochromes dyes such as DAPI (4',6-diamidino-2-phenylindole) for evaluation of the genomic content, CTC (5-cyano-2,3-ditolyl tetrazolium chloride) for respiratory activity and syto 9 and propidium iodide for cytoplasmic membrane damages. The metabolic activity of the cellular population was assessed with the method of Kogure (direct viable count), to enumerate the substrate-responsive cells. These different staining procedures were objectively analysed by an image analysis system. This paper describes the progressive alteration of Salmonella typhimurium physiology under salinity and starvation conditions.

[Evaluation of microbial indicators of health risk related to river swimming places]. / Evaluation des indicateurs microbiens du risque sanitaire lié aux baignades en rivière.

A retrospective follow-up study was conducted among 5,737 tourists in 8 holiday camps, during the 1986 summer, in the Ardèche river basin, in order to study the relationship between the bacteriological water quality and the morbidity that occurred to swimmers. Total morbidity was more frequent among bathers than non-bathers (Risk Ratio = 1.7 [95% confidence interval = 1.4-2.1]); gastro-intestinal illness was the major type of morbidity (RR = 2.8 [1.8-4.4] for "objective gastro-intestinal diseases). After screening for the germs that were best correlated with gastro-intestinal and skin diseases, using simple linear regression, logistic regression models allowed confirmation that fecal streptococci best predicted gastro-intestinal morbidity; it significantly exceeded the risk observed among non-bathers above a concentration of 20 SF/100 ml ("objective" gastro-intestinal morbidity). The relationship with fecal coliforms was less clear. However, they are good indicators of skin diseases risk. These results should help re-evaluation of the current microbiological standards concerning recreational waters.

[Survival of Bulinus truncatus and Biomphalaria pfeifferi in sewer water purified in stabilization ponds in a sudanese-saharan zone]. / Etude de la survie de Bulinus truncatus et de Biomphalaria pfeifferi dans les eaux usées épurées par lagunage en zone soudano-sahélienne.

In subsaharan Africa wastewater purification to protect the health of the population could create stagnate water reservoirs for parasitic vectors such as snails which are intermediate hosts of bilharzia. Laboratory studies of the survival of Bulinus truncatus, an intermediate host of Schistosoma haematobium, and Biomphalaria pfeifferi, an intermediate host of Schistosoma mansoni, in waste water purified in stabilization ponds showed that Biomphalaria pfeifferi thrives to dirty water (60 mg/l < or = COD < or = 1060 mg/l) while Bulinus truncatus survived only in slightly cleaner water (60 mg/l < or = COD < or = 200 mg/l). Field studies showed that Biomphalaria pfeifferi disappeared after 48 hours as compared to 25 days in the laboratory. In both laboratory and field studies Bulinus truncatus survived only 24 hours in raw waste water. The duration of survival grew longer as quality of the water improved. Temperature variations, high amounts of organic material in water, high oxygen content in water, and absence of plant-life are factors which could limit the development of the intermediate snail hosts (i.e. Bulinus truncatus and Biomphalaria pfeifferi) in the waste stabilization ponds of the Interstate School of Rural Equipment Engineers in Ouagadougou, Burkina Faso.

A computer study of the evolution of aerobic heterotrophic bacterial populations in sewage and river waters.

The biodegradation of six surface active agents tested. The biochemical characteristics of the aerobic heterotrophic bacteria present in Montpellier waste waters and in Rhône water, before and after degradation, were studied by a standardized microbiological method. Four hundred strains isolated from these populations were compared to 29 reference strains by computer analysis. The reference strains were first grouped in classes (single linkage). Then the strains were compared first to these classes, and then to each reference strain. Whereas the bacterial populations were widely distributed before biodegradation, after degradation they were restricted to a few prevailing genera:Pseudomonas, Alcaligenes, andKlebsiella.

Distribution and survival of motile Aeromonas spp. in brackish water receiving sewage treatment effluent.

The spatiotemporal distributions of Aeromonas spp. and fecal coliforms in a cove receiving sewage treatment effluent and draining into a brackish lagoon were studied for 34 months with sampling at six stations. A total of 452 strains of Aeromonas spp. were isolated and identified at the outflow of the treatment system and at stations in the cove. Hemolytic activity of 289 Aeromonas strains was determined. The Aeromonas spp. and fecal coliform distributions showed seasonal cycles in the pond effluent. These seasonal bacterial cycles were persistent in effluent, at the discharge point, and in the cove. However, the abundance levels of these bacterial distributions decreased gradually from the coast to the open lagoon. A dilution model showed that the Aeromonas spp. and fecal coliform distributions in the cove water were subject not only to dilution effect but also to other environmental factors, such as salinity. A. sobria is the most common species identified in the Aeromonas population present in the cove water. Survival studies confirmed that Aeromonas spp., especially A. sobria, were more sensitive to saline and/or marine stress than fecal coliforms. Among the Aeromonas hydrophila and A. sobria strains, 96 and 97%, respectively, produced hemolysin, whereas among the Aeromonas caviae strains, 95% were nonhemolytic.

Dynamics of Aeromonas hydrophila, Aeromonas sobria, and Aeromonas caviae in a sewage treatment pond.

The spatiotemporal dynamics of Aeromonas spp. and fecal coliforms in the sewage treatment ponds of an urban wastewater center were studied after 20 months of sampling from five stations in these ponds. Isolation and identification of 247 Aeromonas strains were undertaken over four seasons at the inflow and outflow of this pond system. The hemolytic activity of these strains was determined. The Aeromonas spp. and the fecal coliform distributions showed seasonal cycles, the amplitude of which increased at distances further from the wastewater source, so that in the last pond there was an inversion of the Aeromonas spp. cycle in comparison with that of fecal coliforms. The main patterns in these cycles occurred simultaneously at all stations, indicating control of these bacterial populations by seasonal factors (temperature, solar radiation, phytoplankton), the effects of which were different on each bacterial group. The analysis of the Aeromonas spp. population structure showed that, regardless of the season, Aeromonas caviae was the dominant species at the pond system inflow. However at the outflow the Aeromonas spp. population was dominated by A. caviae in winter, whereas Aeromonas sobria was the dominant species in the treated effluent from spring to fall. Among the Aeromonas hydrophila and A. sobria strains, 100% produced hemolysin; whereas among the A. caviae strains, 96% were nonhemolytic.

Effects of environmental factors present in the St. Lawrence Estuary (Quebec, Canada) on experimental survival of Salmonella salamae as determined by flow cytometry.

Survival of Salmonella salamae in the St. Lawrence Estuary was studied experimentally during an oceanographic cruise using in situ exposure diffusion chambers. The abundance distribution (colony-forming units) of culturable S. salamae on media was compared with the distribution of cells enumerated by flow cytometry. Flow cytometry was also used to characterize the size distribution and DNA content of cells exposed to various environmental factors. Solar radiation, starvation, and a gradual increase in salinity led to an abrupt loss of the ability of S. salamae cells to form cultures and to a gradual reduction in the cell size and DNA content. Conversely, starvation combined with a gradual increase in salinity in the absence of sunlight led to a gradual loss of the cells' ability to form cultures and an abrupt reduction in cell size and DNA content (i.e., a rapid increase in cell damage). Mortality (i.e., a decrease in total cell count) of S. salamae placed in darkness began at a lower salinity (11.4/1000) than did the mortality of cells exposed to sunlight (23.1/1000). Therefore, the S. salamae cells exposed to sunlight seemed to be more resistant to gradual salinity stress than the cells that were not subjected to sunlight.

[Use of a new selective culture medium for isolation of Staphylococcus aureus in different types of water]. / Utilisation d'un nouveau milieu de culture sélectif pour l'isolement de Staphylococcus aureus dans différents types d'eau.

Different mediums actually available for recovering Staphylococcus aureus are not adapted for water analysis because of their low selectivity. This Note propose a new medium using Baird Parker agar medium additionned with sodium azide and incubated at 37 degrees C during 24 hrs. Three kinds of waters are tested: the efficiency of this medium is higher for surface waters using a modified technic of filtration.

[Evaluation of 2 culture media for the isolation and enumeration of motile Aeromonas in different kinds of water]. / Evaluation de deux milieux de culture pour l'isolement et le dénombrement des Aeromonas mobiles dans différents types d'eau.

In recent years an increasing incidence of Aeromonas-related cutaneous infections and gastroenteritis has raised a serious public health problem. It appeared therefore timely to define a specific method allowing the rapid isolation and enumeration of the bacteria in their various aquatic habitats. In this line of research we have compared the growth of Aeromonas originating from different aquatic sources and raised on two media, i.e. RS-agar and PXA-agar. Whatever the aquatic system we observed that the PXA-agar medium clearly was better adapted for a quick enumeration of Aeromonas.

Comparison of flow cytometry and epifluorescence microscopy for counting bacteria in aquatic ecosystems.

Flow cytometry was used to count bacterial cells from diverse origins: one strain of E. coli, one sample of lake water, and 18 samples of estuary water. To verify the accuracy and the precision of this technique, total bacteria counts made by flow cytometry were compared with counts by direct observation using epifluorescence microscopy. The results of this study showed that flow cytometry was a reliable technique for counting a mixture of bacteria in samples from aquatic ecosystems.

Dynamics of pollution-indicator and heterotrophic bacteria in sewage treatment lagoons.

The spatio-temporal dynamics of pollution-indicator bacteria and aerobic heterotrophic bacteria were studied in the sewage treatment lagoons of an urban wastewater center after 26 months of biweekly sampling at eight stations in these lagoons. Robust statistical methods of time-series analysis were used to study successional steps (through chronological clustering) and rhythmic behavior through time (through contingency periodogram). The aerobic heterotrophic bacterial community showed two types of temporal evolution: in the first four stations, it seems mainly controlled by the nutrient support capacity of the sewage input, whereas in the remaining part of the lagoon, it seems likely that the pollution-indicator bacteria are gradually replaced by other bacterial types that are better adapted to this environment. On the other hand, the pollution-indicator bacteria showed an annual cycle which increased in amplitude at distances further from the wastewater source. The main events in this cycle were produced simultaneously at all stations, indicating control of these bacterial populations by climatic factors, which act through physical and chemical factors, and also through other biological components of this ecosystem (phytoplankton and zooplankton). Finally, we use results from this study to suggest a modified design for a future study program.

Dynamics of non-O1 Vibrio cholerae and fecal coliforms in experimental stabilization ponds in the arid region of Marrakesh, Morocco, and the effect of pH, temperature, and sunlight on their experimental survival.

We studied the spatial-temporal dynamics of non-O1 Vibrio cholerae numbers at a stabilization pond treatment plant. This bacterium's seasonal dynamics were the inverse of those of fecal coliforms, with high levels in hot periods and low levels in cold periods. Stabilization pond treatment did not significantly reduce non-O1 V. cholerae numbers between the system's inflow and outflow points. In contrast, fecal coliforms were reduced by 98.95% in hot periods and by 94.91% in cold periods. Significant rho coefficient values for the Spearman correlation between numbers of non-O1 V. cholerae and temperature and pH of 0.91 and 0.76 respectively, were found at the system's outflow point. An experimental study of the effects of pH, temperature, and sunlight on the survival of non-O1 V. cholerae and fecal coliforms confirmed the inverse behaviour of the two bacterial groups noted in the stabilization ponds. Alkaline pH values of 8 and 8.8 promoted the survival of non-O1 V. cholerae and inhibited that of Escherichia coli. Low temperatures (8 degrees C) prolonged E. coli survival (k = 0.002/h), while a temperature of 23 degrees C reduced it markedly (k = 0.022/h). Non-O1 V. cholerae did not survive as well as E. coli at 8 degrees C (k = 0.009/h). The effect of temperature on non-O1 V. cholerae appeared to be closely linked to nutrient levels. Non-O1 V. cholerae appeared to be less sensitive to sunlight than E. coli whose survival was markedly reduced particularly during summer periods. Non-O1 V. cholerae and E. coli did not behave in the same way in water subjected to stabilization pond treatment. The use of fecal coliforms as an indicator of the potential health hazard of the effluent may not be adequate for this treatment procedure.

Modeling of the evolution of bacterial densities in an eutrophic ecosystem (sewage lagoons).

The process of wastewater treatment was studied by modeling the relationships between physical, chemical, and biological (bacteria, phytoplankton, zooplankton) components of the sewage treatment lagoons of an urban wastewater center, based upon a two-year sampling program. The models of interactions between variables were tested by path analysis. The path coefficients were computed from the results of ridge regression, instead of linear multiple regression. The results show that fecal coliforms were effectively controlled by the environmental variables included in the model, which have a cyclic seasonal behavior. This control grew stronger with distance from the input (R (2)=0.71) to the output (R (2)=0.88) of the treatment plant, resulting in effective elimination of most enteric bacteria. Simultaneously, the ecosystem's community of aerobic heterotrophic bacteria became more independent from the model's predictive variables, with increased distance from the sewage input, thus demonstrating its maturation as an autonomous community in the lagoon ecosystem. Consequences of modeling are discussed, with respect to the understanding of biological wastewater treatment mechanisms and ecosystem dynamics and to plant management.

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.

Efficiency of wastewater treatment plants at removing Giardia sp. cysts in southern France.

A study was conducted to evaluate the removal efficiency for Giardia sp. cysts of a number of wastewater treatment plants in France. Of these, five were activated sludge systems, three were trickling filters and three were waste stabilisation pond systems. In addition, the effect upon cyst removal of disinfecting effluents prior to discharge into controlled waters by UV and chlorination was evaluated. Cysts were detected in raw wastewater at all 11 treatment plants in concentrations ranging from 130 to 41,270 cysts/litre. The removal of cysts by sewage treatment was found to range between 99.5 and 99.8% for activated sludge, 99.9 and 100% for waste stabilisation ponds, and for the trickling filter plants up to 98.3%. Despite the high removal efficiencies recorded in this study the range of cysts detected in final effluents discharged into controlled waters ranged from < 1 to 66 cysts/litre. This is undoubtedly an underestimate of actual occurrence and concentration in wastewater, given the limitations of the methods currently employed by investigators. Cysts were detected in final effluents which had been disinfected by both UV and chlorination (range 0.3-19 cysts/litre), however, it is not known whether such cysts were viable or non-viable.

Effects of pili rigidity and energy availability on conjugative plasmid transfer in aquatic environments.

Conjugal transfer frequencies of nonconjugative plasmid pCE325 associated with either the conjugative plasmid R388 (rigid pili) or R100-1 (flexible pili) were measured in waste water and seawater between two strains of Escherichia coli K12. These strains were selected from three strains after estimating (i) their survival capacity in the two water types and (ii) the maintenance and expression of plasmid-located genes in the different strains. Mobilization of plasmid pCE325 was always below the detection limit, but increased when organic matter was added to the microcosms. This mobilization was not related to cell growth, but to the availability of energy conditioning the physiological state of the cells. The transfer frequency was higher when the conjugative plasmid encoded flexible pili.

Viability and virulence of experimentally stressed nonculturable Salmonella typhimurium.

Maintenance of pathogenicity of viable but nonculturable Salmonella typhimurium cells experimentally stressed with UV-C and seawater, was investigated relative to the viability level of the cellular population. Pathogenicity, tested in a mouse model, was lost concomitantly with culturability, whereas cell viability remained undamaged, as determined by respiratory activity and cytoplasmic membrane and genomic integrities.