Isolation of Aeromonas hydrophila from a metropolitan water supply: seasonal correlation with clinical isolates

The occurrence of Aeromonas spp. in the metropolitan water supply of Perth, Western Australia, Australia, was monitored at several sampling points during a period of 1 year. Water within the distribution system conformed to international standards for drinking water but contained Aeromonas spp. in numbers comparable to those in raw surface water, although this water was free of Escherichia coli. Coliforms and E. coli were found in raw surface waters, and Aeromonas spp. were found in raw water from surface and underground sources. Chemical treatment, followed by chlorination at service reservoirs, resulted in water free of E. coli and a decrease in the number of Aeromonas spp. Aeromonas spp. were found in the greatest numbers in summer. Multiple regression analysis showed that growth of Aeromonas spp. in chlorinated water was related to water temperature, residual chlorine, and interaction between these variables. The incidence of Aeromonas-associated gastroenteritis, determined from isolates referred to us for enterotoxin testing, paralleled the pattern of isolation of Aeromonas spp. in water within the distribution systems. We suggest that the presence of Aeromonas spp. in drinking water needs public health appraisal and that further work should be undertaken to permit reevaluation of standards for the quality of drinking water.     

Isolation of Aeromonas hydrophila from a metropolitan water supply: seasonal correlation with clinical isolates.

The occurrence of Aeromonas spp. in the metropolitan water supply of Perth, Western Australia, Australia, was monitored at several sampling points during a period of 1 year. Water within the distribution system conformed to international standards for drinking water but contained Aeromonas spp. in numbers comparable to those in raw surface water, although this water was free of Escherichia coli. Coliforms and E. coli were found in raw surface waters, and Aeromonas spp. were found in raw water from surface and underground sources. Chemical treatment, followed by chlorination at service reservoirs, resulted in water free of E. coli and a decrease in the number of Aeromonas spp. Aeromonas spp. were found in the greatest numbers in summer. Multiple regression analysis showed that growth of Aeromonas spp. in chlorinated water was related to water temperature, residual chlorine, and interaction between these variables. The incidence of Aeromonas-associated gastroenteritis, determined from isolates referred to us for enterotoxin testing, paralleled the pattern of isolation of Aeromonas spp. in water within the distribution systems. We suggest that the presence of Aeromonas spp. in drinking water needs public health appraisal and that further work should be undertaken to permit reevaluation of standards for the quality of drinking water.     

The occurrence of Aeromonas species in drinking water supplies of an area of the Dolomite Mountains, Italy

A study was made of the occurrence of Aeromonas spp. in drinking water supplies in a mountain area in northeast Italy (the Dolomites). On account of its location, the water in question is exposed to a low level of pollution and systematic chemical disinfection is not necessary. Out of 7395 water samples analysed over a 3 year period, 1623 (21·95%) were found to be positive for Aeromonas , with levels ranging from 1 to 240 cfu 100 ml⁻¹ ; 72·4% of the strains were identified as Aer. hydrophila , 14·7% as Aer. caviae and 12·9% as Aer. sobria. The percentage of recovery from surface water (approximately 40%) was found to be higher than that of ground water (springs : 24·9% ; wells : 28·6%). Aeromonas spp. were isolated from 21·7% of samples from the distribution network and showed no significant variations compared with water from reservoirs. There was no evidence, therefore, of after-growth in the distribution system. No correlation was found between the concentrations of Aeromonas spp. and faecal indicator organisms. As the distribution of Aeromonas spp. was unrelated to anthropic pollution, it is believed that the search for these micro-organisms should be adopted as a further indicator of drinking water quality, especially in waters such as those in the present investigation not undergoing systematic purification treatment.     

An evaluation of media for the membrane filtration enumeration of Aeromonas from drinking water

Two laboratory-prepared media (Ampicillin Dextrin Agar, ADA, and Xylose Ampicillin Agar, XAA) were compared with two commercially-available media (Ryan's Aeromonas Medium and Bile Salt-Irgasan-Brilliant Green Agar, BIBA) for the enumeration of Aeromonas spp. from drinking water. Ryan's medium and ADA were superior for both recovery of Aeromonas and selectivity, with 95+% of typical colonies from both media confirming as Aeromonas . Colony characteristics were more consistent on Ryan's medium.     

The occurrence of aerolysin-positive Aeromonas spp. and their cytotoxicity in Norwegian water sources

Aims:  The aim of the study was to investigate the occurrence of Aeromonas spp. and their aerolysin status in Norwegian natural water sources.
Methods and Results:  Seventy-one samples from 33 Norwegian water sources were examined for the presence of Aeromonas spp. From most of the sample sites, the strains were isolated on blood-ampicillin-agar and Difco Aeromonas agar simultaneously. The majority of the samples (73/77) contained Aeromonas spp., with an average of 35–100 cfu 100 ml^–1. The highest counts were found in faecally-contaminated water. Using PCR, 445 isolates were screened for the presence of aerolysin, and 79% of them were found to be carriers of the aerolysin gene. A selection of the isolated strains was tested on Vero cell cultures and 83% of them showed cytotoxicity.
Conclusions:  There is widespread occurrence of aerolysin-positive cytotoxic Aeromonas spp. in many different Norwegian natural waters, including drinking water sources.
Significance and Impact of the Study:  The widespread occurrence of potentially-pathogenic Aeromonas spp. in the environment demands that these bacteria should not be ignored in drinking water supplies and in the food industry.     

Isolation of Aeromonas spp. from water by using anaerobic incubation.

A membrane filtration method incorporating a combination of anaerobic and aerobic incubation has been developed for the enumeration of Aeromonas spp. in drinking water. The use of anaerobic incubation improved the detection of Aeromonas spp. by reducing the growth of nonaeromonads. The confirmation rate of presumptive Aeromonas spp. identified on the initial isolation agar exceeded 92%.     

Isolation of Aeromonas spp. from water by using anaerobic incubation

A membrane filtration method incorporating a combination of anaerobic and aerobic incubation has been developed for the enumeration of Aeromonas spp. in drinking water. The use of anaerobic incubation improved the detection of Aeromonas spp. by reducing the growth of nonaeromonads. The confirmation rate of presumptive Aeromonas spp. identified on the initial isolation agar exceeded 92%.     

Isolation of Aeromonas spp. from an unchlorinated domestic water supply.

The recovery of Aeromonas spp. from the unchlorinated water supply for a Western Australian city of 21,000 people was monitored at several sampling points during a period of 1 year. Membrane filtration techniques were used to count colonies of Aeromonas spp., coliforms, and Escherichia coli in water sampled before entry to service reservoirs, during storage in service reservoirs, and in distribution systems. Aeromonas spp. were identified by subculture on blood agar with ampicillin, oxidase tests, and the use of Kaper medium and then were tested for production of enterotoxins and hemolysins. During the same period, two-thirds of all fecal specimens sent for microbiological examination were cultured on ampicillin-blood agar for Aeromonas spp. Recovery of Aeromonas spp. from water supplies at distribution points correlated with fecal isolations and continued during autumn and winter. Coliforms and E. coli were found most commonly in late summer to autumn. This pattern differs from the summer peak of Aeromonas isolations both from water and from patients with Aeromonas spp.-associated gastroenteritis in Perth, Western Australia, a city with a chlorinated domestic water supply. Of the Aeromonas strains from water, 61% were enterotoxigenic, and 64% produced hemolysins.     

Biochemical fingerprinting for typing of Aeromonas strains from food and water

The PhenePlate (PhP) system for biochemical fingerprinting is based on analysis of the kinetics of biochemical tests in microplates. This was evaluated for typing Aeromonas spp. isolates from drinking water and food and 78 Aeromonas strains isolated on different occasions over 6 months from three public drinking water systems. The system was highly discriminating and the diversity index, as calculated from 65 unrelated isolates, was 0.993, and 53 different biochemical phenotypes (BPTs) were found. Food isolates were more homogeneous than random Aeromonas strains and identical isolates were sometimes found in food of different origin. Each public drinking water system contained several BPTs but some of these were dominant at several sampling sites and on several sampling occasions in a system. The PhP system is suitable for typing Aeromonas strains from food and water. It is simple to handle and can be used with large numbers of isolates.     

Survival ability of cytotoxic strains of motile Aeromonas spp. in different types of water

The ability of motile Aeromonas spp. to survive in drinking water (mineral and tap water) and in sea water was experimentally tested. Clinically isolated cytotoxic strains of A. hydrophila, A. caviae and A. sobria were selected for this study. After contamination of water samples, the survival of Aeromonas strains was studied for at least three months using viable counts. The results obtained show that the survival of the Aeromonas spp. varies considerably depending on species and water type. For all three species, the survival time was longest in mineral water, where viable bacteria of each strain were still detected after 100 d. Moreover, A hydrophila and A. caviae also re-grew on the first day. In tap water all strains showed marked survival, although to a lesser extent than in mineral water. Aeromonas cells showed a rapid decline in sea water (90% reduction in viable cells after about two d) and thus seem to be more sensitive to saline/marine stress than chlorination.     

Characterization of Aeromonas and Vibrio species isolated from a drinking water reservoir

AIMS: To study the phenotypic and chemotaxonomic (i.e. phospholipid and cellular fatty acid composition) characteristics of environmental Aeromonas spp. and Vibrio spp. isolated from a drinking water reservoir near Vladivostok City, and the application of some chemotaxonomic markers for discrimination of the two genera and species. METHODS AND RESULTS: Presumptive Aeromonas species were dominant in surface water samples (up to 25% of the total number of bacteria recovered). These strains were consistent with respect to the cultural and biochemical properties used to define the species Aeromonas sobria (seven strains) and Aer. popoffii (three strains). Vibrio mimicus (two strains) and Vibrio metschnikovii (one strain) were identified according to phenotypic features and cellular fatty acid composition. CONCLUSION: Environmental Aer. sobria isolates were atypical in their ability to grow at 42 degrees C, and were haemolytic, proteolytic and cytotoxic. Although it was present in a high proportion in the water samples, atypical Aer. sobria is not an indicator of polluted water. SIGNIFICANCE AND IMPACT OF THE STUDY: The incidence of Aeromonas in the drinking water reservoirs in the Far East of Russia is reported for the first time.     

Bactericidal effect of chlorine on motile Aeromonas spp. in drinking water supplies and influence of temperature on disinfection efficacy

The susceptibility of toxigenic Aeromonas spp. to free chlorine in drinking water supplies, and the influence of environmental temperature on the bactericidal activity of the oxidant, were evaluated. The results showed inactivation curves characterized by an initial phase of rapid reduction of viable cells followed by a slow inactivation of bacteria. The effect of the chlorine compound was markedly influenced by water temperature. At a summer water temperature (20 °C), the efficacy of the chlorine concentrations tested was found to be two to three times lower compared to that found at a winter temperature (5 °C). Resistance was moderately, but significantly, greater in Aer. hydrophila vs Aer. caviae and Aer. sobria , but all Aeromonas spp. were more susceptible than Escherichia coli . Selective pressure with free chlorine did not produce Aeromonas cells with higher levels of chlorine resistance.     

Incidence of mesophilic Aeromonas within a public drinking water supply in north-east Scotland

The motile mesophilic Aeromonas are ubiquitous to a wide variety of aquatic environments including drinking water distribution systems. Concern over the presence of mesophilic Aeromonas in public drinking water supplies has been expressed in recent years as it has been regarded as a pathogenic organism of importance in gastroenteritis. A major drinking water distribution system in north-east Scotland was monitored over a 12 month period to determine the prevalence of mesophilic Aeromonas. These data were examined in relation to chlorine concentration, pH, temperature, rainfall and the standard bacteriological indicators of water quality. Aeromonas were isolated to varying degrees from 21 of the 31 reservoirs investigated. The maximum recovery observed during the study was 605 cfu in 300 ml. The probability of isolation generally decreased with increasing levels of chlorination, although this oxidant was found to be ineffective in many reservoirs. Certain reservoirs with poor chlorination profiles yielded very few isolates, whereas some highly chlorinated sites liberated Aeromonas frequently and in relatively high numbers. A seasonal pattern in the incidence of Aeromonas emerged with infrequent isolation during the winter period increasing to a peak during the summer, with most isolates recovered when water temperature was >12 °C. An association was demonstrated between the pattern of Aeromonas isolations and that of rainfall. No relationship was apparent between incidence of Aeromonas and total heterotrophic plate counts.     

Molecular typing of Aeromonas isolates in natural mineral waters

A total of 103 isolates of Aeromonas spp. were obtained over a 3-year period from a natural mineral water and from surface streams located within the boundaries of the watershed of the natural mineral water wells and were typed by macrorestriction analysis of genomic DNA with XbaI and by pulsed-field gel electrophoresis. All Aeromonas caviae isolates from the natural mineral water belonged to the same clone, and an analogous clonal identity was found among Aeromonas hydrophila isolates. These two clones expressed no hemolytic or cytotoxic activities. Aeromonas isolates from surface waters showed high molecular heterogeneity and were not related to the clones found in the natural mineral water. The presence of aeromonads chronically found in the natural mineral water was a likely consequence of a localized development of a biofilm, with no exogenous contamination of the aquifer. Molecular fingerprinting of drinking water isolates is a useful tool in explaining possible reasons for bacterial occurrences.     

Detection of Aeromonas hydrophila in a drinking-water distribution system: a field and pilot study

A 16-month study was conducted on the presence of Aeromonas hydrophila in drinking water in Indiana, U.S.A. Enumeration was conducted in source water, in various sites within a water treatment plant, and in the distribution system in both bulk water and biofilm, as well as in a simulated (annular reactors) drinking-water distribution system. Presumptive Aeromonas spp. counts on source waters regularly approached 10(3)-10(4) CFU/100 mL, during summer months and granular activated carbon - filtered water counts ranged from <1 to 490 CFU/100 mL. In source water, presumptive Aeromonas levels were related to water temperature. Aeromonas hydrophila was never detected in the treatment plant effluent or distributed bulk water, showing disinfectant efficiency on suspended bacteria; however, isolates of A. hydrophila were identified in 7.7% of the biofilm samples, indicating a potential for regrowth and contamination of drinking-water distribution systems.     

SGAP-10C agar for the isolation and quantification of Aeromonas from water

Glutamate starch penicillin (GSP) medium was used for the simultaneous isolation of Pseudomonas and Aeromonas. Modifications to reduce the number of Pseudomonas and background flora and to improve the recovery of Aeromonas from water samples are described. The original medium was modified by adding glucose and ampicillin. The addition of 10 micrograms/l of C-glucose to the medium (SGAP-10C) permitted better recuperation of stressed cells of aeromonads and the ampicillin reduced the numbers of Pseudomonas. The best temperature for the recovery of aquatic aeromonads was 28 degrees C. The recovery of different species of Aeromonas on SGAP-10C was 93%. The selectivity of the medium was validated because 95.5% of 28 colonies tested with an Aeromonas-like morphology belonged to the genus Aeromonas. Moreover, when 45 strains of different genera were cultured on the medium, only Vibrio alginolyticus presented a confusing morphology. When the SGAP-10C was compared with GSP with 45 river samples, the new medium gave a significantly better recovery of Aeromonas spp., especially when large numbers of Pseudomonas spp. were present. SGAP-10C used at 28 degrees C and 48 h was an efficient selective medium for the isolation of Aeromonas from fresh waters.     

SGAP-10C agar for the isolation and quantification of Aeromonas from water

Glutamate starch penicillin (GSP) medium was used for the simultaneous isolation of Pseudomonas and Aeromonas . Modifications to reduce the number of Pseudomonas and background flora and to improve the recovery of Aeromonas from water samples are described. The original medium was modified by adding glucose and ampicillin. The addition of 10 μg/l of C-glucose to the medium (SGAP-10C) permitted better recuperation of stressed cells of aeromonads and the ampicillin reduced the numbers of Pseudomonas . The best temperature for the recovery of aquatic aeromonads was 28°C. The recovery of different species of Aeromonas on SGAP-10C was 93%. The selectivity of the medium was validated because 95·5% of 28 colonies tested with an Aeromonas -like morphology belonged to the genus Aeromonas . Moreover, when 45 strains of different genera were cultured on the medium, only Vibrio alginolyticus presented a confusing morphology. When the SGAP-10C was compared with GSP with 45 river samples, the new medium gave a significantly better recovery of Aeromonas spp., especially when large numbers of Pseudomonas spp. were present. SGAP-10C used at 28°C and 48 h was an efficient selective medium for the isolation of Aeromonas from fresh waters.     

Pril-ampicillin-dextrin-ethanol agar for the isolation and quantification of Aeromonas spp. from polluted environmental waters

Several selective media were evaluated for their suitability for the isolation and quantification of mesophilic Aeromonas species from naturally polluted samples. Satisfactory recoveries were obtained with most of them but only when densities of background microflora were low. When analysed samples were from highly polluted waters, results were inconsistent because they did not give quantitative recovery of mesophilic aeromonads or they did not permit ready differentiation of Aeromonas species from the competitive bacteria. A new medium was developed on the basis of the combination of some positive aspects of several published media, pril-ampicillin-dextrin-ethanol (PADE) agar. The medium employs dextrin (Merck 3006) as a fermentable carbohydrate and pril, ampicillin and ethanol as inhibitory substances. Recovery on PADE agar from suspensions of 15 tested strains of Aeromonas prepared from pure cultures was excellent. The confirmation rate of typical colonies designated Aeromonas spp. isolated from polluted samples exceeded 90%. Recoveries of stressed aeromonad strains on both PADE agar and a non-selective medium (TSA) did not show any significant difference ( P 0.05). PADE agar was more reliable for quantitative recovery of mesophilic aeromonads than the other selective media because of its characteristics: (i) inhibition of the swarming of Proteus , (ii) good reduction of the background, (iii) inhibition of the over growth of Klebsiella spp., (iv) absence of NaCl makes it unfavourable for the growth of halophilic vibrios, (v) combination of two pH indicators permitted a very easy differentiation between Aeromonas colonies and the competitive microflora. The medium can also be used for isolation of aeromonads from various sources by membrane filtration.     

Population dynamics of Aeromonas spp. in an urban river watershed

Density of Aeromonas spp. at one site in the Buffalo River and at four sites on its upstream tributaries was followed from June 1992–June 1993. Membrane filtration counts of Aeromonas during the summer ranged between 18 and 4000 ml⁻¹, which were one to two logs higher than faecal coliform and faecal streptococci densities. Aeromonas spp. in the Buffalo River, and faecal coliforms, faecal streptococci, and the heterotrophic plate count throughout the watershed, increased by approximately one log during summer rainstorms. However, Aeromonas spp. increased only by a factor of two during rainstorms at the upstream sites. Aeromonas spp. showed a strong positive correlation with both indicator bacteria and total suspended solids at the upstream sites during the summer but not the winter. Correlations between Aeromonas and indicator bacteria remained strong in the Buffalo River during the winter, signifying that different conditions exist in the Buffalo River and its upstream tributaries. The strong correlation between Aeromonas spp. and indicator bacteria in the Buffalo River suggest that, in the absence of media capable of the quantitative recovery of potentially pathogenic aeromonads, standard faecal coliform analyses may adequately assess public health risks from Aeromonas spp. in an urban river used for recreational purposes.     

冷却猪肉中气单胞菌生长预测模型的建立和检验

为探讨冷却猪肉中气单胞菌的生长规律,将气单胞茵接种到经过80℃无菌水灭菌的冷却猪肉中,构建Gompertz和Baranyi初级模型来描述气单胞菌在不同温度下的生长状况。结果表明：修正的Gompertz模型对气单胞菌生长曲线的拟合效果优于Baranyi模型,R2均在0．97以上。应用平方根模型和Arrhenius模型对由修正的Gompertz模型得出的最大比生长速率进行拟合,所得平方根模型拟合效果略优于Arrhenius模型。实验所建二级模型能预测0-35℃贮藏条件下气单胞菌的生长。