Multiregional evaluation of the SimPlate heterotrophic plate count method compared to the standard plate count agar pour plate method in water

Comparison of PetrifilmTM AC and pour plate techniques used for the heterotrophic aerobic bacterial count in water

Heterotrophic bacteria are commonly found in water samples. While these Heterotrophic Bacterial/Plate Counts (HPC) do not necessarily indicate a health hazard, high counts provide a good indication of the efficiency of water disinfection and integrity of distribution systems. The aim of this study was to compare the PetrifimTM AC method to the pour plate technique for the testing of HPC in water samples. Artificially contaminated (192 samples) and natural water samples (25) were processed using two methods. Both methods accurately detected high, medium and low counts of HPC, producing average Z scores between -2 and +2. Paired-wise student t-test and correlation coefficient showed nonsignificant differences between the results of two methods. Acceptable repeatability and reproducibility was obtained using both the methods. Uncertainty of measurement for PetrifilmTM AC and pour plate method was found to be 2.9% and 5.4%, respectively. PetrifilmTM AC proved to be robust at 33°C and 37°C. In conclusion, PetrifimTM AC, which is easy to process, read, and less time consuming, proved to be comparable to the conventional pour plate method in establishing HPC in water. In addition, PetrifimTM AC requires less space for the processing and incubation, generate small volume of waste for disposal, and requires no equipment, except for the incubator.

Evaluation of biodegradability and biotoxicity of surfactants in soil

In this study, the biodegradability and biotoxicity of four surfactants, i.e. modified heterogeneous alcohol ether, fatty acid methyl ester ethoxylates, Tween-80 and rhamnolipid, under natural soil conditions were investigated.

Evaluation of 3 dental unit waterline contamination testing methods

Previous studies have found inconsistent results from testing methods used to measure heterotrophic plate count (HPC) bacteria in dental unit waterline (DUWL) samples. This study used 63 samples to compare the results obtained from an in-office chairside method and 2 currently used commercial laboratory HPC methods (Standard Methods 9215C and 9215E). The results suggest that the Standard Method 9215E is not suitable for application to DUWL quality monitoring, due to the detection of limited numbers of heterotrophic organisms at the required 35°C incubation temperature. The results also confirm that while the in-office chairside method is useful for DUWL quality monitoring, the Standard Method 9215C provided the most accurate results.

Monitoring and comparison of antibiotic resistant bacteria and their resistance genes in municipal and hospital wastewaters

BACKGROUND

Human exposure to antibiotic resistant bacteria (ARB) is a public health concern which could occur in a number of ways. Wastewaters seem to play an important role in the dissemination of bacteria and antibiotic resistant genes (ARGs) in our environment. The aim of this study was to evaluate the occurrence of three groups of ARB and their resistance genes in hospital and municipal wastewaters (MWs) as possible sources.

METHODS

A total of 66 samples were collected from raw MWs and hospital wastewaters (HWs) and final effluents of related wastewater treatment plants (WWTPs). Samples were analyzed for the detection of three groups of ARB including gentamicin (GM), chloramphenicol (CHL) and ceftazidime resistant bacteria and their ARGs (aac (3)-1, cmlA1 and ctx-m-32, respectively).

RESULTS

The mean concentration of GM, CHL and ceftazidime resistant bacteria in raw wastewater samples was 1.24 × 10(7), 3.29 × 10(7) and 5.54 × 10(7) colony forming unit/100 ml, respectively. There is a variation in prevalence of different groups of ARB in MWs and HWs. All WWTPs decreased the concentration of ARB. However, high concentration of ARB was found in the final effluent of WWTPs. Similar to ARB, different groups of ARGs were found frequently in both MWs and HWs. All genes also detected with a relative high frequency in effluent samples of MWs WWTPs.

CONCLUSIONS

Discharge of final effluent from conventional WWTPs is a potential route for dissemination of ARB and ARGs into the natural environment and poses a hazard to environmental and public health.

A comparison of 2 laboratory methods to test dental unit waterline water quality

The performance of 2 American Public Health Association standard laboratory methods, the R2A spread plate and the SimPlate(TM) for heterotrophic plate count, for quantifying heterotrophic microorganisms in dental waterline samples was evaluated. Microbial counts were underestimated on SimPlate(TM) compared with R2A, and the results indicated a poor correlation between the 2 methods.

Monitoring and evaluation of antibiotic-resistant bacteria at a municipal wastewater treatment plant in China

The prevalence of antibiotic-resistant bacteria in municipal wastewater treatment plants (WWTPs) is becoming a concern of public health. In order to acquire information on the emission of antibiotic-resistant bacteria from WWTP effluents into natural waters, both average antibiotic tolerance and concentrations of antibiotic-resistant bacteria in the effluent of a WWTP in Beijing, China were investigated. A new index of IC(50)/MIC ratio (the antibiotic concentration required to inhibit 50% of total heterotrophic bacteria compared to the highest minimum inhibitory concentration value of a group of pathogens according to a specific antibiotic, as defined by CLSI) was used to reflect the average antibiotic tolerance of total heterotrophic bacteria in the secondary effluent. The results showed that the IC(50)/MIC ratios of heterotrophic bacteria in the secondary effluent to penicillin, ampicillin, cephalothin, chloramphenicol and rifampicin were >2, >1, >1, and 1.08, respectively, which reflected a significantly high general level of heterotrophic bacteria found in the secondary effluent resistant to these five antibiotics. The concentrations of penicillin-, ampicillin-, cephalothin-, and chloramphenicol-resistant bacteria were as high as 1.5×10(4)-1.9×10(5), 1.2×10(4)-1.5×10(5), 8.9×10(3)-1.9×10(5) and 2.6×10(4)-2.0×10(5) CFU/mL, and the average percentages in relation to total heterotrophic bacteria were 63%, 47%, 55%, and 69%, respectively. The concentrations of tetracycline- and rifampicin-resistant bacteria were 840-6.1×10(3) and 310-6.1×10(4) CFU/mL with average percentages of 2.6% and 11%, respectively. Furthermore, our study found that five- and six-antibiotic-resistant bacteria were widely distributed in four types of enterobacteria from the secondary effluent. The presence of multiple-antibiotic-resistant bacteria from effluents of WWTPs into natural waters could pose a serious problem as a secondary pollutant of drinking water.

Effect of Temperature on the Survival of F-Specific RNA Coliphage, Feline Calicivirus, and Escherichia coli in Chlorinated Water

We compared the survival of F-specific RNA coliphage MS2, feline calicivirus, and E. coli in normal tap water and in tap water treated to an initial concentration of 50 ppm free chlorine and held at 4 degrees C, 25 degrees C, or 37 degrees C for up to 28 days. Our aim was to determine which of these two organisms (coliphage or E. coli) was better at indicating norovirus survival under the conditions of the experiment. There was a relatively rapid decline of FCV and E. coli in 50 ppm chlorine treated water and both organisms were undetectable within one day irrespective of the temperature. In contrast, FRNA phage survived for 7 to 14 days in 50 ppm chlorine treated water at all temperatures. All organisms survived for 28 days in tap water at 4 degrees C, but FCV was undetectable on day 21 and day 7 at 25 degrees C and 37 degrees C, respectively. Greater survival of FRNA phage compared to E. coli in 50 ppm chlorine treated water suggests that these organisms should be further investigated as indicators of norovirus in depurated shellfish, sanitized produce, and treated wastewater which are all subject to high-level chlorine treatment.

Effect of temperature and sanitizers on the survival of feline calicivirus, Escherichia coli, and F-specific coliphage MS2 on leafy salad vegetables

We conducted a series of experiments to compare the survival of Escherichia coli, feline calicivirus, and F-specific coliphage MS2 on lettuce and cabbage with and without disinfection. Inoculated produce was held at 4, 25, or 37 degrees C for 21 days or was treated with different concentrations of sodium bicarbonate, chlorine bleach, peroxyacetic acid, or hydrogen peroxide. Survival was measured by the decimal reduction value (time to 90% reduction in titer) and the change in log titers of the test organisms. A stronger correlation of survival measures was observed between feline calicivirus and MS2 than between E. coli and either of the viral agents at 25 and 37 degrees C. The maximum time to detection limit for MS2 at all temperatures was 9 days, whereas feline calicivirus was detected for a maximum of 14 days at 4 degrees C. In contrast, E. coli was detectable for 21 days at 4 and 25 degrees C and for 14 days at 37 degrees C. Significant increases in E. coli titer occurred within the first 5 days, but virus titers decreased steadily throughout the experiments. E. coli was also highly susceptible to all disinfectants except 1% sodium bicarbonate and 50 ppm chlorine bleach, whereas the viruses were resistant to all four disinfectants.

Heterotrophic plate count bacteria—what is their significance in drinking water?

While the literature documents the universal occurrence of heterotrophic plate count (HPC) bacteria in soils, foods, air, and all sources of water, there is a lingering question as to whether this group of organisms may signal an increased health risk when elevated populations are present in drinking water. This paper reviews the relevant literature on HPC bacteria in drinking water, the lack of clinical evidence that elevated populations or specific genera within the HPC flora pose an increased health risk to any segment of the population, and the appropriate uses of HPC data as a tool to monitor drinking water quality changes following treatment. It finds no evidence to support health-based regulations of HPC concentrations.

Survival of F-specific RNA coliphage, feline calicivirus, and Escherichia coli in water: a comparative study

The relationship between the survival of enteric viral pathogens and their indicators (coliform bacteria and coliphages) is not well understood. We compared the survival rates of feline calicivirus (FCV), Escherichia coli, and a male-specific RNA coliphage MS2 at 4, 25, and 37 degrees C for up to 28 days in dechlorinated water. The survival rates of E. coli and FCV, a surrogate of noroviruses (NV), had a high degree of correlation at 4 and 25 degrees C, while MS2 phage survived significantly longer (P < 0.05) at these two temperatures. At 37 degrees C, the survival rates for all three organisms were highly correlated. Decimal reduction values indicating the number of days needed for 90% reduction in titer (D values) decreased for all three organisms as storage temperatures increased. FCV had the shortest D value among all three organisms at all temperatures investigated. These findings indicate that F-specific RNA phages may be useful indicators of NV in the environment.