Levels Of Heterotrophic Bacteria Research Articles

Comparative toxicity of urban wastewater and rainfall overflow in caged freshwater mussel Elliptio complanata.

Municipal effluents are well-recognized as disrupting sexual differentiation and reproduction in mussels. However, the contribution to this problem made by rainfall combined with sewer overflow (increased by rain due to climate change) is not well understood. The purpose of this study was to compare the neuroendocrine effects of municipal discharge and rainfall overflow on caged endemic mussel Elliptio complanata. To this end, mussels were experimentally caged and placed for 3 months at a municipal effluent dispersion plume site and at overflow sites. Data revealed that downstream surface water contained some pharmaceuticals (caffeine and carbamazepine) and accumulated significant levels of heterotrophic bacteria, but these effects were not observed at the overflow sites. The principal effects observed at the downstream site were increased soft tissue mass (and gonad index), inflammation, and Vtg proteins in male mussels as determined by a novel immunostaining methodology. The rainfall overflow sites had no effects on these markers, but were specifically associated with reduced Vtg proteins in females, dopamine (Dop), gonad lipids, and DNA strand breaks, with increased metallothioneins. In conclusion, the observed feminizing effects of municipal effluent were not additionally observed in mussels caged at rainfall overflow sites, although the latter exhibited a different pattern of toxicity.

Contrast the distribution, transformation, and degradation of dissolved and particulate organic matter in the South Yellow Sea, the East China Sea, and its adjacent Kuroshio Current

The distribution and bioavailability of dissolved and particulate organic matter (DOM and POM) were determined throughout the water column in sampling transects across the South Yellow Sea (SYS), East China Sea (ECS), and its adjacent Kuroshio Current (KC) during March–April 2017. The carbon (C), nitrogen (N), and amino acids (AA) levels in DOM and POM, as well as other parameters including temperature, salinity, nutrients, chlorophyll-a, and biological parameters (heterotrophic bacteria, Synechococcus, and picoeukaryotes), were used in the multi-factor analysis to explore the underlying factors contributing to the distribution patterns and degrading status of DOM and POM. The AA contents in POM (PAA) were higher at shallower depths than the deep ones, whereas total dissolved amino acids (TDAA) levels showed minor variation with depth. Specifically, glycine and serine in the PAA were selectively preserved throughout the water column. High levels of heterotrophic bacteria were associated with high temperature and high levels of ammonium in shelf waters, indicating a spot for intensive remineralization of organic nitrogen. High concentrations of bulk organic parameters (POC and PON) were found more along the coast and correlated with arginine and alanine. The Kuroshio surface water was short of PAA, POC, and PON compared with the coastal and middle shelf water. The bioavailability of surface POM indicated by the percentages of AA in POC (PAA-C%) and PON (PAA-N%) was much higher in KC than in shelf and coastal waters. This study found the distinctive characterization of bioavailability and degradation status between KC and its adjacent seas.

Metal- and antibiotic-resistant heterotrophic plate count bacteria from a gold mine impacted river: the Mooi River system, South Africa

The Wonderfonteinspruit, South Africa, is highly impacted by a century of gold mining activities. The aim of this study was to investigate the physico-chemical properties of the Wonderfonteinspruit and the receiving Mooi River system, the levels of antimicrobial (metals and antibiotics) resistance characteristics and heterotrophic bacteria levels in these water systems. Various physico-chemical parameters were determined. R2A agar and R2A agar supplemented with antimicrobials were used to enumerate heterotrophic bacteria. Morphologically distinct antimicrobial-resistant isolates were purified and screened for antibiotic susceptibility by a disc diffusion method. Selected isolates were identified, and minimum inhibitory concentration ranges determined. Among the antimicrobial resistant isolates, 87% were resistant to at least one antibiotic. Of these, almost 50% were resistant to more than 3 antibiotic classes. A large proportion was resistant to all 7 antibiotics tested. Phyla detected were Proteobacteria, Firmicutes and Bacteriodetes. High MIC levels for metals and antibiotics were detected among all the genera. Results demonstrate potential impacts of physico-chemical properties on levels of antimicrobial-resistant bacteria. Metal-resistant bacteria were also resistant to multiple antibiotics, suggesting that metal pollution from mining may be responsible for co-selection and maintenance of antibiotic-resistant bacteria in this aquatic system.

Bacteriological examination of the water and sediments in Palhi and Salog rivers in Western Leyte, Philippines

Rivers around the world are threatened by destruction caused by anthropogenic activities despite the important services they provide for humanity. This study was conducted to determine the water classification and recommended beneficial uses of Palhi and Salog Rivers based on the most probable numbers of total coliforms, and also to evaluate the abundance of heterotrophic bacteria present in the water and sediments of the rivers as potential indicators of environmental disturbance. A Multiple-tube fermentation test was conducted to determine the most probable number of total coliforms in the river waters. Heterotrophic plate count of total aerobic heterotrophic bacteria was determined by counting the colony-forming units that grew on nutrient agar. Geometric most probable number means of total coliforms revealed that only the upstream of Palhi and Salog Rivers could be used for contact recreational activities. The midstream and downstream of both rivers are recommended for non-contact recreational activities only, due to elevated total coliforms. The heterotrophic plate count of total aerobic heterotrophic bacteria of water and sediment samples for the three stations in Palhi River were not significantly different while in Salog River higher numbers of total aerobic heterotrophic bacteria occurred in the downstream compared to the upstream. However, no significant differences on the heterotrophic plate count of total aerobic heterotrophic bacteria levels were found between the water and sediments for the two rivers. The results of this study imply that monitoring and proper management of the rivers should be done by all sectors of the community for the protection of these invaluable resources.

N, N Diethyl-P-Phenylene Diamine (DPD) Free/Total Chlorine, Coliform and Heterotrophic Bacterial Profile of Polyethylene Terephthalate (PET) and Sachet Water Sold Within and Around University of Benin Campus.

Water quality, free/total chlorine (Cl2) and bacteriological standard, determine the shelf life of water in the hands of the consumers. This study was carried out to determine the free/total chlorine, coliform and heterotrophic bacterial profile of Polyethylene Terephthalate (PET) and sachet water sold within and around the University of Benin Campus. PET/sachet water was randomly sampled from sales vendors and transported to the laboratory in ice condition for analysis. Standard microbiological methods have followed the determination of the coliform and heterotrophic bacterial profile of the sampled water. The digital colorimeter methods with N, N Diethyl-P-Phenylene Diamine (DPD) pillow for free chlorine (DPD 1) and total chlorine (DPD 4) determination in water was used. The free chlorine from PET/sachet water samples of UNIBEN, Faithmark, Dandori and Olivia waters were > 0.1 mg/l, falling short of the recommended World Health Organization (WHO) and Center for Disease and Prevention (CDC) permissible limit (0.2 to 0.5 mg/l). The coliform bacterial counts from this study were recorded as <1.8 MPN, which is less than the WHO and CDC recommended permissible limit. Whereas, the Heterotrophic bacterial counts were well above the recommended limit (> 500 cfu/ml). A proper hygienic regime should be employed during the processing, packing, distribution and sales of PET/sachet water to eliminate high levels of heterotrophic bacteria, which may contaminate the water.

Screening and Identification of Naphthalene-Degrading Bacteria from the Coastal Regions of Makran Sea

Makran Sea and its coastal areas are one of the richest marine ecosystems in the world. The primary purpose of this research was to study Naphthalene-degrading bacteria in some coastal areas of Makran Sea. Four coastal areas of Makran Sea were selected and marine samples were taken from each. Naphthalene-degrading bacteria were enriched in ONR medium in the shaker incubator for seven days with Naphthalene as the sole carbon source. This process was carried out in two separate passages. Some screening analyses were conducted for the selection of the best Naphthalene-degrading strains such as growth assay (OD600 nm), Naphthalene-degradation (GC), cell surface hydrophobicity (BATH), and emulsion production (E24). The predominant strain in Naphthalene-degradation was identified by molecular method. The results of this study showed that the quantity of bacteria present in different regions of Makran Sea varies. An example of this was the highest quantity of Naphthalene-degrading bacteria which were observed in Jask Port, however, the level of heterotrophic bacteria was the highest in Konark Station in comparison to other areas. In this research 65 Naphthalene-degrading bacteria were isolated from collected marine samples. Screening analysis confirmed that 9 strains were more efficient in Naphthalene-degradation and these strains were selected for further study. The best Naphthalene degrader isolate in this study was HS-2 strain, which according to molecular identification results belongs to Shewanella alga. This strain was an emulsifier producer (E24: 88%), and had high cell surface hydrophobicity (BATH: 36%) and was able to degrade Naphthalene in 3000 ppm concentration (70.8%). The results of this research confirmed that Makran marine ecosystem has effective bacteria in the degradation of Polycyclic Aromatic Compounds (PAH). By using these bacteria in the field, it is possible to reduce aromatic pollution in these coastal areas.

Environment variables, composition and metabolic characteristics of culturable sediment bacteria isolated around Gökçeada Island, Aegean Sea, Turkey

Determination of bacteriological diversity in marine ecosystems is of great importance in terms of understanding the functioning of the marine ecosystem, as well as being an indicator of alarm for pollution and sudden changes in marine environments. In this study, we aimed to investigate the composition and metabolic characteristics, relative to variable environmental parameters in the sediment sampling points, of cultivable heterotrophic bacteria taken seasonally from the coastal areas of Gökçeada Island, Turkey between February and November of 2015. The counts of the total cultivable heterotrophic aerobic bacteria (HAB) were tested by using the spread plate technique with Marine agar. The living and dead bacteria counts (TB) were tested with an epifluorescent microscope by means of the DAPI–CTCstaining method. The enzyme activation and metabolic responses of the bacterial isolates were screened against certain substrates by using the VITEK 2 Compact 30 automated micro-identification system. Variable environmental parameters were recorded in-situ in the seawater samples surrounding the sediment samples with multiparameter instrument. The spatial variability of trophic parameter values was tested by spectrophotometric methods. The mean HAB and TB counts of sediment samples were recorded as 35x109±0.5 and 79x1010±0.9 CFU g−1, respectively. During the study period, sixteen bacteria species belonging to six classes. Bacilli (6.0%), Gammaproteobacteria (71.1%), Betaproteobacteria (3.6%), Actinobacteria (1.2%), Cocci (1.2%), and Alphaproteobacteria (16.9 %) were recorded. Arylamidase was determined to be the highest enzyme activity. These results showed that nitrogen mineralization occurs at a high rate in the sediment samples of Gökçeada Island. Temporal and spatial variations in total and heterotrophic bacteria levels between seasons were significant (p<0.05) in the study area. There were no significant station variations between TB and HAB levels (p>0.05). It was determined that trophic parameters related to primary environmental conditions affect bacterial composition, frequency, and metabolites in coastal areas.

Level and Health Risk Evaluation of Heavy Metals and Microorganisms in Urban Soils of Lagos, Southwest Nigeria

Heavy metal and microbial pollution of the environment are linked to the increasing prevalence of diseases worldwide. Accordingly, this study assessed the safety of urban soils in Lagos, Nigeria, with regard to the levels of lead (Pb), nickel (Ni), cadmium (Cd), copper (Cu), chromium (Cr), zinc (Zn), and microorganisms. Soil samples were collected from Iwaya, Makoko, and Ilaje areas of the city and subjected to atomic absorption spectroscopy (AAS) and microbiological examinations using standard protocols. The mean values obtained for the heavy metals and microorganisms were compared with the World Health Organization (WHO) permissible limits. The average daily oral ingestion (ADOI), average daily dermal ingestion (ADDI), and the hazard quotient (HQ) of the heavy metals were also calculated. The AAS indicated that the soils in the three areas contained non-permissible levels of the evaluated heavy metals, except Cu and Cd. The microbiological examinations also showed that the soils contained abnormal levels of heterotrophic bacteria (HB), hydrocarbon utilizing bacteria (HUB), heterotrophic fungi (HF), and hydrocarbon utilizing fungi (HUF). The ADOI of the heavy metals in the three areas were above the recommended levels, while ADDI were normal. Moreover, the HQ of oral ingestion of each heavy metal except Cr was greater than one, while the HQ of dermal ingestion of the heavy metals was less than one. These findings suggest that the soils could predispose the residents in the areas to diseases. Thus, there is a need for regular environmental sanitation and environmental pollution control in the areas, and personal hygiene.

The Levels of Plastic-associated Heterotrophic Bacteria on Three Different Types of Plastics

Plastic pollution in marine ecosystems is one of the most important study topics in recent years. The toxicity, mobility and long-term persistence characteristics of plastics create risk in ecosystems, biota and human health. In this study, the levels of heterotrophic bacteria attached to the surfaces of commonly used plastic types; polyvinylchloride (PVC), polyethylene (PE), and polypropylene (PP) were tested in a mechanical experimental system prepared with seawater under controlled conditions in laboratory. The seawater, which was used in the experimental system, was taken under aseptic conditions from the Golden Horn Estuary, located in the Istanbul region of Turkey. Three different types of plastic (PVC, PE and PP), in two different (glass slide (76x26 cm) and virgin micro pellets (5mm diameter) size, were placed in the experiment setup filled with seawater and incubated for 28 days at ambient temperature. At the end of 28 days, the counts of heterotrophic bacteria were tested using the spread plate technique on Marine Agar (Difco), in both plastic surfaces and surrounding seawater. The levels of heterotrophic bacteria were recorded to be lower in the seawater surrounding the micropellets and lam-size plastic samples. The seawater sample bacterial levels were recorded as 12x109 CFU/ml, at the start of the experiment. At the end of the 28th days, it was recorded to be 83x109 CFU/ml. The highest levels of heterotrophic bacteria were recorded as 41x1010 CFU /cm-2 and 61x1010 CFU /cm-2 on the lam-size surfaces and the micropellet surface of the polypropylene samples, respectively. In the experiments, the PP plastic type has been recorded as a more preferred plastic derivative by heterotrophic bacteria according to the PVC and PE plastic types, but there has been no significant difference in the bacterial adhesion rates on the surfaces. The study contributed increasing knowledge on the bacterial approach to microplastics types. However, there is a need for long term studies related to the mechanism of bacteria attached to microplastics.

An outbreak of norovirus infection caused by ice cubes and a leaking air ventilation valve.

A gastrointestinal outbreak was reported among 154 diners who attended a Christmas buffet on the 9 and 10 December 2016. A retrospective cohort study was undertaken. Faecal samples, water, ice and an air ventilation device were tested for indicators and routine pathogens. Altogether 26% (24/91) fulfilled the case definition of having typical viral gastrointestinal symptoms. Norovirus genogroup I was detected in faecal samples from three cases. One of these cases tested positive also for sapovirus and had a family member testing positive for both norovirus and sapovirus. A diner who drank water or drinks with ice cubes (risk ratios (RR) 6.5, 95% confidence intervals (CI) 1.5-113.0) or both (RR 8.2, 95% CI 1.7-145.5) had an increased risk in a dose-response manner. Ice cubes from three vending machines had high levels of heterotrophic bacteria. A faulty air ventilation valve in the space where the ice cube machine was located was considered a likely cause of this outbreak. Leaking air ventilation valves may represent a neglected route of transmission in viral gastrointestinal outbreaks.

The role of heterotrophic bacteria in assessing phosphorus stress to Synechocystis sp. PCC6803

Microalgae biofuel production, a possible source of carbon-neutral energy, requires phosphorus (P), a limited resource. This study investigates the relationship between specific growth rate of the cyanobacterium Synechocystis sp. PCC 6803 and P availability. It has been previously suggested, and we show here, that P-limited growth kinetics are well represented by a quota-type model with a single pool of intracellular P. We also demonstrate that the presence of heterotrophic bacteria plays a large role in understanding these kinetics, because the culture’s intracellular P content depends on the level of heterotrophic bacteria. Using batch-growth experiments containing up to a 0.07 biovolume ratio of heterotrophic bacteria to Synechocystis, we found that Synechocystis could grow with intracellular P content down to approximately 0.5 mg P g−1 dry weight biomass, while heterotrophic bacteria maintained roughly 20 mg P g−1 dry weight. Thus, a small fraction of heterotrophic bacteria in a microalgal culture can dramatically increase the apparent content of P in the biomass, which affects how to assess P-stress to a P-limited culture.

치과대학 임상 시뮬레이션 실습실 치과용 유니트 수계의 세균 오염도 조사

The water supplied from dental unit water systems (DUWS) in dentistry may be heavily contaminated with bacteria and thus may be a potential source of infection for both practice staff and patients. The aim of this study was to evaluate the level of heterotrophic bacteria and to confirm the presence of opportunistic pathogens from DUWS in student clinical simulation laboratory of college of dentistry. Water samples were collected from 36 ultrasonic scalers in student clinical simulation laboratory. The levels of heterotrophic bacteria in water samples were quantified by counting colony forming units (CFUs) on R2A agar media. In addition, opportunistic pathogens were detected by using the polymerase chain reaction (PCR) method. The mean CFUs were 16,095 CFU/ml for water samples and all of water samples exceeded current American Dental Association recommendations of 200 CFU/ml. Pseudomonas species and non-tuberculous Mycobacterium species were detected in the one sample and two samples, respectively, among the 36 water samples by the PCR with specific primers for these bacteria. Our study indicated that DUWS in student clinical simulation laboratory can cause potential infection in students and participants. This study suggested the dental unit water line management and wearing personal protective equipment in student clinical simulation laboratory will be needed to reduce bacterial contamination.

The occurrence of Naegleria fowleri in recreational waters in Arizona

Naegleria fowleri is a free-living amoeba found in waters in warmer regions that causes primary amoebic meningoencephalitis, a rare but almost universally fatal disease. The goal of this project was to assess the occurrence of N. fowleri and other thermophilic amoebae in 33 recreational surface waters across Arizona to determine if their presence could be correlated with seasonal or other environmental factors. First, 1-L grab samples were collected over two years and analyzed using polymerase chain reaction and amoebae viability. Seasonality was observed, with N. fowleri and thermophilic amoebae (20% and 30%, respectively) being detected more often in the winter and spring combined than in the summer and fall combined (7.9% and 9.5%, respectively). The spring and fall both had an average temperature of 18°C, yet had different occurrence data (18.2% versus 5.9% for N. fowleri, respectively; 27.3% versus 0% for viable amoebae, respectively). These results are in stark contrast to previous studies in which N. fowleri has been found almost exclusively during warmer months. Over the two-year study, N. fowleri was detected in six and thermophilic amoebae in eight of the 33 recreational water bodies. Five of these were lakes near Phoenix that tested positive for N. fowleri and thermophilic amoebae over multiple seasons. These lakes differed significantly (P ≤ 0.05) from the other 28 surface waters, with a lower average temperature in the spring, a higher temperature in the fall, a higher pH and turbidity in the summer, and a lower electro-conductivity in the spring. They also had lower Escherichia coli and heterotrophic bacteria levels during colder months. Future N. fowleri monitoring in Arizona should focus on these five lakes to further elucidate the factors that contribute to the low occurrence of this amoeba in the summer or which might explain why these lakes appear to be reservoirs for the organism.

Water movement and fate of nitrogen during drip dispersal of wastewater effluent into a semi-arid landscape

Drip dispersal of partially treated wastewater was investigated as an approach for onsite water reclamation and beneficial reuse of water and nutrients in a semi-arid climate. At the Mines Park Test Site in Golden, Colorado, a drip dispersal system (DDS) was installed at 20- to 30-cm depth in an Ascalon sandy loam soil profile. Two zones with the same layout were established to enable study of two different hydraulic loading rates. Zones 1 and 2 each had one half of the landscape surface with native vegetation and the other with Kentucky bluegrass sod. After startup activities, domestic septic tank effluent was dispersed five times a day at footprint loading rates of 5 L/m2/d for Zone 1 and 10 L/m2/d for Zone 2. Over a two-year period, monitoring included the frequency and volume of effluent dispersed and its absorption by the landscape. After the first year of operation in October a 15N tracer test was completed in the sodded portion of Zone 1 and samples of vegetation and soil materials were collected and analyzed for water content, pH, nitrogen, 15N, and bacteria. Research revealed that both zones were capable of absorbing the effluent water applied at 5 or 10 L/m2/d. Effluent water dispersed from an emitter infiltrates at the emitter and along the drip tubing and water movement is influenced by hydrologic conditions. Based on precipitation and evapotranspiration at the Test Site, only a portion of the effluent water dispersed migrated downward in the soil (approx. 34% or 64% for Zone 1 or 2, respectively). Sampling within Zone 1 revealed water filled porosities were high throughout the soil profile (>85%) and water content was most elevated along the drip tubing (17–22% dry wt.), which is also where soil pH was most depressed (pH 4.5) due to nitrification reactions. NH4+ and NO3− retention occurred near the dispersal location for several days and approximately 51% of the N applied was estimated to be removed by plant uptake and denitrification. Heterotrophic bacteria levels were elevated (up to 1 log) in the subsurface within the DDS but there was effective elimination of effluent fecal coliform and Escherichia coli bacteria.

Effects of Nest Reuse and Onset of Incubation on Microbial Growth and Viability of Wood Duck Eggs

Abstract. In many birds, egg viability declines the longer that eggs remain unincubated (i.e., incubation delay), possibly because of increased levels of microbial infection. Reuse of nests is common in cavity-nesting species and may also increase exposure of eggs to microbes. Starting incubation before the clutch is complete may help protect early-laid eggs from microbial infection. In this study, we tested the effects of nest cleaning, length of incubation delay, and onset of night incubation on growth of microbes on Wood Duck (Aix sponsa) eggshells and examined the effect of microbial infection on hatching success. We used nest boxes that had been cleaned or not cleaned of previous nesting materials and sampled microbes on eggshells during early and mid egg laying and after the start of night incubation. We detected levels of eggshell microbes (101 colony forming units [CFU] egg-1) lower than at more tropical locations (103–4 CFU egg-1). Levels of heterotrophic bacteria were 2.2 times greater in unclea...

Assessment of water quality in Ahor Lake - Ghana

In the bid to boost the tourism industry, West Akyem Municipal Assembly identified Lake Ahor, a manmade lake as a potential tourism site in the municipality. However, the quality of the water is not known hence the assessment of the physical, chemical and bacteriological characteristics of the lake. A total of twelve samples of water from the lake were collected in June 2011 and were subjected to physical, chemical and bacteriological analysis. The measured water quality parameters included pH, colour, turbidity, alkalinity, TDS, total iron, nitrate, nitrite, trace elements like phosphates, zinc, copper, silicon, feacal coliform and Escherichia coli counts. The results showed that the averages for parameters like pH, colour, turbidity, alkalinity, TDS, total iron and nitrate were 6.6, 48.3 TCU, 4.8 NTU, 44.2, 1221.3 and 0.2 mg/l respectively. The tests for total coliform, faecal coliform, E. coli and total heterotrophic bacteria levels showed >8 CFU/100 ml for total coliform, between 1.00 and 8.00CFU/100ml for faecal coliform, 0.00 and 9.00 CFU/100 ml for E. coli and 42.00 and 155.0 CFU/100 ml for total heterotrophic bacteria. The water from the lake met the WHO guidelines in all parameters except the colour of the water which was light brownish which reduced the clarity at the deep areas of the lake. It is recommended that the appropriate authorities must demarcate safe swimming areas in the lake to prevent injury or drowning of those who will patronize the facility. Key words: Recreation, water quality, bacteriological quality, lake

Short-term physiological effects of a xenobiotic mixture on the freshwater mussel Elliptio complanata exposed to municipal effluents

The aim of this study was to investigate the short-term effects of tertiary-treated municipal effluents on the freshwater mussel Elliptio complanata. Caged mussels were immersed during 2 weeks in a river located North of Montreal Island, upstream/downstream the outfall and in one reference site located at the beginning of the Rivière des Prairies. A selection of biomarkers was analyzed to depict changes on various physiological systems: general physiology (mussel viability, condition index and gonado-somatic index), immune status (hemocyte viability, cellularity, phagocytosis efficiency, NK-like cytotoxic activity and lysozyme activity), inflammation (cyclo-oxygenase activity), detoxification (glutathione-S-transferases activity) and vitellogenesis (alkali-labile phosphate level). The analysis of total and fecal coliform counts in water and of heterotrophic bacteria levels in mussel tissues showed that the bacteriological quality of the water strongly decreased from the reference site to the downstream site. This was correlated with a significant loss of weight and an increase of mussel mortality. Cellularity and phagocytosis efficiency were significantly increased in the downstream site compared to the reference site. Though not statistically significant, lysozyme activity was also increased. NK-like cytotoxicity, activity of the pro-inflammatory enzyme COX and the levels of ALP and MT were not significantly changed. Conversely, the municipal effluents induced a significant increase of GST activity in downstream site, indicating a stimulation of detoxification metabolism. Altogether, these results confirm that a short-term exposure to a mixture of bacterial and chemical compounds released by the wastewater treatment plant La Pinière induces adverse physiological effects in E. complanata, as observed with the modulation of immune response and induction of detoxification metabolism.

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 IC50/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 IC50/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 1.5×104–1.9×105, 1.2×104–1.5×105, 8.9×103–1.9×105 and 2.6×104–2.0×105CFU/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 840–6.1×103 and 310–6.1×104CFU/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.

Changes in abundance of heterotrophic and coliform bacteria resident in stored water bodies in relation to incoming bacterial loads following rain events

Microbial properties of harvested rainwater were assessed at two study sites at Newcastle on the east coast of Australia. The investigation monitored daily counts of heterotrophic bacteria (HPC), total coliforms and E. coli during a mid-winter month (July). Immediately after a major rainfall event, increases in bacterial loads were observed at both sites, followed by gradual reductions in numbers to prior baseline levels within 7 days. Baseline HPC levels ranged from 500-1000 cfu/mL for the sites evaluated, and the loads following rain peaked at 3590-6690 cfu/mL. Baseline levels of total coliforms ranged from 0-100 cfu/100 mL and peaked at 480-1200 cfu/100 mL following rain. At Site 1, there was no evidence of E. coli loading associated with the rain events assessed, and Site 2 had no detectable E.coli colonies at baseline, with a peak load of 17 cfu/100 mL following rain which again diminished to baseline levels. It was concluded that rainfall events contributed to the bacterial load in rainwater storage systems, but processes within the rainwater storage ensured these incoming loads were not sustained.

Accelerated chloramine decay and microbial growth by nitrification in premise plumbing

Chloramine decay rates are accelerated by nitrifier colonization of premise plumbing, which compromises the effectiveness of secondary disinfection. As expected, in the absence of nitrification, chloramine was more stable than chlorine; but in the presence of nitrification, the relative stability (and efficacy) of the two disinfectants could be reversed. The net result with chloramination can be higher levels of heterotrophic bacteria in the bulk water and pipe biofilms than would be found with free chlorine. These experimental trends were confirmed using field data collected from homes in systems with active nitrification.