Free chlorine demand and cell survival of microbial suspensions

The utility of chlorine residual and chlorine demand as a surrogate for microbial contamination in the water distribution system was evaluated. The chlorine demanded by and cell survival of pure culture suspensions of Escherichia coli, Staphylococcus epidermidis, and Mycobacterium aurum were quantified in solutions with initial free chlorine concentrations of 0.20, 0.40, and 0.80 mg/L. The chlorine demand increased with initial concentration of cells and free chlorine for all species. At equivalent initial cell concentrations, chlorine demand was greatest for M. aurum, followed by S. epidermidis and E. coli. The chlorine contact time required for a 3-log inactivation of E. coli, S. epidermidis, and M. aurum was calculated as 0.032+/-0.009, 0.221+/-0.080, and 42.9+/-2.71 mg min/L, respectively. The ultimate chlorine demand and cell survival were directly proportional. No chlorine demand was observed at cell concentrations less than 10(5)CFU/mL for E. coli or 10(4)CFU/mL for S. epidermidis. M. aurum demanded chlorine at all initial cell concentrations including 10(3)CFU/mL, which was the detection limit of the cell quantification assay. Chlorine demand was determined to be a suitable surrogate indicator of the organisms studied and its utility may be enhanced in locations of the water distribution system that maintain a higher free chlorine residual.     

UV disinfection of RBC-treated light greywater effluent: kinetics, survival and regrowth of selected microorganisms

The microbial quality of raw greywater was found to be much better than that of municipal wastewater, with 1.6 x 10(7)cfu ml(-1) heterotrophic plate count (HPC), and 3.8 x 10(4), 9.9 x 10(3), 3.3 x 10(3) and 4.6 x 10(0)cfu 100 ml(-1) faecal coliforms (FC), Staphylococcus aureus sp., Pseudomonas aeruginosa sp. and Clostridium perfringes sp., respectively. Further, three viral indicators monitored (somatic phage, host: Escherichia coli CN(13) and F-RNA phages, hosts: E. coli F+(amp), E. coli K12) were not present in raw greywater. The greywater was treated by an RBC followed by sedimentation. The treatment removed two orders of magnitude of all bacteria. UV disinfection kinetics, survival and regrowth of HPC, FC, P. aeruginosa sp. and S. aureus sp. were examined. At doses up to 69 mW s cm(-2) FC were found to be the most resistant bacteria, followed by HPC, P. aeruginosa sp. and S. aureus sp. (inactivation rate coefficients: 0.0687, 0.113, 0.129 and 0.201 cm2 mW(-1)s(-1), respectively). At higher doses (69-439 mW s cm(-2)) all but HPC (which exhibited a tailing curve) were completely eliminated. Microscopic examination showed that FC self-aggregate in the greywater effluent. This provides FC an advantage at low doses, since the concentration of suspended matter (that can provide shelter from UV radiation) in the effluent was very low. FC, P. aeruginosa sp. and S. aureus sp. did not exhibit regrowth up to 6h after exposure to increasing UV doses (19-439 mW s cm(-2)). HPC regrowth was proven to be statistically significant in un-disinfected effluent and after irradiation with high UV doses (147 and 439 mW s cm(-2)). At these doses regrowth resulted from growth of UV-resistant bacteria due to decreased competition with other bacteria eliminated by the irradiation.     

Identification of an IgA inhibitor of neutrophil chemotaxis and its membrane target for the metabolic burst

Affinity-purified IgA from the serum of an 8-year-old boy with a 5-year history of recurrent facial nodules, intermittent neutropenia and elevated immunoglobulin levels, inhibited the chemotaxis of polymorphonuclear neutrophils (PMN) from both patient and normal adults. Preincubation of normal PMN with IgA from the patient''s serum (0.5 mg/ml) inhibited chemotaxis to C5a and to the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) by 80%, while IgA or IgG from pooled human serum and IgG from the patient were without effect. Normal PMN chemotaxis was restored after IgA depletion of the patient''s serum by affinity chromatography. The patient''s IgA, but not IgA from pooled human serum, bound specifically to normal PMN by its antigen-binding sites and recognized a 62,000 MW membrane protein on normal neutrophils, which was distinct from the FMLP receptor, the C5a receptor, or the Fca receptor. Attachment of the patient''s IgA to the 62,000 MW protein activated intracellular oxidative metabolism on a parity with phorbol myristate acetate (PMA) and resulted in a significant up-regulation of membrane receptors for FMLP. After the binding of patient (Pt) IgA, normal neutrophils were rendered significantly less responsive to subsequent stimulation with phorbol esters. These results characterize a novel mechanism of chemotactic inhibition by serum IgA and also identify a neutrophil membrane protein that is linked to intracellular oxidative metabolism.     

The Self-Protection of Escherichia Coli in Seawater

Many environmental variables are known to be involved in the inactivation processes affecting enteric bacteria in seawater. It is commonly believed that bacteria may attempt to reduce adverse effects by adhering together, thereby decreasing the surface area exposed to the hostile environment. This mechanism may be described as self-protection and should enhance the survival of the bacterial population.
Controlled laboratory experiments, epifluorescence microscopy, and Coulter counter analysis were used to examine and elucidate the inactivation mechanisms for the enteric bacterium E. coli. In general, the survival of E. coli was found to be enhanced with increasing initial cell concentration in the absence of any suspended solids.     

Inactivation of Escherichia coli O157:H7 during thermophilic anaerobic digestion of manure from dairy cattle

Inactivation of the pathogenic Escherichia coli serotype O157:H7 and a non-pathogenic E. coli strain isolated from dairy cattle manure was evaluated with batch tests at 50 and 55 degrees C in biosolids from a thermophilic anaerobic digester treating the manure. Using differential-selective plating on sorbitol-MacConkey (SMAC) agar to quantify E. coli, the decline in concentrations of both the sorbitol-negative (putative E. coli O157:H7) and sorbitol-positive (putative non-pathogenic E. coli) organisms followed a model that assumed there was a heat-sensitive fraction and a heat-resistant fraction. Inactivation rates of the heat-sensitive fractions were similar for both colony types at each temperature, suggesting that wild-type E. coli can be used as an indicator of inactivation of serotype O157:H7. The decimal reduction time for the heat-sensitive fractions was in the order of 10min at 55 degrees C and ranged from approximately 1-3h at 50 degrees C. Concentrations of heat-resistant organisms at 55 degrees C were 1.4-1.7log(10)cfu/mL. Confirmatory analyses conducted on 30 randomly selected colonies of heat-resistant sorbitol-negative cells from treatment at 55 degrees C indicated that none were serotype O157:H7, nor were they E. coli. Similar analyses on 10 sorbitol-negative isolates from untreated manure indicated that none were serotype O157:H7, although 16S rRNA gene sequence analysis indicated that eight were E. coli or closely related enteric bacteria. These findings suggest that plating on differential-selective media to quantify E. coli, including serotype O157:H7, in effluent samples from thermophilic anaerobic digestion can lead to false positive results. Therefore, more specific methods should be used to evaluate the extent of thermal inactivation of both pathogenic and non-pathogenic E. coli in manure treatment systems.     

Mortality rates of autochthonous and fecal bacteria in natural aquatic ecosystems

Bacterial mortality has been investigated in freshwater (River Seine) and in marine (North Sea) systems using a method based on following the disappearance of radioactivity from the DNA of assemblages of bacteria previously labeled with tritiated thymidine. Measurement of bacterial mortality of autochthonous and various types of fecal bacteria allowed direct comparisons between their respective first-order mortality rates. Mortality rates obtained for the different types of bacteria in the River Seine were, respectively, 7.9-33.9 x 10(-3)h(-1) for Escherichia coli, 12.2-29.2 x 10(-3)h(-1) for S. faecium and 7.0-18.3 x 10(-3)h(-1) for the autochthonous bacteria. In the Belgian coastal waters, these rates were 4.6-27.3 x 10(-3)h(-1) for E. coli, 6.0-22.0 x 10(-3)h(-1) for S. typhimurium, 10.0-18.9 x 10(-3)h(-1) for S. faecium and 1.0-13.9 x 10(-3)h(-1) for autochthonous bacteria. In both environments, the overall mortality rates of autochthonous and the different fecal bacteria were in the same order of magnitude and overall mortality rates of E. coli were on average about twice as high for autochthonous bacteria. Grazing by protozooplankton was the dominant process of mortality for fecal and autochthonous bacteria in both environments. Except in a few situations, grazing by protozooplankton was responsible for more than 90% of the overall mortality rate of fecal and autochthonous bacteria in the river and in the coastal area.     

纯培养条件下细菌需氯量和存活性的试验研究

以埃希氏大肠杆菌和粪肠球菌作为研究对象,在纯培养条件下考察了自由氯、氯胺和二氧化氯的投加量以及细菌初始浓度对需氯量的影响.结果表明:灭活率达到99.9％时,两种细菌的需氯量均随初始菌浓度和消毒剂投加量的提高而增大,粪肠球菌的需氯量大于埃希氏大肠杆菌;投加自由氯时两种细菌的需氯量差别最大,其次是二氧化氯,氯胺的差别最小.     

Accumulation and fate of green fluorescent labeled Escherichia coli in laboratory-scale drinking water biofilters

Biological filters combining microbial activity and rapid sand filtration are used in drinking water treatment plants for enhanced biodegradable organic matters (BOM) removal. Biofilms formed on filter media comprised of bacteria enclosed in a polymeric matrix are responsible for the adsorption of BOM and attachment of planktonic microorganisms. This study investigated the removal of Escherichia coli cells injected into laboratory-scale biofilters and the role of biofilm in retaining the injected E. coli. Green fluorescent protein was used as a specific marker to detect and quantify E. coli in the biofilms. About 35% of the total injected E. coli cells were observed in the filter effluents, when initial cell concentrations were measured at 7.4 x 10(6) CFU/mL and 1.6 x 10(7) CFU/mL in two separate experiments. The results from real-time PCR and plate count analysis indicated that 95% of the E. coli retained inside the filters were either non-viable or could not be recovered by colony counting techniques. Injected cells were unevenly distributed inside the filter with more than 70% located at the top 1/5 of the filter. Images obtained from an epifluorescent microscope showed that E. coli cells were embedded inside the biofilm matrix and presented mainly as microcolonies intertwined with other microorganisms, which was consistent with findings from standard plate count methods and qPCR.     

Relationships between Bacteroides 16S rRNA genetic markers and presence of bacterial enteric pathogens and conventional fecal indicators

Occurrence and prevalence of different bacterial enteric pathogens as well as their relationships with conventional (total and fecal coliforms) and alternative fecal indicators (host-specific Bacteroides 16S rRNA genetic markers) were investigated for various water samples taken from different sites with different degrees of fecal contamination. The results showed that a wide range of bacterial pathogens could be detected in both municipal wastewater treatment plant samples and in surface water samples. Logistic regression analysis revealed that total and human-specific Bacteroides 16S rRNA genetic markers showed significant predictive values for the presence of Escheriachia coli O-157, Salmonella, heat-labile enterotoxin (LT) of enterotoxigenic E. coli (ETEC), and heat-stable enterotoxin for human (STh) of ETEC. The probability of occurrence of these pathogenic bacteria became significantly high when the concentrations of human-specific and total Bacteroides 16S rRNA genetic markers exceeded 10(3) and 10(4) copies/100 mL. In contrast, Clostridium perfringens was detected at high frequency regardless of sampling sites and levels of Bacteroides 16S rRNA genetic markers. No genes related to Shigella spp., Staphylococcus aureus and Vibrio cholerae were detected in any samples analyzed in this study. Conventional indicator microorganisms had low levels of correlation with the presence of pathogens as compared with the alternative fecal indicators. These results suggested that real-time PCR-based measurement of alternative Bacteroides 16S rRNA genetic markers was a rapid and sensitive tool to identify host-specific fecal pollution and probably associated bacterial pathogens. However, since one fecal indicator might not represent the relative abundance of all pathogenic bacteria, viruses and protozoa, combined application of alternative indicators with conventional ones could provide more comprehensive pictures of fecal contamination, its source and association with pathogenic microorganisms.     

Population structure of Cladophora-borne Escherichia coli in nearshore water of Lake Michigan

We previously reported that the macrophytic green alga Cladophora harbors high densities (up to 10(6) colony-forming units/g dry weight) of the fecal indicator bacteria, Escherichia coli and enterococci, in shoreline waters of Lake Michigan. However, the population structure and genetic relatedness of Cladophora-borne indicator bacteria remain poorly understood. In this study, 835 E. coli isolates were collected from Cladophora tufts (mats) growing on rocks from a breakwater located within the Indiana Dunes National Lakeshore in northwest Indiana. The horizontal fluorophore enhanced rep-PCR (HFERP) DNA fingerprinting technique was used to determine the genetic relatedness of the isolates to each other and to those in a library of E. coli DNA fingerprints. While the E. coli isolates from Cladophora showed a high degree of genetic relatedness (92% similarity), in most cases, however, the isolates were genetically distinct. The Shannon diversity index for the population was very high (5.39). Both spatial and temporal influences contributed to the genetic diversity. There was a strong association of isolate genotypes by location (79% and 80% for lake- and ditch-side samplings, respectively), and isolates collected from 2002 were distinctly different from those obtained in 2003. Cladophora-borne E. coli isolates represented a unique group, which was distinct from other E. coli isolates in the DNA fingerprint library tested. Taken together, these results indicate that E. coli strains associated with Cladophora may be a recurring source of indicator bacteria to the nearshore beach.     

Fecal indicator bacteria are abundant in wet sand at freshwater beaches

Potential fecal contamination of sand in the wave-washed zone of public bathing beaches is overlooked in beach monitoring programs. Activity in this zone can bring pathogens to the sand surface or into the water, presenting a health risk to sensitive populations. On a unit weight basis (colony forming units per 100g), the mean summer abundance of the fecal indicator bacteria enterococci and Escherichia coli was 3-38 times higher in the top 20 cm of wet-sand cores than in the water column at six freshwater bathing beaches. E. coli were 4 times more abundant than enterococci in water but counts were similar in the sand. A correlation (r=0.60) existed between E. coli counts in the water and in the top 5 cm of sand only, whereas no relationship existed between enterococci abundance in water and sand. In general, enterococci were most numerous in the 5-10 cm sand stratum and E. coli in the 0-5 cm stratum. These preliminary data show that wet freshwater beach sand is a reservoir of fecal indicator bacteria. Enteric pathogens may also be present in beach sand.     

北京协和医院外科住院患者细菌耐药性监测

【摘要】 目的 了解北京协和医院外科住院患者临床分离细菌分布及对抗菌药物的耐药性。方法 收集2012年1月1日?至2013年12月31日北京协和医院外科住院患者临床分离的3084株非重复细菌，采用纸片扩散法或自动化仪器法进行药敏试验，按美国临床和实验室标准化协会(Clinical and Laboratory Standards Institute，CLSI)2013年版标准判读药敏结果，采用WHONET5.6软件进行数据分析。结果 3084株非重复细菌中10个最常见的细菌依次为鲍曼不动杆菌（14.1％）、大肠埃希菌（12.4％）、铜绿假单胞菌（12.4％）、肺炎克雷伯菌（11.8％）、金黄色葡萄球菌（8.9％）、粪肠球菌（5.4％）、凝固酶阴性葡萄球菌（5.3％）、阴沟肠杆菌（3.7％）、嗜麦芽窄食单胞菌（3.6％）和屎肠球菌（3.2％），其中革兰阴性菌占71.6％（2208株），革兰阳性菌占28.4％（876株）。耐甲氧西林金黄色葡萄球菌（methicillin-resistant Staphylococcus aureus，MRSA）和耐甲氧西林凝固酶阴性葡萄球菌（methicillin-resistant coagulase negative Staphylococcus，MRCNS）的检出率分别为42.7％（117/274）和77.3％（119/154）。MRS葡萄球菌（MRSA和MRCNS）对β内酰胺类和其他抗菌药物的耐药率明显高于MSS葡萄球菌（MSSA和MSCNS）。MRSA中80.3%菌株对磺胺甲噁唑-甲氧苄啶敏感，MRCNS中95%菌株对利福平敏感。未发现对万古霉素，替考拉宁和利奈唑胺耐药的葡萄球菌。粪肠球菌对大多数抗菌药物的耐药率明显低于屎肠球菌，后者对氯霉素的耐药率仅为4.3%。分别发现1株和5株万古霉素耐药的粪肠球菌和屎肠球菌，根据表型推测为VanA 型耐药；未发现对利奈唑胺耐药的肠球菌。产超广谱β-内酰胺酶（extended spectrum β-lactamases, ESBLs）的大肠埃希菌、克雷伯菌属细菌（肺炎克雷伯菌和产酸克雷伯菌）和奇异变形杆菌的检出率分别为56.7％、23.8％和22.8%。产ESBLs菌株的耐药率明显高于非产ESBLs菌株。肠杆菌科细菌对碳青霉烯类抗菌药物仍高度敏感，总耐药率1.6%～3.3%。泛耐药肺炎克雷伯菌的检出率为0.8%（3/363）。铜绿假单胞菌对亚胺培南和美罗培南的耐药率分别为19.5％和15.0％，对阿米卡星的耐药率最低（8.6％）；鲍曼不动杆菌对上述两种抗菌药物的耐药率分别为74.1％和74.0％，对头孢哌酮－舒巴坦和米诺环素的耐药率最低(51.5％和28.9％)。泛耐药鲍曼不动杆菌和铜绿假单胞菌的检出率分别为44.3％和0.8%。结论 定期进行耐药性监测有助于了解细菌耐药性变迁，为临床经验用药提供依据。     

Seasonal variation in accurate identification of Escherichia coli within a constructed wetland receiving tertiary-treated municipal effluent

As the reuse of municipal wastewater escalates worldwide as a means to extend increasingly limited water supplies, accurate monitoring of water quality parameters, including Escherichia coli (E. coli), increases in importance. Chromogenic media are often used for detection of E. coli in environmental samples, but the presence of unique levels of organic and inorganic compounds alters reclaimed water chemistry, potentially hindering E. coli detection using enzyme-based chromogenic technology. Over seven months, we monitored E. coli levels using m-Coli Blue 24((R)) broth in a constructed wetland filled with tertiary-treated municipal effluent. No E. coli were isolated in the wetland source waters, but E. coli, total coliforms, and heterotrophic bacteria increased dramatically within the wetland on all sampling dates, most probably due to fecal inputs from resident wildlife populations. Confirmatory testing of isolates presumptive for E. coli revealed a 41% rate of false-positive identification using m-Coli Blue 24((R)) broth over seven months. Seasonal differences were evident, as false-positive rates averaged 35% in summer, but rose sharply to 75% in the late fall and winter. Corrected E. coli levels were significantly correlated with electrical conductivity, indicating that water chemistry may be controlling bacterial survival within the wetland. This is the first study to report that accuracy of chromogenic media for microbial enumeration in reclaimed water may show strong seasonal differences, and highlights the importance of validation of microbiological results from chromogenic media for accurate analysis of reclaimed water quality.     

Quantitative evaluation of bacteria released by bathers in a marine water

Enterococci, a common fecal indicator, and Staphylococcus aureus, a common skin pathogen, can be shed by bathers affecting the quality of recreational waters and resulting in possible human health impacts. Due to limited information available concerning human shedding of these microbes, this study focused on estimating the amounts of enterococci and S. aureus shed by bathers directly off their skin and indirectly via sand adhered to skin. Two sets of experiments were conducted at a marine beach located in Miami-Dade County, Florida. The first study, referred to as the "large pool" study, involved 10 volunteers who immersed their bodies in 4700L during four 15min cycles with exposure to beach sand in cycles 3 and 4. The "small pool" study involved 10 volunteers who were exposed to beach sand for 30min before they individually entered a small tub. After each individual was rinsed with off-shore marine water, sand and rinse water were collected and analyzed for enterococci. Results from the "large pool" study showed that bathers shed concentrations of enterococci and S. aureus on the order of 6x10(5) and 6x10(6) colony forming units (CFU) per person in the first 15min exposure period, respectively. Significant reductions in the bacteria shed per bather (50% reductions for S. aureus and 40% for enterococci) were observed in the subsequent bathing cycles. The "small pool" study results indicated that the enterococci contribution from sand adhered to skin was small (about 2% of the total) in comparison with the amount shed directly from the bodies of the volunteers. Results indicated that bathers transport significant amounts of enterococci and S. aureus to the water column, and thus human microbial bathing load should be considered as a non-point source when designing recreational water quality models.     

Recovery of Escherichia coli in fresh water fish, Jenynsia multidentata and Bryconamericus iheringi

Escherichia coli concentration was determined in digestive tract and muscle of Jenynsia multidentata and Bryconamericus iheringi through bioassays. Field experiments were also conducted with J. multidentata collected in the Suquía River, Córdoba, Argentina. E. coli was quantified by the most probable number, using lauryl sulphate tryptose broth with 4-methylumbelliferyl-beta-D-glucuronide. For bioassays, E. coli concentrations 10(2), 10(3), 10(4), 10(5), 10(6)CFU/ml were introduced in aquarium water. E. coli was recovered from the digestive tracts of J. multidentata and B. iheringi in all the concentrations assayed. Bacterial critical load in water for the recovery of bacteria from muscle, was 10(3)CFU/ml for both species. The regression analysis between E. coli loads in water and those found in digestive tract and muscle showed a positive linear relationship for J. multidentata and B. iheringi. The same relation was observed between the concentration of bacteria in digestive tract and muscle in both species. In field experiments, E. coli was recovered from digestive tract and muscle of J. multidentata. The presence of E. coli in the studied fish suggests that they can carry bacteria to non-polluted waters. However, further studies are necessary to evaluate its significance for public and environmental health.     

世界卫生组织关注的临床重要细菌耐药变迁:北京协和医院10年数据分析

目的了解世界卫生组织关注的临床重要细菌在北京协和医院的耐药变迁趋势。方法回顾性分析北京协和医院2007年1月1日至2016年12月31日10年间临床分离的46 168株非重复细菌,采用纸片扩散法或自动化仪器法进行药敏试验,按美国临床实验室标准化协会2016年版标准判读药敏结果,采用WHONET 5.6软件进行数据分析。结果46 168株非重复细菌中,铜绿假单胞菌6679株,鲍曼不动杆菌6422株,肠杆菌科细菌24 001株(其中大肠埃希菌11 046株、肺炎克雷伯菌6034株),屎肠球菌2358株,金黄色葡萄球菌6056株,肺炎链球菌652株。10年来,北京协和医院碳青霉烯类耐药铜绿假单胞菌的检出率从38.3%(2007年)下降至22.4%(2016年);碳青霉烯类耐药鲍曼不动杆菌的检出率从52.8%(2007年)上升至71.9%(2016年);碳青霉烯类耐药肠杆菌科的检出率从1.9%(2007年)上升至5.3%(2016年),其中肺炎克雷伯菌对亚胺培南的耐药率从1.3%(2007年)上升至14.4%(2016年);耐甲氧西林金黄色葡萄球菌(methicillin-resistant Staphylococcus aureus,MRSA)的检出率从56.5%(2007年)下降至27.0%(2016年);屎肠球菌对万古霉素的耐药率近5年为3.3%~5.8%;肺炎链球菌对青霉素不敏感株的检出率近2年为0.9%~6.4%。结论肺炎克雷伯菌和鲍曼不动杆菌对碳青霉烯类的耐药率仍呈上升趋势,给临床的抗感染治疗带来了极大挑战。     

In situ measurement and statistical modelling of Escherichia coli decay in small rivers

Numerous studies have been carried out on the environmental factors associated with the decay of faecal bacteria in open (fresh or marine) waters. The present study aimed at understanding the fate of bacteria in small streams (flow <20 m3 s(-1)) for which there is a lack of knowledge. An original in situ protocol was developed for measuring the die-off of Escherichia coli (E. coli) from wastewater treatment plants. Based upon 80 values of the decay first-order parameter (K or its inverse T90), collected from five rivers in Normandy (France), a median T90 of 10 h and a minimal T90 of 1.3 h were obtained. K was then modelled as a linear function of variables made up from flow, water temperature and suspended particulate matter (SPM). The set of significant co-variables did not include light indicators. E. coli decay is inversely related to the river flow and it becomes highly significant below 0.3 m3 s(-1). The positive effect of small flows on die-off is increased by water temperature over 15 degrees C, whereas it could be reduced by SPM. The major co-variable of the model (p < 10(-9)) is an empiric composite variable integrating the effect of flow and temperature that explains more than 40% of the variance of K. We interpreted this as an expression of predation by benthic micro-grazers which could be the main cause of E. coli die-off in small streams in temperate countries.     

Confirmation of E. coli among other thermotolerant coliform bacteria in paper mill effluents, wood chips screening rejects and paper sludges

Paper sludges are solid wastes material generated from the paper production, which have been characterized for their chemical contents. Some are rich in wood fiber and are a good carbon source, for example the primary and de-inking paper sludges. Others are made rich in nitrogen and phosphorus by pressing the activated sludge, resulting from the biological water treatments, with the primary sludge, yielding the combined paper sludge. Still, in the absence of sanitary effluents very few studies have addressed the characterization of their coliform microflora. Therefore, this study investigated the thermotolerant coliform population of one paper mill effluent and two paper mill sludges and wood chips screening rejects using chromogenic media. For the first series of analyses, the medium used was Colilert broth and positive tubes were selected to isolate bacteria in pure culture on MacConkey agar. In a second series of analyses, double selective media, based on ss-galactosidase and ss-glucuronidase activities, were used to isolate bacteria. First, the presence of thermotolerant coliforms was detected in low numbers in most water effluents, but showed that the entrance of the thermotolerant coliforms was early in the industrial process. Also, large numbers of thermotolerant coliforms, i.e., 7,000,000 MPN/g sludge (dry weight; d.w.), were found in combined sludges. From this first series of isolations, bacteria were purified on MacConkey medium and identified as Citrobacter freundii, Enterobacter sp, E. sakazakii, E. cloacae, Escherichia coli, K. pneumoniae, K. pneumoniae subsp. rhinoscleromatis, K. pneumoniae subsp. ozaenae, K. pneumoniae subsp. pneumoniae, Pantoea sp, Raoultella terrigena, R. planticola. Second, the presence of thermotolerant coliforms was measured at more than 3,700-6,000 MPN/g (d.w) sludge, whereas E. coli was detected from 730 to more than 3,300 MPN/g (d.w.) sludge. The presence of thermotolerant coliform bacteria and E. coli was sometimes detected from wood chips screening rejects in large quantities. Also, indigenous E. coli were able to multiply into the combined sludge, and inoculated E. coli isolates were often able to multiply in wood chips and combined sludge media. In this second series of isolations, API20E and Biolog identified most isolates as E. coli, but others remained unidentified. The sequences of the 16S rDNA confirmed that most isolates were likely E. coli, few Burkholderia spp, but 10% of the isolates remained unidentified. This study points out that the coliform bacteria are introduced by the wood chips in the water effluents, where they can survive throught the primary clarifier and regrow in combined sludges.     

Transport of Escherichia coli in saturated porous media: dual mode deposition and intra-population heterogeneity

Because of heterogeneity among members of a bacteria population, deposition rates of bacteria may decrease upon the distance bacteria are transported in an aquifer. Such deposition rate decreases may result in retained bacteria concentrations, which decrease hyper-exponentially as a function of transport distance, and may therefore significantly affect the transport of colloids in aquifers. We investigated the occurrence of hyper-exponential deposition of Escherichia coli, an important indicator for fecal contamination, and the causes for such behavior. In a series of column experiments with glass beads of various sizes, we found that attachment of E. coli decreased hyper-exponentially, or, on logarithmic scale in a bimodal way, as a function of the transported distance from the column inlet. From data fitting of the retained bacteria concentration profiles, the sticking efficiency of 40% of the E. coli population was high (alpha=1), while the sticking efficiency of 60% was low (alpha=0.01). From the E. coli total population, an E. coli subpopulation consisting of slow attachers could be isolated by means of column passage. In subsequent column experiments this subpopulation attached less than the E. coli total population, consisting of both slow and fast attachers. We concluded that the main driver for the observed dual mode deposition was heterogeneity among members of the bacteria population. Intra-population may result in some microbes traveling surprisingly high distances in the subsurface. Extending the colloid filtration theory with intra-population variability may provide a valuable framework for assessing the transport of bacteria in aquifers.