Genotypic characterization of quinolone resistant-Escherichia coli isolates from retail food in Morocco

This study was conducted to assess the retail food as a possible vehicle for antimicrobial resistant, particularly quinolones resistant and pathogenic Escherichia coli. We determined the prevalence and characteristics of nalidixic acid (Nal) resistant E. coli isolates from diverse retail food samples. In all, 70 (28%) of 250 E. coli isolates studied were Nal-resistant E. coli and 91% of these were multi-drug resistant. Plasmid mediated quinolone resistance genes were identified in 32 isolates, including aac(6′)-Ib-cr (n = 16), qnrS1 (n = 11) and qnrB19 (n = 7). Mutations in gyr A and par C genes were detected among 80% of the isolates, and the isolates showed substitution Ser83-Leu and Asp87-Asn in gyrA and Ser80-Ile in parC. In addition, three different gene cassettes were identified (aadA1, aadA7, aac(3)-Id) in 18%. Virulence-associated genes stx1, eae, sfa, hlyA and stx2 were found in six (8%), three (4%), two (3%), three (4%) and three (4%) isolates, respectively. E. coli isolates of phylogenetic group A were dominant (64%, 45/70). Pulsed field gel electrophoresis revealed none epidemiological relationship between these isolates. The results of this work report the higher frequency of Nal-resistant E. coli isolates from Moroccan retail food samples including MDR and pathogenic isolates.     

Antibiotic resistance and genetic diversity of Escherichia coli isolates from traditional and integrated aquaculture in South China

This study investigated antibiotic resistance profiles including antibiotic resistance frequencies, resistance genes and resistance patterns in Escherichia coli strains isolated from traditional and integrated aquaculture systems in South China by using antibiotic susceptibility testing and real time polymerase chain reaction (PCR) technique. The E. coli isolates were found to be resistant to at least one antibiotic among 12 antibiotics. Higher resistance frequencies to ampicillin, sulfamethoxazole, trimethoprime, streptomycin and tetracycline were found compared to the rest antibiotics. Among the 10 tetracycline resistance genes detected in the resistant isolates, the most prevalent tetracycline resistance genes were tetA, tetW and tetB with the frequency of 69.7%, 63.5% and 21.9%, respectively. Three sulfonamide resistance genes were detected in these resistant isolates, with their detection frequencies in the following order: sul2 (55.3%) > sul3 (28.2%) > sul1 (6.2%). Four resistance genes mainly encoding extended-spectrum β-lactamases (ESBLs) were detected in these resistant isolates, with the detection frequencies of blaTEM (28.4%) > blaOXA (9.7%) > blaCTX (9.3%) > blaCARB (5.2%) > blaSHV (0.0%). It was found that the integrated aquaculture system exhibited generally higher prevalence of antibiotic resistance than the traditional aquaculture system. An integrated aquaculture system could facilitate development of bacterial resistance and spread of the antibiotic resistance genes, and consequently become an important reservoir of resistance genes.     

Antimicrobial resistance in Escherichia coli and Salmonella spp. isolates from fresh produce and the impact to food safety

Foodborne diseases associated with fresh produce consumption have escalated worldwide, causing microbial safety of produce of critical importance. Bacteria that have increasingly been detected in fresh produce are Escherichia coli and Salmonella spp., both of which have been shown to progressively display antimicrobial resistance. The study focused on the assessment of antimicrobial resistance of these enteric bacteria from different kinds of fresh produce from various open air markets and supermarkets in the Philippines. Using the disk diffusion assay on a total of 50 bacterial isolates obtained from 410 fresh produce surveyed, monoresistance to tetracycline was observed to be the most prevalent (38%), followed by multidrug resistance to tetracycline, chloramphenicol, ciprofloxacin, and nalidixic acid (4%), and lastly by dual resistance to tetracycline and chloramphenicol (2%). Using multiplex and simplex polymerase chain reaction (PCR) assays, tetA (75%) and tetB (9%) were found in tetracycline resistant isolates, whereas catI (67%) and catIII (33%) were detected in chloramphenicol resistant isolates. Sequence analysis of gyr and par genes from the ciprofloxacin and nalidixic acid resistant isolates revealed different mutations. Based on the results, fresh produce act as a reservoir of these antibiotic resistant bacteria which may pose health threat to consumers.     

Human health implications of clinically relevant bacteria in wastewater habitats

The objective of this review is to reflect on the multiple roles of bacteria in wastewater habitats with particular emphasis on their harmful potential for human health. Indigenous bacteria promote a series of biochemical and metabolic transformations indispensable to achieve wastewater treatment. Some of these bacteria may be pathogenic or harbour antibiotic resistance or virulence genes harmful for human health. Several chemical contaminants (heavy metals, disinfectants and antibiotics) may select these bacteria or their genes. Worldwide studies show that treated wastewater contain antibiotic resistant bacteria or genes encoding virulence or antimicrobial resistance, evidencing that treatment processes may fail to remove efficiently these bio-pollutants. The contamination of the surrounding environment, such as rivers or lakes receiving such effluents, is also documented in several studies. The current state of the art suggests that only some of antibiotic resistance and virulence potential in wastewater is known. Moreover, wastewater habitats may favour the evolution and dissemination of new resistance and virulence genes and the emergence of new pathogens. For these reasons, additional research is needed in order to obtain a more detailed assessment of the long-term effects of wastewater discharges. In particular, it is important to measure the human and environmental health risks associated with wastewater reuse.     

Prevalence and antimicrobial resistance of Shiga toxin-producing Escherichia coli in milk and dairy products in Egypt

Abstract

Food contaminated with Shiga toxin-producing Escherichia coli (STEC) represents a hazardous public health problem worldwide. Therefore, the present study was performed to elucidate the virulent and antimicrobial resistance characteristics of STEC isolated from milk and dairy products marketed in Egypt. A total of 125 samples (raw market milk, bulk tank milk, Kareish cheese, white soft cheese, and small scale-produced ice cream, 25 each) were collected for determination the prevalence and antimicrobial resistance profiling of STEC. Thirty-six STEC isolates were recovered from milk and dairy products. Serological analysis illustrated that three isolates were E. coli O157:H7 and 33 isolates belonged to different serotypes. Molecular examination indicated that all isolates harboured stx1 and/or stx2 genes, 14 isolates expressed eaeA gene and 3 isolates possessed rfbE gene. Antimicrobial resistance profiling of the isolates was both phenotypically and genetically examined. Interestingly, 31 out of 36 (86.11%) isolates were multidrug-resistant and harboured the extended-spectrum β-lactamase encoding genes, namely, bla_CTX-M-15, bla_SHV-12 and bla_CTX-M-14. Moreover, 12 isolates (33.33%) harboured plasmid-mediated quinolone resistant gene, qnrS. The overall conclusion of the current investigation indicated insufficient hygienic measures adopted during milking, handling, and processing leading to development of pathogenic and multidrug-resistant STEC.     

Detection of Class I and II integrons for the assessment of antibiotic and multidrug resistance among Escherichia coli isolates from agricultural irrigation waters in Bulacan,Philippines

Contaminated irrigation water may greatly affect not only the quality of produce but also the people exposed to it. In this study, agricultural irrigation waters in Bulacan, Philippines were assessed and found to be contaminated with Escherichia coli (E. coli) ranging from 0.58 to 4.51 log₁₀ CFU/mL. A total of 79 isolates of E. coli were confirmed through polymerase chain reaction (PCR) amplifying the uidA gene and were tested for phenotypic resistance using 10 antimicrobials through the Kirby–Bauer disc diffusion method. Forty-six isolates (58.22%) were noted to be multidrug resistant (MDR) with high resistance rate to cephalothin, tetracycline, streptomycin, ampicillin, trimethoprim, nalidixic acid, and chloramphenicol. Moreover, this study also examined the prevalence of Class I and II integrons accounting to 67.39% and 17.39%, respectively, of the MDR E. coli strains using multiplex PCR. The results imply that the agricultural water used in Bulacan is contaminated with the fecal material of man or other animals present in the area, and the presence of MDR bacteria, which pose a potential threat to individuals in these areas, is alarming. In addition, detection of integrons could be a good marker for the identification of MDR isolates. Lastly, this study could develop strategies for the proper management of farming sites leading to the detection of food-borne pathogens and prevention of infectious diseases.     

Quantitative risk analysis for potentially resistant E. coli in surface waters caused by antibiotic use in agricultural systems

Antibiotics are frequently used in agricultural systems to promote livestock health and to control bacterial contaminants. Given the upsurge of the resistant fecal indicator bacteria (FIB) in the surface waters, a novel statistical method namely, microbial risk assessment (MRA) was performed, to evaluate the probability of infection by resistant FIB on populations exposed to recreational waters. Diarrheagenic Escherichia coli, except E. coli O157:H7, were selected for their prevalence in aquatic ecosystem. A comparative study between a typical E. coli pathway and a case scenario aggravated by antibiotic use has been performed via Crystal Ball® software in an effort to analyze a set of available inputs provided by the US institutions including E. coli concentrations in US Great Lakes through using random sampling and probability distributions. Results from forecasting a possible worst-case scenario dose-response, accounted for an approximate 50% chance for 20% of the exposed human populations to be infected by recreational water in the U.S. However, in a typical scenario, there is a 50% chance of infection for only 1% of the exposed human populations. The uncertain variable, E. coli concentration accounted for approximately 92.1% in a typical scenario as the major contributing factor of the dose-response model. Resistant FIB in recreational waters that are exacerbated by a low dose of antibiotic pollutants would increase the adverse health effects in exposed human populations by 10 fold.     

Antibiotic resistance and virulence factors of Escherichia coli from eagles and goshawks

One of the major global problems in medicine is microbial resistance to antibiotics (antimicrobial resistance) and this has become an increasingly frequent research topic. This study focuses on antimicrobial resistance, phylogenetic and genetic characterization of Escherichia coli from wild birds: ten isolates from eagles (Aquila chrysaetos), nine from goshawks (Accipiter gentilis) and 24 from broilers in the Slovak Republic. Twenty-two strains with presence of int1 gene were selected and examined for the presence or absence of transposon gene (tn3), genes of antibiotic resistance and virulence factors. We detected sequence type (ST) in eagles ST 442 with genes iss, papC, iutA, cvaC, tsh, fyuA, iroN, kps, feoB, sitA, irp2, ireA for virulence factors and tetA, sul1, sul2, dfrA, aadA for antibiotic resistance; in goshawks ST 1011 with iss, papC, fyuA, iroN, feoB, sitA and qnrS1, tetA, sul1, sul2, dfrA, aadA, respectively. These ST types have been found in humans too and should be evaluated further for possible zoonotic potential and transfer of resistance genes from the environment.     

Detection of antibiotic resistance and tetracycline resistance genes in Enterobacteriaceae isolated from the Pearl rivers in South China

This study investigated antibiotic resistance profiles and tetracycline resistance genes in Enterobacteriaceae family isolates from the Pearl rivers. The Enterobacteriaceae isolates were tested for susceptibility to seven antibiotics ampicillin, chloramphenicol, ciprofloxacin, levofloxacin, sulphamethoxazole/trimethoprim, tetracycline and trimethoprim. In Liuxi reservoir, with an exception to ampicillin resistant strains (11%) no other antibiotic resistance bacterial strains were detected. However, multiple drug resistance in bacterial isolates from the other sites of Pearl rivers was observed which is possibly due to sewage discharge and input from other anthropogenic sources along the rivers. Four tetracycline resistance genes tet A, tet B, tet C and tet D were detected in the isolates from the rivers. The genes tet A and tet B were widely detected with the detection frequencies of 43% and 40% respectively. Ciprofloxacin and levofloxacin resistant enteric bacteria were also isolated from the pig and duck manures which suggest a wider distribution of human specific drugs in the environment. This investigation provided a baseline data on antibiotic resistance profiles and tetracycline resistance genes in the Pearl rivers delta.     

Resistance in bacteria and indirect beta-lactamase detection in E. coli isolated from Culex pipiens detected by matrix-assisted laser desorption ionization time of flight mass spectrometry

The aim of this study was detections of antibiotic resistance and resistance mechanism in bacteria isolated from mosquitos (Culex pipiens) living near humans. Therefore, antibiotic resistance in bacteria isolated from Culex pipiens was investigated by disk diffusion test and MIC E-test in this study. MALDI-TOF mass spectrometry was used for detection of resistant mechanism. In this study, hydrolytic breakdown products after a few hours of incubation of the bacteria isolated from Culex pipiens were detected. Results show that enzymatic destruction of ampicillin by beta-lactamases is able to be detected by MALDI-TOF mass spectrometry from wild strains of potential pathogens. The MALDI-TOF mass spectrometry is useful method for routine detection of beta-lactamases resistant mechanism, but overnight incubation of pure culture is necessary. The results are important for proper and fast intervention to limit the spread of beta-lactamase-producing wild bacteria and provide information for appropriate initial therapy of the infections caused by these microbes.     

人工湿地中抗生素抗性大肠杆菌和抗性基因的去除与分布

抗生素的滥用导致抗生素抗性菌和抗性基因随生活污水和养殖废水的排放在环境中肆意散播,其去除及环境行为越来越受到关注。采用K-B纸片法测定了9套不同工艺构型模拟人工湿地中大肠杆菌对7种抗生素的抗性率,并应用多重PCR检测磺胺类sul1、2、3与四环素tetA、B、C、D抗性基因,探究人工湿地对抗性菌的去除效率及抗性菌、抗性基因的分布规律。结果显示,人工湿地能有效去除污水中70%左右的抗性大肠杆菌,有效降低了细菌抗性的传播风险;共计分离出535株大肠肝菌中有378株对一种以上抗生素有抗性性,以四环素、磺胺类和氨苄西林抗性率最高,达到25%以上,其他4种抗性率较低,不足20%;2种抗性基因的检出率都在70%以上;对不同采样点大肠杆菌的抗性性及抗性基因的比较发现,各部分大肠杆菌的抗性水平、多重抗性指数(MRI)以及抗性基因(sul、tet)检出率和组合数表现出:基质≥出水>进水,推测抗性菌被湿地基质截留,在基质生物膜上发生抗性基因的重组,并释放抗性菌,提高了出水中抗性水平和抗性基因检出率。     

Studies on the drug resistance profile of Enterococcus faecium distributed from poultry retailers to hospitals

The multidrug resistant Enterococcus faecium (MEF) strains originating from farm animals are proliferating at a substantial pace to impact downstream food chains and could reach hospitals. This study was conducted to elucidate the drug susceptibility profile of MEF strains collected from poultry products in Ann Arbor, MI area and clinical settings from Michigan State Lab and Moffitt Cancer Center (MCC) in Florida. Presumptive positive Enterococcus isolates at species level were identified by Matrix Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) analysis. The antibiotic susceptibility profile for both poultry and clinical strains was determined by the Thermo Scientific's Sensititre conform to the National Committee for Clinical Laboratory Standards (NCCLS) and validated via quantitative real-time PCR (qPCR) methods. Out of 50 poultry samples (Turkey: n = 30; Chicken: n = 20), 36 samples were positive for Enterococcus species from which 20.83% were identified as E. faecium. All the E. faecium isolates were multidrug resistant and displayed resistance to the last alternative drug, quinupristin/dalfopristin (QD) used to treat vancomycin resistant E. faecium (VRE) in hospitals. Results indicate the presence of MEF strains in food animals and clinical settings that are also resistant to QD.     

Molecular and physiological characterization of fluoroquinolone resistance in relation to uropathogenicity among Escherichia coli isolates isolated from Wenyu River, China

Increasing antibacterial resistance and pathogenicity in the environment is of growing concern due to its potential human risk. In the present study, 236 Escherichia coli isolates were collected from Wenyu River in China on drugless (48 isolates) and quinolone-containing plates (189 isolates). Their minimum inhibitory concentrations (MICs) were determined ranging from 0.125 μg mL⁻¹ to 128 μg mL⁻¹. Mutation points related to fluoroquinolone resistance were observed at S83 to L and D87 to N or Y in the GyrA subunit and S80 to R or I and E84 to G in the ParC subunit. Generally, MICs of LEV and GAT are dependent on the patterns of these mutation points. The profile with three mutation points was related to LEV-resistant E. coli isolates, and the (S83L, D87N + S80I) mutation profile was most prevalent (65.7%) in LEV-resistant isolates, while a large proportion of isolates, even those with three mutation points, were susceptive to GAT. The incidence of virulence factors in LEV-resistant isolates (44.7%, 59/132) was much higher than in nonresistant isolates (23.1%, 24/104) (χ² = 11.925, 1° of freedom, p < 0.001) indicating that fluoroquinolone-resistant E. coli would pose a potential risk. A similar distribution was also found in isolates resistant to GAT (χ² = 7.843, 1° of freedom, p = 0.0079).     

Relationship between antibiotic residues and occurrence of resistant bacteria in Nile tilapia (Oreochromisniloticus) cultured in cage-farm

The aim of this study was to investigate the relationship between antibiotic residues found in the muscle of cage-farm-raised Nile tilapia (Oreochromisniloticus), the occurrence of resistant bacteria, and the sanitary practices adopted by farmers in Ilha Solteira reservoir, Brazil. Nine fish (three small fish, 40–200 g; three medium-sized fish, 200–500 g; and three large fish, 500–800 g) were collected from four cage farms every three months from April 2013 to January 2014. Ten antibiotic residues were determined using liquid chromatography-mass spectrometry, and bacteria were isolated and tested for antibiotic resistance to determine the multiple antibiotic resistance (MAR) index. Only three antibiotics (oxytetracycline, tetracycline, and florfenicol) were detected in the muscle of Nile tilapia, and their residues were the highest in small fish; however, the MAR index was higher in large fish. In addition, a direct positive relationship between the MAR index and the concentration of antibiotic residues in Nile tilapia was found. Overall, the adoption of prophylactic management practices improved the sanitary status of cage farms, reducing bacterial infections and hampering the development of antibiotic-resistant bacteria.     

Tetracycline resistance in semi-arid agricultural soils under long-term swine effluent application

Annually, millions pounds of antibiotics are released unmetabolized into environment along with animal wastes. Accumulation of antibiotics in soils could potentially induce the persistence of antibiotic resistant bacteria. Antibiotics such as tetracyclines and tetracycline-resistant bacteria have been previously detected in fields fertilized with animal manure. However, little is known about the accumulation of tetracyclines and the development of tetracycline resistance in semi-arid soils. Here we demonstrate that continuous land application with swine effluent, containing trace amounts of chlortetracycline, does not necessarily induce tetracycline resistance in soil bacteria. Based on the testing of more than 3,000 bacteria isolated from the amended soils, we found no significant increase in the occurrence and level of chlortetracycline resistant bacteria in soils after 15 years of continuous swine effluent fertilization. To account for a possible transfer of tetracycline-resistant bacteria originated from the swine effluent to soils, we analyzed two commonly found tetracycline resistant genes, tet(O) and tet(M), in the swine effluent and fertilized soils. Both genes were present in the swine effluent, however, they were not detectable in soils applied with swine effluent. Our data demonstrate that agronomic application of manure from antibiotic treated swine effluent does not necessarily result in the development of antibiotic bacterial resistance in soils. Apparently, concentrations of chlortetracycline present in manure are not significant enough to induce the development of antibiotic bacterial resistance.     

Investigation on gene transfer from genetically modified corn (Zea mays L.) plants to soil bacteria

Knowledge about the prevalence and diversity of antibiotic resistance genes in soil bacteria communities is required to evaluate the possibility and ecological consequences of the transfer of these genes carried by genetically modified (GM) plants to soil bacteria. The neomycin phosphotransferase gene (nptII) conferring resistance to kanamycin and neomycin is one of the antibiotic resistance genes commonly present in GM plants. In this study, we investigated kanamycin-resistant (Km(R)) and neomycin-resistant (Nm(R)) soil bacterial populations in a 3-year field trial using a commercial GM corn (Zea mays L.) carrying the nptII gene and its near isogenic line. The results showed that a portion (2.3 - 15.6 %) of cultivable soil bacteria was naturally resistant to kanamycin or neomycin. However, no significant difference in the population level of Km(R) or Nm(R) soil bacteria was observed between the GM and non-GM corn fields. The nptII gene was not detected in any of the total 3000 Km(R) or Nm(R) isolates screened by PCR. Further, total soil bacterial cells were collected through Nycodenz gradient centrifugation and bacterial community DNA was subjected to PCR. Detection limit was about 500 cells per gram of fresh soil. Our study suggests that the nptII gene was relatively rare in the soil bacterial populations and there was no evidence of gene transfer from a GM corn plant to soil bacteria based on the data from total soil bacterial communities.     

Enterotoxin production and antimicrobial susceptibility in Staphylococci isolated from traditional raw milk cheeses in Serbia

This study was undertaken to determine the prevalence of coagulase positive staphylococci (CPS) by examining a total of 71 raw milk cheeses. Additionally, enterotoxigenicity, antimicrobial susceptibility and the presence of mecA and mecC genes in the staphylococcal isolates were investigated. The isolation and enumeration procedure of CPS followed the International Organization for Standardization (ISO) standard. The presumptive staphylococci were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) using the VITEK MS system. VIDAS® Staph enterotoxin II assay was used for the detection of classical enterotoxins. Antimicrobial susceptibility testing (AST) was accomplished performing the disk diffusion method. All suspected methicillin resistant staphylococci were investigated for the presence of mecA and mecC genes by PCR assay. A high prevalence (87.32%) of CPS was detected in the cheeses at contamination levels up to 5.58 log CFU g^?1. Among 47 staphylococcal isolates screened for enterotoxin production, only one isolate, identified as S. hyicus, was confirmed as being enterotoxigenic. Resistance to penicillin (63.70%) was the most common resistance among the tested Staphylococcus aureus isolates. The dominant phenotypic resistance patterns in coagulase negative staphylococci (CNS) were resistance to ofloxacin and fusidic acid. All CNS isolates were susceptible to the clinically important antibiotics clindamycin, chloramphenicol, gentamicin, linezolid, rifampicin and trimethoprim-sulfamethoxazole. The mecA and mecC genes were not detected. To the best of our knowledge, this is the first study concerning evaluation of the presence of methicillin resistant staphylococci (MRS) in dairy products in Serbia.     

Distribution of antibiotic-resistant bacteria in chicken manure and manure-fertilized vegetables

Veterinary manure is an important pollution reservoir of antibiotics and antibiotic-resistant bacteria (ARB). However, little is known of the distribution of ARB in plant endophytic bacteria and the number/types of ARB in chicken manure. In this study, 454-pyrosequencing was used to investigate the distribution and composition of ARBs in chicken manure and fertilized vegetables. The prevalence of ARB in the samples of the chicken manure compost recovered from farms on which amoxicillin, kanamycin, gentamicin, and cephalexin were used was 20.91–65.9 % for ARBs and 8.24–20.63 % simultaneously resistant to two or more antibiotics (multiple antibiotic resistant bacteria (MARB)). Antibiotic-resistant endophytic bacteria were widely detected in celery, pakchoi, and cucumber with the highest rate of resistance to cephalexin. The pyrosequencing indicated that the chicken manure dominantly harbored Firmicutes, Bacteroidetes, Synergistetes, and Proteobacteria and that Bacteroidetes was significantly enhanced in farms utilizing antibiotics. In the total cultivable colonies, 62.58–89.43 % ARBs and 95.29 % MARB were clustered in Bacteroidetes with the dominant species (Myroides ordoratimimus and Spningobacterium spp., respectively) related to human clinical opportunistic pathogens.     

The dissemination of antibiotic resistance in various environmental objects (Russia)

Environmental objects (surface and groundwater, soil, bottom sediments, wastewater) are reservoirs in which large-scale multidirectional exchange of determinants of antibiotic resistance between clinical strains and natural bacteria takes place. The review discusses the results of studies on antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARG) isolated from environmental objects (water, soil, sewage, permafrost) of the Russian Federation. Despite the relevance of the topic, the number of available publications examining the resistomes of Russian water bodies and soils is small. The most studied environmental objects are surface waters (rivers, lakes), permafrost deposits. Soil resistomes are less studied. Data on ARG and ARB in wastewater are the least covered in publications. In most of the studies, antibiotic resistance of isolated pure bacterial cultures was determined phenotypically. A significant number of publications are devoted to the resistance of natural isolates of Vibrio cholerae, since the lower reaches of the Volga and Don rivers are endemic to cholera. Molecular genetic methods were used in a small number of studies. Geographically, the south of the European part of Russia is the most studied. There are also publications on the distribution of ARG in water bodies of Siberia and the Russian Far East. There are practically no publications on such developed regions of Russia as the center and northwest of the European part of Russia. The territory of the country is very large, anthropogenic and natural factors in its various regions vary significantly; therefore, it seems interesting to combine all available data in one work.

     

膜生物反应器中生物膜的生长特性

实验采用经甲苯培养驯化而成的单一假单胞菌菌种,通过分析平板式生物膜反应器内,不同阶段假单胞细菌生物膜干重、厚度、活性生物量和生物种群分布的变化,研究生物膜特性与降解效率之间的关系。实验结果表明,在挂膜初期生物膜迅速生长,生物量以及生物膜干重增长很快,有利于甲苯及营养物质的传输,降解效率也快速提升。随着生物膜的生长,生物量及干重也逐步增加,厚度逐渐增加使传质阻力不断增大,生物膜上层微生物的有机底物供应不足,使生物膜上层结构稀疏,最终维持一个甲苯的总传输量与生化降解量的平衡,生物量的生长与衰亡也达到动态平衡,形成了一个较高且稳定的降解效率。