Tetracycline-Resistant Escherichia coli in a Small Stream Receiving Fish Hatchery Effluent

We examined the impact of the effluent discharged from a freshwater (trout and related species) fish hatchery on the presence of antibiotic-resistant microorganisms in a small stream. There had been no documented use of antibiotics in the hatchery for at least 6 months prior to our study, although a variety of biocides were employed routinely for cleaning. Heterotrophic bacteria and Escherichia coli were isolated from both water column and sediment samples at sites above and below the discharge of the hatchery effluent as well as from the hatchery effluent itself. Randomly chosen isolates (≥96 isolates per site) were tested for their resistance to ampicillin, cephalexin, erythromycin, and tetracycline. Resistance to at least one antibiotic was found in greater than 30% of both the heterotrophic isolates and the E. coli isolates from each of the sites. There were no significant differences among the sites in the proportion of the heterotrophic isolates resistant to any specific antibiotic. The proportion of E. coli isolates resistant to tetracycline in the hatchery effluent and in both the downstream water and sediment samples was significantly higher than in either the upstream water or sediment. These results support the possibility of the hatchery as a source of tetracycline-resistant microorganisms even in the absence of recent use of this antibiotic.     

Incidence of plasmid-linked antibiotic-heavy metal resistant enterics in water-sediment from agricultural and harbor sites

This study assesses the impact of antibiotics used in clinical and veterinary practices, on the incidence of antibiotic- heavy metal resistant enterics in fresh water and sediment from agricultural and harbor sample sites. A total of 848 bacterial strains of the familyEnterobacteriaceae was isolated from agricultural and lake harbor samples and identified to genus level. These were examined for antibiotic-heavy metal resistance. A select smaller number of these isolates were also examined for the presence of plasmids and ability to transfer antibiotic resistance via conjugation or transformation. More than 85 % of the 848 isolates from all four sites were resistant to Ph, Zn, and Co while 5.6% to 16% were resistant to Te and 2.4% to 5.7% to Hg. The ranking of metal resistance according to frequency was the same as the frequency of metal occurrence in sediment samples. Of the total isolates tested, 87% were resistant to six or more antibiotics and 74% were also simultaneously resistant to Co, Zn, and Ph. Testing the resistance of the water isolates to antibiotics used solely in animal husbandry-veterinary medicine indicated that 55.6% of the agricultural isolates possessed resistance to these antibiotics while only 31.9% of the isolates from harbor water showed resistance to the same antibiotics. Of 41 ampicillin resistant isolates examined, 16 (39%)were capable of transferring antibiotic-heavy resistance markers via conjugation. From this same group, plasmid DNA preparations were made. Of these latter preparations, 67% transformed recipientE. coli cells while 58% possessed discernible, often multiple plasmids when examined by gel electrophoresis.     

Tetracycline resistance genes persist in soil amended with cattle feces independently from chlortetracycline selection pressure

Antibiotic residues and antibiotic resistance genes originating from animal waste represent environmental pollutants with possible human health consequences. In this study, we addressed the question whether chlortetracycline (CTC) residues in soils can act as selective pressure enhancing the persistence of tetracycline (TC-r) resistance genes in grassland soils receiving cattle feces. We performed a soil microcosm experiment, using 3 grassland soils with different management history, which were incubated with feces from conventionally raised dairy cows. The microcosms included treatments with a low dose (0.2 mg kg⁻¹), a high dose (100 mg kg⁻¹) and no CTC. The presence and abundance of TC-r genes tet(O), tet(Q) and tet(W) and the intI1 gene coding for class 1 integrase were assessed with real-time PCR after 0, 14, 28, 56 and 86 d of incubation. The genes tet(Q) and intI1 persisted in all feces-containing treatments for at least 28 d, and tet(W) and tet(O) for at least 86 d, though they went close to limits of quantification after 14–28 d in most cases. The soil, but not the dose of CTC, significantly affected the gene persistence. Concluding, certain TC-r genes originating from cattle feces may persist in soil for several months independently from antibiotic selection pressure.     

Genomic characterization of multidrug-resistant extraintestinal pathogenic Escherichia coli isolated from grain culture soils

Multidrug-resistant (MDR) Escherichia coli, mainly extraintestinal pathogenic E. coli (ExPEC), has been widely reported in infections worldwide. In agricultural soils, manure is a hotspot for the dissemination of antimicrobial resistance genes (ARGs) and pathogenic bacteria; however, MDR bacteria have also been reported in soils with no history of manure use. In addition, cross-resistance and co-resistance have been described as responsible for the metal-driven selection of bacteria resistant to antimicrobials. Therefore, the aim of this study was to analyze three MDR E. coli isolates obtained from Brazilian grain culture soil samples with no history of manure use by whole-genome sequencing. The MDR E. coli isolates were recovered from soils from corn and coffee fields, and presented resistance to β-lactams, quinolones, aminoglycosides, tetracyclines, sulphonamides, and dihydrofolate reductase inhibitor. Resistome analysis showed ARGs to several antimicrobials (i.e., β-lactams, tetracyclines, aminoglycosides, sulphonamides, trimethoprim, phenicols, fosfomycin, and macrolides) as well as several metal resistance genes and antibacterial biocide resistance genes. In addition, known mutations in quinolone-resistance-determining regions of GyrA (Ser83Leu and Asp87Asn), ParE (Ser458Thr), and ParC (Ser80Ile) were also detected. Virulome analysis showed the presence of virulence genes (lpfA, mcmA, gad, mchF, iroN, cma, and iss) associated with ExPEC. Multidrug-resistant ExPEC isolates were assigned to phylogenetic group B1. The presence of MDR B1-ExPEC in soil samples shows the ability of these isolates to survive in soils. This study reports for the first time some sequence types (i.e., ST345, ST448, and ST1146) of MDR E. coli in Brazilian soils. Therefore, these findings contribute to the monitoring of antimicrobial resistance and surveillance studies based on whole-genome sequencing worldwide.     

Manure as a Source of Antibiotic-Resistant Escherichia coli and Enterococci: a Case Study of a Wisconsin, USA Family Dairy Farm

The spread of antibiotic-resistant bacteria in the environment is raising serious public health concerns, and manure is being increasingly recognized as a major source of antibiotic-resistant bacteria. In this research, we isolated Escherichia coli and enterococci from manure produced in a Wisconsin, USA family dairy farm to determine their resistance to six representative antibiotics. The average densities for E. coli and enterococci were 6.37(±4.38)?×?10⁷ colony formation units (CFU)?g^?1 and 1.60(±1.57)?×?10⁴ CFU g^?1, respectively. The E. coli isolates were found to be resistant to cephalothin, ampicillin, tetracycline, and erythromycin. In addition to these four antibiotics, the Enterococcus isolates were also resistant to gentamicin and ciprofloxacin. Additionally, we examined the survival and growth of E. coli and enterococci in dairy manure over a period of ~3 days. While the densities of enterococci remained stable over the study period, the concentrations of E. coli on average increased by 1.5 log10 units. Further tests of the bacterial antibiotic resistance over time showed no significant changes in the prevalence of antibiotic resistance. This result indicated that slightly aged manure could represent a larger source of antibiotic-resistant E. coli than fresh manure and the accumulation of antibiotic-resistant E. coli and enterococci in the agricultural fields must be accounted for in the modeling of the spread of antibiotic-resistant bacteria in the environment.     

Applying MAR Analysis to Identify Human and Non-Human Fecal Sources in Small Kentucky Watersheds

The recurrence of reports citing water quality impairments in watersheds is evidence that tools are needed to identify pollution sources and facilitate restoration efforts such as implementing total maximum daily limits (TMDLs) or best management practices (BMPs). Fecal bacteria in surface waters are one of the most commonly cited impairments to water quality. This study evaluated microbial source tracking (MST), specifically multiple antibiotic resistance (MAR) analysis, as a management tool to differentiate nonpoint source pollution into source groups. A library containing Escherichia coli (E. coli, EC) and fecal streptococci (FS) isolates from poultry (EC n?=?282, FS n?=?650), human (EC n?=?152, FS n?=?240), wildlife (EC n?=?17, FS n?=?43), horse (EC n?=?79, FS n?=?82), dairy cattle (EC n?=?38, FS n?=?42), and beef cattle (EC n?=?49, FS n?=?46) sources was created. The MAR analysis was conducted on the isolates using a profile of seven antibiotics. The antibiotic signatures of unknown source isolates from Elkhorn and Hickman Creek watersheds were evaluated against the library to determine the contributions of potential fecal inputs from the respective sources. Correct classification was >60% when analyzed at the human and non-human-level of classification. On a watershed basis, both watersheds produced similar results; inputs from non-human sources were the greatest contributors to nonpoint source pollution. The results from the multiple antibiotic resistance (MAR) analysis revealed that the information produced, coupled with knowledge of the watershed and its associated land uses, would be helpful in allocating resources to remediate impaired water quality in such watersheds.     

白颈长尾雉圈养种群大肠杆菌耐药性及其耐药基因

对白颈长尾雉圈养条件下的38个样品进行大肠杆菌分离及PCR检定,并采用肠杆菌基因间重复共有序列PCR指纹法（ERIC）剔除各个样品的重叠分离株,检测获得的170个大肠杆菌分离株对9种抗生素的耐药性、Ⅰ型整合子携带率及其可变区抗性基因,结果显示：（1）来自白颈长尾雉的分离株对实验用的9种抗生素的抗性比率和多重耐药性远高于环境源和人源者（来自白颈长尾雉的分离株100%耐受3种及以下的抗生素,而环境源者为50.7%,人源者66.7%）;（2）来自白颈长尾雉的分离株的Ⅰ型整合子携带率（92%）高于环境源（87%）和人源（78%）;（3）来自白颈长尾雉和来自人的大肠杆菌分离株的Ⅰ型整合子可变区抗生素抗性基因检出率相同（36%）,但高于环境源（24%）;（4）携带Ⅰ型整合子的分离株对实验用的抗生素的抗性百分率一般高于不携带者,只有个别种类抗生素这种差异为非显著性差异;（5）Ⅰ型整合子可变区基因盒的基因为3类,即aadA、dfrA和未知功能的orfF;aadA、dfrA的频率相同;3类基因均以基因盒形式存在,分别是dfrA17-aadA5、dfrA12-ofrF-aadA2、dfrA12-aadA2。     

牛粪沼渣中多重耐药细菌的环境风险

为研究牛粪厌氧发酵沼渣中多重耐药细菌的环境污染风险，选用畜禽养殖中常用的5种抗生素(红霉素、氨苄青霉素、金霉素、链霉素、环丙沙星)对牛粪沼渣中可培养抗生素抗性细菌进行筛选。结果表明：多重耐药细菌的比例高达76.5%,其中，抗5种和4种抗生素的细菌分别有11,21株。所有多重耐药细菌均对氨苄青霉素具有抗性，抗红霉素、金霉素和链霉素的细菌分别占总多重耐药细菌数的92.0%,89.3%,61.3%。通过细菌16S rRNA测序鉴定，32株具有4种以上抗性的细菌分别属于福氏志贺氏菌、摩根氏菌和假中间苍白杆菌，均为重要的临床致病菌。使用全基因组测序对7株典型多重耐药细菌携带的抗性基因进行分析，共检测出28种抗生素抗性基因，对应9种抗生素抗性类型。通过分析抗性基因及插入序列所在位点信息发现，多重耐药细菌普遍携带含有抗性基因和插入序列共存的质粒，表明抗性基因具有高度的可移动性和较强的传播风险。综上所述，牛粪沼渣中含有大量的多重耐药细菌，可视作抗生素抗性基因的储存库，应重视沼渣农业资源化利用过程中的环境风险监测与评估。     

市售散装白斩鸡表面四环素耐药菌污染初探

为探究市售散装白斩鸡表面四环素耐药菌的污染特征,评价耐药基因的迁移潜势,本试验从上海市4个区的25个熟食店中采集25份散装即食白斩鸡样品,采用梯度稀释法和脑心浸液肉汤培养基对四环素耐药菌(TETr)进行计数,利用实时荧光定量PCR(qRT-PCR)技术分析6种四环素耐药基因(tet A、tet B、tet C、tet ...     

Screening of bacterial isolates from various European soils for in vitro antagonistic activity towards Rhizoctonia solani and Fusarium oxysporum: Site-dependent composition and diversity revealed

A cultivation-based approach was used to determine the in vitro antagonistic potential of soil bacteria towards Rhizoctonia solani AG3 and Fusarium oxysporum f. sp. lini (Foln3). Four composite soil samples were collected from four agricultural sites with previous documentation of disease suppression, located in France (FR), the Netherlands (NL), Sweden (SE) and the United Kingdom (UK). Similarly, two sites from Germany (Berlin, G-BR; and Braunschweig, G-BS) without documentation of disease suppression were sampled. Total bacterial counts were determined by plating serial dilutions from the composite soil samples onto R2A, AGS and King's B media. A total of 1,788 isolates (approximately 100 isolates per medium and site) was screened for antifungal activity, and in vitro antagonists (327 isolates) were found amongst the dominant culturable bacteria isolated from all six soils. The overall proportion of antagonists and the number of isolates with inhibitory activity against F. oxysporum were highest in three of the suppressive soils (FR, NL and SE). Characterization of antagonistic bacteria revealed a high phenotypic and genotypic diversity. Siderophore and protease activity were the most prominent phenotypic traits amongst the antagonists. The composition and diversity of antagonists in each soil was site-specific. Nevertheless, none of the antimicrobial traits of bacteria potentially contributing to soil suppressiveness analyzed in this study could be regarded as specific to a given site.     

The use of clams as bioindicator of fecal pollution in seawater

The coastal waters of Kuwait are widely used for bathing during the long summer season. In order to assess the water quality along the beaches, a new approach was developed. It involves the use of clam, Circenita callipyga, as a bioindicator for seawater pollution by fecal coliform bacteria (FC), antibotic resistant fecal coliform (ABR-FC) and Salmonella spp. These organisms were detected in clam and water samples and the efficiency of clam in concentrating Salmonella was confirmed. The number of FC and ABR-FC in clam and water samples were compared and a higher number was detected in clams than in water. Five isolates of Salmonella from clams were also multidrug resistant. The data suggests that clam can be used as a bioindicator of seawater pollution and is preferable to direct testing of water. The resistance to antibiotics in E. coli isolated from water and clams collected at the same time and site was of similar pattern and was determined by R-plasmid.     

An Application of Landsat-5TM Image Data for Water Quality Mapping in Lake Beysehir, Turkey

The main goal of this study was to investigate spatial patterns in water quality in Lake Beysehir, which is the largest freshwater reservoir in Turkey, by using Landsat-5TM (Thematic Mapper) data and ground surveys. Suspended sediment (SS), turbidity, Secchi disk depth (SDD), and chlorophyll-a (chl-a) data were collected from 40 sampling stations in August, 2006. Spatial patterns in these parameters were estimated using bivariate and multiple regression (MR) techniques based on Landsat-5TM multispectral data and water quality sampling data. Single TM bands, band ratios, and combinations of TM bands were estimated and correlated with the measured water quality parameters. The best regression models showed that the measured and estimated values of water quality parameters were in good agreement (0.60 < R ² < 0.71). TM3 provided a significant relationship (R ²?=?0.67, p?<?0.0001) with SS concentration. MR between chl-a and various combinations of TM bands showed that TM1, TM2, and TM4 are strongly correlated with measured chl-a concentrations (R ²?=?0.60, p?<?0.0001). MR of turbidity showed that TM1, TM2, and TM3 explain 60% (p?<?0.0001) of the variance in turbidity. MR of SDD showed a strong relationship with measured SDD, with R ²?=?0.71 (p?<?0.0001) for the ratio TM1/TM3 and TM1 band combinations. The spatial distribution maps present apparent spatial variations of selected parameters for the study area covering the largest freshwater lake and drinking water reservoir in Turkey. Interpretation of thematic water quality maps indicated similar spatial distributions for SS, turbidity, and SDD. A large area in the middle portion of the lake showed very low chl-a concentrations as it is far from point and nonpoint sources of incoming nutrients. The trophic state index values were calculated from chl-a and SDD measurements. Lake Beysehir was classified as a mesotrophic or eutrophic lake according to chl-a or SDD parameters, respectively.     

Water Quality Characterization in the Northern Florida Everglades

The Loxahatchee National Wildlife Refuge (Refuge) developed as a system with waters low in nutrients. Today, the Refuge wetlands are impacted by inflows containing elevated nutrient concentrations originating from agricultural sources flowing into canals surrounding the west side and from urban and horticultural areas flowing into canals surrounding the eastern side of the Refuge. We analyzed water quality sampled at 40 sites divided into eastern and western areas and four zones in the Refuge. We defined four zones as the canals surrounding the Refuge marsh, the perimeter zone, the transition zone, and the interior zone. The canal receiving agricultural inflows had greater alkalinity and conductivity (SpC), Si and SO₄ but lower turbidity and total suspended solids than the canal receiving urban and horticultural inflows. Alkalinity, total dissolved solids (TDS), SpC, Ca, Cl, and SO₄ concentrations were greater in the perimeter than in transition and interior zones. Alkalinity and SpC values and SO₄ concentrations were greater in the transition than in interior zone. Alkalinity, SpC, and TDS values and Ca, SO₄, and Cl concentrations correlated in negative curvilinear relationships with distance from the canal (r ²?=?0.78, 0.70, 0.61, 0.78, 0.64, 0.57, respectively). Analysis of multiple water quality parameters may reveal the complexity of interactions that might be overlooked in a simple single parameter analysis. These data show an impact of canal water containing high nutrient concentrations on water quality flowing from the canal towards the Refuge interior.     

Overwintering management on upland pasture causes shifts in an abundance of denitrifying microbial communities, their activity and N2O-reducing ability

Pasture soils used for cattle overwintering may represent significant sources of N₂O emissions from soils. Therefore, the long-term effect of cattle overwintering on the abundance and activity of a denitrifying community was explored. The study was performed at a cattle overwintering area in South Bohemia (Czech Republic), where three sites differing in the degree of animal impact were selected: severely impacted (SI) and moderately impacted (MI), as well as a control site with no impact (NI). N₂O flux measurement and soil sampling were performed in spring and fall of 2005. The activity was measured in terms of potential denitrification activity. Bacterial nirK, nirS and nosZ genes were used as functional markers of the denitrifying communities; abundance was analyzed using a real-time PCR assay. Surprisingly, in situ N₂O emissions were the highest in spring at MI and significantly differed from those at SI and NI, while in autumn, rates of emissions generally decreased. In contrast potential denitrification rates were highest at SI, followed by MI, and the lowest at NI. An overall significant shift in N₂O/N₂ molar ratio was shown in cattle impacted sites. The highest abundance of all genes measured at both sampling times was found at site SI, whereas at site MI increased numbers were observed only in spring. Our results indicate a strong influence of cattle on the abundance as well as the activity of microbes involved in denitrification.     

Investigation of environmental and land use impacts in forested permafrost headwaters of the Selenga-Baikal river system,Mongolia - Effects on discharge,water quality and macroinvertebrate diversity

Headwater streams play a major role for provision of ecosystem services, e.g. drinking water. We investigated a high-altitude headwater catchment of the Kharaa River (including 41 1st-order rivers) to understand the impact of land cover (especially forest cover), environment and human usage on runoff, chemical water quality and macroinvertebrate fauna in a river basin under discontinuous permafrost conditions in an arid, sparsely populated region of Mongolia. To verify our hypotheses that different landuses and environmental impacts in permafrost headwaters influence water quality, we investigated 105 sampling sites, 37 of them at intermittent stream sections without water flow. Discharge was positively impacted by land cover types steppe, grassland and forest and negatively by shrubland, forest burnt by wild fires (indicating a reduction of permafrost) and slope. Water quality was affected by altitude, longitude and latitude, shrub growth and water temperature. Shannon diversity of macroinvertebrates was driven by water temperature, iron content of the water, flow velocity, and subbasin size (adjusted R² = 0.54). Sample plots clustered in three groups that differed in water chemistry, macroinvertebrate diversity, species composition and bio-indicators. Our study confirms that steppes and grasslands have a higher contribution to runoff than forests, forest cover has a positive impact on water quality, and diversity of macroinvertebrates is higher in sites with less nutrients and pollutants. The excellent ecological status of the upper reaches of the Kharaa is severely threatened by forest fires and human-induced climate change and urgently needs to be conserved.     

Influence of microorganisms on arsenic mobilization and speciation in a submerged contaminated soil: Effects of citrate

Batch-type leaching experiments were performed on polluted soil contaminated by pyrite cinders to evaluate the effect of indigenous bacteria on arsenic mobilization. The bacteria, under submerged conditions using citrate as the carbon source, enhanced the solubilization of arsenic, iron and manganese. At the same time, 85 mg kg⁻¹ of copper were abiotically released. Iron reduction significantly (p < 0.05) enhanced the release of arsenic. During 7 days of incubation at high redox potential, the arsenite content increased suggesting aerobic arsenic-resistant bacteria bearing arsC genes as key players for arsenate reduction. Arsenate became prevalent in consequence of arsenic liberation from iron oxides and the lowering of redox potential, driven by citrate, inhibited the growth and activity of arsenate-resistant bacteria. Populations of Bacillus, Pseudomonas, and Geobacter were stimulated by the addition of citrate as evidenced by denaturing gradient gel electrophoresis analysis of 16S rRNA genes. Putative ars genes were retrieved in isolates of Bacillus and Pseudomonas. These isolates were able to reduce 2 mmol l⁻¹ of arsenate in liquid cultures. These results confirm that microorganisms play an important role in As cycling in soils and highlight the complex role of citrate on biotic and abiotic transformations of inorganic contaminants. The environmental dispersion of arsenic can be retarded by resorption or coprecipitation processes occurring during flooding. Nevertheless, periodic flooding can be a crucial factor for the groundwater quality and the soil–water–plant systems.     

Spraying of oxytetracycline and gentamicin onto field-grown coriander did not affect the abundance of resistant bacteria, resistance genes, and broad host range plasmids detected in tropical soil bacteria

Horticultural supplements containing oxytetracycline and gentamicin, two clinically relevant biocides, are widely marketed to prevent or control infections by bacterial phytopathogens. Despite their regular consumption in the world’s less developed countries, it is unknown whether exposure of tropical farmlands to these drugs results in an enrichment of resistant bacteria, resistance genes, and/or mobile genetic elements in the soil. These concerns were investigated under field conditions by repeatedly spraying recommended amounts of a commercial product containing oxytetracycline-HCl, and gentamicin- onto two coriander plots. Subsequent to five applications within 16 months, composite soil samples from control and treated sections were compared with respect to the abundance of resistant bacteria and the prevalence of conserved nucleotide sequences from tetracycline efflux proteins, tetracycline ribosomal protection proteins, four different families of gentamicin-modifying enzymes, and broad host range plasmids of the IncP-1 and IncQ incompatibility groups. The isolation frequency of oxytetracycline- and gentamicin-resistant bacteria and the detection rate of the aforementioned genes and elements were unrelated to application of the supplement. Despite the omnipresence of sequences from IncP-1 plasmids, conjugative plasmids conferring resistance to oxytetracycline or gentamicin were not captured in biparental matings. The widespread occurrence of resistant bacteria and resistance genes at the beginning of the trial emerges as a reasonable explanation for the lack of anticipated responses. Moreover, we assume that the biocides applied were inactivated by biotic and abiotic factors under tropical conditions.     

Investigation of outgrowths of Klebsiella spp in distributed potable water

The boundary of the study in this organisation involved laboratory experiments on the facets of the nature of coliform (Klebsiella) bacteria in parts of the Sydney water system which supplies 3.3 × 10⁶ people. After September 1976 they appeared increasingly throughout the 18 000 km of reticulation system. Non-thermotolerant Klebsiella spp were persistent despite swabbing and flushing, their survival being enhanced by deposits in mains and turbidity greater than one unit in 75 % of 813 water samples. A multiple approach (biochemistry, genetics, typing, antibiotic and metallic sensitivity, and plasmid transfer) was adopted using 848 isolates in 1980 from 38 sampling runs. While the species persisted from 1980 to 1982, their designation of oxytoca remained unclear despite usage of 57 biochemical tests and G + C of 56.3. Cultures from both dates were bacteriocin typed, half being untypable as were the majority of 73 environmental cultures collected between Traralgon and Townsville in adjoining states. Antibiotic sensitivity testing by diffusion and agar dilution procedures demonstrated multi-resistance to twenty antibiotics that exceeded or equalled results reported from other habitats. Heavy metal resistance was considerably elevated. These two sets of markers are plasmid home and were more actively transferred at 37 than 20° C by environmental Klebsiella to E. coli K12. Because of the inability of the typing method, the pattern or origin of the contamination could not be found. The clinical significance of this activity at 37° C would require another study elsewhere because these bacteria are ingested.     

Composition and field distribution of the population of Rhizobium meliloti in root nodules of uninoculated field-grown alfalfa

Only four antibiotics (kanamycin, spectinomycin, ampicillin and novobiocin) of ten tested were capable of discriminating between root nodule isolates of Rhizobium meliloti obtained from uninoculated field-grown alfalfa (Medicago sativa L.). The 300 isolates in the collection were subdivided into seven groups based on their intrinsic antibiotic resistance characteristics with 204 and 55 isolates placed into two groups, C and F, respectively. Isolates from group C dominated the root nodule population on plants in eight of the nine quadrats analyzed. Furthermore they were one of the two dominant groups found in nodules formed on plants grown in a plant infection-soil dilution experiment and challenged with a composite soil sample from the field site. Antiserum raised to a group C isolate (No. 31) cross-agglutinated with 46 of 55 group C isolates to a titer identical with that of the parent antigen. There were no cross-reactions between isolates from any of the other six groups. Only 9 of 34 isolates from group F cross-agglutinated with antiserum raised to a group F isolate (No. 17). Thirty-three of 35 cross-agglutinating field isolates from group C had the same sodium dodecyl sulphate-polyacrylamide-gel electrophoretic protein-profile pattern as isolate No. 31 whereas non-agglutinating isolates from the same group had distinctly different protein profile patterns. The data suggest that intrinsic antibiotic resistance characteristics can be a useful complementary tool to be used in conjunction with other methods to identify and discriminate isolates of R. meliloti. It should not be used on its own as a strain identification method.     

Empirical models for estimating the concentrations and exports of metals in rural rivers and streams

Concentrations of Al, Fe, Mn, Zn and Cu were measured monthly at 24 sites in 21 rivers in Ontario and Quebec. Relationships between metal and suspended particulate matter (SPM), turbidity, colour (g440), temperature and system hydrology were quantified, and used to derive empirical models for predicting metal concentrations. In a test of the models using an independent data set, they explained a significant proportion of the variation in Al (90%), Fe (85%), and Mn (57%), but only 37% of the variation in riverine Zn concentrations. Metals concentrations are most strongly associated with SPM concentrations. The proportion of the total metal load associated with particulates (>0.45 μm) is highly variable below 10 ppm SPM, indicating that this concentration approximates the division between systems dominated by weathered (solution) versus eroded (particulate) inputs. Annual metal exports were calculated, and empirical models for predicting catchment exports were developed using system hydrology and average SPM concentrations. These simple models can be used to estimate metals concentrations and exports from routine water quality monitoring data, without requiring chemical analyses. They also serve to distinguish background levels from those indicating metal contamination, and will, therefore, be useful for water quality evaluation.