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.     

Effects of long-term manure applications on the occurrence of antibiotics and antibiotic resistance genes (ARGs) in paddy soils: Evidence from four field experiments in south of China

Most studies of the effects of manure amendment on the occurrence of antibiotics and antibiotic resistance genes (ARGs) in soil employ the investigation of grab samples or short-term laboratory studies. However, the effects of long-term manure applications on antibiotics, ARGs and their vertical distribution in paddy soil in field experiments are lacking. We assessed the concentrations of antibiotics, ARGs and their vertical distribution in paddy soil receiving long-term manure applications in four field experiments. High concentrations of tetracyclines were detected in most manured soils, while sulfonamides were not detectable. Long-term manure amendments generally increased the antibiotic concentrations and ARGs abundances in the paddy soil over decades. However, in some sites such significant trends of ARGs could not be observed. The abundance of ARGs was statistically correlated with antibiotics and soil properties including pH and soil organic matter (SOM), indicating their importance in the selection of resistance genes. Tetracyclines could be detected in soil at different depths and the concentrations of tetracyclines and abundance of ARGs generally decreased with increasing soil depths.     

Effect of Manure Application Rate and Rainfall Timing on the Leaching of Antibiotic-Resistant Bacteria and Their Associated Genes

In this study, we investigate the effect of application rate and timing of liquid swine slurry on leaching of antibiotic-resistant bacteria (ARB) and their antibiotic resistance genes (ARGs) through soil columns. Swine slurry was added to laboratory soil columns at rates of 5000 or 30,000 gal ac^?1. For both application rates, rainfall was applied at either 1, 7, or 21 days after slurry application. Column effluent and the top centimeter of soil in the columns were sampled post-rainfall for cultivable bacteria and quantitative PCR was used to quantify tetracycline, methicillin, β-lactam, and erythromycin resistance genetic determinants. We also conducted similar experiments using swine lagoon slurry spiked with antibiotic-resistant E. coli and Salmonella. We found that the concentration of ARB and ARG recovered in the column effluent following application of the swine lagoon slurry generally decreased with increasing lag time between slurry application and simulated rainfall, though most of these decreases were not statistically significant. Moreover, no statistically significant differences in CFU or GU concentration in the column leachate were observed between the low and high slurry application rates. In the experiments using swine slurry spiked with E. coli and Salmonella, concentrations of both microorganisms eluted from fine sand columns were affected by both slurry application rate and lag time; recovery of ARGs, however, was mostly unaffected, but some differences were observed. In columns packed with loamy sand, no recovery was detected in the column effluent for either organism and recovery of ARG was unaffected by manure application rate or rainfall lag time.     

Inactivation of Escherichia coli O157:H7 and Salmonella Typhimurium in manure-amended soils studied in outdoor lysimeters

The inactivation of Escherichia coli O157:H7 (CCUG 44857) and Salmonella enterica serovar Typhimurium was investigated in two agricultural soils (sandy loam and silty clay) amended with poultry manure, cattle manure slurry or human urine. The study was performed in soil lysimeters placed outdoors, and was repeated over two consecutive years. The amendments, inoculated with E. coli O157:H7 and Salmonella Typhimurium, were mixed with soil on the top of the lysimeters. Samples were collected from the top 5-cm layer of each lysimeter at regular intervals, and the inactivation was monitored over 6 months, by the plate spread method and by enrichment. The inactivation was modelled by fitting a non-linear model to the data, and pathogen reduction times were calculated (90 and 99% reduction). The results showed that the inactivation of E. coli O157:H7 and Salmonella Typhimurium varied depending on the manure type used and its carbon content. The longest inactivation time occurred in samples amended with poultry manure, in which both E. coli O157:H7 and Salmonella Typhimurium were detected up to day 90 with the spread plate method. The most rapid inactivation for both pathogens occurred in soil amended with urine. However, low amounts of culturable E. coli O157:H7 and Salmonella Typhimurium were detected by enrichment throughout the study period (180 days), regardless of manure type.     

Discharge of Escherichia Coli from Agricultural Surface and Subsurface Drainage Water: Tillage Effects

Drainage water from agricultural fields with applied manure can degrade the bacterial quality of surface and groundwater. The impact of conventional tillage (CT) and zero tillage (ZT) practices on Escherichia coli (E.coli) discharge through artificially drained soils is not well understood. Consequently, two field trials were conducted during 2002–2004. The first trial involved fall applications of beef manure while the second involved spring applications of dairy manure. Both surface and subsurface drainage water were monitored in the first trial while only subsurface drainage water was monitored in the second. Under fall applied beef manure (trial 1), no differences (p?>?0.05) were observed in E.coli concentrations (cfu/100 ml) in combined drainage water under both tillage systems. However, during 2003–2004, subsurface drainage water under ZT had higher E.coli concentrations and loads than drainage water under CT. When the combined (surface + subsurface) annual E.coli loads were considered, CT loads were greater than ZT during 2002–2003 with an opposite situation during 2003–2004. Overall, annual E.coli loads were similar under ZT (4.7?×?10¹⁰ cfu/ha) and CT (4.8?×?10¹⁰ cfu/ha). Spring dairy manure application (trial 2) produced significant (p?>?0.03) tillage effect on E.coli loads in subsurface drainage water only during the second year. During the study period, ZT plots (1.55?×?10¹⁰ cfu/ha) discharged 5× more E.coli than CT (0.23?×?10¹⁰ cfu/ha). A longer duration of ZT practices resulted in higher subsurface flow volumes and subsequently greater loads of E.coli discharge in both trials.     

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。     

Co-selection for antibiotic resistance genes is induced in a soil amended with zinc

The likelihood of co-selection for antibiotic resistance induced by heavy metals is a potential threat to human health, however, direct evidence of heavy metal-induced co-selection of antibiotic resistance is lacking in soil. By using a metagenomic sequencing approach, zinc (Zn) driven co-selection of antibiotic resistance genes (ARGs) in soil was investigated through a microcosm experiment where Zn salts were added at different levels. The results showed that the abundance and diversity of ARGs had a tendency to increase along the gradient of increasing Zn contents, with the maximum values recorded in the soil amended with 800 mg Zn kg⁻¹. The abundance of mobile genetic elements (MGEs) such as integrons and insertion sequences was significantly increased by Zn exposure. Network analysis demonstrated significant associations between ARGs and MGEs, suggesting that Zn treatment might enhance the potential for horizontal transfer of ARGs. Furthermore, structural equation models revealed that the types of ARGs were primarily driven by variations in bacterial compositions and Zn exposure, followed by integrons. Thus, these results indicate that added Zn salts considerably changed the diversity, abundance and mobility potential of antibiotic resistance, and imply that application of amendments containing high levels of Zn to soil could be causing the emergence and release of ARGs to the environment, and should be carefully monitored.     

Caution of intensified spread of antibiotic resistance genes by inadvertent introduction of beneficial bacteria into soil

The use of beneficial bacteria isolated especially from rhizosphere soils called plant growth-promoting rhizobacteria (PGPR) has been attracting particular interests. However, a potential source of antibiotic resistance genes (ARGs) carried by PGPRs and derived biocontrol agents and/or bio-fertilizers is widely forgotten and ignored. It is very urgent to raise the question if large-scale introduction of beneficial bacteria into soils can aggravate the situation in the spread of ARGs in environment. In this article, we conclude and analyze the possibility of a potential ARGs reservoir associated with introduction of PGPR strains into soils, and offer some advice on PGPR isolation, development and application.     

Effects of long-term organic and mineral fertilizers on bulk density and penetration resistance in semi-arid Mediterranean soil conditions

Soil aggregation is of great importance in agriculture due to its positive effect on soil physical properties, plant growth and the environment. A long-term (1996-2008) field experiment was performed to investigate the role of mycorrhizal inoculation and organic fertilizers on some of soil properties of Mediterranean soils (Typic Xerofluvent, Menzilat clay-loam soil). We applied a rotation with winter wheat (Triticum aestivum L.) and maize (Zea mays L.) as a second crop during the periods of 1996 and 2008. The study consisted of five experimental treatments; control, mineral fertilizer (300-60-150 kg N-P-K ha⁻¹), manure at 25 t ha⁻¹, compost at 25 t ha⁻¹ and mycorrhiza-inoculated compost at 10 t ha⁻¹ with three replicates. The highest organic matter content both at 0-15 cm and 15-30 cm soil depths were obtained with manure application, whereas mineral fertilizer application had no effect on organic matter accumulation. Manure, compost and mycorrhizal inoculation + compost application had 69%, 32% and 24% higher organic matter contents at 0-30 cm depth as compared to the control application. Organic applications had varying and important effects on aggregation indexes of soils. The greatest mean weight diameters (MWD) at 15-30 cm depth were obtained with manure, mycorrhiza-inoculated compost and compost applications, respectively. The decline in organic matter content of soils in control plots lead disintegration of aggregates demonstrated on significantly lower MWD values. The compost application resulted in occurring the lowest bulk densities at 0-15 and 15-30 cm soil depths, whereas the highest bulk density values were obtained with mineral fertilizer application. Measurements obtained in 2008 indicated that manure and compost applications did not cause any further increase in MWD at manure and compost receiving plots indicated reaching a steady state. However, compost with mycorrhizae application continued to significant increase (P < 0.05) in MWD values of soils. Organic applications significantly lowered the soil bulk density and penetration resistance. The lowest penetration resistance (PR) at 0-50 cm soil depth was obtained with mycorrhizal inoculated compost, and the highest PR was with control and mineral fertilizer applications. The results clearly revealed that mycorrhiza application along with organic fertilizers resulted in decreased bulk density and penetration resistance associated with an increase in organic matter and greater aggregate stability, indicated an improvement in soil structure.     

Phenotypic Diversity of Multiple Antibiotic Resistant Enterococci with Emphasis on Enterococcus gallinarum Carrying vanA and vanB Genes

The prevalence and diversity of antibiotic resistant enterococci populations in samples collected four times from urban sewage treatment plant in Tehran, Iran between June 2005 and July 2006 were studied. Filtered samples were grown on mEnterococci medium containing 4 μg/ml vancomycin after which the enterococci isolates were identified to the species level. All strains were then tested for their resistance against nine antibiotics. Of the 131 isolates, 98 (75%) isolates were identified as Enterococcus gallinarum, followed by 24 (18%) and 9 (7%) for E. faecium and E. casseliflavus, respectively. All E. gallinarum isolates carried vanC1 gene with 64 (65%) and 14 (14%) isolates concomitantly harboured either vanA or vanB gene, respectively. Some E. casseliflavus concomitantly harboured vanA and vanC2 or vanB and vanC2. Typing the total enterococci isolates with a high resolution biochemical fingerprinting method showed a high diversity (D _i?=?0.91). We have shown by biochemical fingerprinting the presence of highly diverse glycopeptide resistant E. gallinarum and E. casseliflavus that have captured vanA and vanB genetic determinants under natural conditions. To our knowledge this is the first report in this geographical region showing high frequency antibiotic resistant enterococcal populations in particular E. gallinarum carrying assorted vancomycin resistance genes.     

Response of Escherichia coli O157:H7 survival to pH of cultivated soils

Purpose

The Escherichia coli (E. coli) O157:H7 survival dynamics in original and pH-modified agricultural soils were investigated to determinate how E. coli O157:H7 survival responded to the pH values of different soils, identify the relationships between E. coli O157:H7 survival time (t _d ) and soil properties, and assess the potential pathogen contamination after soil pH changed.

Materials and methods

The six soil samples were collected from different provinces of China, and 18 pH-modified soil samples were obtained from original soils by treating the original soils with direct electric current. The E. coli O157:H7 cells were inoculated into 24 soils and incubated at soil moisture of ?33 kPa and 25 °C. The soils were sampled for determining the numbers of E. coli O157:H7 at given time intervals over the incubation. The effects of soil pH change and other properties on the t _d values were analyzed.

Results and discussion

The t _d values in the test soils were between 7.1—24.7 days. Results indicate that soil pH, texture, and free Fe₂O₃ (Fe_d) were the most important factors impacting the t _d values in the test soils. Further, the response of E. coli O157:H7 survival to pH change varied with different soils. In the acidic soils (shorter t _d values), the t _d values decreased as the pH decreased and Fe_d increased, while in the neutral or alkaline soils (pH?≥?6.45, longer t _d values), the t _d values did not change significantly with pH.

Conclusions

The changes of amorphous and free sesquioxides induced by pH change might strengthen the response of E. coli O157:H7 survival to soil pH. Closer attention should be paid to E. coli O157:H7 long survival in soils and its potential environmental contamination risk.     

Transport Of Fecal Bacteria From Poultry Litter and Cattle Manures Applied to Pastureland

Land applications of manure from confined animal systems and direct deposit by grazing animals are both major sources of bacteria in streams. An understanding of the overland transport mechanisms from land applied waste is needed to improve design of best management practices (BMPs) and modeling of nonpoint source (NPS) pollution. Plots were established on pasturelands receiving phosphorus-based livestock waste applications to measure the concentrations of Escherichia coli (E. coli), fecal coliform (FC), and Enterococcus present in overland flow at the edge of the field. The flow-weighted bacteria concentrations were highest in runoff samples from the plots treated with cowpies (1.37×10⁵ colony forming units (cfu)/100 ml of E. coli) followed by liquid dairy manure (1.84×10⁴ cfu/100 ml of E. coli) and turkey litter (1.29×10⁴ cfu/100 ml of E. coli). The temporal distribution of fecal bacterial concentrations appeared to be dependent upon both the animal waste treatment and the indicator species, with peak concentrations occurring either at the beginning of the runoff event or during peak flow rates. BMPs could be selected to reduce peak flows or first flush effects depending upon the litter or manure applied to the land. The commercial Biolog System was used to identify the dominant species of Enterococcus present in the cowpie source manure (Enterococcus mundtii 55%) and in the runoff collected from the transport plots treated with cowpies (Enterococcus faecalis 37%). The identification of predominant species of Enterococcus that are associated with specific sources of fecal pollution could greatly assist with identifying the origins of NPS pollution.     

Fecal coliform and E. coli estimates,tip of the iceberg

Pure cultures of E. coli, Klebsiella and Enterobacter, obtained from hospital patients and from natural waters were tested for their growth patterns by spread plate and membrane filtration procedures at the following temperatures; 35°, 41.5°, 43°, 44.5°, and 35°C for 4 h followed by 18 h at 44.5°C. Results indicated that 44.5°C incubation produces the lowest population estimate and that the application of the membrane filtration technique also reduced the potential population. Three water samples collected during June, August and November were tested for fecal coliform and E. coli populations, with 11 different media (broth and agar) and incubation temperatures of 35°, 41.5°, 43°, 44.5°, and 35°C for 4 h followed by 18 h at 44.5°C. During the study, isolates were collected from all positive MPN tubes at each temperature and from each MF medium-temperature regime, 24 to 50 isolates were collected. From the isolate data corrected coliform (oxidase negative), fecal coliform and E. coli population estimates were made. A sample of feces was diluted in lake water and maintained at 20°C for 56 days. Samples were collected at various times and tested for fecal coliform densities using five media and the same temperature regime as for the lake water samples. Data from these studies indicate that, depending on the age of the population being measured, the temperature of the water sample, and the temperature-media-procedure combination used, fecal coliform and E. coli population estimate techniques measure from 5 to 100% of the potential population.     

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.     

Exploring the Serbian GenBank barley (Hordeum vulgare L. subsp. vulgare) collection for powdery mildew resistance

Unlocking resistance genes in genbank collections are of prime importance for securing sustainable crop production. In this regard, the Serbian GenBank barley collection, comprising 93 local landraces and 36 commercial cultivars and elite barley breeding lines, was screened for novel resistances to powdery mildew (Blumeria graminis f. sp. hordei) using a set of 28 isolates with a wide spectrum of virulences/avirulences. No line was resistant to all the isolates, but one and three accessions showed resistance to 27 and 26 isolates, respectively. Twenty landraces (21.51 %) and ten cultivars (27.78 %) exhibited resistance to 50 % of the isolates. Infection type 2 was most frequent among resistant accessions. Nine B. graminis isolates were sufficient for gene postulation in 73 barley lines. In total, thirty-five different resistance spectra were recorded and the following known resistance genes were postulated namely, Mlra,Mlh,Mla12, Mla7(Mlu), Mlg, MlLa, Mla6, Mla7, Mlt, Mla22, Mlat, Mla1, Mlk. The majority of resistance profiles was constituted by only one line. Unidentified genes alone or in combination were proposed for twenty landraces and six cultivars. This report demonstrated that the barley collection held at the Serbian GenBank could be exploited as a new source for powdery mildew resistance.     

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.     

Effect of the expression of Escherichia coli fhuA gene in Rhizobium sp. IC3123 and ST1 in planta: Its role in increased nodule occupancy and function in pigeon pea

The inability to utilize a fungal siderophore as source of iron nutrition by most of the rhizobial cultures isolated from pigeon pea, could be considered a negative fitness factor since hydroxamate siderophores are found in significant amounts in natural soils. Thus these cultures were engineered to use ferrichrome a prototype of hydroxamate type siderophore. Pigeon pea Rhizobium spp. IC3123 and ST1 harboring Escherichia coli fhuA gene, responsible for uptake of Fe³⁺-ferrichrome, were obtained by transformation with pGR1, a broad host range plasmid carrying the fhuA gene under the control of the lac promoter of E. coli. Expression of fhuA in transformed rhizobial strains IC3123::pGR1 and ST1::pGR1 was confirmed by the ability of the plasmid-bearing strains to utilize iron bound to ferrichrome. Inoculation of pigeon pea plants with fhuA expressing rhizobial strains in pot experiments showed a significant increase in plant growth as well as nodule density as compared to those inoculated with the parent as well as the empty vector-bearing strain. Inoculation of pigeon pea seedlings with IC3123::pGR1 and ST1::pGR1 led to marked increase in shoot fresh weight, nodule number per plant, chlorophyll content of leaves and effective nodule symbiosis when compared with plants inoculated with the parent strains IC3123 and ST1. The positive effect of IC3123::pGR1 and ST1::pGR1 treatment on plant growth was more significantly observed when ferrichrome producing Ustilago maydis, known to secrete ferrichrome, was co-inoculated along with the transformed rhizobia. The presence of fhuA gene in rhizobial strains also led to an increased survival and root colonization.     

Changes in the structure of fungal communities of soil treated with sewage sludge

The influence of a single addition of sewage sludges to soils on the composition of fungal communities, soil pH (physical factor) and presence of Eschericha coli (sanitary factor) during 1 year was studied. Only the pH of soil treated with limed sewage sludge increased significantly from 7.01 to 7.58 after 3 months. E. coli was still present in soil 1 year after application of sewage sludge. Fungal numbers increased in the sewage-sludge-treated soil up to 6 months after application (maximum value was 7.5 times that of the control) and then decreased to reach values comparable to those of the control. Treated soils showed different fungal communities to the control with presence of keratinolytic fungi (Sporothrix schenckii, Microsporum sp.), yeasts (Geotrichum candidum, Candida sp., Rhodotorula sp. Cryptococcus sp.), and other potential pathogenic fungi (Aspergillus niger, Fusarium solani). The results indicate that fungi belonging to the genus Candida could be used as specific indicator organisms of the sanitary condition of soils treated with sewage sludge.     

Antibiotic resistant coliform and faecal coliform bacteria in drinking water

Coliform and faccal coliform were isolated from drinking water samples obtained from tap water (TW) and storage tanks (ST) in Baghdad city. All isolates were identified and tested for their resistance to twelve antibiotics. Bacterial identification revealed that Ent. cloacae and Kl. pneumoniae were the predominant organisms from TW and ST water samples, respectively. Overall, 66% of the isolates from TW and 38% from ST were resistant to one or more of the drugs tested. Ampicillin, Carbenicillin, Cefalotin and Colistin resistance in particular were more frequent among bacterial isolates. The overall frequency of multiple antibiotic resistance among bacterial isolates in TW and ST samples were 47% and 33%, respectively. All bacterial strains isolated from drinking water were sensitive to Rifampicin. Results demonstrated the need for periodical bacteriological examination of drinking water and restriction in the use of antibiotics in this country.     

我国小麦农家品种和近缘种对白粉病的苗期抗性

由布氏白粉菌小麦专化型引起的白粉病是最重要的小麦叶部病害之一。抗性资源和抗性基因的发掘对控制该病害起了重要作用。小种专化抗性基因的抗性水平较高, 成为当前小麦生产上使用最为广泛的白粉病抗性基因。然而,这类抗性基因的广泛使用会导致菌系结构的改变, 并产生新的毒性小种。因此, 从大量小麦种质资源中鉴定新的、有效的白粉病抗性基因是一个长期的目标。为鉴定有效的白粉病抗源, 通过苗期接种国内流行白粉菌生理小种E09, 来评价258 份国内小麦农家品种和42 份小麦近缘种的抗性。结果表明, 有5份农家品种和20 份小麦近缘种对E09 表现免疫、近免疫或高抗。这25 份抗源被用来进一步接种另外5 个不同的国内生理小种E03、E05、E18、E20 和E23, 以推知它们所携带的未知抗性基因。通过与28 个已知白粉病抗性基因的抗谱进行比较发现, 这25 份小麦种质的抗性基因不同于Pm1a、Pm2、Pm3a、Pm3b、Pm3c、Pm3d、Pm3e、Pm3f、Pm4a、Pm4b、Pm4c、Pm5a、Pm6、Pm7、Pm8、Pm9、Pm17、Pm19、Pm24、Pm28 和Pm33等21 个已知抗性基因, 但与Pm1c、Pm1e、Pm12、Pm13、Pm16、Pm20 和Pm21 等7 个已知抗性基因仍需要进一步的区分。鉴于这25 份抗源与上述7 个已知抗性基因载体的来源不尽相同, 因此, 这些抗源很可能携带有未知的抗白粉病新基因, 但还需用更多的白粉菌生理小种来鉴定。本研究旨在从小麦农家品种及其近缘种中发掘新的有效抗源, 从而为抗白粉病新基因的发掘和有效利用奠定基础。