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.     

Comparative recovery rates of MPN and Pour Plate methods for the enumeration of faecal streptococci in shellfish

Faecal streptococci in mollusks were detected according to the MPN methodology (Azide Dextrose broth followed by Ethyl Violet Azide broth) and the Pour Plate (PP) technique on two agarized media (KF agar and m-Enterococcus agar). Samples of the bivalve mollusks Donax trunculus, Ensis siliqua and Chamelea gallina were collected in different marine areas and examined. Results showed that the various media and techniques yielded different faecal streptococci counts. The MPN procedure almost always gave lower titres than those recovered according to the PP technique. Accompanying and competitive bacterial flora, more abundant in the highest volumes examined according to this procedure, may explain these lower counts. m-Enterococcus agar generally gave lower yields than KF agar, but it was also more selective for faecal streptococci than the latter medium. Notwithstanding the partitioning of the examined samples, the findings may suggest that different shellfish species may differentially concentrate and/or retain microorganisms present in the environment.     

Comparison of two rapid test procedures with the standard EC test recovery of fecal coliform bacteria from shellfish-growing waters.

A study was conducted to compare recovery and enumeration capability of two 24-hr multitube fermentation tests with the standard EC test for fecal coliform levels in shellfish-growing waters. The 2 tests were the A-1 test developed by Andrews and Presnell, specifying 24-hr incubation in A-1 medium at 44.5 degree C; and a modification of the A-1 test requiring a 3-hr resuscitation of 35 degree C before incubation at 44.5 degree C for 21 hr. Fifteen State, Federal, and Provincial laboratories examined 10 routine shellfish-growing area samples per month in parallel by the 3 methods for 1 year. IMViC tests (indole, methyl red, Voges-Proskauer, and citrate) were conducted on all gas-positive tubes. The modified A-1 test recovered higher levels of fecal coliforms than the A-1 test. Although there were seasonal and geographic variations in recovery and enumeration by the modified A-1 test, overall there was good correlation of the modified A-1 test with the EC test. Both the A-1 and modified A-1 tests were more specific for Escherichia coli than the EC test. Results of the study indicate that the 24-hr modified A-1 test can be used as an alterantive test for the standard 72-hr EC test as an adjunct to the sanitary survey for the classification and control of shellfish-growing areas waters.     

Comparison of some methods for determination of sulfate in soils

Abstract

Sulfate (SO₄ ^2‐) is present in soils as salts of various metals, and the different metals associated with sulfate may influence adsorption of SO₄ ^2‐by soils. The analytical method used for determination of SO₄ ^2‐could be affected by the type of metal associated with the SO₄ ^2‐. Four analytical methods based on different principles were evaluated for determination of SO₄ ^2‐in different metal salts and in soil extracts obtained with three extractants {0.1M lithium chloride (LiCl), 0.15% calcium chloride (CaCl₂), and 500 mg P/L as calcium phosphate [Ca(H₂PO₄)2]}. The analytical methods were: (i) a methylene blue (MB) colorimetric method after the reduction of SO₄ ^2‐to hyrogen sulfide (H₂S), (ii) an ion Chromatographie (IC) method, (iii) a turbidimetric (TD) method, and (iv) an indirect barium (Ba) atomic absorption spectrophotometric (SP) method. The recovery of SO₄ ^2‐associated with various mono‐, di‐, and tri‐valent metals was quantitative by the MB method. But, trivalent metals, such as aluminum (Al), indium (In), lanthanum (La), and scandium (IC), decreased the recovery of SO₄ ^2‐by the other three methods. The MB and IC methods gave similar values for SO₄ ^2‐in soils by using the three extractants. The TD and SP methods gave variable results and, in general, underestimated the amounts of SO₄ ^2‐in soils. Among the four methods, the MB and IC methods were the most accurate and precise.     

Limitations of the A-1M method for fecal coliform enumeration in the Pacific oyster (Crassostrea gigas)

Use of the A-1M method, which was originally devised for testing water samples, has recently been extended for enumeration of fecal coliforms and Escherichia coli in shellfish and other food products. Results of our study indicate that while this method is reliable for analysis of growing waters, the use of the A-1M method for testing Pacific oysters may be less reliable because bacteria not belonging to the coliform group but which are sometimes present in these animals also give a positive reaction.     

Hydrophobic grid membrane filter/MUG method for total coliform and Escherichia coli enumeration in foods: collaborative study

Twenty-four laboratories participated in a collaborative study to validate a hydrophobic grid membrane filter (HGMF) method incorporating the use of 4-methylumbelliferyl-beta-D-glucuronide (MUG) for enumeration of total coliform and Escherichia coli bacteria in foods by comparing its performance against the AOAC 3-tube MPN method (46.013-46.016). Raw milk, raw ground poultry, whole egg powder, cheese powder, and ground black pepper were included in the study. The total coliform methods did not differ significantly, except that the 3-tube method detected a significantly higher level of total coliforms than did the HGMF method in the ground black pepper. Conversely, the HGMF/MUG E. coli method detected significantly higher numbers of E. coli present in the egg powder, cheese powder, and ground black pepper samples, while not differing significantly from the 3-tube method for the raw milk and raw ground poultry samples. The overall confirmation rate of MUG-positive colonies isolated using the HGMF method was 99.5%. The hydrophobic grid membrane filter/MUG method has been adopted official first action as an additional method to AOAC official final action method 46.030-46.034.     

Effect of heating on phosphate sorption and availability in some north-east Nigerian soils

Studies on phosphate sorption and availability in some north-east Nigerian soils showed that phosphate adsorption and inorganic-P concentrations increased considerably after the soil was heated either in a furnace or during the field-burning of straw. The increase in phosphate adsorption after heating was thought to be caused by an increase in free Fe and A1 oxides, whereas the high contents of exchangeable Ca and possibly carbonates and hydroxyl ions in the ash were probably responsible for the increase in phosphate sorption after field-burning of straw. Investigations into the availability of P to maize over a 7-d period of growth showed that there was no significant nutritional benefit from the P released after soil heating. The effect of heating was to increase P sorption and so reduce P in solution and P availability.     

Fecal coliform methods for examination of sea water: interlaboratory evaluation of split sample analysis.

An interlaboratory study was conducted to compare the effectiveness of the following 3 multiple-tube fermentation methods for determining the most probable number (MPN) of Escherichia coli in a split artificial sea water sample: (1) the 72-hr standard methods procedure of the American Public Health Association, (2) a 24-hr elevated-temperature test using A-1 medium, and (3) a 24-hr elevated temperature test modified to include an initial 3-hr resuscitation period using A-1 medium. The capability of the laboratories to perform the 3 test procedures was also compared. Split sample replicates with low, medium, and high levels of E. coli were examined in 18 laboratories in the United States and Canada. Data indicate that the laboratories performed each test with equal capability, and all 3 procedures were equally effective in enumerating the strain of E. coli used in this investigation. By virtue of its homogeneity and stability, the split sample served as an appropriate specimen for this study and could probably be used as a proficiency test specimen for evaluating laboratory analyst performance in the bacteriological examination of sea water.     

Estimates of viral abundance in soils are strongly influenced by extraction and enumeration methods

Viruses are highly abundant in temperate soils, ranging from 10⁷ to 10⁹?g^?1, and outnumbering soil bacteria from 5- to over 1,000-fold. In order to determine the potential impacts of viruses on soil microbial communities, it is important to establish reliable methods for comparing changes in viral abundances within and across soil samples. The goals of this study were to optimize extraction-enumeration methods to accurately determine viral abundances in a range of soil types, to evaluate the feasibility of simultaneously enumerating bacterial cells and virus particles using a single extraction procedure, and to assess the utility of flow cytometry (FCM) for enumerating virus particles in soil extracts. Comparisons of extraction approaches indicated that sonication or blender extraction of soils with potassium citrate buffer yielded the highest viral abundances for most soil types. Combined viral and bacterial extractions underestimate abundances compared to separately-optimized extractions for each. Flow cytometric counts were anywhere between 350- and 1,400-fold higher than epifluorescence microscopy (EFM)-based counts for the same soil. Trends in viral abundance across soil types were different from those via EFM, and different relationships between viral abundance and soil properties were observed depending on the enumeration method. Thus, FCM is not currently recommended for enumeration of viruses in soil extracts. Based on EFM results, soil moisture and organic matter content were the most important factors determining viral abundance in soils.     

Assessment of the accuracy of different standard methods for determining reservoir capacity and sedimentation

Purpose

Determination of reservoir volume has been used in the calculation of sedimentation, hydrodynamic modelling, and dam safety assessment, among others, and the method used as well as its associated error play an important role in the quality of these studies. This study assessed the accuracy of reservoir volume calculations based on different standards for the definition of the spacing between bathymetric range lines. A technique for terrain modelling and a method for determining the survey accuracy are also proposed.

Materials and methods

The reference reservoir volume was based on highly detailed bathymetry (10 m resolution). Seven different spacings were selected, which generated 99 separate bathymetric data sets. For each data set, the volume was calculated based on a digital terrain model according to the usual model (triangular irregular network (TIN)) and according to the insertion of mesh points (IMP) method. This was then compared with the reference volume, and the accuracy of each survey was determined.

Results and discussion

Utilization of a highly detailed and reliable bathymetric survey allowed for the assessment of the associated error in each of the bathymetric data sets, as well as of the spacing standards analyzed. The accuracy of the standards analyzed using TIN modeling ranged from 0.31% to 14.40% (30 and 300 m, respectively). The high errors are attributed to the limitation of the TIN in representing regions near shores, producing incorrect shallow depth readings, resulting in a lower calculated volume than the real volume. IMP modeling exhibited great improvement in performance over the standard TIN (i.e., for 300 m accuracy of 5.51% for IMP and 14.40% for standard TIN), and in none of the cases were the generated volumes greater than the reference volume.

Conclusions

The IMP method proved to be consistent, improving quality of the data while reducing effort in field work. The low accuracies found showed that even surveys following the widely accepted standards contain errors of a magnitude that cannot be ignored. Thus, knowing and evaluating the survey accuracy is of fundamental importance. Definition of standard spacing for reservoirs proved to be unfeasible. This must be defined on a case-to-case basis, considering the error acceptable for the purpose of the survey.     

An assessment of non-symbiotic nitrogen fixation in some Nigerian soils by the acetylene reduction technique

Short-term incubation studies of non-symbiotic nitrogen fixation using acetylene as the substrate for nitrogenase were carried out on six soil samples collected from various locations in the Western State of Nigeria, and on one soil sample collected from Wisconsin, U.S.A. Unamended soils reduced a very small amount of acetylene but with added organic materials (5% organic matter, 2% glucose or sucrose) acetylene reduction became substantial and in one case was more than 30,000 times that in the unamended soil. In general, more acetylene was reduced in anaerobic than in aerobic soils. Two of the soils were tested for suppression of acetylene reduction by NH₄⁺-N. With the addition of up to 100 ppm nitrogen as (NH₄)₂SO₄ to the soils incubated with sucrose, no depression of acetylene reduction was observed in one soil while it was reduced by about half in the other.     

Precision parameters of standard methods of analysis for dairy products

The available collaborative studies for standard methods of analysis for various constituents of milk and milk products were examined in an attempt to assign specific repeatability and reproducibility precision parameters to these methods. The different collaborative assays for the primary constituents (moisture/solids, fat, protein), the nutritionally important elements (calcium, sodium, potassium, phosphorus), and miscellaneous analytes/physical constants (ash, lactose, salt, freezing point) produced different estimates of the precision parameters for the same method. A suitable summary of the precision estimates from collaborative studies is given by the reproducibility relative standard deviation, RSDg, which is relatively constant within a product and permits comparisons across products. An estimate of the variation of RSDR for an analyte from a number of collaborative studies is presented in terms of the median and 90% interval (the range of the centermost 90% of values). These estimates are only informative when a substantial number of independent studies are available for pooling the independent estimates to form a distribution of RSDR values. The RSDR for the determination of the primary constituents of milk and milk products is characterized by a median RSDR of 1% and a 90% interval of 0.3-3%, with RSDR estimates occasionally occurring below 0.3% and above 4%. These overall estimates appear to be independent of analyte, matrix, and method and apply to concentrations of primary constituents that range from about 2 to 80%. The repeatability relative standard deviation, RSDr, is unstable, although it tends to converge to about 0.5-0.7 X RSDR. Too few collaborative assays are available to characterize RSDR for the determination of certain other constituents (acidity, ash, lactose, salt, and the nutritionally important elements) unless RSDR values for different analytes, methods, and matrixes are pooled on the basis of similar analyte concentrations. When pooled, the RSDR values are generally better than predicted from the Horwitz equation, RSDR (%) = 2 exp (1-0.5 log10C), where C is the concentration expressed as a decimal fraction; all but one of 661 RSDR values are within the upper empirical limit of twice this curve.     

Comparison of analytical methods for metribuzin.

Determinations of the active ingredient in technical and formulated metribuzin were compared by gas-liquid chromatography (GLC) using various solvents, infrared (IR) spectrophotometry, and high-pressure liquid chromatography (HPLC). Ketones could not be used as a solvent for GLC analysis because of Schiff base formation. The GLC method using ethylene glycol monomethyl ether gave results about 1% higher for technical metribuzin than the other methods. GLC using methylene chloride solvent agreed with IR and HPLC results to within 0.4%. GLC using methylene chloride is the preferred method.     

Comparison of methods for the quantitative determination of phospholipids in lecithins and flour improvers

Phospholipid classes were determined qualitatively and quantitatively in eight commercial lecithins and three flour improvers by thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and (31)P nuclear magnetic resonance spectroscopy ((31)P NMR). The total amounts of phospholipids as well as the amounts of phospholipid classes in the samples were comparable but depended on the method used for quantification. Highest selectivity was provided by (31)P NMR as all phospholipids and lysophospholipids could easily be quantified. By TLC only lysophosphatidylcholine could not be quantified, whereas HPLC was the method with the lowest selectivity, because lysophospholipids, except lysophosphatidylethanolamine, could not be determined. Sensitivity was best for HPLC and TLC with detection limits of 20-170 mug/mL. By means of (31)P NMR these figures increased by a factor of 10-70. The coefficients of variation were 5.5, 6.8, and 12.8% for quantification by TLC, HPLC, and (31)P NMR, respectively, showing that TLC was the method with the best reproducibility. Altogether, (31)P NMR can be recommended for the quantification of phospholipids, because it is easy to perform and results can be obtained quickly. As it requires minimum instrumental equipment, TLC is a good alternative to (31)P NMR. If high sensitivity is required, HPLC is the best method.     

Comparison of standard and total Colwell procedures for measuring soil test phosphorus

Abstract

When soils are extracted with sodium bicarbonate to measure soil test phosphorus (P) by the standard Colwell procedure, the concentration of P in the extract solution is measured using the Murphy and Riley procedure. This measures P as orthophosphate (PO₄) and most of the organic P extracted is not measured. The total (inorganic plus organic) P extracted can be measured by digesting an aliquot of the extract solution with perchloric acid to convert all the extracted P to PO₄ before measuring the P concentration by the Murphy and Riley procedure. This is called total Colwell P. Data from one crop and two pasture field experiments in Western Australia are presented in which soil test P measured in 1991 and 1992 by the standard and total Colwell procedures were compared. Fertiliser P residues, including organic P, accumulate in the topsoil because, (i) the fertiliser is applied to the surface of pastures, and (ii) crops are being increasingly sown by minimum (conservation) tillage when P is concentrated in the top approximate 5 cm of the soil compared with about 10 cm when crops are sown conventionally. Consequently, to measure soil test P in the present study, soil samples were collected in February 1991 to either 5 or 10 cm depth. For the two Colwell procedures and both sampling depths, soil test P was related to: (i) the level of P applied in previous years and to (ii) plant yield measured later on that year (the soil test P calibration). Soil test P was larger for the total Colwell procedure and for soil samples collected to 5 cm depth. Total Colwell P as the dependent variable was closely correlated with standard Colwell P as the independent variable. The relationship between soil test P and the level of P applied, and the calibration relating yield to soil test P, were different for standard and total Colwell P. Neither method can be claimed to be significantly better than the other. It is concluded that use of the total Colwell procedure instead of the standard procedure is not warranted. Likewise, there was no evidence that collecting soil samples to 5 cm to measure soil test P provided better estimates of the current P status of soils than collecting soils to the standard 10 cm depth. There is therefore no need to change the sampling depth.     

Comparison among soil Series and extraction methods for the analysis of trifluralin

Accurate analytical procedures are needed to improve understanding of the fate and transport of trifluralin, a chemical widely used as a herbicide. Analytical determination of trifluralin is challenging due to its hydrophobic, yet volatile, character and its tendency to degrade into numerous metabolites. In this research, efficient analytical methods for fortified and field-incurred soils were developed for simultaneous quantitation of trifluralin, I [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine, CAS Registry No. 1582-09-8; CAS Registry No. have been provided by the author], a trifluralin metabolite, II [2,6-dinitro-N-propyl-4-(trifluoromethyl)benzenamine, CAS Registry No. 2077-99-8], and a related trifluoromethyldinitroaniline isomer of trifluralin, III [2,4-dinitro-N,N-dipropyl-6-(trifluoromethyl)benzenamine, CAS Registry No. 23106-20-9]. Extractions of trifluralin (0.5 and 2.5 microg/g) from silt loam, sandy loam, and silty clay soils were compared. A method was developed for the supercritical fluid extraction of trifluralin from soil using modified supercritical carbon dioxide, and the effects of cosolvent, pressure, and flow rate on recovery were evaluated. Supercritical fluid extraction was compared to liquid vortex extraction and automated Soxhlet (soxtec) extraction. Solid-phase extraction was examined for purifying soil extracts. Protocols were developed for analysis of extracts by gas and/or liquid chromatography. Immunoassay was investigated but proven to be impractical for this analysis. Soil properties and extraction methods were observed to affect the level of coextracted background interferences. Trifluralin exhibited concentration-dependent recovery regardless of soil series or extraction method.