Multiple Tube Tests

There are numerous variations on this medium using mannitol instead of lactose, teepol or sodium lauryl sulfate instead of bile salts, and alternative indicators such as Phenol Red. However, all the tests are based on the ability of coliforms to grow in the presence of some inhibitor, and ferment lactose or mannitol to acid and gas, the acid changing the colour of the indicator. 

The differential tests make use of the positive samples obtained in the presumptive tests. These differential tests are intended to differentiate E. coli from non-thermotolerant coliforms, and coliforms in general from non-coliforms. Samples from each of the positive presumptive tubes are inoculated into each of the four following media  

Tube (a) is examined for the production of acid and gas within 24 hours. A positive result is given by E. coli and a negative result by non-thermotolerant coliforms. 

Tube (b) is tested for indole by the addition of Kovacs reagent (page 62). E. coli rapidly gives a positive reaction. 

Tube (c) is split into two. Methyl Red is added to one portion (page 61). E.coli produces an acid reaction. To the second portion is added O Mearas reagent (page 62) to test for the production of acetoin. E. coli gives a negative reaction. The colour only develops slowly and the tests should be retained for several hours. 

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One standard test used to determine the presence of the coliform group is called the multiple-tube fermentation technique (sometimes called the presumptive test). If this test indicates the presence of these bacteria, then a confirmed test must be done. If only negative colonies or no colonies develop during this test, it is considered negative otherwise, a completed test must be undertaken. Positive results obtained in the completed test are evidence for the presence of coliform bacteria. Testing methods have been given by the APHA, and the detailed procedures contained therein should be consulted (20). 

Fecal Goliforms. Eecal coliforms are those originating from the intestines of warm-blooded animals. Eecal coliforms can be deterrnined by a multiple-tube procedure, which must be appHed to a positive presumptive test for optimum recovery of fecal coliforms (20). Incubation must be at 44.5 0.2°C for 24 2 h. Gas production during incubation is positive evidence of fecal coliform poUution. 

Both multiple-tube and membrane-filter methods are also available for testing for the fecal streptococcal group (20). These assays can be used to provide supplementary data regarding the bacteriological quaUty of water. Other fecal indicators should also be used concurrendy because of the survival characteristics of the fecal streptococci. 

The water analysis is incomplete unless the number of coliform bacteria present is determined as well. A multiple-tube fermentation technique can be used to enumerate positive presumptive, confirmed, and fecal coliform tests. Results of the tests are expressed in terms of the most probable number (MPN). That is, the count is based on a statistical analysis of sets of tubes in a series of serial dilutions. MPN is related to a sample volume of 100 ml. Thus, an MPN of 10 means 10 coliforms per 100 ml of water. 

The torsion-tube test described by Whitney, Pagano, and Pipes [2-14] involves a thin circular tube subjected to a torque, T, at the ends as in Figure 2-29. The tube is made of multiple laminae with their fiber directions aligned either all parallel to the tube axis or all circumferentially. Reasonable assurance of a constant stress state through the tube thickness exists if the tube is only a few laminae thick. However, then serious end-grip difficulties can arise because of the flimsy nature of the tube. Usually, the thickness of the tube ends must be built up by bonding on additional layers to introduce the load so that failure occurs in the central uniformly stressed portion of the tube (recall the test specimen criteria). Torsion tubes are expensive to fabricate and require relatively sophisticated instrumentation. If the shearing strain y 2 is measured under shear stress t.,2, then... 

The Zymark robotic laboratory automation system Although detail procedures differ in each laboratory, the basic elements of binding and enzyme assays are similar. The generalized procedure shown in Table 1.10 highlights the common steps and indicates which Zymate laboratory systems are required. These procedures are performed using common laboratory glassware such as test tubes or in multiple tube devices such as microtitre plates. 

Figure 13 Multiple CPC test bed and experimental scheme. Each reactor tube contains five small glass tubes inside, supporting the Ti02 catalyst.

This is termed the a rent miscibility pressure because there is a considerable amount of evidence that asphaltenes, which are colloidally dispersed in most crude oils, will aggregate under appropriate dilution conditions and precipitate, so that the physicochemical definition of miscibility (single-phase for all proportions of the fluids in question) is not realized. There are also conditions, particularly found in oil reservoirs at temperatures below about 135 F, at which two liquid phases, or two liquid phases plus a gas phase, appear in addition to an asphaltene precipitate (11-13). In general, however, this does not prevent the attainment of 95 % oil recovery or more in slim-tube tests at the same pressures at which these multiple phases appear. Hence, the process is deemed "miscible," for all practical purposes. 

Quantitative tests. In some situations, actual enumeration of the number of organisms present may be necessary. This is the case, for example, for limitations imposed on a discharge permit. Generally, two methods are used to enumerate conforms the membrane-filter technique and the multiple-tube technique. 

The other method of enumerating coliforms is through the use of the multiple-tube technique. This method is statistical in nature and the result is reported as the most probable number (MPN) of organisms. Hence, the other name of this method is the MPN technique. This technique is an extension of the qualitative techniques of presumptive, confirmed, and completed tests. In other words, MPN results can be a presumptive, confirmed, and completed MPNs. The number of tubes liberating gases is counted from each of the set of hve tubes. This information is then used to compute the most probable number of organisms in the sample per 100 mL. 

In microbiology two fundamental types of measurements are used by the analyst. The simplest ones consist in counting colonies on culture media in a Petri dish. Another principle consists in evaluating the most probable number of microbes by inoculating sub-samples into multiple tubes. The result of the latter is given by statistical tables. For both types of methods results are only available after a few days. For the presence of very few microbes, so-called presence/absence tests have been developed by microbiologists. They are mainly used for the detection of pathogenic microbes. For the last two types... 

Check the apparatus and compare it to Figure El6-2. The directions that follow involve a 12.2 mL column and collecting fractions manually. If you have a fraction collector then please use it. Otherwise, place a multiple unit test tube rack filled with 20 10 X 75 mm test tubes at the outlet. 

The tests used to determine the presence of indicator organisms fall into two groups, multiple tube methods and membrane filtration methods. 

Figure 9.1 Water testing procedure for multiple tube method...

Completed test The final test for coliforms in multiple-tube fermentation in which organisms from colonies grown on eosin methylene blue agar are used to inoculate broth and agar slants. 

Multiple-tube fermentation method Three-step method of testing for coliform bacteria in drinking water. 

Presumptive test First stage of testing in multiple-tube fermentation in which gas production in lactose broth provides presumptive evidence that coliform bacteria are present. 

As noted in Table 3 [77], the results of multiple alloy tests in seawater are correlated to the Pitting Resistance Equivalence (PRE) number [47,48,72,77], which also correlates to alloy pterformance in FeCly. Anderson [78] and Streicher [79] used MCA in seawater tests to compare alloy performance. More recently, a simple, flat, plastic (specifically, polymethylmethacrylate, which is often referred to as "perspex ) washer has been successfully used to evaluate a series of alloys in seawater [77]. One application of the ASTM G 48 test has been in simulating leaking tube-to-tube sheet joints in seawater heat exchangers and condensers [87]. When certain highly corrosion-resistant alloys were paired in a dissimilar metal crevice (DMC) with alloys that would be expected to suffer crevice corrosion in the particular test solution, the more corrosion-resistant alloy was found to corrode due to the accelerating effects of the corrosion products from the less resistant alloy. The results of DMC tests in ferric chloride were confirmed by long-term DMC exposures in seawater [82],... 

Termite Bioassays. Multiple choice tests were conducted using wood blocks of birch, red oak, redwood and Alaska yellow cedar where blocks were decayed by P. chrysosporium for either 3,8, or 12 wk. Bioassays were conducted using rectangular Rubbermaid storage containers (14.5 cm X 8.5 cm X 4 cm) (Consolidated Plastics, Twinsburg, Ohio). Each container served as a replicate and was filled with 100 g of sand (Standard Sand and Silica Company, Davenport, FL) moistened with 20 ml of water. Each container had four 2-cm diameter holes, one hole on each side. A 14 ml (17 x 100 mm) polystyrene round-bottom Falcon test tube (Becton Dickinson, Franklin Lakes, NJ) was inserted into each hole and sealed in place using a glue gun. The position of treatment tubes was alternated between replicates to preclude any positional effects. Two hundred termites (190 workers 10 soldiers) were placed in the center of each container. The termites were able to move freely between the container and the tubes. 

Four methods may be used to detect and enumerate total coliforms, fecal coliforms, and E. coli in water samples. These are grouped as (a) multiple tube fermentation technique also known as the MPN technique, (b) membrane filtration technique, (c) presence/absence test, and (d) use of the enzymatic substrates test also known as the chromogenic-fluorogenic substrate test. 

The multiple tube fermentation method requires the use of replicate tubes and dilutions of samples. The fermentation products of lactose include mixed acids and gas, which is usually detectable. Coliforms are reported in terms of MPN of organisms present. MPN tables are based on a random dispersion of coliforms (Poisson distribution). Failure to shake the samples very well will result in a nonrandom distribution that will underestimate the actual density of the bacteria. If testing drinking water, a single bottle containing 100 mL may be used or 5 replicate tubes with 20 mL each or 10 replicate tubes with 10 mL each. If testing nonpotable water such as salt water, brackish water, or sediments, multiples and subsamples of 10 mL (e.g., 0.1 1.0 10 mL) should be used. 

It Is expected that by periodically subjecting seunples cut from one or two process tubes removed from the reactor to crack propagation tests, Emd comparing the data obtained to existing reactor operating conditions of stress and temperature, the rate of approach to limits of stress and/or total neutron dose will be monitored and In this way multiple tube failures should be prevented. 

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