Resistance determination

Table 2. Classification and Distribution of Tetracycline Resistance Determinants in Microorganisms ...

There is a direct and an indirect method of measuring specific soil resistivity. The direct method is carried out in the laboratoiy on a soil sample using a soil box as shown in Fig. 3-16. The resistivity of a soil specimen of cross-section, S, and length, I, is measured and the specific resistivity determined ... 

Protection current density and coating resistance are important for the current distribution and for the range of the electrochemical protection. The coating resistance determines, as does the polarization resistance, the polarization parameter (see Sections 2.2.5 and 24.5). For pipelines the protection current density determines the length of the protection range (see Section 24.4.3). 

The characteristics of the pump relate the applied pressure on the cake to the flowrate at the exit face of the filter medium. The cake resistance determines the pressure drop. During filtration, liquid flows through the porous filter cake in the direction of decreasing hydraulic pressure gradient. The porosity (e) is at a minimum at the point of contact between the cake and filter plate (i.e., where x = 0) and at a maximum at the cake surface (x = L) where sludge enters. A schematic definition of this system is illustrated in Figure 2. 

An exchanger has heen examined, and the following individual coefficients and resistances determined. What is the overall coefficient of heat transfer referenced to outside coefficients (Methods for determining these film coefficients are given later). 

Select a shale interval. Using MWD data, gamma ray, and resistivity, determine R.. 

It has been shown that an AAC enzyme variant (AAC (6 )-Ib-cr, cr for ciprofloxacin resistance) found in various Enterobacteriaceae is capable of A-acetylating fluoroquinolones with an unmodified piperazinyl substituent at the amino nitrogen. Although the increase in MIC is low, this plasmid encoded quinolone resistance determinant can augment further development of clinically relevant resistance. 

Accessory DHPS enzymes confer resistance to sulfonamides. Two different types encoded by the genes sull (located on transposons) and sulll (located on plasmids) have been described. These resistance determinants are often genetically linked to trimethoprim resistance genes. Therefore, the combination of sulfonamide antibiotics with trimethoprim does not prevent resistance selection. 

Noguchi N, A Emura, H Matsuyama, K O Hara, M Sasatsu, M Kono (1995) Nucleotide sequence and characterization of erythromycin resistance determinant that encodes macrolide 2 phosphotransferas I in Escherichia coli. Antimicrob Agents Chemother 39 2359-2363. 

Babich, K., Engle, M., Skinner, J.S., and Laddaga, R.A., Deletion mutant analysis of the Staphylococcus aureus plasmid pI258 mercury-resistance determinant, Can J Microbiol, 37 (8), 624-631, 1991. 

Wang, Y., Moore, M., Levinson, H.S., Silver, S., Walsh, C., and Mahler, I., Nucleotide sequence of a chromosomal mercury resistance determinant from a Bacillus sp. with broad-spectrum mercury resistance, J Bacteriol, 171 (1), 83-92,1989. 

Weeks, S. A., and Dumbill, P., Method Speeds FCC Catalyst Attrition Resistance Determinations, Oil GasJ., 88 38 (1990)... 

Sulfur dioxide was the major volatile product and was used as a probe to correlate the radiation resistance with polymer structure. The use of biphenol in the polymer reduced G(SO ) by 60% compared with bisphenol A based systems (Bis-A PSF). Surprisingly, the isopro-pylidene group was shown to be remarkably radiation resistant. The ultimate tensile strain decreased with dose for all polysulfones investigated and the rate of decrease correlated well with the order of radiation resistance determined from volatile product measurements. The fracture toughness (K ) of Bis-A PSF also decreased with irradiation dose, but the biphenol based system maintained its original ductility. 

In comparison with culture-dependent procedures, culture-independent methods are more sensitive and have an increased potential to survey the diversity of antibiotic resistance genes in the environment. A weakness of these methods is the impossibility to elucidate about the bacteria in the community that host specific resistance determinants. On the other hand, the possibility to explore the genetic environment (mobile element, associated genes, promoter, etc.) in which the resistance determinant is integrated offers relevant clues about the gene transfer potential and gene acquisition history. 

Table 3 Examples of antibiotic resistance genes of clinical relevance distributed worldwide in aquatic environments and illustration of some methodological approaches commonly used to detect resistance determinants in the environment... 

The dramatic increase of severe or lethal infections caused by antibiotic-resistant bacteria triggered numerous studies on antibiotic resistance, not only from clinical but also from environmental sources. Nowadays it is clear that environment, and water in particular, plays a central role on antibiotic resistance dispersion to and from clinical settings. However, the current state of the art clearly suggests that only a small fraction of the environmental resistome is known. The modes and mechanisms of emergence, evolution and transmission of resistance determinants are still not very well understood. Although environmental pollution is recognized to play an important role on antibiotic resistance evolution and spreading, it is still very difficult to draw cause-effect relationships, which sometimes seems to be strain/species dependent. 

Martinez JL (2009) Environmental pollution by antibiotics and by antibiotic resistance determinants. Environ Pollut 157(11) 2893-2902... 

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