Antibiotics resistance determination

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

DBs of Virulence Factors, Tojdns, and Antibiotic Resistance Determinants... 

Although the antibiotic resistance could be detected by analysis of specific genes, the question remains are these genes fimctional and will they be expressed The bottom-up proteomics approach can easily address these issues by searching for specific proteins associated with antibiotic resistance (see Section DBs of dra-lence Factors, Toxins, and Antibiotic Resistance Determinants ). More importantly, the mass spectra acquired during proteomic analysis may be used to provide information both on strain identity and the expression of genes associated with antibiotic resistance. 

D. Behnke and M. S. Gilmore, Location of Antibiotic Resistance Determinants, Copy Control and Replication Functions on the Double-Selective Streptococcal Cloning Vector pGB301, Mol. Gen. Genet., 184 115-120 (1981). 

B. Jeon, W. Muraoka, O. Sahin and Q. Zhang, Role of Cjl211 in natural transformation and transfer of antibiotic resistance determinants in Campylobacter jejuni, Antimicrob. Agents Chemother., 2008, 52, 2699-2708. 

One approach to combating antibiotic resistance caused by P-lactamase is to inhibit the enzyme (see Enzyme inhibition). Effective combinations of enzyme inhibitors with P-lactam antibiotics such as penicillins or cephalosporins, result in a synergistic response, lowering the minimal inhibitory concentration (MIC) by a factor of four or more for each component. However, inhibition of P-lactamases alone is not sufficient. Pharmacokinetics, stability, ability to penetrate bacteria, cost, and other factors are also important in determining whether an inhibitor is suitable for therapeutic use. Almost any class of P-lactam is capable of producing P-lactamase inhibitors. Several reviews have been pubUshed on P-lactamase inhibitors, detection, and properties (8—15). 

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. 

Phenotypic resistance assays directly measure the ability of HlV-1 to replicate in a cell culture in the presence of different antiretroviral drug concentrations. This process is similar to that used to determine antibiotic resistance and is, therefore, more familiar to most clinicians. The recombinant virus, composed of a virus s reverse transcripfase and protease genes, is inserted into a standard reference strain of virus. The recombinant virus is then tested in vitro for fhe amount of drug needed to inhibit virus replication by 50%, relative to the amount of drug needed to inhibit a reference strain of virus. Phenotypic resistance testing is limited by the fact that it is conducted in vitro and not in vivo. 

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. 

The vast majority of the smdies on antibiotic resistance in the environment have focussed on the survey of resistance genes. However, the mere detection of the antibiotic resistance genes may be insufficient to get a clear perspective of their function in the environment. If the role of antibiotic resistance genes in the environment is to be assessed, it is also important to determine the factors capable of triggering gene expression and to measure the expression levels [24]. Such an approach requires transcriptomic analyses supported, for instance, by reverse-transcription PCR or microarrays. 

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... 

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