Resistance Molecular Detection of Antimicrobial

INTRODUCTION The determination of antimicrobial susceptibility of a clinical isolate is often crucial for the optimal antimicrobial therapy of infected patients. This need is only increasing with increasing resistance and the emergence of multidrug-resistant microorganisms (88, 89, 91). Testing is required not only for therapy but also to monitor the spread of resistant organisms or resistance genes throughout the hospital and community. Standard procedures and breakpoints have been defined to predict therapeutic outcome both in time and at different geographic locations. In some cases the presence of a resistance gene is highly predictive for clinical outcome of antimicrobial therapy. For example, the presence of a ␤-lactamase in Neisseria gon-orrhoeae correlates well with the outcome of penicillin treatment. However, the presence of a resistance gene does not necessarily lead to treatment failure (198), because the level of expression may be to low. For example, ␤-lactamase production among members of the Enterobacteriaceae is common, but the development of resistance is dependent on the mode and level of expression (180, 183). Resistance can be caused by a variety of mechanisms: (i) the presence of an enzyme that inactivates the antimicrobial agent; (ii) the presence of an alternative enzyme for the enzyme that is inhibited by the antimicrobial agent; (iii) a mutation in the antimicrobial agent's target, which reduces the binding of the antimicrobial agent; (iv) posttranscriptional or posttrans-lational modification of the antimicrobial agent's target, which reduces binding of the antimicrobial agent; (v) reduced uptake of the antimicrobial agent; (vi) active efflux of the antimicrobial agent; and (vii) overproduction of the target of the antimicrobial agent. In addition, resistance may be caused by a previously unrecognized mechanism. On the other hand, a gene which is not expressed in vitro may be expressed in vivo. Nucleic acid-based detection systems offer rapid and sensitive methods to detect the presence of resistance genes and play a critical role in the elucidation of resistance mechanisms. During the last decade, nucleic acid-based detection systems have expanded tremendously and are becoming more accessible for clinical microbiology laboratories. This accessibility is not limited to the detection and identification of microorganisms but is extended to the detection of properties of these microorganisms, such as virulence factors and antimicrobial resistance. The application of nucleic acid-based technology is particularly useful for slow-growing or nonculturable microorganisms and for the detection of point mutations or certain genotypes. Nucleic acid-based technology can be divided into hybridization systems …