Chapter 12.5 : Molecular Methods for Antimicrobial Agent Resistance Determination

Abstract:

Antimicrobial agent resistance is an increasing problem worldwide, particularly among critically ill hospitalized patients. For this reason, there is a renewed interest in monitoring the development and spread of antimicrobial agent resistance and a recognition of the need for effective interventions to limit the spread of resistance to prolong the therapeutic life of the available antimicrobial agents. Unfortunately, conventional methods to perform antimicrobial agent susceptibility testing may be too slow and insensitive in detecting antimicrobial agent resistance to be of much use clinically. The techniques of molecular biology have been used to characterize resistance at the DNA level and may provide rapid, sensitive, and specific information to the clinician for use in therapeutic decision making ( 1 – 4 ). Genetic material that confers antimicrobial agent resistance may be carried on the bacterial chromosome or on transposons or plasmids and has been detected by probe hybridization or by DNA amplification with PCR (Table 12.1-6). Molecular detection of resistance has potential value for decisions directly related to patient care and is useful for calibration of conventional susceptibility tests and for precise definition of the mechanisms of resistance to selected antimicrobial agents. Molecular techniques have been used to detect genes encoding several different mechanisms of resistance against antimicrobial agents, e.g., β-lactam agents, aminoglycosides, macrolides, and fluoroquinolones, after isolation of a clinical isolate (Table 12.1-6).