Molecular Typing Techniques: State of the Art

Abstract

The treatment of infectious disease centers around the goals of both curing the patient and preventing or at least restricting the spread of disease. In a perfect world, health care professionals would know that these goals have been achieved when the patient’s health is restored and there are no new occurrences of infected patients. However, the real world of infectious disease is far from perfect. The individual patient may present with evidence of recurring or additional infection by a pathogen (e.g., at a different body site). Different members of a patient population may yield cultures of the same organism. In both instances, the question commonly asked is whether multiple isolates of a given pathogen represent the same strain. In the individual patient, this question commonly relates to issues of therapeutic efficacy while in a patient population the concern is infection control. However, in both settings, the resolution of these questions is aided by specific epidemiological assessment. In the past, a variety of methods based on phenotypic characteristics have been used for this purpose including biotype, serotype, susceptibility to antimicrobial agents, or bacteriophages, etc. [1–4]. However, in the 1970, techniques developed for the recombinant DNA laboratory began to find application in the molecular characterization of clinical isolates. These included comparing protein molecular weight distributions by polyacrylamide gel electrophoresis, relative mobility of specific enzymes by starch-gel electrophoresis (multi-locus enzyme electrophoresis), specific antibody reactions with immobilized cellular proteins (immunoblotting), and cellular plasmid content (i.e., plasmid fingerprinting) [2, 5, 6]. However, by 1980 it was clear that comparisons at the genomic level would provide the most fundamental measure of epidemiological relatedness. Thus, molecular typing was born. While a wide range of etiological agents are of clinical concern, this review focuses on molecular approaches to the epidemiological analysis of bacterial pathogens.