Polymerase chain reaction-mediated typing of microorganisms: tracking dissemination of genes and genomes.

The polymerase chain reaction (PCR) is a powerful molecular biology tool which can be used for the identification of species and strains of diverse microorganisms. By aimed amplification of characteristic genes (i.e., genes encoding ribosomal RNA molecules) and subsequent genetic analysis of amplified fragments, information on microbiological systematics and phylogeny can be obtained in a fast and efficient manner. Similar types of gene identification can be used to verify or detect genes responsible for phenotypic characteristics, whereas modified forms of the PCR enable whole genome searches for genetic polymorphisms among strains of a given species. In medical sciences, both strategies, gene and genome variability analysis by PCR, have an increasing impact on the study of the spread of especially those microbes that are multiply resistant to clinically used antibiotics. In this communication we will exemplify the usefulness of PCR-mediated typing of microorganisms from a clinical perspective while focusing on gene- versus genome-scanning. Special emphasis will be placed on analysis of the dissemination and characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains and bacterial factors providing resistance to penicillin and other beta-lactam antibiotics. Technical limitations and possibilities for improvement will be discussed.