Phage-mediated transfer of virulence genes

Bacteriophages as accessory genetic elements play a crucial role in the dis semination of genes and the promotion of genetic diversity within bacterial populations. Such horizontal transfer of DNA is critical in the emergence of new pathogenic organisms, through the dissemination of genes encoding vi rulence factors such as toxins, adhesins and agressins. Phages can transfer genes that are not necessary for bacteriophage persistence and are general ly recognised by their ability to convert their host bacteria to new phenot ypes. This phenomenon is known as phage conversion. If such converting gene s encode for virulence factors, the consequences of phage infection may inc lude increased virulence of the host bacteria, and the conversion of a non- pathogenic strain to a potentially dangerous pathogen. A number of virulenc e factors in bacteria causing diseases in plants, animals and humans are en coded by converting phages, the vast majority of which are temperate as opp osed to lytic in nature. (C) 2001 Society of Chemical Industry.