Pathogenicity Islands Clusters of Virulence Factors

reliable incidence figures for endemic diseases in many region. It is now known that uropathogenic E. coli contains at least four PAIs inserted into various tRNA sites, countries, this may be only a technicality. ranging in size from 40 kb to 190 kb, encoding diverse Another book with the same title was published in virulence factors such as fimbriae, iron utilization, and 1998, edited by William M. Krause, the Director of the ␣-hemolysin. Two of the PAIs are flanked by direct re-National Institute of Allergy and Infectious Diseases for peats, indicative of genetic mobility. many years. It includes a chapter on mathematical models The PAIs of uropathogenic E. coli exemplify the com-of epidemics by Roy Anderson from Oxford, 14 chapters position and definition of pathogenicity islands. PAIs, on specific diseases, and one on antibiotic resistance. by definition, encode one or more virulence factors such The chapters range in length from a comprehensive 80-as adhesins, invasions, or secretion systems needed to page treatise on tuberculosis, to brief chapters that dis-export virulence factors. PAIs are present in the genome cuss cholera and E. coli O157 almost exclusively from of pathogenic bacteria but absent from nonpathogenic the perspective of the new discovery of mobile genetic members of the same or closely related species. Al-elements that contain almost all the genetic information though originally defined as chromosomal elements, it that make them pathogens (see the following review by is now apparent that regions of virulence plasmids also Finlay). The chapter on influenza by Robert Webster is constitute PAIs. The size of a PAI is usually relatively a model of clarity. All the chapters in both books are large, ranging from 10 to 200 kb. Small insertion se-well referenced. quences encoding single virulence factors are consid-Neither book is a comprehensive textbook of infec-ered islets, although they obviously share some proper-tious diseases, nor even a comprehensive treatise on ties with PAIs. " emerging infections. " Both are well-written and authori-A hallmark of PAIs is that their GϩC DNA content is tative texts that should provide readers with a starting usually quite different from the remainder of the genome, place to learn about these problems. Both are reminders indicating horizontal gene transfer as a mechanism of of Louis Pasteur's famous maxim, " Messieurs, c'est les acquisition. Because of their potential genetic mobility, microbes qui auront le denier mot. " they are often, but not always, flanked by …