Gripping Tales of Bacterial Pathogenesis

Bacterial Adhesion to Host Tissues: Mechanisms and Consequences Edited by Michael Wilson Cambridge: Cambridge University Press (2002). 328 pp. $90.00There is one fact that reliably arouses amazed murmurs in an introductory microbiology audience: within the human body, microbes outnumber our own cells by at least one order of magnitude. When considering this extraordinary microbial burden, which is mostly comprised of bacteria, one gains a great appreciation for the interspecies crosstalk that continuously reverberates within us all. This crosstalk, at its best, can help shape our development and aid our digestive processes and, at its worst, can send us to an early grave. Whether a bacterium triggers illness or coexists peacefully within our system often depends on where a microbe is able to set up shop. Strains of Escherichia coli, for example, may be quite innocuous, and even beneficial, as part of the immense microflora of the human gut, but their presence within the bloodstream, brain, or urinary tract can have disastrous effects on the host. Arguably, the primary factors that dictate the tissue tropism of a microbe, and hence its capacity to cause disease, are its adhesive properties. Bacterial pathogens that can't stick to target cells and tissues are usually rapidly dispatched from the host.Adhesion does not occur by any protocol that is standardized among bacterial species or environmental situations. Bacteria produce a number of products that can mediate adherence, including proteins, lipopolysaccharides, and lipoteichoic acid. Adhesive molecules (adhesins) may be presented distally on hair-like fibers called pili (aka fimbriae) or directly expressed on the bacterial surface. Adhesins can interact with a wide range of host receptor proteins, glycoproteins, glycolipids, and other molecules on host cells, with extracellular matrix proteins, or even with organic and inorganic films deposited on teeth and medical implants. In order to bind, physical forces—van der Waals, hydrophobic, and electrostatic repulsions—must be overcome. Many bacteria make use of several structures to synergistically enhance adherence to a particular substrate, and may also encode within their genetic repertoire other sets of adhesins for binding alternate attachment surfaces. Adhesins can mediate interbacterial interactions as well, facilitating genetic exchange and biofilm formation.The attachment event can trigger dramatic responses in both bacterial and host cells that can directly impact the outcome of an infection. Bacterial attachment that results in the intimate positioning of bacterial components such as lipopolysaccharide near host cell receptors can simultaneously enhance both host inflammatory responses and bacterial expression of toxins and other virulence factors. Our bodies have evolved strategies to thwart bacterial attachment, such as lining the more vulnerable tissues with mucus and/or cilia, and continually shedding many mucosal and epithelial surfaces. Still, bacteria manage to find their way into niches that most of us would prefer remain sterile. With the increasing frequency of antibiotic-resistant bacterial infections, adhesion, the crucial first stage, is gaining increased attention from microbiologists and others interested in exploring new targets for preventing and treating major infections.During the 1990s, cellular microbiology emerged as a bona fide discipline, complete with its own specialized journals and symposia. This area of study, which is focused at the interface between cell biology and microbiology, aims to expand our understanding of how bacteria manage to live and thrive within host cells and tissues. Now, into the midst of this explosive field comes Bacterial Adhesion to Host Tissues, the first book in a series entitled Advances in Molecular and Cellular Microbiology. This book has the ambitious goal of defining the mechanisms and consequences of bacterial adherence, providing both a broad view and an examination of current research.The book covers a variety of gram-negative and gram-positive organisms that target the skin, oral cavity, respiratory tract, gut, and urogenital tract with varying degrees of pathogenicity. As a whole, this work does provide a reasonable overview of bacterial adhesion. However, there is little sense of cohesion and a notable amount of redundancy between chapters. Often, we felt as if we were reading loosely connected back-to-back review articles pulled from PubMed. Each chapter, to the authors' credit, stands on its own and most provide some genuinely fascinating information. The book also benefits from a number of exceptional diagrams and micrographs. However, several hoped-for figures appear too late, not at all, or with only the blurry quality of Sasquatch-sighting photos.A great deal of ink is used describing the regulation of adhesin-coding genes. Though this is certainly interesting and valuable information to researchers in the field, more detail on the adhesins themselves would have been useful. Particularly noticeable is a paucity of discussion on the wealth of detailed adhesin structural data that now exists. In the past eighteen months, for example, high-resolution structures of the adhesins internalin A and B of Listeria monocytogenes (Schubert et al., J. Mol. Biol. 312, 783–794, 2001) and PapGII of uropathogenic E. coli (Dodson et al., Cell 105, 733–743, 2001; Sung et al., EMBO Rep. 7, 621–627, 2001) have been reported. These and similar biophysical data provide detailed insight into how adhesion occurs at the molecular level, and a more extensive discussion regarding structure-function analyses would have been welcome.This volume does present a wealth of useful and at times intriguing information. Its major problem is not content, but packaging. As it stands, one of the most useful features of the book is probably its index; it will be handy for finding a quick reference to a description of an injectisome, or the hemagglutinating properties of various pathogens. With increased introductory information, some improved graphics, and perhaps some revision to improve overall flow, it could become a far more readable, and thus more thoroughly usable, work.