Liu and Wang (27), another 3 new serotypes were added to the scheme. Until recently, serotyping of P. aeruginosa was largely done by using rabbit antisera raised against each of the serotypes. The use of these typing sera has certain disadvantages, including variability from batch to batch and a high incidence of cross-reactivity. Even after extensive cross absorptions, cross-reactions among closely related serotypes could be observed (10,32 aeruginosa, it became apparent that these cross-reactions could be attributed to the similarities in the chemical structure of the 0-antigen repeats common to all strains of the same group. Among 02, 05, and 016 serotypes, the 0 antigens share a trisaccharide repeating unit which consists of two uronic acid derivatives and one N-acetyl fucosamine residue (Fig. 1). These three serotypes were designated by Lanyi and Bergan (25) the 3-acetamidino-2-acetamido-2,3-dideoxy-D-mannuronic acid residue. Serotype differences among strains in this group were believed to be caused by configurational variations in the diacetamidohexuronic acid and the glycosidic bond of N-acetyl fucosamine (15). In order to improve the efficiency of serotyping P. aeruginosa, monoclonal antibodies (MAbs) would be a logical alternative to the polyclonal antisera. Gaston et al. (7)

A-band, a D-rhamnose-containing common lipopolysaccharide antigen isolated from Pseudomonas aeruginosa AK1401, was found to be a receptor for bacteriophage A7. The phage-borne rhamnanase was capable of hydrolyzing the A-band to expose core-lipid A containing only two or three rhamnose repeats. Interaction of the hydrolyzed A-band with core-or lipid A-specific monoclonal antibodies revealed that common epitopes exist in the inner core and lipid A regions, while the outer core of A-band appears to be different from that of the serotype-specific (B-band) lipopolysaccharide.Lipopolysaccharide (LPS), a major component of the gram-negative outer membrane (17), is composed of heteropolysaccharide covalently linked to lipid A (9, 21). The heteropolysaccharide consists of three regions: a diglucosamine backbone, the oligosaccharide core, and the 0-antigenic polysaccharide chain. Specific structures within the LPS molecule serve as receptors for a variety of bacteriophages (15,29). Phage adsorption to its receptor is highly specific (15). Phage resistance that results from changes in LPS structure usually indicates that the LPS is the surface receptor (29), and the structural change identifies the region of the LPS comprising the receptor. Since the structure of the 0-serotype-specific antigen varies from strain to strain, the host range of a phage whose receptor is the 0 polysaccharide is rather narrow (9,15). One characteristic of 0-specific phage is that during infection they often hydrolyze the 0 antigen, destroying the initial receptor (29). In many strains of Pseudomonas aeruginosa, a second LPS species whose polysaccharide chain differs serologically and structurally from the 0-antigen chain is present (10, 14, 16, 22-24, 30, 31). This LPS has been termed A-band or common antigen LPS. The common antigen polysaccharide of P. aeruginosa is a regular homopolymer of rhamnose. On the basis of nuclear magnetic resonance and chemical analyses, the structure has been shown to consist of the repeating unit (2,10,30,31). Interestingly, the structure proposed for the repeating unit of the rhamnan chain in the common antigen LPS of P. aeruginosa is identical to that reported for the O-polysaccharide chain in the LPS of Pseudomonas syringae pv. morsprunorum C28 (26).The 0 polysaccharide of P. syringae pv. morsprunorum C28 LPS, which is composed entirely of rhamnose (26), is specifically cleaved and released as oligosaccharides by the action of a rhamnanase borne on the typing phage A7 (25). This phage uses the LPS as its initial binding site (20,25). Thus, it is expected that the common antigen (A-band) LPS from P. aeruginosa will also serve as a substrate for phage A7. This phage will serve as a tool to remove the polyrhamnose chain from the A-band LPS for detailed analysis of the core and lipid A of this molecule. In this report, we present evidence to show that phage A7 binds to and hydrolyzes the * Corresponding author. polyrhamnose chain of the A-band LPS from P. aeruginosa AK1401 and that the phage-digested A-band LPS ca...