Jeffries, J

Jeffries, J. accumulated in bacterial populations during selection with this antibody. Strain 8047 was outcompeted in this assay by the 8047 strain due to the elevated PV rate of this mismatch repair mutant and hence the greater proportion of preexisting phase variants of in the inoculum. This mutant was also more virulent than strain 8047 during escape from passive protection by MAb B5 in an in vivo infant rat model of bacteremia. These results provide an example of how PV rates can modulate the occurrence and severity of infection and have important implications for understanding the evolution of bacterial fitness in species subject to environmental variations that occur during persistence within and transmission between hosts. One determinant of the mutation rate of a DNA molecule is the PSI-7977 nucleotide sequence (8). Evolution has acted on this intrinsic feature of different DNA sequences to focus the production of genetic variation in regions of genomes subject to intense environmental selection (28). One outcome of such localized hypermutation is phase variation (PV) (27, 40) or the rapid and reversible generation of variants exhibiting different expression states (e.g., on and off) of a particular phenotype. Mutations in simple sequence repeat tracts, also termed microsatellites, are a widespread mechanism responsible for PV and are thought to mediate adaptation to specific environmental alterations (6). The mutation rates of these repeat tracts are likely, therefore, to PSI-7977 have a major impact on the fitness of the bacterial commensals and pathogens in which this mechanism of PV occurs. is a PSI-7977 commensal of the upper respiratory tract of humans and has the potential to cause serious invasive diseases, such as septicemia and meningitis. Like CBFA2T1 a number of other pathogens and commensals, this species contains multiple loci (40 loci/genome) which are subject to PV due to simple sequence repeat tracts (26, 39). Most of these loci encode surface proteins (e.g., adhesins, iron acquisition proteins, and porins) or enzymes involved in biosynthesis of surface molecules, such as lipopolysaccharide (LPS) (18, 37). The fitness advantages associated with the different PV states (on and off) have been demonstrated for some of these loci and include significant roles in adhesion, resistance to the bactericidal activities of human serum, iron acquisition, and other phenotypes critical for host adaptation (references 5, 27, 33, and 40 and references therein). In many cases, it is assumed that specific antibodies drive selection for one of the PV states (usually the off phenotype). While PV can mediate evasion of antibody-mediated killing (for example, PV of LPS sialylation that results in general resistance to antibody-mediated killing due to dysfunctional activation of complement [41]), escape due to alterations in the structure or expression of the binding site for a specific antibody is also likely to be important. Escape from specific antibodies by PV in has not been robustly documented even though bactericidal antibodies are associated with protection against this pathogen and antibodies specific for phase-variable surface structures are present in sera from patients and carriers (7, 17, 19, 21, 29). A major determinant of adaptation by PV is likely to be the rate of generation of phase variants. The majority of the phase-variable loci of meningococci contain poly(C) or poly(G) tracts consisting of more than seven repeat units whose mutation rates are controlled by the mismatch repair proteins MutS and MutL (25, 26, 34). High numbers of mismatch repair mutants with elevated PV rates have been observed among epidemic isolates of serogroup A strains of (35). This finding was interpreted as an indication that a meningococcal mutator phenotype increases the transmission and spread of this bacterial pathogen during epidemics. Monoclonal antibody (MAb) B5 (also designated L3B5) recognizes an inner core LPS epitope and has an absolute requirement for a phosphoethanolamine (PEtn) moiety attached at the 3 position of the second heptose (PEtn-3) (32). Attachment of PEtn is mediated by the product of (22). Binding of MAb B5 to the LPS of some meningococcal strains is subject to PV, and for strain BZ157, loss of binding was correlated with alterations to an in-frame number of repeats PSI-7977 in the mononucleotide repeat tract of (22). The gonococcal gene is 96% identical to the gene and mediates the phase-variable addition of a glucose to the 3 position of the second heptose (4). Attachment of this glucose prevents addition of PEtn-3 such that a gain of expression of is associated with loss of the MAb B5 epitope. Some meningococcal isolates are subject to MAb B5-mediated bactericidal activity and opsonophagocytosis, and these activities are most pronounced in strains, such as 8047, which possess truncated LPS glycoforms and PEtn-3 (31). In addition, MAb B5 was demonstrated to protect infant rats against challenge with strain 8047 (31). Antibodies specific.