The colonization dynamics of Moraxella catarrhalis were studied in a population comprising 1079 healthy children living in Rotterdam, The Netherlands (the Generation R Focus cohort). A total of 2751 nasal swabs were obtained during four clinic visits timed to take place at 1.5, 6, 14 and 24 months of age, yielding a total of 709 M. catarrhalis and 621 Haemophilus influenzae isolates. Between January 2004 and December 2006, approximate but regular 6-monthly cycles of colonization were observed, with peak colonization incidences occurring in the autumn/winter for M. catarrhalis, and winter/spring for H. influenzae. Co-colonization was significantly more likely than single-species colonization with either M. catarrhalis or H. influenzae, with genotypic analysis revealing no clonality for co-colonizing or single colonizers of either bacterial species. This finding is especially relevant considering the recent discovery of the importance of H. influenzae-M. catarrhalis quorum sensing in biofilm formation and host clearance. Bacterial genotype heterogeneity was maintained over the 3-year period of the study, even within this relatively localized geographical region, and there was no association of genotypes with either season or year of isolation. Furthermore, chronological and genotypic diversity in three immunologically important M. catarrhalis virulence genes (uspA1, uspA2 and hag/mid ) was also observed. This study indicates that genotypic variation is a key factor contributing to the success of M. catarrhalis colonization of healthy children in the first years of life. Furthermore, variation in immunologically relevant virulence genes within colonizing populations, and even within genotypically identical M. catarrhalis isolates, may be a result of immune evasion by this pathogen. Finally, the factors facilitating M. catarrhalis and H. influenzae co-colonization need to be further investigated. INTRODUCTIONMoraxella catarrhalis is part of the normal bacterial flora in the nasopharynx of children, although over the past two decades, it has emerged as a significant bacterial pathogen and not simply a commensal colonizer (Verduin et al., 2002). Studies have shown that the bacterium rapidly colonizes the nasopharynx soon after birth and that the carriage rate of M. catarrhalis in healthy children varies between 7 and 36 % (Verhaegh et al., 2010). However, in children with upper respiratory tract infections (URTI), including acute otitis media (AOM), the carriage rate increases to approximately 50 % (Berner et al., 1996;Konno et al., 2006;Pettigrew et al., 2008). Otitis media itself is a particularly important URTI during early Abbreviations: AOM, acute otitis media; CEACAM, carcinoembryonic antigen-related cell adhesion molecule; LOS, lipooligosaccharide; MLST, multilocus sequence typing; OMP, outer-membrane protein; OR, odds ratio; OMV, outer-membrane vesicle; URTI, upper respiratory tract infection. childhood and the primary reason for children to visit a physician (Freid et al., 1998;Plasschaert et al., 2006). Furt...

Investigations into the genetic basis of reproductive barriers among recognized and putative varieties in Phacelia dubia have provided evidence that even among closely related taxa, multiple pathways can lead to reproductive isolation. A nuclear-based reproductive barrier, expressed as partial hybrid sterility of both pollen and ovules, isolated each pair of recognized varieties. There was no evidence of pre-or post-fertilization barriers; all reproductive barriers were manifested as hybrid gametic sterility. Reproductive relationships of two putative varieties were studied to examine the early stages of reproductive isolation in this group. Both putative varieties exhibited partial reproductive isolation from the recognized varieties in spite of their lack of morphological differentiation from recognized varieties. The barrier isolating one putative variety was similar to the barrier among recognized varieties. The second putative variety and a recognized variety were partially isolated by a unidirectional, nuclear-cytoplasmic barrier that reduced only pollen fertility. The nuclear-cytoplasmic barrier suggested a new application of Haldane's rule.

For neutral genes, uniparental inheritance is expected to reduce e ective population size relative to biparentally inherited genes. In ®nite populations, the ensuing genetic drift can cause stronger spatial and temporal di erentiation. An intrapopulation polymorphism in chloroplast DNA was used to examine relative spatial and temporal population structure of chloroplast and allozyme markers in the annual plant Phacelia dubia. There was signi®cant di erentiation among populations at chloroplast markers but not for allozyme loci. A ®ne-scale analysis showed signi®cant structure among sites within populations for chloroplast markers and local heterozygote de®ciencies at allozyme loci. These spatial analyses suggest that gene¯ow via pollen exceeds that via seed. Temporal variation in chloroplast markers, assessed over a 10-year period, was evident in two of four populations, and allozyme loci were characterized by temporal variation in rare-allele frequencies. Population structure appeared to be related to the intensity and type of human disturbance in¯uencing each population. Habitat destruction promoted isolation and enhanced di erentiation, whereas mowing increased seed dispersal and reduced di erentiation for chloroplast markers. At this time, genetic drift appears to be the primary force shaping chloroplast gene frequencies.

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Methods: One thousand four hundred and forty M. catarrhalis isolates originating from seven world regions were investigated. The isolates were recovered from 411 children ,5 years of age and 1029 adults .20 years of age. PCR-restriction fragment length polymorphism (RFLP) was performed to determine bro prevalence and to distinguish between bro types. MIC values of 12 different antibiotics were determined using the CLSI (formerly NCCLS) broth microdilution method.Results: Of the 1440 isolates, 1313 (91%) possessed the bro-1 gene and 64 (4%) possessed the bro-2 gene. Additionally, the prevalence of bro positivity between the child and adult age groups was significantly different (P,0.0001), though bro-1 and bro-2 prevalences within age groups were not significantly different. Consistently higher b-lactam MICs were observed for M. catarrhalis isolates originating in the Far East. Significant correlations in MICs were observed for several antibiotic combinations, including all five b-lactams with each other, and among the two quinolones. Conclusions:The worldwide prevalence of bro gene carriage in clinical isolates of M. catarrhalis is now approaching 95%, with children significantly more likely to harbour bro-positive isolates than adults. Further, statistically significant differences in the distribution of b-lactam MICs were observed between different world regions, particularly with respect to the Far East.