Apparently between 1980 and 1984, Cyprinodon variegatus was introduced into an area of the Pecos River in Texas, where it hybridized with an endemic species, C. pecosensis. Protein electrophoresis indicated that, by 1985, panmictic admixtures of these two pupfishes occupied approximately 430 river-kilometers of the Pecos River, roughly one-half of the historic range of the endemic species. The average frequency of introduced alleles at four diagnostic loci ranged from 0.18 to 0.84 at the 15 sites sampled from the Pecos River in Texas. Clinal patterns in allele frequencies suggest that C. variegatus was introduced into a mid-reach of the river and that this was followed by both upstream and downstream dispersal of the introduced alleles. All pairwise combinations of loci showed significant linkage disequilibrium. The level of disequilibrium indicates chromosomal linkage for one gene-pair, Gpi-A and Est-1. The change in pupfish allele frequencies in the Pecos River represents an extreme example of rapid natural selection in a seminatural situation.

SUMMARYBackground SPD476 (MMX TM mesalazine), is a novel, once daily, high-strength mesalazine formulation (1.2 g/tablet) that utilizes Multi Matrix System TM (MMX) technology to delay and extend delivery of the active drug throughout the colon.

Although colonization of atopic dermatitis by Staphylococcus aureus is universal and bacterial infection is common, it is not known whether antibiotic therapy is helpful in eczematous children who do not have any signs suggestive of bacterial infection. Fifty children aged 1-16 years with atopic dermatitis took part in a randomized double-blind placebo-controlled study of 4 weeks treatment with oral flucloxacillin, with an 8-week follow-up period. The change in the mean of the log10 of the counts/cm2 of S. aureus after 4 weeks of treatment was significantly different for patients receiving treatment, compared with the change for those receiving the placebo (P = 0.008). However, the difference in the change at 14 days after stopping treatment was not significant (P = 0.32). Methicillin-resistant strains of S. aureus were cultured from five children during or after treatment. Flucloxacillin did not improve the symptoms or clinical appearance of atopic dermatitis and only temporarily changed skin colonization by S. aureus.

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