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Natural products produced by biological organisms have played an important role in human health. The genomes of several Aspergillusspecies and several Streptomycesspecies have recently been sequenced. Interestingly the genomes revealed a large range of secondary metabolite genes, for many of which the products are currently unknown, suggesting that there is a wealth of secondary metabolites yet to be discovered. This brief review will discuss the current knowledge in polyketides produced by the various different classes of polyketide synthases (PKSs) present in the Aspergillusand Streptomycesgenomes.

Heterologous expression of the minimal oxytetracycline polyketide synthase and the amidotransferase OxyD in Streptomyces coelicolorstrain CH999 afforded two novel amidated polyketides, WJ85 (4) and WJ85b (5). WJ85 is a C-9 unreduced decaketide that is primed by a malonamyl starter unit. WJ85 is cyclized via an unusual C-11 to C-16 intramolecular aldol condensation not observed among known aromatic polyketides. The structures of WJ85 and the previously characterized WJ35 suggest that the presence of an amide starter unit has a profound effect on the cyclization regioselectivity and reactivity of a polyketide backbone. WJ85b is an anthraquinone and is an oxidized product of WJ85.

Ninety-three clinical isolates of vancomycin-resistant enterococci (VRE) collected from nine hospitals in Taiwan were examined for the presence of vanA, vanB, vanC1, or vanC2/vanC3 genes by a multiplex PCR. Forty-seven of these VRE isolates were vanA positive, 1 contained both vanC1 and vanA, 40 harboured vanB, 2 were vanC1, and 3 were identified to be vanC2/vanC3. Twenty-four vanA isolates were sensitive to teicoplanin and thus did not have a typical VanA phenotype. Five isolates with the VanC phenotype harboured vanB. None of the 40 clinically isolated vancomycin-susceptible E. faecium or E. faecalis and the vancomycin-resistant Leuconostoc and Pediococcus isolates were positive for any of the van genes. While performing nosocomial surveillance, VRE were isolated from 47 of 467 rectal swabs by culture. Compared with the conventional culture method, the sensitivity and specificity of the multiplex PCR for detecting and identifying vancomycin-resistance genes in enterococci directly from culture-positive broth were 97·9% and 100%, respectively. The results suggest that genotypic characterization of vancomycin-resistance is necessary for all clinical VRE isolates and that the multiplex PCR assay can be an alternative method for this purpose.