pkspositive

pkspositive refers to bacterial strains that carry the pks genomic island, a polyketide synthase (PKS) gene cluster that enables the production of the genotoxin colibactin. The term is used in microbiology to denote isolates with this island, most commonly in Escherichia coli but also detected in related Enterobacteriaceae. Presence of the island indicates potential for colibactin production, though actual expression can vary with environmental conditions and regulatory factors.

The pks island is approximately 54 kilobases in size and contains the clb gene set (such as clbA through clbS), which encodes enzymes that assemble and modify colibactin precursors. The island is often integrated at asn tRNA loci and can be transferred between bacteria via horizontal gene transfer. Expression of the pathway is regulated, and not all pkspositive strains produce detectable levels of colibactin in a given environment.

Colibactin is a DNA-damaging natural product that can alkylate DNA and induce double-strand breaks in host cells, triggering DNA damage responses and cell cycle effects in vitro. In animal models, pkspositive bacteria can increase intestinal DNA damage. The role of pks islands in human disease is an area of active research, with associations reported between pkspositive bacteria and colorectal cancer risk and other inflammatory conditions, though causality has not been established.

Detection of pks status is typically done by molecular methods targeting clb genes (for example clbB or clbN) or by whole-genome sequencing. pkspositive strains are enriched in certain E. coli lineages, particularly phylogroup B2, and their prevalence varies by population and sampling. The concept remains important for understanding host-microbiome interactions and potential disease implications.