Pathogenicity Island Markers, Virulence DeterminantsmalXandusp, and the Capacity ofEscherichia coliTo Persist in Infants' Commensal Microbiotas

Abstract

ABSTRACTVirulence-associated genes in bacteria are often located on chromosomal regions, termed pathogenicity islands (PAIs). Several PAIs are found inEscherichia colistrains that cause extraintestinal infections, but their role in commensal bowel colonization is unknown. Resident strains are enriched in adhesins (P fimbriae and type 1 fimbriae), capsular antigens (K1 and K5), hemolysin, and aerobactin and mostly belong to phylogenetic group B2. Here, we investigated whether six pathogenicity islands and the virulence determinantsmalXanduspare associated with fitness ofE. coliin the infant bowel microbiota.E. colistrains isolated from stools of 130 Swedish infants during the first year of life were examined for their carriage of PAI markers,malX, anduspby PCR. Carriage was related to strain persistence: long-term colonizers (≥12 months) carried significantly more of PAI II from strain CFT703 (IICFT703), IV536,and IIJ96andmalXanduspthan intermediate colonizers (1 to 11 months) and transient strains (<3 weeks). The accumulation of PAI markers in each individual strain correlated positively with its time of persistence in the colon. Phylogenetic group B2 accounted for 69% of long-term colonizers, 46% of intermediate colonizers and 14% of transient strains. These results support the hypothesis that some bacterial traits contributing to extraintestinal infections have in fact evolved primarily because they increase the fitness ofE. coliin its natural niche, the colon; accordingly, they may be regarded as fitness islands in the gut.