Time to acquire and lose carriership of ESBL/pAmpC producing E. coli in humans in the Netherlands

A subset of the study population from a cross–sectional study of carriership of ESBL/pAmpC–producing E. coli (ESBL–E) in the general population was followed up by five successive samples over an approximate half year period, leading to six samples in 333 persons. Fecal samples were cultured and analyzed for the presence of E. coli types as characterized by MLST, and ESBL/pAmpC genes were analysed by PCR and sequencing. The study included 255 persons who had a negative first sample, to allow observations of acquiring carriership of ESBL–E. Any individual record thus consisted of a series of snapshots of episodes of presence and absence of ESBL–E carriage. A survival model was built to estimate times to acquire or lose carriership, allowing for any combination of ESBL/pAmpC gene and E. coli MLST type. In carriers, the mean time to lose carriership was 1.1 (95% range 0.8–1.6) years. The estimated mean time to acquire carriership was 3.0 (95% range 1.6–6.3) years. Analysis of these times by ESBL/pAmpC gene found substantial variation among resistance genes both in persistence of carriership and in rates of acquiring carriership: bla(CTX-M-1), bla(CTX-M-14), bla(CTX-M-15), bla(CTX-M-27) and bla(SHV-12) were easily acquired, but bla(CTX-M-1) and bla(SHV-12) were also easily lost, while bla(CTX-M-15), bla(CTX-M-27) and bla(CMY-2) were more likely to persist. When in addition bacterial host types were included, some combinations appeared more persistent than others (bla(CTX-M-1) in ST10 and ST58; bla(CTX-M-14), bla(CMY-2), and bla(SHV-12) in ST69), or were acquired with higher frequency (bla(CTX-M-14) in ST38, ST69, and ST131; bla(CTX-M-15) and bla(CTX-M-27) in ST131; bla(SHV-12) in ST69). The relatively short duration of carriership means that when an intervention drastically reduces the exposure of humans to ESBL-E, the prevalence will be halved in 0.66 years. The observed differences between carriage rates of ESBL/pAmpC genes and E. coli strains need further investigation.