Levofloxacin extended prophylaxis (LEP), recommended in oncohaematological neutropenic
patients to reduce infections, might select resistant bacteria in the intestine acting
as a source of endogenous infection. In a prospective observational study we evaluated
intestinal emergence and persistence of ampicillin-resistant Enterococcus faecium
(AREfm), a marker of hospital adapted high-risk clones. AREfm was recovered from the
faeces of 52 patients with prolonged neutropenia after chemotherapy, at admission
(Basal), during LEP, and twice weekly until discharge (Pos-LEP). Antibiotic susceptibility,
virulence traits and population structure (pulsed-field gel electrophoresis and multilocus
sequence typing) were determined and compared with bacteraemic isolates. Gut enterococcal
population was monitored using a quantitative PCR quantification approach. AREfm colonized
61.4% of patients (194/482 faecal samples). Sequential AREfm acquisition (25% Basal,
36.5% LEP, 50% Pos-LEP) and high persistent colonization rates (76.9-89.5%) associated
with a decrease in clonal diversity were demonstrated. Isolates were clustered into
24 PFGE-patterns within 13 sequence types, 95.8% of them belonging to hospital-associated
Bayesian analysis of population structure subgroups 2.1a and 3.3a. Levofloxacin resistance
and high-level streptomycin resistance were a common trait of these high-risk clones.
AREfm-ST117, the most persistent clone, was dominant (60.0% isolates, 32.6% patients).
It presented esp gene and caused 18.2% of all bacteraemia episodes in 21% of patients
previously colonized by this clone. In AREfm-colonized patients, intestinal enrichment
in the E. faecium population with a decline in total bacterial load was observed.
AREfm intestinal colonization increases during hospital stay and coincides with enterococci
population enrichment in the gut. Dominance and intestinal persistence of the ST117
clone might increase the risk of bacteraemia.