  As part of the VLT/X-shooter science verification, we obtained the first
optical medium-resolution spectrum of a previously identified bright O-type
object in NGC55, an LMC-like galaxy at a distance of \sim2.0 Mpc. Based on the
stellar and nebular spectrum, we investigate the nature and evolutionary status
of the central object(s) and its influence on the surrounding interstellar
medium. We conclude that the source, NGC55_C1_31, is a composite object, likely
a stellar cluster, which contains one or several hot (T_eff \simeq 50000 K) WN
stars with a high mass-loss rate (\sim3 \times 10^{-5} M_\odot yr^{-1}) and a
helium-rich composition (N_He/N_H = 0.8). The visual flux is dominated by
OB-type (super)giant stars with T_eff \sim< 35000 K, solar helium abundance
(N_He/N_H = 0.1), and mass-loss rate \sim2 \times 10^{-6} M_\odot yr^{-1}. The
surrounding H II region has an electron density n_e < 10^2 cm^{-3} and an
electron temperature T(OIII) \simeq 11500 \pm 600 K. The oxygen abundance of
this region is [O/H] = 8.18 \pm 0.03 which corresponds to Z = 0.31 \pm 0.04
Z_\odot. We observed no significant gradients in T(OIII), n_e or [O/H] on a
scale of 73 pc extending in four directions from the ionising source. The
properties of the HII region can be reproduced by a CLOUDY model which uses the
central cluster as ionising source, thus providing a self-consistent
interpretation of the data. We also report on the serendipitous discovery of
HeII nebular emission associated with the nearby source NGC55_C2_35, a feature
usually associated with strong X-ray sources.
