When this paper was first published one conflict of interest statement was omitted from the section. The correct statement is printed below in full:
Conflict of interest statement
M.H.W. has received honoraria from the European Tissue Symposium (ETS) for microbiological advice and lectures, and travel expenses to attend meetings. F.B. has received honoraria from ETS for microbiological advice and travel expenses to attend meetings. S.B. has received honoraria from ETS for microbiological advice and travel expenses to attend meetings.