FIG 1.

(A) MALDI-TOF MS spectra obtained for a single strain of E. coli grown on different media. The top spectrum shows results obtained after culture on Columbia–5% sheep blood agar, whereas the data shown below were from cells grown on Drigalski agar. (B) Theoretical representation of a PFGE gel after staining. Restriction fragments are visible, and differences between the individual lanes can be explained on the basis of presumed genetic events which are indicated on the right. Based on theoretical exercises such as the one presented, adapted from Tenover et al. (3), rules suggesting that up to three fragment differences can be ignored in order to still define clear epidemiological relatedness were developed. (C) The MALDI-TOF MS analogs for the PFGE data displayed in panel B. Fragments have been translated into peaks, and the events potentially leading to changes from the reference spectrum in row A are proposed (left). This relates to the emergence and disappearance of protein peaks and distinct shifts in protein peaks for various (epi)genetic reasons.