VANCOMYCIN-RESISTANT LEUCONOSTOC-MESENTEROIDES AND LACTOBACILLUS-CASEI SYNTHESIZE CYTOPLASMIC PEPTIDOGLYCAN PRECURSORS THAT TERMINATE IN LACTATE

The emergence of acquired high-level resistance among Enterococcus spe cies has renewed interest in mechanisms of resistance to glycopeptide antibiotics in gram-positive bacteria. In Enterococcus faecalis and En terococcus faecium, resistance is encoded by the van gene cluster and is due to the production of a peptidoglycan precursor terminating in D -alanyl-D-lactate, to which vancomycin does not bind. Most Leuconostoc and many Lactobacillus species are intrinsically resistant to high le vels of glycopeptide antibiotics, but the mechanism of resistance has not been elucidated. To determine whether the mechanisms of resistance are similar in intrinsically resistant bacteria, cytoplasmic peptidog lycan precursors were isolated from Leuconostoc mesenteroides and Lact obacillus casei and analyzed by mass spectrometry, revealing structure s consistent with lmuramyl-L-Ala-D-GIU-L-LYs-(L-Ala)-D-Ala-D-lactate a nd N-acetylmuramyl-L-Ala-D-Glu-L-Lys-D-Ala-D-lactate, respectively.