Distribution of the mosaic structured murM genes among natural populationsof Streptococcus pneumoniae

The presence and sequence variation of the murM gene were studied in a larg e collection (814 strains) of genetically diverse Streptococcus pneumoniae isolates, which included 27 different serogroups and both penicillin-resist ant (423 isolates, 67 pulsed-field gel electrophoretic [PFGE] types) and in termediately penicillin-resistant (165 isolates, 66 PFGE types) and penicil lin-susceptible (226 isolates, 135 PFGE types) strains. Diversity of the mu rM sequences was tested by hybridization with mainly two kinds of probes: o ne derived from the amplification of the nucleotide sequence between nucleo tides 201 and 624 in the penicillin-susceptible laboratory strain R36A (mur MA probe) and a second probe that amplified the comparable, highly divergen t sequence in the penicillin-resistant strain Pen6 (murMB probe). The great majority of the strains (761 of 814), including both penicillin-susceptibl e and penicillin-resistant isolates, reacted exclusively with the murMA pro be. A smaller group of penicillin-resistant strains (48 of 814 isolates) re acted only with the murMB DNA probe, and an additional 5 isolates reacted w ith both probes. High-pressure liquid chromatography analysis of the peptid oglycan of strains hybridizing with murMB showed that they invariably conta ined an increased proportion of branched peptides, Complete sequencing of m urM from a group of penicillin-resistant isolates allowed the identificatio n of a number of different murMB alleles that differed in the length and ex act position of the divergent (Pen6 type) sequences within the particular m urM. The close similarity of these divergent sequences in the various murM alleles suggests a possible common heterologous origin.