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J. Bacteriol., 04 1996, 1788-1792, Vol 178, No. 7
A Severin, AM Figueiredo and A Tomasz
Compared with most penicillin-susceptible isolates of Streptococcus
pneumoniae, penicillin-resistant clinical isolate Hun 663 contains mosaic
penicillin-binding protein (PBP) genes encoding PBPs with reduced
penicillin affinities, anomalous molecular sizes, and also cell walls of
unusual chemical composition. Chromosomal DNA prepared from Hun 663 was
used to transform susceptible recipient cells to donor level penicillin
resistance, and a resistant transformant was used next as the source of DNA
in the construction of a second round of penicillin-resistant
transformants. The greatly reduced penicillin affinity of the
high-molecular-weight PBPs was retained in all transformants through both
genetic crosses. On the other hand, PBP pattern and abnormal cell wall
composition, both of which are stable, clone-specific properties of strain
Hun 663, were changed: individual transformants showed a variety of new,
abnormal PBP patterns. Furthermore, while the composition of cell walls
resembled that of the DNA donor in the first-round transformants, it became
virtually identical to that of susceptible pneumococci in the second-round
transformants. The findings indicate that genetic elements encoding the low
affinity of PBPs and the penicillin resistance of the bacteria are
separable from determinants that are responsible for the abnormal cell wall
composition that often accompanies penicillin resistance in clinical
strains of pneumococci.
Copyright © 1996, American Society for Microbiology
Separation of abnormal cell wall composition from penicillin resistance through genetic transformation of Streptococcus pneumoniae
Laboratory of Microbiology, The Rockefeller University, New York, New York, USA.
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