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Antimicrob. Agents Chemother., Oct 1997, 2121-2126, Vol 41, No. 10
JP Maskell, AM Sefton and LM Hall
The genetic basis of sulfonamide resistance in six clinical isolates of
Streptococcus pneumoniae was demonstrated to be 3- or 6-bp duplications
within sulA, the chromosomal gene encoding dihydropteroate synthase. The
duplications all result in repetition of one or two amino acids in the
region from Arg58 to Tyr63, close to but distinct from the sul-d mutation,
a duplication previously reported in a resistant laboratory strain (P.
Lopez, M. Espinosa, B. Greenberg, and S. A. Lacks, J. Bacteriol.
169:4320-4326, 1987). Six sulfonamide-susceptible clinical isolates lacked
such duplications. The role of the duplications in conferring sulfonamide
resistance was confirmed by transforming 319- or 322-bp PCR fragments into
the chromosome of a susceptible recipient. Two members of a clone of
serotype 9V, one susceptible and one resistant to sulfonamide, which are
highly related by other criteria, were shown to have sulA sequences that
differ in 7.2% of nucleotides in addition to the duplication responsible
for resistance. It is postulated that horizontal gene exchange has been
involved in the acquisition (or loss) of resistance within this clone.
However, five of the six resistant isolates have distinct duplications and
other sequence polymorphisms, suggesting that resistance has arisen
independently on many occasions.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Mechanism of sulfonamide resistance in clinical isolates of Streptococcus pneumoniae
Department of Medical Microbiology, St. Bartholomew's and the Royal London School of Medicine and Dentistry, United Kingdom. J.Maskell@mds.qmw.ac.uk
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