ASSOCIATION OF A THR-371 SUBSTITUTION IN A CONSERVED AMINO-ACID MOTIFOF PENICILLIN-BINDING PROTEIN 1A WITH PENICILLIN RESISTANCE OF STREPTOCOCCUS-PNEUMONIAE
Y. Asahi et K. Ubukata, ASSOCIATION OF A THR-371 SUBSTITUTION IN A CONSERVED AMINO-ACID MOTIFOF PENICILLIN-BINDING PROTEIN 1A WITH PENICILLIN RESISTANCE OF STREPTOCOCCUS-PNEUMONIAE, Antimicrobial agents and chemotherapy, 42(9), 1998, pp. 2267-2273
We determined the nucleotide sequence between 1,903 and 3,097 bp of pb
p1a, which encodes the transpeptidase domain of PBP 1A, from clinical
isolates of penicillin-resistant Streptococcus pneumoniae (PRSP) serot
ypes 19 (n = 8), 6 (n = 9), 23 (n = 6), and 14 (n = 2) and two penicil
lin-susceptible S. pneumoniae (PSSP) isolates. These serotyped PRSP st
rains were isolated predominantly in Japan from 1993 through 1997. The
25 resistant strains were classified into five groups on the basis of
the extent of sequence differences. Strains in groups I (n = 5; serot
ype 6), II (n = 3; serotype 19), and III (n = 12; different serotypes)
had sequences highly homologous to the sequence of pbp1a of PRSP stra
ins from South AG-ica, Spain, and the United States. The group TV stra
in (n = 1; serotype 14) had unique deletions from or insertions in the
sequences. The sequences of group V strains (n = 4; serotypes 6 and 2
3) had relatively few differences from the sequences of the PSSP strai
ns. For strains (n = 18) for which the threonine at codon 371 (Thr-371
) in a conserved STMK motif of PBP 1A was substituted with an alanine
or a serine (in addition to having altered pbp2x and pbp2b genes), pen
icillin MICs were greater than or equal to 1.0 mu g/ml. The PBPs 1A of
these strains showed decreased affinities for [H-3]benzylpenicillin a
nd slightly faster mobilities on sodium dodecyl sulfate-polyacrylamide
gels. In contrast, for strains (n = 4) without a substitution at Thr-
371 in PBP 1A but with mutations in both pbp2x and pbp2b, penicillin M
ICs were 0.125 to 0.25 mu g/ml, and the affinities of their PBPs 1A we
re similar to that of PSSP PBPs LA. Furthermore, for the Thr-371-subst
ituted strains (n = 3) with altered pbp2x genes but native pbp2b genes
, penicillin MICs were 0.125 to 0.25 mu g/ml. These results suggest th
at amino acid substitution of Thr-371 contributes to the development o
f penicillin resistance in PRSP strains with altered pbp2x and pbp2b g
enes.