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Antimicrobial Agents and Chemotherapy, June 2000, p. 1575-1577, Vol. 44, No. 6
Institut National de la Santé et de la
Recherche Médicale, EMI-U 9933, Hôpital Bichat-Claude
Bernard, 75877 Paris Cedex 18, France
Received 26 July 1999/Returned for modification 26 November
1999/Accepted 17 March 2000
We examined the relationship between penicillin susceptibility,
peritoneal virulence in Swiss mice, and capsular type in a selection of
122 clinical Streptococcus pneumoniae isolates belonging to
24 serotypes. Regardless of the serotype, all 32 virulent strains were susceptible to penicillin, and all 41 strains with diminished susceptibility or resistance to penicillin were avirulent. The remaining 49 strains were both susceptible to penicillin
and avirulent, irrespective of the serotype. On the basis of their
capsular type and pathogenic behavior, strains fell into one of four
groups. In the group consisting of serotypes 1, 3, and 4 (n = 16), strains were predominantly
virulent (81.3%), and all were penicillin susceptible. In the serotype
6 group (n = 32), the frequency of virulence was significantly lower (34.4 versus 81.3%, P = 0.002),
and strains were predominantly penicillin susceptible (71.9%). In the
group composed of serotypes 9, 14, 19, and 23 (n = 50), all strains were avirulent, and 56% had decreased susceptibility
(n = 12) or resistance to (n = 16)
penicillin. The fourth group was heterogenous, as it pooled 24 strains
of 15 different serotypes; in this group the frequency of virulence was
33.3%, and strains were predominantly penicillin susceptible (83.3%).
These data point to a complex relationship between penicillin
susceptibility and virulence in mice but do not entirely separate these
characteristics from the role of the capsular type. The possibility
that the mechanisms conferring penicillin resistance are related to
those leading to a loss of virulence is supported by these findings.
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Relationship between Capsular Type, Penicillin Susceptibility,
and Virulence of Human Streptococcus pneumoniae Isolates
in Mice
*
Corresponding author. Mailing address: INSERM EMI-U
9933, Bâtiment U13, Hôpital Bichat-Claude Bernard, 170 Bd
Ney, 75877 Paris Cedex 18, France. Phone: 33 1 40 25 86 08. Fax: 33 1 40 25 86 02. E-mail: eazoulay{at}bichat.inserm.fr.
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