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Relationship between capsular type, penicillin susceptibility, and virulence of human Streptococcus pneumoniae
E Azoulay-Dupuis1, V Rieux, M Muffat-Joly
1Institut National de la Santé et de la Recherche Médicale, EMI-U 9933, Hôpital Bichat-Claude Bernard, 75877 Paris Cedex 18, France. eazoulay@bichat.inserm.fr
Abstract:
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.
Insights
Penicillin susceptibility in Streptococcus pneumoniae is complexly linked to virulence and capsular type. Penicillin resistance in these bacteria may correlate with reduced virulence, suggesting shared resistance mechanisms.
Area of Science:
- Microbiology
- Infectious Diseases
- Bacterial Pathogenesis
Background:
- Streptococcus pneumoniae is a significant human pathogen.
- Understanding the factors influencing its virulence and antibiotic resistance is crucial for public health.
- Penicillin resistance is a growing concern in S. pneumoniae infections.
Purpose of the Study:
- To investigate the relationship between penicillin susceptibility, capsular type, and peritoneal virulence in clinical isolates of Streptococcus pneumoniae.
- To explore potential links between mechanisms of penicillin resistance and virulence.
Main Methods:
- Analysis of 122 clinical Streptococcus pneumoniae isolates from 24 distinct serotypes.
- Assessment of penicillin susceptibility (susceptible, diminished susceptibility, resistant).
- Evaluation of peritoneal virulence in Swiss mice.
- Categorization of strains based on capsular type and pathogenic behavior.
Main Results:
- All virulent strains were penicillin susceptible; all strains with diminished susceptibility or resistance were avirulent.
- Serotypes 1, 3, and 4 were predominantly virulent and penicillin susceptible.
- Serotypes 9, 14, 19, and 23 were all avirulent, with a significant proportion showing penicillin resistance.
- Serotype 6 showed lower virulence frequency and predominantly penicillin susceptibility.
- A heterogeneous group of 15 serotypes exhibited low virulence and predominantly penicillin susceptibility.
Conclusions:
- A complex interplay exists between penicillin susceptibility, virulence, and capsular type in Streptococcus pneumoniae.
- Findings suggest that mechanisms conferring penicillin resistance may be associated with a loss of virulence.
- Capsular type remains an important factor influencing both virulence and antibiotic susceptibility.