Interactions between serotype and mutations in quinolone-resistance determining regions of Streptococcus pneumoniae

Abstract number: P1236

Melano R., McGeer A., Drews S., Pong-Porter S., Gubbay J., Seah C., Higgins R., Tyrrell G., Green K., Low D.E.

Background: Mutations in QRDR regions are the primary cause of fluoroquinolone resistance (FQR) in S. pneumoniae (SPN). It is not known whether the distribution of mutations and/or the association of QRDR with increasing MIC is similar in different SPN serotypes (STs).

Methods: The Canadian Bacterial Surveillance Network (CBSN) has been monitoring trends in antimicrobial resistance in SPN in Canada. From 1995–2006, 27,951 isolates from across Canada have been collected. Serotyping and sequencing of the gyrA and parC regions was performed for all FQR isolates FQ (N=451), and a sample of others (N=3438).

Results: The most common parC mutations were: K137N (N=870), S79F (293), S79Y (106), D83N (36), D83Y (17), D83G (9), S52G (6), N91D (6), R95C (5), Y129S (5), D78N (4), S79A (2), A115P (2). 14 other mutations were identified once. S79F, S79Y, D83N/Y/G, D78N/A, and A115P were associated with increased MICs to FQ; other mutations were not. K137N was present in <5% of isolates of SGs 3, 4, 10, 11, 15, 18, 20, 22, 33, 35, 38, >85% of isolates of SGs 12 and 9, and an intermediate percentage of other SGs. Among FQR, S79Y is significantly more common in isolates of ST 22F, 6A and 6B, and mutations at position 83 are more common in ST 9N and 9V (P < 0.01). Of isolates with parC mutations, those of ST 12F had significantly lower MICs to all FQ than those of other STs. 27% of FQS SPN with a parC mutation at position 79 were ST 12F, compared to 3% of FQR isolates. The most common gyrA mutations were S81F (N=179), S81Y (33), E85K (33), S114G (14), E85G (4). 12 other mutations were identified once. Only mutations at position 81 and 85 were associated with increased FQ MICs. The prevalence of gyrA mutations in the presence of parC mutations varied significantly with ST; eg. 10/12 (83%) 19A and 32/40 (80%) 19F strains with a parC mutation also had a gyrA mutation, compared to 9/24 (38%) ST 3 and 6/17 (35%) ST 12F (P < 0.001). When isolates were categorised by whether or not their serotypes were included in 7- or 23-valent pneumococcal vaccines, there were no significant differences in the prevalence of parC mutations. Isolates of STs in the 23-valent vaccine with a parC mutation were somewhat less likely to have a gyrA mutation than other isolates (66% vs 55%, P = 0.07).

Conclusion: Mutations in QRDR determining regions occur with differing frequencies in isolates of different ST. Changing ST distributions associated with pneumococcal vaccination programs may have an impact on FQR rates.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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