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Published on: January 17, 2014
Antimicrobial susceptibility testing of invasive isolates of Streptococcus pneumoniae from Canadian patients: the
Morgan A Alford1, James A Karlowsky1,2, Heather J Adam1,2
1Department of Medical Microbiology and Infectious Diseases, Max Rady College of Medicine, University of Manitoba, Room 543-745 Bannatyne Avenue, Winnipeg, Manitoba R3E 0J9, Canada.
Objectives:
To assess the antimicrobial susceptibility of 14 138 invasive Streptococcus pneumoniae isolates collected in Canada from 2011 to 2020.
Methods:
Antimicrobial susceptibility testing was performed using the CLSI M07 broth microdilution reference method. MICs were interpreted using 2022 CLSI M100 breakpoints.
Results:
In 2020, 90.1% and 98.6% of invasive pneumococci were penicillin-susceptible when MICs were interpreted using CLSI meningitis or oral and non-meningitis breakpoints, respectively; 96.9% (meningitis breakpoint) and 99.5% (non-meningitis breakpoint) of isolates were ceftriaxone-susceptible, and 99.9% were levofloxacin-susceptible. Numerically small, non-temporal, but statistically significant differences (P < 0.05) in the annual percentage of isolates susceptible to four of the 13 agents tested was observed across the 10-year study: chloramphenicol (4.4% difference), trimethoprim-sulfamethoxazole (3.9%), penicillin (non-meningitis breakpoint, 2.7%) and ceftriaxone (meningitis breakpoint, 2.7%; non-meningitis breakpoint, 1.2%). During the same period, annual differences in percent susceptible values for penicillin (meningitis and oral breakpoints) and all other agents did not achieve statistical significance. The percentage of isolates with an MDR phenotype (resistance to ≥3 antimicrobial classes) in 2011 and 2020 (8.5% and 9.4%) was not significantly different (P = 0.109), although there was a significant interim decrease observed between 2011 and 2015 (P < 0.001) followed by a significant increase between 2016 and 2020 (P < 0.001). Statistically significant associations were observed between resistance rates to most antimicrobial agents included in the MDR analysis (penicillin, clarithromycin, clindamycin, doxycycline, trimethoprim/sulfamethoxazole and chloramphenicol) and patient age, specimen source, geographic location in Canada or concurrent resistance to penicillin or clarithromycin, but not biological sex of patients. Given the large isolate collection studied, statistical significance did not necessarily imply clinical or public health significance in some analyses.
Conclusions:
Invasive pneumococcal isolates collected in Canada from 2011 to 2020 generally exhibited consistent in vitro susceptibility to commonly tested antimicrobial agents.
Insights
Antimicrobial susceptibility of invasive Streptococcus pneumoniae in Canada remained largely consistent from 2011-2020. While minor fluctuations occurred, overall resistance to key antibiotics like penicillin and ceftriaxone showed stability, indicating sustained treatment efficacy.
Area of Science:
- Microbiology
- Infectious Diseases
- Public Health
Background:
- Invasive pneumococcal disease (IPD) remains a significant global health concern.
- Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and sepsis.
- Monitoring antimicrobial susceptibility is crucial for guiding effective treatment strategies.
Purpose of the Study:
- To evaluate the antimicrobial susceptibility trends of invasive Streptococcus pneumoniae isolates in Canada.
- To analyze changes in susceptibility patterns over a ten-year period (2011-2020).
- To identify potential associations between resistance and patient or isolate characteristics.
Main Methods:
- Analysis of 14,138 invasive Streptococcus pneumoniae isolates collected nationwide.
- Antimicrobial susceptibility testing using the Clinical and Laboratory Standards Institute (CLSI) M07 broth microdilution method.
- Interpretation of Minimum Inhibitory Concentrations (MICs) based on CLSI M100 breakpoints (2022).
Main Results:
- High susceptibility rates observed in 2020 for penicillin (90.1-98.6%), ceftriaxone (96.9-99.5%), and levofloxacin (99.9%).
- Minor, statistically significant annual variations noted for chloramphenicol, trimethoprim-sulfamethoxazole, penicillin, and ceftriaxone, but not clinically significant.
- Multidrug-resistant (MDR) phenotype prevalence remained stable (8.5% in 2011 vs. 9.4% in 2020), with interim fluctuations.
Conclusions:
- Invasive pneumococcal isolates in Canada demonstrated consistent in vitro susceptibility to commonly used antimicrobial agents between 2011 and 2020.
- The study highlights the general stability of antimicrobial resistance patterns, supporting current therapeutic guidelines.
- Further surveillance is warranted to detect any emerging resistance trends impacting IPD management.
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