Antimicrobial susceptibility testing of invasive isolates of Streptococcus pneumoniae from Canadian patients: the SAVE study, 2011-15.

OBJECTIVES

To assess antimicrobial susceptibility for 14 agents tested against 6001 invasive isolates of Streptococcus pneumoniae cultured from invasive patient samples from 2011 to 2015 as a part of the annual SAVE study.

METHODS

Isolates of S. pneumoniae were tested using the standard CLSI broth microdilution method (M07-A10, 2015) with MICs interpreted by CLSI M100 27th Edition (2017) MIC breakpoints.

RESULTS

From 2011 to 2015, small but significant increases (P ≤ 0.05) in the percentage susceptibility for penicillin (interpreted by all three CLSI MIC breakpoint criteria) (increase of 1.7%-3.2%), clindamycin (3.1%) and ceftriaxone (interpreted by non-meningitis and meningitis CLSI MIC breakpoint criteria) (1.1%-1.5%) were observed. Susceptibility rates for clarithromycin and other commonly tested antimicrobial agents remained unchanged (P > 0.05) over the 5 year period. Isolates with an MDR phenotype (resistance to three or more antimicrobial agent classes) decreased significantly (P < 0.001) from 8.5% in 2011 to 5.6% in 2015. Antimicrobial susceptibility rates were not generally associated (P > 0.05) with patient gender (exception: clarithromycin) but were associated (P ≤ 0.05) with patient age (chloramphenicol and clindamycin) or specimen source (penicillin, doxycycline, trimethoprim/sulfamethoxazole and clindamycin), as well as geographic location in Canada and concurrent resistance to penicillin or clarithromycin.

CONCLUSIONS

The in vitro susceptibility of invasive isolates of S. pneumoniae in Canada to penicillin, clindamycin and ceftriaxone increased from 2011 to 2015, coincident with a significant decrease in MDR phenotypes.