Impact of the revised penicillin susceptibility breakpoints for Streptococcus pneumoniae on antimicrobial resistance rates of meningeal and non-meningeal pneumococcal strains.

Background And Objectives: In January 2008, the Clinical Laboratory Standard Institute (CLSI) revised the Streptococcus pneumoniae breakpoints for penicillin to define the susceptibility of meningeal and non-meningeal isolates. We studied the impact of these changes. In addition, the pneumococcal resistance rate to other antimicrobial agents was reviewed.

Design And Setting: Laboratory data on peumococcal isolates collected retrospectively from hospitalized children in tertiary care hospital in Riyadh, Saudi Arabia from January 2006 to March 2012.

Patients And Methods: Only sterile samples were included from cerebrospinal fluids, blood, sterile body fluids and surgical tissue. Other samples such as sputum and non sterile samples were excluded. We included samples from children 14 years old or younger. The minimum inhibitory concentration (MIC) for penicillin, cefuroxime, ceftriaxone and meropenem were determined by using the E-test, while susceptibility to erythromycin, cotrimoxazole and vancomycin were measured using the disc diffusion methods following the guideline of CLSI.

Results: Specimens were analyzed in two different periods: from January 2006 to December 2007 and from January 2008 to March 2012. During the two periods there were 208 samples of which 203 were blood samples. Full penicillin resistance was detected in 6.6% in the first period. There was decrease in penicillin nonmeningeal resistance to 1.5% and an increase in resistance in penicillin meningeal 68.2% in the second period (P=.0001). There was an increase in rate of resistance among S pneumoniae isolates over the two periods to parenteral cefuroxime, erythromycin and cotrimoxazole by 34.6%, 35.5% and 51.9%, respectively. Total meropenem resistance found 4.3% and no vancomycin resistance was detected.

Conclusions: The current study supports the use of the revised CLSI susceptibility breakpoints that promote using penicillin to treat nonmeningeal pneumococcal disease, and might slow the development of resistance to broader-spectrum antibiotics.