Pediatric Erythromycin-Resistant and Clindamycin-Susceptible Pneumococcal Isolates Lack Inducible Clindamycin Resistance

Erythromycin-resistant and clindamycin-susceptible pneumococcal isolates lack inducible clindamycin resistance among children in US-based hospitals, according to new data. Multicenter studies are needed to determine whether inducible clindamycin resistance (ICR) testing is required for macrolide‑resistant pneumococcal isolates.

Of the 8% of isolates expressing high erythromycin resistance, none had the resistance-conferring ermB gene.

Testing of macrolide-resistant Streptococcus pneumoniae isolates for ICR was recommended by the Clinical and Laboratory Standards Institute in 2013. To characterize the prevalence of ICR among pneumococcal isolates from pediatric patients seen at Children’s Mercy Hospital in Kansas City, Missouri, the researchers identified erythromycin-resistant and clindamycin-susceptible pneumococcal isolates taken from children who visited their hospital from 2007 to 2017. These children’s median age was 19 months.

After the minimum inhibitory concentrations (MICs) for both antibiotics were determined in isolates, D-zone testing with standard erythromycin and clindamycin disks was used to determine ICR. In addition, isolates with high erythromycin resistance, defined as those with an MIC of 32 μg/mL or more, were also tested for ermB by using polymerase chain reaction test. Positive and negative controls were used for the tests.

Of the 289 erythromycin-resistant isolates identified, 194 (67%) were clindamycin-susceptible. In addition, of the 169 isolates available for ICR testing, none showed ICR based on results of the D-zone test. Furthermore, high erythromycin resistance was found in 13 (8%) of those isolates, but they all had a negative test result for ermB.

As a result, the researchers concluded that the erythromycin-resistant and clindamycin-susceptible pneumococcal isolates they evaluated did not express ICR, and none of the highly erythromycin-resistant isolates they studied carried the ermB gene.

According to the presenting author, Liset Olarte, MD, MSc, “Multicenter studies are needed to determine if ICR testing is required for macrolide-resistant pneumococcal isolates in the [pneumococcal conjugate vaccine] era.”

—Ellen Kurek


Olarte L, Swanson DS, Tabakh JE, Banerjee D, Selvarangan R. Inducible clindamycin resistance testing on pediatric Streptococcus pneumonia isolates. Paper presented at: IDWeek 2021; September 29-October 3, 2021; Virtual.