Persistent S. pneumoniae strains causing ≥3 episodes of acute exacerbations in patients with chronic respiratory diseases.

a

S, susceptible (CPX MICs ≤2 mg/L); LL-R, low- level of resistance (MICs 4–8 mg/L); HL-R, high level of resistance (MICs ≥16 mg/L).

b

hol1 + indicates PCR detection for hol1 gene; MitC + indicates cell lysis of the culture in the presence of MitC.