Streptococcus pseudopneumoniae: prospective detection among community lower respiratory isolates in Eastern Saudi Arabia.

Streptococcus pseudopneumoniae is a distinct pathogen and the available evidence suggests its significance in lower respiratory tract infections. The purpose of this study is to investigate the occurrence of this new species in patients presenting with community-acquired pneumonia in a university hospital setting using routine laboratory tests. Sputum samples (n = 213) submitted to the microbiology laboratory for culture from cases clinically diagnosed as community-acquired pneumonia are studied. Optochin variability in ambient air and 5% CO2 was the criterion used to identify S. pseudopneumoniae. Disc-diffusion and E-test on Muller Hinton blood-based agar were used for antibiotic susceptibility testing following Clinical Laboratory Standard Institute breakpoints. Out of the screened isolates, only six (3%) were identified as S. pseudopneumoniae. None of the commercial tests differentiated the pathogens from viridans streptococci so diagnostic laboratories need to provide an alternative identification algorithm. The six isolates showed susceptibility to penicillin, and five isolates were susceptible to vancomycin, but one exhibited low-level resistance (minimum inhibitory concentration [MIC]: 1 μg/mL). All isolates showed high-level resistance to macrolides (MIC: 24- > 256 μg/mL). Although S. pseudopneumoniae strains were not sufficiently frequent to justify routine additional incubation of sputum samples in ambient air, the high resistance pattern is alarming. Further surveillance is needed in diagnostic laboratories to understand the epidemiology and clinical significance of the newly described pathogen.