Screening of antagonistic strains of respiratory origin and analysis of their bacteriostatic effects on pathogens

OBJECTIVE: To find antagonistic strains in the respiratory tract having bacteriostatic properties against common pathogens. METHODS: The oropharyngeal microbiota of five healthy children aged 4–6 years were collected and α‐hemolytic bacteria screened on 15% sheep blood agar. Bacteriostatic effects of the isolated α‐hemolytic bacteria on Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Streptococcus pyogenes were evaluated by the Oxford cup method. Antagonistic strains were identified by mass spectrometry, and the16S rDNAs were sequenced, and their best bacteriostatic concentrations and antagonistic spectra for Klebsiella pneumoniae, Proteus vulgaris, Enterobacter cloacae, Acinetobacter Baumanii, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Streptococcus pyogenes were evaluated. RESULTS: Of 300 isolated α‐hemolytic bacterial clones, four exhibited bacteriostatic activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Streptococcus pyogenes. Mass spectrometric analyses revealed that two of them were Streptococcus mitis and two others were Streptococcus parasanguinis strains. Further tests showed that all 4 antagonistic strains also had bacteriostatic effects on Klebsiella pneumoniae, Proteus vulgaris, Enterobacter cloacae, and Acinetobacter Baumanii, and the mode of action was not mediated by lactic acid production. CONCLUSION: Four antagonistic Streptococcus strains derived from oropharyngeal microbiotas showed bacteriostatic effects on pathogens and may be involved in pharyngeal microbiome homeostasis.