Enhanced expression of pore-forming toxins in Staphylococcus aureus induced by Streptococcus intermedius in cystic fibrosis

The airways of patients with cystic fibrosis (CF) are frequently colonized by Staphylococcus aureus . The oral bacterial community in CF patients may influence infection severity, and the microbiota consortium might modulate the expression of key virulence factors of S. aureus . Thus, this study aimed to evaluate the frequency of S. aureus and Streptococcus anginosus group (SAG) in the airways of CF patients and investigate the potential effects of SAG on the expression of hla and pvl genes in S. aureus . Ninety-one sputum samples were collected from CF patients to recover SAG and S. aureus isolates using conventional microbial methods. SAG species were confirmed by 16 S rRNA sequencing, and antibiotic susceptibility was assessed by disk diffusion assay. The presence of hla and pvl genes in S. aureus isolates was detected by PCR. Furthermore, the expression levels of these genes were measured in mono- and co-culture with S. constellatus and S. intermedius under biofilm conditions using RT-qPCR. Out of 91 samples, 47 (51.6%) S. aureus isolates were identified, of which 51% were MRSA. All S. aureus isolates were susceptible to linezolid. The hla and pvl genes were detected in 93.6% and 4.25% of isolates, respectively. Six SAG isolates (6.59%) were identified, including five S. intermedius and one S. constellatus , all susceptible to linezolid, penicillin, and vancomycin. Co-culture with S. intermedius resulted in a more pronounced overexpression of hla and pvl genes of S. aureus . The notably increased expression of hla and pvl under co-culture conditions suggests cross-species signaling between SAG and S. aureus . These findings highlight the importance of understanding polymicrobial interactions between resident microbiota and key pathogens such as S. aureus in CF patients. Variations in the frequency of SAG species within the oral microbiome may help explain differences in infection severity among CF patients.