From the Guidelines
Streptococcus mitis bacteremia is primarily caused by this oral commensal bacterium entering the bloodstream through breaches in the oral mucosa or during invasive dental procedures, as supported by the American Heart Association guidelines 1. The main causes of strep mitis bacteremia can be attributed to:
- Dental extractions or other dental procedures
- Routine daily activities that cause trauma to the oral mucosa
- Poor oral hygiene
- Immunocompromised states
- Endoscopic procedures involving the gastrointestinal tract
- Breaches in the oral mucosa, allowing the bacterium to enter the bloodstream As noted in the guidelines from the American Heart Association 1, the frequency and intensity of the resulting bacteremias are believed to be related to the nature and magnitude of the tissue trauma, the density of the microbial flora, and the degree of inflammation or infection at the site of trauma. Patients with certain conditions, such as heart valve abnormalities, prosthetic heart valves, or indwelling catheters, are at higher risk for complications from S. mitis bacteremia, and therefore, prevention and prompt treatment are crucial in these cases, as emphasized by the guidelines 1. Prevention involves proper oral hygiene, antibiotic prophylaxis before dental procedures in high-risk patients, and prompt treatment of oral infections, with treatment typically including penicillin-based antibiotics, with vancomycin as an alternative for penicillin-allergic patients.
From the Research
Causes of Strep Mitis Bacteremia
- Strep mitis bacteremia can be caused by various factors, including:
- Infective endocarditis, which was the predominant source of infection in a study of complicated VGS bacteremia 2
- Neutropenia, as 34% of patients with BSI caused by S. mitis/oralis had febrile neutropenia 3
- Previous antibiotic use and trimethoprim-sulfamethoxazole prophylaxis, which were more common in the case group, although not significant 3
- Immune-compromised patients, as S. mitis can use its colonization and immune modulation factors as virulence factors promoting its opportunistic pathogenesis 4
- The bacterium can escape from its normal commensal niche in the human oropharynx and cause infectious complications, including bacteremia and septicaemia 4
- The oral microbiota of patients at risk of infective endocarditis can harbor VGS, including S. mitis, which may exhibit resistance to antibiotics such as penicillin and ampicillin 5
Risk Factors
- Patients with underlying hematologic and oncologic diseases may be at risk of developing S. mitis/oralis bacteremia 3
- Patients with a history of previous antibiotic use and trimethoprim-sulfamethoxazole prophylaxis may be at increased risk 3
- Immune-compromised patients may be more susceptible to S. mitis infection 4
Microbiological Characteristics
- S. mitis can express adhesins, immunoglobulin A proteases, and toxins, which allow it to colonize the human oropharynx and compete with other microbial neighbors 4
- The bacterium can modulate the host immune system, which may contribute to its pathogenesis 4
- S. mitis isolates may exhibit resistance to antibiotics such as penicillin and ampicillin, but are generally susceptible to vancomycin 5