Streptococcus Viridans in Pediatric Cancer Patients
For children fighting cancer, the most dangerous enemy might not be what you expect.
When we think of the bacteria in our mouths, we typically imagine harmless residents that help maintain oral health. But for children undergoing cancer treatment, these common microbes can transform into life-threatening invaders.
Streptococcus viridans—a group of bacteria normally responsible for dental caries—emerges as an unexpected foe in pediatric oncology wards, capable of causing severe bloodstream infections that complicate already challenging cancer treatments 2 7 .
Harmlessly resides in mouth, throat, and digestive system
Prevents colonization by dangerous pathogens through bacteriocin production
From Latin "viridans" meaning "green" due to discoloration on blood agar plates
The transformation from commensal to culprit begins with cancer treatments, particularly chemotherapy and stem cell transplantation 4 . These life-saving therapies damage the protective lining of the mouth and gastrointestinal tract—a condition known as mucositis 4 6 . This breakdown of mucosal barriers allows the normally harmless bacteria to enter the bloodstream, causing viridans streptococcal bacteremia (VSB) 2 4 .
Streptococcus viridans resides harmlessly in the oral cavity, performing protective functions against more dangerous pathogens 7 .
Chemotherapy and stem cell transplantation begin, targeting cancer cells but also affecting healthy rapidly dividing cells 4 .
The protective mucosal lining of the mouth and GI tract breaks down, creating portals for bacterial entry 4 6 .
Research indicates that 18-39% of neutropenic patients with VSB develop severe complications such as septic shock and acute respiratory distress syndrome (ARDS), with mortality rates reaching up to 20% in some studies 6 .
Creates entry points for bacteria
Eliminates the body's ability to control invasion
Central venous catheters provide pathways for bacteria
Children undergoing cancer treatment represent a uniquely vulnerable population. Their immune defenses are systematically weakened, both by the cancer itself and by the treatments designed to eradicate it. Neutropenia—dangerously low levels of infection-fighting white blood cells—leaves these children exceptionally susceptible to infections that would be trivial in healthy individuals 6 .
The risk emerges from a perfect storm of conditions: mucositis creates the entry point, neutropenia eliminates the body's ability to control the invasion, and medical devices like central venous catheters provide potential pathways for bacteria to bypass normal defense mechanisms 4 .
Immune System
Mucositis Severity
Neutropenia
Device Use
| Symptom | Adults | Children | Statistical Significance |
|---|---|---|---|
| Oral Mucositis | More Frequent | Less Frequent | p = 0.005 |
| Abdominal Pain | More Frequent | Less Frequent | p = 0.001 |
| Cough | Less Frequent | More Frequent | p = 0.004 |
A comprehensive study comparing adults and children with hematologic malignancies found that while clinical presentation differed somewhat between age groups—with adults experiencing more oral mucositis and abdominal pain, and children showing more respiratory symptoms—the occurrence of severe complications and death attributable to VSB was not significantly different between adults and children 6 .
One of the most puzzling aspects of viridans streptococcal infections in oncology patients has been their tendency to cause a toxic shock-like illness resembling the devastating syndrome typically associated with Group A Streptococcus pyogenes 3 . This severe presentation often includes shock, acute respiratory distress, and multiple organ failure—clinical features seemingly disproportionate to the usual behavior of these ordinarily benign bacteria.
For years, the medical community struggled to explain this phenomenon. The similar presentation to streptococcal toxic shock syndrome suggested the involvement of superantigens—powerful bacterial toxins that can trigger massive, dysregulated immune responses by activating large populations of T-cells simultaneously 3 .
To solve this mystery, researchers conducted a crucial investigation to determine whether viridans group streptococci isolated from pediatric oncology patients with streptococcal toxic shock-like illnesses were producing superantigens 3 .
Researchers collected viridans streptococci strains from pediatric oncology patients who had developed toxic shock-like illnesses during bacteremic episodes 3 .
They performed sophisticated genetic testing to screen these isolates for homologs of known superantigen genes 3 .
The team cultured the bacteria and collected the supernatants, then exposed T-cells to observe whether abnormal proliferation occurred 3 .
| Research Step | Methodology | Key Finding |
|---|---|---|
| Bacterial Collection | Isolated from pediatric oncology patients with shock-like illness | Confirmed viridans streptococci as causative agents |
| Genetic Screening | Tested for known superantigen genes | No homologs of superantigen genes detected |
| Functional Assay | Exposed T-cells to bacterial culture supernatants | No abnormal T-cell proliferation observed |
The results were surprising: the viridans streptococci isolates did not possess homologs of known superantigen genes 3 . Even more convincingly, the bacterial culture supernatants failed to stimulate T-cell proliferation, providing clear evidence that these bacteria were not producing functional superantigens 3 .
This finding had immediate clinical implications: it suggested that adjuvant treatments with intravenous immunoglobulin (IVIG)—which can be beneficial in classic streptococcal toxic shock syndrome by neutralizing superantigens—might not effectively treat these viridans streptococcal infections 3 .
Treating viridans streptococcal bacteremia in pediatric oncology patients presents unique challenges. The standard approach typically involves β-lactam antibiotics 6 , but treatment must be tailored to individual patients and local resistance patterns.
Antibiotic resistance is a growing concern. A comprehensive study of antibiotic susceptibility patterns from 2010 to 2020 revealed some worrying trends . While susceptibility to ceftriaxone and vancomycin remains high (96-100%), resistance to other antibiotics has been increasing . Particularly concerning is the declining susceptibility of Streptococcus mitis to erythromycin and of non-speciated VGS isolates to clindamycin .
| Antibiotic | S. mitis | S. oralis | Non-speciated VGS |
|---|---|---|---|
| Penicillin | 71.0% | 80.9% | 86.3% |
| Ceftriaxone | 96.0% | 100% | 98.5% |
| Clindamycin | 81.3% | 84.5% | 83.2% |
| Vancomycin | 99.7% | 100% | 99.9% |
The investigation into why viridans streptococci cause such severe disease in immunocompromised children continues. Since superantigens have been largely ruled out, researchers are exploring alternative mechanisms, potentially involving other bacterial components that might trigger exaggerated inflammatory responses in already vulnerable patients.
Managing this threat requires integrated care spanning oncology, infectious disease, and dental specialties.
Exploring alternative mechanisms beyond superantigens that trigger severe inflammatory responses.
Through continued research and multidisciplinary cooperation, outcomes continue to improve for vulnerable patients.
The story of viridans streptococci in pediatric oncology serves as a powerful reminder that in medicine, the most significant threats aren't always the exotic pathogens, but sometimes the familiar ones that exploit moments of vulnerability.