Carcinoma of the buccal mucosa is a prevalent subtype of oral squamous cell carcinoma, particularly in regions with high tobacco and betel quid consumption (1,2). Standard treatment modalities include surgery, radiation therapy (RT), and chemotherapy, either as monotherapies or in combination (3). While RT is effective in targeting malignant cells, it also adversely affects normal tissues, notably the oral mucosa, leading to complications such as oral mucositis (4,5).

Oral mucositis is characterized by erythematous and ulcerative lesions of the oral mucosa, resulting from RT-induced damage (6). This condition is not only painful but also significantly impairs a patient's ability to eat and speak, thereby diminishing their quality of life (7,8). Moreover, the ulcerative lesions serve as potential entry points for pathogens, increasing the risk of local and systemic infections (9,10). The incidence and severity of oral mucositis are influenced by several factors, including the anatomical location of the tumor, total radiation dose, fractionation schedule, and concurrent chemotherapy (11). Patients with primary tumors in the oral cavity, such as carcinoma of the buccal mucosa, who receive concomitant chemotherapy or altered fractionation schedules, and those who receive a total dose over 5,000 cGy, are particularly susceptible to developing severe mucositis (12).

The pathogenesis of RT-induced mucositis involves a complex interplay of direct epithelial damage, generation of reactive oxygen species, and activation of pro-inflammatory pathways (13,14). These processes culminate in mucosal barrier breakdown and ulceration. The management of oral mucositis remains predominantly supportive, focusing on pain control, nutritional support, and maintenance of oral hygiene (15,16). Emerging therapeutic interventions, such as the use of keratinocyte growth factors like Palifermin, have shown promise in mitigating mucosal injury (17). However, their application is limited by cost and accessibility, particularly in resource-constrained settings (18,19).

Given the high prevalence of carcinoma of the buccal mucosa in specific populations and the substantial impact of RT-induced mucositis on treatment outcomes and patient well-being, it is imperative to explore strategies that can prevent or alleviate this debilitating side effect. Understanding the underlying mechanisms and identifying effective interventions are crucial steps toward improving the quality of life and clinical outcomes for these patients (20,21)

Study Design and Setting

A prospective study was conducted at the Radiation Oncology Department in association with department of Otorhinolaryngology and Microbiology, JIET Medical College and Hospital, Jodhpur, Rajasthan, over 12 months.

Patient Selection Criteria

Inclusion Criteria:

• Patients with histologically confirmed CBM.
• Patients undergoing curative or palliative RT.
• Age ≥18 years.

Exclusion Criteria:

• Patients on systemic immunosuppressants.
• Prior antibiotic or antifungal therapy within four weeks.

Sample Collection and Microbiological Analysis

Oral swabs were collected at three time points:

1. Before RT (Baseline sample)
2. At the end of RT
3. Three weeks post-RT

Since the Microbiology lab at the institute is a resource limiting setting, samples were cultured on UTI Hichrom agar and incubated at 37°C for 24–48 hours. Bacterial and fungal species were identified using standard conventional  microbiological techniques [7]. Since oral swab samples usually grow a number of commensal organisms from the oral cavity, only the significant growth microorganisms were identified and enlisted for the study.

Demographic and Clinical Characteristics

A total of 111 CBM patients were analyzed. 67% were male. Most patients underwent IMRT (52%), and 56% received a total dose of 60 Gy. The results have been shown in tables 1 , 2 and 3

Microbial Analysis

Correlation between Radiation Dose and Microbial Shifts

Radiation therapy plays a crucial role in the management of carcinoma of the buccal mucosa, but it significantly alters the oral microbiome, predisposing patients to secondary infections and radiation-induced mucositis (1,2). Mucositis is a common and debilitating side effect that occurs in nearly all patients receiving radiation therapy for head and neck cancers (3). The inflammatory changes in the oral mucosa, combined with altered salivary flow, create a favorable environment for opportunistic bacterial and fungal infections (4,5).

Impact of Radiation on Oral Microbiota

Our study demonstrates a substantial increase in the prevalence of pathogenic organisms, including Klebsiella pneumoniae, Pseudomonas aeruginosa, Candida albicans, and Staphylococcus aureus, over the course of radiation therapy. The increase in Gram-negative bacteria, such as Klebsiella pneumoniae (from 25.5% to 40.2%) and Pseudomonas aeruginosa (16.8% to 30.1%), aligns with previous studies that have reported a significant rise in bacterial colonization in post-radiation patients (6,7). The prolonged inflammatory state and compromised mucosal immunity are likely responsible for these microbial shifts (8).

Among fungal infections, Candida albicans showed the highest increase (from 45.6% to 70.3%), consistent with earlier research highlighting the role of radiation-induced xerostomia in Candida overgrowth (9). The increased Candida colonization was particularly notable in patients receiving higher radiation doses (66 Gy), emphasizing the need for prophylactic antifungal strategies (10).

Microbial Differences Based on Radiation Dose

A significant correlation was observed between radiation dose and microbial colonization patterns. Patients receiving 60 Gy were more likely to have Gram-negative infections, particularly Klebsiella pneumoniae (40.2%) and Pseudomonas aeruginosa (30.1%), whereas those receiving 66 Gy had higher Candida albicans (70.3%) and Staphylococcus aureus (25.7%) prevalence. These findings suggest that higher doses of radiation may selectively favor fungal overgrowth, while lower doses allow for Gram-negative bacterial proliferation, possibly due to varying levels of mucosal integrity loss and immune suppression (11,12).

Clinical Implications and Preventive Strategies

The presence of opportunistic pathogens in post-radiation patients has significant clinical implications. Gram-negative bacilli such as Klebsiella pneumoniae and Pseudomonas aeruginosa have been associated with increased morbidity, hospitalizations, and secondary infections, including pneumonia and bloodstream infections (13,14). Similarly, Candida albicans has been implicated in oral candidiasis and systemic fungal infections, particularly in immunocompromised individuals (6).

Given the high prevalence of radiation-induced mucositis, strategies such as prophylactic antifungal therapy, routine microbiological surveillance, and enhanced oral hygiene measures may help mitigate infection risk (15). Several studies have suggested that chlorhexidine mouth rinses, antifungal prophylaxis, and probiotics may play a role in reducing microbial burden and maintaining oral microbial balance (16,17).

Comparison With Previous Studies

Our results are in line with existing literature reporting similar trends in microbial colonization post-radiation therapy. For instance, a study by Vokurka et al. (2006) documented a significant rise in Candida species following radiation therapy, with a pattern comparable to our findings (18). Similarly, Rubenstein et al. (2004) emphasized the role of oral mucositis and microbial colonization in increasing infection-related complications in patients undergoing radiation therapy for head and neck cancers (19).

Overall, this study underscores the importance of microbial monitoring and infection control strategies in patients with carcinoma of the buccal mucosa undergoing radiation therapy. The observed microbial shifts, particularly the increase in Candida species and Gram-negative bacteria, warrant proactive interventions to improve patient outcomes and reduce post-treatment complications (20,21).

In conclusion, Radiation therapy significantly disrupts the oral microbiome in CBM patients, increasing the prevalence of opportunistic pathogens. Regular microbiological monitoring and targeted prophylactic interventions are essential to reduce infection-related morbidity. Further research is warranted to explore personalized microbiome-based therapeutic approaches.

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