Acute tonsillitis is one of the most common infectious conditions encountered in otorhinolaryngology practice, particularly among children and young adults. It is characterized by acute inflammation of the palatine tonsils, presenting clinically with sore throat, fever, odynophagia, and cervical lymphadenopathy. The condition may be caused by viral or bacterial pathogens, with Group A β-hemolytic Streptococcus (Streptococcus pyogenes) traditionally regarded as the most important bacterial etiology due to its association with suppurative and non-suppurative complications [1,2]. In addition to S. pyogenes, several other organisms including Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and gram-negative bacilli have been increasingly isolated in patients with acute tonsillitis [3–5]. The microbial spectrum appears to vary with age, geography, socioeconomic factors, and antibiotic exposure patterns. Empirical antibiotic therapy is commonly initiated in clinical practice; however, inappropriate and indiscriminate use of antibiotics has contributed to the growing problem of antimicrobial resistance [6]. Recent studies from India and other developing countries have demonstrated changing trends in bacteriological profiles and increasing resistance to commonly prescribed antibiotics such as penicillins and macrolides [7–9]. This highlights the importance of periodic local surveillance of causative organisms and their antibiotic susceptibility patterns to guide rational therapy. Against this background, the present study was undertaken to evaluate the clinical profile, microbiological spectrum, and antibiotic sensitivity pattern of bacterial isolates in patients with acute tonsillitis presenting to a tertiary care hospital, with the aim of providing evidence-based guidance for empirical antibiotic selection.

This hospital-based observational study was conducted in the Departments of Microbiology at a tertiary care teaching hospital over a period of one year. Ethical approval was obtained from the Institutional Ethics Committee prior to the commencement of the study. Written informed consent was obtained from all adult patients and from parents or guardians in the case of pediatric patients. All patients clinically diagnosed with acute tonsillitis, irrespective of age and sex, were included in the study. Acute tonsillitis was diagnosed based on symptoms of sore throat, fever, painful swallowing, and examination findings of congested or enlarged tonsils with or without exudates. Patients who had received antibiotics within the preceding seven days, those with chronic or recurrent tonsillitis, peritonsillar abscess, immunocompromised states, or those unwilling to participate were excluded. A detailed clinical history was recorded, including age, sex, presenting symptoms, duration of illness, and prior antibiotic use. Thorough ENT examination findings were documented. Under aseptic precautions, two tonsillar swabs were collected from the surface of the inflamed tonsils, avoiding contamination from surrounding oral structures. One swab was used for Gram staining, and the other was inoculated onto blood agar, chocolate agar, and MacConkey agar. The plates were incubated aerobically at 37°C for 24–48 hours. Bacterial identification was performed based on colony morphology, Gram staining, and standard biochemical tests. Antimicrobial susceptibility testing was carried out using the Kirby–Bauer disc diffusion method on Mueller–Hinton agar, and results were interpreted according to Clinical and Laboratory Standards Institute (CLSI) guidelines [10]. The antibiotics tested included penicillin, amoxicillin-clavulanate, azithromycin, erythromycin, ceftriaxone, cefixime, ciprofloxacin, gentamicin, doxycycline, and linezolid. Data were entered into Microsoft Excel and analyzed using appropriate descriptive statistics. Results were expressed as frequencies and percentages.

Table 1: Age Distribution of Patients with Acute Tonsillitis (n = 120) Age group (years) Number Percentage ≤10 42 35.0% 11–20 36 30.0% 21–40 28 23.3% >40 14 11.7% Description: Acute tonsillitis predominantly affected children and adolescents, with 65% of cases occurring below 20 years of age. Table 2: Gender Distribution Gender Number Percentage Male 72 60.0% Female 48 40.0% Description: A male predominance was observed, with a male-to-female ratio of 1.5:1. Table 3: Bacteriological Profile of Tonsillar Swabs Organism Number Percentage Staphylococcus aureus 46 38.3% Streptococcus pyogenes 28 23.3% Pseudomonas aeruginosa 16 13.3% Klebsiella spp. 10 8.3% Mixed growth / others 8 6.7% No growth 12 10.0% Description: Bacterial growth was obtained in 90% of cases. Staphylococcus aureus was the most common isolate, followed by Streptococcus pyogenes. Table 4: Antibiotic Sensitivity and Resistant Pattern of Major Isolates Antibiotic Resistant n (%) Sensitive n (%) Penicillin 18 (30.0) 42 (70.0) Amoxicillin 20 (33.3) 40 (66.7) Amoxicillin–Clavulanate 8 (13.3) 52 (86.7) Erythromycin 15 (25.0) 45 (75.0) Azithromycin 14 (23.3) 46 (76.7) Cefixime 6 (10.0) 54 (90.0) Ceftriaxone 4 (6.7) 56 (93.3) Clindamycin 7 (11.7) 53 (88.3) Ciprofloxacin 5 (8.3) 55 (91.7) Linezolid 0 (0.0) 60 (100) Vancomycin 0 (0.0) 60 (100) The antibiotic susceptibility profile demonstrates variable resistance patterns among the bacterial isolates causing acute tonsillitis. Higher resistance rates were observed with commonly used first-line antibiotics, particularly amoxicillin (33.3%) and penicillin (30.0%), indicating reduced effectiveness of these agents in a substantial proportion of cases. Moderate resistance was also noted with macrolides, including erythromycin (25.0%) and azithromycin (23.3%), suggesting emerging resistance within this antibiotic class. In contrast, β-lactam/β-lactamase inhibitor combinations such as amoxicillin–clavulanate showed lower resistance (13.3%) and higher sensitivity (86.7%), highlighting their improved efficacy over plain β-lactams. Third-generation cephalosporins demonstrated excellent activity, with ceftriaxone and cefixime showing sensitivity rates of 93.3% and 90.0%, respectively. Similarly, high sensitivity was observed with ciprofloxacin (91.7%) and clindamycin (88.3%). Notably, no resistance was detected against linezolid and vancomycin, with 100% of isolates being sensitive to these agents, indicating preserved efficacy of these antibiotics against Gram-positive pathogens. Overall, the findings emphasize a trend toward increasing resistance to conventional first-line agents and underscore the importance of culture-guided therapy and judicious antibiotic selection in the management of acute tonsillitis.

Acute tonsillitis remains one of the most common upper respiratory tract infections encountered in ENT practice, particularly among children and young adults. Appropriate antimicrobial therapy plays a pivotal role in symptom resolution, prevention of complications, and reduction of disease recurrence. However, the rising trend of antimicrobial resistance has significantly influenced treatment outcomes, necessitating periodic evaluation of local bacteriological profiles and antibiotic sensitivity patterns. In the present study, Streptococcus pyogenes was the most frequently isolated organism, consistent with findings reported in earlier Indian and international studies [3,4,11]. This organism remains the principal bacterial pathogen implicated in acute tonsillitis, particularly in pediatric and adolescent populations. Other organisms such as Staphylococcus aureus and Gram-negative bacilli were isolated less frequently, reflecting secondary colonization or mixed infections. With regard to antibiotic sensitivity, β-lactam/β-lactamase inhibitor combinations, particularly amoxicillin–clavulanate, demonstrated high sensitivity in the present study. Similar high sensitivity rates have been reported by Agrawal et al., Ingale et al., and Shevale et al., suggesting that these agents remain effective first-line options, especially in recurrent or partially treated cases [4,7,9]. The enhanced efficacy of these combinations is attributed to their ability to counter β-lactamase–producing commensal organisms residing in tonsillar crypts. Third-generation cephalosporins, including cefixime and ceftriaxone, also showed excellent sensitivity (>90%) in the present study. This finding is in agreement with reports by Raoof et al. and Kumar et al., who highlighted the sustained effectiveness of cephalosporins in moderate to severe tonsillitis [5,11]. However, their routine use should be judicious to prevent the emergence of resistance and preserve their role as second-line agents. Clindamycin demonstrated good sensitivity and remains an important alternative, particularly in penicillin-allergic patients and those with recurrent tonsillitis. Its efficacy against both aerobic and anaerobic organisms and its ability to penetrate tonsillar tissue have been well documented [12]. Linezolid and vancomycin exhibited 100% sensitivity in the present study, consistent with existing literature; however, their use should be strictly reserved for multidrug-resistant infections to avoid future resistance [13]. Conversely, significant resistance was observed against commonly used antibiotics such as penicillin, amoxicillin, and macrolides. Resistance to penicillin and amoxicillin, though traditionally considered rare in S. pyogenes, has been increasingly reported in clinical practice [3,11]. This resistance is often functional rather than genetic and may be explained by biofilm formation, intracellular persistence, and protection conferred by β-lactamase–producing commensals [1,12]. Macrolide resistance, particularly to erythromycin and azithromycin, was notable in the present study. Comparable resistance rates have been reported by Ingale et al., Raoof et al., and Priyadarshini et al., reflecting the widespread empirical and often inappropriate use of macrolides in upper respiratory tract infections [5,7,13]. Over-the-counter availability, incomplete treatment courses, and frequent prescription in viral infections are key contributors to this trend. The coexistence of high sensitivity to higher antibiotics and resistance to commonly prescribed oral agents highlight a concerning shift in antimicrobial susceptibility patterns. This underscores the importance of culture-guided therapy, especially in recurrent, severe, or non-responsive cases. Empirical antibiotic therapy should be guided by local antibiograms, and unnecessary antibiotic use must be discouraged. Overall, the present study emphasizes that while several effective antibiotics remain available for the treatment of acute tonsillitis, increasing resistance to first-line agents poses a significant therapeutic challenge. Rational antibiotic prescribing, strict adherence to treatment guidelines, patient education, and implementation of antimicrobial stewardship programs are essential to curb the rising burden of resistance and ensure optimal patient outcomes.

Acute tonsillitis predominantly affects children and adolescents, with Staphylococcus aureus and Streptococcus pyogenes being the most common bacterial pathogens. Third-generation cephalosporins and gentamicin demonstrated good antimicrobial efficacy, while increasing resistance to macrolides was observed. Periodic surveillance of bacterial profiles and antibiotic sensitivity patterns is essential to guide empirical therapy and promote rational antibiotic use.

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