CSOM is characterized by chronic inflammation of the middle ear and mastoid cavity with persistent or recurrent otorrhoea through a perforated tympanic membrane. It remains an important cause of preventable hearing loss, particularly in children and in resource-limited settings. The disease is associated with recurrent infection, Eustachian-tube dysfunction, poor ear hygiene and prolonged or inappropriate antimicrobial exposure. P. aeruginosa, Staphylococcus aureus, Enterobacterales and other non-fermenters are frequently implicated, while Aspergillus and Candida may contribute to chronic or refractory disease [1,4]. Microbial patterns vary geographically, making local surveillance important for empiric treatment. Indian studies have reported P. aeruginosa and S. aureus as leading bacterial isolates, with fungal recovery generally ranging around 12–27% [5,8]. Increasing ESBL and carbapenemase production further limits therapeutic choices and emphasizes susceptibility-guided treatment [9,12]. The present study was undertaken to determine the bacterial and fungal profile of CSOM and the antimicrobial susceptibility pattern of aerobic bacterial isolates in a tertiary-care hospital.

This prospective observational study was conducted in the Department of Microbiology from July 2023 to June 2025. Ethical clearance was obtained from institutional ethical committee prior to study .All age groups and all sexes with clinically diagnosed CSOM and ear discharge for >3 months and patients without recent antibiotic exposure were included, while those with previous invasive ear procedures, immunocompromised or prolonged steroid therapy were excluded. After dry mopping and with aseptic precautions,collection was done using aural speculum in three sterile swabs . Collected Samples were subjected to Gram staining, KOH examination, aerobic culture on blood, chocolate and MacConkey agar, and fungal culture on Sabouraud dextrose agar. Bacterial identification was done by colony morphology, Gram stain and biochemical tests. Antimicrobial susceptibility testing was performed by Kirby–Bauer disc diffusion method . Methicillin resistance and inducible clindamycin resistance were assessed among Staphylococci, ESBL and carbapenemase production were evaluated phenotypically [13].

A total of 318 clinically diagnosed CSOM cases were studied in which 183 (57.5%) were male and 135 (42.5%) female. The 0–10 year age group contributed the largest proportion (33.3%). Culture yielded growth in 206 (64.8%) samples, while 112 (35.2%) showed no growth. Table 1. Demographic/culture summary Finding n (percentage)% Total CSOM cases 318 100 Male 183 57.5 Female 135 42.5 0–10 years 106 33.3 Culture positive 206 64.8 Culture negative 112 35.2 Table 2a. Microbial profile of bacterial culture-positive cases. Organism No. isolates (percentage)% Pseudomonas aeruginosa 72 35.0 Staphylococcus spp. 59 28.6 Klebsiella pneumoniae 27 13.0 Acinetobacter spp. 11 5.3 Proteus mirabilis 6 3.0 Escherichia coli 3 1.4 Total bacterial isolates 178 86.3 Table 2b. Microbial profile of fungus culture-positive cases Organism No. of isolates Percentage (%) Aspergillus niger 17 8.2 Candida albicans 11 5.3 Total fungal isolates 28 13.5 Antimicrobial susceptibility and resistance Among 59 staphylococcal isolates, susceptibility was highest to linezolid (98%), followed by clindamycin (89%), erythromycin (78%) and gentamicin (75%); trimethoprim–sulfamethoxazole showed the lowest susceptibility (42%). Of 45 S. aureus isolates, 18 (30.5%) were MRSA and 27 (45.7%) MSSA; inducible clindamycin resistance was detected in 10 isolates overall. Among Enterobacterales, piperacillin–tazobactam and meropenem retained comparatively good activity. P. aeruginosa showed 92% susceptibility to aztreonam, 85% to piperacillin–tazobactam and 77% to meropenem, whereas Acinetobacter spp. showed 88% susceptibility to tobramycin and 82% to piperacillin–tazobactam . Table 3. Antimicrobial susceptibility pattern. Group Drug Susceptibility Staphylococcus spp. Linezolid 98% Staphylococcus spp. Clindamycin 89% Staphylococcus spp. Gentamicin 75% Staphylococcus spp. TMP-SMX 42% P. aeruginosa Aztreonam 92% P. aeruginosa Piperacillin–tazobactam 85% P. aeruginosa Meropenem 77% Acinetobacter spp. Tobramycin 88% Enterobacterales Piperacillin–tazobactam 84–100% Enterobacterales Meropenem 74–100% Resistance phenotyping: ESBL production was confirmed in 8/27 (29%) K. pneumoniae and 1/6 (16%) P. mirabilis; no E. coli isolate was confirmed. Carbapenemase production was detected in 4/27 (14.8%) K. pneumoniae and 9/72 (12.5%) P. aeruginosa, with none detected in E. coli or P. mirabilis.

The present study demonstrated a predominance of P. aeruginosa (35%) followed by Staphylococcus spp. (28.6%). This pattern closely resembles the Indian studies of Kumar et al. and Ghogare et al., in which P. aeruginosa accounted for approximately 38% and 41%, respectively, while Staphylococcus spp remained the second major group [5,9]. The consistency across regions supports the importance of local antibiograms when selecting empirical therapy. Culture positivity in the present study was 64.8%, comparable with reports from Tamil Nadu (67.5%), Gujarat (65.2%), Uttar Pradesh (63.7%), Bangladesh (66.3%) and Nepal (62.8%) [5,6,10,11]. The 35.2% culture-negative rate may reflect prior antimicrobial exposure, fastidious or anaerobic organisms, specimen limitations or transport factors. This supports improving specimen collection and considering additional diagnostic approaches in refractory disease. Fungal isolates accounted for 13.5%, with A. niger (8.2%) and C. albicans (5.3%) predominating. The fungal rate is comparable to reports from Kerala, Tamil Nadu, Karnataka and Ethiopia, where fungal isolation ranged approximately 11.8–15% [7,8,12,17]. In contrast, higher fungal rates reported in some Indian studies may relate to differences in patient selection, climate, prior antibiotic/steroid exposure and laboratory methods. These findings support fungal culture in persistent or recurrent CSOM. Antimicrobial resistance is an important finding in which high linezolid susceptibility among Staphylococci was similar to observations from Maharashtra and Tamil Nadu, whereas reduced activity of ciprofloxacin and cotrimoxazole has also been reported [9,18]. ESBL production in K. pneumoniae (29%) and carbapenemase production in K. pneumoniae (14.8%) and P. aeruginosa (12.5%) were clinically relevant and broadly comparable with regional studies reporting carbapenemase rates around 13–16% [19,20]. These findings reinforce culture-directed treatment, resistance surveillance and antimicrobial stewardship.

In this study of 318 CSOM cases, children formed the largest affected group and males were more frequent. Culture positivity was 64.8%, with P.aeruginosa and Staphylococcus spp. as the leading bacterial pathogens. A. niger and C. albicans were the principal fungal isolates. The detection of MRSA, inducible clindamycin resistance, ESBL-producing Enterobacterales and carbapenemase-producing K. pneumoniae and P. aeruginosa demonstrates the need for continued resistance surveillance. Routine culture, susceptibility testing and selective fungal evaluation can help guide targeted therapy and reduce inappropriate antimicrobial use.

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