Integrated Phenotypic Profiles of Bacterial Isolates Recovered from Otitis Media in Misurata, Libya: An Analytical Cross-Sectional Study

Otitis media can involve bacterial populations with overlapping antimicrobial-resistance and surface-associated phenotypes. This analytical cross-sectional study characterised ear-discharge isolates from 58 patients with clinician-diagnosed acute or chronic otitis media in Misurata, Libya, between April and August 2026. Aerobic cultures, conventional biochemical tests supplemented by an API identification system, antimicrobial disk diffusion, Congo red agar (CRA), and a clavulanate double-disk synergy assay were used. Culture was positive in 52/58 patients (89.7%), yielding 66 isolates. Pseudomonas aeruginosa accounted for 19/66 (28.8%) and Staphylococcus aureus for 18/66 (27.3%). CRA positivity and reported multidrug resistance (MDR) occurred in 53.0% and 54.5% of isolates, respectively. A clavulanate-synergy phenotype occurred in 18/40 (45.0%) Gram-negative isolates and in 10/15 (66.7%) Enterobacterales; 7/18 (38.9%) S. aureus isolates were classified as methicillin-resistant. Acinetobacter baumannii and Klebsiella pneumoniae each showed 100% reported MDR, with median multiple-antibiotic-resistance indices of 0.62 and 0.60. The combined CRA-positive/MDR/clavulanate-synergy profile occurred in 30.0% of Gram-negative isolates; the reported species comparison yielded adjusted p = 0.0193. CRA positivity was associated with reported MDR (odds ratio 5.88, 95% confidence interval 1.86–20.34; adjusted p = 0.001). Previous antibiotic exposure was associated with patient-level MDR (79.2% vs 39.3%; adjusted p = 0.020). These descriptive findings indicate co-occurrence of several laboratory phenotypes, but CRA staining does not directly establish biofilm formation, and clavulanate synergy is not confirmatory ESBL evidence in non-fermenters. Local organism-aware surveillance and verified susceptibility interpretation are priorities.