Multicenter Yemeni Study Reveals Bacteria and Antibiotic Resistance in Ear
Ear infections are often treated as routine ailments, yet a new multicenter study from Sana’a, Yemen, suggests that the bacteria responsible are increasingly resistant to medicines commonly used in everyday clinical practice. The investigation, published in BMC Infectious Diseases, examined ear-discharge samples from 313 patients treated or tested at four medical laboratories and two referral hospitals between January 2022 and December 2023. Researchers found bacterial growth in 271 samples, meaning that 86.6 percent of the specimens produced a positive culture. The findings provide one of the clearest recent snapshots of the organisms associated with ear infections in Sana’a and the resistance patterns that may complicate treatment.
The study focused on infections involving the external ear canal and middle ear, conditions commonly grouped under terms such as otitis externa and otitis media. Although ear infections may begin with relatively localized symptoms, including pain, discharge, itching, hearing changes or fever, their management depends heavily on identifying the underlying pathogen and selecting an antibiotic that can inhibit it. When treatment is chosen without microbiological guidance, resistant bacteria may survive, prolonging illness and increasing the possibility of complications. In settings where laboratory access is limited and antibiotics are frequently prescribed empirically, local surveillance becomes particularly important because resistance patterns can vary substantially between regions.
Among the positive cultures, Staphylococcus aureus was the dominant organism, accounting for 54.6 percent of the bacterial isolates. This species is a common colonizer of human skin and mucosal surfaces, but it can cause infection when it enters damaged tissue or accumulates in vulnerable areas. In the ear, S. aureus may contribute to inflammation and discharge, particularly in infections of the external auditory canal. Its prominence in the Sana’a samples is clinically significant because the species includes strains with a wide range of resistance mechanisms, including resistance to beta-lactam antibiotics and, in some cases, methicillin-class drugs.
The second most frequent organism was Pseudomonas aeruginosa, which represented 15.9 percent of the isolates. This environmental bacterium thrives in moist conditions and is strongly associated with otitis externa, especially when the ear canal is exposed to water, trauma or prolonged moisture. P. aeruginosa is also an important hospital-associated pathogen because it possesses multiple intrinsic and acquired resistance mechanisms. These include reduced permeability of its outer membrane, drug-efflux systems that pump antibiotics out of the cell, and enzymes capable of breaking down certain antimicrobial compounds. Its presence in ear infections can therefore narrow therapeutic options, particularly when resistance testing is unavailable.
The most striking result involved amoxicillin, to which 96.8 percent of tested bacterial isolates were resistant. Resistance was also high for cefoxitin, at 70.3 percent, and amoxicillin-clavulanic acid, at 58.6 percent. These medicines belong to or are closely related to the beta-lactam family, a major group of antibiotics that includes penicillins and cephalosporins. Beta-lactams work by interfering with bacterial cell-wall construction. Resistant bacteria can defeat them through several routes, including the production of beta-lactamase enzymes, alterations in the proteins targeted by the drugs, and changes that reduce antibiotic entry into the cell.
The results do not mean that every patient with an ear infection would fail treatment with these medicines, nor do they establish which drug should be prescribed to an individual. Instead, the figures describe the proportion of tested isolates that were classified as resistant under laboratory conditions. The researchers performed susceptibility testing using the Kirby–Bauer disk diffusion method, in which antibiotic-containing disks are placed on a culture medium seeded with bacteria. After incubation, the clear zones around the disks are measured and interpreted using standards from the Clinical and Laboratory Standards Institute. A small inhibition zone indicates that the organism is less susceptible to the tested medicine, while a larger zone suggests greater susceptibility.
Several antibiotics showed substantially more favorable laboratory activity. Clindamycin demonstrated sensitivity in 83.5 percent of tests, while ofloxacin and levofloxacin showed sensitivity rates of 75.6 percent and 70.5 percent, respectively. These drugs belong to different antimicrobial classes and act through mechanisms distinct from beta-lactams. Clindamycin interferes with bacterial protein production by binding to the 50S subunit of the ribosome. Ofloxacin and levofloxacin are fluoroquinolones that inhibit bacterial DNA gyrase and topoisomerase IV, enzymes needed for DNA replication and repair. However, laboratory sensitivity alone is not sufficient to determine the safest or most appropriate treatment. Clinical diagnosis, infection site, patient age, previous antibiotic exposure, local prescribing guidance and the risk of adverse effects must also be considered.
Across 2,644 antibiotic susceptibility tests, 48.8 percent recorded resistance. This overall figure points to a substantial antimicrobial-resistance burden, but it must be read alongside the study design. The investigation was retrospective and cross-sectional, relying on existing laboratory and hospital records rather than prospectively enrolling patients according to a standardized clinical protocol. Culture results may also reflect the patient population served by the participating facilities and may not represent every community in Yemen. In addition, the abstract does not provide detailed information on infection type, prior antibiotic use, bacterial distribution by facility or the specific number of isolates tested against each drug. Those factors can influence resistance estimates.
The demographic analysis found that infections were slightly more common among males, who accounted for 50.2 percent of cases, and that the 21-to-30-year age group represented the largest share of patients. These patterns may reflect healthcare-seeking behavior, occupational or environmental exposures, referral practices or the composition of the laboratories’ patient populations rather than an inherent biological difference in susceptibility. The study’s value lies principally in its integration of bacterial identification and susceptibility testing across multiple institutions, offering a regional baseline that clinicians and public-health authorities can use to design more informed treatment policies.
The authors argue that the findings strengthen the case for antimicrobial-stewardship programs in Sana’a. Such programs seek to ensure that antibiotics are used only when indicated, at the correct dose and for an appropriate duration, while encouraging culture-guided treatment when feasible. Regular surveillance could reveal whether resistance to beta-lactams continues to rise and whether susceptibility to alternative agents begins to decline. For patients, the broader message is that persistent or recurrent ear discharge should not automatically lead to repeated courses of the same antibiotic. Better diagnostic testing, updated empirical-treatment guidelines, infection-prevention measures and coordinated monitoring will be essential if clinicians are to preserve effective options against the bacteria circulating in Yemen’s ear infections.
Subject of Research: Bacterial causes of ear infections and their antimicrobial resistance patterns in Sana’a, Yemen.
Article Title: Bacterial isolates and antimicrobial resistance patterns in ear infections: a multicenter study from medical laboratories in Sana’a, Yemen
Article References: Al-Shami, A. S., Al-Mehdar, A. A., Maad, A. H., et al. “Bacterial isolates and antimicrobial resistance patterns in ear infections: a multicenter study from medical laboratories in Sana’a, Yemen.” BMC Infectious Diseases (2026).
Image Credits: AI Generated
DOI: 10.1186/s12879-026-14280-9
Keywords: Otitis media; otitis externa; Staphylococcus aureus; Pseudomonas aeruginosa; drug resistance; microbial sensitivity tests.
Tags: antibiotic efficacy in Yemenantimicrobial resistance in otitis mediabacterial pathogens in ear infectionschallenges in treating ear infections Yemenclinical management of ear infections in resource-limited settingsear infection bacteria resistancemicrobiological diagnosis of otitis externamulticenter infectious disease research Yemenmultidrug-resistant ear infectionspublic health implications of resistant bacteriasurveillance of antibiotic resistanceYemen ear infection study