Chronic simple otitis media due to Vibrio alginolyticus

Simple chronic otitis media (SCOM) is a disease characterised by chronic inflammation of the mucosa of the middle ear and mastoids, tympanic membrane perforation and otorrhoea. Unlike acute otitis media, it is not accompanied by otalgia or fever. It is a rare health condition in developed countries and is a cause of childhood hearing loss in socially disadvantaged populations.

We present the case of a 15-year-old male with a history of bilateral tympanic membrane perforation since he was 16 months old, mild conductive hearing loss, and subclinical hypothyroidism. He had a recent history of a holiday, where he stayed on the island of Menorca and swam in the sea. Three weeks after his return, he went to his primary care doctor due to symptoms of bilateral otorrhoea lasting approximately one month, without accompanying fever. Physical examination revealed mucoid otorrhoea in both external auditory canals without apparent fungal superinfection. Topical antibiotic treatment was started with ciprofloxacin 1 mg/0.5 ml (one drop every eight hours for six days), with no clinical improvement and persistent discharge from both ears, so a sample of ear exudate was collected for aerobic and fungal culture. The sample was sent to the hospital's microbiology laboratory for processing.

At 24 h of incubation, numerous colonies with a mucous and shiny appearance, brownish in colour and with discreet swarming effect, grew in pure culture (Fig. 1) in blood agar and chocolate agar (Becton Dickinson®, Spain) incubated in an atmosphere enriched with CO₂. Culture media did not contain additional nutritional supplements. The oxidase test was positive and the Gram stain showed pleomorphic gram-negative bacilli, showing bacillary, coccobacillary and coccoid forms (Fig. 1). The microorganism was identified as Vibrio alginolyticus by mass spectometry (MALDI-TOF, Bruker®, Beckman Coulter®) with a score of 2.11. The microorganism was sensitive to amoxicillin/clavulanic acid (≤2/1 mg/l), gentamicin (≤2 mg/l), tobramycin (≤2 mg/l), ciprofloxacin (≤0.25 mg/l), levofloxacin (≤0.12 mg/l) and trimethoprim/sulfamethoxazole (≤2/38 mg/l) (MicroScan® WalkAway System, panel EN51, Beckman Coulter), following the European Committee on Antimicrobial Susceptibility Testing (EUCAST) 2021 criteria for Enterobacterales. Culture for fungi was negative after 48 h of incubation.

Figure 1.

Left: appearance of the colonies after 24 h of incubation in blood agar medium and CO₂ enriched atmosphere. Right: pleomorphic gram-negative bacilli on Gram stain.

With this microbiological result, the patient was assessed by an ENT specialist and started antibiotic treatment with amoxicillin/clavulanic acid 500/125 mg (one tablet orally every eight hours for seven days) and with ciprofloxacin/fluocinolone acetonide 3/0.25 mg/mL in ear drops (six-eight drops/day for five days). The otorrhoea subsided in both ears.

SCOM in childhood it is a potentially serious condition, so it is important to make an accurate aetiological diagnosis to start targeted and early antibiotic treatment. In the case presented here, the relationship between the aetiological infectious agent and exposure to seawater with its high salt content is documented in the literature, as well as the requirement for the existence of an underlying otic pathology that facilitates infection.^1–5

V. alginolyticus is the most halotolerant species of the genus, requiring a minimum NaCl concentration of 1% for optimal growth. This microorganism is not part of the usual saprophytic microbiota of the upper respiratory tract, so its acquisition is by direct contact with seawater or its derivatives, as in the case of our patient. The incubation period of ear infection from aquatic immersion to the onset of symptoms is highly variable, with some cases described with a latency between exposure and disease of up to seven months.³ The clinical manifestations are very similar to those of otitis caused by other more prevalent microorganisms such as Pseudomonas aeruginosa, Staphylococcus aureus or E. coli. Presentation in children and monomicrobial aetiology due to V. alginolyticus is extremely rare in our setting, and very few cases have been described in Spain to date. Cases of otitis media have been documented where this microorganism has been isolated together with others, such as coagulase-negative staphylococci, diphtheroids and Moraxella catarrhalis,^2,3 and the clinical symptoms and duration of the infectious process do not vary between one type of infection or another.

Regarding antibiotic sensitivity, on an ongoing basis, this microorganism is sensitive to quinolones, macrolides, third-generation cephalosporins, and trimethoprim/sulfamethoxazole, as well as aminopenicillins with beta-lactamase inhibitors.^1–4 Therefore, once the targeted antibiotic treatment has been started, the clinical evolution is always satisfactory.

In this paper we found the limitation of not having an identification of the microorganism through a molecular method, although the degree of precision obtained through MALDI-TOF was adequate for the genus and species, with a high score (>2.0).

To conclude, it is important to consider V. alginolyticus in the microbiological diagnosis of ear infections in those patients who have a history of exposure to seawater and underlying ear pathology.