Abstract
Vibrio alginolyticus, a Gram-negative rod bacterium found in marine environments, is known to cause opportunistic infections in humans, including ear infections, which can be difficult to diagnose. We investigated the microbiological and otopathogenic characteristics of a V. alginolyticus strain isolated from an ear exudate specimen obtained from a patient with chronic otitis externa to provide a basis for the future diagnosis of V. alginolyticus-associated infections. The identification of V. alginolyticus was accomplished using a combination of matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS), classical biochemical identification methods, and the use of Vibrio-selective media and advanced molecular identification methodologies. Antimicrobial susceptibility testing revealed that the strain was resistant to ampicillin and sensitive to β-lactam, aminoglycosides, fluoroquinolones, and sulfonamide antibiotics. The potential otopathogenic effects of V. alginolyticus were determined through the performance of cell viability, cell apoptosis, and cell death assays in tympanic membrane (TM) keratinocytes and HEI-OC1 cells treated with V. alginolyticus-conditioned medium using cell-counting kit (CCK)-8 assay, a wound-healing migration assay, Annexin V/propidium iodide (PI) flow cytometric analysis, and terminal deoxynucleotidyl transferase deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL staining). The results indicated that the identified V. alginolyticus strain exerts cytotoxic effects on keratinocytes and HEI-OC1 cells by inhibiting cell proliferation and migration and inducing apoptosis and cell death. To evaluate the ototoxicity of V. alginolyticus, the cell density and morphological integrity of hair cells (HCs) and spiral ganglion neurons (SGNs) were analyzed after exposing cochlear organotypic explants to the bacterial supernatant, which revealed the pre-dominant susceptibility and vulnerability of HCs and SGNs in the basal cochlear region to the ototoxic insults exerted by V. alginolyticus. Our investigation highlights the challenges associated with the identification and characteristic analysis of the Vibrio strain isolated in this case and ultimately aims to increase the understanding and awareness of clinicians and microbiologists for the improved diagnosis of V. alginolyticus-associated ear infections and the recognition of its potential otopathogenic and ototoxic effects.
Highlights
Otitis externa is a common ear affliction characterized by inflammation of the external ear canal, with or without infection (Wipperman, 2014)
Acute gastroenteritis with diarrhea was the most common clinical presentation of V. alginolyticus infections associated with the ingestion of raw seafood (Uh et al, 2001)
Ear infections (Levine et al, 1993), including otitis externa (García-Martos et al, 1993; Orden and Franco, 1993; Mukherji et al, 2000; Schets et al, 2006), myringitis (Citil et al, 2015), and otitis media (Ciufecu et al, 1979; Hasyn et al, 1987; Tsakris et al, 1995; Ardiç and Ozyurt, 2004; Feingold and Kumar, 2004), caused by V. alginolyticus have increased in prevalence in subtropical regions
Summary
Otitis externa is a common ear affliction characterized by inflammation of the external ear canal, with or without infection (Wipperman, 2014). The most common causative pathogens associated with otitis externa are human commensal bacteria, including Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes, some rare cases of fungal species have been described, including Candida or Aspergillus. Otitis media represents a complex, infectious, and inflammatory condition within the middle ear, which is frequently caused by a group of commensal bacteria that colonize the upper respiratory tract, including Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. Infectious agents from the otitis externa, Gram-negative bacteria, and anaerobic bacteria can cause middle ear infections (Neeff et al, 2016; Szmuilowicz and Young, 2019). The generation of bacterial toxins, combined with an excessive immune response (Wong and Ryan, 2015; Jung et al, 2019), can lead to inflammatory damage to the cochlear structures and sensory cells, such as hair cells (HCs) and spiral ganglion neurons (SGNs), resulting in devastating sensorineural hearing loss (Sun et al, 2020, 2021)
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