Purpose: To investigate molecular characteristics, antimicrobial resistance, and biofilm formation ability of Pseudomonas aeruginosa  strains isolated from patients with aural infections.
Methods: Isolates (n = 199) were collected from ear discharges of patients with aural infections from January 2019 to December 2020. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute guidelines. All isolates were subjected to multilocus sequence typing (MLST) with amplification and sequencing of seven housekeeping genes. Biofilm formation and eradication were quantitatively assessed in microtiter plates. Genes associated with biofilm formation and the quinolone-resistance-determining region (QRDR) of genes gyrA  and parC  were investigated using polymerase chain reaction amplification and sequencing.
Results: Of the 199 P. aeruginosa  strains isolated, 109 (54.77%) were from females and 90 (45.23%) were from males. The isolates exhibited very low rates of resistance to most antibiotics tested, including piperacillin (1.51%), ceftazidime (0.50%), and imipenem (3.52%); however, the quinolones ciprofloxacin (80.40%) and levofloxacin (82.91%) were notable exceptions. The QRDR sequence results of the quinolone-resistant P. aeruginosa  isolates showed Thr83Ile (n = 155) was the most common amino acid mutation in gyrA  (n = 165), while Se r87Leu (n = 157) was widely detected in parC  (n = 165). MLST analysis identified 34 sequence types (STs) with most isolates belonging to ST316 (73.87%). Almost all of the P. aeruginosa  isolates (96.98%) produced biofilms and biofilm-forming genes algD  (98.49%), pslD  (96.98%), and pelF  (96.48%) were highly prevalent.
Conclusion: The P. aeruginosa  strains isolated from aural discharges in this study exhibited very low rates of resistance to most antibiotics tested, except for the resistance rates to quinolones, which were relatively high. The isolates also exhibited a strong biofilm formation ability and low susceptibility to eradication, indicating that more effective drugs and treatment methods are needed to combat these infections.
Keywords: Pseudomonas aeruginosa  isolate, ear infection, antimicrobial resistance, ST316, biofilm