Antimicrobial and Antibiofilm Activities of Highly Soluble Polypyrrole Combined with Benzoic Acid against Multidrug-Resistant <i>Klebsiella pneumoniae</i>

Multidrug-resistant <i>Klebsiella pneumoniae</i> represents a critical global public health threat, with limited therapeutic options available due to its biofilm-forming capacity. This study investigated the antimicrobial and antibiofilm potential of benzoic acid (BA), an organic acid, and highly soluble polypyrrole (Hs-PPy), a synthetic polymer, against <i>K. pneumoniae</i> isolates. Forty-seven clinical isolates from infected/colonized patients and one reference strain were evaluated. Antimicrobial susceptibility was determined for 16 antibiotics. Antimicrobial activity was assessed via broth microdilution against 25/47 isolates and the reference strain. Biofilm formation and substance interference were evaluated using crystal violet staining. All isolates demonstrated multidrug resistance, with >91% showing resistance to ampicillin, cefepime, ceftriaxone, levofloxacin, ertapenem, piperacillin-tazobactam, ampicillin-sulbactam, cefoxitin, ciprofloxacin, meropenem, imipenem, and trimethoprim-sulfamethoxazole, while 57.44% were resistant to polymyxin B. Susceptibility to amikacin and gentamicin was observed in 95.74% and 51.06% of isolates, respectively. Hs-PPy showed no intrinsic antimicrobial activity, whereas BA exhibited inhibitory and bactericidal effects at 2-4 mg/mL. Among biofilm producers, one isolate demonstrated strong formation, while others showed weak production. The Hs-PPy/BA combination effectively inhibited biofilm formation in the strong producer. These findings suggest that Hs-PPy/BA combination therapy offers significant advantages for controlling biofilm formation in multidrug-resistant <i>K. pneumoniae</i> infections.