Bactericidal Activity of Lactic Acid against Clinical, Carbapenem-Hydrolyzing, Multi-Drug-Resistant Klebsiella pneumoniae Planktonic and Biofilm-Forming Cells

Carbapenem resistantKlebsiella pneumoniaehas been highlighted to be a critical pathogen by the World Health Organization. The objectives of this study were to assess the efficacy of lactic acid (LA) against planktonic cells and biofilms formed by carbapenem-hydrolyzingK. pneumoniaeisolates obtained from the nares of preterm neonates. Time-kill assays with graded percentages of (v/v) LA in water were initially carried out against planktonic cells of a meropenem (MRP)-resistantK. pneumoniaeisolate, JNM11.C4. The efficacy parameters such as optimal incubation time and minimum inhibitory concentration were determined by comparing colony-forming unit counts (log(10)CFU). Scanning electron microscopy was used to visualize cell damage. Likewise, JNM11.C4 biofilms were treated with graded series of (v/v) LA. Six carbapenem-hydrolyzing isolates were next used to validate the results. A reduction of 3.6 ± 0.6 log(10)CFU/mL in JNM11.C4 planktonic cells and >3 ± 0.03log(10)CFU/mL in biofilm-forming cells were observed using 0.225% and 2% LA, respectively, after three hours. Similar decreases in viable cell-counts were observed both in the case of planktonic (˃3.6 ± 0.3log(10)CFU/mL) and biofilm-forming cells (3.8 ± 0.3log(10)CFU/mL) across all the six clinical isolates. These results indicate that LA is an effective antimicrobial against planktonic carbapenem-hydrolyzingK. pneumoniaecells and biofilms.Keywords:Klebsiella pneumoniae;carbapenem-hydrolyzing;lactic acid;meropenem;planktonic;biofilm-forming;bactericidal