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Carbapenem resistant <i>Klebsiella pneumoniae</i> has 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-hydrolyzing <i>K. pneumoniae</i> isolates obtained from the nares of preterm neonates. Time-kill assays with graded percentages of (<i>v</i>/<i>v</i>) LA in water were initially carried out against planktonic cells of a meropenem (MRP)-resistant <i>K. pneumoniae</i> isolate, 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 (<i>v</i>/<i>v</i>) LA. Six carbapenem-hydrolyzing isolates were next used to validate the results. A reduction of 3.6 &#177; 0.6 log₍₁₀₎ CFU/mL in JNM11.C4 planktonic cells and &gt;3 &#177; 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 &#177; 0.3log₍₁₀₎ CFU/mL) and biofilm-forming cells (3.8 &#177; 0.3log₍₁₀₎ CFU/mL) across all the six clinical isolates. These results indicate that LA is an effective antimicrobial against planktonic carbapenem-hydrolyzing <i>K. pneumoniae</i> cells and biofilms.