Non-thermal atmospheric pressure plasma inactivation of Paenibacillus larvae, the causative agent of American foulbrood in honeybees (Apis mellifera)

American foulbrood (AFB), caused by Paenibacillus larvae, is a major threat to honeybee (Apis mellifera) health. This study evaluated the antimicrobial efficacy of direct non-thermal atmospheric pressure plasma (NTAPP) against P. larvae and its effects on bacterial infectivity in honeybee larvae. Air and argon plasma treatments significantly inhibited bacterial growth on agar, producing inhibition zones up to 17.5 mm, and reduced viable counts to 5.21–5.54 log CFU/mL (p < 0.0001). Plasma exposure compromised membrane integrity, as evidenced by increased leakage of intracellular nucleic acids and proteins, resulting in a 5.49–36.21% reduction in viable cells depending on the plasma conditions. Consistently, SEM analysis revealed pronounced plasma-induced morphological alterations in P. larvae cells. Larvae fed with plasma-treated P. larvae, particularly air plasma–treated cells, exhibited markedly reduced bacterial loads. However, Kaplan–Meier survival analysis showed no significant differences in larval survival among treatment groups, indicating that although plasma treatment reduced bacterial viability, this effect did not translate into improved larval survival under the conditions tested. Overall, NTAPP effectively reduced P. larvae viability, demonstrating its antimicrobial potential against this pathogen. Further optimization, particularly targeting spore inactivation, is required to enhance its impact on larval survival and support practical applications in apiculture.