Liquid and vapor-phase vinegar reduces Klebsiella pneumoniae on fresh coriander

- The incidence of K. pneumoniae (KP) on fresh coriander is firstly reported.
- Inhibition of surface contaminations of KP by vinegar was measured in vitro.
- Liquid-phase exposure, levels above 2.4% (v/v) acetic acid completely inhibited KP.
- Vinegar vapor, an effective control agent for KP contamination on fresh coriander.

Samples of fresh coriander were sourced from several markets in the Ladkrabang and Minburi areas of Bangkok, Thailand. These were examined in the laboratory for fecal coliform contamination. The bacterium Klebsiella pneumoniae was the predominant contaminant in 48.5-84.0% of the 30 samples tested. Inhibition of surface contaminations of K. pneumoniae by vinegar was measured in vitro for either liquid- or vapor-phase exposures. For liquid-phase exposure, levels above 2.4% (v/v) acetic acid (AA) completely inhibited K. pneumoniae. After 50 min of vapor-phase exposure, 8% AA completely inhibited K. pneumoniae spread on Mueller Hilton agar (4.10 ± 0.04 log CFU/ml, 30 ± 2 °C, 80 ± 2% RH). Reduction of K. pneumoniae contamination on fresh coriander leaves using vinegar vapor was also examined. The effectiveness of inhibition was related to the level of K. pneumoniae inoculation, with vinegar vapor being shown to be an effective control agent for surface contaminations on fresh coriander so reducing the potential health risks to consumers.