Purpose: To phenotypically characterize Lm isolated from a RTE fish FPE in BC to determine if strains possess traits that may allow persistence in the FPE and proliferation in RTE products.
Methods: Lm (n = 28) isolates were subjected to PCR-based lineage typing and phenotypic characterization as described. Surface adherence was determined at 20°C by a crystal violet microtiter plate assay. Minimum inhibitory concentration (MIC) of quaternary ammonium compounds (QACs) was determined by agar dilution methods. Salt and cold stress were assayed in 6% NaCl-BHI at 30°C or BHI at 4°C, respectively. Optical densities or plate counts were taken at regular intervals and lag phase duration (LPD) was computed with DmFit. ANOVA was used to assess statistical differences.
Results: Lineage II isolates (n = 17) had increased AC surface adherence compared to Lineage I isolates (n = 11) on both polyvinyl chloride (PVC) and polystyrene (PS) (P < 0.005). Although adherence to PS was increased relative to PVC, a positive correlation was seen between adherence to PS and PVC (r = 0.827; P < 0.001). Three isolates showed increased resistance to QACs (MIC ≥ 15 μg/ml). LPD in salt ranged from 3 - 6 h and 28 - 53 h at 4°C. No differences in stress adaptation were observed between lineages (P > 0.25).
Significance: The ability of Lm recovered from a BC FPE to adhere to surfaces, resist sanitizers, and quickly adapt to stress may allow persistence of these isolates and growth in contaminated food. These results confirm the need for comprehensive sanitation measures to eliminate Lm from the FPE and reduce potential for RTE food contamination.