PFGE Characterization and Adhesion Capability of Listeria monocytogenes Isolates Obtained from Bovine Carcasses and Beef Processing Facilities

Introduction: Listeria monocytogenes is a pathogen capable of adhering to many surfaces and forming biofilms, which may explains its persistence in food processing environments, especially beef processing facilities. In addition, this pathogen is relatively resistant to variations in pH, NaCl and several antimicrobial substances, facilitating its permanence in the environment.

Purpose: This study aimed to genetically characterize L. monocytogenes isolates obtained from bovine carcasses and beef processing facilities and to evaluate their adhesion capabilities.

Methods: DNA from twenty-nine L. monocytogenes isolates was subjected to enzymatic restriction digestion using AscI and ApaI. All isolates were evaluated for the adhesion capability in microtitre plates considering the following variables: inoculum concentration, culture media, carbohydrate source, NaCl concentration, incubation temperature, and pH. Results were compared by ANOVA and Tukey (P < 0.05).

Results: Two clusters were identified for serotypes 4b and 1/2a, with similarities of 48% and 68%, respectively. The isolates presented best adhesion performance when tested at 8 log CFU/ml, being classified according to its capability as weak (8 isolates), moderate (17) or strong (4). The isolates showed higher adhesion capability in non-diluted culture media, medium at pH 7.0, incubation at 25 °C and 37 °C, and medium with NaCl concentrations of 5% and 7%. No relevant differences were observed for adhesion capability with respect to the carbohydrate source (P > 0.05).

Significance: The results indicated that despite a wide variation of characterized PFGE profiles, L. monocytognes adhesion might be related to optimal growing conditions.