Purpose: To investigate the attachment properties of Salmonella and E. coli strains proposed as surrogates as affected by the beef carcass topography and surface composition.
Methods: Five rifampicin-resistant Salmonella strains and four ampicillin-resistant E. coli strains were inoculated on beef tissues (1.5 cm2 on muscle, fascia, tendon, fat) and 1.0 cm2 (bone) pieces (0.1-0.5 mm depth). The pieces were individually placed in the inoculum into polystyrene 12-well plates and stored for two different temperature conditions. Temperature conditions included 26.6 ± 2.2°C (RT) for 24h or alternating RT (30 min) -refrigeration (4.8 ± 1.3°C, 24h) -RT (30 min). After incubation time tissues were rinsed and loosely and strongly cells were enumerated on appropriate culture media and Sr value was expressed as percent of bacterial population physically attached to the surface (Sr= #loosely attached cells - #strongly attached cells /#strongly attached cells) .
Results: No differences were observed (P ≥ 0.05) on Sr values for all beef carcass tissues (n = 60). At 26.6 ± 2.2°C, Sr values ranged from 0.47 ± 0.00 to 0.54 ± 0.02 and at alternating temperatures ranged from 0.46 ± 0.01 to 0.54 ± 0.03. No differences were observed (P ≥ 0.05) between Sr values for Salmonella and E. coli on all beef carcass tissues and temperature conditions. The Sr values for Salmonella ranged from 0.52 ± 0.01and for E. coli from 0.52 ± 0.02.
Significance: The topography and superficial composition of tissues did not influence the attachment of bacteria. E. coli strains showed similar attachment properties to Salmonella strains confirming that they may be used as surrogates for validations studies on beef carcasses.