Surface Type and Inoculum Level Impacts the Integration of Escherichia coli Strain 0811 into Complex Biofilm Communities Formed under Simulated Meat Processing Conditions

Introduction: Most biofilm studies involving bacterial foodborne pathogens have been conducted using monocultures. However, to better understand the persistence of these bacteria within food-processing environments, studies involving multi-species systems need to be implemented.

Purpose: To investigate the fate of E. coli strain 0811 (serotype O103) during the development of polymicrobic biofilms formed under simulating-meat-processing-conditions (SMPC).

Methods: Biofilms were grown on stainless steel (SS) and high density polyethylene (HDPE) coupons during SMPC for 12 days at 15°C in replicated trials. Homogenates derived from environmental swabs (floor drains from processing facility) were used to inoculate bioreactors. After 24 h E. coli was introduced at high or low levels (10⁶ or 10³ CFU/ml, respectively). Total planktonic bacteria and E. coli were monitored daily, whereas biofilms were analyzed during days 2, 5, 8, and 12. Community profiling was conducted by 16S rRNA gene sequencing.

Results: Biofilm cell counts for E. coli monocultures were greater (P < 0.05) on HDPE (1.5 x 10⁷ CFU/cm²) than SS (7.6 x 10⁶ CFU/cm²). However, when competing with environmental microflora, E. coli only survived (at low levels) if introduced at high levels. E. coli planktonic levels of 5.2 x 10⁴ CFU/ml and 3.1 x 10² CFU/ml after 3 and 10 days, respectively, were maintained against a total bacterial population ranging up to 3 x 10⁸ CFU/ml. On day 12 total counts for biofilm populations on HDPE (4.2 x 10⁷ CFU/cm²) exceeded those on SS (2.1 x 10⁷ CFU/cm²) (P < 0.05) while E. coli levels were 1.8 x 10³ CFU/cm² on HDPE and not consistently detectable on SS. The HDPE community profile was dominated by Lactococcus spp. and Yersinia spp. (~70%) whereas on SS, Yersinia spp. (36%) and Janthinobacterium spp. (23%) were most prominent.

Significance: Although E. coli strain 0811 is a proficient biofilm-producer in monoculture it does not compete well within the complex biofilm community formed during our SMPC regimen.