Biofilm Forming Capabilities of Shiga-toxigenic Escherichia coli Recovered from Cow/Calf Operations in Oklahoma and Louisiana

Introduction:  Shiga-toxigenic Escherichia coli (STEC) is one of the most common groups of foodborne pathogens and has been associated with foodborne outbreaks throughout the United States. The ability to form biofilms on both food and food processing equipment contributes to STEC persistence, as well as the number of widespread outbreaks. This shows the importance of characterizing STEC biofilms and understanding how these bacteria travel through the food supply chain from pre-harvest to consumer goods.

Purpose:  Determine biofilm forming capabilities of STEC isolates recovered from cow calf operations.

Methods: Seven STEC serogroups (O157, O26, O45, O103, O111, O121, O145) were tested for their biofilm capability. Of the several wild-type (WT) STEC, isolated from cattle operations in Oklahoma, 14 (O157-LF4, O157-KF10, 0157-JEQ1, O26-QF6, O26-BF8, O26-AF5, O45-HF9, O45-AF1, O45-EF2, O103-SF2, O103-GF8, O103-AF10, O121-GF6, O145-BF9) were tested for their biofilm forming capacity along with seven lab strains (O157-43895, O121, O111, O103, O26, O145, O45). Microtiter plates (96-well) were inoculated with ~ seven log CFU/ml of the aforementioned STEC, and incubated for 24 h to allow for biofilm formation. After incubation, unattached cells were removed; wells washed with phosphate buffered saline; and stained using crystal violet. The crystal violet stain was released in ethanol:acetone solution and absorbance was recorded at 595 nm.

Results:  Based on the absorbance, the biofilm-forming capability of tested STEC strains was categorized as follows: Very Strong (A₅₉₅>0.9), Strong (0.9<A₅₉₅> 0.6), Medium (0.6<A₅₉₅>0.3), Weak (0.3<A_595>0.1) and nonbiofilm formers (A₅₉₅<0.1). All 21 STEC strains were found to be capable of biofilm formation. All STEC (lab and WT) strains produced very strong biofilms, except O111 (lab) and O103-SF2 (WT), which were only capable of strong (0.916 and 0.887 respectively) biofilm formation.

Significance:  Identifying and measuring the biofilm forming capability of STEC strains can lead to the development of better intervention strategies for the food industry.