Phenotypic and Genotypic Characterization of Biofilm Forming Capabilities in Non-O157 Shiga Toxin-Producing Escherichia coli Strains

Abstract

The biofilm life style helps bacteria resist oxidative stress, desiccation, antibiotic treatment, and starvation. Biofilm formation involves a complex regulatory gene network controlled by various environmental signals. It was previously shown that prophage insertions in mlrA and heterogeneous mutations in rpoS constituted major obstacles limiting biofilm formation and the expression of extracellular curli fibers in strains of Escherichia coli serotype O157:H7. The purpose of this study was to test strains from other important serotypes of Shiga toxin-producing E. coli (STEC) (O26, O45, O103, O111, O113, O121, and O145) for similar regulatory restrictions. In a small but diverse collection of biofilm-forming and non-forming strains, mlrA prophage insertions were identified in only 4 of the 19 strains (serotypes O103, O113, and O145). Only the STEC O103 and O113 strains could be complemented by a trans-copy of mlrA to restore curli production and Congo red (CR) dye affinity. RpoS mutations were found in 5 strains (4 serotypes), each with low CR affinity, and the defects were moderately restored by a wild-type copy of rpoS in 2 of the 3 strains attempted. Fourteen strains in this study showed no or weak biofilm formation, of which 9 could be explained by prophage insertions or rpoS mutations. However, each of the remaining five biofilm-deficient strains, as well as the two O145 strains that could not be complemented by mlrA, showed complete or nearly complete lack of motility. This study indicates that mlrA prophage insertions and rpoS mutations do limit biofilm and curli expression in the non-serotype O157:H7 STEC but prophage insertions may not be as common as in serotype O157:H7 strains. The results also suggest that lack of motility provides a third major factor limiting biofilm formation in the non-O157:H7 STEC. Understanding biofilm regulatory mechanisms will prove beneficial in reducing pathogen survival and enhancing food safety.

Growth media and temperature effects on biofilm formation by serotype O157:H7 and non-O157 Shiga toxin-producingEscherichia coli

“…In non‐O157:H7 STEC, strong biofilm formation was more readily observed. The lowest expression was seen in strains with motility deficiencies, RpoS mutations, or prophage insertions in mlrA (Chen et al ., ). These studies were performed using Congo red indicator (CRI) agar for CR affinity studies (Hammar et al ., ), Luria–Bertani (LB) broth with no salt (LB‐NS) to maximize biofilm expression (Uhlich et al ., ), and 23–25 °C incubations to simulate environmental conditions.…”

“…Strain and/or serotype differences in csgD expression would be expected due to the high number of regulators and the complexity of the network. We previously showed that Shiga toxin‐producing E. coli (STEC) varied greatly in their ability to express curli and generate biofilm (Chen et al ., ; Uhlich et al ., ). Curli and biofilm deficiencies in serotype O157:H7 likely stem from bacteriophage insertions in mlrA , a DNA‐binding protein that enhances RpoS‐driven csgD transcription (Uhlich et al ., ).…”

Biofilm formation, invasiveness and colicinogeny in locus of enterocyte and effacement negative O113:H21 ShigatoxigenicEscherichia coli

“…More recently, some attention has also been dispensed on the LEE‐carrying non‐O157 STEC belonging to the ‘ big six ’ serogroups, that is, O26, O45, O103, O111, O121 and O145 (Chen et al . ; Nesse et al . ; Uhlich et al .…”

“…Although few previous studies have suggested the ability of O113:H21 STEC strains to produce biofilms (Chen et al . ) and invade (Luck et al . ; Cordeiro et al .…”

“…; Chen et al . ). There is some speculation that the ability of O113:H21 strains to interact with biological and abiotic systems could be advantageous for them, contributing to their greater survival and persistence (Nesse et al .…”