Escherichia coli Biofilms Formed under Low-Shear Modeled Microgravity in a Ground-Based System

Abstract

Bacterial biofilms cause chronic diseases that are difficult to control. Since biofilm formation in space is well documented and planktonic cells become more resistant and virulent under modeled microgravity, it is important to determine the effect of this gravity condition on biofilms. Inclusion of glass microcarrier beads of appropriate dimensions and density with medium and inoculum, in vessels specially designed to permit ground-based investigations into aspects of low-shear modeled microgravity (LSMMG), facilitated these studies. Mathematical modeling of microcarrier behavior based on experimental conditions demonstrated that they satisfied the criteria for LSMMG conditions. Experimental observations confirmed that the microcarrier trajectory in the LSMMG vessel concurred with the predicted model. At 24 h, the LSMMG Escherichia coli biofilms were thicker than their normal-gravity counterparts and exhibited increased resistance to the general stressors salt and ethanol and to two antibiotics (penicillin and chloramphenicol). Biofilms of a mutant of E. coli, deficient in s , were impaired in developing LSMMG-conferred resistance to the general stressors but not to the antibiotics, indicating two separate pathways of LSMMG-conferred resistance.

Characterization of the Salmonella enterica Serovar TyphimuriumydcIGene, Which Encodes a Conserved DNA Binding Protein Required for Full Acid Stress Resistance

“…In addition, induction of ydcI expression in S. Typhimurium resulted in the formation of a biofilm in stationary-phase cultures. These data indicate the ydcI gene encodes a conserved DNA binding protein involved with aspects of prokaryotic biology related to stress resistance and possibly virulence.Bacterial growth environments characterized by low fluid shear force have been shown to induce a multitude of phenotypic responses, including altered acid, oxidative, thermal, and osmotic stress resistance (7,33,36,41,(52)(53)(54)(55), increased biofilm formation (6, 33, 52), altered protein secretion (14, 15), altered cell surface lipid and polysaccharide profiles (6, 7, 55), and increased survival in cellular and animal hosts (39,(52)(53)(54). Notably, the virulence of Salmonella enterica serovar Typhimurium is increased by low fluid shear growth conditions as measured using murine infection assays and tissue culture models (39,(52)(53)(54).…”

New Device for High-Throughput Viability Screening of Flow Biofilms

“…As a further check of the reliability of rapid plate reader scanning for determination of viability, we analyzed biofilm images obtained by fluorescence microscopy (Fig. 4, insets), as reported previously (25,26). The biofilm viability calculated from fluorescence ratios obtained using microscope images agreed with that measured with the plate reader (Fig.…”

“…Phase-contrast images were also collected to verify that all of the cells remained fluorescent. The fluorescence intensity of images was quantified using the NIH freeware ImageJ (http: //rsb.info.nih.gov/ij/index.html) as described previously (25,26). Fluorescence values (obtained using both methods) were integrated and used to calculate the ratio of green fluorescence to red fluorescence.…”

“…Better control of biofilms requires elucidation of the molecular basis of their superior resistance (by identifying resistance-compromised mutants) and identification of compounds with antibiofilm activity. While our understanding of these aspects of biofilms has increased (11,15,(25)(26)(27)36), further work, including development of accurate high-throughput (HTP) methods for screening biofilm viability, is needed.Two major biofilm models are studied in the laboratory, biofilms grown without a continuous flow of fresh medium and biofilms grown with a continuous flow of fresh medium; examples of these two models are microtiter well biofilms and flow cell biofilms, respectively. Methods have been developed for HTP screening of the viability of static biofilms (6,28,32,33), but there are no methods for HTP screening of flow biofilms.…”

“…Better control of biofilms requires elucidation of the molecular basis of their superior resistance (by identifying resistance-compromised mutants) and identification of compounds with antibiofilm activity. While our understanding of these aspects of biofilms has increased (11,15,(25)(26)(27)36), further work, including development of accurate high-throughput (HTP) methods for screening biofilm viability, is needed.…”