Eileen B. Somers’s research while affiliated with University of Wisconsin–Madison and other places

We have investigated bottom-up chemical synthesis of quaternary ammonium (QA) groups exhibiting antibacterial properties on stainless steel (SS) and filter paper surfaces via nonequilibrium, low-pressure plasma-enhanced functionalization. Ethylenediamine (ED) plasma under suitable conditions generated films rich in secondary and tertiary amines. These functional structures were covalently attached to the SS surface by treating SS with O 2 and hexamethyldisiloxane plasma prior to ED plasma treatment. QA structures were formed by reaction of the plasma-deposited amines with hexyl bromide and subsequently with methyl iodide. Structural compositions were examined by electron spectroscopy for chemical analysis and Fourier transform infrared spectroscopy, and surface topography was investigated with atomic force microscopy and water contact angle measurements. Modified SS surfaces exhibited greater than a 99.9% decrease in Staphylococcus aureus counts and 98% in the case of Klebsiella pneumoniae. The porous filter paper surfaces with immobilized QA groups inactivated 98.7% and 96.8% of S. aureus and K. pneumoniae, respectively. This technique will open up a novel way for the synthesis of stable and very efficient bactericidal surfaces with potential applications in development of advanced medical devices and implants with antimicrobial surfaces.

The foodborne pathogen Bacillus cereus can form biofilms on various food contact surfaces, leading to contamination of food products. To study the mechanisms of biofilm formation by B. cereus, a Tn5401 library was generated from strain UW101C. Eight thousand mutants were screened in EPS, a low nutrient medium. One mutant (M124), with a disruption in codY, developed fourfold less biofilm than the wild-type, and its defective biofilm phenotype was rescued by complementation. Addition of 0.1% casamino acids to EPS prolonged the duration of biofilms in the wild-type but not codY mutant. When decoyinine, a GTP synthesis inhibitor, was added to EPS, biofilm formation was decreased in the wild-type but not the mutant. The codY mutant produced three times higher protease activity than the wild-type. Zymogram and SDS-PAGE data showed that production of the protease ( approximately 130 kDa) was repressed by CodY. Addition of proteinase K to EPS decreased biofilm formation by the wild-type. Using a dpp-lacZ fusion reporter system, it was shown that that the B. cereus CodY can sense amino acids and GTP levels. These data suggest that by responding to amino acids and intracellular GTP levels CodY represses production of an unknown protease and is involved in biofilm formation.

Oxygen/water vapor-plasma treated polished aluminum substrates were coated with poly(acrylic acid) (PAA) using deeping-coating technique, and subsequently heated. ESCA, chemical derivatization and SEM confirmed the successful coating of substrates. It was shown that the covalently attached PAA macromolecules exhibit anti-bacterial characteristics. Samples coated with PAA exposed to a 5 strain mixture of Listeria monocytogenes for 24 hours resulted in 98% decrease in the bacterial population. A mix of three different bacteria, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Escherichia coli was also tested. A reduction of 82 to 96% of bacterial numbers was obtained. Experimental results indicated that double layer structures could also be prepared from PAA-coated surfaces. PAA and poly(vinylpyridine) (PVP) double layers were successfully generated.

Bacillus cereus ATCC 14579 can respond to nutrient changes by adopting different forms of surface translocation. The B. cereus ATCC 14579 ΔplcR mutant, but not the wild type, formed dendritic (branched) patterns on EPS [a low-nutrient medium that contains 7.0 g K2HPO4, 3.0 g KH2PO4, 0.1 g MgSO4·7H2O, 0.1 g (NH4)2SO4, 0.01 g CaCl2, 0.001 g FeSO4, 0.1 g NaCl, 1.0 g glucose, and 125 mg yeast extract per liter] containing 0.7% agar. The dendritic patterns formed by sliding translocation of nonflagellated cells are enhanced under low-nutrient conditions and require sufficient production of a biosurfactant, which appears to be repressed by PlcR. The wild-type and complemented strains failed to slide on the surface of EPS agar because of the production of low levels of biosurfactant. Precoating EPS agar surfaces with surfactin (a biosurfactant produced by Bacillus subtilis) or biosurfactant purified from the ΔplcR mutant rescued the ability of the wild-type and complemented strains to slide. When grown on a nutrient-rich medium like Luria-Bertani agar, both the wild-type and ΔplcR mutant strains produced flagella. The wild type was hyperflagellated and elongated and exhibited swarming behavior, while the ΔplcR mutant was multiflagellated and the cells often formed long chains but did not swarm. Thin-layer chromatography and mass spectrometry analyses suggested that the biosurfactant purified from the ΔplcR mutant was a lipopeptide and had a mass of 1,278.1722 (m/z). This biosurfactant has hemolytic activity and inhibited the growth of several gram-positive bacteria.

The antibotulinal effectiveness of nisin in TPYG broth was increased somewhat by lowering the pH to pH 5.5. The ability of nisin to inhibit the outgrowth of strain 56A spores was markedly increase at pH 5.5 by comparison to its effectiveness at higher pHs observed in previous studies. The increased effectiveness of nisin at pH 5.5 was less notable for the strain 69A, 113B, and 213B spores. The nisin sensitivity of the type E spores was essentially unchanged from that observed in earlier studies at higher pHs. At pH 6, nisin levels of 5000 I.U./ml were insufficient to prevent spore outgrowth by C. botulinum in cooked meat medium. Comparatively, much lower levels of nisin were effective in preventing botulinal outgrowth in TPYG broth at pH 6. The decreased effectiveness of nisin in cooked meat medium may be due to the binding of nisin to meat particles, and this binding is apparently not affected by lowering the pH to pH 6.0.

ABSTRACT Poly(ethylene glycol) (PEG)-like structures were generated on stainless steel under di(ethylene glycol) vinyl ether (DiEGVE) radio frequency-plasma environments. Electron spectroscopy for chemical analysis and attenuated total reflectance Fourier transform infrared spectroscopy indicated a PEG-like deposition, which was stable to cleaning, sanitizing, and storage for up to 2 mo. Atomic force microscopy and water contact angle analysis indicated that the modified stainless-steel surfaces were less rough and more hydrophilic than the unmodified surfaces. Listeria monocytogenes attachment and biofilm formation on modified surfaces decreased more than 90% compared with the unmodified stainless steel (P < 0.01). DiEGVE cold plasma was demonstrated to be a promising technique to reduce bacterial contamination on surfaces encountered in food-processing environments.

Stenotrophomonas maltophilia WR-C is capable of forming biofilm on polystyrene and glass. The lipopolysaccharide/exopolysaccharide-coupled biosynthetic genes rmlA, rmlC, and xanB are necessary for biofilm formation and twitching motility. Mutants with mutations in rmlAC and xanB display contrasting biofilm phenotypes on polystyrene and glass and differ in swimming motility.

The ΔplcR mutant of Bacillus cereus strain ATCC 14579 developed significantly more biofilm than the wild type and produced increased amounts of biosurfactant. Biosurfactant production is required for biofilm formation and may be directly or indirectly repressed by PlcR, a pleiotropic regulator. Coating polystyrene plates with surfactin, a biosurfactant from Bacillus subtilis, rescued the deficiency in biofilm formation by the wild type.