Antimicrobial efficacy of plant essential oils and extracts against Escherichia coli.

The efficacies of 11 plant-derived antimicrobials were evaluated against Escherichia coli in vitro in solution at room temperature. These included lemongrass, cinnamon, and oregano essential oils and their active components (citral, cinnamaldehyde, and carvacrol, respectively). Allspice and clove bud oils and olive, green tea, and grape seed extracts were also studied. The efficacies of the antimicrobials were both concentration- and exposure time-dependent. The essential oils and their active components demonstrated statistically significant >5.0-log10 reductions within 1-10 min. The plant extracts were less effective; green tea and grape seed extracts required 24 h before significant reductions were observed (1.93-log10 and 5.05-log10, respectively). Nevertheless, olive extract exhibited a reduction of ∼5-log10 within 30 min. Most of these plant-derived compounds exhibited strong bactericidal activity and can potentially be applied as alternatives to chemicals for foods/food contact surfaces since they are generally recognized as safe (GRAS) for human consumption. They may also be useful in applications in which other antimicrobials have reduced efficacy (e.g., in the presence of organics) or used with sensitive populations that are unable to tolerate exposure to harsher chemicals (e.g., elderly care facilities). These compounds could be used alone, in combination, or with fast-acting antimicrobials to provide a long-lasting residual.

Crystallographic insights into the structure-activity relationships of diazaborine enoyl-ACP reductase inhibitors.

Enoyl-ACP reductase, the last enzyme of the fatty-acid biosynthetic pathway, is the molecular target for several successful antibiotics such as the tuberculosis therapeutic isoniazid. It is currently under investigation as a narrow-spectrum antibiotic target for the treatment of several types of bacterial infections. The diazaborine family is a group of boron heterocycle-based synthetic antibacterial inhibitors known to target enoyl-ACP reductase. Development of this class of molecules has thus far focused solely on the sulfonyl-containing versions. Here, the requirement for the sulfonyl group in the diazaborine scaffold was investigated by examining several recently characterized enoyl-ACP reductase inhibitors that lack the sulfonyl group and exhibit additional variability in substitutions, size and flexibility. Biochemical studies are reported showing the inhibition of Escherichia coli enoyl-ACP reductase by four diazaborines, and the crystal structures of two of the inhibitors bound to E. coli enoyl-ACP reductase solved to 2.07 and 2.11 Šresolution are reported. The results show that the sulfonyl group can be replaced with an amide or thioamide without disruption of the mode of inhibition of the molecule.

Mechanisms of antiviral action of plant antimicrobials against murine norovirus.

Numerous plant compounds have antibacterial or antiviral properties; however, limited research has been conducted with nonenveloped viruses. The efficacies of allspice oil, lemongrass oil, and citral were evaluated against the nonenveloped murine norovirus (MNV), a human norovirus surrogate. The antiviral mechanisms of action were also examined using an RNase I protection assay, a host cell binding assay, and transmission electron microscopy. All three antimicrobials produced significant reductions (P ≤ 0.05) in viral infectivity within 6 h of exposure (0.90 log10 to 1.88 log10). After 24 h, the reductions were 2.74, 3.00, and 3.41 log10 for lemongrass oil, citral, and allspice oil, respectively. The antiviral effect of allspice oil was both time and concentration dependent; the effects of lemongrass oil and citral were time dependent. Based on the RNase I assay, allspice oil appeared to act directly upon the viral capsid and RNA. The capsids enlarged from ≤ 35 nm to up to 75 nm following treatment. MNV adsorption to host cells was not significantly affected. Alternatively, the capsid remained intact following exposure to lemongrass oil and citral, which appeared to coat the capsid, causing nonspecific and nonproductive binding to host cells that did not lead to successful infection. Such contrasting effects between allspice oil and both lemongrass oil and citral suggest that though different plant compounds may yield similar reductions in virus infectivity, the mechanisms of inactivation may be highly varied and specific to the antimicrobial. This study demonstrates the antiviral properties of allspice oil, lemongrass oil, and citral against MNV and thus indicates their potential as natural food and surface sanitizers to control noroviruses.

The Identification and Differentiation between Burkholderia mallei and Burkholderia pseudomallei Using One Gene Pyrosequencing.

The etiologic agents for melioidosis and glanders, Burkholderia mallei and Burkholderia pseudomallei respectively, are genetically similar making identification and differentiation from other Burkholderia species and each other challenging. We used pyrosequencing to determine the presence or absence of an insertion sequence IS407A within the flagellin P (fliP) gene and to exploit the difference in orientation of this gene in the two species. Oligonucleotide primers were designed to selectively target the IS407A-fliP interface in B. mallei and the fliP gene specifically at the insertion point in B. pseudomallei. We then examined DNA from ten B. mallei, ten B. pseudomallei, 14 B. cepacia, eight other Burkholderia spp., and 17 other bacteria. Resultant pyrograms encompassed the target sequence that contained either the fliP gene with the IS407A interruption or the fully intact fliP gene with 100% sensitivity and 100% specificity. These pyrosequencing assays based upon a single gene enable investigators to reliably identify the two species. The information obtained by these assays provides more knowledge of the genomic reduction that created the new species B. mallei from B. pseudomallei and may point to new targets that can be exploited in the future.

Identification of pBC218/pBC210 Genes of Bacillus cereus G9241 in Five Florida Soils Using qPCR.

The distribution of the virulent plasmid pBC210 of B. cereus that carries several B. anthracis genes and has been implicated in lethal anthrax-like pulmonary disease is unknown. We screened our collection of 103 B. cereus isolates and 256 soil samples using a quantitative PCR (qPCR) assay that targeted three open reading frames putatively unique to pBC210. When tested with DNA from 2 B. cereus strains carrying pBC210, and 64 Gram-positive and 55 Gram-negative bacterial species, the assay had 100% sensitivity and specificity. None of the DNA from the B. cereus isolates yielded positive amplicons but DNA extracted from five soils collected in Florida gave positive results for all three target sequences of pBC210. While screening confirms that pBC210 is uncommon in B. cereus, this study is the first to report that pBC210 is present in Florida soils. This study improves our knowledge of the distribution of pBC210 in soils and, of public health importance, the potential threat of B. cereus isolates carrying the toxin-carrying plasmid. We demonstrated that sequences of pBC210 can be found in a larger geographical area than previously thought and that finding more B. cereus carrying the virulent plasmid is a possibility in the future.