Tolerance of Old World Climbing Fern (Lygodium microphyllum) Spores to Herbicides

Old World climbing fern (OWCF) is a highly invasive fern that disrupts natural communities in central and southern Florida. OCWF produces copious, wind-blown spores that have propelled its rapid invasion of Florida's natural areas over the last few decades. Current management of OWCF is limited to herbicides and natural resource managers in Florida have questioned if herbicides inhibit spore germination. This study compared spore germination rates of OWCF exposed to six herbicides and a surfactant from 1 to 24 h under laboratory conditions. Spores of OWCF were highly susceptible to metsulfuron, but exhibited tolerance to imazapyr, glyphosate, fluroxypyr, asulam, and triclopyr. Spore germination rates were 0.4% for spores exposed to 0.1 g ai L−1 of metsulfuron, but 0% for rates greater than or equal to 0.2 g ai L−1 at 30 d after treatment (DAT). Reduction in spore germination was observed with all other concentrations of herbicides tested, ranging from 10.4% with triclopyr (40 g ai L−1) to 42.6% with asulam (4.2 g ai L−1) compared to 47.9% germination for untreated checks 30 DAT. Spores were highly sensitive to metsulfuron with herbicide concentrations required for 50 and 95% inhibition of spore germination (I50 and I95) measuring 0.014 and 0.063 g ai L−1, respectively; spores were greater than 1,000-fold more sensitive to metsulfuron compared to I95 concentrations of any other herbicide tested. These results indicate that metsulfuron exhibits potential to control OWCF spore germination but spores are tolerant to the five other herbicides tested.

The Weak-Acid Preservative Sorbic Acid Is Decarboxylated and Detoxified by a Phenylacrylic Acid Decarboxylase, PadA1, in the Spoilage Mold Aspergillus niger

ABSTRACT Resistance to sorbic and cinnamic acids is mediated by a phenylacrylic acid decarboxylase (PadA1) in Aspergillus niger. A. niger ΔpadA1 mutants are unable to decarboxylate sorbic and cinnamic acids, and the MIC of sorbic acid required to inhibit spore germination was reduced by ∼50% in ΔpadA1 mutants.

Carvacrol, Cinnamaldehyde, Oregano Oil, and Thymol Inhibit Clostridium perfringens Spore Germination and Outgrowth in Ground Turkey during Chilling†

Inhibition of Clostridium perfringens by plant-derived carvacrol, cinnamaldehyde, thymol, and oregano oil was evaluated during abusive chilling of cooked ground turkey. Test substances were mixed into thawed turkey product at concentrations of 0.1, 0.5, 1.0, or 2.0% (wt/wt) along with a heat-activated three-strain C. perfringens spore cocktail to obtain final spore concentrations of ca. 2.2 to 2.8 log CFU spores per g of turkey meat. Aliquots (5 g) of the ground turkey mixtures were vacuum packaged and then cooked in a water bath, where the temperature was raised to 60°C in 1 h. The products were cooled from 54.4 to 7.2°C in 12, 15, 18, or 21 h, resulting in 2.9-, 5.5-, 4.9-, and 4.2-log CFU/g increases, respectively, in C. perfringens populations in samples without antimicrobials. Incorporation of test compounds (0.1 to 0.5%) into the turkey completely inhibited C. perfringens spore germination and outgrowth (P ≤ 0.05) during exponential cooling in 12 h. Longer chilling times (15, 18, and 21 h) required greater concentrations (0.5 to 2.0%) to inhibit spore germination and outgrowth. Cinnamaldehyde was significantly (P < 0.05) more effective (<1.0-log CFU/g growth) than the other compounds at a lower concentration (0.5%) at the most abusive chilling rate evaluated (21 h). These findings establish the value of the plant-derived antimicrobials for inhibiting C. perfringens in commercial ground turkey products.

Control of Clostridium perfringens in Cooked Ground Beef by Carvacrol, Cinnamaldehyde, Thymol, or Oregano Oil during Chilling†

Inhibition of Clostridium perfringens spore germination and outgrowth by carvacrol, cinnamaldehyde, thymol, and oregano oil was evaluated during abusive chilling of cooked ground beef (75% lean) obtained from a local grocery store. Test substances were mixed into thawed ground beef at concentrations of 0.1, 0.5, 1.0, or 2.0% (wt/wt) along with a heat-activated three-strain C. perfringens spore cocktail to obtain final spore concentrations of ca. 2.8 log spores per g. Aliquots (5 g) of the ground beef mixtures were vacuum-packaged and then cooked in a water bath, the temperature of which was raised to 60°C in 1 h. The products were cooled from 54.4 to 7.2°C in 12, 15, 18, or 21 h, resulting in 3.18, 4.64, 4.76, and 5.04 log CFU/g increases, respectively, in C. perfringens populations. Incorporation of test compounds (≥0.1%) into the beef completely inhibited C. perfringens spore germination and outgrowth (P ≤ 0.05) during exponential cooling of the cooked beef in 12 h. Longer chilling times (15, 18, and 21 h) required greater concentrations to inhibit spore germination and outgrowth. Cinnamaldehyde was significantly (P < 0.05) more effective (<1.0 log CFU/g growth) at a lower concentration (0.5%) at the most abusive chilling rate evaluated (21 h) than the other compounds. Incorporation of lower levels of these test compounds with other antimicrobials used in meat product formulations may reduce the potential risk of C. perfringens germination and outgrowth during abusive cooling regimes.

Germination-Induced Bioluminescence, a Route To Determine the Inhibitory Effect of a Combination Preservation Treatment on Bacterial Spores

ABSTRACT In this work, we have used spores of Bacillus subtilisthat specifically induce bioluminescence upon initiation of germination as a rapid, real-time monitor of the effects of preservative treatments on germination. Using this tool, we have demonstrated that the combination of mild acidity (pH 5.5 to 5.0), lactic acid (0.5%), and a pasteurization step (90�C for 5 min) results in enhanced inhibition of spore germination compared with the effects of the individual treatments alone. Inhibition by the combination treatment occurred as a result of both direct but reversible inhibition, entirely dependent on the physical presence of the preservative factors, and permanent, nonreversible damage to the l-alanine germination apparatus of the spore. However, we were able to restore germination of the preservative-damaged spores unable to germinate onl-alanine by supplementing the medium with the nonnutrient germinant calcium dipicolinic acid. The demonstration that simple combinations of preservative factors inhibit spore germination indicates that food preservation systems providing ambient stability could be designed which do not adhere to the strict limits set by commonly accepted processes and which are based on precise understanding of their inhibitory action.

Synergism between Bacillus thuringiensis Spores and Toxins against Resistant and Susceptible Diamondback Moths (Plutella xylostella)

ABSTRACT We studied the effects of combinations of Bacillus thuringiensis spores and toxins on the mortality of diamondback moth (Plutella xylostella) larvae in leaf residue bioassays. Spores of B. thuringiensis subsp.kurstaki increased the toxicity of crystals of B. thuringiensis subsp. kurstaki to both resistant and susceptible larvae. For B. thuringiensis subsp.kurstaki, resistance ratios were 1,200 for a spore-crystal mixture and 56,000 for crystals without spores. Treatment of a spore-crystal formulation of B. thuringiensissubsp. kurstaki with the antibiotic streptomycin to inhibit spore germination reduced toxicity to resistant larvae but not to susceptible larvae. In contrast, analogous experiments withB. thuringiensis subsp.aizawai revealed no significant effects of adding spores to crystals or of treating a spore-crystal formulation with streptomycin. Synergism occurred between Cry2A and B. thuringiensis subsp. kurstaki spores against susceptible larvae and between Cry1C and B. thuringiensis subsp. aizawai spores against resistant and susceptible larvae. The results show thatB. thuringiensis toxins combined with spores can be toxic even though the toxins and spores have little or no independent toxicity. Results reported here and previously suggest that, for diamondback moth larvae, the extent of synergism between spores and toxins of B. thuringiensis depends on the strain of insect, the type of spore, the set of toxins, the presence of other materials such as formulation ingredients, and the concentrations of spores and toxins.

Inhibition of Bacterial Spore Growth by Fatty Acids and Their Sodium Salts

The antimicrobial activity of 11 fatty acids and their salts was tested on spores of Clostridium botulinum 62A, Clostridium sporogenes PA3679, and Bacillus cereus F4165/75. Linolenic acid was the most inhibitory fatty acid and lauric acid was the most inhibitory of the saturated fatty acids. Minimum inhibitory concentrations ranged from 50–150 μg/ml for lauric acid, ≥150 μg/ml for myristic acid, 30–100 μg/ml for linoleic acid, and 10–75 μg/ml for linolenic acid depending on the strain. Caprylic, capric, palmitic, stearic, arachidic, and erucic acids showed only partial inhibition (44 to 90%) at concentrations as high as 150 μg/ml. Addition of 0.2–0.3% (wt/vol) starch neutralized the inhibitory effect of palmitic, linoleic, and linolenic acids but had no effect on lauric acid even when increased to 1%. Lauric, linoleic, and linolenic acids were shown to inhibit spore germination as measured by loss of spore heat resistance.

The effect on fungal growth of some 2,5-dihydroxy-1,4-benzoquinones

It has been shown that 2,5-dihydroxy-1,4-benzoquinones decrease vegetative growth and inhibit spore germination of 12 species of fungi belonging to six diverse genera. The nature of the substituents at the 3 and 6 positions of the quinone ring also affected their growth-inhibitory properties; generally those substituents of lower polarity inhibited growth at lower concentrations. As in the case of cochliodinol, chemical modification of the quinone group, or the hydroxyl groups of the quinone ring, in compounds of the polyporic acid series, also led to loss of biological activity.