It has been demonstrated in several taxa that generalists grow better when they ingest a mixed diet than when they are restricted to just one or two items, but there are few cases that provide definitive evidence for how this benefit is achieved. Two hypotheses are addressed concerning the possible benefits of feeding on a variety of foods: (l) mixing foods increases the quality of the overall diet by improving the nutrient balance and (2) mixing improves the diet due to dilution of any one plant secondary compound. The generalist grasshopper Schistocerca americana was used in a series of experiments to distinguish between the two hypotheses.Experiments using artificial foods with complementary nutrients demonstrated that ~ieta'!' mixing iJ?pr~ves. growth while the amount ingested is decreased. Nutritionally ~denttcal foods ":tth dtffenng plant secondary compounds led to different growth rates, but msects able to mtx generally grew at intermediate rates. Experiments with domestic or wild plan~ mixtures gave results generally closer to the pattern found with complementary nutnents than the pattern found with differing poisons, but both hypotheses are supported to some extent.

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Aims: To investigate the antiviral efficacy of oregano oil and its primary active component, carvacrol, against the nonenveloped murine norovirus (MNV), a human norovirus surrogate. Methods and Results: Along with an observed loss in cell culture infectivity, the antiviral mechanisms of action were determined in side-by-side experiments including a cell-binding assay, an RNase I protection assay and transmission electron microscopy (TEM). Both antimicrobials produced statistically significant reductions (P ≤ 0Á05) in virus infectivity within 15 min of exposure (c. 1Á0-log 10 ). Despite this, the MNV infectivity remained stable with increasing time exposure to oregano oil (1Á07-log 10 after 24 h), while carvacrol was far more effective, producing up to 3Á87-log 10 reductions within 1 h. Based on the RNase I protection assay, both antimicrobials appeared to act directly upon the virus capsid and subsequently the RNA. Under TEM, the capsids enlarged from ≤35 nm in diameter to up to 75 nm following treatment with oregano oil and up to 800 nm with carvacrol; with greater expansion, capsid disintegration could be observed. Virus adsorption to host cells did not appear to be affected by either antimicrobial.Conclusions: Our results demonstrate that carvacrol is effective in inactivating MNV within 1 h of exposure by acting directly on the viral capsid and subsequently the RNA. Significance and Impact of the Study: This study provides novel findings on the antiviral properties of oregano oil and carvacrol against MNV and demonstrates the potential of carvacrol as a natural food and surface (fomite) sanitizer to control human norovirus.

Enteric viruses are a cause of waterborne disease worldwide, and low numbers in drinking water can present a significant risk of infection. Because the numbers are often quite low, large volumes (100-1,000 L) of water are usually processed. The VIRADEL method using microporous filters is most commonly used today for this purpose. Negatively charged filters require the addition of multivalent salts and acidification of the water sample to effect virus adsorption, which can make large-volume sampling difficult. Positively charged filters require no preconditioning of samples, and are able to concentrate viruses from water over a greater pH range than electronegative filters. The most widely used electropositive filter is the Virosorb 1MDS; however, the Environmental Protection Agency has added the positively charged NanoCeram filters to their proposed Method 1615. Ultrafilters concentrate viruses based on size exclusion rather than electrokinetics, but are impractical for field sampling or processing of turbid water. Elution (recovery) of viruses from filters following concentration is performed with organic (e.g., beef extract) or inorganic solutions (e.g., sodium polyphosphates). Eluates are then reconcentrated to decrease the sample volume to enhance detection methods (e.g., cell culture infectivity assays and molecular detection techniques). While the majority of available filters have demonstrated high virus retention efficiencies, the methods to elute and reconcentrate viruses have met with varying degrees of success due to the biological variability of viruses present in water.

Arcanobacterium (Actinomyces) pyogenes, an animal pathogen, produces a hemolytic exotoxin, pyolysin (PLO). The gene encoding PLO was cloned, and sequence analysis revealed an open reading frame of 1,605 bp encoding a protein of 57.9 kDa. PLO has 30 to 40% identity with the thiol-activated cytolysins (TACYs) of a number of gram-positive bacteria. The activity of PLO was found to be very similar to those of other TACYs, except that it was not thiol activated. The highly conserved TACY undecapeptide is divergent in PLO; in particular, the cysteine residue required for thiol activation has been replaced with alanine. However, mutagenesis of the alanine residue to cysteine did not confer thiol activation on PLO, suggesting a conformational difference in the undecapeptide region of this toxin. Specific antibodies against purified, recombinant PLO completely neutralized the hemolytic activity of A. pyogenes, suggesting that this organism produces a single hemolysin. Furthermore, these antibodies could passively protect mice against lethal challenge with A. pyogenes, suggesting that like other TACYs PLO is an important virulence factor in the pathogenesis of this organism.Arcanobacterium (Actinomyces) pyogenes (36), a gram-positive, normally commensal bacterium, resides on the mucous membranes of cattle, sheep, swine, and other economically important animals (10). It can, through an as yet unknown mechanism, disseminate to cause a wide variety of nonspecific purulent infections involving the visceral organs (19,25,45) and joints (18), as well as acute purulent mastitis (20), chronic abscessing mastitis (37), and abortion (42).Despite the versatility of A. pyogenes as an agent of disease in domestic animals, specific determinants of its virulence have not been characterized. A. pyogenes produces several potential virulence factors including a DNase (24) and several proteases (40,44). In addition to these factors, A. pyogenes produces hemolytic exotoxin pyolysin (PLO) (13), which is cytolytic for the erythrocytes of a number of animal species (14), as well as dermonecrotic and lethal for laboratory animals (27). PLO also exhibits cytotoxic effects on bovine polymorphonuclear leukocytes (PMN) and kangaroo kidney cells (13). PLO was reported to be oxygen stable, and its activity was reported to be unaffected by cholesterol (14). The role of this toxin in pathogenesis is unclear. However, it is expressed in vivo and is immunogenic, as antihemolysin antibodies have been found in the sera of naturally (26) and experimentally (28) infected animals.In order to investigate the role of this toxin in the virulence of A. pyogenes, the gene encoding PLO was cloned and sequenced. The work reported here examines the activity of PLO, its similarity to a family of thiol-activated cytolysins (TACYs) produced by a number of gram-positive bacteria (1,8,12), and its potential role in virulence. MATERIALS AND METHODS Bacterial strains and growth conditions. Escherichia coli DH5␣ (Bethesda Research Laboratories [BRL]), DH5␣FЈlacIq (BRL), and L...