Influence of antimicrobial agents on the spoilage of a meat-based entomophage diet

The microbial decomposition of a meat-based entomophage diet presented in Parafilm packets was investigated. Considerable bacteria but not fungi were associated with components used to prepare the diet (i.e., hens' eggs, liver, and ground beef). At the initial sampling time, there were no differences among diet treatments in the size of bacterial or fungal populations. Bacterial populations in diets not containing antibacterial agents rapidly increased and reached an asymptote by 24 h (approximately 10(10) colony-forming units per gram). Bacterial populations also increased in diets containing antibacterial agents, but they were significantly smaller than in diets not containing antibacterial agents. The most prevalent bacteria isolated were Carnobacterium piscicola, Carnobacterium divergens, Lactobacillus curvatus, Lactobacillus sakei, Leuconostoc mesenteroides, and Enterococcus spp., regardless of the antibacterial treatment used. The proliferation of fungi was delayed relative to bacteria, but significant differences were observed among the diet treatments. Fungi were most inhibited by sorbic acid and propionic acid in the absence of antibacterial agents. The most common fungi isolated were the yeasts Candida zeylanoides, Torulaspora globosa, and Yarrowia lipolytica. The pH of diets not containing antibacterial agents decreased rapidly and was highly correlated with increases in bacteria but not fungi. The results of this study demonstrate that antimicrobial agents significantly inhibit spoilage microorganisms in a meat-based diet and that alternative management strategies to delay the decomposition of such diets presented in Parafilm packets should target lactic acid spoilage bacteria, particularly Carnobacterium and Lactobacillus species.     

Pathogens associated with southwestern corn borers and southern corn stalk borers (Lepidoptera: Crambidae)

A study was undertaken to isolate entomopathogens of southwestern corn borer, Diatraea grandiosella Dyer, and southern corn stalk borer, Diatraea crambidoides (Grote). Field-collected diapausing larvae of southwestern corn borer (three sites in Mississippi) and southern corn stalk borer (one site in North Carolina), and a laboratory strain of D. grandiosella in the diapause state were maintained in a simulated winter followed by a simulated spring environnent. Few larvae (< or = 6%) collected from any of the field sites died in the winter environment, and most insect mortality (11-25%) occurred after transfer of the larvae to the simulated spring environment. Mortality during the simulated spring period differed among the collection sites, and the highest mortality was recorded for southwestern corn borers from Washington County (25%), followed by Marshall (16%) and Oktibbeha (11%) Counties. A high level of mortality was also observed in southern corn stalk borers during the simulated spring period (27%). No viruses were observed, but a number of bacteria, microsporidia, and fungi were isolated from both southwestern corn borer and southern corn stalk borer larvae and pupae. In most instances, numerous bacterial taxa were isolated from cadavers, but on some occasions a single taxon predominated. The most prevalent bacterial taxon from larval and pupal cadavers was Enterococcus faecalis (Andrewes & Horder) Schleifer & Kilppel-Balz, but Bacillus spp., Pseudomonas aeruginosa (Schroeter) Migula, and Serratia marcescens Bizio were frequently isolated as well. Few fungi (1-7%) were recovered from southwestern corn borer and southern corn stalk borer larvae and pupae. The most common entomopathogenic taxon isolated was Beauveria bassiana (Balsamo) Vuillemin from southern corn stalk borer larvae. Microsporidia were not isolated from southern corn stalk borers. However, Nosema spp. were isolated from southwestern corn borer cadavers from Washington (15%), Marshall (1%), and Oktibbeha (3%) Counties in Mississippi. In addition, we observed parasitism of southern corn stalk borer larvae by Macrocentrus cingulum Reinhard (Hymenoptera: Braconidae). No parasitism of southwestern corn borers was observed. Isolates of Bacillus, Beauveria, Entercoccus, Nosema, Pseudomonas and Serratia were all pathogenic to southwestern corn borer larvae under controlled environmental conditions, and with the exception of B. bassiana, these are novel pathogens of Diatraea corn borers.     

Production of cellulases and xylanases by low-temperature basidiomycetes

Three of four isolates, representing phylogenetically distinct groupings of low-temperature basidiomycetes (LTB), were capable of utilizing wheat straw, and to a lesser extent conifer wood at 15 degrees C. A cottony snow mould LTB (LRS 013) and a fruit rot LTB (LRS 241) grown on straw significantly degraded filter paper, carboxymethylcellulose (CMC), p-nitrophenyl beta-glucopyranoside (i.e., beta-glucosidases), and xylan. Enzymes produced by Coprinus psychromorbidus (LRS 067) were limited to xylanases from straw and wood and beta-glucosidases from wood. A sclerotia-forming LTB (LRS 131) exhibited poor growth on both substrates, and did not produce detectable quantities of extracellular enzymes. None of the LTB isolates tested degraded avicel. The temperature optima of CMCases and xylanases in the filtrates from the straw medium ranged from 25 degrees C to 55 degrees C, and with the exception of LRS 067, significant activity was observed at 5 degrees C. Two cellulases (25 and 31 kDa) and two xylanases (24 and 34 kDa) were observed on zymograms for LRS 013 and 241. Reduction of enzymes with 2-mercaptoethanol adversely affected their activity on zymograms, and an additional cellulase band was observed for non-reduced samples. This study indicates that LTB produce an array of cellulolytic and xylanolytic enzymes, and that some of these enzymes possess low-temperature optima which may facilitate degradation of plant fibre under low-temperature conditions.     

Inverting character of alpha-glucuronidase A from Aspergillus tubingensis

Alpha-glucuronidase A from Aspergillus tubingensis was found to be capable of liberating 4-O-methyl-D-glucuronic acid (MeGlcA) only from those beechwood glucuronoxylan fragments in which the acid is attached to the non-reducing terminal xylopyranosyl residue. Reduced aldotetrauronic acid, 4-O-methyl-D-glucuronosyl-alpha-1,2-D-xylopyranosyl-beta-1,4-xylopyranosyl-beta-1,4-xylitol, was found to be a suitable substrate to follow the stereochemical course of the hydrolytic reaction catalyzed by the purified enzyme. The configuration of the liberated MeGlcA was followed in a D(2)O reaction mixture by (1)H-NMR spectroscopy. It was unambiguously established that MeGlcA was released from the substrate as its beta-anomer from which the alpha-anomer was formed on mutarotation. This result represents the first experimental evidence for the inverting character of a microbial alpha-glucuronidase, a member of glycosyl hydrolase family 67 (EC 3.1.1.139).     

Effects of subtherapeutic administration of antimicrobial agents to beef cattle on the prevalence of antimicrobial resistance in Campylobacter jejuni and Campylobacter hyointestinalis

The influence of antimicrobial agents on the development of antimicrobial resistance (AMR) in Campylobacter isolates recovered from 300 beef cattle maintained in an experimental feedlot was monitored over a 315-day period (11 sample times). Groups of calves were assigned to one of the following antimicrobial treatments: chlortetracycline and sulfamethazine (CS), chlortetracycline alone (Ct), virginiamycin, monensin, tylosin phosphate, and no antimicrobial agent (i.e., control treatment). In total, 3,283 fecal samples were processed for campylobacters over the course of the experiment. Of the 2,052 bacterial isolates recovered, 92% were Campylobacter (1,518 were Campylobacter hyointestinalis and 380 were C. jejuni). None of the antimicrobial treatments decreased the isolation frequency of C. jejuni relative to the control treatment. In contrast, C. hyointestinalis was isolated less frequently from animals treated with CS and to a lesser extent from animals treated with Ct. The majority (> or =94%) of C. jejuni isolates were sensitive to ampicillin, erythromycin, and ciprofloxacin, but more isolates with resistance to tetracycline were recovered from animals fed Ct. All of the 1,500 isolates of C. hyointestinalis examined were sensitive to ciprofloxacin. In contrast, 11%, 10%, and 1% of these isolates were resistant to tetracycline, erythromycin, and ampicillin, respectively. The number of animals from which C. hyointestinalis isolates with resistance to erythromycin and tetracycline were recovered differed among the antimicrobial treatments. Only Ct administration increased the carriage rates of erythromycin-resistant isolates of C. hyointestinalis, and the inclusion of CS in the diet increased the number of animals from which tetracycline-resistant isolates were recovered. The majority of C. hyointestinalis isolates with resistance to tetracycline were obtained from cohorts within a single pen, and most of these isolates were recovered from cattle during feeding of a forage-based diet as opposed to a grain-based diet. The findings of this study show that the subtherapeutic administration of tetracycline, alone and in combination with sulfamethazine, to feedlot cattle can select for the carriage of resistant strains of Campylobacter species. Considering the widespread use of in-feed antimicrobial agents and the high frequency of beef cattle that shed campylobacters, the development of AMR should be monitored as part of an on-going surveillance program.     

The differential contribution of tumour necrosis factor to thermal and mechanical hyperalgesia during chronic inflammation

Therapies directed against tumour necrosis factor (TNF) are effective for the treatment of rheumatoid arthritis and reduce pain scores in this condition. In this study, we sought to explore mechanisms by which TNF contributes to inflammatory pain in an experimental model of arthritis. The effects of an anti-TNF agent, etanercept, on behavioural pain responses arising from rat monoarthritis induced by complete Freund's adjuvant were assessed and compared with expression of TNF receptors (TNFRs) by dorsal root ganglion (DRG) cells at corresponding time points. Etanercept had no effect on evoked pain responses in normal animals but exerted a differential effect on the thermal and mechanical hyperalgesia associated with rat arthritis induced by complete Freund's adjuvant (CFA). Joint inflammation was associated with increased TNFR1 and TNFR2 expression on DRG cells, which was maintained throughout the time course of the model. TNFR1 expression was increased in neuronal cells of the DRG bilaterally after arthritis induction. In contrast, TNFR2 expression occurred exclusively on non-neuronal cells of the macrophage–monocyte lineage, with cell numbers increasing in a TNF-dependent fashion during CFA-induced arthritis. A strong correlation was observed between numbers of macrophages and the development of mechanical hyperalgesia in CFA-induced arthritis. These results highlight the potential for TNF to play a vital role in inflammatory hyperalgesia, both by a direct action on neurons via TNFR1 and by facilitating the accumulation of macrophages in the DRG via a TNFR2-mediated pathway.     

高等植物中的磷酸烯醇式丙酮酸羧激酶

简要介绍了近年来有关高等植物中磷酸烯醇式丙酮酸羧激酶（ＰＥＰＣＫ）的研究进展,并讨论了此酶的结构、功能和调节等方面的问题。     

Enriched sensory experience in adulthood increases subsequent exploratory behaviour in the rat

Hooded rats were reared under identical conditions until 3 months old. They were then exposed for 5 weeks to either a sensorily enriched or an impoverished environment. Each subject was then observed for 15 min in a novel Y-maze. Animals exposed to the enriched environment showed the strongest exploration tendency, particularly early in the trial. The results are discussed in relation to the emphasis placed by earlier workers upon the role of early stimulation in setting adult levels of exploratory behaviour.