Bacteria colonies from gut homogenates of fifth instar velvetbean caterpillars (Lepidoptera: Noctuidae) were subjected to antibiotic sensitivity experiments using discs containing 22 antibiotics. The antibiotic tetracycline provided the best results, followed by chloramphenicol. Tetracycline also provided higher inhibition of colony forming units than chloramphenicol and was therefore provided to the caterpillars in increasing diet concentrations to assess the contribution of gut bacteria to their digestion and development. The activity of proteases (general), serine-proteinases and lipases were significantly suppressed by tetracycline. Concentration-inhibition curves were successfully established for tetracycline and this antibiotic was effective in suppressing them, particularly serine-proteinases, suggesting that gut bacteria may significantly contribute with lipid- and mainly protein-digestion in velvetbean caterpillars. Increased diet concentrations of tetracycline led only to mild increase in insect mortality (ca. 20%), with the surviving insects showing faster development (< or =4 days) and higher pupa weight (<0.04 mg) with increased concentrations of tetracycline. Therefore, the gut bacteria inhibited by tetracycline does not seem to play a crucial role in the survival and development of the velvetbean caterpillar, but may be important in the adaptation of this pest species to hosts rich in protease inhibitors, such as soybean.

Staphylococcus aureus is a significant pathogen frequently causing persistent intramammary infections (IMI) in dairy cows. We compared some genotypic and phenotypic characteristics of 285 strains collected from quarter milk samples from cows with persistent and nonpersistent subclinical IMI across Canada. Variable number of tandem repeats typing was used to infer the persistence of the same S. aureus strain in 3 consecutive quarter milk samples collected at intervals of 3 wk during lactation or before and after dry-off. All first isolates of the series were used as the representative strains from persistent IMI and were compared with nonpersistent strains for the presence of genes seg, sen, sec, and tst as well as by spa typing. Biofilm production in vitro and hld-RNAIII expression levels were also quantified. The gene seg was associated with a reduction in the likelihood of the bacteria to cause a persistent IMI during lactation. Strains persisting through the dry period produced significantly more biofilm in vitro than strains that do not persist after calving. Also, we showed that strains expressing more hld were more likely to be nonpersistent during either lactation or through the dry period. Three spa types were predominant (t529, t267, and a novel type: t13401). In the strains studied, the spa type tbl 2645 was the most frequent, and 97.0% of the strains of this spa type carried both sen and seg. Strains from the spa type tbl 2645 were less likely to cause a persistent IMI in the dry period. Most (86.7%) of the strains of the novel spa type (t13401) were negative for seg, sen, or both and produced significantly more biofilm in vitro than tbl 2645 and t267. The present study expanded our current knowledge on the genotypic and phenotypic traits of S. aureus strains recovered from persistent and nonpersistent IMI in Canada.

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One manner in which plant-derived compounds exert their antibiotic potential is the synergism, a positive interaction between two compounds. Studies indicate that the use of plant extracts combined with antimicrobials may promote a significant reduction of the minimum inhibitory concentrations of antibiotics for bacterial strains. this study aimed to evaluate the activity of plant extracts and antibiotics as well as their combination on Staphylococcus aureus. the activity of 15 plant extracts was evaluated using diffusion assay. The minimum inhibitory concentrations (MICs) and the interactions between the extracts and antibiotics as well as compound emodin were evaluated with the checkerboard method. the active extracts were a hexane extract of the leaves of Baccharis dracunculifolia and the ethanol extracts of the leaves of Plectranthus ornatus, Inga edulis, Salvia officinalis and Senna macranthera. the Plectranthus ornatus extract displayed synergism with ampicillin (a β-lactam), kanamycin and gentamicin (aminoglycosides), with 8-fold reductions in the MIC. the same reduction was observed for the extracts of Salvia officinalis and Senna macranthera, which displayed the lowest MIC. Using these combinations resulted in a reduction in the minimum dose required for effective antimicrobial effects, which is interesting because it may decrease both the risk of side effects and the costs of treatment.

Penicillium griseoroseum has been studied by our group because of its good pectinase production. Attempts have been done to clone pectinolytic genes, aiming to obtain pectinase-overproducing strains for industrial purposes. Here, two genes coding for pectin lyase were isolated from the P. griseoroseum genome. The plg1 gene has an open reading frame of 1341 bp coding for a putative protein of 374 amino acids with a calculated molecular mass of 40.1 kDa. The plg2 gene is characterized by an open reading frame of 1400 nucleotides and codes for a polypeptide of 383 amino acids. The plg1 gene 5'-flanking region contains putative binding sites for the transcription factors involved in regulation by ambient pH and catabolite repression. The primary structure of Plg1 and Plg2 proteins showed a relatively high homology (varying between 32.4% and 74.8%) to fungal pectin lyases characterized to date. Southern blotting analysis revealed that both genes are present as single copies in the fungus genome. Expression studies revealed a differing pattern of gene expression of plg1 and plg2 when mycelium was cultivated on medium containing different pectic components. Citric pectin followed by apple pectin were the carbon sources that best induced plg1 expression, and transcripts were detected from 24 to 76 h. The expression of the plg2 gene was monitored by reverse transcriptase - polymerase chain reaction, since Northern analysis failed to detect hybridization signals. The differential expression of these genes may provide means for the fungus to adapt to various growth conditions.