Sulfonamide-based non-alkyne LpxC inhibitors as Gram-negative antibacterial agents.

We attempted to optimize sulfonamide-based non-alkyne LpxC inhibitors by focusing on improvements in enzyme inhibitory and antibacterial activity. It was discovered that inhibitors possessing 2-aryl benzofuran as a hydrophobe exhibited good activity. In particular, compound 21 displayed impressive antibacterial activity (E. coli MIC=0.063µg/mL, K. pneumoniae MIC=0.5µg/mL, and P. aeruginosa MIC=0.5µg/mL), and is a promising lead for further exploration as an antibacterial agent.

LpxC Inhibitors: Design, Synthesis, and Biological Evaluation of Oxazolidinones as Gram-negative Antibacterial Agents.

Herein we report a scaffold-hopping approach to identify a new scaffold with a zinc binding headgroup. Structural information was used to give novel oxazolidinone-based LpxC inhibitors. In particular, the most potent compound, 23j, showed a low efflux ratio, nanomolar potencies against E. coli LpxC enzyme, and excellent antibacterial activity against E. coli and K. pneumoniae. Computational docking was used to predict the interaction between 23j and E. coli LpxC, suggesting that the interactions with C207 and C63 contribute to the strong activity. These results provide new insights into the design of next-generation LpxC inhibitors.

Inhibitory effect of gut bacteria from the Japanese honey bee, Apis cerana japonica, against Melissococcus plutonius, the causal agent of European foulbrood disease.

European foulbrood is a contagious bacterial disease of honey bee larvae. Studies have shown that the intestinal bacteria of insects, including honey bees, act as probiotic organisms. Microbial flora from the gut of the Japanese honey bee, Apis cerana japonica F. (Hymenoptera: Apidae), were characterized and evaluated for their potential to inhibit the growth of Melissococcus plutonius corrig. (ex White) Bailey and Collins (Lactobacillales: Enterococcaceae), the causative agent of European foulbrood. Analysis of 16S rRNA gene sequences from 17 bacterial strains isolated by using a culture-dependent method revealed that most isolates belonged to Bacillus, Staphylococcus, and Pantoea. The isolates were screened against the pathogenic bacterium M. plutonius by using an in vitro growth inhibition assay, and one isolate (Acja3) belonging to the genus Bacillus exhibited inhibitory activity against M. plutonius. In addition, in vivo feeding assays revealed that isolate Acja3 decreased the mortality of honey bee larvae infected with M plutonius, suggesting that this bacterial strain could potentially be used as a probiotic agent against European foulbrood.

Inhibition of Paenibacillus larvae by lactic acid bacteria isolated from fermented materials.

We evaluated the potential application of lactic acid bacteria (LAB) isolated from fermented feeds and foods for use as probiotics against Paenibacillus larvae, the causal agent of American foulbrood (AFB) in vitro. We also assessed the ability of LAB to induce the expression of antimicrobial peptide genes in vivo. Screening of the 208 LAB isolated from fermented feeds and foods revealed that nine strains inhibited the in vitro growth of P. larvae. The LAB strains were identified by 16S rRNA gene sequencing as Enterococcus sp., Weissella sp. and Lactobacillus sp. These strains were screened for their abilities of immune activation in honeybees by real-time RT-PCR using antimicrobial peptide genes as markers. After oral administration of several of the screened LAB to larvae and adults, the transcription levels of antimicrobial peptide genes, such as abaecin, defensin and hymenoptaecin, were found to increase significantly. These findings suggested that selected LAB stimulate the innate immune response in honeybees, which may be useful for preventing bacterial diseases in honeybees. This is the first report to characterize the probiotic effects of LAB isolated from fermented feeds and foods in honeybees.

Characterization of bifidobacteria in the digestive tract of the Japanese honeybee, Apis cerana japonica.

Bifidobacteria were isolated from the intestinal tract of the Japanese honeybee, Apis cerana japonica, and investigated for potential application as a probiotic agent against Melissococcus plutonius, the causal agent of European foulbrood (EFB), based on the findings of in vitro inhibition assays. A total of 11 bifidobacteria strains (designated as AcjBF1-AcjBF11) were isolated using a culture-dependent method and their 16S rRNA gene sequences were analyzed. The AcjBF isolates belonged to three distinct bifidobacterial phylotypes that were similar to those found in the European honeybee, Apis mellifera. Although the Japanese and European honeybees are distinct species with different traits and habits, the observation that they share highly similar bifidobacterial phylotypes suggests that bifidobacteria are conserved among honeybee species. Despite having extremely high 16S rRNA gene sequence similarities, the AcjBF isolates had markedly different carbohydrate fermentation profiles. In addition, in vitro growth inhibition assays revealed that the cell-free supernatants of all AcjBF isolates exhibited antagonistic effects on M. plutonius growth. These results indicate that the bifidobacteria isolated from the gut of Japanese honeybee could potentially be employed as a new biological agent to control EFB.