Acne is a chronic inflammatory disease of the pilosebaceous follicle. One of the main pathogenetic factors in acne is the increased proliferation of Propionibacterium acnes (P. acnes) in the pilosebaceous unit. We investigated whether direct interaction of P. acnes with keratinocytes might be involved in the inflammation and ductal hypercornification in acne. The capacities of different P. acnes strains to activate the innate immune response and the growth of cultured keratinocytes were investigated. We have found that two clinical isolates of P. acnes significantly induced human beta-defensin-2 (hBD2) messenger RNA (mRNA) expression; in contrast a third clinical isolate and the reference strain (ATCC11828) had no effect on hBD2 mRNA expression. In contrast, all four strains significantly induced the interleukin-8 (IL-8) mRNA expression. The P. acnes-induced increase in hBD2 and IL-8 gene expression could be inhibited by anti-Toll-like receptor 2 (TLR2) and anti-TLR4 neutralizing antibodies, suggesting that P. acnes-induced secretion of soluble factors in keratinocytes are both TLR2 and TLR4 dependent. In addition, the clinical isolate P. acnes (889) was capable of inducing keratinocyte cell growth in vitro. Our findings suggest that P. acnes modulates the antimicrobial peptide and chemokine expression of keratinocytes and thereby contributes to the recruitment of inflammatory cells to the sites of infections.

Antimicrobial peptides are promising alternative antimicrobial agents. However, little is known about whether resistance to small-molecule antibiotics leads to cross-resistance (decreased sensitivity) or collateral sensitivity (increased sensitivity) to antimicrobial peptides. We systematically addressed this question by studying the susceptibilities of a comprehensive set of 60 antibiotic-resistant Escherichia coli strains towards 24 antimicrobial peptides. Strikingly, antibiotic-resistant bacteria show a high frequency of collateral sensitivity to antimicrobial peptides, whereas cross-resistance is relatively rare. We identify clinically relevant multidrug-resistance mutations that increase bacterial sensitivity to antimicrobial peptides. Collateral sensitivity in multidrug-resistant bacteria arises partly through regulatory changes shaping the lipopolysaccharide composition of the bacterial outer membrane. These advances allow the identification of antimicrobial peptide-antibiotic combinations that enhance antibiotic activity against multidrug-resistant bacteria and slow down de novo evolution of resistance. In particular, when co-administered as an adjuvant, the antimicrobial peptide glycine-leucine-amide caused up to 30-fold decrease in the antibiotic resistance level of resistant bacteria. Our work provides guidelines for the development of efficient peptide-based therapies of antibiotic-resistant infections.

SummaryUsing correlated live-cell imaging and electron tomography we found that actin branch junctions in protruding and treadmilling lamellipodia are not concentrated at the front as previously supposed, but link actin filament subsets in which there is a continuum of distances from a junction to the filament plus ends, for up to at least 1 mm. When branch sites were observed closely spaced on the same filament their separation was commonly a multiple of the actin helical repeat of 36 nm. Image averaging of branch junctions in the tomograms yielded a model for the in vivo branch at 2.9 nm resolution, which was comparable with that derived for the in vitro actinArp2/3 complex. Lamellipodium initiation was monitored in an intracellular wound-healing model and was found to involve branching from the sides of actin filaments oriented parallel to the plasmalemma. Many filament plus ends, presumably capped, terminated behind the lamellipodium tip and localized on the dorsal and ventral surfaces of the actin network. These findings reveal how branching events initiate and maintain a network of actin filaments of variable length, and provide the first structural model of the branch junction in vivo. A possible role of filament capping in generating the lamellipodium leaflet is discussed and a mathematical model of protrusion is also presented.

Eukaryotic cells can initiate movement using the forces exerted by polymerizing actin filaments to extend lamellipodial and filopodial protrusions. In the current model, actin filaments in lamellipodia are organized in a branched, dendritic network. We applied electron tomography to vitreously frozen 'live' cells, fixed cells and cytoskeletons, embedded in vitreous ice or in deep-negative stain. In lamellipodia from four cell types, including rapidly migrating fish keratocytes, we found that actin filaments are almost exclusively unbranched. The vast majority of apparent filament junctions proved to be overlapping filaments, rather than branched end-to-side junctions. Analysis of the tomograms revealed that actin filaments terminate at the membrane interface within a zone several hundred nanometres wide at the lamellipodium front, and yielded the first direct measurements of filament densities. Actin filament pairs were also identified as lamellipodium components and bundle precursors. These data provide a new structural basis for understanding actin-driven protrusion during cell migration.

The susceptibilities of 824 Bacteroides fragilis group isolates against nine antibiotics were evaluated in a Europe-wide study involving 13 countries. Species determination, by different methods, was carried out on all but one isolate. Resistance rates were evaluated according to species and geographical areas via CLSI and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. The present data were compared with those obtained 10 and 20 years ago at a European level. High-level resistance (MIC ≥ 64 mg/L) to ampicillin was observed in 44.5% of the strains, which is a significant increase relative to 20 years ago (16%). Piperacillin/tazobactam was more active than amoxicillin/clavulanic acid (3.1% and 10.4% resistance, respectively), again with a resistance increase relative to earlier studies. Dramatic increases in resistance were observed for cefoxitin, clindamycin and moxifloxacin, with rates of 17.2%, 32.4% and 13.6%, respectively. The lowest resistances were found for imipenem, metronidazole and tigecycline (1.2%, <1% and 1.7%). Nonsusceptible strains to imipenem and metronidazole were more resistant to other anti-anaerobic drugs. Differences were detected between geographical areas, with higher resistance rates for moxifloxacin in Scandinavian countries (21.4%) than in Mediterranean countries (5.4%), whereas, for clindamycin, the resistance rates were higher in Mediterranean (41.8%) and lower in Scandinavian countries (22.5%). Piperacillin/tazobactam resistance was also higher in Scandinavian countries.