Although lichen planus is a relatively common mucocutaneous disorder in adults, it has only rarely been described in children. Moreover, even less data has been published regarding mucosal lesions in children. Six case reports of childhood oral lichen planus are presented and the available literature reviewed. It is believed that this paper documents the largest series of cases of childhood oral mucosal lichen planus to be reported in the literature to date. Lichen planus should be considered in the differential diagnosis of oral mucosal white patches in children, particularly those of Asian origin.

Background Pseudomonas aeruginosa is an opportunistic bacterium that infects the airways of cystic fibrosis patients, surfaces of surgical and burn wounds, and indwelling medical devices. Patients are prone to secondary fungal infections, with Candida albicans being commonly co-isolated with P. aeruginosa. Both P. aeruginosa and C. albicans are able to form extensive biofilms on the surfaces of mucosa and medical devices. Objectives To determine whether the presence of C. albicans enhances antibiotic tolerance of P. aeruginosa in a dual-species biofilm. Methods Single- and dual-species biofilms were established in microtitre plates and the survival of each species was measured following treatment with clinically relevant antibiotics. Scanning electron microscopy and confocal microscopy were used to visualize biofilm structure. Results C. albicans enhances P. aeruginosa biofilm tolerance to meropenem at the clinically relevant concentration of 5 mg/L. This effect is specific to biofilm cultures and is dependent upon C. albicans extracellular matrix polysaccharides, mannan and glucan, with C. albicans cells deficient in glycosylation structures not enhancing P. aeruginosa tolerance to meropenem. Conclusions We propose that fungal mannan and glucan secreted into the extracellular matrix of P. aeruginosa/C. albicans dual-species biofilms play a central role in enhancing P. aeruginosa tolerance to meropenem, which has direct implications for the treatment of coinfected patients.

The ATPase SecA is an essential component of the bacterial Sec machinery, which transports proteins across the cytoplasmic membrane. Most SecA proteins contain a long C-terminal tail (CTT). In Escherichia coli, the CTT contains a structurally flexible linker domain and a small metal-binding domain (MBD). The MBD coordinates zinc via a conserved cysteine-containing motif and binds to SecB and ribosomes. In this study, we screened a high-density transposon library for mutants that affect the susceptibility of E. coli to sodium azide, which inhibits SecA-mediated translocation. Results from sequencing this library suggested that mutations removing the CTT make E. coli less susceptible to sodium azide at subinhibitory concentrations. Copurification experiments suggested that the MBD binds to iron and that azide disrupts iron binding. Azide also disrupted binding of SecA to membranes. Two other E. coli proteins that contain SecA-like MBDs, YecA and YchJ, also copurified with iron, and NMR spectroscopy experiments indicated that YecA binds iron via its MBD. Competition experiments and equilibrium binding measurements indicated that the SecA MBD binds preferentially to iron and that a conserved serine is required for this specificity. Finally, structural modeling suggested a plausible model for the octahedral coordination of iron. Taken together, our results suggest that SecA-like MBDs likely bind to iron in vivo.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen frequently isolated from chronic infections of the cystic fibrosis lung and burn wounds, and is a major cause of antimicrobial-resistant nosocomial infections. P. aeruginosa is frequently co-isolated with the opportunistic fungal pathogen Candida albicans, with the presence of C. albicans in dual-species biofilms promoting tolerance to meropenem. Here, transcription profiling of mature P. aeruginosa single- or dual-species biofilms was carried out to understand the molecular mechanism(s) by which C. albicans enhances meropenem tolerance. C. albicans appeared to have a mild impact on the transcriptome of P. aeruginosa mature biofilms, with most differentially regulated genes being involved in interkingdom interactions (i.e. quorum sensing and phenazine biosynthesis). The addition of meropenem to mature single- or dual-species biofilms resulted in a significant bacterial transcriptional response, including the induction of the beta-lactamase, ampC, genes involved in biofilm formation. P. aeruginosa elicited a similar transcriptional response to meropenem in the presence of C. albicans, but C. albicans promoted the expression of additional efflux pumps, which could play roles in increasing the tolerance of P. aeruginosa to meropenem.

23Sodium azide prevents bacterial growth by inhibiting the activity of SecA, which is required 24 for translocation of proteins across the cytoplasmic membrane. Azide inhibits ATP turnover in 25 vitro, but its mechanism of action in vivo is unclear. To investigate how azide inhibits SecA in 26 cells, we used transposon directed insertion-site sequencing (TraDIS) to screen a library of 27 transposon insertion mutants for mutations that affect the susceptibility of E. coli to azide. 28 Insertions disrupting components of the Sec machinery generally increased susceptibility to 29 azide, but insertions truncating the C-terminal tail (CTT) of SecA decreased susceptibility of E. 30 coli to azide. Treatment of cells with azide caused increased aggregation of the CTT, suggesting 31 that azide disrupts its structure. Analysis of the metal-ion content of the CTT indicated that SecA 32 binds to iron and the azide disrupts the interaction of the CTT with iron. Azide also disrupted 33 binding of SecA to membrane phospholipids, as did alanine substitutions in the metal-34 coordinating amino acids. Furthermore, treating purified phospholipid-bound SecA with azide in 35 the absence of added nucleotide disrupted binding of SecA to phospholipids. Our results suggest 36 that azide does not inhibit SecA by inhibiting the rate of ATP turnover in vivo. Rather, azide 37 inhibits SecA by causing it to "backtrack" from the ADP-bound to the ATP-bound conformation, 38 which disrupts the interaction of SecA with the cytoplasmic membrane. 40Significance statement 41 SecA is a bacterial ATPase that is required for the translocation of a subset of secreted proteins 42 across the cytoplasmic membrane. Sodium azide is a well-known inhibitor of SecA, but its 43 mechanism of action in vivo is poorly understood. To investigate this mechanism, we examined 44 the effect of azide on the growth of a library of > 1 million transposon insertion mutations. Our 45 3 results suggest that azide causes SecA to backtrack in its ATPase cycle, which disrupts binding 46 of SecA to the membrane and to its metal cofactor, which is iron. Our results provide insight into 47 the molecular mechanism by which SecA drives protein translocation and how this essential 48 biological process can be disrupted. 49 50 51 52 53 In bacteria, protein substrates of the Sec machinery are transported across, or inserted into, 54 the cytoplasmic membrane through a channel composed of integral membrane proteins SecY, -E 55 and -G (Sec61α, -β and -γ in eukaryotes). In bacteria, translocation of most soluble periplasmic 56 proteins and outer membrane proteins also requires the assistance of a motor ATPase, SecA, 57 which drives translocation through repeated rounds of ATP binding and hydrolysis (1). In 58 Escherichia coli, the catalytic core of SecA contains four domains: nucleotide binding domain-1 59 (NBD-1; amino acids 1-220 & 378-411), nucleotide binding domain-2 (NBD-2; 412-620), the 60 polypeptide crosslinking domain (PPXD; 221-377) and the α-helical C-terminal domai...