In vitro bactericidal activity of diterpenoids isolated from Aframomum melegueta K.Schum against strains of Escherichia coli, Listeria monocytogenes and Staphylococcus aureus

Ethnopharmacological relevance: The ethnobotanical use of Aframomum melegueta in the treatment of urinary tract and soft tissue infection suggested that the plant has antimicrobial activity.

Materials and methods: To substantiate the folkloric claims, an acetone, 50:50 acetone:methanol and 2:1 chloroform:methanol extracts were tested against Escherichia coli K12; acetone extract and the fractions of acetone extracts were tested against Listeria monocytogenes. Bioassay-guided fractionation was performed on the extract using L. monocytogenes as the test organism to isolate the bioactive compounds which were then tested against all the other organisms.

Results: Four known labdane diterpenes (G3 and G5) were isolated for the first time from the rhizomes of A. melegueta and purified. These were tested against E. coli, L. monocytogenes, methicillin resistant Staphylococus aureus (MRSA) and S. aureus to determine antibacterial activity. The result showed that two compounds G3 and G5 exhibited more potent antibacterial activity compared to the current clinically used antibiotics ampicillin, gentamicin and vancomycin and can be potential antibacterial lead compounds. The structure of the labdane diterpenes were elucidated using nuclear magnetic resonance (NMR) spectroscopy and Mass spectrometry. A possible mode of action of the isolated compound G3 and its potential cytotoxicity towards mammalian cells were also discussed.

Conclusion: The results confirmed the presence of antibacterial compounds in the rhizomes of A. melegueta with a favourable toxicity profile which could be further optimized as antibacterial lead compounds.

Field-Isolated Genotypes of Mycobacterium bovis Vary in Virulence and Influence Case Pathology but Do Not Affect Outbreak Size

Strains of many infectious agents differ in fundamental epidemiological parameters including transmissibility, virulence and pathology. We investigated whether genotypes of Mycobacterium bovis (the causative agent of bovine tuberculosis, bTB) differ significantly in transmissibility and virulence, combining data from a nine-year survey of the genetic structure of the M. bovis population in Northern Ireland with detailed records of the cattle population during the same period. We used the size of herd breakdowns as a proxy measure of transmissibility and the proportion of skin test positive animals (reactors) that were visibly lesioned as a measure of virulence. Average breakdown size increased with herd size and varied depending on the manner of detection (routine herd testing or tracing of infectious contacts) but we found no significant variation among M. bovis genotypes in breakdown size once these factors had been accounted for. However breakdowns due to some genotypes had a greater proportion of lesioned reactors than others, indicating that there may be variation in virulence among genotypes. These findings indicate that the current bTB control programme may be detecting infected herds sufficiently quickly so that differences in virulence are not manifested in terms of outbreak sizes. We also investigated whether pathology of infected cattle varied according to M. bovis genotype, analysing the distribution of lesions recorded at post mortem inspection. We concentrated on the proportion of cases lesioned in the lower respiratory tract, which can indicate the relative importance of the respiratory and alimentary routes of infection. The distribution of lesions varied among genotypes and with cattle age and there were also subtle differences among breeds. Age and breed differences may be related to differences in susceptibility and husbandry, but reasons for variation in lesion distribution among genotypes require further investigation. © 2013 Wright et al.

Complex organic molecules along the accretion flow in isolated and externally irradiated protoplanetary disks

(Abridged) The birth environment of the Sun will have influenced the conditions in the pre-solar nebula, including the attainable chemical complexity, important for prebiotic chemistry. The formation and distribution of complex organic molecules (COMs) in a disk around a T Tauri star is investigated for two scenarios: (i) an isolated disk, and (ii) a disk irradiated externally by a nearby massive star. The chemistry is calculated along the accretion flow from the outer disk inwards using a comprehensive network. Two simulations are performed, one beginning with complex ices and one with simple ices only. For the isolated disk, COMs are transported without major alteration into the inner disk where they thermally desorb into the gas reaching an abundance representative of the initial assumed ice abundance. For simple ices, COMs efficiently form on grain surfaces under the conditions in the outer disk. Gas-phase COMs are released into the molecular layer via photodesorption. For the irradiated disk, complex ices are also transported inwards; however, they undergo thermal processing caused by the warmer conditions in the irradiated disk which tends to reduce their abundance along the accretion flow. For simple ices, grain-surface chemistry cannot synthesise COMs in the outer disk because the necessary grain-surface radicals, which tend to be particularly volatile, are not sufficiently abundant on the grain surfaces. Gas-phase COMs are formed in the inner region of the irradiated disk via gas-phase chemistry induced by the desorption of strongly bound molecules such as methanol; hence, the abundances are not representative of the initial molecular abundances injected into the outer disk. These results suggest that the composition of comets formed in isolated disks may differ from those formed in externally irradiated disks with the latter composed of more simple ices.

The Host Defence Peptide LL-37 is Susceptible to Proteolytic Degradation by Wound Fluid Isolated from Foot Ulcers of Diabetic Patients

The pleiotropic effects of host defence peptides (HDPs), including the ability to kill microorganisms, enhance re-epithelialisation and increase angiogenesis, indicates a role for these important peptides as potential therapeutic agents in the treatment of chronic, non-healing wounds. However, the maintenance of peptide integrity, through resistance to degradation by the array of proteinases present at the wound site, is a prerequisite for clinical success. In this study we explored the degradation of exogenous LL-37, one such HDP, by wound fluid from diabetic foot ulcers to determine its susceptibility to proteolytic degradation. Our results suggest that LL-37 is unstable in the diabetic foot ulcer microenvironment. Following overnight treatment with wound fluid, LL-37 was completely degraded. Analysis of cleavage sites suggested potential involvement of both host- and bacterial-derived proteinases. The degradation products were shown to retain some antibacterial activity against Pseudomonas aeruginosa but were inactive against Staphylococcus aureus. In conclusion, our data suggest that stabilising selected peptide bonds within the sequence of LL-37 would represent an avenue for future research prior to clinical studies to address its potential as an exogenously-applied therapeutic in diabetic wounds. 

Mechanisms of reduced susceptibility and genotypic prediction of antibiotic resistance in Prevotella isolated from cystic fibrosis (CF) and non-CF patients

OBJECTIVES: To investigate mechanisms of reduced susceptibility to commonly used antibiotics in Prevotella cultured from patients with cystic fibrosis (CF), patients with invasive infection and healthy control subjects and to determine whether genotype can be used to predict phenotypic resistance.

METHODS: The susceptibility of 157 Prevotella isolates to seven antibiotics was compared, with detection of resistance genes (cfxA-type gene, ermF and tetQ), mutations within the CfxA-type β-lactamase and expression of efflux pumps.

RESULTS: Prevotella isolates positive for a cfxA-type gene had higher MICs of amoxicillin and ceftazidime compared with isolates negative for this gene (P < 0.001). A mutation within the CfxA-type β-lactamase (Y239D) was associated with ceftazidime resistance (P = 0.011). The UK CF isolates were 5.3-fold, 2.7-fold and 5.7-fold more likely to harbour ermF compared with the US CF, UK invasive and UK healthy control isolates, respectively. Higher concentrations of azithromycin (P < 0.001) and clindamycin (P < 0.001) were also required to inhibit the growth of the ermF-positive isolates compared with ermF-negative isolates. Furthermore, tetQ-positive Prevotella isolates had higher MICs of tetracycline (P = 0.001) and doxycycline (P < 0.001) compared with tetQ-negative isolates. Prevotella spp. were also shown, for the first time, to express resistance nodulation division (RND)-type efflux pumps.

CONCLUSIONS: This study has demonstrated that Prevotella isolated from various sources harbour a common pool of resistance genes and possess RND-type efflux pumps, which may contribute to tetracycline resistance. The findings indicate that antibiotic resistance is common in Prevotella spp., but the genotypic traits investigated do not reflect phenotypic antibiotic resistance in every instance.