Richard Kerry Phipps

Why chronic wounds will not heal: a novel hypothesis

The present paper presents a hypothesis aimed at explaining why venous leg ulcers, pressure ulcers, and diabetic foot ulcers develop into a chronic state. We propose that the lack of proper wound healing is at least in part caused by inefficient eradication of infecting, opportunistic pathogens, a situation reminiscent of chronic Pseudomonas aeruginosa infections found in patients suffering from cystic fibrosis (CF). We have analyzed sections from chronic wounds by fluorescence in situ hybridization and found distinct microcolonies—the basal structures of bacterial biofilms. Several researchers have previously reported that another important hallmark of biofilm formation is development of increased tolerance to various antimicrobial measures and treatments. Furthermore, the immune response to infecting bacteria in the cystic fibrosis lung is dominated by polymorphonuclear neutrophils (PMNs), and we have recently shown that in vitro biofilms of P. aeruginosa produce a shielding mechanism that offers protection from the phagocytic activity of PMNs. 1,2 We hypothesize that the presence of P. aeruginosa in biofilms, and the lack of concomitant elimination by attended PMNs, are the main causes of inefficient eradication by antibiotic treatment and antimicrobial activity of the innate immune system, respectively.

Effects of Antibiotics on Quorum Sensing in Pseudomonas aeruginosa

ABSTRACT During infection, Pseudomonas aeruginosa employs bacterial communication (quorum sensing [QS]) to coordinate the expression of tissue-damaging factors. QS-controlled gene expression plays a pivotal role in the virulence of P. aeruginosa, and QS-deficient mutants cause less severe infections in animal infection models. Treatment of cystic fibrosis (CF) patients chronically infected with P. aeruginosa with the macrolide antibiotic azithromycin (AZM) has been demonstrated to improve the clinical outcome. Several studies indicate that AZM may accomplish its beneficial action in CF patients by impeding QS, thereby reducing the pathogenicity of P. aeruginosa. This led us to investigate whether QS inhibition is a common feature of antibiotics. We present the results of a screening of 12 antibiotics for their QS-inhibitory activities using a previously described QS inhibitor selector 1 strain. Three of the antibiotics tested, AZM, ceftazidime (CFT), and ciprofloxacin (CPR), were very active in the assay and were further examined for their effects on QS-regulated virulence factor production in P. aeruginosa. The effects of the three antibiotics administered at subinhibitory concentrations were investigated by use of DNA microarrays. Consistent results from the virulence factor assays, reverse transcription-PCR, and the DNA microarrays support the finding that AZM, CFT, and CPR decrease the expression of a range of QS-regulated virulence factors. The data suggest that the underlying mechanism may be mediated by changes in membrane permeability, thereby influencing the flux of N-3-oxo-dodecanoyl-l-homoserine lactone.

Ajoene, a Sulfur Rich Molecule from Garlic, Inhibits Genes Controlled by Quorum Sensing

ABSTRACT In relation to emerging multiresistant bacteria, development of antimicrobials and new treatment strategies of infections should be expected to become a high-priority research area. Quorum sensing (QS), a communication system used by pathogenic bacteria like Pseudomonas aeruginosa to synchronize the expression of specific genes involved in pathogenicity, is a possible drug target. Previous in vitro and in vivo studies revealed a significant inhibition of P. aeruginosa QS by crude garlic extract. By bioassay-guided fractionation of garlic extracts, we determined the primary QS inhibitor present in garlic to be ajoene, a sulfur-containing compound with potential as an antipathogenic drug. By comprehensive in vitro and in vivo studies, the effect of synthetic ajoene toward P. aeruginosa was elucidated. DNA microarray studies of ajoene-treated P. aeruginosa cultures revealed a concentration-dependent attenuation of a few but central QS-controlled virulence factors, including rhamnolipid. Furthermore, ajoene treatment of in vitro biofilms demonstrated a clear synergistic, antimicrobial effect with tobramycin on biofilm killing and a cease in lytic necrosis of polymorphonuclear leukocytes. Furthermore, in a mouse model of pulmonary infection, a significant clearing of infecting P. aeruginosa was detected in ajoene-treated mice compared to a nontreated control group. This study adds to the list of examples demonstrating the potential of QS-interfering compounds in the treatment of bacterial infections.

Silver against Pseudomonas aeruginosa biofilms.

Silver has been recognized for its antimicrobial properties for centuries. Most studies on the antibacterial efficacy of silver, with particular emphasis on wound healing, have been performed on planktonic bacteria. Our recent studies, however, strongly suggest that colonization of wounds involves bacteria in both the planktonic and biofilm modes of growth. The action of silver on mature in vitro biofilms of Pseudomonas aeruginosa, a primary pathogen of chronic infected wounds, was investigated. The results show that silver is very effective against mature biofilms of P. aeruginosa, but that the silver concentration is important. A concentration of 5–10 μg/mL silver sulfadiazine eradicated the biofilm whereas a lower concentration (1 μg/mL) had no effect. The bactericidal concentration of silver required to eradicate the bacterial biofilm was 10–100 times higher than that used to eradicate planktonic bacteria. These observations strongly indicate that the concentration of silver in currently available wound dressings is much too low for treatment of chronic biofilm wounds. It is suggested that clinicians and manufacturers of the said wound dressings consider whether they are treating wounds primarily colonized either by biofilm‐forming or planktonic bacteria.

Quorum Sensing and Virulence of Pseudomonas aeruginosa during Lung Infection of Cystic Fibrosis Patients

Pseudomonas aeruginosa is the predominant microorganism in chronic lung infection of cystic fibrosis patients. The chronic lung infection is preceded by intermittent colonization. When the chronic infection becomes established, it is well accepted that the isolated strains differ phenotypically from the intermittent strains. Dominating changes are the switch to mucoidity (alginate overproduction) and loss of epigenetic regulation of virulence such as the Quorum Sensing (QS). To elucidate the dynamics of P. aeruginosa QS systems during long term infection of the CF lung, we have investigated 238 isolates obtained from 152 CF patients at different stages of infection ranging from intermittent to late chronic. Isolates were characterized with regard to QS signal molecules, alginate, rhamnolipid and elastase production and mutant frequency. The genetic basis for change in QS regulation were investigated and identified by sequence analysis of lasR, rhlR, lasI and rhlI. The first QS system to be lost was the one encoded by las system 12 years (median value) after the onset of the lung infection with subsequent loss of the rhl encoded system after 17 years (median value) shown as deficiencies in production of the 3-oxo-C12-HSL and C4-HSL QS signal molecules respectively. The concomitant development of QS malfunction significantly correlated with the reduced production of rhamnolipids and elastase and with the occurrence of mutations in the regulatory genes lasR and rhlR. Accumulation of mutations in both lasR and rhlR correlated with development of hypermutability. Interestingly, a higher number of mucoid isolates were found to produce C4-HSL signal molecules and rhamnolipids compared to the non-mucoid isolates. As seen from the present data, we can conclude that P. aeruginosa and particularly the mucoid strains do not lose the QS regulation or the ability to produce rhamnolipids until the late stage of the chronic infection.

Characterization of Emetic Bacillus weihenstephanensis, a New Cereulide-Producing Bacterium†

ABSTRACT Cereulide production has until now been restricted to the species Bacillus cereus. Here we report on two psychrotolerant Bacillus weihenstephanensis strains, MC67 and MC118, that produce cereulide. The strains are atypical with regard to pheno- and genotypic characteristics normally used for identification of emetic B. cereus strains. MC67 and MC118 produced cereulide at temperatures of as low as 8°C.

Food as a Source for Quorum Sensing Inhibitors: Iberin from Horseradish Revealed as a Quorum Sensing Inhibitor of Pseudomonas aeruginosa

ABSTRACT Foods with health-promoting effects beyond nutritional values have been gaining increasing research focus in recent years, although not much has been published on this subject in relation to bacterial infections. With respect to treatment, a novel antimicrobial strategy, which is expected to transcend problems with selective pressures for antibiotic resistance, is to interrupt bacterial communication, also known as quorum sensing (QS), by means of signal antagonists, the so-called QS inhibitors (QSIs). Furthermore, QSI agents offer a potential solution to the deficiencies associated with use of traditional antibiotics to treat infections caused by bacterial biofilms and multidrug-resistant bacteria. Several QSIs of natural origin have been identified, and in this study, several common food products and plants were extracted and screened for QSI activity in an attempt to isolate and characterize previously unknown QSI compounds active against the common opportunistic pathogen Pseudomonas aeruginosa. Several extracts displayed activity, but horseradish exhibited the highest activity. Chromatographic separation led to the isolation of a potent QSI compound that was identified by liquid chromatography-diode array detector-mass spectrometry (LC-DAD-MS) and nuclear magnetic resonance (NMR) spectroscopy as iberin—an isothiocyanate produced by many members of the Brassicaceae family. Real-time PCR (RT-PCR) and DNA microarray studies showed that iberin specifically blocks expression of QS-regulated genes in P. aeruginosa.

Isolation and NMR Characterization of Fumonisin B2 and a New Fumonisin B6 from Aspergillus niger

A new fumonisin, fumonisin B(6) (1), has been isolated by cation-exchange and reverse-phase chromatography, together with fumonisin B(2) (2), from stationary cultures of the fungus Aspergillus niger NRRL 326. Analysis of mass spectrometric and NMR data determined that FB(6) is a positional isomer of FB(1) and iso-FB(1), having hydroxyl functions at C3, C4, and C5. Analysis of the NMR data for FB(2) showed very similar chemical shift values when compared to an authentic Fusarium FB(2) standard, strongly indicating identical molecules despite that an absolute stereochemical assignment of FB(2) from A. niger was not possible.

Analysis of Fusarium avenaceum Metabolites Produced during Wet Apple Core Rot

Wet apple core rot (wACR) is a well-known disease of susceptible apple cultivars such as Gloster, Jona Gold, and Fuji. Investigations in apple orchards in Slovenia identified Fusarium avenaceum, a known producer of several mycotoxins, as the predominant causal agent of this disease. A LC-MS/MS method was developed for the simultaneous detection of thirteen F. avenaceum metabolites including moniliformin, acuminatopyrone, chrysogine, chlamydosporol, antibiotic Y, 2-amino-14,16-dimethyloctadecan-3-ol (2-AOD-3-ol), aurofusarin, and enniatins A, A1, B, B1, B2, and B3 from artificially and naturally infected apples. Levels of moniliformin, antibiotic Y, aurofusarin, and enniatins A, A1, B, and B1 were quantitatively examined in artificially inoculated and naturally infected apples, whereas the remaining metabolites were qualitatively detected. Metabolite production was examined in artificially inoculated apples after 3, 7, 14, and 21 days of incubation. Most metabolites were detected after 3 or 7 days and reached significantly high levels within 14 or 21 days. The highest levels of moniliformin, antibiotic Y, aurofusarin, and the combined sum of enniatins A, A1, B, and B1 were 7.3, 5.7, 152, and 12.7 microg g(-1), respectively. Seventeen of twenty naturally infected apples with wACR symptoms contained one or more of the metabolites. Fourteen of these apples contained moniliformin, antibiotic Y, aurofusarin, and enniatins in levels up to 2.9, 51, 167, and 3.9 microg g(-1), respectively. Acuminatopyrone, chrysogine, chlamydosporol, and 2-AOD-3-ol were detected in 4, 11, 4, and 10 apples, respectively. During wet apple core rot, F. avenaceum produced high amounts of mycotoxins, which may pose a risk for consumers of apple or processed apple products.

Novofumigatonin, a new orthoester meroterpenoid from Aspergillus novofumigatus.

Novofumigatonin (1), a new metabolite, has been isolated from Aspergillus novofumigatus. The structure and relative stereochemistry were determined from HR ESI MS, one- and two-dimensional NMR, and single-crystal X-ray analysis. The absolute configuration was assigned using vibrational circular dichroism in combination with density functional calculations.