The Challenges and Promises of New Therapies for Cystic Fibrosis

Therapeutic intervention in cystic fibrosis (CF) remains a challenge, partly because of the number of organs and tissues affected by the lack of a functional cystic fibrosis transmembrane conductance regulator (CFTR) protein. CF was originally regarded primarily as a gastrointestinal (GI) disease because of the failure to thrive and early death from malnutrition in infants with CF. However, successful interventions for the GI manifestations of CF have left chronic lung infections as the primary cause of morbidity and mortality. Despite a complex microbiology within the CF lung, one pathogen, Pseudomonas aeruginosa, remains the critical determinant of pulmonary pathology. Treatment and management of this infection and its associated symptoms are the major targets of extant and developing CF therapies. Understanding the multitude of effects of CFTR on mucosal physiology and susceptibility and progression of chronic lung disease, and how host immune responses fail to adequately control lung infection, will be essential for the development of improved therapies for CF

Poly-N-Acetylglucosamine Expression by Wild-Type Yersinia pestis Is Maximal at Mammalian, Not Flea, Temperatures

Numerous bacteria, including Yersinia pestis, express the poly-N-acetylglucosamine (PNAG) surface carbohydrate, a major component of biofilms often associated with a specific appearance of colonies on Congo red agar. Biofilm formation and PNAG synthesis by Y. pestis have been reported to be maximal at 21 to 28°C or “flea temperatures,” facilitating the regurgitation of Y. pestis into a mammalian host during feeding, but production is diminished at 37°C and thus presumed to be decreased during mammalian infection. Most studies of PNAG expression and biofilm formation by Y. pestis have used a low-virulence derivative of strain KIM, designated KIM6+, that lacks the pCD1 virulence plasmid, and an isogenic mutant without the pigmentation locus, which contains the hemin storage genes that encode PNAG biosynthetic proteins. Using confocal microscopy, fluorescence-activated cell sorter analysis and growth on Congo red agar, we confirmed prior findings regarding PNAG production with the KIM6+ strain. However, we found that fully virulent wild-type (WT) strains KIM and CO92 had maximal PNAG expression at 37°C, with lower PNAG production at 28°C both in broth medium and on Congo red agar plates. Notably, the typical dark colony morphology appearing on Congo red agar was maintained at 28°C, indicating that this phenotype is not associated with PNAG expression in WT Y. pestis. Extracts of WT sylvatic Y. pestis strains from the Russian Federation confirmed the maximal expression of PNAG at 37°C. PNAG production by WT Y. pestis is maximal at mammalian and not insect vector temperatures, suggesting that this factor may have a role during mammalian infection

Comparative evaluation of coagulase-negative staphylococci (CoNS) adherence to acrylic by a static method and a parallel-plate flow dynamic method

The main goal of this work was to evaluate the adhesion to acrylic of several clinical strains of Staphylococcus epidermidis and Staphylococcus haemolyticus using both static and dynamic adhesion methods, and to compare the results obtained with these two methods. Adhesion was evaluated using the static slide method with different washing procedures, and the parallel plate flow chamber method. The extent of S. epidermidis adhesion, assessed by both methods, was greater than that of S. haemolyticus. The number of bacteria which adhered using the static method was lower than that using the dynamic method. It was found that the simple static method, when performed with an accurate washing procedure, can be as effective as the dynamic flow method for assessing differences in the adherence capacity of strains. Although the dynamic flow method yielded more overall information, its greater complexity and cost may not always justify its use for certain experimental comparisons. This investigation has shown that simple static adhesion methods, when performed accurately, can be used to evaluate differences in adhesion capacity.NIH - grant AI 46706.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI) - POCTI/ESP/42688/2001, grant SFRH/BD/8676/2002

Inhibition of adherence of coagulase-negative Staphylococci (CoNS) to acrylic by subinhibitory concentrations of antibiotics

CoNS are major nosocomial pathogens associated with infections of indwelling medical devices. The major virulence factor for these organisms is their ability to adhere to devices and form biofilms. Antibiotics interacting with the cell wall may influence bacterial adhesion by causing changes in the cell surface. These cell surface modifications may increase or decrease bacterial adherence to biomaterials. In this study the effect of sub-mic concentrations of cefazolin, vancomycin and dicloxacilin on adhesion to acrylic of several CoNS clinical isolates was determined. The results showed a minimal effect for vancomycin on reducing adhesion, although this antibiotic had a very low MIC value, and thus a high efficiency in killing bacteria in suspension. Cefazolin and dicloxacilin induced a higher inhibition of adhesion, reaching more than 60% for some strains, although being antibiotics that have a lower efficiency of killing bacteria in suspension. Combinations of the drugs were evaluated and a synergistic effect was observed. Use of antibiotics that inhibit adherence of CoNS to biomaterials may augment other treatment strategies for device-related infections

Differences in adhesion and biofilm formation of several clinical isolates of Staphylococcus epidermidis

Staphylococcus epidermidis and similar coagulase-negative staphylococci (CoNS) are now well established as major nosocomial pathogens associated with infections of indwelling medical devices. The major virulence factor of these organisms is mainly due to their ability to adhere to devices and form a biofilm.however, it is not known if adherence and biofilm formation are closely linked phenotypes for clinical isolates. since different clinical isolates of s. epidermidis would be expected to exhibit different phenotypic behaviours it is further expected that strains of s. epidermidis might have different abilities to adhere to synthetic surfaces and subsequently produce biofilms. in this study the initial adherence and subsequent biofilm formation properties of 9 clinical isolates of s. epidermidis along with biofilm+ and biofilm– control strains were assayed. the adherence results were interpreted in terms of the physico-chemical interaction established between the cells and the adhesion substratum as assessed by contact angle measurements.as expected, the clinical isolates exhibited different abilities to adhere to hydrophilic glass and to form biofilms. moreover, the strains that produced the highest amounts of biofilms were not the ones able to adhere to the largest extent and vice-versa. for example, the biofilm- control strain actually showed the highest level of initial adhesion capability and did not produce biofilm. these results indicate that high levels of initial adherence do not necessarily lead to strong biofilm formation and that some strains do not have a high initial adherence but can subsequently form a strong biofilm. these two aspects of the pathogenesis of medical device related-infection may need to be evaluated independently to ascertain the contribution of each to the virulence of cons causing device related infections

S. epidermidis response to human blood and its cellular and soluble components

Staphylococcus epidermidis, a normal inhabitant of healthy human skin and mucosae, can cause persistent and relapsing infections due to its ability to adhere to medical devices and form biofilms. Hence, S epidermidis is considered one of the most important medical device-associated nosocomial agents, being particularly associated with vascular catheters. Although the biofilms formed on these catheters are in constant contact with human blood, their mutual interaction is poorly understood. Here, we evaluated the expression of genes associated with biofilm formation (icaA, aap, bhp), immune evasion (icaA, mprF, sepA) and programmed cell death (lrgB), as well as biofilm structure and viability, upon bacterial interaction with human blood and its components. We observed that contact with human blood increased the transcription of icaA and bhp but decreased aap, sepA and lrgB gene expression, when compared with plasma. In contrast, no significant transcriptional alterations were detected upon contact with purified mononuclear cells, whereas purified polymorphonuclear cells lead to increased bhp and mprF gene expression. Furthermore, human blood reduced by 50% the number of viable cells within the biofilm and induced significant alterations in its structure, with the creation of a fibre-like matrix. In conclusion, our study reveals that S. epidermis biofilms adapt to particular environmental stress by changing the expression of specific genes and by altering their structure. Despite these overall observations, significant variability was found between different blood donors, suggesting that particularities of the host immune system may strongly affect the outcome of S. epidermidis infections

Environmental regulation of the pgaABCD locus in Escherichia coli

Background : The staphylococci are a major cause of catheter-related infections, due, in part, to their ability to form a biofilm. The major constituent of the biofilm matrix is the polysaccharide PNAG, synthesized by the proteins encoded in the icaADBC locus. Recently, it has been demonstrated that the Escherichia coli locus ycdSRQP (re-named pgaABCD) has homology to the staphylococcal icaADBC locus, and also encodes proteins that direct the synthesis of a polysaccharide that is biochemically identical to PNAG. Furthermore, PNAG promotes biofilm formation in E. coli. The aim of this work was to determine environmental factors that regulate transcription of the pgaABCD locus and the production of PNAG. Methods: We cloned the promoter of the locus pgaABCD into a green fluorescent protein (GFP) reporter plasmid, and transformed the plasmid into a competent E. coli strain. The transformed cells were grown in TSB supplemented with a variety of factors, including glucose, sucrose, mannose, magnesium, manganese and ethanol. The production of GFP was detected with a fluorimeter. Factors that augmented the production of GFP were further tested for their influence on PNAG production and biofilm formation in 18 E. coli urinary tract clinical isolates by immunoblot using IgG raised against staphylococcal PNAG and by microtiter well biofilm assay, respectively. Results: Transcription of pgaABCD was augmented by glucose, manganese, potassium, and ethanol. PNAG production, as detected by immunoblot, was also increased by the same factors. However, glucose was the only factor to significantly increase biofilm formation. Conclusions: Environmental regulation of transcription of the E. coli pgaABCD locus, as determined by reporter gene activation was correlated with the production of PNAG in E. coli clinical isolates. However, biofilm formation by E.coli may not be entirely dependent on PNAG production

Effect of a single locus deletion on global genome expression : the ica locus in Staphyloccocus spp : a case study

Recent technological advances have made it possible to study global gene expression in bacteria. Microarrays have emerged as the premier tool for studying gene expression on a genomic scale and have been used in a broad range of studies1. Staphylococcus epidermidis and Staphylococcus aureus can form biofilms on medical devices. The major constituent of the biofilm matrix is the polysaccharide PNAG, synthesized by the proteins encoded in the icaADBC locus2. A knockout of the ica locus in a biofilm-forming strain will cause that strain to lose its ability to form a biofilm. However, what is not known is the effect of the loss of the icaADBC locus on the overall gene expression by the bacteria. We used a strong biofilm forming strain of S. aureus and an isogenic icaADBC knock out and grew them under the same conditions (16H, TSB with 1% glucose, 37°C, 300rpm) after which we extracted the total RNA, and converted it to cDNA. We then labeled the cDNA with 2 different dyes, and hybridized the product on a microarray slide containing the genome of S. aureus. The microarrays were analyzed using an open source software (TM4)3. Data analysis verified that the majority of the genes were equally expressed by both strains, as expected. However, approximately 60 genes were differentially expressed between the wild type and the isogenic mutant, demonstrating that a deletion mutation within a single locus can influence the expression of many other genes in the bacteria