Non-invasive ventilation in chronic obstructive pulmonary disease: management of acute type 2 respiratory failure

Non-invasive ventilation (NIV) in the management of acute type 2 respiratory failure in patients with chronic obstructive pulmonary disease (COPD) represents one of the major technical advances in respiratory care over the last decade. This document updates the 2002 British Thoracic Society guidance and provides a specific focus on the use of NIV in COPD patients with acute type 2 respiratory failure. While there are a variety of ventilator units available most centres now use bi-level positive airways pressure units and this guideline refers specifically to this form of ventilatory support although many of the principles encompassed are applicable to other forms of NIV. The guideline has been produced for the clinician caring for COPD patients in the emergency and ward areas of acute hospitals.

Phi29 polymerase based random amplification of viral RNA as an alternative to random RT-PCR

BACKGROUND

Phi29 polymerase based amplification methods provides amplified DNA with minimal changes in sequence and relative abundance for many biomedical applications. RNA virus detection using microarrays, however, can present a challenge because phi29 DNA polymerase cannot amplify RNA nor small cDNA fragments (<2000 bases) obtained by reverse transcription of certain viral RNA genomes. Therefore, ligation of cDNA fragments is necessary prior phi29 polymerase based amplification. We adapted the QuantiTect Whole Transcriptome Kit (Qiagen) to our purposes and designated the method as Whole Transcriptome Amplification (WTA).

RESULTS

WTA successfully amplified cDNA from a panel of RNA viruses representing the diversity of ribovirus genome sizes. We amplified a range of genome copy numbers from 15 to 4 x 10(7) using WTA, which yielded quantities of amplified DNA as high as 1.2 microg/microl or 10(10) target copies. The amplification factor varied between 10(9) and 10(6). We also demonstrated that co-amplification occurred when viral RNA was mixed with bacterial DNA.

CONCLUSION

This is the first report in the scientific literature showing that a modified WGA (WTA) approach can be successfully applied to viral genomic RNA of all sizes. Amplifying viral RNA by WTA provides considerably better sensitivity and accuracy of detection compared to random RT-PCR.

Massively parallel pathogen identification using high-density microarrays

Identification of microbial pathogens in clinical specimens is still performed by phenotypic methods that are often slow and cumbersome, despite the availability of more comprehensive genotyping technologies. We present an approach based on whole-genome amplification and resequencing microarrays for unbiased pathogen detection. This 10 h process identifies a broad spectrum of bacterial and viral species and predicts antibiotic resistance and pathogenicity and virulence profiles. We successfully identify a variety of bacteria and viruses, both in isolation and in complex mixtures, and the high specificity of the microarray distinguishes between different pathogens that cause diseases with overlapping symptoms. The resequencing approach also allows identification of organisms whose sequences are not tiled on the array, greatly expanding the repertoire of identifiable organisms and their variants. We identify organisms by hybridization of their DNA in as little as 1-4 h. Using this method, we identified Monkeypox virus and drug-resistant Staphylococcus aureus in a skin lesion taken from a child suspected of an orthopoxvirus infection, despite poor transport conditions of the sample, and a vast excess of human DNA. Our results suggest this technology could be applied in a clinical setting to test for numerous pathogens in a rapid, sensitive and unbiased manner.

Persistence of Mycoplasma synoviae in hens after two enrofloxacin treatments and detection of mutations in the parC gene

The ability of Mycoplasma synoviae, an avian pathogen, to persist despite fluoroquinolone treatments was investigated in hens. Groups of Mycoplasma-free hens were experimentally infected with the M. synoviae 317 strain and treated twice with enrofloxacin at the therapeutic dose. The results show that the two treatments did not have any influence on this strain of M. synoviae recovery from tracheal swabs. Mycoplasmas were isolated from tracheal swab cultures, but not from inner organs such as the liver or spleen, suggesting that this strain of M. synoviae was not able to cross the mucosal barrier to disseminate throughout the host. A significant increase of the resistance level to enrofloxacin of five re-isolated mycoplasma clones, was observed after the second treatment. This increase was associated in two clones to a Ser81-->Pro substitution, found in the ParC quinolone-resistance determining region (QRDR) of DNA topoisomerase IV. This is the first time that a mutation in a gene coding for topoisomerase IV is described in M. synoviae after in vivo enrofloxacin treatments in experimentally infected hens.

Persistence of Mycoplasma gallisepticum in chickens after treatment with enrofloxacin without development of resistance

The ability of the avian pathogen Mycoplasma gallisepticum to persist despite fluoroquinolone treatment was investigated in chickens. Groups of specific pathogen free chickens were experimentally infected with M. gallisepticum and treated with enrofloxacin at increasing concentrations up to the therapeutic dose. When M. gallisepticum could no longer be re-isolated from chickens, birds were stressed by inoculation of infectious bronchitis virus or avian pneumovirus. Although M. gallisepticum could not be cultured from tracheal swabs collected on several consecutive sampling days after the end of the enrofloxacin treatments, the infection was not eradicated. Viral infections reactivated the mycoplasma infection. Mycoplasmas were isolated from tracheal rings cultured for several days, suggesting that M. gallisepticum persisted in the trachea despite the enrofloxacin treatment. The minimal inhibitory concentration (MIC) of enrofloxacin for most of the re-isolated mycoplasmas was the same as that of the strain with which the birds were inoculated. Furthermore, no mutation could be detected in the fluoroquinolone target genes. These results suggest that M. gallisepticum can persist in chickens without development of resistance despite several treatments with enrofloxacin.

Fluoroquinolone resistance in Mycoplasma gallisepticum: DNA gyrase as primary target of enrofloxacin and impact of mutations in topoisomerases on resistance level

Resistant mutants of Mycoplasma gallisepticum were selected in vitro by passaging strains 10 times in increasing concentrations of enrofloxacin. The regions of gyrA/gyrB and parC/parE, encoding the quinolone resistance-determining regions (QRDRs) of DNA gyrase and DNA topoisomerase IV, respectively, of the mutants obtained during different passages were sequenced. Several mutations were found in the four fluoroquinolone targets. Substitution of Ser-83-->Arg in GyrA and Ser-80-->Leu or Trp in ParC QRDRs seem to have the greatest impact on resistance to fluoroquinolones. The results obtained also suggest that the preferential target of enrofloxacin in M. gallisepticum is DNA gyrase.

In vitro development of resistance to enrofloxacin, erythromycin, tylosin, tiamulin and oxytetracycline in Mycoplasma gallisepticum, Mycoplasma iowae and Mycoplasma synoviae

The in vitro emergence of resistance to enrofloxacin, erythromycin, tylosin, tiamulin, and oxytetracycline in three avian Mycoplasma species, Mycoplasma gallisepticum, Mycoplasma synoviae and Mycoplasma iowae was studied. Mutants were selected stepwise and their MICs were determined after 10 passages in subinhibitory concentrations of antibiotic. High-level resistance to erythromycin and tylosin developed within 2-6 passages in the three Mycoplasma species. Resistance to enrofloxacin developed more gradually. No resistance to tiamulin or oxytetracycline could be evidenced in M. gallisepticum or M. synoviae after 10 passages whereas, resistant mutants were obtained with M. iowae. Cross-sensitivity tests performed on mutants demonstrated that mycoplasmas made resistant to tylosin were also resistant to erythromycin, whereas mutants made resistant to erythromycin were not always resistant to tylosin. Some M. iowae tiamulin-resistant mutants were also resistant to both macrolide antibiotics. Enrofloxacin and oxytetracycline did not induce any cross-resistance to the other antibiotics tested. These results show that Mycoplasma resistance to macrolides can be quickly selected in vitro, and thus, providing that similar results could be obtained under field conditions, that development of resistance to these antibiotics in vivo might also be a relatively frequent event.

Characterization of mutations in DNA gyrase and topoisomerase IV Involved in quinolone resistance of Mycoplasma gallisepticum mutants obtained in vitro

Mycoplasma gallisepticum enrofloxacin-resistant mutants were generated by stepwise selection in increasing concentrations of enrofloxacin. Alterations were found in the quinolone resistance-determining regions of the four target genes encoding DNA gyrase and topoisomerase IV from these mutants. This is the first description of such mutations in an animal mycoplasma species.