Mucus clearance, MyD88-dependent and MyD88-independent immunity modulate lung susceptibility to spontaneous bacterial infection and inflammation.

It has been postulated that mucus stasis is central to the pathogenesis of obstructive lung diseases. In Scnn1b-transgenic (Scnn1b-Tg⁺ mice, airway-targeted overexpression of the epithelial Na⁺ channel ß subunit causes airway surface dehydration, which results in mucus stasis and inflammation. Bronchoalveolar lavage from neonatal Scnn1b-Tg⁺ mice, but not wild-type littermates, contained increased mucus, bacteria, and neutrophils, which declined with age. Scnn1b-Tg⁺ mice lung bacterial flora included environmental and oropharyngeal species, suggesting inhalation and/or aspiration as routes of entry. Genetic deletion of the Toll-interleukin-1 receptor adapter molecule MyD88 in Scnn1b-Tg⁺ mice did not modify airway mucus obstruction, but caused defective neutrophil recruitment and increased bacterial infection, which persisted into adulthood. Scnn1b-Tg⁺ mice derived into germ-free conditions exhibited mucus obstruction similar to conventional Scnn1b-Tg⁺ mice and sterile inflammation. Collectively, these data suggest that dehydration-induced mucus stasis promotes infection, compounds defects in other immune mechanisms, and alone is sufficient to trigger airway inflammation.

Use of culture and molecular analysis to determine the effect of antibiotic treatment on microbial community diversity and abundance during exacerbation in patients with cystic fibrosis.

BACKGROUND: Anaerobic bacteria are increasingly regarded as important in cystic fibrosis (CF) pulmonary infection. The aim of this study was to determine the effect of antibiotic treatment on aerobic and anaerobic microbial community diversity and abundance during exacerbations in patients with CF. METHODS: Sputum was collected at the start and completion of antibiotic treatment of exacerbations and when clinically stable. Bacteria were quantified and identified following culture, and community composition was also examined using culture-independent methods. RESULTS: Pseudomonas aeruginosa or Burkholderia cepacia complex were detected by culture in 24/26 samples at the start of treatment, 22/26 samples at completion of treatment and 11/13 stable samples. Anaerobic bacteria were detected in all start of treatment and stable samples and in 23/26 completion of treatment samples. Molecular analysis showed greater bacterial diversity within sputum samples than was detected by culture; there was reasonably good agreement between the methods for the presence or absence of aerobic bacteria such as P aeruginosa (κ=0.74) and B cepacia complex (κ=0.92), but agreement was poorer for anaerobes. Both methods showed that the composition of the bacterial community varied between patients but remained relatively stable in most individuals despite treatment. Bacterial abundance decreased transiently following treatment, with this effect more evident for aerobes (median decrease in total viable count 2.3×10(7) cfu/g, p=0.005) than for anaerobes (median decrease in total viable count 3×10(6) cfu/g, p=0.046). CONCLUSION: Antibiotic treatment targeted against aerobes had a minimal effect on abundance of anaerobes and community composition, with both culture and molecular detection methods required for comprehensive characterisation of the microbial community in the CF lung. Further studies are required to determine the clinical significance of and optimal treatment for these newly identified bacteria.

Charged tmRNA but not tmRNA-mediated proteolysis is essential for Neisseria gonorrhoeae viability.

tmRNA, through its tRNA and mRNA properties, adds short peptide tags to abnormal proteins, targeting these proteins for proteolytic degradation. Although the conservation of tmRNA throughout the bacterial kingdom suggests that it must provide a strong selective advantage, it has not been shown to be essential for any bacterium. We report that tmRNA is essential in Neisseria gonorrhoeae. Although tagging per se appears to be required for gonococcal viability, tagging for proteolysis does not. This suggests that the essential roles of tmRNA in N.gonorrhoeae may include resolving stalled translation complexes and/or preventing depletion of free ribosomes. Although derivatives of N.gonorrhoeae expressing Escherichia coli tmRNA as their sole tmRNA were isolated, they appear to form colonies only after acquiring an extragenic suppressor(s).