Secondary messenger signalling influences Pseudomonas aeruginosa adaptation to sinus and lung environments

Pseudomonas aeruginosa is a cause of chronic respiratory tract infections in people with cystic fibrosis (CF), non-CF bronchiectasis and chronic obstructive pulmonary disease. Prolonged infection allows accumulation of mutations and horizontal gene transfer, increasing the likelihood of adaptive phenotypic traits. Adaptation is proposed to arise first in bacterial populations colonising upper airway environments. Here, we model this process using an experimental evolution approach. P. aeruginosa PAO1, which is not airway adapted, was serially passaged, separately, in media chemically reflective of upper or lower airway environments. To explore whether the CF environment selects for unique traits, we separately passaged PAO1 in airway-mimicking media with or without CF-specific factors. Our findings demonstrated that all airway environments - sinus and lungs, under CF and non-CF conditions - selected for loss of twitching motility, increased resistance to multiple antibiotic classes and a hyper-biofilm phenotype. These traits conferred increased airway colonisation potential in an in vivo model. CF-like conditions exerted stronger selective pressures, leading to emergence of more pronounced phenotypes. Loss of twitching was associated with mutations in type IV pili genes. Type IV pili mediate surface attachment, twitching and induction of cAMP signalling. We additionally identified multiple evolutionary routes to increased biofilm formation involving regulation of cyclic-di-GMP signalling. These included loss of function mutations in bifA and dipA phosphodiesterase genes and activating mutations in the siaA phosphatase. These data highlight that airway environments select for traits associated with sessile lifestyles and suggest upper airway niches support emergence of phenotypes that promote establishment of lung infection.

Comparison of current paediatric contrast sensitivity assessments using simulated reduced contrast thresholds

PURPOSE

There are limited tests of contrast sensitivity (CS) for use in children. The Hiding Heidi (HH) is suitable for all cognitive abilities, but has a ceiling effect. The Double Happy (DH) test has comparable thresholds to the Pelli Robson (PR), however the ability to detect changes in contrast has not been established. This study aims to compare contrast thresholds and agreement between HH and the DH, comparing to the PR chart in normal conditions and under reduced visual and lighting conditions.

METHODS

Tests were repeated under different conditions to reduce the contrast. Room illumination was 20,900{plus minus}2% lux in bright conditions and 2,000{plus minus}2% lux in dim conditions, both conditions were repeated with the addition of simulation spectacles to reduce the clarity of vision. Participants' CS was measured uniocularly using the PR, HH and DH tests.

RESULTS

50 participants, age 18-62 years (mean{plus minus}standard deviation: 24.5{plus minus}7.98), were assessed. On HH 94% (n = 47) reached the maximum score, with the DH it was 18% (n = 9). The difference in reduction between conditions was smaller with HH in comparison to PR and DH, but significantly different from baseline conditions. Under dim conditions the reduction in PR and DH was -0.21 logCS units, but only -0.04 logCS for HH.

CONCLUSION

The DH test has better agreement with PR than HH and is better at detecting CS changes, highlighting the advantages of use in clinical practice.