Proteomic characterization of a natural host-pathogen interaction: repertoire of in vivo expressed bacterial and host surface-associated proteins.

Interactions between a host and a bacterial pathogen are mediated by cross-talk between molecules present on, or secreted by, pathogens and host binding-molecules. Identifying proteins involved at this interface would provide substantial insights into this interaction. Although numerous studies have examined in vitro models of infection at the level of transcriptional change and proteomic profiling, there is virtually no information available on naturally occurring host-pathogen interactions in vivo. We employed membrane shaving to identify peptide fragments cleaved from surface-expressed bacterial proteins and also detected proteins originating from the infected host. We optimized this technique for media-cultured Corynebacterium pseudotuberculosis, a sheep pathogen, revealing a set of 247 surface proteins. We then studied a natural host-pathogen interaction by performing membrane shaving on C. pseudotuberculosis harvested directly from naturally infected sheep lymph nodes. Thirty-one bacterial surface proteins were identified, including 13 not identified in culture media, suggesting that a different surface protein repertoire is expressed in this hostile environment. Forty-nine host proteins were identified, including immune mediators and antimicrobial peptides such as cathelicidin. This novel application of proteolytic shaving has documented sets of host and pathogen proteins present at the bacterial surface in an infection of the native host.

Smoking bans in secure psychiatric hospitals and prisons.

The proposal of complete smoking bans in closed institutions, such as prisons and psychiatric hospitals, creates a tension between individual "rights" and the health of all members of that community. Smokers in closed institutions generally smoke more, suffer more health consequences and are less likely to quit than smokers in other settings. Complete smoking bans do not cause an increase in behavioural problems, nor do bans cause worsening of mental illness or quality of life. Although infrequently tested, the responsibility of public institutions to protect others from second-hand smoke has usually outweighed any individual "right to smoke" in legal judgments. A substantial cultural shift may be required from considering smoking a "rare pleasure" during detention to the realisation that smoking is the most significant reversible health risk factor for this population. The implementation of complete smoking bans in closed institutions is challenging and requires careful and proactive planning by staff. As complete smoking bans are being considered in many institutions and jurisdictions, this column presents a review of the evidence base and ethical issues involved.

Use of tuberculin skin test, chest radiograph and interferon-gamma release assay to select migrants for treatment of latent tuberculosis.

Australian guidelines recommend the tuberculin skin test (TST) as the preferred test for latent tuberculosis infection (LTBI) with interferon-gamma release assay (IGRA) as a supplemental test to improve specificity. For many years the chest radiograph has been used to interpret a TST in the 5-9 mm range. The chest radiograph is known to predict subsequent reactivation of tuberculosis (TB). We report a retrospective database review of the Migrant Screening Clinic at Western Health Footscray Hospital during the period April 2010 to November 2011. Of 129 migrants under 35 years of age with TST 5-14 mm, IGRA was positive in 37 (28.7%). IGRA was positive in 7.7% of those with TST 5-9 mm and chest radiograph not suggestive of TB disease, 28.6% in those with TST 5-9 mm and chest radiograph that was suggestive of TB disease, and 39.5% in those with TST 10-14 mm (? 2 trend=12.5, p=0.0004). There were 21 (16%) of 129 persons who had a negative IGRA but both TST >= 5 mm and a chest radiograph suggestive of TB disease. These data support existing recommendations to use the chest radiograph when interpreting a TST of 5-9 mm and recommending treatment of LTBI.

Changes in protein abundance are observed in bacterial isolates from a natural host.

Bacterial proteomic studies frequently use strains cultured in synthetic liquid media over many generations. It is uncertain whether bacterial proteins expressed under these conditions will be the same as the repertoire found in natural environments, or when bacteria are infecting a host organism. Thus, genomic and proteomic characterization of bacteria derived from the host environment in comparison to reference strains grown in the lab, should aid understanding of pathogenesis. Isolates of Corynebacterium pseudotuberculosis were obtained from the lymph nodes of three naturally infected sheep and compared to a laboratory reference strain using bottom-up proteomics, after whole genome sequencing of each of the field isolates. These comparisons were performed following growth in liquid media that allowed us to reach the required protein amount for proteomic analysis. Over 1350 proteins were identified in the isolated strains, from which unique proteome features were revealed. Several of the identified proteins demonstrated a significant abundance difference in the field isolates compared to the reference strain even though there were no obvious differences in the DNA sequence of the corresponding gene or in nearby non-coding DNA. Higher abundance in the field isolates was observed for proteins related to hypoxia and nutrient deficiency responses as well as to thiopeptide biosynthesis.