The sensor of the bacterial histidine kinase CpxA is a novel dimer of extracytoplasmic Per-ARNT-Sim domains.

Histidine kinases are key bacterial sensors that recognize diverse environmental stimuli. While mechanisms of phosphorylation and phosphotransfer by cytoplasmic kinase domains are relatively well-characterized, the ways in which extracytoplasmic sensor domains regulate activation remain mysterious. The Cpx envelope stress response is a conserved Gram-negative two-component system which is controlled by the sensor kinase CpxA. We report the structure of the Escherichia coli CpxA sensor domain (CpxA-SD) as a globular Per-ARNT-Sim (PAS)-like fold highly similar to that of Vibrio parahaemolyticus CpxA as determined by X-ray crystallography. Because sensor kinase dimerization is important for signaling, we used AlphaFold2 to model CpxA-SD in the context of its connected transmembrane domains, which yielded a novel dimer of PAS domains possessing a distinct dimer organization compared to previously characterized sensor domains. Gain of function cpxA∗ alleles map to the dimer interface, and mutation of other residues in this region also leads to constitutive activation. CpxA activation can be suppressed by mutations that restore inter-monomer interactions, suggesting that inhibitory interactions between CpxA-SD monomers are the major point of control for CpxA activation and signaling. Searching through hundreds of structural homologs revealed the sensor domain of Pseudomonas aeruginosa sensor kinase PfeS as the only PAS structure in the same novel dimer orientation as CpxA, suggesting that our dimer orientation may be utilized by other extracytoplasmic PAS domains. Overall, our findings provide insight into the diversity of the organization of PAS sensory domains and how they regulate sensor kinase activation.

NlpE Is an OmpA-Associated Outer Membrane Sensor of the Cpx Envelope Stress Response.

Gram-negative bacteria utilize several envelope stress responses (ESRs) to sense and respond to diverse signals within a multilayered cell envelope. The CpxRA ESR responds to multiple stresses that perturb envelope protein homeostasis. Signaling in the Cpx response is regulated by auxiliary factors, such as the outer membrane (OM) lipoprotein NlpE, an activator of the response. NlpE communicates surface adhesion to the Cpx response; however, the mechanism by which NlpE accomplishes this remains unknown. In this study, we report a novel interaction between NlpE and the major OM protein OmpA. Both NlpE and OmpA are required to activate the Cpx response in surface-adhered cells. Furthermore, NlpE senses OmpA overexpression and the NlpE C-terminal domain transduces this signal to the Cpx response, revealing a novel signaling function for this domain. Mutation of OmpA peptidoglycan-binding residues abrogates signaling during OmpA overexpression, suggesting that NlpE signaling from the OM through the cell wall is coordinated via OmpA. Overall, these findings reveal NlpE to be a versatile envelope sensor that takes advantage of its structure, localization, and cooperation with other envelope proteins to initiate adaptation to diverse signals. IMPORTANCE The envelope is not only a barrier that protects bacteria from the environment but also a crucial site for the transduction of signals critical for colonization and pathogenesis. The discovery of novel complexes between NlpE and OmpA contributes to an emerging understanding of the key contribution of OM ß-barrel protein and lipoprotein complexes to envelope stress signaling. Overall, our findings provide mechanistic insight into how the Cpx response senses signals relevant to surface adhesion and biofilm growth to facilitate bacterial adaptation.

Bacterial envelope stress responses: Essential adaptors and attractive targets.

Millions of deaths a year across the globe are linked to antimicrobial resistant infections. The need to develop new treatments and repurpose of existing antibiotics grows more pressing as the growing antimicrobial resistance pandemic advances. In this review article, we propose that envelope stress responses, the signaling pathways bacteria use to recognize and adapt to damage to the most vulnerable outer compartments of the microbial cell, are attractive targets. Envelope stress responses (ESRs) support colonization and infection by responding to a plethora of toxic envelope stresses encountered throughout the body; they have been co-opted into virulence networks where they work like global positioning systems to coordinate adhesion, invasion, microbial warfare, and biofilm formation. We highlight progress in the development of therapeutic strategies that target ESR signaling proteins and adaptive networks and posit that further characterization of the molecular mechanisms governing these essential niche adaptation machineries will be important for sparking new therapeutic approaches aimed at short-circuiting bacterial adaptation.

Medical Redeployment in Soldiers With and Without Medical Deployment Waivers.

BACKGROUND: Historically, disease and nonbattle injuries (DNBI) have caused more casualties during military operations than enemy combatants. Recent deployments to U.S. Central Commands (USCENTCOM) area of operation (AOR) have demonstrated similar outcomes. Intuitively, appropriate medical standards for our deploying Soldiers should result in no greater redeployments rates for those Soldiers who are waived for various medical conditions. However, no formal study has been published on redeployment rates of Soldiers with medical deployment waivers. The objective of this report was to evaluate the redeployment rates of Soldiers with and without medical waivers. METHODS: A matched retrospective cohort study design was used in this study. Data were obtained from USCENTCOM, Army Central Command, Transportation Command, and the Armed Forces Health Surveillance Center. All U.S. Soldiers deploying to USCENTCOM's AOR with a medical deployment waiver during the calendar years of 2008-2013 were eligible for inclusion into the exposure group of this study. Soldiers with a medical deployment waiver were matched 1:5 to Soldiers without a medical deployment waiver. The Soldiers with a medical deployment waiver and their matched counterparts were then subdivided into 5 strata on the basis of their diagnosis. A McNemar's χ2 test was performed to calculate risk ratios (RRs) per strata and for the group as a whole. RESULTS: The overall risk of being medically evacuated because of DNBI for all medical deployment waivers was an RR of 2.03 (CI: 1.74, 2.36). The greatest risk of being medically evacuated because of DNBI was from the group of Soldiers on a waiver for neurological conditions with an RR of 3.81 (CI: 1.99, 7.30). The RR of medical evacuation because of DNBI was increased and statistically significant for all strata (p < 0.05). CONCLUSION: There is a statistically significant increased RR of Soldiers with a Modification of the Operational Order waiver being medically redeployed for a DNBI reason from USCENTCOM's AOR from 2008 to 2013 compared with their matched peers without a waiver. The results of this study provide Commanders with additional information when making decisions regarding Soldier deployment.

Military Occupations Most Affected by Head/Sensory Injuries and the Potential Job Impact of Those Injuries.

OBJECTIVE: Identifying Department of Defense (DoD) occupations affected by injuries to the head and sensory systems. METHODS: We explored the Defense Medical Epidemiology Database to identify occupations with the highest incidence of injured personnel, then ranked how frequently they occurred in a top 10 list for each of four injury categories (head/brain, visual, auditory, vestibular) encompassing 25 injury codes. Across all four categories, the most affected occupations were identified, among which we chose three Army combat-related military occupational specialties (MOSs) for detailed study. We identified skills needed to perform these MOSs and explored whether MOS-critical deficits could be expected following the injuries. RESULTS: Some DoD occupations are more likely to suffer from these injuries, including Infantry, Combat Operations Control, Artillery/Gunnery, Motor Vehicle Operator, Combat Engineering, and Armor/Amphibious. Within these DoD occupations, we explored three Army combatant MOSs: Infantry (11B), Cavalry Scout (19D), and Artillery (13B), confirming that these jobs are likely to be disrupted by injuries within the four categories. CONCLUSIONS: Head and sensory injuries disproportionately affect certain military occupations. Relatively few injuries disrupt combat-related abilities that are job critical (e.g., firearms operation) and job specific (e.g., Artillery gunnery problems); these should be the focus of efforts to improve rehabilitation and RTD outcomes.

Functional screening for vestibular and balance problems soon after head injury: options in development for the field or aid station.

Vestibular balance dysfunction has been documented as a military problem after duty-related barotrauma and/ or traumatic head acceleration. We are fostering the development of rapid, portable, fieldable tests of balance function after such vestibular insults. We consulted on military-relevant tests with more than 50 vestibular researchers, scientific advisors, clinicians, and biomedical engineers working for government agencies, universities, clinics, hospitals, or businesses. Screening tests and devices appropriate for early (post-injury) military functional assessment were considered. Based on these consultations, we recommend that military field tests emphasize dynamic, functional, and duty-relevant aspects of standing balance, gait, visual acuity, perception of visual vertical, and vertigo. While many current tests are useful for the clinic, they often require modification before they are suitable for military field and aid station settings. This report summarizes likely future military testing needs, giving priority to testing approaches in development that promise to be rapid, portable, fieldready, semiautomated, usable by a nonspecialist, and suitable during testing and rehabilitation.

In-flight speech intelligibility evaluation of a service member with sensorineural hearing loss: case report.

This case report describes the in-flight speech intelligibility evaluation of an aircraft crewmember with pure tone audiometric thresholds that exceed the U.S. Army's flight standards. Results of in-flight speech intelligibility testing highlight the inability to predict functional auditory abilities from pure tone audiometry and underscore the importance of conducting validated functional hearing evaluations to determine aviation fitness-for-duty.

Risk propensity and health risk behaviors in U.S. army soldiers with and without psychological disturbances across the deployment cycle.

Anecdotal and preliminary evidence suggests that Soldiers returning from a combat deployment engage in an increased number of health risk behaviors. Three potential factors driving this change were examined in this study; posttraumatic stress disorder (PTSD), concussion and traumatic brain injury (TBI), and perceived invincibility. We studied members of a combat arms brigade one month prior to a deployment to Iraq and approximately one month after their return (N = 319). Participants anonymously completed surveys characterizing attitudes about risk, risk propensity, invincibility, engagement in health risk behaviors, and personality. Using standardized screening instruments, participants were categorized with respect to PTSD and probable TBI. Results suggest that Soldiers engage in more alcohol use and reckless driving behaviors post-deployment. These changes were exaggerated in those who screened positive for PTSD. Perception of one's invincibility and survival skills increased post-deployment thus suggesting that participants felt less susceptible to adverse consequences and more adept at surviving dangerous situations. This study provides documentation of the pattern of health behavior in Soldiers engaged in the deployment cycle. Our findings suggest increases in the number of risks Soldiers' engage in post-deployment are not limited to those with PTSD symptomtotology. This study has implications for not only adjustment to life post-deployment at the individual level but also operational readiness.