An MltA-Like Lytic Transglycosylase Secreted by Bdellovibrio bacteriovorus Cleaves the Prey Septum during Predatory Invasion.

Lytic transglycosylases cut peptidoglycan backbones, facilitating a variety of functions within bacteria, including cell division, pathogenesis, and insertion of macromolecular machinery into the cell envelope. Here, we identify a novel role of a secreted lytic transglycosylase associated with the predatory lifestyle of Bdellovibrio bacteriovorus strain HD100. During wild-type B. bacteriovorus prey invasion, the predator rounds up rod-shaped prey into spherical prey bdelloplasts, forming a spacious niche within which the predator grows. Deleting the MltA-like lytic transglycosylase Bd3285 still permitted predation but resulted in three different, invaded prey cell shapes: spheres, rods, and "dumbbells." Amino acid D321 within the catalytic C-terminal 3D domain of Bd3285 was essential for wild-type complementation. Microscopic analyses revealed that dumbbell-shaped bdelloplasts are derived from Escherichia coli prey undergoing cell division at the moment of Δbd3285 predator invasion. Prelabeling of E. coli prey peptidoglycan prior to predation with the fluorescent D-amino acid HADA showed that the dumbbell bdelloplasts invaded by B. bacteriovorus Δbd3285 contained a septum. Fluorescently tagged Bd3285, expressed in E. coli, localized to the septum of dividing cells. Our data indicate that B. bacteriovorus secretes the lytic transglycosylase Bd3285 into the E. coli periplasm during prey invasion to cleave the septum of dividing prey, facilitating prey cell occupation. IMPORTANCE Antimicrobial resistance is a serious and rapidly growing threat to global health. Bdellovibrio bacteriovorus can prey upon an extensive range of Gram-negative bacterial pathogens and thus has promising potential as a novel antibacterial therapeutic and is a source of antibacterial enzymes. Here, we elucidate the role of a unique secreted lytic transglycosylase from B. bacteriovorus which acts on the septal peptidoglycan of its prey. This improves our understanding of mechanisms that underpin bacterial predation.

The Safety and Utility of Fiberoptic Bronchoscopy in the Very Elderly.

BACKGROUND: Flexible bronchoscopy (FB) is a common modality for diagnostic sampling within the thorax. It is utilized often in the elderly population, but there is limited data on the safety and utility of the procedure in the very elderly. METHODS: FBs performed outside the intensive care unit in the San Antonio Military Health System on patients 85 years and older were reviewed. Outcomes including indications, complications, diagnostic yield, and final diagnosis were compared with a control group consisting of patients' ages of 65 to 79 years old. RESULTS: Seventy-three bronchoscopies were performed in each group. The mean age of the older group was 87.1±2.6 years, and had a higher American Society of Anesthesiology (ASA) class than the younger group (P=0.03). There were no significant differences in the indications for bronchoscopy (P>0.05), sampling performed (P>0.05), complication rates (P>0.05), diagnostic yield (P>0.05), or final diagnoses (P>0.05). Similar proportions of each group with a malignancy diagnosis received some form of therapy (P>0.05), although fewer of the older group underwent surgery (P=0.03). Analysis of the cohort demonstrated that ASA class 3 to 4 was associated with increased rate of complications and use of anesthesia compared with lower ASA class (P<0.02). CONCLUSION: FB in the elderly demonstrated no differences in procedural complications, diagnostic yield, and utility of the procedure for an underlying diagnosis. This study suggests bronchoscopy is as safe and useful in the very elderly as a population of the age of 65 to 79.

Exertional Dyspnea and Excessive Dynamic Airway Collapse.

Excessive dynamic airway collapse is a relatively new diagnosis separate from tracheobronchomalacia that is manifested by functional collapse of the large airways. Most commonly described in patients with underlying obstructive lung disease such as chronic obstructive pulmonary disease and asthma, it may contribute to increased dyspnea, cough, or exacerbations. There are few data published on the role of excessive dynamic airway collapse as related specifically to exercise. It was recently described as the cause for exertional dyspnea in individuals without underlying lung disease.