Genetic and Phenotypic Features of a Novel Acinetobacter Species, Strain A47, Isolated From the Clinical Setting

Targeting PilA in Acinetobacter baumannii: A Computational Approach for Anti-Virulent Compound Discovery

Acinetobacter baumannii (A. baumannii) has emerged as a critical global pathogen due to its ability to acquire resistance traits. This bacterium exhibits two distinct forms of motility: twitching, mediated by type IV pili (T4P), and surface-associated motility, independent of appendages. T4P is crucial in various bacterial species, facilitating twitching motility, biofilm formation, and host-cell adhesion. The synthesis of T4P is a common feature among Gram-negative pathogens, particularly A. baumannii, suggesting that PilA could be a viable target for biofilm-related treatments. This study aims to develop drug molecules to mitigate A. baumannii virulence by targeting PilA. Using Schrodinger software, we screened 60,766 compounds from the CMNPD, ChemDiv, and Enamine antibacterial databases through high-throughput virtual screening. The top two compounds from each database, identified through extra precision (XP) mode, were subjected to further studies. Among the six compounds identified (CMNPD18469, CMNPD20698, Z2377302405, Z2378175729, N039-0021, and N098-0051), docking scores ranged from - 5.0 to - 7.5 kcal/mol. Subsequently, we conducted 300 ns molecular dynamics simulations and Molecular Mechanics Poisson-Boltzmann Surface Area (MMPBSA) analysis of the PilA-ligand complexes. Analysis of the simulation trajectories indicated structural stability and consistent behavior of the PilA-ligand complexes in a dynamic environment. Notably, the PilA-N098-0051 complex exhibited enhanced stability and robust binding interactions, underscoring its potential as a therapeutic agent. These findings suggest that the identified compounds, particularly N098-0051, hold promise as potent molecules targeting PilA, necessitating further validation through in vitro and in vivo studies.

Characterization of BLUF-photoreceptors present in Acinetobacter nosocomialis

Acinetobacter nosocomialis is a Gram-negative opportunistic pathogen, whose ability to cause disease in humans is well recognized. Blue light has been shown to modulate important physiological traits related to persistence and virulence in this microorganism. In this work, we characterized the three Blue Light sensing Using FAD (BLUF) domain-containing proteins encoded in the A. nosocomialis genome, which account for the only canonical light sensors present in this microorganism. By focusing on a light-modulated bacterial process such as motility, the temperature dependence of light regulation was studied, as well as the expression pattern and spectroscopic characteristics of the different A. nosocomialis BLUFs. Our results show that the BLUF-containing proteins AnBLUF65 and AnBLUF46 encode active photoreceptors in the light-regulatory temperature range when expressed recombinantly. In fact, AnBLUF65 is an active photoreceptor in the temperature range from 15°C to 37°C, while AnBLUF46 between 15°C to 32°C, in vitro. In vivo, only the Acinetobacter baumannii BlsA’s ortholog AnBLUF65 was expressed in A. nosocomialis cells recovered from motility plates. Moreover, complementation assays showed that AnBLUF65 is able to mediate light regulation of motility in A. baumannii ΔblsA strain at 30°C, confirming its role as photoreceptor and in modulation of motility by light. Intra-protein interactions analyzed using 3D models built based on A. baumannii´s BlsA photoreceptor, show that hydrophobic/aromatic intra-protein interactions may contribute to the stability of dark/light- adapted states of the studied proteins, reinforcing the previous notion on the importance of these interactions in BLUF photoreceptors. Overall, the results presented here reveal the presence of BLUF photoreceptors in A. nosocomialis with idiosyncratic characteristics respect to the previously characterized A. baumannii’s BlsA, both regarding the photoactivity temperature-dependency as well as expression patterns, contributing thus to broaden our knowledge on the BLUF family.

Human Pleural Fluid and Human Serum Albumin Modulate the Behavior of a Hypervirulent and Multidrug-Resistant (MDR) Acinetobacter baumannii Representative Strain

Acinetobacter baumannii is a nosocomial pathogen capable of causing serious infections associated with high rates of morbidity and mortality. Due to its antimicrobial drug resistance profile, A. baumannii is categorized as an urgent priority pathogen by the Centers for Disease Control and Prevention in the United States and a priority group 1 critical microorganism by the World Health Organization. Understanding how A. baumannii adapts to different host environments may provide critical insights into strategically targeting this pathogen with novel antimicrobial and biological therapeutics. Exposure to human fluids was previously shown to alter the gene expression profile of a highly drug-susceptible A. baumannii strain A118 leading to persistence and survival of this pathogen. Herein, we explore the impact of human pleural fluid (HPF) and human serum albumin (HSA) on the gene expression profile of a highly multi-drug-resistant strain of A. baumannii AB5075. Differential expression was observed for ~30 genes, whose products are involved in quorum sensing, quorum quenching, iron acquisition, fatty acid metabolism, biofilm formation, secretion systems, and type IV pilus formation. Phenotypic and further transcriptomic analysis using quantitative RT-PCR confirmed RNA-seq data and demonstrated a distinctive role of HSA as the molecule involved in A. baumannii’s response.