Uncovering the Secretion Systems of Acinetobacter baumannii: Structures and Functions in Pathogenicity and Antibiotic Resistance

Pathogenicity and virulence of Acinetobacter baumannii: Factors contributing to the fitness in healthcare settings and the infected host

Acinetobacter baumannii is a common cause of healthcare-associated infections and hospital outbreaks, particularly in intensive care units. Much of the success of A. baumannii relies on its genomic plasticity, which allows rapid adaptation to adversity and stress. The capacity to acquire novel antibiotic resistance determinants and the tolerance to stresses encountered in the hospital environment promote A. baumannii spread among patients and long-term contamination of the healthcare setting. This review explores virulence factors and physiological traits contributing to A. baumannii infection and adaptation to the hospital environment. Several cell-associated and secreted virulence factors involved in A. baumannii biofilm formation, cell adhesion, invasion, and persistence in the host, as well as resistance to xeric stress imposed by the healthcare settings, are illustrated to give reasons for the success of A. baumannii as a hospital pathogen.

Characterization of the diversity of type IV secretion system-encoding plasmids in Acinetobacter

The multi-drug resistant pathogen Acinetobacter baumannii has gained global attention as an important clinical challenge. Owing to its ability to survive on surfaces, its capacity for horizontal gene transfer, and its resistance to front-line antibiotics, A. baumannii has established itself as a successful pathogen. Bacterial conjugation is a central mechanism for pathogen evolution. The epidemic multidrug-resistant A. baumannii ACICU harbours a plasmid encoding a Type IV Secretion System (T4SS) with homology to the E. coli F-plasmid, and plasmids with homologous gene clusters have been identified in several A. baumannii sequence types. However the genetic and host strain diversity, global distribution, and functional ability of this group of plasmids is not fully understood. Using systematic analysis, we show that pACICU2 belongs to a group of almost 120 T4SS-encoding plasmids within four different species of Acinetobacter and one strain of Klebsiella pneumoniae from human and environmental origin, and globally distributed across 20 countries spanning 4 continents. Genetic diversity was observed both outside and within the T4SS-encoding cluster, and 47% of plasmids harboured resistance determinants, with two plasmids harbouring eleven. Conjugation studies with an extensively drug-resistant (XDR) strain showed that the XDR plasmid could be successfully transferred to a more divergent A. baumanii, and transconjugants exhibited the resistance phenotype of the plasmid. Collectively, this demonstrates that these T4SS-encoding plasmids are globally distributed and more widespread among Acinetobacter than previously thought, and that they represent an important potential reservoir for future clinical concern.

Pan-Genome Plasticity and Virulence Factors: A Natural Treasure Trove for Acinetobacter baumannii

Acinetobacter baumannii is a Gram-negative pathogen responsible for a variety of community- and hospital-acquired infections. It is recognized as a life-threatening pathogen among hospitalized individuals and, in particular, immunocompromised patients in many countries. A. baumannii, as a member of the ESKAPE group, encompasses high genomic plasticity and simultaneously is predisposed to receive and exchange the mobile genetic elements (MGEs) through horizontal genetic transfer (HGT). Indeed, A. baumannii is a treasure trove that contains a high number of virulence factors. In accordance with these unique pathogenic characteristics of A. baumannii, the authors aim to discuss the natural treasure trove of pan-genome and virulence factors pertaining to this bacterial monster and try to highlight the reasons why this bacterium is a great concern in the global public health system.

Comparative genomics and host range analysis of four Ralstonia pseudosolanacearum strains isolated from sunflower reveals genomic and phenotypic differences

BACKGROUND

Bacterial wilt caused by Ralstonia solanacearum species complex (RSSC) is one of the devastating diseases in crop production, seriously reducing the yield of crops. R. pseudosolanacearum, is known for its broad infrasubspecific diversity and comprises 36 sequevars that are currently known. Previous studies found that R. pseudosolanacearum contained four sequevars (13, 14, 17 and 54) isolated from sunflowers sown in the same field.

RESULTS

Here, we provided the complete genomes and the results of genome comparison of the four sequevars strains (RS639, RS642, RS647, and RS650). Four strains showed different pathogenicities to the same cultivars and different host ranges. Their genome sizes were about 5.84 ~ 5.94 Mb, encoding 5002 ~ 5079 genes and the average G + C content of 66.85% ~ 67%. Among the coding genes, 146 ~ 159 specific gene families (contained 150 ~ 160 genes) were found in the chromosomes and 34 ~ 77 specific gene families (contained 34 ~ 78 genes) in the megaplasmids from four strains. The average nucleotide identify (ANI) values between any two strains ranged from 99.05% ~ 99.71%, and the proportion of the total base length of collinear blocks accounts for the total gene length of corresponding genome was all more than 93.82%. Then, we performed a search for genomic islands, prophage sequences, the gene clusters macromolecular secretion systems, type III secreted effectors and other virulence factors in these strains, which provided detailed comparison results of their presence and distinctive features compared to the reference strain GMI1000. Among them, the number and types of T2SS gene clusters were different in the four strains, among which RS650 included all five types. T4SS gene cluster of RS639 and RS647 were missed. In the T6SS gene cluster, several genes were inserted in the RS639, RS647, and RS650, and gene deletion was also detected in the RS642. A total of 78 kinds of type III secreted effectors were found, which included 52 core and 9 specific effectors in four strains.

CONCLUSION

This study not only provided the complete genomes of multiple R. pseudosolanacearum strains isolated from a new host, but also revealed the differences in their genomic levels through comparative genomics. Furthermore, these findings expand human knowledge about the range of hosts that Ralstonia can infect, and potentially contribute to exploring rules and factors of the genetic evolution and analyzing its pathogenic mechanism.

The role of type VI secretion system genes in antibiotic resistance and virulence in Acinetobacter baumannii clinical isolates

Introduction

The type VI secretion system (T6SS) is a crucial virulence factor in the nosocomial pathogen Acinetobacter baumannii. However, its association with drug resistance is less well known. Notably, the roles that different T6SS components play in the process of antimicrobial resistance, as well as in virulence, have not been systematically revealed.

Methods

The importance of three representative T6SS core genes involved in the drug resistance and virulence of A. baumannii, namely, tssB, tssD (hcp), and tssM was elucidated.

Results

A higher ratio of the three core genes was detected in drug-resistant strains than in susceptible strains among our 114 A. baumannii clinical isolates. Upon deletion of tssB in AB795639, increased antimicrobial resistance to cefuroxime and ceftriaxone was observed, alongside reduced resistance to gentamicin. The ΔtssD mutant showed decreased resistance to ciprofloxacin, norfloxacin, ofloxacin, tetracycline, and doxycycline, but increased resistance to tobramycin and streptomycin. The tssM-lacking mutant showed an increased sensitivity to ofloxacin, polymyxin B, and furazolidone. In addition, a significant reduction in biofilm formation was observed only with the ΔtssM mutant. Moreover, the ΔtssM strain, followed by the ΔtssD mutant, showed decreased survival in human serum, with attenuated competition with Escherichia coli and impaired lethality in Galleria mellonella.

Discussion

The above results suggest that T6SS plays an important role, participating in the antibiotic resistance of A. baumannii, especially in terms of intrinsic resistance. Meanwhile, tssM and tssD contribute to bacterial virulence to a greater degree, with tssM being associated with greater importance.

Insights into the Microbiome and Antibiotic Resistance Genes from Hospital Environmental Surfaces: A Prime Source of Antimicrobial Resistance

Hospital environmental surfaces are potential reservoirs for transmitting hospital-associated pathogens. This study aimed to profile microbiomes and antibiotic resistance genes (ARGs) from hospital environmental surfaces using 16S rRNA amplicon and metagenomic sequencing at a tertiary teaching hospital in Malaysia. Samples were collected from patient sinks and healthcare staff counters at surgery and orthopaedic wards. The samples' DNA were subjected to 16S rRNA amplicon and shotgun sequencing to identify bacterial taxonomic profiles, antibiotic resistance genes, and virulence factor pathways. The bacterial richness was more diverse in the samples collected from patient sinks than those collected from staff counters. Proteobacteria and Verrucomicrobia dominated at the phylum level, while Bacillus, Staphylococcus, Pseudomonas, and Acinetobacter dominated at the genus level. Staphylococcus epidermidis and Staphylococcus aureus were prevalent on sinks while Bacillus cereus dominated the counter samples. The highest counts of ARGs to beta-lactam were detected, followed by ARGs against fosfomycin and cephalosporin. We report the detection of mcr-10.1 that confers resistance to colistin at a hospital setting in Malaysia. The virulence gene pathways that aid in antibiotic resistance gene transfer between bacteria were identified. Environmental surfaces serve as potential reservoirs for nosocomial infections and require mitigation strategies to control the spread of antibiotic resistance bacteria.

Genome sequence of an Acinetobacter pittii strain obtained from a red-lored parrot with pneumonia

Acinetobacter pittii 978-A_19 was obtained from a parrot with pneumonia. It is resistant to ampicillin, carbenicillin, cephalosporins, clindamycin, and trimethoprim + sulfamethoxazole. The genome encodes a new blaADC allele, a blaOXA-502 gene, possesses several virulence genes related to adherence and biofilm formation, and has types I, II, and IV secretion systems.

Advances in Nanotechnology for Biofilm Inhibition

Biofilm-associated infections have emerged as a significant public health challenge due to their persistent nature and increased resistance to conventional treatment methods. The indiscriminate usage of antibiotics has made us susceptible to a range of multidrug-resistant pathogens. These pathogens show reduced susceptibility to antibiotics and increased intracellular survival. However, current methods for treating biofilms, such as smart materials and targeted drug delivery systems, have not been found effective in preventing biofilm formation. To address this challenge, nanotechnology has provided innovative solutions for preventing and treating biofilm formation by clinically relevant pathogens. Recent advances in nanotechnological strategies, including metallic nanoparticles, functionalized metallic nanoparticles, dendrimers, polymeric nanoparticles, cyclodextrin-based delivery, solid lipid nanoparticles, polymer drug conjugates, and liposomes, may provide valuable technological solutions against infectious diseases. Therefore, it is imperative to conduct a comprehensive review to summarize the recent advancements and limitations of advanced nanotechnologies. The present Review encompasses a summary of infectious agents, the mechanisms that lead to biofilm formation, and the impact of pathogens on human health. In a nutshell, this Review offers a comprehensive survey of the advanced nanotechnological solutions for managing infections. A detailed presentation has been made as to how these strategies may improve biofilm control and prevent infections. The key objective of this Review is to summarize the mechanisms, applications, and prospects of advanced nanotechnologies to provide a better understanding of their impact on biofilm formation by clinically relevant pathogens.