Acinetobacter baumannii: Virulence Strategies and Host Defense Mechanisms

Material modification of electrodes in microbial electrochemical system to enhance electrons utilization on the electrode and its impact on microorganisms

Previous research has established a MES embedding a microbial electrode to facilitate the degradation of antibiotics in water. We modified microbial electrodes in the MES with PEDOT and rGO to enhance electron utilization on electrodes and to further promote antibiotic degradation. Density functional theory calculations on the SMX molecule indicated that the C4-S8 and S8-N27 bonds are the most susceptible to electron attack. The introduction of various functional groups and multivalent elements enhanced the electrodes' capacitance and electron mediation capabilities. This led to enhance both electron utilization on the electrodes and the removal efficiency of SMX. After 120 h, the degradation efficiency of SMX by PEDOT and rGO-modified electrodes increased by 45.47 % and 25.19 %, respectively, compared to unmodified electrodes. The relative abundance of sulfate-reducing and denitrifying bacteria significantly increased in PEDOT and rGO-modified electrodes, while the abundance of nitrifying bacteria and potential antibiotic resistance gene host microbes significantly decreased. The impact of PEDOT modification positively influenced microbial Cellular Processes, including cell growth, death, and motility. This study provides insights into the mechanisms of direct electron involvement in antibiotic degradation steps in microbial electrochemistry, and provides a possible path for improved strategies in antibiotic degradation and sustainable environmental remediation.

An insight into MDR Acinetobacter baumannii infection and its pathogenesis: Potential therapeutic targets and challenges

Acinetobacter baumannii is observed as a common species of Gram-negative bacteria that exist in soil and water. Despite being accepted as a typical component of human skin flora, it has become an important opportunistic pathogen, especially in healthcare settings. The pathogenicity of A. baumannii is attributed to its virulence factors, which include adhesins, pili, lipopolysaccharides, outer membrane proteins, iron uptake systems, autotransporter, secretion systems, phospholipases etc. These elements provide the bacterium the ability to cling to and penetrate host cells, get past the host immune system, and destroy tissue. Its infection is a major contributor to human pathophysiological conditions including pneumonia, bloodstream infections, urinary tract infections, and surgical site infections. It is challenging to treat infections brought on by this pathogen since this bacterium has evolved to withstand numerous drugs and further emergence of drug-resistant A. baumannii results in higher rates of morbidity and mortality. The long-term survival of this bacterium on surfaces of medical supplies and hospital furniture facilitates its frequent spread in humans from one habitat to another. There is a need for urgent investigations to find effective drug targets for A. baumannii as well as designing novel drugs to reduce the survival and spread of infection. In the current review, we represent the specific features, pathogenesis, and molecular intricacies of crucial drug targets of A. baumannii. This would also assist in proposing strategies and alternative therapies for the prevention and treatment of A. baumannii infections and their spread.

Polydopamine-based nano adjuvant as a promising vaccine carrier induces significant immune responses against Acinetobacter baumannii-associated pneumonia

The objective of this study was to assess the effectiveness of polydopamine nanoparticles (PDANPs) as a delivery system for intranasal antigen administration to prevent Acinetobacter baumannii (A. baumannii)-associated pneumonia. In the in vitro phase, the conserved outer membrane protein 22 (Omp22)-encoding gene of A. baumannii was cloned, expressed, and purified, resulting in the production of recombinant Omp22 (rOmp22), which was verified using western blot. PDANPs were synthesized using dopamine monomers and loaded with rOmp22 through physical adsorption. The rOmp22-loaded PDANPs were characterized in terms of size, size distribution, zeta potential, field emission scanning electron microscopy (FESEM), loading capacity, Fourier transform infrared spectroscopy (FTIR), release profile, and cytotoxicity. In the in vivo phase, the adjuvant effect of rOmp22-loaded PDANPs was evaluated in terms of eliciting immune responses, including humoral and cytokine levels (IL-4, IL-17, and IFN-γ), as well as protection challenge. The rOmp22-loaded PDANPs were spherical with a size of 205 nm, a zeta potential of -14 mV, and a loading capacity of approximately 35.7 %. The released rOmp22 from nontoxic rOmp22-loaded PDANPs over 20 days was approximately 41.5 %, with preserved rOmp22 integrity. The IgG2a/IgG1 ratio and IFN-γ levels were significantly higher in immunized mice with rOmp22-loaded-PDANPs than in rOmp22-alum, naive Omp22, and control groups. Furthermore, rOmp22-loaded PDANPs induced effective protection against infection in the experimental challenge and showed more normal structures in the lung histopathology assay. The results of this study suggest the potential of PDANPs as a nano-adjuvant for inducing strong immune responses to combat A. baumannii.

Genomic Characterization of Mobile Genetic Elements Associated with Multidrug-Resistant Acinetobacter Non-baumannii Species from Southern Thailand

This study investigated the genetic diversity, antimicrobial resistance profiles, and virulence characteristics of Acinetobacter non-baumannii isolates obtained from four hospitals in southern Thailand. Clinical data, genome information, and average nucleotide identity (ANI) were analyzed for eight isolates, revealing diverse genetic profiles and novel sequence types (STs). Minimum spanning tree analysis indicated potential clonal spread of certain STs across different geographic regions. Antimicrobial resistance genes (ARGs) were detected in all isolates, with a high prevalence of genes conferring resistance to carbapenems, highlighting the challenge of antimicrobial resistance in Acinetobacter spp. infections. Mobile genetic elements (MGEs) carrying ARGs were also identified, emphasizing the role of horizontal gene transfer in spreading resistance. Evaluation of virulence-associated genes revealed a diverse range of virulence factors, including those related to biofilm formation and antibiotic resistance. However, no direct correlation was found between virulence-associated genes in Acinetobacter spp. and specific clinical outcomes, such as infection severity or patient mortality. This complexity suggests that factors beyond gene presence may influence disease progression and outcomes. This study emphasizes the importance of continued surveillance and molecular epidemiological studies to combat the spread of multidrug-resistant (MDR) Acinetobacter non-baumannii strains. The findings provide valuable insights into the epidemiology and genetic characteristics of this bacteria in southern Thailand, with implications for infection control and antimicrobial management efforts.

Virulence genes and plasmid replicon profiles of selected β-lactamase-producing Acinetobacter baumannii from orthopaedic patients and the environment in a tertiary referral hospital in Tanzania, East Africa

Acinetobacter baumannii has emerged as an important nosocomial pathogen due to its high resistance to multi-drugs and disinfectants plus its ability to survive in hospital environments. Rectal swabs were collected for screening β-lactamases-producing Acinetobacter baumannii among hospitalized orthopedic patients at a tertiary referral hospital in Tanzania. Swabs were also taken from patients' caretakers, healthcare workers, and the neighboring inanimate environment. A total of 26 confirmed β-lactamases producing Acinetobacter baumannii were isolated, of which 4 representative isolates (two from patients and two from hospital environment) underwent whole-genome sequencing (WGS) to detect sequence types (ST), β-lactamases genes, plasmid replicon types, and virulence genes. All four isolates harbored multiple β-lactamases genes including blaADC-25(3), blaOXA(4), blaCTX-M-15(2) and blaNDM-1(2). Furthermore, isolates harbored virulence genes encoding outer membrane protein (ompA), curli protein (csg), siderophore biosynthesis systems (enterobactin [entABCDEFS, fepABCDG, fes]; yersiniabactin [ybtAEPQSTUX, irp1, irp2, fyuA] and aerobactin [iucABCD, iutA]), transport secretion system type II (T2SS) and type III (T3SS), E. coli common pilus (ecpRABCDE operon), type 1 fimbriae (fim), arylsulfatase (aslA) and adhesions (fedC). Only isolates from patients harbored 4 plasmid replicons each, with the most common plasmid replicons being IncFIA_1; IncY_1 and IncFIB(AP001918)_1. Admitted orthopedic patients and the hospital environment act as a reservoir of multiple β-lactamases producing Acinetobacter baumannii (including those against carbapenems like blaOXA and blaNDM-1) endowed with virulence genes, highlighting the necessity to routinely screening of orthopedic patients with open fractures on admission as well as reinforcing infection prevention and control measures to reduce the dissemination of nosocomial infection within the hospital environment.

Acinetobacter baumannii in the critically ill: complex infections get complicated

Acinetobacter baumannii is increasingly associated with various epidemics, representing a serious concern due to the broad level of antimicrobial resistance and clinical manifestations. During the last decades, A. baumannii has emerged as a major pathogen in vulnerable and critically ill patients. Bacteremia, pneumonia, urinary tract, and skin and soft tissue infections are the most common presentations of A. baumannii, with attributable mortality rates approaching 35%. Carbapenems have been considered the first choice to treat A. baumannii infections. However, due to the widespread prevalence of carbapenem-resistant A. baumannii (CRAB), colistin represents the main therapeutic option, while the role of the new siderophore cephalosporin cefiderocol still needs to be ascertained. Furthermore, high clinical failure rates have been reported for colistin monotherapy when used to treat CRAB infections. Thus, the most effective antibiotic combination remains disputed. In addition to its ability to develop antibiotic resistance, A. baumannii is also known to form biofilm on medical devices, including central venous catheters or endotracheal tubes. Thus, the worrisome spread of biofilm-producing strains in multidrug-resistant populations of A. baumannii poses a significant treatment challenge. This review provides an updated account of antimicrobial resistance patterns and biofilm-mediated tolerance in A. baumannii infections with a special focus on fragile and critically ill patients.

Putative Role of an ABC Efflux System in Aliarcobacter butzleri Resistance and Virulence

Aliarcobacter butzleri is considered a ubiquitous microorganism and emergent pathogen, for which increasing rates of multidrug resistance have been described. In line with this, the present work aimed to evaluate for the first time the contribution of an ABC efflux system, the YbhFSR, in the resistance and virulence of this bacterium. Following the in silico characterization of the YbhFSR transporter, a mutant strain was constructed by inactivating the gene responsible for ATP-binding. After ensuring that the mutation did not have an impact on bacterial growth, the resistance profile of parental and mutant strains to different antimicrobial agents was evaluated. The results suggest that the efflux pump may influence the resistance to benzalkonium chloride, ethidium bromide, and cadmium, and several other compounds were identified as potential substrates. Regarding the evaluation of the accumulation of ethidium bromide, a slight increase was observed for the mutant strain, demonstrating a potential role of the YbhFSR efflux pump in the extrusion of toxic compounds from A. butzleri. Subsequently, the role of this efflux pump on the A. butzleri known virulence properties was evaluated, but no difference was seen among mutant and parental strains for the motility, biofilm formation ability, susceptibility to oxidative stress, or the ability to adhere and invade Caco-2 cells. However, in contrast to the parental strain, the mutant strain showed a resistance to human serum. Overall, the results support the role of efflux pumps in A. butzleri resistance to antimicrobials, highlighting the particular role of the YbhFSR system.

Characterization of Acinetobacter baumannii Isolated from Raw Milk

Acinetobacter baumannii (A. baumannii) is an opportunistic pathogen associated with nosocomial infections. In this study, 100 raw milk samples were collected from Qena, Egypt, and subjected to conventional and molecular assays to determine the presence of A. baumannii and investigate their antimicrobial resistance and biofilm formation. Our findings revealed that, among the 100 samples, Acinetobacter spp. were found in 13 samples based on CHROM agar results. We further characterized them using rpoB and 16S-23SrRNA sequencing and gyrB multiplex PCR analysis and confirmed that 9 out of the 13 Acinetobacter spp. isolates were A. baumannii and 4 were other species. The A. baumannii isolates were resistant to β-lactam drugs, including cefotaxime (44%), ampicillin-sulbactam and levofloxacin (33.3% for each), imipenem, meropenem and aztreonam (22.2% for each). We observed different antimicrobial resistance patterns, with a multi-antibiotic resistant (MAR) index ranging from 0.2 to 0.3. According to the PCR results, bla_OXA-51 and bla_OXA-23 genes were amplified in 100% and 55.5% of the A. baumannii isolates, respectively, while the bla_OXA-58 gene was not amplified. Furthermore, the metallo-β-lactamases (MBL) genes bla_IMP and bla_NDM were found in 11.1% and 22.2% of isolates, respectively, while bla_VIM was not amplified. Additionally, eight A. baumannii isolates (88.8%) produced black-colored colonies on Congo red agar, demonstrating their biofilm production capacity. These results showed that, besides other foodborne pathogens, raw milk should also be examined for A. baumannii, which could be a public health concern.

Differential Gene Expression of Efflux Pumps and Porins in Clinical Isolates of MDR Acinetobacter baumannii

Background: Acinetobacter baumannii is an opportunistic pathogen associated with healthcare infections and high mortality rates in intensive care units all over the globe. Porins and efflux pumps over-expression have been reported as contributing factors in escalating drug resistance and rendering treatment ineffective. In this study, we investigated the mechanisms of multidrug resistance (MDR) in A. baumannii clinical isolates. Methods: A total of 30 A. baumannii isolates were included in the present study from Nehru Hospital (PGIMER-Chandigarh) located in North India. Kirby Bauer disk diffusion assay and MIC were performed to determine the antimicrobial susceptibility pattern. Screening of beta-lactamases was performed using PCR. Relative gene expression of four RND, one MATE efflux pump, and two outer membrane proteins were determined using RT-PCR. Molecular typing of 22 isolates was carried out using MLST Oxford scheme. Results: CarO porin genes showed over-expression in 63% isolates followed by adeGandabeM efflux pump downregulation/underexpression (<0.5 fold), suggesting the carbapenem-susceptible phenotypic nature of the isolates. High prevalence of VIM-2, NDM-1, and OXA-23 genes was observed in A. baumannii isolates. Interestingly, NDM-1 and OXA-58 were traced in 10 and3 A. baumannii isolates respectively; 13 of 22 (59%) isolates showed novel Sequence Types (STs) in the Multi-Locus Sequence Typing (MLST) analysis. ST 1087 was most commonly found ST among all others (16 STs). Conclusions: This study indicated a possible role of carO porin genes and adeG (RND) andabeM (MATE) efflux pumps in carbapenem susceptibility of A. baumannii. New STs were also reported in the majority of the isolates.