Acinetobacter baumannii biofilm was inhibited by tryptanthrin through disrupting its different stages and genes expression

AbOmpA in Acinetobacter baumannii: exploring virulence mechanisms of outer membrane-integrated and outer membrane vesicle-associated AbOmpA and developing anti-infective agents targeting AbOmpA

Acinetobacter baumannii is notorious for its antimicrobial resistance and its potential to cause epidemics in hospital settings, which pose a global health threat. Although this microorganism is traditionally considered a low-virulence pathogen, extensive research has been conducted on its virulence and pathogenesis in recent years. Advances in understanding the virulence mechanisms of A. baumannii have prompted a shift in the development of anti-infective agents. The outer membrane protein A (AbOmpA) of A. baumannii is a key virulence factor both in vitro and in vivo. AbOmpA exists in three forms: outer membrane-integrated AbOmpA, outer membrane vesicle (OMV)-associated AbOmpA, and free proteins. Given that outer membrane-integrated AbOmpA has been implicated in the virulence and antimicrobial resistance of A. baumannii, many studies have focused on outer membrane-integrated AbOmpA as a therapeutic target for combating drug-resistant A. baumannii, and have led to the discovery of small molecules, polypeptides, and antimicrobial peptides targeting AbOmpA. However, the pathophysiological role of OMV-associated AbOmpA and its impact on AbOmpA-targeting agents remain unclear. This review summarizes the current knowledge of AbOmpA and critically discusses OMV-associated AbOmpA in relation to virulence and its potential impact on AbOmpA-targeted therapies to provide a better understanding of AbOmpA for the development of novel therapeutics against A. baumannii.

Synergistic pathogenesis: exploring biofilms, efflux pumps and secretion systems in Acinetobacter baumannii and Staphylococcus aureus

Antimicrobial resistance (AMR) is a growing global health crisis, particularly among ESKAPE pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species. Among them, A. baumannii and S. aureus are major contributors to nosocomial infections, with high prevalence in intensive care units and immunocompromised patients. Their ability to resist multiple antibiotic classes complicates treatment strategies, leading to increased morbidity and mortality. Key resistance mechanisms, including biofilm formation, efflux pump activity, and horizontal gene transfer, enhance their survival and persistence. Furthermore, interactions during polymicrobial infections intensify disease severity through synergistic effects that promote both virulence and resistance. The epidemiological burden of these pathogens highlights the urgent need for novel antimicrobial strategies and targeted interventions. This review explores their virulence factors, resistance mechanisms, pathogenic interactions, and clinical implications, emphasizing the necessity of innovative therapeutic approaches to combat their growing threat.

Indole derivatives display antimicrobial and antibiofilm effects against extensively drug-resistant Acinetobacter baumannii

Acinetobacter baumannii is a critical priority gram-negative bacterial species featured with multidrug resistance and biofilm formation. This study screened 46 indole derivative agents for their antimicrobial activities against clinical isolates of extensively drug-resistant A. baumannii (XDRAB) with various degrees of biofilm production. Three selected indole agents-5-iodoindole, 3-methylindole, and 7-hydroxyindole-were revealed to display potent antimicrobial and antibiofilm activity, including synergistic interplay with anti-A. baumannii antimicrobial drugs against XDRAB. Sub-inhibitory concentrations of these agents (particularly 7-hydroxyindole at 1/64 of MIC) not only inhibited XDRAB biofilm formation but also eradicated the mature biofilm. The survival rate of XDRAB-infected Galleria mellonella was improved with the treatment of 7-hydroxyindole. Mechanistically, 7-hydroxyindole was found to reduce the expression of quorum sensing/biofilm-implicated genes abaI and abaR. Together, the findings highlight the potential of indole derivatives against A. baumannii infections.

IMPORTANCE

Extensively drug-resistant Acinetobacter baumannii (XDRAB) isolates pose a major public health threat to antimicrobial therapy and are highly prevalent in hospital settings. This study identified and characterized indole derivative agents for their antimicrobial and antibiofilm activities against XDRAB. Sub-inhibitory indole agents such as 7-hydroxyindole can both inhibit XDRAB biofilm formation and eradicate the mature biofilm. Indole agents warrant further investigation against hard-to-treat antimicrobial-resistant pathogens.

A chionodracine-derived peptide, KHS-Cnd, as an anti-virulence agent against multidrug-resistant Acinetobacter baumannii clinical strains

About 71% of healthcare-associated infections are due to antibiotic-resistant bacteria, such as carbapenem-resistant A. baumannii, classified by World Health Organization into a critical priority group of pathogens. The antimicrobial resistance profile of A. baumannii relies on its ability to produce several virulence factors, including biofilm formation. Its ability to adhere and persist on surfaces as biofilm has contributed to its pathogenicity and drug resistance. In this study, the ability of an antimicrobial peptide (a chionodracine-derived peptide named KHS-Cnd) to inhibit or reduce biofilm formation was investigated as an example of a potential strategy to counteract infections caused by biofilm-forming pathogens. To this aim, the antimicrobial profiles were first analyzed in selected A. baumannii strains, two reference and six clinical strains, all biofilm-forming with different capability, regardless of whether they are drug resistant or sensitive. Successively, we investigated the bactericidal activity of the peptide that showed MIC values ranging from 5 to 10 µM and a significative antibiofilm activity on all tested strains at sub-inhibitory concentrations. In fact, KHS-Cnd can hinder biofilm A. baumannii strains formation with an inhibition percentage ranging between 65% and 10%. Also a statistically significant reduction of mature biofilm ranging from 20% to 50% was observed in four out of eight tested A. baumannii strains. KHS-Cnd impacts various stages of biofilm formation, including the inhibition of surface-associated and twitching motilities depending on the different strain. In particular, our results showed that only two strains possessed surface-associated motility that was strongly impaired by KHS-Cnd treatment; three clinical strains, instead, showed twitching motility, whose inhibition for two of them was evident after 24 h of incubation with peptide. Moreover, the invasion of pulmonary cells by A. baumannii was significantly impaired with a reduction of about 32% after treatment with 1.25 µM KHS-Cnd. Finally, when the peptide was used together with ceftazidime/avibactam against resistant A. baumannii strains, it was able to reduce the minimal inhibitory concentration of antibiotics needed to inhibit the microorganism growth.