Acinetobacter nosocomialis Causes as Severe Disease as Acinetobacter baumannii in Northeast Thailand: Underestimated Role of A. nosocomialis in Infection

Harnessing anti-infective efficacy of Cinnamomum verum in synergy with β-lactam and fluoroquinolones drugs to combat virulence and biofilms of Pseudomonas aeruginosa PAO1

Multidrug resistance (MDR) Gram-negative bacteria are increasingly resistant to multiple antibiotics, posing a serious challenge to infection control and treatment. Combining plant-derived bioactives with antibiotics offers a promising approach to overcome the challenges posed by MDR pathogens like Pseudomonas aeruginosa. This study investigated the synergistic effects of Cinnamomum verum with beta-lactam and fluoroquinolones against P. aeruginosa PAO1. The ethyl acetate fraction of C. verum (CVEF) was obtained through fractionation in organic solvents with progressively higher polarity. The interaction of CVEF with selected antibiotics was assessed by checkerboard synergy assay. The effects of synergistic combinations on pyocyanin, pyoverdine, protease, EPS production, and biofilm development were measured using spectroscopic assays. CVEF combined with cefepime, ceftazidime, and levofloxacin significantly enhanced antibacterial efficacy with FICIs between 0.156 and 0.5. The most active combinations i.e., CVEF-cefepime and CVEF-ceftazidime inhibited viable cell count of growth by 3.6 and 4.2 log10 CFU/ml respectively. The combination also inhibited virulence factors (>75 %) and biofilms (>80 %) at lower 1/2 × FICs. The viable count of biofilm cells was also reduced from 6.4 to 3.3 and 3.6 log10 CFU/ml. Membrane permeability was decreased by 60.34 % and biofilm cell viability by 22.53-38.44 %. Key phytochemicals analyzed by GC/MS and LC/MS/MS, include cinnamaldehyde, trans-chlorogenic acid, quercetin, and quercetin 3'-O-glucuronide. In molecular docking investigations, quercetin 3'-O-glucuronide had the highest binding affinity with quorum sensing (QS) and biofilm-associated protein. The findings suggest CVEF, in combination with antibiotics, effectively targets resistance phenotypes of P. aeruginosa, impairing growth, virulence, and biofilms. This supports further research into natural compounds alongside antibiotics to treat drug-resistant infections.

Heterogeneity and Genomic Plasticity of Acinetobacter baumannii and Acinetobacter nosocomialis Isolates Recovered from Clinical Samples in India

Acinetobacter baumannii and Acinetobacter nosocomialis are the imperious pathogens in the intensive care units. We aimed to explore the genomic features of these pathogens to understand the factors influencing their plasticity. Using next-generation sequencing, two carbapenem-resistant A. baumannii (AbaBS-3, AbaETR-4) isolates and a pan-susceptible A. nosocomialis (AbaAS-5) isolate were characterised. All genomes exhibited 94% similarity with a degree of heterogeneity. AbaBS-3 and AbaETR-4 harboured antibiotic resistance gene (ARG) repertoire to most antibiotic classes. Carbapenem resistance was due to blaOXA-23 and blaOXA-66 besides the antibiotic efflux pumps. Diverse mobile genetic elements (MGE), insertion sequences (IS), prophages and virulence determinants with a plethora of stress response genes were identified in all three genomes. Class-1 integron in AbaETR-4, encoded genes that confer resistance to aminoglycosides, phenicol, sulfonamides and disinfectants. Substitutions in LpxACD and PmrCAB of AbaETR-4 confirmed the colistin resistance in vitro. Novel mutations in piuA, responsible for transporting cefiderocol, were found in AbaBS-3 and AbaETR-4. Plasmids carrying toxin-antitoxin systems, ARGs and ISs were present in these genomes. All three genomes harboured diverse protein secretion systems, virulence determinants related to immune evasion, adherence, biofilm formation and iron acquisition systems. AbaAS-5 exclusively harboured serine protease pkf, and CpaA substrate of type-II secretion system but lacked the acinetobactin-iron acquisition system. Our work delivers a holistic genome characterization of A. baumannii, coupled with a trailblazing attempt to study A. nosocomialis from India. The presence of ARGs and potential virulence factors interspersed with MGE is a cause for concern, depicting the dynamic adaptability mediated by genetic recombination.

Acinetobacter nosocomialis utilizes a unique type VI secretion system to promote its survival in niches with prey bacteria

Pathogenic bacteria of the Acinetobacter genus pose a severe threat to human health worldwide due to their strong adaptability, tolerance, and antibiotic resistance. Most isolates of these bacteria harbor a type VI secretion system (T6SS) that allows them to outcompete co-residing microorganisms, but whether this system is involved in acquiring nutrients from preys remains less studied. In this study, we found that Ab25, a clinical isolate of Acinetobacter nosocomialis, utilizes a T6SS to kill taxonomically diverse microorganisms, including bacteria and fungi. The T6SS of Ab25 is constitutively expressed, and among the three predicted effectors, T6e1, a member of the RHS effector family, contributes the most for its antimicrobial activity. T6e1 undergoes self-cleavage, and a short carboxyl fragment with nuclease activity is sufficient to kill target cells via T6SS injection. Interestingly, strain Ab25 encodes an orphan VgrG protein, which when overexpressed blocks the firing of its T6SS. In niches such as dry plastic surfaces, the T6SS promotes prey microorganism-dependent survival of Ab25. These results reveal that A. nosocomialis employs T6SSs that are highly diverse in their regulation and effector composition to gain a competitive advantage in environments with scarce nutrient supply and competing microbes.IMPORTANCEThe type VI secretion system (T6SS) plays an important role in bacterial adaptation to environmental challenges. Members of the Acinetobacter genus, particularly A. baumannii and A. nosocomialis, are notorious for their multidrug resistance and their ability to survive in harsh environments. In contrast to A. baumannii, whose T6SS has been well-studied, few research works have focused on A. nosocomialis. In this study, we found that an A. nosocomialis strain utilizes a contitutively active T6SS to kill diverse microorganisms, including bacteria and fungi. Although T6SS structural proteins of A. nosocomialis are similar to those of A. baumannii, the effector repertoire differs greatly. Interestingly, the T6SS of the A. nosocomialis strain codes for an ophan VgrG protein, which blocks the firing of the system when overexpressed, suggesting the existence of a new regulatory mechanism for the T6SS. Importantly, although the T6SS does not provide an advantage when the bacterium is grown in nutrient-rich medium, it allows A. nosocomialis to survive better in dry surfaces that contain co-existing bacteria. Our results suggest that killing of co-residing microorganisms may increase the effectiveness of strategies designed to reduce the fitness of Acinetobacter bacteria by targeting their T6SS.

Limited impact of bacterial virulence on early mortality risk factors in Acinetobacter baumannii bacteremia observed in a Galleria mellonella model

Acinetobacter baumannii (AB) has emerged as a major pathogen in vulnerable and severely ill patients. It remains unclear whether early mortality (EM) due to AB bacteremia is because of worse clinical characteristics of the infected patients or the virulence of the pathogen. In this study, we aimed to investigate the effect of AB virulence on EM due to bacteremia. This retrospective study included 138 patients with AB bacteremia (age: ≥ 18 years) who were admitted to a tertiary care teaching hospital in South Korea between 2015 and 2019. EM was defined as death occurring within 7 days of bacteremia onset. The AB clinical isolates obtained from the patients' blood cultures were injected into 15 Galleria mellonella larvae each, which were incubated for 5 days. Clinical isolates were classified into high- and low-virulence groups based on the number of dead larvae. Patients' clinical data were combined and subjected to multivariate Cox regression analyses to identify the risk factors for EM. In total, 48/138 (34.8%) patients died within 7 days of bacteremia onset. The Pitt bacteremia score was the only risk factor associated with EM. In conclusion, AB virulence had no independent effect on EM in patients with AB bacteremia.

Evaluating anti-GPL-core IgA as a diagnostic tool for non-tuberculous mycobacterial infections in Thai patients with high antibody background

Diagnosis of non-tuberculous mycobacterial (NTM) infection is difficult due to low sensitivity and time-consuming laboratory tests. Current serological assays fail in tropical countries due to high antibody background. This study aimed to investigate an appropriate method for detecting anti-glycopeptidolipid (GPL)-core antibodies to diagnose NTM infection in Thailand. Heparinized plasma samples were collected from 20 patients with NTM-pulmonary disease (NTM-PD) and 22 patients with disseminated NTM (dNTM) for antibody detection by ELISA. The results were compared with those from patients with tuberculosis, other bacterial pulmonary infections and healthy controls. Among the different antibody isotypes, anti-GPL-core IgA exhibited the highest suitability. Therefore, anti-GPL-core IgA and its subclass IgA2 were further investigated. A significant increase in antibody levels was observed during the active infection stage, whereas NTM-PD with culture conversion at the 6-month follow-up showed reduced IgA levels. The diagnostic cut-off for IgA and IgA2 was newly defined as 1.4 and 1.0 U/ml, respectively. Using our IgA cut-off, the sensitivity and specificity for diagnosing NTM-PD were 77.3% and 81.4%, respectively. The new IgA cut-off demonstrated significantly improved specificity compared to the manufacturer's cut-off. Thus, serological detection of anti-GPL-core IgA, with a cut-off of 1.4 U/ml, can be a valuable tool for supporting NTM diagnosis in Thailand.

High rates of extensively drug-resistant Acinetobacter baumannii in a Peruvian hospital 2013–2019

Multidrug-resistant (MDR) Acinetobacter baumannii has become a major concern of hospital care. The objective of the study was to evaluate the evolution of antimicrobial resistance of A. baumannii in a Peruvian hospital from 2013 to 2019. A total of 993 A. baumannii clinical isolates were recovered. Antimicrobial resistance levels were extremely high, except for colistin. Among the remaining antibacterial agents, ampicillin plus sulbactam (AMS) was the most active (71.4% of resistance), with resistance levels to the remaining agents ranging from 75.9% to amikacin to 99.2% to ertapenem. The presence of significant differences was observed in extensively drug-resistant (XDR) A. baumannii according to samples origin. No association was observed between MDR or XDR isolates and seasonality. An impressive rate of XDR A. baumannii isolates was found, including a growing number of only-colistin-susceptible isolates highlighting the urgent need for new therapeutic alternatives.