Two Acinetobacter baumannii Isolates Obtained From a Fatal Necrotizing Fasciitis Infection Display Distinct Genomic and Phenotypic Characteristics in Comparison to Type Strains

Risk factors and genetic characteristics of the carriage of hypervirulent and carbapenem-resistant Acinetobacter baumannii among pregnant women

Background

Carbapenem-resistant Acinetobacter baumannii (CRAB) and its emerging evolutionary branch toward hypervirulence have been neglected in pregnancy.

Methods

From September 2020 to August 2021, an active surveillance culture program encompassed 138 randomly selected pregnant women, with five subjected to sample collection at two different time points. The clinical characterization was explored through statistical analysis. Whole-genome sequencing, a Galleria mellonella infection model, and a global database were used to investigate the genetic characterization, pathogenicity, evolutionary history, and phylogenetic relationships of the isolates.

Results

Of the 41 CRAB isolates obtained, they were divided into four ClustersRS and an orphan pattern. ClusterRS 1 (n = 31), with eight complex types in pregnancy, was also the dominant ClusterRS globally, followed by ClusterRS 13 (n = 5), identified as hypervirulent KL49 CRAB, exhibiting phylogeographical specificity to Guangdong. A maternal carriage CRAB rate of 26.09% (36/138) was revealed, with half of the isolates representing novel complex types, prominently including CT3071, as the first KL7 isolates identified in Shenzhen. Both KL49 and KL7 isolates were most commonly found in the same participant, suggesting potential intraspecific competition as a possible reason for CRAB infection without carriers during pregnancy. The independent risk factors for carriers were revealed for the first time, including advanced maternal age, gestational diabetes mellitus, and Group B Streptococcus infection.

Conclusion

The significant carriage rate and enhanced virulence of CRAB during pregnancy emphasize the imperative for routine surveillance to forestall dissemination within this high-risk group, especially in Guangdong for ClusterRS 13 isolates.

The intracellular life of Acinetobacter baumannii

Acinetobacter baumannii is a Gram-negative opportunistic bacterium responsible for nosocomial and community-acquired infections. This pathogen is globally disseminated and associated with high levels of antibiotic resistance, which makes it an important threat to human health. Recently, new evidence showed that several A. baumannii isolates can survive and proliferate within eukaryotic professional and/or nonprofessional phagocytic cells, with in vivo consequences. This review provides updated information and describes the tools that A. baumannii possesses to adhere, colonize, and replicate in host cells. Additionally, we emphasize the high genetic and phenotypic heterogeneity detected amongst A. baumannii isolates and its impact on the bacterial intracellular features. We also discuss the need for standardized methods to characterize this pathogen robustly and consequently consider some strains as facultative intracellular bacteria.

Natural Antibodies Mediate Protection Against Acinetobacter baumannii Respiratory Infections

BACKGROUND

Acinetobacter baumannii causes a wide range of dangerous infections due to the emergence of pandrug-resistant strains. Therefore, there is a need for alternative therapeutics to treat these infections, including those targeting the host immune responses. However, immune responses, especially the humoral response against this pathogen, are poorly understood.

METHODS

This study investigated the lymphocyte-mediated innate immune resistance to A. baumannii AB5075 pulmonary infection using B- and T-cell-deficient (Rag2-/-) mice, the protective effect of natural antibodies (NAbs), and the expression of complement-mediated responses using a mouse pneumonia model.

RESULTS

Our results showed that intranasally infected Rag2-/- mice are impaired in clearing bacteria from lung, liver, and spleen at 24 hours postinfection compared to wildtype mice. Animal pretreatment with normal mouse serum or purified antibodies from naive mice rescued Rag2-/- mice from infection. Analysis of C3 complement protein binding demonstrated that NAbs increased C3 protein deposition on A. baumannii cells, indicating the activation of the classical complement pathway by NAbs.

CONCLUSIONS

Overall, our study shows that NAbs mediate innate immune resistance against A. baumannii, a finding that may lead to the development of effective therapies against human infections caused by this antibiotic-resistant A. baumannii.

Understanding bacterial biofilms: From definition to treatment strategies

Bacterial biofilms are complex microbial communities encased in extracellular polymeric substances. Their formation is a multi-step process. Biofilms are a significant problem in treating bacterial infections and are one of the main reasons for the persistence of infections. They can exhibit increased resistance to classical antibiotics and cause disease through device-related and non-device (tissue) -associated infections, posing a severe threat to global health issues. Therefore, early detection and search for new and alternative treatments are essential for treating and suppressing biofilm-associated infections. In this paper, we systematically reviewed the formation of bacterial biofilms, associated infections, detection methods, and potential treatment strategies, aiming to provide researchers with the latest progress in the detection and treatment of bacterial biofilms.

Exposure to Nanoplastic Particles Enhances Acinetobacter Survival, Biofilm Formation, and Serum Resistance

The interaction between nanoplastics and bacteria remains still largely unclear. In this study, we determined the effect of nanopolystyrene particle (NP) on a bacterial pathogen of Acinetobacter johnsonii AC15. Scanning electron microscopy (SEM) analysis indicated the aggregation of NPs from 10 μg/L to 100 μg/L on surface of A. johnsonii AC15, suggesting that A. johnsonii AC15 acted as the vector for NPs. Exposure to 100−1000 μg/L NPs increased the growth and colony-forming unit (CFU) of A. johnsonii AC15. In addition, exposure to 100−1000 μg/L NPs enhanced the amount of formed biofilm of A. johnsonii AC15. Alterations in expressions of 3 survival-related (zigA, basD, and zur), 5 biofilm formation-related (ompA, bap, adeG, csuC, and csuD), and 3 serum resistance-related virulence genes (lpxC, lpxL, and pbpG) were observed after exposure to 1000 μg/L NPs. Moreover, both CFU and survival rate of A. johnsonii AC15 in normal human serum (NHS) were significantly increased by 1−1000 μg/L NPs, suggesting the enhancement in serum resistance of Acinetobacter pathogen by NPs. In the NHS, expressions of 3 survival-related (zigA, basD, and zur), 9 biofilm formation-related (ompA, bap, adeF, adeG, csuA/B, csuC, csuD, csuE, and hlyD), and 3 serum resistance-related virulence genes (lpxC, lpxL, and pbpG) were affected by 1000 μg/L NPs. Expressions of 1 survival-related (zigA), 5 biofilm formation-related (bap, adeG, csuC, csuD, and csuE), and 3 serum resistance-related virulence genes (lpxC, lpxL, and pbpG) were also altered by 10 μg/L NPs after the addition of NHS. Therefore, exposure to NPs in the range of μg/L has the potential to enhance bacterial virulence by increasing their growth, biofilm formation, and serum resistance.

Na+ homeostasis in Acinetobacter baumannii is facilitated via the activity of the Mrp antiporter

The human opportunistic pathogen Acinetobacter baumannii is a global threat to healthcare institutions worldwide, since it developed very efficient strategies to evade host defense and to adapt to the different environmental conditions of the host. This worked focused on the importance of Na⁺ homeostasis in A. baumannii with regards to pathobiological aspects. In silico studies revealed a homologue of a multicomponent Na⁺ /H⁺ antiporter system. Inactivation of the Mrp antiporter through deletion of the first gene (mrpA') resulted in a mutant that was sensitive to increasing pH values. Furthermore, the strain was highly sensitive to increasing Na⁺ and Li⁺ concentrations. Increasing Na⁺ sensitivity is thought to be responsible for growth impairment in human fluids. Furthermore, deletion of mrpA' is associated with energetic defects, inhibition of motility and survival under anoxic and dry conditions.