Identification of antigens from nosocomial Acinetobacter baumannii clinical isolates in sera from ICU staff and infected patients using the antigenome technique

Production and characterization of novel monoclonal antibodies against outer membrane protein A (OmpA) of Acinetobacter baumannii

BACKGROUND

Infection caused by Acinetobacter baumannii has emerged as a significant clinical problem with unacceptably high mortality rate due to the increase in antibiotic-resistant strains. Producing novel monoclonal antibody (MAb) against outer membrane protein A (OmpA) could be considered as a potential tool to improve treatment of A. baumannii infections.

OBJECTIVES

In this study, we aimed to produce murine MAbs against OmpA peptide of A. baumannii.

MATERIALS AND METHODS

BALB/c mice were immunized with 18-mer amino acid peptide as a part of the OmpA protein. Four antibody-secreting hybridomas were obtained using hybridoma technology and then characterized according to isotypes, affinity constant, reactivity in ELISA, flow cytometry, indirect immunofluorescence (IFA) and opsonophagocytic killing assays.

RESULTS

All four produced MAbs (1A1-D10, 1G1-E7, 2C11-F10, and 4H2-H9) had IgG1 isotype with Kappa light chain. One of these MAbs, 1G1-E7 was purified and selected for further characterizations. 1G1-E7 showed a high reactivity with both immunogenic peptide and A. baumannii in ELISA. Our results indicated that 1G1-E7 MAb reacted with 95.3% of A. baumannii in flow cytometry as well as IFA. Moreover, the affinity of the 1G1-E7 MAb was measured 1.37 × 10⁸ M^-1. The 1G1-E7 significantly improved opsonophagocytic killing of a clinical isolate of A. baumannii.

CONCLUSION

Our findings showed that the OmpA can be identified by produced MAbs. The efficacy of novel anti-OmpA antibodies in A. baumannii targeting needs to be further investigated in challenging models, and then could be subjected for genetic engineering to produce therapeutic antibody against A. baumannii.

Virulence Potential and Treatment Options of Multidrug-Resistant (MDR) Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen which is undoubtedly known for a high rate of morbidity and mortality in hospital-acquired infections. A. baumannii causes life-threatening infections, including; ventilator-associated pneumonia (VAP), meningitis, bacteremia, and wound and urinary tract infections (UTI). In 2017, the World Health Organization listed A. baumannii as a priority-1 pathogen. The prevalence of A. baumannii infections and outbreaks emphasizes the direct need for the use of effective therapeutic agents for treating such infections. Available antimicrobials, such as; carbapenems, tigecycline, and colistins have insufficient effectiveness due to the appearance of multidrug-resistant strains, accentuating the need for alternative and novel therapeutic remedies. To understand and overcome this menace, the knowledge of recent discoveries on the virulence factors of A. baumannii is needed. Herein, we summarized the role of various virulence factors, including; outer membrane proteins, efflux pumps, biofilm, penicillin-binding proteins, and siderophores/iron acquisition systems. We reviewed the recent scientific literature on different A. baumannii virulence factors and the effective antimicrobial agents for the treatment and management of bacterial infections.

Advanced strategies for development of vaccines against human bacterial pathogens

Infectious diseases are one of the main grounds of death and disabilities in human beings globally. Lack of effective treatment and immunization for many deadly infectious diseases and emerging drug resistance in pathogens underlines the need to either develop new vaccines or sufficiently improve the effectiveness of currently available drugs and vaccines. In this review, we discuss the application of advanced tools like bioinformatics, genomics, proteomics and associated techniques for a rational vaccine design.

Where are we and how far is there to go in the development of an Acinetobacter vaccine?

INTRODUCTION

Healthcare-associated infections caused by multidrug-resistant Acinetobacter baumannii are becoming alarming worldwide. However, the pipeline of new antibiotics is very limited. Vaccination is one of the most cost effective and promising strategies to prevent infections and can play an important role in combat multidrug resistance A. baumannii and prevent the development of new drug resistance.

AREA COVERED

This review gives an overview of the research and development of A. baumannii vaccines during the past five years (2015-2020), discusses the key progresses and current challenges of the field, and speculates on the future of A. baumannii vaccine development.

EXPERT OPINION

Moderate progresses have been made in the research and development of A. baumannii vaccine in the last five years, in particular in the areas of identification of new protein targets, development of multicomponent vaccines, and use of vaccines and antibodies as adjuncts for antibiotics therapies. However, substantial scientific and logistic challenges, such as selection of lead vaccine candidates and formulation, vaccine clinical trials and targeted population, and financial incentives, remain. Thus, innovative strategies will be needed before an A. baumannii vaccine candidate can be brought into late stage of preclinical development in next five years.

Microevolution in the major outer membrane protein OmpA of Acinetobacter baumannii

Acinetobacter baumannii is nowadays a relevant nosocomial pathogen characterized by multidrug resistance (MDR) and concomitant difficulties to treat infections. OmpA is the most abundant A. baumannii outer membrane (OM) protein, and is involved in virulence, host-cell recognition, biofilm formation, regulation of OM stability, permeability and antibiotic resistance. OmpA members are two-domain proteins with an N-terminal eight-stranded β-barrel domain with four external loops (ELs) interacting with the environment, and a C-terminal periplasmic domain binding non-covalently to the peptidoglycan. Here, we combined data from genome sequencing, phylogenetic and multilocus sequence analyses from 975 strains/isolates of the Acinetobacter calcoaceticus/Acinetobacter baumannii complex (ACB), 946 from A. baumannii, to explore ompA microevolutionary divergence. Five major ompA variant groups were identified (V1 to V5) in A. baumannii, encompassing 52 different alleles coding for 23 different proteins. Polymorphisms were concentrated in five regions corresponding to the four ELs and the C-terminal end, and provided evidence for intra-genic recombination. ompA variants were not randomly distributed across the A. baumannii phylogeny, with the most frequent V1(lct)a1 allele found in most clonal complex 2 (CC2) strains and the second most frequent V2(lct)a1 allele in the majority of CC1 strains. Evidence was found for assortative exchanges of ompA alleles not only between separate A. baumannii lineages, but also different ACB species. The overall results have implications for A. baumannii evolution, epidemiology, virulence and vaccine design.

Decreased carO gene expression and OXA-type carbapenemases among extensively drug-resistant Acinetobacter baumannii strains isolated from burn patients in Tehran, Iran

A major challenge in the treatment of infections has been the rise of extensively drug resistance (XDR) and multidrug resistance (MDR) in Acinetobacter baumannii. The goals of this study were to determine the pattern of antimicrobial susceptibility, blaOXA and carO genes among burn-isolated A. baumannii strains. In this study, 100 A. baumannii strains were isolated from burn patients and their susceptibilities to different antibiotics were determined using disc diffusion testing and broth microdilution. Presence of carO gene and OXA-type carbapenemase genes was tested by PCR and sequencing. SDS-PAGE was done to survey CarO porin and the expression level of carO gene was evaluated by Real-Time PCR. A high rate of resistance to meropenem (98%), imipenem (98%) and doripenem (98%) was detected. All tested A. baumannii strains were susceptible to colistin. The results indicated that 84.9% were XDR and 97.9% of strains were MDR. In addition, all strains bore blaOXA-51 like and blaOXA-23 like and carO genes. Nonetheless, blaOXA-58 like and blaOXA-24 like genes were harbored by 0 percent and 76 percent of strains, respectively. The relative expression levels of the carO gene ranged from 0.06 to 35.01 fold lower than that of carbapenem-susceptible A. baumannii ATCC19606 and SDS - PAGE analysis of the outer membrane protein showed that all 100 isolates produced CarO. The results of current study revealed prevalence of blaOXA genes and changes in carO gene expression in carbapenem resistant A.baumannii.