Multidrug-Resistant Acinetobacter: Detection of ESBL, MBL, bla NDM-1 Genotype, and Biofilm Formation at a Tertiary Care Hospital in Eastern Nepal

Characterization and Biofilm Inhibition of Multidrug-Resistant Acinetobacter baumannii Isolates

Multidrug-resistant (MDR) Acinetobacter baumannii poses a significant therapeutic challenge due to its resistance to multiple antibiotics and its ability to form biofilm. This study aimed to characterize MDR A. baumannii isolates for their biofilm-forming capabilities and the presence of common biofilm-related genes at a tertiary care university hospital in Nepal. In addition, it assessed the efficacy of various compounds, particularly essential oils, in inhibiting biofilm formation. Identification and antibiotic sensitivity testing of A. baumannii isolates from clinical specimens were conducted according to the guidelines of the American Society for Microbiology. Isolates were screened for motility profiles, biofilm production in a microtiter plate assay, and the presence of biofilm-related gene(s) by conventional polymerase chain reaction. The ability of cinnamaldehyde, ethylenediaminetetraacetic acid (EDTA), Tween 80, amino acids (glycine and glutamic acid), and natural plant extracts to inhibit biofilm formation was also tested using the microtiter plate system. Out of the total 200 A. baumannii isolates, 195 were MDR, with 192 able to produce biofilms. Among them, 83.1% were strong biofilm producers. In this study, 42.0% and 66.2% of the isolates exhibited twitching motility and surface-associated motility, respectively. Thirty MDR A. baumannii isolates from medical devices contained biofilm-related genes csuE, ompA, bap, and bla PER-1, in 90.0%, 53.3%, 46.6%, and 26.6% of strains, respectively. Cinnamaldehyde (0.875 mg/mL) was the most effective compound, inhibiting biofilm formation by 77.3%, followed by ethanolic extract of onion (77.2%), 0.5% Tween 80 (76.8%), and essential oil of ginger (70.8%). The majority of A. baumannii clinical isolates were strong biofilm producers and often possessed the biofilm-related genes csuE and ompA. Essential oils at 200 mg/L, along with Tween 80, were the most effective (≥ 67%) at inhibiting the formation of biofilms. These findings help to understand biofilm production and provide valuable insights into MDR A. baumannii isolates in this clinical setting.

Carbapenem Resistance in Acinetobacter calcoaceticus-baumannii Complex Isolates From Kathmandu Model Hospital, Nepal, Is Attributed to the Presence of bla OXA-23-like and bla NDM-1 Genes

The Acinetobacter calcoaceticus-baumannii (ACB) complex, also known as ACB complex, consists of four bacterial species that can cause opportunistic infections in humans, especially in hospital settings. Conventional therapies for susceptible strains of the ACB complex include broad-spectrum cephalosporins, β-lactam/β-lactamase inhibitors, and carbapenems. Unfortunately, the effectiveness of these antibiotics has declined due to increasing rates of resistance. The predominant resistance mechanisms identified in the ACB complex involve carbapenem-resistant (CR) oxacillinases and metallo-β-lactamases (MBLs). This research, conducted at Kathmandu Model Hospital in Nepal, sought to identify genes associated with CR, specifically blaNDM-1, blaOXA-23-like, and blaOXA-24-like genes in carbapenem-resistant Acinetobacter calcoaceticus-baumannii (CR-ACB) complex. Additionally, the study is aimed at identifying the ACB complex through the sequencing of the 16s rRNA gene. Among the 992 samples collected from hospitalized patients, 43 (approximately 4.334%) tested positive for the ACB complex. These positive samples were mainly obtained from different hospital units, including intensive care units (ICUs); cabins; and neonatal, general, and maternity wards. The prevalence of infection was higher among males (58.14%) than females (41.86%), with the 40-50 age group showing the highest infection rate. In susceptibility testing, colistin and polymyxin B exhibited a susceptibility rate of 100%, whereas all samples showed resistance to third-generation cephalosporins. After polymyxins, gentamicin (30.23%) and amikacin (34.88%) demonstrated the highest susceptibility. A substantial majority (81.45%) of ACB complex isolates displayed resistance to carbapenems, with respiratory and pus specimens being the primary sources. Polymerase chain reaction (PCR) revealed that the primary CR gene within the ACB complex at this hospital was bla OXA-23-like, followed by bla NDM-1. To ensure the accuracy of the phenotypic assessment, 12 samples were chosen for 16s rRNA sequencing using Illumina MiSeq™ to confirm that they are Acinetobacter species. QIIME 2.0 analysis confirmed all 12 isolates to be Acinetobacter species. In the hospital setting, a substantial portion of the ACB complex carries CR genes, rendering carbapenem ineffective for treatment.

The Molecular Characterization of blaNDM-1-Positive Acinetobacter baumannii Isolated in Central Greece

The objective of the present study is to report the detection and the molecular characterization of nine blaNDM-1-positive Acinetobacter baumannii isolates, which were isolated from patients in a tertiary care hospital in Central Greece from December 2022 to August 2023. The isolates were characterized by whole genome sequencing to obtain Pasteur multilocus sequencing typing (MLST) and to identify the blaNDM-1-environment, resistome, and virulence genes content. In silico MLST analysis showed that the isolates belonged to four different clones (STs 160, 2, 85, and 2493). All strains, apart from the blaNDM-1-gene, possessed at least eight different genes, encoding resistance to various antimicrobial agents. Whole genome sequencing revealed two different structures of the blaNDM-1 environment. The first, detected in ST160 strain, was identical with the Tn125, whereas the second, found in STs 2, 85, and 2493 was associated with Tn7382. To our knowledge, after a sole strain reported in 2016 and imported by a patient hospitalized in a Libyan hospital, this is the first report of the emergence of polyclonal blaNDM-1-positive Acinetobacter baumannii in Greece. Our findings re-emphasize the need to apply diligent surveillance protocols in order to limit the horizontal transfer of the blaNDM-1 gene to other A. baumannii clones or to other recipient strains.