Prevalence, genetic diversity, antibiotic resistance and biofilm formation of Acinetobacter baumannii isolated from urban environments

Molecular identification, antibiotic susceptibility, and biofilm formation of airborne bacteria

Pathogenic bacterial communities present in urban green spaces significantly affect human health, particularly for immunocompromised populations. The diverse range of pathogenic bacteria found in these areas poses substantial management challenges because of their high prevalence of antibiotic resistance, which can be life-threatening, particularly for immunocompromised individuals, including older adults and children. This study identified airborne bacterial species from 14 natural parks in the Hail region of the Kingdom of Saudi Arabia. Bacterial colonies isolated on blood agar plates were purified and characterised based on their morphological traits and their ability to secrete various virulence factors. A total of 28 distinct airborne bacterial species were isolated and purified. Antibiotic susceptibility tests revealed high resistance to fosfomycin (41.17%), ampicillin (17.64%), tetracycline (17.64%), and gentamicin (11.76%). Biofilm formation was evaluated qualitatively by slime production and quantitatively by crystal violet technique. The results revealed that 41.17% of the tested strains were non biofilm producers on polystyrene surfaces, 17.64% were weak biofilm formers, and 23.52% exhibited moderate biofilm formation. Notably, six strains exhibited strong biofilm-forming capabilities. Additionally, two bacteria from the Arthrobacter genus (A. crystallopoietes and A. saudimassiliensis) were identified. These findings provide valuable insights into the microbial composition of natural parks in the Hail region and highlight effective management strategies to mitigate health risks.

Predominance of extensively-drug resistant Acinetobacter baumannii carrying bla OXA-23 in Jordanian patients admitted to the intensive care units

BACKGROUND AND AIM

The global emergence of Acinetobacter baumannii is of great concern, especially inside intensive care units (ICUs). This study investigated the prevalence, antibiotic resistance, biofilm formation and genetic relatedness of A. baumannii recovered from ICU patients in three major hospitals in Jordan.

METHODS

The A. baumannii isolates included in this study were identified by the detection of the blaOXA-51 gene, and a multiplex PCR assay. Antibiotic susceptibility testing was performed using the disk diffusion and broth microdilution methods, and the ability of the isolates to form biofilms was tested using the 96-well plate assay. All isolates were tested for the presence of carbapenemases-encoding genes by PCR. Clonal relatedness was assessed by Rep-PCR and dendrogram analysis.

RESULTS

Overall, 148 A. baumannii isolates were identified, with 96.7% of the isolates recognized as carbapenem resistant A. baumannii. Based on their resistance patterns, 90% of the isolates were extensively resistant (XDR). The highest prevalence of carbapenemases-encoding genes was for blaOXA-23-like (96.7%), followed by blaADC (93.9.2%), blaVIM (56.8%) and blaNDM-1 (7.4%). Almost 80% of the isolates were able to form biofilms, with 63.2% classified as strong biofilm former. Rep-PCR and clustering analysis revealed 26 different clusters and the circulation of hospital-specific clones.

CONCLUSIONS

Our study revealed an alarming high prevalence of XDR, blaOXA-23-carrying and strong biofilm-producing A. baumannii among ICU patients. These findings call for continuous epidemiological surveillance and implementation of prevention strategies to reduce infections and dissemination of such a problematic pathogen inside the ICUs.

Antimicrobial Peptide Assembly on Zwitterionic Polymer Films to Slow Down Biofilm Formation

Formation of biofilms on equipment used in various fields, such as medicine, domestic sanitation, and marine transportation, can cause serious problems. The use of antibiofouling and bactericidal modifications is a promising strategy for inhibiting bacterial adhesion and biofilm formation. To further enhance the antibiofilm properties of a surface, various combinations of bactericidal modifications alongside antibiofouling modifications have been developed. Optimization of the arrangements of antimicrobial peptides on the antibiofouling surface would allow us to design longer-life antibiofilm surface modifications. In this study, a postmodification was conducted with different design using the antimicrobial peptide KR12 on an antibiofouling copolymer film consisting of 2-methacryloyloxyethyl phosphorylcholine, 3-methacryloxypropyl trimethoxysilane, and 3-(methacryloyloxy) propyl-tris(trimethylsilyloxy) silane. The distance of KR12 from the film was adjusted by combining different lengths of poly(ethylene glycol) (PEG) spacers (molecular weights are 2000 and 5000). The density of KR12 was ranged from 0.06 to 0.22 nm-2. When these modified surfaces were exposed to a nutrient-rich TSB suspension, the bacterial area formed by E. coli covered 5-127% of the original copolymer film. We found that a significant distance between the bactericidal and antibiofouling modifications, along with a higher density of bactericidal modifications, slows down the biofilm formation.

Acinetobacter baumannii, a Multidrug-Resistant Opportunistic Pathogen in New Habitats: A Systematic Review

In recent years, humanity has begun to face a growing challenge posed by a rise in the prevalence of antibiotic-resistant bacteria. This has resulted in an alarming surge in fatalities and the emergence of increasingly hard-to-manage diseases. Acinetobacter baumannii can be seen as one of these resilient pathogens due to its increasing prevalence in hospitals, its resistance to treatment, and its association with elevated mortality rates. Despite its clinical significance, the scientific understanding of this pathogen in non-hospital settings remains limited. Knowledge of its virulence factors is also lacking. Therefore, in this review, we seek to shed light on the latest research regarding the ecological niches, microbiological traits, and antibiotic resistance profiles of Acinetobacter baumannii. Recent studies have revealed the presence of this bacterium in a growing range of environmental niches, including rivers, treatment plants, and soils. It has also been discovered in diverse food sources such as meat and vegetables, as well as in farm animals and household pets such as dogs and cats. This broader presence of Acinetobacter baumannii, i.e., outside of hospital environments, indicates a significant risk of environmental contamination. As a result, greater levels of awareness and new preventive measures should be promoted to address this potential threat to public health.

Characteristics of a Carbapenem-Resistant Acinetobacter baumannii Strain Causing Community-Acquired Pneumonia in a Young Healthy Women

Background

Multidrug-resistant Acinetobacter baumannii rarely causes community-acquired pneumonia. Here, we report the clinical and genomic characteristics of a multidrug-resistant A. baumannii strain responsible for community-acquired pneumonia in a 31-year-old healthy young women.

Methods

A. baumannii strain W2LL was recovered from the alveolar lavage fluid sample of a hospitalized patient with pulmonary infection. Growth rate studies were conducted under various conditions, and virulence assessments were performed using Galleria Mellonella larvae. Whole Genome Sequencing (WGS) was carried out using Oxford Nanopore MinIon and Illumina HiSeq. In silico multilocus sequence typing (MLST), plasmid replicons, antimicrobial resistance genes, and virulence genes were determined using the BacWGSTdb webserver. Phylogenetic analysis between strain W2LL and other closely related A. baumannii genomes retrieved from NCBI database was performed.

Results

WGS identified strain W2LL as a rare sporadic lineage sequence type (ST) 1431. In addition to the detection of the β-lactamase gene (blaOXA-98) on the chromosome, blaOXA-58 was found on a 92,034 bp plasmid. Antimicrobial susceptibility testing revealed this strain was resistant to cephalosporins and carbapenems, with initial treatment using cefoxitin proving ineffective. Subsequent treatment with piperacillin-sulbactam combined with levofloxacin led to gradual improvement. Compared to A. baumannii ATCC 17978, W2LL exhibited similar growth rates at 37°C and 42°C, as well as in the presence of zinc. However, strain W2LL exhibited higher virulence phenotype compared to ATCC 17978 in G. mellonella model. The closest relative of A. baumannii W2LL was CAM180_1, another isolate recovered from Cambodia, which differed by 191 SNPs.

Conclusion

W2LL is a rare ST1431 carbapenem-resistant A. baumannii strain recovered from a patient with no prior hospitalization or typical risk factors. This underscores the growing menace posed by carbapenem-resistant A. baumannii, no longer limited to hospitalized patients, potentially impacting the broader, younger population.

Extensive Drug Resistance of Strong Biofilm-Producing Acinetobacter baumannii Strains Isolated from Infections and Colonization Hospitalized Patients in Southern Poland

Acinetobacter baumannii (AB) is a bacterium that causes infections, particularly in immunocompromised patients. Treatment is challenging due to biofilm formation by AB strains, which hinders antibiotic effectiveness and promotes drug resistance. The aim of our study was to analyze the biofilm-producing capacity of AB isolates from various forms of infections in relation to biofilm-related genes and their drug resistance. We tested one hundred isolates for biofilm formation using the crystal violet microplate method. Drug resistance analyses were performed based on EUCAST and CLSI guidelines, and biofilm genes were detected using PCR. All tested strains were found to form biofilms, with 50% being ICU strains and 72% classified as strong biofilm producers. Among these, 87% were extensively drug-resistant (XDR) and 2% were extra-extensively drug-resistant (E-XDR). The most common gene set was bap, bfmS, csuE, and ompA, found in 57% of all isolates. Our research shows that, regardless of the form of infection, biofilm-forming strains can be expected among AB isolates. The emergence of E-XDR and XDR strains among non-ICU infections highlights the necessity for the rational use of antibiotics to stop or limit the further acquisition of drug resistance by A. baumannii.

Prevalence and Characterization of Beta-Lactam and Carbapenem-Resistant Bacteria Isolated from Organic Fresh Produce Retailed in Eastern Spain

Fresh fruits and vegetables are potential reservoirs for antimicrobial resistance determinants, but few studies have focused specifically on organic vegetables. The present study aimed to determine the presence of third-generation cephalosporin (3GC)- and carbapenem-resistant Gram-negative bacteria on fresh organic vegetables produced in the city of Valencia (Spain). Main expanded spectrum beta-lactamase (ESBL)- and carbapenemase-encoding genes were also detected in the isolates. One hundred and fifteen samples were analyzed using selective media supplemented with cefotaxime and meropenem. Resistance assays for twelve relevant antibiotics in medical use were performed using a disc diffusion test. A total of 161 isolates were tested. Overall, 33.5% presented multidrug resistance and 16.8% were resistant to all β-lactam antibiotics tested. Imipenem resistance was observed in 18% of isolates, and low resistance levels were found to ceftazidime and meropenem. Opportunistic pathogens such as Acinetobacter baumannii, Enterobacter spp., Raoultella sp., and Stenotrophomonas maltophilia were detected, all presenting high rates of resistance. PCR assays revealed blaVIM to be the most frequently isolated ESBL-encoding gene, followed by blaTEM and blaOXA-48. These results confirm the potential of fresh vegetables to act as reservoirs for 3GC- and carbapenem-producing ARB. Further studies must be carried out to determine the impact of raw organic food on the spread of AMRs into the community.

Extensively drug-resistant Acinetobacter baumannii: role of conjugative plasmids in transferring resistance

Acinetobacter baumannii is one of the most successful pathogens that can cause difficult-to-treat nosocomial infections. Outbreaks and infections caused by multi-drug resistant A. baumannii are prevalent worldwide, with only a few antibiotics are currently available for treatments. Plasmids represent an ideal vehicle for acquiring and transferring resistance genes in A. baumannii. Five extensively drug-resistant A. baumannii clinical isolates from three major Jordanian hospitals were fully sequenced. Whole-Genome Sequences (WGS) were used to study the antimicrobial resistance and virulence genes, sequence types, and phylogenetic relationship of the isolates. Plasmids were characterized In-silico, followed by conjugation, and plasmid curing experiments. Eight plasmids were recovered; resistance plasmids carrying either aminoglycosides or sulfonamide genes were detected. Chromosomal resistance genes included bla_OXA-66, bla_OXA-91, and bla_OXA-23, and the detected virulence factors were involved in biofilm formation, adhesion, and many other mechanisms. Conjugation and plasmid curing experiments resulted in the transfer or loss of several resistance phenotypes. Plasmid profiling along with phylogenetic analyses revealed high similarities between two A. baumannii isolates recovered from two different intensive care units (ICU). The high similarities between the isolates of the study, especially the two ICU isolates, suggest that there is a common A. baumannii strain prevailing in different ICU wards in Jordanian hospitals. Three resistance genes were plasmid-borne, and the transfer of the resistance phenotype emphasizes the role and importance of conjugative plasmids in spreading resistance among A. baumannii clinical strains.

Epidemiology and Multidrug Resistance of Pseudomonas aeruginosa and Acinetobacter baumanni Isolated from Clinical Samples in Ethiopia

Background

A. baumannii and P. aeruginosa are important nosocomial pathogens in health-care settings. Both are intrinsically resistant to many drugs and are able to become resistant to the virtually most antimicrobial agents. An increasing prevalence of infections caused by multidrug-resistant isolates has been reported in many countries.

Methods

An institutional-based cross-sectional five-year retrospective study was conducted to assess the antimicrobial resistance trend of P. aeruginosa and A. baumani. 893 A. baumani and 729 P. aeruginosa isolates were included in the study. Conventional method was used for identification and antimicrobial susceptibility was determined by Kirby-Bauer disc-diffusion method. The isolates were from suspected bloodstream infections, wound infections, urinary tract, or surgical site nosocomial infections. Socio-demographic and other variables of interest were collected using a structured check list from a patient record data. Data were analyzed using SPSS version 26 software. P value <0.05 was considered statistically significant.

Results

A total of 1622 A. baumanii and P. aeruginosa were isolated from various clinical specimens recorded from the year 2017-2021. Out of which A. baumanni was 893 (60.6%) and P. aeruginosa was 729 (39.4%). Blood was the major source of the isolates (18.3%), followed by urine (16%), and tracheal aspirate (10.6%). Antimicrobial resistance among A. baumanni over the five years were; ampicillin (86% to 92%), ceftriaxone (66.7% to 82.2%), and ciprofloxacin (58.5% to 66.7%). In P. aeruginosa a significant increase in resistance was seen from 2017 to 2021 to Amoxicillin-clavulanate (74.1% to 84.2%), chloramphenicol (62% to 81.9%), and gentamicin (40% to 44.8%).

Conclusion

A five-year antimicrobial resistance trend analysis of A. baumanni and P. aeruginosa showed increasing multi drug resistance and resistance to highly potent antimicrobial agents in Ethiopia. It should be addressed with infection control measures, surveillance, and alternative new therapeutic strategies to circumvent the spread of multi-drug resistance.

Effects of Sub-Minimum Inhibitory Concentrations of Imipenem and Colistin on Expression of Biofilm-Specific Antibiotic Resistance and Virulence Genes in Acinetobacter baumannii Sequence Type 1894

Antibiotics at suboptimal doses promote biofilm formation and the development of antibiotic resistance. The underlying molecular mechanisms, however, were not investigated. Here, we report the effects of sub-minimum inhibitory concentrations (sub-MICs) of imipenem and colistin on genes associated with biofilm formation and biofilm-specific antibiotic resistance in a multidrug-tolerant clinical strain of Acinetobacter baumannii Sequence Type (ST) 1894. Comparative transcriptome analysis was performed in untreated biofilm and biofilm treated with sub-MIC doses of imipenem and colistin. RNA sequencing data showed that 78 and 285 genes were differentially expressed in imipenem and colistin-treated biofilm cells, respectively. Among the differentially expressed genes (DEGs), 48 and 197 genes were upregulated exclusively in imipenem and colistin-treated biofilm cells, respectively. The upregulated genes included those encoding matrix synthesis (pgaB), multidrug efflux pump (novel00738), fimbrial proteins, and homoserine lactone synthase (AbaI). Upregulation of biofilm-associated genes might enhance biofilm formation when treated with sub-MICs of antibiotics. The downregulated genes include those encoding DNA gyrase (novel00171), 30S ribosomal protein S20 (novel00584), and ribosome releasing factor (RRF) were downregulated when the biofilm cells were treated with imipenem and colistin. Downregulation of these genes affects protein synthesis, which in turn slows down cell metabolism and makes biofilm cells more tolerant to antibiotics. In this investigation, we also found that 5 of 138 small RNAs (sRNAs) were differentially expressed in biofilm regardless of antibiotic treatment or not. Of these, sRNA00203 showed the highest expression levels in biofilm. sRNAs regulate gene expression and are associated with biofilm formation, which may in turn affect the expression of biofilm-specific antibiotic resistance. In summary, when biofilm cells were exposed to sub-MIC doses of colistin and imipenem, coordinated gene responses result in increased biofilm production, multidrug efflux pump expression, and the slowdown of metabolism, which leads to drug tolerance in biofilm. Targeting antibiotic-induced or repressed biofilm-specific genes represents a new strategy for the development of innovative and effective treatments for biofilm-associated infections caused by A. baumannii.