Longitudinal Analysis of the Temporal Evolution of Acinetobacter baumannii Strains in Ohio, USA, by Using Rapid Automated Typing Methods

Genotyping methods are essential to understand the transmission dynamics of Acinetobacter baumannii. We examined the representative genotypes of A. baumannii at different time periods in select locations in Ohio, using two rapid automated typing methods: PCR coupled with electrospray ionization mass spectrometry (PCR/ESI-MS), a form of multi-locus sequence typing (MLST), and repetitive-sequence-based-PCR (rep-PCR). Our analysis included 122 isolates from 4 referral hospital systems, in 2 urban areas of Ohio. These isolates were associated with outbreaks at 3 different time periods (1996, 2000 and 2005–2007). Type assignments of PCR/ESI-MS and rep-PCR were compared to each other and to worldwide (WW) clone types. The discriminatory power of each method was determined using the Simpson's index of diversity (DI). We observed that PCR/ESI-MS sequence type (ST) 14, corresponding to WW clone 3, predominated in 1996, whereas ST 12 and 14 co-existed in the intermediate period (2000) and ST 10 and 12, belonging to WW clone 2, predominated more recently in 2007. The shift from WW clone 3 to WW clone 2 was accompanied by an increase in carbapenem resistance. The DI was approximately 0.74 for PCR/ESI-MS, 0.88 for rep-PCR and 0.90 for the combination of both typing methods. We conclude that combining rapid automated typing methods such as PCR/ESI-MS and rep-PCR serves to optimally characterize the regional molecular epidemiology of A. baumannii. Our data also sheds light on the changing sequence types in an 11 year period in Northeast Ohio

In vitro and in vivo antimicrobial activities of gallium nitrate against multidrug-resistant Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii poses a tremendous challenge to traditional antibiotic therapy. Due to the crucial role of iron in bacterial physiology and pathogenicity, we investigated iron metabolism as a possible target for anti-A. baumannii chemotherapy using gallium as an iron mimetic. Due to chemical similarity, gallium competes with iron for binding to several redox enzymes, thereby interfering with a number of essential biological reactions. We found that Ga(NO(3))(3), the active component of an FDA-approved drug (Ganite), inhibits the growth of a collection of 58 A. baumannii strains in both chemically defined medium and human serum, at concentrations ranging from 2 to 80 μM and from 4 to 64 μM, respectively. Ga(NO(3))(3) delayed the entry of A. baumannii into the exponential phase and drastically reduced bacterial growth rates. Ga(NO(3))(3) activity was strongly dependent on iron availability in the culture medium, though the mechanism of growth inhibition was independent of dysregulation of gene expression controlled by the ferric uptake regulator Fur. Ga(NO(3))(3) also protected Galleria mellonella larvae from lethal A. baumannii infection, with survival rates of ≥75%. At therapeutic concentrations for humans (28 μM plasma levels), Ga(NO(3))(3) inhibited the growth in human serum of 76% of the multidrug-resistant A. baumannii isolates tested by ≥90%, raising expectations on the therapeutic potential of gallium for the treatment of A. baumannii bloodstream infections. Ga(NO(3))(3) also showed strong synergism with colistin, suggesting that a colistin-gallium combination holds promise as a last-resort therapy for infections caused by pan-resistant A. baumannii

In Vitro and In Vivo Antimicrobial Activities of Gallium Nitrate against Multidrug-Resistant Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii poses a tremendous challenge to traditional antibiotic therapy. Due to the crucial role of iron in bacterial physiology and pathogenicity, we investigated iron metabolism as a possible target for anti-A. baumannii chemotherapy using gallium as an iron mimetic. Due to chemical similarity, gallium competes with iron for binding to several redox enzymes, thereby interfering with a number of essential biological reactions. We found that Ga(NO3)(3), the active component of an FDA-approved drug (Ganite), inhibits the growth of a collection of 58 A. baumannii strains in both chemically defined medium and human serum, at concentrations ranging from 2 to 80 mu M and from 4 to 64 mu M, respectively. Ga(NO3)(3) delayed the entry of A. baumannii into the exponential phase and drastically reduced bacterial growth rates. Ga(NO3)(3) activity was strongly dependent on iron availability in the culture medium, though the mechanism of growth inhibition was independent of dysregulation of gene expression controlled by the ferric uptake regulator Fur. Ga(NO3)(3) also protected Galleria mellonella larvae from lethal A. baumannii infection, with survival rates of >= 75%. At therapeutic concentrations for humans (28 mu M plasma levels), Ga(NO3)(3) inhibited the growth in human serum of 76% of the multidrug-resistant A. baumannii isolates tested by >= 90%, raising expectations on the therapeutic potential of gallium for the treatment of A. baumannii bloodstream infections. Ga(NO3)(3) also showed strong synergism with colistin, suggesting that a colistin-gallium combination holds promise as a last-resort therapy for infections caused by pan-resistant A. baumannii

GENOTYPIC AND PHENOTYPIC DIVERSITY IN ACINETOBACTER BAUMANNII ISOLATES FROM DIFFERENT SOURCES

Objectives: Acinetobacter baumannii is an opportunistic pathogen responsible for outbreaks of infection worldwide. Contrary to other species of its genus, it is almost exclusively found in the nosocomial environment, and external reservoirs of infection have not been identified. In addition, although some studies have isolated strains from non-clinical sources, the diversity between A. baumannii from clinical and non-clinical sources is unknown. We compared the genotypic and phenotypic diversity of A. baumannii strains isolated from non-human sources, in order to understand the intra-species diversity and to gain clues on how A. baumannii adapted to become a successful human pathogen. Methods: Sequence group typing of a collection of A. baumannii strains from non-human sources (veterinary, soil, water, food-associated) was performed by PCR amplification and genotypic diversity was determined by RAPD-DAF4 analysis. Strain growth was tested on Acinetobacter isolation agar and in liquid culture media at temperatures from 18-44°C. Resistance to antimicrobial agents and heavy metals was tested by the agar-dilution methods. Biofilm formation on polystyrene plates and resistance to desiccation on nitrocellulose membranes were also determined. Culture supernatants were assayed for iron-chelating, haemolytic, phospholipase C and proteolytic activities. Hydrolysis of polysaccharides was tested on agar plates supplemented with different substrates. Results: A. baumannii isolates were divided into different genotypes, some of which corresponding to the three International clonal lineages. Phenotypic assays demonstrated considerable intra-specific diversity. All strains to grew at temperatures ranging from 18-37°C, and had the ability to form biofilm and to produce a number of exoproducts with enzymatic activity, although to a different extent. Differences were observed between veterinary and environmental strains, with veterinary isolates showing higher antibiotic resistance and exoproduct production. Several environmental isolates were unable to grow on Acinetobacter isolation media. Conclusion: A. baumannii strains isolated from different origins show genotypic and phenotypic diversity, suggesting that different A. baumannii populations might have emerged as a result of adaptation to different habitats. Keywords: adaptation, environment, diversity, exoenzyme, habitat, phenotype Topic: Taxonomy, Population Genetics, Evolution and Comparative Genomic

Promises and failures of gallium as an antibacterial agent

none5nononeMinandri F; Bonchi C; Frangipani E; Imperi F; Visca P.Minandri, F; Bonchi, C; Frangipani, E; Imperi, F; Visca, P

The dual personality of iron chelators: Growth inhibitors or promoters?

[No abstract available

The dual personality of iron chelators: Growth inhibitors or promoters?

[No abstract available

Repurposing of gallium-based drugs for antibacterial therapy

While the occurrence and spread of antibiotic resistance in bacterial pathogens is vanishing current anti-infective therapies, the antibiotic discovery pipeline is drying up. In the last years, the repurposing of existing drugs for new clinical applications has become a major research area in drug discovery, also in the field of anti-infectives. This review discusses the potential of repurposing previously approved gallium formulations in antibacterial chemotherapy. Gallium has no proven function in biological systems, but it can act as an iron-mimetic in both prokaryotic and eukaryotic cells. The activity of gallium mostly relies on its ability to replace iron in redox enzymes, thus impairing their function and ultimately hampering cell growth. Cancer cells and bacteria are preferential gallium targets due to their active metabolism and fast growth. The wealth of knowledge on the pharmacological properties of gallium has opened the door to the repurposing of gallium-based drugs for the treatment of infections sustained by antibiotic-resistant bacterial pathogens, such as Acinetobacter baumannii or Pseudomonas aeruginosa, and for suppression of Mycobacterium tuberculosis growth. The promising antibacterial activity of gallium both in vitro and in different animal models of infection raises the hope that gallium will confirm its efficacy in clinical trials, and will become a valuable therapeutic option to cure otherwise untreatable bacterial infections