Differentiation of hypervirulent and classical Klebsiella pneumoniae with acquired drug resistance.

Distinguishing hypervirulent (hvKp) from classical Klebsiella pneumoniae (cKp) strains is important for clinical care, surveillance, and research. Some combinations of iucA, iroB, peg-344, rmpA, and rmpA2 are most commonly used, but it is unclear what combination of genotypic or phenotypic markers (e.g., siderophore concentration, mucoviscosity) most accurately predicts the hypervirulent phenotype. Furthermore, acquisition of antimicrobial resistance may affect virulence and confound identification. Therefore, 49 K. pneumoniae strains that possessed some combinations of iucA, iroB, peg-344, rmpA, and rmpA2 and had acquired resistance were assembled and categorized as hypervirulent hvKp (hvKp) (N = 16) or cKp (N = 33) via a murine infection model. Biomarker number, siderophore production, mucoviscosity, virulence plasmid's Mash/Jaccard distances to the canonical pLVPK, and Kleborate virulence score were measured and evaluated to accurately differentiate these pathotypes. Both stepwise logistic regression and a CART model were used to determine which variable was most predictive of the strain cohorts. The biomarker count alone was the strongest predictor for both analyses. For logistic regression, the area under the curve for biomarker count was 0.962 (P = 0.004). The CART model generated the classification rule that a biomarker count = 5 would classify the strain as hvKP, resulting in a sensitivity for predicting hvKP of 94% (15/16), a specificity of 94% (31/33), and an overall accuracy of 94% (46/49). Although a count of ≥4 was 100% (16/16) sensitive for predicting hvKP, the specificity and accuracy decreased to 76% (25/33) and 84% (41/49), respectively. These findings can be used to inform the identification of hvKp.IMPORTANCEHypervirulent Klebsiella pneumoniae (hvKp) is a concerning pathogen that can cause life-threatening infections in otherwise healthy individuals. Importantly, although strains of hvKp have been acquiring antimicrobial resistance, the effect on virulence is unclear. Therefore, it is of critical importance to determine whether a given antimicrobial resistant K. pneumoniae isolate is hypervirulent. This report determined which combination of genotypic and phenotypic markers could most accurately identify hvKp strains with acquired resistance. Both logistic regression and a machine-learning prediction model demonstrated that biomarker count alone was the strongest predictor. The presence of all five of the biomarkers iucA, iroB, peg-344, rmpA, and rmpA2 was most accurate (94%); the presence of ≥4 of these biomarkers was most sensitive (100%). Accurately identifying hvKp is vital for surveillance and research, and the availability of biomarker data could alert the clinician that hvKp is a consideration, which, in turn, would assist in optimizing patient care.

Differentiation of hypervirulent and classical Klebsiella pneumoniae with acquired drug resistance.

Distinguishing hypervirulent (hvKp) from classical Klebsiella pneumoniae (cKp) strains is important for clinical care, surveillance, and research. Some combination of iucA, iroB, peg-344, rmpA, and rmpA2 are most commonly used, but it is unclear what combination of genotypic or phenotypic markers (e.g. siderophore concentration, mucoviscosity) most accurately predicts the hypervirulent phenotype. Further, acquisition of antimicrobial resistance may affect virulence and confound identification. Therefore, 49 K. pneumoniae strains that possessed some combination of iucA, iroB, peg-344, rmpA, and rmpA2 and had acquired resistance were assembled and categorized as hypervirulent hvKp (hvKp) (N=16) or cKp (N=33) via a murine infection model. Biomarker number, siderophore production, mucoviscosity, virulence plasmid's Mash/Jaccard distances to the canonical pLVPK, and Kleborate virulence score were measured and evaluated to accurately differentiate these pathotypes. Both stepwise logistic regression and a CART model were used to determine which variable was most predictive of the strain cohorts. The biomarker count alone was the strongest predictor for both analyses. For logistic regression the area under the curve for biomarker count was 0.962 (P = 0.004). The CART model generated the classification rule that a biomarker count = 5 would classify the strain as hvKP, resulting in a sensitivity for predicting hvKP of 94% (15/16), a specificity of 94% (31/33), and an overall accuracy of 94% (46/49). Although a count of ≥ 4 was 100% (16/16) sensitive for predicting hvKP, the specificity and accuracy decreased to 76% (25/33) and 84% (41/49) respectively. These findings can be used to inform the identification of hvKp. Importance: Hypervirulent Klebsiella pneumoniae (hvKp) is a concerning pathogen that can cause life-threatening infections in otherwise healthy individuals. Importantly, although strains of hvKp have been acquiring antimicrobial resistance, the effect on virulence is unclear. Therefore, it is of critical importance to determine whether a given antimicrobial resistant K. pneumoniae isolate is hypervirulent. This report determined which combination of genotypic and phenotypic markers could most accurately identify hvKp strains with acquired resistance. Both logistic regression and a machine-learning prediction model demonstrated that biomarker count alone was the strongest predictor. The presence of all 5 of the biomarkers iucA, iroB, peg-344, rmpA, and rmpA2 was most accurate (94%); the presence of ≥ 4 of these biomarkers was most sensitive (100%). Accurately identifying hvKp is vital for surveillance and research, and the availability of biomarker data could alert the clinician that hvKp is a consideration, which in turn would assist in optimizing patient care.

A one-year genomic investigation of Escherichia coli epidemiology and nosocomial spread at a large US healthcare network.

BACKGROUND: Extra-intestinal pathogenic Escherichia coli (ExPEC) are a leading cause of bloodstream and urinary tract infections worldwide. Over the last two decades, increased rates of antibiotic resistance in E. coli have been reported, further complicating treatment. Worryingly, specific lineages expressing extended-spectrum ß-lactamases (ESBLs) and fluoroquinolone resistance have proliferated and are now considered a serious threat. Obtaining contemporary information on the epidemiology and prevalence of these circulating lineages is critical for containing their spread globally and within the clinic. METHODS: Whole-genome sequencing (WGS), phylogenetic analysis, and antibiotic susceptibility testing were performed for a complete set of 2075 E. coli clinical isolates collected from 1776 patients at a large tertiary healthcare network in the USA between October 2019 and September 2020. RESULTS: The isolates represented two main phylogenetic groups, B2 and D, with six lineages accounting for 53% of strains: ST-69, ST-73, ST-95, ST-131, ST-127, and ST-1193. Twenty-seven percent of the primary isolates were multidrug resistant (MDR) and 5% carried an ESBL gene. Importantly, 74% of the ESBL-E.coli were co-resistant to fluoroquinolones and mostly belonged to pandemic ST-131 and emerging ST-1193. SNP-based detection of possible outbreaks identified 95 potential transmission clusters totaling 258 isolates (12% of the whole population) from ≥ 2 patients. While the proportion of MDR isolates was enriched in the set of putative transmission isolates compared to sporadic infections (35 vs 27%, p = 0.007), a large fraction (61%) of the predicted outbreaks (including the largest cluster grouping isolates from 12 patients) were caused by the transmission of non-MDR clones. CONCLUSION: By coupling in-depth genomic characterization with a complete sampling of clinical isolates for a full year, this study provides a rare and contemporary survey on the epidemiology and spread of E. coli in a large US healthcare network. While surveillance and infection control efforts often focus on ESBL and MDR lineages, our findings reveal that non-MDR isolates represent a large burden of infections, including those of predicted nosocomial origins. This increased awareness is key for implementing effective WGS-based surveillance as a routine technology for infection control.

IS26-mediated plasmid reshuffling results in convergence of toxin-antitoxin systems but loss of resistance genes in XDR Klebsiella pneumoniae from a chronic infection.

Carbapenem-resistant Enterobacterales pose an urgent threat to human health worldwide. Klebsiella pneumoniae sequence type (ST) 14, initially identified in the Middle East and South-Asia and co-harbouring the carbapenemase genes bla OXA-232 and bla NDM-1, is now emerging globally. One such strain was detected in the USA in 2013 from a patient initially treated in India that also carried armA, a 16S rRNA methyltransferase that confers resistance to all clinically relevant aminoglycosides. Genetic and phenotypic changes were observed in 14 serial isolates collected from this chronically infected patient. The index isolate carried five plasmids, including an IncFIB-IncHI1B (harbouring armA and bla NDM-1), an IncFIA (bla CTX-M-15) and a ColE-like (bla OXA-232), and was extensively resistant to antibiotics. Four years later, a subsequent isolate had accumulated 34 variants, including a loss-of-function mutation in romA, resulting in tigecycline non-susceptibility. Importantly, this isolate now only carried two plasmids, including a large mosaic molecule made of fragments, all harbouring distinct toxin-antitoxin systems, from three of the canonical plasmids. Of the original acquired antibiotic resistance genes, this isolate only retained bla CTX-M-15, and as a result susceptibility to the carbapenems and amikacin was restored. Long-read sequencing of a subset of five representative isolates, collected between 2013 and 2017, allowed for the elucidation of the complex plasmid patterns and revealed the role of IS26-mediated plasmid reshuffling in the evolution of this clone. Such investigations of the mechanisms underlying plasmid stability, together with global and local surveillance programmes, are key to a better understanding of plasmid host range and dissemination.

First Report: Colistin Resistance Gene mcr-3.1 in Salmonella enterica Serotype Choleraesuis Isolated from Human Blood Sample from Thailand.

This study describes the first finding of Salmonella enterica serotype Choleraesuis (Salmonella Choleraesuis) isolate harboring mobile colistin resistance (mcr)-3.1 obtained from human blood sample. The clinical relevant blood sample was collected during October 2018. The phenotypic identification and antimicrobial susceptibility testing (AST) were studied by using automate microbiology platform (Phoenix M50, BD), and in-depth characterization by whole genome sequencing. The phenotypic identification was reported Salmonella Choleraesuis. AST result demonstrated that this isolate had high minimum inhibitory concentrations (MICs) against colistin, fluoroquinolone, and cephalosporin III and IV, which are first-line antibiotic treatment choices for Gram-negative bacterial pathogen infections. This Salmonella Choleraesuis is harboring mcr-3.1 and presented a diversity carbapenemase including blaTEM and blactx-m-55. Regarding the multilocus sequence typing result, this Salmonella presented ST139 that related to the Choleraesuis variant sensu stricto. Swine is not the host specific for the Salmonella Choleraesuis since it also causes enteric and other diseases in human. Hence, the presence of the mobile plasmid colistin mcr-3.1 resistant gene in human sample is resulting to the public health concerns due to the fact that it is enable to transmit to other hosts and distribute into an environment.

Emergence of the E484K Mutation in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Lineage B.1.1.345 in Upstate New York.

A severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.345 variant carrying the E484K mutation was detected in 4 patients with no apparent epidemiological association from a hospital network in upstate New York. Subsequent analysis identified an additional 11 B.1.1.345 variants from this region between December 2020 and February 2021.

Anatomy of an extensively drug-resistant Klebsiella pneumoniae outbreak in Tuscany, Italy.

A protracted outbreak of New Delhi metallo-ß-lactamase (NDM)-producing carbapenem-resistant Klebsiella pneumoniae started in Tuscany, Italy, in November 2018 and continued in 2020 and through 2021. To understand the regional emergence and transmission dynamics over time, we collected and sequenced the genomes of 117 extensively drug-resistant, NDM-producing K. pneumoniae isolates cultured over a 20-mo period from 76 patients at several healthcare facilities in southeast Tuscany. All isolates belonged to high-risk clone ST-147 and were typically nonsusceptible to all first-line antibiotics. Albeit sporadic, resistances to colistin, tigecycline, and fosfomycin were also observed as a result of repeated, independent mutations. Genomic analysis revealed that ST-147 isolates circulating in Tuscany were monophyletic and highly genetically related (including a network of 42 patients from the same hospital and sharing nearly identical isolates), and shared a recent ancestor with clinical isolates from the Middle East. While the blaNDM-1 gene was carried by an IncFIB-type plasmid, our investigations revealed that the ST-147 lineage from Italy also acquired a hybrid IncFIB/IncHIB-type plasmid carrying the 16S methyltransferase armA gene as well as key virulence biomarkers often found in hypervirulent isolates. This plasmid shared extensive homologies with mosaic plasmids circulating globally including from ST-11 and ST-307 convergent lineages. Phenotypically, the carriage of this hybrid plasmid resulted in increased siderophore production but did not confer virulence to the level of an archetypical, hypervirulent K. pneumoniae in a subcutaneous model of infection with immunocompetent CD1 mice. Our findings highlight the importance of performing genomic surveillance to identify emerging threats.

Characterization of KPC-82, a KPC-2 Variant Conferring Resistance to Ceftazidime-Avibactam in a Carbapenem-Nonsusceptible Clinical Isolate of Citrobacter koseri.

KPC-82 is a KPC-2 variant identified in a carbapenem-nonsusceptible Citrobacter koseri that confers high-level resistance to ceftazidime-avibactam. Genomic analysis revealed that blaKPC-82 is carried by a chromosomally integrated Tn4401 transposon (disrupting porin gene phoE) and evolved by a 6-nucleotide tandem repeat duplication causing a two-amino-acid insertion (Ser-Asp) within the Ala267-Ser275 loop. Similar to related KPC variants, KPC-82 showed decreased carbapenemase activity when expressed in a heterologous background and remained susceptible to carbapenem/ß-lactamase inhibitor combinations.

Synergistic Killing and Re-Sensitization of Pseudomonas aeruginosa to Antibiotics by Phage-Antibiotic Combination Treatment.

Multidrug-resistant (MDR) Pseudomonas aeruginosa infections pose a serious health threat. Bacteriophage-antibiotic combination therapy is a promising candidate for combating these infections. A 5-phage P. aeruginosa cocktail, PAM2H, was tested in combination with antibiotics (ceftazidime, ciprofloxacin, gentamicin, meropenem) to determine if PAM2H enhances antibiotic activity. Combination treatment in vitro resulted in a significant increase in susceptibility of MDR strains to antibiotics. Treatment with ceftazidime (CAZ), meropenem, gentamicin, or ciprofloxacin in the presence of the phage increased the number of P. aeruginosa strains susceptible to these antibiotics by 63%, 56%, 31%, and 81%, respectively. Additionally, in a mouse dorsal wound model, seven of eight mice treated with a combination of CAZ and PAM2H for three days had no detectable bacteria remaining in their wounds on day 4, while all mice treated with CAZ or PAM2H alone had ~107 colony forming units (CFU) remaining in their wounds. P. aeruginosa recovered from mouse wounds post-treatment showed decreased virulence in a wax worm model, and DNA sequencing indicated that the combination treatment prevented mutations in genes encoding known phage receptors. Treatment with PAM2H in combination with antibiotics resulted in the re-sensitization of P. aeruginosa to antibiotics in vitro and a synergistic reduction in bacterial burden in vivo.

An Assessment of Siderophore Production, Mucoviscosity, and Mouse Infection Models for Defining the Virulence Spectrum of Hypervirulent Klebsiella pneumoniae.

Hypervirulent Klebsiella pneumoniae (hvKp) bacteria are more virulent than classical K. pneumoniae (cKp) with resultant differences in clinical manifestations and management. It is unclear whether all hvKp isolates share a similar pathogenic potential. This report assessed the utility of siderophore production, mucoviscosity, and murine infection for defining the virulence spectrum of hvKp. Three strain cohorts were identified and defined based on the CD1 mouse subcutaneous (SQ) challenge model: (i) fully virulent hvKp strains (fvhvKp), lethal at a challenge inoculum (CI) of ≤103 CFU; (ii) partially virulent hvKp strains (pvhvKp), lethal at a CI of >103 to 107 CFU; (iii) classical K. pneumoniae, not lethal at a CI of 107 CFU. Quantitative siderophore and mucoviscosity assays differentiated fvhvKp and pvhvKp strains from cKp strains but were unable to differentiate between the fvhvKP and pvhvKP strain cohorts. However, SQ challenge of CD1 mice and intraperitoneal (IP) challenge of CD1 and BALB/c mice, but not C57BL/6 mice, were able to discriminate between an fvhvKp and a pvhvKp strain; SQ challenge of CD1 mice may have the greatest sensitivity. cKp was differentiated from hvKp both by SQ challenge of CD1 mice and IP challenge of all three mouse strains. These data identify a means to define the relative virulence of hvKP strains. It remains unclear whether the observed differences of hvKp virulence in mice translates to human infection. However, these data can be used to sort random collections of K. pneumoniae strains into fvhvKp and pvhvKp strain cohorts and assess for differences in clinical manifestations and outcomes.IMPORTANCE The pathogenic potential of hvKp strains is primarily mediated by a large virulence plasmid. The minimal set of genes required for the full expression of the hypervirulent phenotype is undefined. A number of reports describe hvKp strains possessing only a portion of the virulence plasmid; the clinical consequences of this are unclear. Therefore, the goal of this report was to determine whether virulence among hvKp strains varied and, if so, how to best identify the relative virulence of hvKp isolates. Data demonstrate hvKp pathogenic potential varies in CD1 and BALB/c murine infection models. In contrast, measurements of siderophore production and mucoviscosity were unable to discriminate the differences in hvKp isolate virulence observed in mice. This information can be used in future studies to determine the mechanisms responsible for differences between fully virulent hvKp and partially virulent hvKp and whether the differences observed in mice translate to disease in humans.

Bacteroides Fragilis Vertebral Osteomyelitis and Discitis: "Back" to Susceptibility Testing.

Genetic testing of anaerobic isolates can be important for proper antimicrobial stewardship to identify the appropriate narrow-spectrum treatment for a polymicrobial infection.

Analysis of Serial Isolates of mcr-1-Positive Escherichia coli Reveals a Highly Active ISApl1 Transposon.

The emergence of a transferable colistin resistance gene (mcr-1) is of global concern. The insertion sequence ISApl1 is a key component in the mobilization of this gene, but its role remains poorly understood. Six Escherichia coli isolates were cultured from the same patient over the course of 1 month in Germany and the United States after a brief hospitalization in Bahrain for an unconnected illness. Four carried mcr-1 as determined by real-time PCR, but two were negative. Two additional mcr-1-negative E. coli isolates were collected during follow-up surveillance 9 months later. All isolates were analyzed by whole-genome sequencing (WGS). WGS revealed that the six initial isolates were composed of two distinct strains: an initial ST-617 E. coli strain harboring mcr-1 and a second, unrelated, mcr-1-negative ST-32 E. coli strain that emerged 2 weeks after hospitalization. Follow-up swabs taken 9 months later were negative for the ST-617 strain, but the mcr-1-negative ST-32 strain was still present. mcr-1 was associated with a single copy of ISApl1, located on a 64.5-kb IncI2 plasmid that shared >95% homology with other mcr-1 IncI2 plasmids. ISApl1 copy numbers ranged from 2 for the first isolate to 6 for the final isolate, but ISApl1 movement was independent of mcr-1 Some movement was accompanied by gene disruption, including the loss of genes encoding proteins involved in stress responses, arginine catabolism, and l-arabinose utilization. These data represent the first comprehensive analysis of ISApl1 movement in serial clinical isolates and reveal that, under certain conditions, ISApl1 is a highly active IS element whose movement may be detrimental to the host cell.

1,2,4-Triazolidine-3-thiones as Narrow Spectrum Antibiotics against Multidrug-Resistant Acinetobacter baumannii.

With only two new classes of antibiotics developed in the last 40 years, novel antibiotics are desperately needed to combat the growing problem of multidrug-resistant and extensively drug resistant bacteria, particularly Gram-negative bacteria. Described in this letter is the synthesis and antibiotic activity of 1,2,4-triazolidine-3-thiones as narrow spectrum antibiotics. Optimization of the 1,2,4-triazolidine-3-thione scaffold identified a small molecule with potent antibiotic activity against multiple strains of multidrug-resistant and extensively drug-resistant Acinetobacter baumannii. This small molecule also shows single dose, in vivo activity in a Galleria mellonella infection model with A. baumannii and represents a promising start in the development of a class of drugs that can target this bacterial pathogen.

1,2,4-Triazolidine-3-thiones Have Specific Activity against Acinetobacter baumannii among Common Nosocomial Pathogens.

Acinetobacter baumannii are Gram-negative bacilli that pose a constant threat to susceptible patients because of increased resistance to multiple antibiotics and persistence in the hospital environment. After genome analysis, we discovered that A. baumannii harbors genes that share homology to an enzymatic pathway that elongates long-chain fatty acids (LCFA) in fungi. Previously, 1,2,4-triazolidine-3-thiones (T-3-Ts) were shown to inhibit hyphae production in fungi, and this same LCFA elongation pathway was implicated as the possible target. Therefore, we investigated if T-3-Ts also have activity against multidrug-resistant A. baumannii. Surprisingly, all of the clinical isolates of A. baumannii that were tested have susceptibility to ECC145 and ECC188 with MIC90 values of 8.0 µg/mL. In contrast, reference strains and clinical isolates of other common nosocomial bacteria that lack the LCFA pathway also lacked susceptibility. Time-kill experiments revealed that both ECC145 and ECC188 have a bacteriostatic effect against A. baumannii. Mass spectrometry analysis suggested that exposure to T-3-Ts resulted in less LCFA production. Supplementation of media with either 0.02% w/v oleic or linoleic acid abrogated the bacteriostatic effect of the compounds, which again implicated LCFA elongation as the target. Our results suggest these molecules could be a promising start to further exploit what appears to be an important aspect of A. baumannii membrane function and integrity.

Personalized Therapeutic Cocktail of Wild Environmental Phages Rescues Mice from Acinetobacter baumannii Wound Infections.

Multidrug-resistant bacterial pathogens are an increasing threat to public health, and lytic bacteriophages have reemerged as a potential therapeutic option. In this work, we isolated and assembled a five-member cocktail of wild phages against Acinetobacter baumannii and demonstrated therapeutic efficacy in a mouse full-thickness dorsal infected wound model. The cocktail lowers the bioburden in the wound, prevents the spread of infection and necrosis to surrounding tissue, and decreases infection-associated morbidity. Interestingly, this effective cocktail is composed of four phages that do not kill the parent strain of the infection and one phage that simply delays bacterial growth in vitro via a strong but incomplete selection event. The cocktail here appears to function in a combinatorial manner, as one constituent phage targets capsulated A. baumannii bacteria and selects for loss of receptor, shifting the population to an uncapsulated state that is then sensitized to the remaining four phages in the cocktail. Additionally, capsule is a known virulence factor for A. baumannii, and we demonstrated that the emergent uncapsulated bacteria are avirulent in a Galleria mellonella model. These results highlight the importance of anticipating population changes during phage therapy and designing intelligent cocktails to control emergent strains, as well as the benefits of using phages that target virulence factors. Because of the efficacy of this cocktail isolated from a limited environmental pool, we have established a pipeline for developing new phage therapeutics against additional clinically relevant multidrug-resistant pathogens by using environmental phages sourced from around the globe.

Genetic Manipulation of Acinetobacter baumannii.

Acinetobacter baumannii is a Gram-negative nosocomial pathogen of clinical importance. A lack of genetic tools has hindered the research of this organism in the past; however, recently, various methods have been designed, modified, and optimized to facilitate the genetic manipulation of A. baumannii. This unit describes some of the recent genetic advances and new recombinant tools developed for this pathogen, including standard transformation and conjugation techniques specifically developed for the bacteria. As the need to understand the basic biology of A. baumannii increases with the prospect of developing new therapeutics, the use of the basic genetic methods herein can provide the critical first step to identify genes required for infection.

AB5075, a Highly Virulent Isolate of Acinetobacter baumannii, as a Model Strain for the Evaluation of Pathogenesis and Antimicrobial Treatments.

UNLABELLED: Acinetobacter baumannii is recognized as an emerging bacterial pathogen because of traits such as prolonged survival in a desiccated state, effective nosocomial transmission, and an inherent ability to acquire antibiotic resistance genes. A pressing need in the field of A. baumannii research is a suitable model strain that is representative of current clinical isolates, is highly virulent in established animal models, and can be genetically manipulated. To identify a suitable strain, a genetically diverse set of recent U.S. military clinical isolates was assessed. Pulsed-field gel electrophoresis and multiplex PCR determined the genetic diversity of 33 A. baumannii isolates. Subsequently, five representative isolates were tested in murine pulmonary and Galleria mellonella models of infection. Infections with one strain, AB5075, were considerably more severe in both animal models than those with other isolates, as there was a significant decrease in survival rates. AB5075 also caused osteomyelitis in a rat open fracture model, while another isolate did not. Additionally, a Tn5 transposon library was successfully generated in AB5075, and the insertion of exogenous genes into the AB5075 chromosome via Tn7 was completed, suggesting that this isolate may be genetically amenable for research purposes. Finally, proof-of-concept experiments with the antibiotic rifampin showed that this strain can be used in animal models to assess therapies under numerous parameters, including survival rates and lung bacterial burden. We propose that AB5075 can serve as a model strain for A. baumannii pathogenesis due to its relatively recent isolation, multidrug resistance, reproducible virulence in animal models, and genetic tractability. IMPORTANCE: The incidence of A. baumannii infections has increased over the last decade, and unfortunately, so has antibiotic resistance in this bacterial species. A. baumannii is now responsible for more than 10% of all hospital-acquired infections in the United States and has a >50% mortality rate in patients with sepsis and pneumonia. Most research on the pathogenicity of A. baumannii focused on isolates that are not truly representative of current multidrug-resistant strains isolated from patients. After screening of a panel of isolates in different in vitro and in vivo assays, the strain AB5075 was selected as more suitable for research because of its antibiotic resistance profile and increased virulence in animal models. Moreover, AB5075 is susceptible to tetracycline and hygromycin, which makes it amenable to genetic manipulation. Taken together, these traits make AB5075 a good candidate for use in studying virulence and pathogenicity of this species and testing novel antimicrobials.

Antibacterial activities of iron chelators against common nosocomial pathogens.

The activities of iron chelators (deferoxamine, deferiprone, Apo6619, and VK28) were evaluated against type strains of Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli. Deferiprone, Apo6619, and VK28 each inhibited growth in standard and RPMI tissue culture medium, while deferoxamine had no effect. Additionally, time-kill assays revealed that VK28 had a bacteriostatic effect against S. aureus. Therefore, these newly developed iron chelators might provide a nontraditional approach for treatment of bacterial infections.