In vitro activities of imipenem, vancomycin, and rifampicin against clinical Elizabethkingia species producing BlaB and GOB metallo-beta-lactamases

Antimicrobial Susceptibility Patterns and Antimicrobial Therapy of Infections Caused by Elizabethkingia Species

Background and Objectives: Elizabethkingia species have become significant sources of infections acquired in hospital settings and are commonly linked to high mortality rates. Antimicrobial resistance can be influenced by Elizabethkingia species, geographical location, antimicrobial susceptibility testing methods, and the time of bacterial isolation. There are distinct antimicrobial susceptibility patterns among species, and the investigation into potential antibiotic susceptibility variations among species is beneficial. There is no guidance on the treatment of Elizabethkingia species infections in the literature. Consequently, the purpose of this review was to elaborate on the antimicrobial susceptibility patterns of Elizabethkingia species through a scoping review of existing studies on the antibiograms of the Elizabethkingia species and on the illness caused by Elizabethkingia species. Materials and Methods: A comprehensive literature search in PubMed and Web of Science between 1 January 2000 and 30 April 2024 identified all studies, including those that examined antimicrobial susceptibility patterns and antimicrobial therapy of infections caused by Elizabethkingia species. I considered studies on antimicrobial susceptibility testing for Elizabethkingia species in which only broth microdilution methods and agar dilution methods were used. Results: The sensitivity levels of Elizabethkingia meningoseptica to piperacillin-tazobactam (5-100%), ciprofloxacin (0-43.4%), levofloxacin (30-81.8%), trimethoprim-sulfamethoxazole (0-100%), tigecycline (15-100%), minocycline (60-100%), and rifampicin (94-100%) varied. The sensitivity levels of Elizabethkingia anophelis to piperacillin-tazobactam (3.3-93.3%), ciprofloxacin (1-75%), levofloxacin (12-100%), trimethoprim-sulfamethoxazole (1.02-96.7%), tigecycline (0-52.2%), minocycline (97.5-100%), and rifampicin (20.5-96%) varied. The sensitivity levels of Elizabethkingia miricola to piperacillin-tazobactam (41.6-94.0%), ciprofloxacin (14-75%), levofloxacin (77.0-100%), trimethoprim-sulfamethoxazole (18.0-100%), tigecycline (50%), minocycline (100%), and rifampicin (66-85.7%) varied. Conclusions: The majority of the isolates of Elizabethkingia species were susceptible to minocycline and rifampin. This issue requires professional knowledge integration and treatment recommendations.

Imipenem reduces the efficacy of vancomycin against Elizabethkingia species

BACKGROUND

Elizabethkingia spp. are emerging as nosocomial pathogens causing various infections. These pathogens express resistance to a broad range of antibiotics, thus requiring antimicrobial combinations for coverage. However, possible antagonistic interactions between antibiotics have not been thoroughly explored. This study aimed to evaluate the effectiveness of antimicrobial combinations against Elizabethkingia infections, focusing on their impact on pathogenicity, including biofilm production and cell adhesion.

METHODS

Double-disc diffusion, time-kill, and chequerboard assays were used for evaluating the combination effects of antibiotics against Elizabethkingia spp. We further examined the antagonistic effects of antibiotic combinations on biofilm formation and adherence to A549 human respiratory epithelial cells. Further validation of the antibiotic interactions and their implications was performed using ex vivo hamster precision-cut lung sections (PCLSs) to mimic in vivo conditions.

RESULTS

Antagonistic effects were observed between cefoxitin, imipenem and amoxicillin/clavulanic acid in combination with vancomycin. The antagonism of imipenem toward vancomycin was specific to its effects on the genus Elizabethkingia. Imipenem further hampered the bactericidal effect of vancomycin and impaired its inhibition of biofilm formation and the adhesion of Elizabethkingia meningoseptica ATCC 13253 to human cells. In the ex vivo PCLS model, vancomycin exhibited dose-dependent bactericidal effects; however, the addition of imipenem also reduced the effect of vancomycin.

CONCLUSIONS

Imipenem reduced the bactericidal efficacy of vancomycin against Elizabethkingia spp. and compromised its capacity to inhibit biofilm formation, thereby enhancing bacterial adhesion. Clinicians should be aware of the potential issues with the use of these antibiotic combinations when treating Elizabethkingia infections.

Clinical manifestations, antimicrobial resistance and genomic feature analysis of multidrug-resistant Elizabethkingia strains

BACKGROUND

Elizabethkingia is emerging as an opportunistic pathogen in humans. The aim of this study was to investigate the clinical epidemiology, antimicrobial susceptibility, virulence factors, and genome features of Elizabethkingia spp.

METHODS

Clinical data from 71 patients who were diagnosed with Elizabethkingia-induced pneumonia and bacteremia between August 2019 and September 2021 were analyzed. Whole-genome sequencing was performed on seven isolates, and the results were compared with a dataset of 83 available Elizabethkingia genomes. Genomic features, Kyoto Encyclopedia of Genes and Genomes (KEGG) results and clusters of orthologous groups (COGs) were analyzed.

RESULTS

The mean age of the patients was 56.9 ± 20.7 years, and the in-hospital mortality rate was 29.6% (21/71). Elizabethkingia strains were obtained mainly from intensive care units (36.6%, 26/71) and emergency departments (32.4%, 23/71). The majority of the strains were isolated from respiratory tract specimens (85.9%, 61/71). All patients had a history of broad-spectrum antimicrobial exposure. Hospitalization for invasive mechanical ventilation or catheter insertion was found to be a risk factor for infection. The isolates displayed a high rate of resistance to cephalosporins and carbapenems, but all were susceptible to minocycline and colistin. Genomic analysis identified five β-lactamase genes (blaGOB, blaBlaB, blaCME, blaOXA, and blaTEM) responsible for β-lactam resistance and virulence genes involved in stress adaptation (ureB/G, katA/B, and clpP), adherence (groEL, tufA, and htpB) and immune modulation (gmd, tviB, cps4J, wbtIL, cap8E/D/G, and rfbC). Functional analysis of the COGs revealed that "metabolism" constituted the largest category within the core genome, while "information storage and processing" was predominant in both the accessory and unique genomes. The unique genes in our 7 strains were mostly enriched in KEGG pathways related to microRNAs in cancer, drug resistance (β-lactam and vancomycin), ABC transporters, biological metabolism and biosynthesis, and nucleotide excision repair mechanisms.

CONCLUSION

The Elizabethkingia genus exhibits multidrug resistance and carries carbapenemase genes. This study presents a comparative genomic analysis of Elizabethkingia, providing knowledge that facilitates a better understanding of this microorganism.

A Genetic Locus in Elizabethkingia anophelis Associated with Elevated Vancomycin Resistance and Multiple Antibiotic Reduced Susceptibility

The Gram-negative Elizabethkingia express multiple antibiotic resistance and cause severe opportunistic infections. Vancomycin is commonly used to treat Gram-positive infections and has also been used to treat Elizabethkingia infections, even though Gram-negative organisms possess a vancomycin permeability barrier. Elizabethkingia anophelis appeared relatively vancomycin-susceptible and challenge with this drug led to morphological changes indicating cell lysis. In stark contrast, vancomycin growth challenge revealed that E. anophelis populations refractory to vancomycin emerged. In addition, E. anophelis vancomycin-selected mutants arose at high frequencies and demonstrated elevated vancomycin resistance and reduced susceptibility to other antimicrobials. All mutants possessed a SNP in a gene (vsr1 = vancomycin-susceptibility regulator 1) encoding a PadR family transcriptional regulator located in the putative operon vsr1-ORF551, which is conserved in other Elizabethkingia spp as well. This is the first report linking a padR homologue (vsr1) to antimicrobial resistance in a Gram-negative organism. We provide evidence to support that vsr1 acts as a negative regulator of vsr1-ORF551 and that vsr1-ORF551 upregulation is observed in vancomycin-selected mutants. Vancomycin-selected mutants also demonstrated reduced cell length indicating that cell wall synthesis is affected. ORF551 is a membrane-spanning protein with a small phage shock protein conserved domain. We hypothesize that since vancomycin-resistance is a function of membrane permeability in Gram-negative organisms, it is likely that the antimicrobial resistance mechanism in the vancomycin-selected mutants involves altered drug permeability.

Successful Eradication of a Highly Resistant Elizabethkingia anophelis Species in a Premature Neonate With Bacteremia and Meningitis

Elizabethkingia anophelis is a Gram-negative bacillus that can exhibit highly resistant phenotypes against most antibiotics with evidence of efficacy and safety in the neonatal population. Given the limited antimicrobial options, clinicians may be forced into challenging treatment scenarios when faced with central nervous system infections in premature neonates caused by E. anophelis . We report a case of successful treatment of hospital-acquired meningitis and bacteremia caused by E. anophelis at 11 days of life in a male infant born at 29 weeks, 1 day gestation and birth weight of 1.41 kg. Therapy consisted of vancomycin, dose adjusted to maintain goal troughs of 15-20 mg/L, and rifampin 10 mg/kg/dose every 12 hours, with ciprofloxacin 15 mg/kg/dose every 12 hours and trimethoprim/sulfamethoxazole 5 mg/kg/dose every 12 hours added due to antimicrobial susceptibilities and unsatisfactory response, for a total of 21 days. Following initiation of this multidrug regimen, repeat cultures were negative, laboratory parameters improved [with exception of elevated cerebrospinal fluid (CSF) white blood cell count], the patient remained otherwise stable, and there were no adverse effects noted from therapy. Complications after treatment included the requirement of bilateral hearing aids and the development of hydrocephalus necessitating ventriculoperitoneal shunt placement. To our knowledge, we report the first case of meningitis in a premature neonate initially identified as E. anophelis in the United States treated with this regimen which led to successful microbiologic eradication with no antimicrobial safety concerns.

Emerging infections in vulnerable hosts: Stenotrophomonas maltophilia and Elizabethkingia anophelis

PURPOSE OF REVIEW

This systematic review aimed to explore the recent trends in the epidemiology, risk factors, and antimicrobial susceptibility of two emerging opportunistic pathogens, Stenotrophomonas maltophilia and Elizabethkingia anophelis .

RECENT FINDINGS

Since 2020, numerous outbreaks of S. maltophilia and E. anophelis have been reported worldwide. Most of these outbreaks have been associated with healthcare facilities, although one outbreak caused by E. anophelis in France was considered a community-associated infection. In terms of antimicrobial susceptibility, trimethoprim/sulfamethoxazole (TMP-SMZ), levofloxacin, and minocycline have exhibited good efficacy against S. maltophilia . Additionally, cefiderocol and a combination of aztreonam and avibactam have shown promising results in in vitro susceptibility testing. For E. anophelis , there is currently no consensus on the optimal treatment. Although some studies have reported good efficacy with rifampin, TMP-SMZ, piperacillin/tazobactam, and cefoperazone/sulbactam, minocycline had the most favourable in vitro susceptibility rates. Cefiderocol may serve as an alternative due to its low minimum inhibitory concentration (MIC) against E. anophelis . The role of vancomycin in treatment is still uncertain, although several successful cases with vancomycin treatment, even with high MIC values, have been reported.

SUMMARY

Immunocompromised patients are particularly vulnerable to infections caused by S. maltophilia and E. anophelis , but the optimal treatment strategy remains inconclusive. Further research is necessary to determine the most effective use of conventional and novel antimicrobial agents in combatting these multidrug-resistant pathogens.

Population genomics of emerging Elizabethkingia anophelis pathogens reveals potential outbreak and rapid global dissemination

Elizabethkingia anophelis is an emerging species and have increasingly been reported to cause life-threatening infections and even outbreaks in humans. Nevertheless, there is little data regarding the E. anophelis geographical distribution, phylogenetic structure, and transmission across the globe, especially in Asia. We utilize whole genome sequencing (WGS) data to define a global population framework, phylogenetic structure, geographical distribution, and transmission evaluation of E. anophelis pathogens. The geographical distribution diagram revealed the emerging pathogenic bacteria already distributed in various countries worldwide, especially in the USA and China. Strikingly, phylogenetic analysis showed a part of our China original E. anophelis shared the same ancestor with the USA outbreak strain, which implies the possibility of localized outbreaks and global spread. These closer related strains also contained ICEEaI, which might insert into a disrupted DNA repair mutY gene and made the strain more liable to mutation and outbreak infection. BEAST analysis showed that the most recent common ancestor for ICEEaI E. anophelis was dated twelve years ago, and China might be the most likely recent source of this bacteria. Our study sheds light on the potential possibility of E. anophelis causing the large-scale outbreak and rapid global dissemination. Continued genomic surveillance of the dynamics of E. anophelis populations will generate further knowledge for optimizing future prevent global outbreak infections.

Epidemiology and Characteristics of Elizabethkingia spp. Infections in Southeast Asia

Elizabethkingia spp. is a ubiquitous pathogenic bacterium that has been identified as the causal agent for a variety of conditions such as meningitis, pneumonia, necrotizing fasciitis, endophthalmitis, and sepsis and is emerging as a global threat including in Southeast Asia. Elizabethkingia infections tend to be associated with high mortality rates (18.2–41%) and are mostly observed in neonates and immunocompromised patients. Difficulties in precisely identifying Elizabethkingia at the species level by traditional methods have hampered our understanding of this genus in human infections. In Southeast Asian countries, hospital outbreaks have usually been ascribed to E. meningoseptica, whereas in Singapore, E. anophelis was reported as the main Elizabethkingia spp. associated with hospital settings. Misidentification of Elizabethkingia spp. could, however, underestimate the number of cases attributed to the bacterium, as precise identification requires tools such as MALDI-TOF MS, and particularly whole-genome sequencing, which are not available in most hospital laboratories. Elizabethkingia spp. has an unusual antibiotic resistance pattern for a Gram-negative bacterium with a limited number of horizontal gene transfers, which suggests an intrinsic origin for its multidrug resistance. Efforts to prevent and further understand Elizabethkingia spp. infections and limit its spread must rise to this new challenge.

Comparative genomic analysis of Escherichia coli strains obtained from continuous imipenem stress evolution

The carbapenem-resistant Escherichia coli has aroused increasing attention worldwide, especially in terms of imipenem (IMP) resistance. The molecular mechanism of IMP resistance remains unclear. This study aimed to explore the resistance mechanisms of IMP in E. coli. Susceptible Sx181-0-1 strain was induced into resistance strains by adaptive laboratory evolution. The drug resistance spectrum was measured using the disk diffusion and microbroth dilution methods. Whole-genome sequencing and resequencing were used to analyze the nonsynonymous single-nucleotide polymorphisms (nsSNPs) between the primary susceptible strain and resistant strains. The expression levels of these genes with nsSNPs were identified by real-time quantitative PCR (RT-qPCR). Resistance phenotype appeared in the induced 15th generation (induction time = 183 h). Sx181-32 and Sx181-256, which had the minimum inhibitory concentrations of IMP of 8 and 64 µg ml-1, were isolated during continuous subculture exposed to increasing concentrations of IMP, respectively. A total of 19 nsSNPs were observed both in Sx181-32 and Sx181-256, distributed in rpsU, sdaC, zwf, ttuC, araJ, dacC, mrdA, secF, dacD, lpxD, mrcB, ftsI, envZ, and two unknown function genes (orf01892 and orf01933). Among these 15 genes, five genes (dacC, mrdA, lpxD, mrcB, and ftsI) were mainly involved in cell wall synthesis. The mrdA (V338A, L378P, and M574I) and mrcB (P784L, A736V, and T708A) had three amino acid substitutions, respectively. The expression levels of rpsU, ttuC, and orf01933 were elevated in both Sx181-32 and Sx181-256 compared to Sx181-0-1. The expression levels of these genes were elevated in Sx181-256, except for araJ. Bacteria developed resistance to antimicrobials by regulating various biological processes, among which the most involved is the cell wall synthesis (dacC, mrdA, lpxD, mrcB, and ftsI). The combination mutations of mrdA, envZ, and ftsI genes may increase the resistance to IMP. Our study could improve the understanding of the molecular mechanism of IMP resistance in E. coli.

Genomic analysis of Elizabethkingia species from aquatic environments: Evidence for potential clinical transmission

•

Identification of closely related (< 50 SNV) clinical and environmental aquatic Elizabethkingia anophelis isolates.

•

Identification of a provisional novel species Elizabethkingia umaracha.

•

Novel bla_GOB and bla_B carbapenemases and extended spectrum β-lactamase bla_CME alleles identified in Elizabethkingia spp.

•

Analysis of the global phylogeny and pangenome of Elizabethkingia spp.

•

Identification of novel ICE elements carrying uncharacterised genetic cargo in 67 / 94 (71.3%) of the aquatic environments Elizabethkingia spp.

Elizabethkingia species are ubiquitous in aquatic environments, colonize water systems in healthcare settings and are emerging opportunistic pathogens with reports surfacing in 25 countries across six continents. Elizabethkingia infections are challenging to treat, and case fatality rates are high. Chromosomal bla_B, bla_GOB and bla_CME genes encoding carbapenemases and cephalosporinases are unique to Elizabethkingia spp. and reports of concomitant resistance to aminoglycosides, fluoroquinolones and sulfamethoxazole-trimethoprim are known. Here, we characterized whole-genome sequences of 94 Elizabethkingia isolates carrying multiple wide-spectrum metallo-β-lactamase (bla_Band bla_GOB) and extended-spectrum serine‑β-lactamase (bla_CME) genes from Australian aquatic environments and performed comparative phylogenomic analyses against national clinical and international strains. qPCR was performed to quantify the levels of Elizabethkingia species in the source environments. Antibiotic MIC testing revealed significant resistance to carbapenems and cephalosporins but susceptibility to fluoroquinolones, tetracyclines and trimethoprim-sulfamethoxazole. Phylogenetics show that three environmental E. anophelis isolates are closely related to E. anophelis from Australian clinical isolates (∼36 SNPs), and a new species, E. umeracha sp. novel, was discovered. Genomic signatures provide insight into potentially shared origins and a capacity to transfer mobile genetic elements with both national and international isolates.

Comparison of three species of Elizabethkingia genus by whole-genome sequence analysis

Elizabethkingia are found to cause severe neonatal meningitis, nosocomial pneumonia, endocarditis and bacteremia. However, there are few studies on Elizabethkingia genus by comparative genomic analysis. In this study, three species of Elizabethkingia were found: E. meningoseptica, E. anophelis and E. miricola. Resistance genes and associated proteins of seven classes of antibiotics including beta-lactams, aminoglycosides, macrolides, tetracyclines, quinolones, sulfonamides and glycopeptides, as well as multidrug resistance efflux pumps were identified from 20 clinical isolates of Elizabethkingia by whole-genome sequence. Genotype and phenotype displayed a good consistency in beta-lactams, aminoglycosides and glycopeptides, while contradictions exhibited in tetracyclines, quinolones and sulfonamides. Virulence factors and associated genes such as hsp60 (htpB), exopolysaccharide (EPS) (galE/pgi), Mg2+ transport (mgtB/mgtE) and catalase (katA/katG) existed in all clinical and reference strains. The functional analysis of the clusters of orthologous groups indicated that 'metabolism' occupied the largest part in core genome, 'information storage and processing' was the largest group in both accessory genome and unique genome. Abundant mobile elements were identified in E. meningoseptica and E. anophelis. The most significant finding in our study was that a single clone of E. anophelis had been circulating within diversities of departments in a clinical setting for nearly 18 months.

Comparative Genomics and Antimicrobial Resistance Profiling of Elizabethkingia Isolates Reveal Nosocomial Transmission and In Vitro Susceptibility to Fluoroquinolones, Tetracyclines, and Trimethoprim-Sulfamethoxazole

The Elizabethkingia genus has gained global attention in recent years as containing sporadic, worldwide, nosocomial pathogens. Elizabethkingia spp. are intrinsically multidrug resistant, primarily infect immunocompromised individuals, and are associated with high mortality (∼20 to 40%). As yet, gaps remain in our understanding of transmission, global strain relatedness, antimicrobial resistance, and effective therapy. Over a 16-year period, 22 clinical and 6 hospital environmental isolates were collected from Queensland, Australia. Identification using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) (Vitek MS) and whole-genome sequencing was compared with a global strain data set. Phylogenomic reconstruction robustly identified 22 Elizabethkingia anophelis, 3 Elizabethkingia miricola, 2 Elizabethkingia meningoseptica, and 1 Elizabethkingia bruuniana isolates, most of which branched as unique lineages. Global analysis revealed that some Australian E. anophelis isolates are genetically closely related to strains from the United States, England, and Asia. Comparative genomics of clinical and environmental strains identified evidence of nosocomial transmission in patients, indicating probable infection from a hospital reservoir. Furthermore, broth microdilution against 39 antimicrobials revealed almost ubiquitous resistance to aminoglycosides, carbapenems, cephalosporins, and penicillins. Like other international strains, our isolates expressed susceptibility to minocycline and levofloxacin and the less common trimethoprim-sulfamethoxazole. Our study demonstrates important new insights into the genetic diversity, environmental persistence, and transmission of and potential effective therapy for Australian Elizabethkingia species.

Risk Factors for Mortality in Patients with Elizabethkingia Infection and the Clinical Impact of the Antimicrobial Susceptibility Patterns of Elizabethkingia Species

Elizabethkingia species (spp.), which can colonize hospital environments, are emerging nosocomial pathogens presenting high mortality. Due to their intrinsic resistance to a broad range of antibiotics, optimal antibiotic dosage has yet to be determined against infections caused by Elizabethkingia spp. This study aimed to investigate the risk factors for the mortality of infections caused by Elizabethkingia spp. and assess the clinical implications of their antimicrobial susceptibility patterns. Data from 210 patients affected by Elizabethkingia-induced pneumonia and bacteremia between 1 November 2005 and 31 May 2016, were analyzed. Further antimicrobial susceptibility tests for moxifloxacin, rifampin, and vancomycin using Elizabethkingia isolates were performed to compensate for the Elizabethkingia spp. susceptibility panel in patients affected after 2013. The mean age of the patients was 66.5 ± 18 years and the 28-day mortality rate was 25.2% (53/210). In the univariate analysis, history of prior stay in an intensive care unit, central venous catheter use, presented thrombocytopenia, immunocompetent status, a high simplified acute physiology score II (SAPS II score), a high C-reactive protein (CRP)/albumin ratio on the day of isolation and seven days later, and a high minimum inhibitory concentration (MIC) value of rifampin were significantly associated with a higher mortality rate. In the multivariate logistic regression analysis, the MIC values of rifampin (odds ratio (OR): 1.045; 95% confidence interval (CI): 1.006–1.085; p = 0.023), SAPS II score (OR: 1.053; 95% CI: 1.022–1.084; p = 0.001), and initial CRP/albumin ratio (OR: 1.030; 95% CI: 1.009–1.051; p = 0.004) were significantly associated with 28-day mortality. To reduce the mortality associated with Elizabethkingia infections, prediction of the clinical course using initial CRP/albumin ratio and SAPS II and early intervention are essential. Rifampin is a promising candidate as the drug of choice in treating Elizabethkingia infections.

Molecular Characteristics and Antimicrobial Susceptibility Profiles of Elizabethkingia Clinical Isolates in Shanghai, China

Purpose

To investigate molecular characteristics and antimicrobial susceptibility profiles of clinical isolates of Elizabethkingia in Shanghai, China.

Methods

Elizabethkingia isolates were collected in a university-affiliated hospital in 2012–2015 and 2017–2018. They were re-identified to species level by 16S rRNA gene and species-specific gene sequencing. Antimicrobial susceptibility testing, screening for metallo-beta-lactamase production, identification of antimicrobial resistance genes and pulsed-field gel electrophoresis (PFGE) were performed.

Results

Among 52 Elizabethkingia isolates, E. anophelis was the most prevalent species (67.3%), followed by E. meningoseptica (26.9%). High carriage rates of bla_CME, bla_BlaB and bla_GOB genes were consistent with the poor in vitro activity of most β-lactams including carbapenems. Nevertheless, β-lactamase inhibitors increased susceptibility rates significantly for cefoperazone and piperacillin. Susceptibility rates for minocycline, tigecycline, rifampin and levofloxacin were 100%, 78.8%, 76.9% and 71.2%, respectively. Ser83Ile or Ser83Arg substitution in the DNA gyrase A unit was associated with resistance to fluoroquinolones. MIC₅₀/MIC₉₀ values of vancomycin and linezolid were 16/16 mg/L and 16/32 mg/L, respectively. Molecular typing showed twenty-one different types of PFGE and more than one indistinguishable isolates were observed in each of the eight subtypes.

Conclusion

Tetracyclines, tigecycline, β-lactam/β-lactamase inhibitor combinations, rifampin and fluoroquinolones demonstrated high rates of in vitro activity against clinical isolates of Elizabethkingia. Both genetic diversity and clonality were observed from this health-care facility. Our report provides potential alternative treatment options for Elizabethkingia infections.