IMP-1 encoded by a novel Tn402-like class 1 integron in clinical Achromobacter xylosoxidans, China

Phenotypic and genomic characteristics of clinical IMP-producing Klebsiella spp. Isolates in China

BACKGROUND

IMP-producing Klebsiella spp. (IMPKsp) strains have spread globally, including in China. Currently, the prevalence and genomic characterization of IMPKsp is largely unknown nationwide. Here we aimed to provide a general overview of the phenotypic and genomic characteristics of IMPKsp strains.

METHODS

61 IMPKsp strains were obtained from 13 provinces in China during 2016-2021. All strains were tested for their susceptibility to antimicrobial agents by the microdilution broth method and sequenced with Illumina next-generation sequencing. We performed conjugation experiments on thirteen representative strains which were also sequenced by Oxford nanopore sequencing technology to characterize blaIMP-encoding plasmids.

RESULTS

We find that all IMPKsp strains display multidrug-resistant (MDR) phenotypes. All strains belong to 27 different STs. ST307 emerges as a principal IMP-producing sublineage. blaIMP-4 is found to be the major isoform, followed by blaIMP-38. Seven incompatibility types of blaIMP-encoding plasmids are identified, including IncHI5 (32/61, 52.5%), IncN-IncR (10/61, 16.4%), IncFIB(K)-HI1B (7/61, 11.5%), IncN (5/61, 8.2%), IncN-IncFII (2/61, 3.3%), IncFII (1/61, 1.6%) and IncP (1/61, 1.6%). The strains carrying IncHI5 and IncN plasmids belong to diverse ST types, indicating that these two plasmids may play an important role in the transmission of blaIMP genes among Klebsiella spp. strains.

CONCLUSIONS

Our results highlight that multi-clonal transmission, multiple genetic environments and plasmid types play a major role in the dissemination process of blaIMP genes among Klebsiella spp. IncHI5 type plasmids have the potential to be the main vectors mediating the spread of the blaIMP genes in Klebsiella spp.

Genetic and Biochemical Characterization of AXC-2 from Achromobacter ruhlandii

Achromobacter spp. are intrinsically resistant to multiple antibiotics and can also acquire resistance to those commonly used for the treatment of respiratory infections, especially in patients with cystic fibrosis. The aim of this study was to perform the genetic and biochemical characterization of AXC-2 from A. ruhlandii and to analyze all available AXC variants. Steady-state kinetic parameters were determined on a purified AXC-2 enzyme. It exhibited higher catalytic efficiencies towards amino-penicillins and older cephalosporins, while carbapenems behaved as poor substrates. Phylogenetic analysis of all blaAXC variants available in the NCBI was conducted. AXC was encoded in almost all A. ruhlandii genomes, whereas it was only found in 30% of A. xylosoxidans. AXC-1 was prevalent among A. xylosoxidans. AXC variants were clustered in two main groups, correlating with the Achromobacter species. No association could be established between the presence of blaAXC variants and a specific lineage of A. xylosoxidans; however, a proportion of AXC-1-producing isolates corresponded to ST 182 and ST 447. In conclusion, this study provides valuable insights into the genetic context and kinetic properties of AXC-2, identified in A. ruhlandii. It also provides a thorough description of all AXC variants and their association with Achromobacter species and various lineages.

Polymyxin Resistance and Heteroresistance Are Common in Clinical Isolates of Achromobacter Species and Correlate with Modifications of the Lipid A Moiety of Lipopolysaccharide

The Achromobacter genus includes opportunistic pathogens that can cause chronic infections in immunocompromised patients, especially in people with cystic fibrosis (CF). Treatment of Achromobacter infections is complicated by antimicrobial resistance. In this study, a collection of Achromobacter clinical isolates, from CF and non-CF sources, was investigated for polymyxin B (PmB) resistance. Additionally, the effect of PmB challenge in a subset of isolates was examined and the presence of PmB-resistant subpopulations within the isolates was described. Further, chemical and mass spectrometry analyses of the lipid A of Achromobacter clinical isolates enabled the determination of the most common structures and showed that PmB challenge was associated with lipid A modifications that included the addition of glucosamine and palmitoylation and the concomitant loss of the free phosphate at the C-1 position. This study demonstrates that lipid A modifications associated with PmB resistance are prevalent in Achromobacter and that subresistant populations displaying the addition of positively charged residues and additional acyl chains to lipid A can be selected for and isolated from PmB-sensitive Achromobacter clinical isolates. IMPORTANCE Achromobacter species can cause chronic and potentially severe infections in immunocompromised patients, especially in those with cystic fibrosis. Bacteria cannot be eradicated due to Achromobacter's intrinsic multidrug resistance. We report that intrinsic resistance to polymyxin B (PmB), a last-resort antimicrobial peptide used to treat infections by multiresistant bacteria, is prevalent in Achromobacter clinical isolates; many isolates also display increased resistance upon PmB challenge. Analysis of the lipopolysaccharide lipid A moiety of several Achromobacter species reveals a penta-acylated lipid A, which in the PmB-resistant isolates was modified by the incorporation of glucosamine residues, an additional acyl chain, loss of phosphates, and hydroxylation of acyl chains, all of which can enhance PmB resistance in other bacteria. We conclude that PmB resistance, particularly in Achromobacter isolates from chronic respiratory infections, is a common phenomenon, and that Achromobacter lipid A displays modifications that may confer increased resistance to polymyxins and potentially other antimicrobial peptides.

Immunoinformatic Approach to Contrive a Next Generation Multi-Epitope Vaccine Against Achromobacter xylosoxidans Infections

Achromobacter xylosoxidans, previously identified as Alcaligenes xylosoxidans, is a rod-shaped, flagellated, non-fermenting Gram-negative bacterium that has the ability to cause diverse infections in humans. As a part of its intrinsic resistance to different antibiotics, Achromobacter spp. is also increasingly becoming resistant to Carbapenems. Lack of knowledge regarding the pathogen’s clinical features has led to limited efforts to develop countermeasures against infection. The current study utilized an immunoinformatic method to map antigenic epitopes (Helper T cells, B-cell and Cytotoxic-T cells) to design a vaccine construct. We found that 20 different epitopes contribute significantly to immune response instigation that was further supported by physicochemical analysis and experimental viability. The safety profile of our vaccine was tested for antigenicity, allergenicity, and toxicity against all the identified epitopes before they were used as vaccine candidates. The disulfide engineering was carried out in an area of high mobility to increase the stability of vaccine proteins. In order to determine if the constructed vaccine is compatible with toll-like receptor, the binding affinity of vaccine was investigated via molecular docking approach. With the in silico expression in host cells and subsequent immune simulations, we were able to detect the induction of both arms of the immune response, i.e., humoral response and cytokine induced response. To demonstrate its safety and efficacy, further experimental research is necessary.

The first report of the blaIMP-10 gene and complete sequence of the IMP-10-encoding plasmid p12NE515 from Pseudomonas aeruginosa in China

OBJECTIVE

To investigate a detailed genomic characterization of the bla_IMP-10-carrying plasmid p12NE515 from a Pseudomonas aeruginosa isolate in China.

METHODS

Plasmid p12NE515 was subjected to whole-genome sequencing and the complete sequence was compared with related plasmid sequences. Transferability of plasmid, carbapenemase activity and bacterial susceptibility profiles were determined to assess p12NE515-mediated resistance phenotypes.

RESULTS

P. aeruginosa 12NE515 was identified as a less common sequence type of ST1976. p12NE515 harboring bla_IMP-10 possessed a backbone identical to plasmid p60512-IMP (carrying bla_IMP-1), but the accessory resistance regions differed. Only one accessory module, Tn7339, was carried in p12NE515, and this transposon was an insertion sequence-mediated transposition unit generated by the insertion of a novel class 1 integron, In1814, at the downstream end of ISPa17. Here, bla_IMP-10 together with aacA7 was located in In1814, being at evolution stage III of Tn402-associated integron due to truncation of the tni module.

CONCLUSION

This study is the first to determine the complete sequence of a bla_IMP-10-carrying plasmid, and this is also the first report of a bla_IMP-10-producing strain in China. The prevalence of the bla_IMP-10 gene and the genetic characterization of the bla_IMP-10-carrying plasmid should be analyzed to provide deeper insight into the transmission mechanism of antimicrobial resistance genes.

Structure and Molecular Recognition Mechanism of IMP-13 Metallo-β-Lactamase

Multidrug resistance among Gram-negative bacteria is a major global public health threat. Metallo-β-lactamases (MBLs) target the most widely used antibiotic class, the β-lactams, including the most recent generation of carbapenems. Interspecies spread renders these enzymes a serious clinical threat, and there are no clinically available inhibitors. We present the crystal structures of IMP-13, a structurally uncharacterized MBL from the Gram-negative bacterium Pseudomonas aeruginosa found in clinical outbreaks globally, and characterize the binding using solution nuclear magnetic resonance spectroscopy and molecular dynamics simulations. The crystal structures of apo IMP-13 and IMP-13 bound to four clinically relevant carbapenem antibiotics (doripenem, ertapenem, imipenem, and meropenem) are presented. Active-site plasticity and the active-site loop, where a tryptophan residue stabilizes the antibiotic core scaffold, are essential to the substrate-binding mechanism. The conserved carbapenem scaffold plays the most significant role in IMP-13 binding, explaining the broad substrate specificity. The observed plasticity and substrate-locking mechanism provide opportunities for rational drug design of novel metallo-β-lactamase inhibitors, essential in the fight against antibiotic resistance.

Shigella flexneri: an emerging pathogen

Shigella flexneri is a leading etiologic agent of diarrhea in low socioeconomic countries. Notably, various serotypes in S. flexneri are reported from different regions of the world. The precise approximations of illness and death owing to shigellosis are missing in low socioeconomic countries, although it is widespread in different regions. The inadequate statistics available reveal S. flexneri to be a significant food and waterborne pathogen. All over the world, different antibiotic-resistant strains of S. flexneri serotypes have been emerged especially multidrug-resistant strains. Recently, increased resistance was observed in cephalosporins (3rd generation), azithromycin, and fluoroquinolones. There is a need for a continuous surveillance study on antibiotic resistance that will be helpful in the update of the antibiogram. The shigellosis burden can be reduced by adopting preventive measures like delivery of safe drinking water, suitable sanitation, and development of an effective and inexpensive multivalent vaccine. This review attempts to provide the recent findings of S. flexneri related to epidemiology and the emergence of multidrug resistance.

Proteomic identification of Axc, a novel beta-lactamase with carbapenemase activity in a meropenem-resistant clinical isolate of Achromobacter xylosoxidans

The development of antibiotic resistance during treatment is a threat to patients and their environment. Insight in the mechanisms of resistance development is important for appropriate therapy and infection control. Here, we describe how through the application of mass spectrometry-based proteomics, a novel beta-lactamase Axc was identified as an indicator of acquired carbapenem resistance in a clinical isolate of Achromobacter xylosoxidans. Comparative proteomic analysis of consecutively collected susceptible and resistant isolates from the same patient revealed that high Axc protein levels were only observed in the resistant isolate. Heterologous expression of Axc in Escherichia coli significantly increased the resistance towards carbapenems. Importantly, direct Axc mediated hydrolysis of imipenem was demonstrated using pH shift assays and ¹H-NMR, confirming Axc as a legitimate carbapenemase. Whole genome sequencing revealed that the susceptible and resistant isolates were remarkably similar. Together these findings provide a molecular context for the fast development of meropenem resistance in A. xylosoxidans during treatment and demonstrate the use of mass spectrometric techniques in identifying novel resistance determinants.

Dissemination of KPC-2-Encoding IncX6 Plasmids Among Multiple Enterobacteriaceae Species in a Single Chinese Hospital

Forty-five KPC-producing Enterobacteriaceae strains were isolated from multiple departments in a Chinese public hospital from 2014 to 2015. Genome sequencing of four representative strains, namely Proteus mirabilis GN2, Serratia marcescens GN26, Morganella morganii GN28, and Klebsiella aerogenes E20, indicated the presence of bla_KPC-2-carrying IncX6 plasmids pGN2-KPC, pGN26-KPC, pGN28-KPC, and pE20-KPC in the four strains, respectively. These plasmids were genetically closely related to one another and to the only previously sequenced IncX6 plasmid, pKPC3_SZ. Each of the plasmids carried a single accessory module containing the bla_KPC-2/3-carrying ΔTn6296 derivatives. The ΔTn6292 element from pGN26-KPC also contained qnrS, which was absent from all other plasmids. Overall, pKPC3_SZ-like bla_KPC-carrying IncX6 plasmids were detected by PCR in 44.4% of the KPC-producing isolates, which included K. aerogenes, P. mirabilis, S. marcescens, M. morganii, Escherichia coli, and Klebsiella pneumoniae, and were obtained from six different departments of the hospital. Data presented herein provided insights into the genomic diversity and evolution of IncX6 plasmids, as well as the dissemination and epidemiology of bla_KPC-carrying IncX6 plasmids among Enterobacteriaceae in a hospital setting.

Characterization of Tail Sheath Protein of N4-Like Phage phiAxp-3

Achromobacter phage phiAxp-3, an N4-like bacteriophage, specifically recognize Achromobacter xylosoxidans lipopolysaccharide (LPS) as its receptor. PhiAxp-3 tail sheath protein (TSP, ORF69) shares 54% amino acid sequence identity with the TSP of phage N4 (gp65); the latter functions as a receptor binding protein and interacts with the outer membrane receptor NfrA of its host bacterium. Thus, we hypothesized that ORF69 is the receptor-binding protein of phiAxp-3. In the present study, a series of ORF69 truncation variants was constructed to identify the part(s) of this protein essential for binding to A. xylosoxidans LPS. Phage adsorption and enzyme-linked immunosorbent assay showed that amino acids 795-1195 of the TSP, i.e., ORF69(795-1195), are sufficient and essential for receptor and binding. The optimum temperature and pH for the functions of ORF69 and ORF69(795-1195) are 4/25°C and 7, respectively. In vitro cytotoxicity assays showed that ORF69 and ORF69(795-1195) were respectively toxic and non-toxic to a human immortalized normal hepatocyte cell line (LO2; doses: 0.375-12 μg). The potential of this non-toxic truncated version of phiASP-3 TSP for clinical applications is discussed.

p1220-CTXM, a pKP048-related IncFIIK plasmid carrying bla CTX-M-14 and qnrB4

AIM

This study aimed to characterize plasmid-mediated antimicrobial resistance in clinical Klebsiella pneumoniae 1220 carrying bla _CTX-M-14 and qnrB4.

MATERIALS & METHODS

Plasmid p1220-CTXM was transformed from the 1220 isolate into Escherichia coli through conjugal transfer and then fully sequenced. Antimicrobial susceptibility was determined by VITEK.

RESULTS

p1220-CTXM was an IncFII_K plasmid genetically closely related to pKP048 and carried resistance markers including bla _CTX-M-14, bla _DHA-1, qnrB4, sul1 and qacEΔ1, all of which were harbored in a 35.7-kb multidrug-resistant region. bla _CTX-M-14 was located in a truncated ISEcp1-bla _CTX-M-14-orf477 transposition unit, and qnrB4 and bla _DHA-1 were in a truncated qnrB4-bla _DHA-1 region.

CONCLUSION

This study provided the insight into the co-occurrence of bla _CTX-M-14 and qnrB4 and the evolution of pKP048-related IncFII_K plasmids.

pSY153-MDR, a p12969-DIM-related mega plasmid carrying blaIMP-45 and armA, from clinical Pseudomonas putida

This work characterized mega plasmid pSY153-MDR, carrying bla_IMP-45 and armA, from a multidrug-resistant (MDR) Pseudomonas putida isolate from the urine of a cerebral infarction patient in China. The backbone of pSY153-MDR was closely related to Pseudomonas plasmids p12969-DIM, pOZ176, pBM413, pTTS12, and pRBL16, and could not be assigned to any of the known incompatibility groups. The accessory modules of pSY153-MDR were composed of 10 individual insertion sequence elements and two different MDR regions, and differed dramatically from the above plasmids. Fifteen non-redundant resistance markers were identified to be involved in resistance to at least eight distinct classes of antibiotics. All of these resistance genes were associated with mobile elements, and were embedded within the two MDR regions. bla_IMP-45 and armA coexisted in a Tn1403–Tn1548 region, which was generated from homologous recombination of Tn1403- and Tn1548-like transposons. The second copy of armA was a component of the ISCR28–armA–∆ISCR28 structure, representing a novel armA vehicle. This vehicle was located within In48, which was related to In363 and In1058. Data presented here provide a deeper insight into the evolutionary history of SY153, especially in regard to how it became extensively drug-resistant.

Sequencing of blaIMP-Carrying IncN2 Plasmids, and Comparative Genomics of IncN2 Plasmids Harboring Class 1 Integrons

This work presents the complete nucleotide sequences of p0801-IMP from Klebsiella pneumoniae, p7121-IMP from K. oxytoca, and p17285-IMP from Citrobacter freundii, which are recovered from three different cases of nosocomial infection. These three plasmids represent the first fully sequenced bla_IMP-carrying IncN2 plasmids. Further comparative genomics analysis of all the five integron-carrying IncN2 plasmids p0801-IMP, p7121-IMP, p17285-IMP, pJIE137, and p34983-59.134kb indicates that they possess conserved IncN2 backbones with limited genetic variations with respect to gene content and organization. Four class 1 integrons (bla_IMP-1-carrying In1223 in p0801-IMP/p7121-IMP, bla_IMP-8-carrying In655 in p17285-IMP, In27 in pJIE137, and In1130 in p34983-59.134kb), two insertion sequence-based transposition units (ISEcp1-orfRA1-14 in p17285-IMP, and ISEcp1-bla_CTX-M-62-Δorf477-orfRA1-14 in pJIE137), and a novel Tn1696-related transposon Tn6325 carrying In1130 in p34983-59.134kb are indentified in the plasmid accessory regions. In1223 and In655 represent ancestral Tn402-associated integrons, while In27 and In1130 belong to complex class 1 integrons. The relatively small IncN2 backbones are able to integrate different mobile elements which carry various resistance markers, promoting the accumulation and spread of antimicrobial resistance genes among enterobacterial species.

Architecture of Class 1, 2, and 3 Integrons from Gram Negative Bacteria Recovered among Fruits and Vegetables

The spread of antibiotic resistant bacteria throughout the food chain constitutes a public health concern. To understand the contribution of fresh produce in shaping antibiotic resistance bacteria and integron prevalence in the food chain, 333 antibiotic resistance Gram negative isolates were collected from organic and conventionally produced fruits (pears, apples, and strawberries) and vegetables (lettuces, tomatoes, and carrots). Although low levels of resistance have been detected, the bacterial genera identified in the assessed fresh produce are often described not only as environmental, but mostly as commensals and opportunistic pathogens. The genomic characterization of integron-harboring isolates revealed a high number of mobile genetic elements and clinically relevant antibiotic resistance genes, of which we highlight the presence of as mcr-1, qnrA1, bla_GES−11, mphA, and oqxAB. The study of class 1 (n = 8), class 2 (n = 3) and class 3 (n = 1) integrons, harbored by species such as Morganella morganii, Escherichia coli, Klebsiella pneumoniae, led to the identification of different integron promoters (PcW, PcH1, PcS, and PcW_TNG−10) and cassette arrays (containing drfA, aadA, cmlA, estX, sat, and bla_GES). In fact, the diverse integron backbones were associated with transposable elements (e.g., Tn402, Tn7, ISCR1, Tn2^*, IS26, IS1326, and IS3) that conferred greater mobility. This is also the first appearance of In1258, In1259, and In3-13, which should be monitored to prevent their establishment as successfully dispersed mobile resistance integrons. These results underscore the growing concern about the dissemination of acquired resistance genes by mobile elements in the food chain.

Characterization of integrons and novel cassette arrays in bacteria from clinical isloates in China, 2000-2014

Rapid dissemination of antibiotic resistance genes among bacterial isolates is an increasing problem in China. Integron, a conserved DNA sequence, which is carried on episomal genetic structures, plays a very important role in development of antibiotic resistance. This systematic analysis was based on MEDLINE and EMBASE databases. We summarized the distribution and proportion of different types of gene cassette arrays of integrons (including class 1, 2, 3 and atypical class 1 integron) from clinical bacteria isolates in China. Fifty-six literatures were included in this study. Most of the strains were Gram-negative bacteria (94.1%, 7,364/7,822) while only 5.9% strains were Gram-positive bacteria. Class 1 integrons were detected in 54.2% (3956/7295) Gram-negative strains. aadA2 was the most popular gene cassette array detected from 60 Gram-positive bacteria while dfrA17-aadA5 were detected in 426 Gram-negative bacteria. This study identified 12 novel gene cassette arrays which have not been previously found in any species. All the novel gene cassette arrays were detected from Gram-negative bacteria. A regional characteristic of distribution of integrons was presented in this study. The results highlight a need for continuous surveillance of integrons and provide a guide for future research on integron-mediated bacteria resistance.

Complete Nucleotide Sequence of IncP-1β Plasmid pDTC28 Reveals a Non-Functional Variant of the blaGES-Type Gene

Plasmid pDTC28 was isolated from the sediments of Haihe River using E. coli CV601 (gfp-tagged) as recipient and indigenous bacteria from the sediment as donors. This plasmid confers reduced susceptibility to tetracycline and sulfamethoxazole. The complete sequence of plasmid pDTC28 was 61,503 bp in length with an average G+C content of 64.09%. Plasmid pDTC28 belongs to the IncP-1β group by phylogenetic analysis. The backbones of plasmid pDTC28 and other IncP-1β plasmids are very classical and conserved, whereas the accessory regions of these plasmids are diverse. A bla_GES-5-like gene was found on the accessory region, and this bla_GES-5-like gene contained 18 silent mutations and 7 missense mutations compared with the bla_GES-5 gene. The mutations resulted in 7 amino acid substitutions in GES-5 carbapenemase, causing the loss of function of the bla_GES-5-like gene on plasmid pDTC28 against carbapenems and even β-lactams. The enzyme produced by the bla_GES-5-like gene cassette may be a new variant of GES-type enzymes. Thus, the plasmid sequenced in this study will expand our understanding of GES-type β-lactamases and provide insights into the genetic platforms used for the dissemination of GES-type genes.

Isolation and molecular characterisation of Achromobacter phage phiAxp-3, an N4-like bacteriophage

Achromobacter xylosoxidans, an opportunistic pathogen, is responsible for various nosocomial and community-acquired infections. We isolated phiAxp-3, an N4-like bacteriophage that infects A. xylosoxidans, from hospital waste and studied its genomic and biological properties. Transmission electron microscopy revealed that, with a 67-nm diameter icosahedral head and a 20-nm non-contractile tail, phiAxp-3 has features characteristic of Podoviridae bacteriophages (order Caudovirales). With a burst size of 9000 plaque-forming units and a latent period of 80 min, phiAxp-3 had a host range limited to only four A. xylosoxidans strains of the 35 strains that were tested. The 72,825 bp phiAxp-3 DNA genome, with 416-bp terminal redundant ends, contains 80 predicted open reading frames, none of which are related to virulence or drug resistance. Genome sequence comparisons place phiAxp-3 more closely with JWAlpha and JWDelta Achromobacter phages than with other N4 viruses. Using proteomics, we identified 25 viral proteins from purified phiAxp-3 particles. Notably, investigation of the phage phiAxp-3 receptor on the surface of the host cell revealed that lipopolysaccharide serves as the receptor for the adsorption of phage phiAxp-3. Our findings advance current knowledge about A. xylosoxidans phages in an age where alternative therapies to combat antibiotic-resistant bacteria are urgently needed.

Characterization of a novel Achromobacter xylosoxidans specific siphoviruse: phiAxp-1

Bacteriophages have recently been considered as an alternative biocontrol tool because of the widespread occurrence of antimicrobial-resistant Achromobacter xylosoxidans. Herein, we isolated a virulent bacteriophage (phiAxp-1) from a water sample of the Bohai sea of China that specifically infects A. xylosoxidans. Transmission electron microscopy revealed that phage phiAxp-1 belongs to the Siphoviridae. We sequenced the genome of phiAxp-1, which comprises 45,045 bp with 64 open reading frames. Most of the proteins encoded by phiAxp-1 have no similarity to sequences in the public databases. Twenty-one proteins with assigned functions share weak homology with those of other dsDNA bacteriophages infecting diverse hosts, such as Burkholderia phage KL1, Pseudomonas phage 73, Pseudomonas phage vB_Pae-Kakheti25, Pseudomonas phage vB_PaeS_SCH_Ab26, Acinetobacter phage IME_AB3 and Achromobacter phage JWX. The genome can be divided into different clusters for the head and tail structure, DNA replication and mazG. The sequence and genomic organization of bacteriophage phiAxp-1 are clearly distinct from other known Siphoviridae phages; therefore, we propose that it is a member of a novel genus of the Siphoviridae family. Furthermore, one-step growth curve and stability studies of the phage were performed, and the specific receptor of phiAxp-1 was identified as the lipopolysaccharide of A. xylosoxidans.