Clinical emergence of a novel extended-spectrum variant deriving from the OXY-1 β-lactamase

The genomic comparison of two Klebsiella michiganensis clinical isolates recovered from the same patient, one resistant to piperacillin-tazobactam and intermediate to cefotaxime, the other resistant to ceftazidime but susceptible to piperacillin-tazobactam, revealed one mutation in the blaOXY-1-24 gene accounting for a L169M substitution in the Ω loop. Cloning experiment in Escherichia coli demonstrated the contribution of this mutation to the hydrolysis spectrum extension towards ceftazidime and cefepime, whereas the resistance to piperacillin-tazobactam was reduced. To the best of our knowledge, this study shows for the first time that ceftazidime resistance can occur in vivo from OXY-1 precursor by structural alteration.

Whole-Genome Sequence and Pathogenicity Analysis of Providencia Heimbachae Causing Diarrhea in Weaned Piglets

Providencia heimbachae was previously identified in piglets with post-weaned diarrhea and associated with hindlimb paralysis. However, the pathogenic mechanisms and virulence factors of P. heimbachae are not fully known. Whole-genome sequence analysis will be helpful to extend our understanding of the characterization of P. heimbachae at a genomic level. In this study, we sequenced the whole genome of P. heimbachae for the first time using PacBio RS II sequencers and assembled de novo through hierarchical genome assembly process (HGAP). Furthermore, we performed further genome annotation. The genome of P. heimbachae 99101 consists of a circular chromosome (4,262,828 bp) and a circular plasmid (231,957 bp) with G + C contents of 40.43 and 47.16%, respectively. Genome-wide sequence analysis yielded a total of 286 predicted virulence factors, 178 resistance genes, 17 chaperone protein manipulators of fimbriae, 47 genes involved in the encoding of flagellin, 12 cell membrane-associated virulence genes, 18 Enterobacteriaceae common antigens, etc. Based on genome analysis, we preliminarily confirmed through animal experiments that the capsule was the virulence factor of P. heimbachae causing hindlimb paralysis in animals. Our study provides a genetic basis for further elucidation of the characteristics and functional mechanisms of P. heimbachae as a conditionally pathogenic bacterium, as well as a direction for research into the mechanism of action of P. heimbachae infecting humans, extending knowledge of P. heimbachae as an important zoonotic pathogen.

Enhanced activity against a third-generation cephalosporin by destabilization of the active site of a class A beta-lactamase

The β-lactamase BlaC conveys resistance to a broad spectrum of β-lactam antibiotics to its host Mycobacterium tuberculosis but poorly hydrolyzes third-generation cephalosporins, such as ceftazidime. Variants of other β-lactamases have been reported to gain activity against ceftazidime at the cost of the native activity. To understand this trade-off, laboratory evolution was performed, screening for enhanced ceftazidime activity. The variant BlaC Pro167Ser shows faster breakdown of ceftazidime, poor hydrolysis of ampicillin and only moderately reduced activity against nitrocefin. NMR spectroscopy, crystallography and kinetic assays demonstrate that the resting state of BlaC P167S exists in an open and a closed state. The open state is more active in the hydrolysis of ceftazidime. In this state the catalytic residue Glu166, generally believed to be involved in the activation of the water molecule required for deacylation, is rotated away from the active site, suggesting it plays no role in the hydrolysis of ceftazidime. In the closed state, deacylation of the BlaC-ceftazidime adduct is slow, while hydrolysis of nitrocefin, which requires the presence of Glu166 in the active site, is barely affected, providing a structural explanation for the trade-off in activities.

Evaluation of Phenotypic Tests to Detect Extended-Spectrum β-Lactamase (ESBL)-Producing Klebsiella oxytoca Complex Strains

Klebsiella oxytoca complex (KoC) species may overproduce their chromosomal class A OXY β-lactamases, conferring reduced susceptibility to piperacillin-tazobactam, expanded-spectrum cephalosporins and aztreonam. Moreover, since clavulanate maintains its ability to inhibit these enzymes, the resulting resistance phenotype may falsely resemble the production of acquired extended-spectrum β-lactamases (ESBLs). In this work, a collection of 44 KoC strains of human and animal origin was characterized with whole-genome sequencing (WGS) and broth microdilution (BMD) susceptibility testing. Comparison of ESBL producers (n = 11; including CTX-M-15 [n = 6] and CTX-M-1 [n = 5] producers) and hyperproducers of OXYs (n = 21) showed certain phenotypic differences: piperacillin-tazobactam (MIC_90s: 16 versus >64 μg/mL), cefotaxime (MIC_90s: 64 versus 4 μg/mL), ceftazidime (MIC_90s: 32 versus 4 μg/mL), cefepime (MIC_90s: 8 versus 4 μg/mL) and associated resistance to non-β-lactams (e.g., trimethoprim-sulfamethoxazole: 90.9% versus 14.3%, respectively). However, a clear phenotype-based distinction between the two groups was difficult. Therefore, we evaluated 10 different inhibitor-based confirmatory tests to allow such categorization. All tests showed a sensitivity of 100%. However, only combination disk tests (CDTs) with cefepime/cefepime-clavulanate and ceftazidime/ceftazidime-clavulanate or the double-disk synergy test (DDST) showed high specificity (100%, 95.5%, and 100%, respectively). All confirmatory tests in BMD or using the MIC gradient strip did not perform well (specificity, ≤87.5%). Of note, ceftazidime/ceftazidime-avibactam tests also exhibited low specificity (CDT, 87.5%; MIC gradient strip, 77.8%). Our results indicate that standard antimicrobial susceptibility profiles can raise some suspicion, but only the use of cefepime/cefepime-clavulanate CDT or DDST can guarantee distinction between ESBL-producing KoC strains and those hyperproducing OXY enzymes.

GAMBIT (Genomic Approximation Method for Bacterial Identification and Tracking): A methodology to rapidly leverage whole genome sequencing of bacterial isolates for clinical identification

Whole genome sequencing (WGS) of clinical bacterial isolates has the potential to transform the fields of diagnostics and public health. To realize this potential, bioinformatic software that reports identification results needs to be developed that meets the quality standards of a diagnostic test. We developed GAMBIT (Genomic Approximation Method for Bacterial Identification and Tracking) using k-mer based strategies for identification of bacteria based on WGS reads. GAMBIT incorporates this algorithm with a highly curated searchable database of 48,224 genomes. Herein, we describe validation of the scoring methodology, parameter robustness, establishment of confidence thresholds and the curation of the reference database. We assessed GAMBIT by way of validation studies when it was deployed as a laboratory-developed test in two public health laboratories. This method greatly reduces or eliminates false identifications which are often detrimental in a clinical setting.

Molecular Epidemiology of Extended-Spectrum Beta-Lactamase and AmpC Producing Enterobacteriaceae among Sepsis Patients in Ethiopia: A Prospective Multicenter Study

Extended-spectrum beta-lactamases (ESBLs) and AmpC producing Enterobacteriaceae are public health threats. This study aims to characterize ESBL and AmpC producing Enterobacteriaceae isolated from sepsis patients. A multicenter study was conducted at four hospitals located in central (Tikur Anbessa and Yekatit 12), southern (Hawassa) and northern (Dessie) parts of Ethiopia. Blood culture was performed among 1416 sepsis patients. Enterobacteriaceae (n = 301) were confirmed using MALDI-TOF and subjected for whole genome sequencing using the Illumina (HiSeq 2500) system. The overall genotypic frequencies of ESBL and AmpC producing Enterobacteriaceae were 75.5% and 14%, respectively. The detection of ESBL producing Enterobacteriaceae at Hawassa, Yekatit 12, Tikur Anbessa and Dessie was 95%, 90%, 82% and 55.8%, respectively. The detection frequency of bla_CTX-M, bla_TEM and bla_SHV genes was 73%, 63% and 33%, respectively. The most frequently detected ESBL gene was bla_CTX-M-15 (70.4%). The common AmpC genes were bla_ACT (n = 22) and bla_CMY (n = 13). Of Enterobacteriaceae that harbored AmpC (n = 42), 71% were ESBL co-producers. Both bla_TEM-1B (61.5%) and bla_SHV-187 (27.6%) were the most frequently detected variants of bla_TEM and bla_SHV, respectively. The molecular epidemiology of ESBL producing Enterobacteriaceae showed high frequencies and several variants of ESBL and AmpC genes. Good antimicrobial stewardship and standard bacteriological laboratory services are necessary for the effective treatment of ESBL producing Enterobacteriaceae.

Klebsiella oxytoca Complex: Update on Taxonomy, Antimicrobial Resistance, and Virulence

Klebsiella oxytoca is actually a complex of nine species-Klebsiella grimontii, Klebsiella huaxiensis, Klebsiella michiganensis, K. oxytoca, Klebsiella pasteurii, Klebsiella spallanzanii, and three unnamed novel species. Phenotypic tests can assign isolates to the complex, but precise species identification requires genome-based analysis. The K. oxytoca complex is a human commensal but also an opportunistic pathogen causing various infections, such as antibiotic-associated hemorrhagic colitis (AAHC), urinary tract infection, and bacteremia, and has caused outbreaks. Production of the cytotoxins tilivalline and tilimycin lead to AAHC, while many virulence factors seen in Klebsiella pneumoniae, such as capsular polysaccharides and fimbriae, have been found in the complex; however, their association with pathogenicity remains unclear. Among the 5,724 K. oxytoca clinical isolates in the SENTRY surveillance system, the rates of nonsusceptibility to carbapenems, ceftriaxone, ciprofloxacin, colistin, and tigecycline were 1.8%, 12.5%, 7.1%, 0.8%, and 0.1%, respectively. Resistance to carbapenems is increasing alarmingly. In addition to the intrinsic bla_OXY, many genes encoding β-lactamases with varying spectra of hydrolysis, including extended-spectrum β-lactamases, such as a few CTX-M variants and several TEM and SHV variants, have been found. bla_KPC-2 is the most common carbapenemase gene found in the complex and is mainly seen on IncN or IncF plasmids. Due to the ability to acquire antimicrobial resistance and the carriage of multiple virulence genes, the K. oxytoca complex has the potential to become a major threat to human health.

KPC Beta-Lactamases Are Permissive to Insertions and Deletions Conferring Substrate Spectrum Modifications and Resistance to Ceftazidime-Avibactam

To explore the mutational possibilities of insertions and deletions (indels) in the Klebsiella pneumoniae carbapenemase (KPC) beta-lactamase, we selected for ceftazidime-avibactam-resistant mutants. Of 96 screened mutants, we obtained 19 indels (2 to 15 amino acids), all located in the loops surrounding the active site. Three antibiotic susceptibility phenotypes emerged: an extended-spectrum-beta-lactamase-like phenotype, an activity restricted to ceftazidime, and a carbapenem-susceptible KPC-like phenotype. Tolerance for indels reflects the evolvability of KPC beta-lactamase, which could challenge the therapeutic management of patients.

A Lateral Flow Immunoassay for the Rapid Identification of CTX-M-Producing Enterobacterales from Culture Plates and Positive Blood Cultures

We have developed a lateral flow immunoassay (LFIA), named NG-Test CTX-M MULTI (NG-Test), to detect group 1, 2, 8, 9, 25 CTX-M producers from agar plates and from positive blood cultures in less than 15 min. The NG-Test was validated retrospectively on 113 well-characterized enterobacterial isolates, prospectively on 102 consecutively isolated ESBL-producers from the Bicêtre hospital and on 100 consecutive blood cultures positive with a gram-negative bacilli (GNB). The NG-Test was able to detect all CTX-M producers grown on the different agar plates used in clinical microbiology laboratories. No false positive nor negative results were observed. Among the 102 consecutive ESBL isolates, three hyper mucous isolates showed an incorrect migration leading to invalid results (no control band). Using an adapted protocol, the results could be validated. The NG-Test detected 99/102 ESBLs as being CTX-Ms. Three SHV producers were not detected. Among the 100 positive blood cultures with GNB tested 10/11 ESBL-producers were detected (8 CTX-M-15, 2 CTX-M-27). One SHV-2-producing-E. cloacae was missed. The NG-Test CTX-M MULTI showed 100% sensitivity and specificity with isolates cultured on agar plates and was able to detect 98% of the ESBL-producers identified in our clinical setting either from colonies or from positive blood cultures.

Investigating colistin drug resistance: The role of high-throughput sequencing and bioinformatics

Bacterial infections involving antibiotic-resistant gram-negative bacteria continue to increase and represent a major global public health concern. Resistance to antibiotics in these bacteria is mediated by chromosomal and/or acquired resistance mechanisms, these give rise to multi-drug resistant (MDR), extensive-drug resistant (XDR) or pan-drug resistant (PDR) bacterial strains. Most recently, plasmid-mediated resistance to colistin, an antibiotic that had been set apart as the last resort antibiotic in the treatment of infections involving MDR, XDR and PDR gram-negative bacteria has been reported. Plasmid-mediated colistin resistant gram-negative bacteria have been described to be PDR, implying a state devoid of alternative antibiotic therapeutic options. This review concisely describes the evolution of antibiotic resistance to plasmid-mediated colistin resistance and discusses the potential role of high-throughput sequencing technologies, genomics, and bioinformatics towards improving antibiotic resistance surveillance, the search for novel drug targets and precision antibiotic therapy focused at combating colistin resistance, and antibiotic resistance as a whole.

Investigating colistin drug resistance: The role of high-throughput sequencing and bioinformatics

Bacterial infections involving antibiotic resistant gram-negative bacteria continue to increase and represent a major global public health concern. Resistance to antibiotics in these bacteria is mediated by chromosomal and/or acquired resistance mechanisms, these give rise to multi-drug resistant (MDR) or extensive drug resistant (XDR) bacterial strains. Most recently, a novel acquired plasmid mediated resistance mechanism to colistin, an antibiotic that had been set apart as the last resort antibiotic in the treatment of infections involving MDR and XDR gram-negative bacteria, has been reported. Plasmid mediated colistin resistant gram-negative bacteria have been described to be pan-drug resistant, implying a state devoid of alternative antibiotic therapeutic options. This review describes the evolution of antibiotic resistance to plasmid mediated colistin resistance, and discusses the potential role of high-throughput sequencing technologies, genomics and bioinformatics towards improving antibiotic resistance surveillance, the search for novel drug targets and precision antibiotic therapy focused at combating colistin resistance, and antimicrobial resistance as a whole.

The proper structure of a biosafety system as a way of reducing the vulnerability of a society, economy or state in the face of a biogenic threat

To understand how vulnerable are a society, an economy and a state in the face of a biohazard, one should attempt to identify any potential holes in the national biosafety system, such as the lack of important components or technologies for biological monitoring and the inadequacy of existing analytical methods used to prevent or counteract biogenic threats. In Russia, biological monitoring is quite advanced. However, the agencies that ensure proper functioning of its components lack collaboration and do not form a well-coordinated network. Each of such agencies alone cannot provide comprehensive information on the subject. In the Russian Federation, there are at least 4 state-funded programs that collect epidemiological data and are quite efficient in performing the narrow task of monitoring infections. But because there is no central database where epidemiological data can be channeled and subsequently shared, these agencies do not complete each other. This leaves the Russian society, economy and state vulnerable to biogenic threats. We need an adequately organized, modern, fully functional and effective system for monitoring biohazards that will serve as a basis for the national biosafety system and also a tool for the identification and elimination of its weaknesses.

Practical issues in implementing whole-genome-sequencing in routine diagnostic microbiology

BACKGROUND

Next generation sequencing (NGS) is increasingly being used in clinical microbiology. Like every new technology adopted in microbiology, the integration of NGS into clinical and routine workflows must be carefully managed.

AIM

To review the practical aspects of implementing bacterial whole genome sequencing (WGS) in routine diagnostic laboratories.

SOURCES

Review of the literature and expert opinion.

CONTENT

In this review, we discuss when and how to integrate whole genome sequencing (WGS) in the routine workflow of the clinical laboratory. In addition, as the microbiology laboratories have to adhere to various national and international regulations and criteria for their accreditation, we deliberate on quality control issues for using WGS in microbiology, including the importance of proficiency testing. Furthermore, the current and future place of this technology in the diagnostic hierarchy of microbiology is described as well as the necessity of maintaining backwards compatibility with already established methods. Finally, we speculate on the question of whether WGS can entirely replace routine microbiology in the future and the tension between the fact that most sequencers are designed to process multiple samples in parallel whereas for optimal diagnosis a one-by-one processing of the samples is preferred. Special reference is made to the cost and turnaround time of WGS in diagnostic laboratories.

IMPLICATIONS

Further development is required to improve the workflow for WGS, in particular to shorten the turnaround time, reduce costs, and streamline downstream data analyses. Only when these processes reach maturity will reliance on WGS for routine patient management and infection control management become feasible, enabling the transformation of clinical microbiology into a genome-based and personalized diagnostic field.

Reprint of "Application of next generation sequencing in clinical microbiology and infection prevention"

Current molecular diagnostics of human pathogens provide limited information that is often not sufficient for outbreak and transmission investigation. Next generation sequencing (NGS) determines the DNA sequence of a complete bacterial genome in a single sequence run, and from these data, information on resistance and virulence, as well as information for typing is obtained, useful for outbreak investigation. The obtained genome data can be further used for the development of an outbreak-specific screening test. In this review, a general introduction to NGS is presented, including the library preparation and the major characteristics of the most common NGS platforms, such as the MiSeq (Illumina) and the Ion PGM™ (ThermoFisher). An overview of the software used for NGS data analyses used at the medical microbiology diagnostic laboratory in the University Medical Center Groningen in The Netherlands is given. Furthermore, applications of NGS in the clinical setting are described, such as outbreak management, molecular case finding, characterization and surveillance of pathogens, rapid identification of bacteria using the 16S-23S rRNA region, taxonomy, metagenomics approaches on clinical samples, and the determination of the transmission of zoonotic micro-organisms from animals to humans. Finally, we share our vision on the use of NGS in personalised microbiology in the near future, pointing out specific requirements.

Exploring the Role of the Ω-Loop in the Evolution of Ceftazidime Resistance in the PenA β-Lactamase from Burkholderia multivorans, an Important Cystic Fibrosis Pathogen

The unwelcome evolution of resistance to the advanced generation cephalosporin antibiotic, ceftazidime is hindering the effective therapy of Burkholderia cepacia complex (BCC) infections. Regrettably, BCC organisms are highly resistant to most antibiotics, including polymyxins; ceftazidime and trimethoprim-sulfamethoxazole are the most effective treatment options. Unfortunately, resistance to ceftazidime is increasing and posing a health threat to populations susceptible to BCC infection. We found that up to 36% of 146 tested BCC clinical isolates were nonsusceptible to ceftazidime (MICs ≥ 8 μg/ml). To date, the biochemical basis for ceftazidime resistance in BCC is largely undefined. In this study, we investigated the role of the Ω-loop in mediating ceftazidime resistance in the PenA β-lactamase from Burkholderia multivorans, a species within the BCC. Single amino acid substitutions were engineered at selected positions (R164, T167, L169, and D179) in the PenA β-lactamase. Cell-based susceptibility testing revealed that 21 of 75 PenA variants engineered in this study were resistant to ceftazidime, with MICs of >8 μg/ml. Under steady-state conditions, each of the selected variants (R164S, T167G, L169A, and D179N) demonstrated a substrate preference for ceftazidime compared to wild-type PenA (32- to 320-fold difference). Notably, the L169A variant hydrolyzed ceftazidime significantly faster than PenA and possessed an ∼65-fold-lower apparent K_i (K_iapp) than that of PenA. To understand why these amino acid substitutions result in enhanced ceftazidime binding and/or turnover, we employed molecular dynamics simulation (MDS). The MDS suggested that the L169A variant starts with the most energetically favorable conformation (-28.1 kcal/mol), whereas PenA possessed the most unfavorable initial conformation (136.07 kcal/mol). In addition, we observed that the spatial arrangement of E166, N170, and the hydrolytic water molecules may be critical for enhanced ceftazidime hydrolysis by the L169A variant. Importantly, we found that two clinical isolates of B. multivorans possessed L169 amino acid substitutions (L169F and L169P) in PenA and were highly resistant to ceftazidime (MICs ≥ 512 μg/ml). In conclusion, substitutions in the Ω-loop alter the positioning of the hydrolytic machinery as well as allow for a larger opening of the active site to accommodate the bulky R1 and R2 side chains of ceftazidime, resulting in resistance. This analysis provides insights into the emerging phenotype of ceftazidime-resistant BCC and explains the evolution of amino acid substitutions in the Ω-loop of PenA of this significant clinical pathogen.

Application of next generation sequencing in clinical microbiology and infection prevention

Current molecular diagnostics of human pathogens provide limited information that is often not sufficient for outbreak and transmission investigation. Next generation sequencing (NGS) determines the DNA sequence of a complete bacterial genome in a single sequence run, and from these data, information on resistance and virulence, as well as information for typing is obtained, useful for outbreak investigation. The obtained genome data can be further used for the development of an outbreak-specific screening test. In this review, a general introduction to NGS is presented, including the library preparation and the major characteristics of the most common NGS platforms, such as the MiSeq (Illumina) and the Ion PGM™ (ThermoFisher). An overview of the software used for NGS data analyses used at the medical microbiology diagnostic laboratory in the University Medical Center Groningen in The Netherlands is given. Furthermore, applications of NGS in the clinical setting are described, such as outbreak management, molecular case finding, characterization and surveillance of pathogens, rapid identification of bacteria using the 16S-23S rRNA region, taxonomy, metagenomics approaches on clinical samples, and the determination of the transmission of zoonotic micro-organisms from animals to humans. Finally, we share our vision on the use of NGS in personalised microbiology in the near future, pointing out specific requirements.

Kinetic characterization of GES-22 β-lactamase harboring the M169L clinical mutation

The class A β-lactamase GES-22 has been identified in Acinetobacter baumannii isolates in Turkey, and subsequently shown to differ from GES-11 by a single substitution (M169L). Because M169 is part of the omega loop, a structure that is known to have major effects on substrate selectivity in class A β-lactamases, we expressed, purified and kinetically characterized this novel variant. Our results show that compared with GES-11^{6 × His}, GES-22^{6 × His} displays more efficient hydrolysis of penicillins, and aztreonam, but a loss of efficiency against ceftazidime. In addition, the M169L substitution confers on GES-22 more efficient hydrolysis of the mechanistic inhibitors clavulanic acid and sulbactam. These effects are highly similar to other mutations at the homologous position in other class A β-lactamases, suggesting that this methionine has a key structural role in aligning active site residues and in substrate selectivity across the class.