Evaluation of susceptibility testing methods for Burkholderia cepacia complex: a comparison of broth microdilution, agar dilution, gradient strip and EUCAST disc diffusion

Evaluation of antimicrobial susceptibility testing methods for Burkholderia cepacia complex isolates from people with and without cystic fibrosis

The Burkholderia cepacia complex (BCC) is a group of Gram-negative bacteria that cause opportunistic infections, most notably in people with cystic fibrosis (CF), and have been associated with outbreaks caused by contaminated medical products. Antimicrobial susceptibility testing (AST) is often used to guide treatment for BCC infections, perhaps most importantly in people with CF who are being considered for lung transplant. However, recent studies have highlighted problems with AST methods. Here, we address limitations from previous studies to further evaluate BCC AST methods. We assessed the performance of reference broth microdilution (BMD), disk diffusion (DD) using Mueller-Hinton agar (MHA) from three manufacturers, agar dilution (AD), and gradient diffusion (ETEST) for ceftazidime (CAZ), levofloxacin (LVX), meropenem (MEM), minocycline (MIN), and trimethoprim-sulfamethoxazole (TMP-SMX) on a set of 205 BCC isolates. The isolate set included 100 isolates from people with CF and 105 isolates from people without CF from a variety of sources, which enabled us to systematically evaluate whether specimen source impacts AST performance. For all BCC isolates, BMD reproducibility was 93%, 98%, 99%, 98%, and 96% for CAZ, LVX, MEM, MIN, and TMP-SMX, respectively. Using BMD as the comparator method, we show that DD, AD, and ETEST perform poorly, with neither MHA manufacturer nor specimen source significantly impacting method performance. Based on our data, we recommend that routine AST should not be performed for BCC isolates. If a provider requests AST, clinical microbiology laboratories should perform Clinical and Laboratory Standards Institute reference methodology for BMD (stored frozen) and report MIC only.IMPORTANCEAntimicrobial susceptibility testing for the Burkholderia cepacia complex (BCC) is often used to determine eligibility for lung transplant in people with cystic fibrosis. However, problems with method performance have been reported. Here, we systematically evaluate the performance of reference broth microdilution, disk diffusion, agar dilution, and gradient diffusion (ETEST) for BCC organisms isolated from people with and without cystic fibrosis. We show that broth microdilution reproducibility is acceptable for levofloxacin, meropenem, minocycline, and trimethoprim-sulfamethoxazole, while ceftazidime was just below the acceptability cut-off. Regardless of specimen source, the results from disk diffusion, agar dilution, and ETEST do not correlate with broth microdilution. Based on these findings, we recommend that antimicrobial susceptibility testing should not be routinely performed for BCC, and if requested by the provider, only broth microdilution following Clinical and Laboratory Standards Institute guidelines should be used. Providers should be aware of the significant limitations of antimicrobial susceptibility testing methods for BCC.

Urinary tract infections with Burkholderia cepacia. A narrative review

Burkholderia cepacia is an opportunistic Gram-negative bacillus that is found naturally in soil and water and usually causes respiratory infections in patients with cystic pulmonary fibrosis. Few cases of urinary tract infections with B. cepacia have been described in the literature, all of them clinical case presentations or case series. Therefore, we have compiled the data from the literature on this topic in a review to gain a better understanding of the etiopathogenesis, diagnosis and treatment methods of this disease. B. cepacia can lead to multidrug-resistant urinary tract infections in hospitals when surfaces and medical equipment are contaminated. The diagnosis is made after the onset of postoperative febrile syndrome or prolonged hospitalization in the intensive care unit. The evolution can be unfavorable, with the occurrence of sepsis and increased mortality.

Case Report: The Conundrum of What to Pick? Antibiotic Susceptibility Variability in Burkholderia cenocepacia in Cystic Fibrosis: Implications for Antibiotic Susceptibility Testing and Treatment

Within cystic fibrosis microbiology, there is often mismatch between the antibiotic susceptibility result of an isolated bacterial pathogen and the clinical outcome, when the patient is treated with the same antibiotic. The reasoning for this remains largely elusive. Antibiotic susceptibility to four antibiotics (ceftazidime, meropenem, minocycline and trimethoprim-sulfamethoxazole) was determined in consecutive isolates (n = 11) from an adult cystic fibrosis patient, over a 63 month period. Each isolate displayed its own unique resistotype. The first isolate was sensitive to all four antibiotics, in accordance with Clinical and Laboratory Standards Institute methodology and interpretative criteria. Resistance was first detected at four months, showing resistance to ceftazidime and meropenen and intermediate resistance to minocycline and trimethoprim-sulfamethoxazole. Pan resistance was first detected at 18 months (resistotype IV), with three resistotypes (I, II and III) preceding this complete resistotype. The bacterium continued to display further antibiotic susceptibility heterogeneity for the next 45 months, with the description of an additional seven resistotypes (resistotypes V-XI). The Relative Resistance Index of this bacterium over the 63 month period showed no relationship between the development of antibiotic resistance and time. Adoption of mathematical modelling employing multinomial distribution demonstrated that large numbers of individual colony picks (>40/sputum), would be required to be 78% confident of capturing all 11 resistotypes present. Such a requirement for large numbers of colony picks combined with antibiotic susceptibility-related methodological problems creates a conundrum in biomedical science practice, in providing a robust assay that will capture antibiotic susceptibility variation, be pragmatic and cost-effective to deliver as a pathology service, but have the reliability to help clinicians select appropriate antibiotics for their patients. This study represents an advance in biomedical science as it demonstrates potential variability in antibiotic susceptibility testing with Burkholderia cenocepacia. Respiratory physicians and paediatricians need to be made aware of such variation by biomedical scientists at the bench, so that clinicians can contextualise the significance of the reported susceptibility result, when selecting appropriate antibiotics for their cystic fibrosis patient. Furthermore, consideration needs to be given in providing additional guidance on the laboratory report to highlight this heterogeneity to emphasise the potential for misalignment between susceptibility result and clinical outcome.

Showing the limitations of available phenotypic assays to detect Burkholderia pseudomallei from clinical specimens in Nigeria

The genus Burkholderia comprises Gram-negative bacteria that are metabolically complex and versatile, often thriving in hostile settings. Burkholderia pseudomallei , the causative agent of melioidosis, is a prominent member of the genus and a clinical pathogen in tropical and sub-tropical regions. This pathogen is well known for its multidrug resistance and possible bioweapon potential. There is currently no report of the pathogen from clinical specimens in Nigeria, which might be due to misdiagnosis with phenotypic assays. This study aims to explore the accuracy of the use of phenotypic assays to diagnose B. pseudomallei in Nigeria. Two hundred and seventeen clinical samples and 28 Gram-negative clinical isolates were collected and analysed using Ashdown's selective agar and monoclonal antibody-based latex agglutination. Species-level identification was achieved using the analytical profile index (API) 20NE system. The susceptibility of the isolates to nine different antimicrobial agents was determined using the disc diffusion method. A total of seventy-four culture-positive isolates were obtained using Ashdown's selective agar. Twenty-two of these isolates were believed to be B. pseudomallei through the monoclonal antibody-based latex agglutination test and the API 20NE system subsequently identified 14 isolates as Burkholderia . The predominant Burkholderia species was B. cepacia with an isolation rate of 30.8 % (8/26). No isolate was distinctively identified as B. pseudomallei but five isolates were strongly suspected to be B. pseudomallei with similarity indices ranging from 81.9-91.3 %. Other bacterial species with definitive identity include Aeromonas sp., Sphingomonas sp. and Pseudomonas aeruginosa . The antibiotic susceptibility results revealed an overall resistance to amoxicillin-clavullanic acid of 71.4 %, to cefepime of 33.3 %, to trimethoprim-sulfamethoxazole of 38.1 %, to piperacillin-tazobactam of 33.3 %, to imipenem of 66.7 %, to doxycycline of 57.1% and to ceftazidime of 66.7 %. The highest intermediate resistance was observed for cefepime and piperacillin-tazobactam with a value of 66.7 % each, while there was no intermediate resistance for gentamicin, colistin and imipenem. Our findings, therefore, show that phenotypic assays alone are not sufficient in the diagnosis of melioidosis. Additionally, they provide robust support for present and future decisions to expand diagnostic capability for melioidosis beyond phenotypic assays in low-resource settings.

In vitro susceptibility of nonfermenting Gram-negative rods to meropenem-vaborbactam and delafloxacin

Aim: Meropenem-vaborbactam and delafloxacin activities were not assessed against Achromobacter spp. (Achr), Burkholderia cepacia complex (Bcc) and Stenotrophomonas maltophilia (Smal). Methodology: A total of 106 Achr, 57 Bcc and 100 Smal were tested with gradient diffusion test of meropenem-vaborbactam, delafloxacin and comparators. Results: Meropenem-vaborbactam MIC₅₀ were 4 μg/ml for Achr, 1 μg/ml for B. cepacia, 2 μg/ml for B. cenocepacia and B. multivorans, and 32 μg/ml for Smal. Delafloxacin MIC₅₀ were 4 μg/ml for Achr, 0.25 μg/ml for B. cepacia and B. multivorans, 2 μg/ml for B. cenocepacia, and 0.5 μg/m for Smal. meropenem-vaborbactam MICs were fourfold lower than meropenem for 28.3% Achr, 77.2% B. cepacia, 53.8% B. cenocepacia and 77.2% B. multivorans. Conclusion: Meropenem-vaborbactam and delafloxacin are in vitro active against Bcc and Achr.

Hinokitiol inhibits Aspergillus fumigatus by interfering with the cell membrane and cell wall

Hinokitiol (β-thujaplicin) is an important component of the essential oil extracted from Chamaecyparis obtuse, which prevents the decay and decomposition of temple and shrine buildings in Japan. Hinokiol has been shown to have a detrimental effect on various fungi such as Candida albicans and saprophytic fungi. However how hinokitiol works against Aspergillus fumigatus (A. fumigatus) has not been claimed. This study aims to investigate the adverse effects of hinokitiol on the disruption of the cell wall and cell membrane of A. fumigatus and to explore possible potential mechanisms or pathways. According to our results, hinokitiol negatively altered mycelium morphology, growth density, and cell plasma composition content. When incubated with human corneal epithelial cells (HCECs), hinokitiol saw a safe effect with concentrations below 12 μg/ml. Hinokitiol was shown to increase the cell membrane's permeability by decreasing the cell membrane's ergosterol content. The integrity of the cell wall was disrupted, as well as a significant increase in chitin degradation and chitinase activity. As determined by RNA-seq results, subsequent analysis, and qRT-PCR, altered transcript levels of cell walls and cell membranes-related genes (such as eglC) illustrated how hinokitiol affected the genetic profile of A. fumigatus. With this study, we recommend hinokitiol as an effective anti-A. fumigatus agent by reducing the amounts of key components in the cell wall and membrane by preventing production and accelerating breakdown.

Burkholderia cepacia Infections at Sites Other than the Respiratory Tract: A Large Case Series from a Tertiary Referral Hospital in Lebanon

Objectives

The Burkholderia cepacia complex (Bcc), which was originally thought to be a single species, represents a group of 24 distinct species that are often resistant to multiple antibiotics, and usually known to cause life-threatening pulmonary infections in cystic fibrosis patients. Herein we describe a series of non-respiratory Bcc infections, the risk factors and epidemiologic factors, in addition to the clinical course.

Patients and methods

This is a retrospective chart review of 44 patients with documented B. cepacia infections isolated from sites other than the respiratory tract admitted between June 2005 and February 2020 to the American University of Beirut Medical Center (AUBMC), a tertiary referral hospital for Lebanon and the Middle East region. The epidemiological background of these patients, their underlying risk factors, the used antibiotic regimens, and the sensitivities of the B. cepacia specimens were collected.

Results

The majority of the Bcc infections (26/44, 59.1%) were hospital-acquired infections. The most common nationality of the patients was Iraqi (18/44, 40.9%), and the most common site of infection was bacteremia (17/44, 38.6%), followed by skin and soft tissues infections (16/44, 36.4%) and vertebral osteomyelitis (8/44, 18.2%). Most of the isolated B. cepacia were susceptible to ceftazidime, carbapenems, followed by TMP-SMX. Patients responded well to therapy with good overall outcome.

Conclusions

Bcc can cause infections outside the respiratory tract, mostly as hospital-acquired infections and in immunocompromised patients. Most patients were referred from countries inflicted by wars raising the possibility of a potential role of conflicts which need to be investigated in future studies. Directed therapy according to susceptibility results proved effective in most patients.

Susceptibility of Burkholderia cepacia Complex to Ceftazidime/Avibactam and Standard Drugs of Treatment for Cystic Fibrosis Patients

Burkholderia cepacia complex (Bcc) in airways of patients with cystic fibrosis (CF) is associated with an increased morbidity and mortality. A huge range of intrinsic antimicrobial resistances challenges the treatment of Bcc infections. The aim was to assess the susceptibility of Bcc to ceftazidime/avibactam and standard drugs for the treatment for CF patients and to determine the respective genomic determinants of resistance. Bcc isolates (n = 64) from a prospective multicenter study of CF airway pathogens (2004-2020, Germany) were subjected to broth microdilution and minimal inhibitory concentrations were interpreted with European Committee on Antimicrobial Susceptibility Testing and Clinical & Laboratory Standards Institute breakpoints. A synergism between aztreonam and avibactam was tested using ceftazidime/avibactam disks with or without aztreonam. Plasmids and chromosomes of all isolates were screened for antimicrobial resistance genes. The highest susceptibility rate was detected for trimethoprim/sulfamethoxazole (83%), followed by ceftazidime/avibactam (78%), ceftazidime (53%), levofloxacin (39%) and meropenem (27%). The median inhibition zone diameters of ceftazidime-avibactam and ceftazidime/avibactam plus aztreonam were equal. This was in line with the absence of known class B metallo-β-lactamases in any of the isolates. The majority of isolates carried bla_penA (98%) and bla_ampC (86%). Trimethoprim/sulfamethoxazole and ceftazidime/avibactam showed high susceptibility rates. Aztreonam in combination with ceftazidime/avibactam had no synergistic effect in our Bcc isolates.

Evaluation of Antimicrobial Susceptibility Testing Methods for Burkholderia cenocepacia and Burkholderia multivorans Isolates from Cystic Fibrosis Patients

The Burkholderia cepacia complex (BCC) is known for causing serious lung infections in people with cystic fibrosis (CF). These infections can require lung transplantation, eligibility for which may be guided by antimicrobial susceptibility testing (AST). While the Clinical and Laboratory Standards Institute recommends AST for BCC, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) does not, due to poor method performance and correlation with clinical outcomes. Furthermore, limited data exist on the performance of automated AST methods for BCC. To address these issues, reproducibility and accuracy were evaluated for disk diffusion (DD), broth microdilution (BMD), and MicroScan WalkAway using 50 B. cenocepacia and 50 B. multivorans isolates collected from people with CF. The following drugs were evaluated in triplicate: chloramphenicol (CAM), ceftazidime (CAZ), meropenem (MEM), trimethoprim-sulfamethoxazole (TMP-SMX), minocycline (MIN), levofloxacin (LVX), ciprofloxacin (CIP), and piperacillin-tazobactam (PIP-TAZ). BMD reproducibility was ≥ 95% for MEM and MIN only, and MicroScan WalkAway reproducibility was similar to BMD. DD reproducibility was < 90% for all drugs tested when a 3 mm cut-off was applied. When comparing the accuracy of DD to BMD, only MEM met all acceptance criteria. TMP-SMX and LVX had high minor errors, CAZ had unacceptable very major errors (VME), and MIN, PIP-TAZ, and CIP had both unacceptable minor errors and VMEs. For MicroScan WalkAway, no drugs met acceptance criteria. Analyses also showed that errors were not attributed to one species. In general, our data agree with EUCAST recommendations.