In vitro susceptibility testing of imipenem-relebactam and tedizolid against 102 Mycobacterium abscessus isolates

OBJECTIVES

Mycobacterium abscessus is an emerging infection in people living with lung diseases, including cystic fibrosis (CF) and bronchiectasis, and it has limited treatment options and low cure rates. The off-label use of novel antibiotics developed for other bacterial pathogens offers potential new therapeutic options. We aimed to describe the in vitro activity of imipenem, imipenem-relebactam and tedizolid against comparator antibiotics in M. abscessus isolates from Australian patients with and without CF.

METHODS

We performed susceptibility testing for imipenem-relebactam, tedizolid and comparator antibiotics by Clinical and Laboratory Standards Institute (CLSI) criteria against 102 clinical M. abscessus isolates, including 46 from people with CF.

RESULTS

In this study, the minimum inhibitory concentration (MICs) of imipenem-relebactam was one-fold dilution less than of imipenem alone. The MIC50 and MIC90 of imipenem-relebactam were 8 and 16 mg/L, respectively, whereas for imipenem they were 16 and 32 mg/L. Tedizolid had an MIC50 and MIC90 of 2 and 4 mg/L, respectively. Forty non-CF isolates had linezolid susceptibility performed, with MIC50 and MIC90 values of 16 and 32 mg/L, respectively, measured.

CONCLUSIONS

This study shows lower MICs for imipenem-relebactam and tedizolid compared to other more commonly used antibiotics and supports their consideration in clinical trials for M. abscessus treatment.

A multi-centre retrospective study of Nocardia speciation and antimicrobial susceptibility in Queensland, Australia

The study aims to characterise the species identification and antimicrobial susceptibility testing (AST) results of Nocardial isolates from adult patients across major public hospitals in Queensland, Australia, over a 15-year period. A multi-centre retrospective observational study of Nocardia sp. isolates was conducted from 7 major public hospitals in Queensland, Australia, over a 15-year period. Clinical samples from patients aged ≥ 18 years that isolated Nocardia sp. were included. Demographic and clinical data were collected, along with species identification and AST results. Overall, 484 Nocardia sp. were isolated. Most patients were male (297, 61%) with a mean (IQR) age of 60 (51-75) and a median (IQR) Charlson Comorbidity Index of 4 (2-6). Of these, 239 (49%) patients were immunosuppressed. Organisms were most frequently isolated from sputum (174, 36%), and superficial swabs (102, 21%). Patients presented with pulmonary infections (165, 35%) and superficial skin and soft tissue infections (87, 18%) most commonly. One hundred (21%) isolates were deemed pulmonary colonisation and were not treated. Of the speciated organisms, N. nova complex was the most common (93, 19%), followed by N. farcinica complex (79, 16%). Organisms were reliably susceptible to linezolid (240/245, 98%), amikacin (455/470, 97%), and trimethoprim/sulfamethoxazole (459/476, 96%), but less so to imipenem (243/472, 51%) and ceftriaxone (261/448, 58%). This is the largest Australian description of Nocardia sp. to date. Given antimicrobials are often commenced prior to AST results and sometimes even speciation, characterisation of local species and antibiogram data is important to guide empiric choices and local guidelines.

A systematic review of antimicrobial susceptibility testing as a tool in clinical trials assessing antimicrobials against infections due to gram-negative pathogens

BACKGROUND

Antimicrobial susceptibility testing (AST) is the standard of care for treating bacterial infections. In randomized clinical trials of new antimicrobials, AST might not be performed or reported in real time.

OBJECTIVES

To determine local, real-time laboratory AST performance, its usage in the trial flow, quality control (QC) of the local testing, central AST performance and the effect of using AST categorization on the trials' primary outcomes.

DATA SOURCES

We systematically searched PubMed, Embase, PsychINFO and Web of Science.

ELIGIBILITY CRITERIA

We included registered randomized controlled trials published in journals between January 2015 and December 2019.

PARTICIPANTS AND INTERVENTIONS

We included trials comparing different antibiotics for the treatment of infections caused predominantly by Gram-negative bacteria.

METHODS

Primary outcomes for different trial populations were extracted and differences between trial arms were compared for patients with infections caused by susceptible versus non-susceptible bacteria. Results are described narratively.

RESULTS

Of 32 randomized trials, 25 trials reported that local AST was performed, 1312 reported the local laboratory AST methods, no trial reported QC, but post-hoc referral for AST at a reference laboratory was common. Patients' outcomes were superior when patients with infections due to susceptible and non-susceptible pathogens were compared post hoc (median difference 14%, interquartile range 8%-24%) in trials allowing this comparison (seven antimicrobials), except for colistin, where 14-day mortality was 9% higher when patients were treated with colistin for colistin-susceptible versus colistin-resistant carbapenem-resistant Acinetobacter baumannii. When excluding patients with pathogens that were non-susceptible to either antimicrobial in the trials, the difference in the primary outcome between the trial arms was reduced in five out of six trials.

CONCLUSIONS

Trials should perform AST to guide patient inclusion or exclusion from the study and consider the impact of the central laboratory susceptibility results on the study outcomes when using post-hoc reference testing.

Self-collection: An appropriate alternative during the SARS-CoV-2 pandemic

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First study providing evidence of equivalence of self-collection for SARS-CoV-2.

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Self-collection has potential to increase accessibility and detection of SARS-CoV-2.

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Self-collection has potential to preserve PPE supplies.

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Self-collection has potential to reduce exposure to others.

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Self-collection was easy to perform and preferred by the majority of participants.

Objectives

To evaluate the reliability of self-collection for SARS-CoV-2 and other respiratory viruses because swab collections for SARS-CoV-2 put health workers at risk of infection and require use of personal protective equipment (PPE).

Methods

In a prospective study, patients from two states in Australia attending dedicated COVID-19 collection clinics were offered the option to first self-collect (SC) nasal and throat swabs (SCNT) prior to health worker collect (HC) using throat and nasal swabs (Site 1) or throat and nasopharyngeal swabs (Site 2). Samples were analysed for SARS-CoV-2 as well as common respiratory viruses. Concordance of results between methods was assessed using Cohen's kappa (κ) and Cycle threshold (Ct) values were recorded for all positive results as a surrogate measure for viral load.

Results

Of 236 patients sampled by HC and SC, 25 had SARS-CoV-2 (24 by HC and 25 by SC) and 63 had other respiratory viruses (56 by HC and 58 by SC). SC was highly concordant with HC (κ = 0.890) for all viruses including SARS-CoV-2 and more concordant than HC to positive results by any method (κ = 0.959 vs 0.933). Mean SARS-CoV-2 E-gene and N-gene, rhinovirus and parainfluenza Ct values did not differ between HC and SCNT.

Conclusions

Self-collection of nasal and throat swabs offers a reliable alternative to health worker collection for the diagnosis of SARS-CoV-2 and other respiratory viruses and provides patients with easier access to testing, reduces exposure of the community and health workers to those being tested and reduces requirement for PPE.

First case report of human infection with Mycobacterium stomatepiae

Introduction

We describe the first detailed case report of human infection with Mycobacterium stomatepiae. Infection with non-tuberculous mycobacteria (NTM) related to M. stomatepiae is well described, despite the lack of previous confirmed reports of M. stomatepiae-related human disease. Localised cervical lymphadenitis is the most common NTM disease in children, with species closely related to M. stomatepiae, such as Mycobacterium triplex and Mycobacterium florentinum, having been shown to be rare causative agents.

Case presentation

A 19-month-old girl presented with persistent unilateral neck lumps which developed following a facial laceration. Both lumps were fluctuant with overlying erythema and no fistulae present. Incision and drainage with curettage was performed. The operative sample of purulent fluid revealed pleomorphic bacilli on Ziehl–Neelsen staining. The isolate cultured was referred for further genotypic identification via 16S rRNA gene sequencing, identifying the organism as M. stomatepiae.

Conclusion

We describe the first detailed case report of human infection with M. stomatepiae. This organism can now be added to the growing list of NTM that are opportunistic human pathogens, though it is likely to remain a very rare causative agent of this clinical syndrome. Early diagnosis relies on clinical suspicion by the treating doctor, flagging potential cases to the microbiology laboratory and hence allowing correct specimen set-up. Laboratory diagnosis requires incubation of cultures at lower temperatures, and definitive identification is best performed by sequencing methods, including 16S rRNA gene sequencing. The description of novel species of NTM causing human disease is likely to increase with further advancements in diagnostic methods.

Free living amoebae and human disease

Pathogenic FLA are ubiquitous protozoans and despite frequent human contact remain a rare cause of often devastating infection with poor prognosis. Given changes in climate, human encroachment into the environment, increasing immunosuppression, and improving diagnostic capacity, it is likely we will see increased cases in the future. Early diagnosis is challenging but crucial to achieving a favourable outcome. It is best facilitated by improved awareness of FLA disease, appropriate clinical suspicion and early diagnostic testing.

Even high-dose extended infusions may not yield desired concentrations of β-lactams: the value of therapeutic drug monitoring

A 35-year-old patient in intensive care with severe burn injury developed episodes of sepsis. Blood culture yielded a multidrug-resistant Pseudomonas aeruginosa and treatment was commenced with amikacin (minimum inhibitory concentration (MIC) 2-4 mg/L, dose 20 mg/kg adjusted body weight 24-hourly) and meropenem (MIC 8 mg/L, dose 2 g IV 8-hourly and later 6-hourly). Despite the use of extended infusions with β-lactam therapeutic drug monitoring and doses that were more than 2.5 times higher than standard meropenem doses, resistance emerged. This case report describes the application of therapeutic drug monitoring to optimize β-lactam therapy in a difficult-to-treat critically ill patient.