Poor Correlation between Meropenem and Piperacillin Plasma Concentrations and Delivered Dose of Continuous Renal Replacement Therapy.

There is insufficient data on the relationship between antibiotic dosing and plasma concentrations in patients treated with continuous renal replacement therapy (CRRT). In this prospective observational study, we explored the variability in plasma concentrations of meropenem and piperacillin in critically ill patients treated with CRRT and the correlation between concentrations and CRRT intensity. Antibiotic concentrations were measured at the middle and end of the dosing interval and repeated after 2 to 3 days when feasible. Measured concentrations were compared to the clinical susceptible breakpoints for Pseudomonas aeruginosa, 16 and 2 mg/liter for piperacillin and meropenem, respectively. CRRT intensity was estimated by delivered, time-averaged, total effluent flow (Qeff), corrected for predilution. Concentrations were also compared between patients with different residual diuresis. We included 140 meropenem concentrations from 98 patients and 47 piperacillin concentrations from 37 patients. Concentrations at the middle of the dosing interval were above target at all occasions for both antibiotics. For meropenem, 6.5% of trough concentrations were below target, and for piperacillin, 22%. Correlations between Qeff and antibiotic concentrations or the concentration half-life (t1/2) were either statistically not significant or weak. Meropenem concentrations and t1/2 values differed between patients with different residual diuresis. Thus, when treating intensive care patients with CRRT and recommended doses of meropenem or piperacillin, both low, suboptimal plasma concentrations and unnecessarily high, potentially toxic, plasma concentrations are common. Plasma concentrations cannot be predicted from CRRT intensity. Residual diuresis is associated with lower meropenem concentrations, but the correlation is weak. Concentration measurement is probably the most useful approach to avoid suboptimal treatment.

Genomic analysis revealed distinct transmission clusters of vancomycin-resistant Enterococcus faecium ST80 in Stockholm, Sweden.

Vancomycin-resistant Enterococcus faecium (VREfm) belonging to sequence type (ST)80 has become the predominant clonal lineage in Stockholm in the last three years. ST80 accounted for 75% and 46% of VRE cases in 2018 and 2019, respectively, and gave rise to both vanA-type and vanB-type outbreaks. Non-duplicate ST80-VREfm isolates (N = 188) were subjected to whole genome sequencing. Genomic analysis revealed three distinct transmission clusters. Our study indicated that difficulties in detecting low-grade vancomycin-resistant isolates by phenotypic testing might be one of the explanatory factors for the prolonged course of vanB-type outbreaks. Herein, we also report the first optrA-positive linezolid-resistant VRE isolate in Stockholm.

Daptomycin in the treatment of enterococcal bloodstream infections and endocarditis: a EUCAST position paper.

SCOPE: This position paper describes the view adopted by EUCAST on the role of daptomycin in the treatment of serious infections caused by Enterococcus species. BACKGROUND: High-dose daptomycin is considered effective in the treatment of enterococcal bloodstream infection (BSI) and endocarditis, although published clinical experience with the latter condition is limited. METHODS: EUCAST reviewed the available published data on pharmacokinetics-pharmacodynamics (PK-PD), resistance selection, clinical efficacy and safety for the use of 10-12 mg/kg/day of daptomycin for these conditions, noting that the doses licensed by the European Medicines Agency are only 4-6 mg/kg/day, and only for infections caused by Staphylococcus aureus. FINDINGS AND RECOMMENDATIONS: The PK-PD evidence shows that, even with doses of 10-12 mg/kg/day, it is not possible to treat infections caused by isolates at the upper end of the wild-type distributions of Enterococcus faecalis (with MICs of 4 mg/L) and E. faecium (with MICs of 4 or 8 mg/L). For this reason, and because there are ongoing issues with the reliability of laboratory testing, EUCAST lists daptomycin breakpoints for Enterococcus species as "IE"-insufficient evidence. EUCAST advises increased vigilance in the use of high-dose of daptomycin to treat enterococcal BSI and endocarditis. Additional PK-PD studies and prospective efficacy and safety studies of serious Enterococcal infections treated with high-dose daptomycin may permit the setting of breakpoints in the future.

Isothermal microcalorimetry minimal inhibitory concentration testing in extensively drug resistant Gram-negative bacilli: a multicentre study.

OBJECTIVES: To evaluate the performance of an isothermal microcalorimetry (IMC) method for determining the MICs among extensively drug-resistant Gram-negative bacilli. METHODS: A collection of 320 clinical isolates (n = 80 of each) of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii from Sweden, Spain, Italy and the Netherlands were tested. The MICs were determined using the IMC device calScreener (Symcel, Stockholm, Sweden) and ISO-broth microdilution as the reference method. Essential agreement, categorical agreement, very major errors (VME), major errors (ME) and minor (mE) errors for each antibiotic were determined. RESULTS: Data from 316 isolates were evaluated. Four errors (two ME, one VME, one mE) among 80 K. pneumoniae, six errors (four ME, one VME, one mE) among 79 E. coli, 15 errors (seven VME, three ME, five mE) among 77 P. aeruginosa and 18 errors (12 VME, two ME, four mE) among 80 A. baumannii were observed. Average essential agreement and categorical agreement of the IMC method were 96.6% (95% confidence interval, 94.2-99) and 97.1% (95% confidence interval, 95.4-98.5) respectively when the MICs were determined at the end of 18 hours. Categorical agreement of the IMC method for prediction of MIC by the end of 8 hours for colistin, meropenem, amikacin, ciprofloxacin and piperacillin/tazobactam were 95%, 91.4%, 94%, 95.2% and 93.7% respectively. CONCLUSIONS: The IMC method could accurately determine the MICs among extensively drug-resistant clinical isolates of E. coli, K. pneumoniae, P. aeruginosa and A. baumannii isolates.

Transmission events and antimicrobial susceptibilities of methicillin-resistant Staphylococcus argenteus in Stockholm.

OBJECTIVES: Staphylococcus argenteus has been increasingly reported since the species was defined as a novel staphylococcal species in 2015. This study aims to investigate genetic epidemiological links and antimicrobial susceptibilities of methicillin-resistant S. argenteus isolates recovered in Stockholm. METHODS: Sixteen methicillin-resistant S. argenteus isolates were identified from a collection of methicillin-resistant Staphylococcus aureus in Stockholm 2007-2018, by using whole-genome sequencing and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The genomes of the isolates were investigated by pulsed-field gel electrophoresis, single-nucleotide polymorphism (SNP)-based phylogeny, k-mer analysis, core-genome multi-locus sequence typing (cgMLST), resistance traits and virulence factors. The MICs of 19 antimicrobial agents for each isolate were determined by using the broth microdilution method. RESULTS: Of the 16 isolates, seven, seven and two isolates were assigned to ST1223, ST2250 and ST2793, respectively, with the S. aureus MLST-scheme. Analyses based on SNPs and cgMLST revealed a likely clonal spread of methicillin-resistant S. argenteus in 2007. Four isolates were found to be resistant to non-ß-lactams in antimicrobial susceptibility testing. CONCLUSIONS: A transmission event of methicillin-resistant S. argenteus in family was identified by this study. Among our limited number of isolates, non-ß-lactam resistance was detected, which highlights the necessity of a continued surveillance on this emerging pathogen. S. argenteus could be correctly identified by MALDI-TOF MS with the updated database, enabling its detection also in clinical laboratories.

Risk factors for community-onset bloodstream infection with extended-spectrum ß-lactamase-producing Enterobacteriaceae: national population-based case-control study.

OBJECTIVES: The aim was to investigate risk factors for community-onset bloodstream infections with extended-spectrum ß-lactamase-producing Enterobacteriaceae (EPE BSI). METHODS: It is mandatory to report EPE BSI to a national register at the Public Health Agency of Sweden. Using this register, we performed a population-based case-control study from 2007 to 2012 of 945 cases and 9390 controls. Exposure data on comorbidity, hospitalization, in- and outpatient antibiotic consumption and socio-economic status were collected from hospital and health registers. RESULTS: The overall incidence of EPE BSI was 1.7 per 100 000 person-years. The 30-day mortality was 11.3%. Urological disorders inferred the highest EPE BSI risk, adjusted odds ratio (aOR) 4.32 (95% Confidence Interval (CI) 3.41-5.47), followed by immunological disorders, aOR 3.54 (CI 2.01-6.23), haematological malignancy, aOR 2.77 (CI 1.57-4.87), solid tumours, aOR 2.28 (1.76-2.94) and diabetes, aOR 2.03 (1.58-2.61). Consumption of fluoroquinolones or mostly non-EPE-active antibiotics with selective Gram-negative spectrum of activity within the previous 3 months was associated with EPE BSI, aORs 5.52 (CI 2.8-11.0) and 3.8, CI 1.9-7.7) respectively. There was a dose-response relationship in EPE BSI risk with increasing number of consecutive regimens. Antibiotic consumption >3 months before EPE BSI was not associated with increased risk. Higher age, malignancies and education ≤12 years (aORs >2) were associated with increased 30-day mortality. CONCLUSIONS: Targeted interventions should be directed towards improving care for patients with immunosuppression, urological disorders and subjects with lower socio-economic status. Antibiotic stewardship should focus on reduction of fluoroquinolones.

Invasive infection caused by Klebsiella pneumoniae is a disease affecting patients with high comorbidity and associated with high long-term mortality.

Klebsiella pneumoniae (KP) is after Escherichia coli (EC) the most common gram-negative species causing invasive infections. Herein, we analyzed risk factors and prognosis in invasive infections caused by KP versus EC, in an area with low antimicrobial resistance. Moreover, we compared antimicrobial resistance and relative prevalence of KP and EC (KP/EC-ratio) in different European countries, using EARS-Net data. Adult patients admitted to Karolinska University Hospital 2006-2012 with invasive infection caused by KP (n = 599) were matched regarding sex and age with patients infected by EC. The medical records were retrospectively reviewed. Comorbidity was adjusted for with multivariable analysis. European data were retrieved from the EARS-Net database. No differences were observed in 7- and 30-day mortality between the groups. The 90-day mortality was significantly higher in the KP cohort (26% versus 17%, p<0.001), but not after adjusting for comorbidity. Malignancy was seen in 53% of the patients with KP versus 38% with EC, OR 1.86 (1.34-2.58). A significant increase in the rate of ESBL-production was observed in EC, but not in KP. The KP/EC-ratio remained stable. In contrast, European data showed increasing percentages of isolates non-susceptible to third-generation cephalosporins in EC and KP, and increasing KP/EC-ratio. Invasive infection caused by KP is a disease affecting patients with high comorbidity and associated with high 90-d mortality. The stable KP/EC-ratio and low occurrence of antimicrobial resistance in data from Karolinska University Hospital compared to aggregate data from 20 EARS-Net countries could be related to absence of clonal spread of multidrug-resistant KP.

Neonatal intestinal colonization with extended-spectrum ß-lactamase-producing Enterobacteriaceae-a 5-year follow-up study.

OBJECTIVES: To analyse Klebsiella pneumoniae (KP) isolates from an outbreak of extended-spectrum ß-lactamase (ESBL)-producing KP and Escherichia coli (EC) among infants admitted to neonatal intensive care units and to determine the duration of the intestinal colonization. METHODS: We performed a prospective cohort study of intestinal ESBL-KP/ESBL-EC colonized neonates after a 5-month outbreak in two neonatal intensive care units. Whole genome sequencing, multilocus sequence typing, core genome multilocus sequence typing, pulsed-field electrophoresis and PCR for blaCTX-M were performed on the first isolates. Stool cultures were performed every second month after discharge until 2 years after discharge and at 5 years of age. The last positive samples were analysed with pulsed-field gel electrophoresis and PCR for blaCTX-M. The intestinal relative dominance of ESBL-producing Enterobacteriaceae was determined. RESULTS: Thirteen of 17 patients colonized with ESBL-KP/ESBL-EC survived. Isolates from 16 of 17 patients were available for analysis and featured the same strain type of ESBL-KP: sequence type 101. The strain had capsule type K29 and harboured blaCTX-M-15. The virulence genes irp1, irp2, iutA, kfu and mrk were detected in all isolates. The median length of colonization was 12.5 months (range, 5-68 months). After 2 years, two of 13 patients were carriers of ESBL-KP and one of 13 of ESBL-EC. At 5 years of age, one neonate was colonized with ESBL-EC. No infant experienced an ESBL-KP/EC-infection during follow-up. CONCLUSIONS: Two years after discharge, almost one fourth of the study participants were ESBL/KP-EC carriers. ESBL-KP sequence type 101 persisted in two of 13 children for 23 to 26 months. One patient was colonized with ESBL-EC at age 5 years.

Molecular characterization of intestinal carriage of carbapenem-resistant Enterobacteriaceae among inpatients at two Iranian university hospitals: first report of co-production of bla NDM-7 and bla OXA-48.

Gastrointestinal colonization of carbapenem-resistant Enterobacteriaceae (CRE) could serve as a reservoir for the transmission of these pathogens in the clinical setting. The aim of this study was to investigate the intestinal carriage of CRE and to analyze risk factors for CRE carriage. Rectal swabs were collected from 95 patients at two Iranian university hospitals. CRE screening was performed using selective media (CHROMagar and MacConkey agar). Polymerase chain reaction (PCR) was used to detect carbapenemase-encoding genes. Clonal relatedness was investigated by pulsed-field gel electrophoresis (PFGE). The rate of carriage of CRE in hospitalized patients was 37.9%. Overall, 54 CRE isolates were identified, of which 47 were carbapenemase-producers. All of the 54 CRE were detected using CHROMagar compared with 52 CRE detected using MacConkey agar. Fifteen patients were colonized by multiple CRE isolates. Three significant risk factors for CRE carriage were detected: intensive care unit (ICU) hospitalization, antibiotic exposure, and mechanical ventilation. bla OXA-48 was the most frequent carbapenemase detected, followed by bla NDM-1 and bla NDM-7. Eleven carbapenemase-producing Enterobacteriaceae (CPE) isolates co-harbored bla NDM-1 and bla OXA-48. Also, six CPE isolates co-harbored bla NDM-7 and bla OXA-48. We did not detect bla KPC, bla GES, bla IMP, or bla VIM. PFGE analysis showed that Escherichia coli clones were diverse, while Klebsiella pneumoniae isolates were divided into four clusters. Cluster I was the major clone carrying bla OXA-48 and bla CTX-M-15 genes. In our study, the carriage rate of CRE was high and the emergence of CPE isolates among patients is alarming. The implementation of adequate preventive measures such as active surveillance is urgently needed to control the spread of CPE in the healthcare setting.

The role of whole genome sequencing in antimicrobial susceptibility testing of bacteria: report from the EUCAST Subcommittee.

Whole genome sequencing (WGS) offers the potential to predict antimicrobial susceptibility from a single assay. The European Committee on Antimicrobial Susceptibility Testing established a subcommittee to review the current development status of WGS for bacterial antimicrobial susceptibility testing (AST). The published evidence for using WGS as a tool to infer antimicrobial susceptibility accurately is currently either poor or non-existent and the evidence / knowledge base requires significant expansion. The primary comparators for assessing genotypic-phenotypic concordance from WGS data should be changed to epidemiological cut-off values in order to improve differentiation of wild-type from non-wild-type isolates (harbouring an acquired resistance). Clinical breakpoints should be a secondary comparator. This assessment will reveal whether genetic predictions could also be used to guide clinical decision making. Internationally agreed principles and quality control (QC) metrics will facilitate early harmonization of analytical approaches and interpretive criteria for WGS-based predictive AST. Only data sets that pass agreed QC metrics should be used in AST predictions. Minimum performance standards should exist and comparative accuracies across different WGS laboratories and processes should be measured. To facilitate comparisons, a single public database of all known resistance loci should be established, regularly updated and strictly curated using minimum standards for the inclusion of resistance loci. For most bacterial species the major limitations to widespread adoption for WGS-based AST in clinical laboratories remain the current high-cost and limited speed of inferring antimicrobial susceptibility from WGS data as well as the dependency on previous culture because analysis directly on specimens remains challenging. For most bacterial species there is currently insufficient evidence to support the use of WGS-inferred AST to guide clinical decision making. WGS-AST should be a funding priority if it is to become a rival to phenotypic AST. This report will be updated as the available evidence increases.

Standard dosing of piperacillin and meropenem fail to achieve adequate plasma concentrations in ICU patients.

BACKGROUND: Controversies remain regarding optimal dosing and the need for plasma concentration measurements when treating intensive care patients with beta-lactam antibiotics. METHODS: We studied ICU patients treated with either antibiotic, excluding patients on renal replacement therapy. Antibiotic concentrations were measured at the mid and end of the dosing interval, and repeated after 2-3 days when feasible. Glomerular filtration rate (GFR) was estimated from plasma creatinine and cystatin C, GFR calculated from cystatin C (eGFR) and measured creatinine clearance (CrCl). Measured concentrations were compared to the clinical susceptible breakpoints for Pseudomonas aeruginosa, 16 and 2 mg/l for piperacillin and meropenem respectively. RESULTS: We analysed 33 and 31 paired samples from 20 and 19 patients treated with piperacillin-tazobactam and meropenem respectively. Antibiotic concentrations at the mid and end of the dosing interval were for piperacillin, 27.0 (14.7-52.9) and 8.6 (2.7-30.3); and for meropenem, 7.5 (4.7-10.2) and 2.4 (1.0-3.5). All values median (interquartile range) and concentrations in mg/l. The percentage of measured concentrations below the breakpoint at the mid and end of the dosing interval were for piperacillin, 27% and 61%; and for meropenem, 6% and 48%. Lower estimates of GFR were associated with higher concentrations but concentrations varied greatly between patients with similar GFR. The correlation with terminal concentration half-life was similar for eGFR and CrCl. CONCLUSIONS: With standard doses of meropenem and piperacillin-tazobactam, plasma concentrations in ICU patients vary > 10-fold and are suboptimal in a significant percentage of patients. The variation is large also between patients with similar renal function.

Frequent acquisition of low-virulence strains of ESBL-producing Escherichia coli in travellers.

OBJECTIVES: International travel is a risk factor for intestinal colonization with ESBL-producing Enterobacteriaceae (EPE). This prospective cohort study focuses on molecular features of and risk factors for travel-acquired EPE. METHODS: Rectal swabs and survey data were collected from 188 Swedes travelling to four regions of high EPE prevalence. Samples were plated onto selective agars. ESBL producers were determined using phenotypic methods. Molecular characterization regarding virulence factors and phylogenetic grouping of ESBL-producing Escherichia coli was done using PCR. Isolates were also screened for the plasmid-mediated colistin resistance gene mcr-1. RESULTS: Among 175 pre-travel EPE-negative participants, 32% were positive upon return. No carbapenemase-producing Enterobacteriaceae were found, but one CTX-M-producing E. coli harboured mcr-1 (travel to Thailand). Most E. coli strains (43.1%) belonged to phylogroup A and were rarely associated with extraintestinal infections and a few (9.2%) expressed uropathogenicity pap genes. During 10-26 months of follow-up, no clinical infections were observed. Colonization rates varied by visited region: the Indian subcontinent, 49.2%; northern Africa, 44.0%; South-East Asia, 19.1%; and Turkey, 9.5%. Travellers' diarrhoea (OR 2.5, P = 0.04) or antimicrobial treatment during the trip (OR 5.9, P = 0.02) were both independent risk factors for EPE colonization. CONCLUSIONS: EPE acquired during travel have seemingly low pathogenicity, possibly indicating a low risk of clinical infection. Pre-travel advice should emphasize avoiding unnecessary antibiotic treatment during travel.

Evaluation of antibacterial activities of colistin, rifampicin and meropenem combinations against NDM-1-producing Klebsiella pneumoniae in 24 h in vitro time-kill experiments.

OBJECTIVES: To investigate the activity of colistin alone or in double and triple combination with rifampicin and meropenem against NDM-1-producing Klebsiella pneumoniae. METHODS: Eight isolates of NDM-1-producing K. pneumoniae were exposed to clinically relevant antibiotic concentrations in 24 h time-kill experiments. Three colistin concentrations were used for two of the strains. Resistance development was assessed with population analysis and sequencing of the mgrB and pmrB genes. RESULTS: Initial killing was achieved with colistin alone, but with considerable regrowth at 24 h. Combinations including colistin and rifampicin were bacteriostatic or bactericidal against all strains. Colistin plus meropenem was bactericidal against one strain, but, overall, meropenem showed little additive effects. Higher concentrations of colistin did not enhance antibacterial activity. Resistant populations and deletion or mutations in the mgrB and pmrB genes were frequently detected in endpoint samples after exposure to colistin alone. CONCLUSIONS: Based on the results of this and previous studies, the combination of colistin and rifampicin seems promising and should be further explored in vivo and considered for clinical evaluation. Meropenem seems less useful in the treatment of infections caused by high-level carbapenem-resistant NDM-1-producing K. pneumoniae. Higher colistin concentrations did not result in significantly better activity, suggesting that combination therapy might be superior to monotherapy also when colistin is prescribed using high-dose regimens in accordance with current recommendations.

Metagenomic analysis of bloodstream infections in patients with acute leukemia and therapy-induced neutropenia.

Leukemic patients are often immunocompromised due to underlying conditions, comorbidities and the effects of chemotherapy, and thus at risk for developing systemic infections. Bloodstream infection (BSI) is a severe complication in neutropenic patients, and is associated with increased mortality. BSI is routinely diagnosed with blood culture, which only detects culturable pathogens. We analyzed 27 blood samples from 9 patients with acute leukemia and suspected BSI at different time points of their antimicrobial treatment using shotgun metagenomics sequencing in order to detect unculturable and non-bacterial pathogens. Our findings confirm the presence of bacterial, fungal and viral pathogens alongside antimicrobial resistance genes. Decreased white blood cell (WBC) counts were associated with the presence of microbial DNA, and was inversely proportional to the number of sequencing reads. This study could indicate the use of high-throughput sequencing for personalized antimicrobial treatments in BSIs.

Escherichia coli: an old friend with new tidings.

Escherichia coli is one of the most-studied microorganisms worldwide but its characteristics are continually changing. Extraintestinal E. coli infections, such as urinary tract infections and neonatal sepsis, represent a huge public health problem. They are caused mainly by specialized extraintestinal pathogenic E. coli (ExPEC) strains that can innocuously colonize human hosts but can also cause disease upon entering a normally sterile body site. The virulence capability of such strains is determined by a combination of distinctive accessory traits, called virulence factors, in conjunction with their distinctive phylogenetic background. It is conceivable that by developing interventions against the most successful ExPEC lineages or their key virulence/colonization factors the associated burden of disease and health care costs could foreseeably be reduced in the future. On the other hand, one important problem worldwide is the increase of antimicrobial resistance shown by bacteria. As underscored in the last WHO global report, within a wide range of infectious agents including E. coli, antimicrobial resistance has reached an extremely worrisome situation that 'threatens the achievements of modern medicine'. In the present review, an update of the knowledge about the pathogenicity, antimicrobial resistance and clinical aspects of this 'old friend' was presented.

Contemporary resistance trends and mechanisms for the old antibiotics colistin, temocillin, fosfomycin, mecillinam and nitrofurantoin.

Recently there has been a renewed interest in reviving older antimicrobial agents, particularly those with activity against multidrug-resistant Gram-negative bacilli. Because many such antimicrobials are not licensed in all countries, there is a paucity of international surveillance data, and none of these agents is part of any antimicrobial resistance surveillance on the level of the EU. Some of the agents are used in lower urinary tract infection, whereas most available supranational surveillance data pertain to severe infections such as bloodstream infections. Among old antimicrobial agents, the most interesting compounds from a clinical perspective are the two intravenous agents colistin and temocillin, the two oral agents pivmecillinam and nitrofurantoin, and fosfomycin, which is available both for intravenous and oral use. The most interesting target microorganisms are Enterobacteriaceae, although colistin also has good activity against Pseudomonas aeruginosa and Acinetobacter species. Recent European surveillance data point to approximately 5% resistance to colistin in general among Klebsiella pneumoniae, whereas resistance in carbapenemase-producing Enterobacteriaceae may be up to 15% to 20% in some settings. Temocillin is stable against many extended-spectrum ß-lactamase-producing Enterobacteriaceae and some carbapenemase producers, but low-level resistance is not uncommon in extended-spectrum ß-lactamase producers, and high-level resistance is always seen with OXA-48 group carbapenemases. Fosfomycin resistance is rare in areas with limited use but increasing is in countries with higher usage. Resistance levels to mecillinam and nitrofurantoin are generally low in EU countries, but clinical data supporting treatment efficacy of multidrug-resistant strains are few. Systematic surveillance of the above-mentioned agents will be important, particularly for those agents used in severe infections.

Meropenem-clavulanic acid has high in vitro activity against multidrug-resistant Mycobacterium tuberculosis.

We investigated the activity of meropenem-clavulanic acid (MEM-CLA) against 68 Mycobacterium tuberculosis isolates. We included predominantly multi- and extensively drug-resistant tuberculosis (MDR/XDR-TB) isolates, since the activity of MEM-CLA for resistant isolates has previously not been studied extensively. Using Middlebrook 7H10 medium, all but four isolates showed an MIC distribution of 0.125 to 2 mg/liter for MEM-CLA, below the non-species-related breakpoint for MEM of 2 mg/liter defined by EUCAST. MEM-CLA is a potential treatment option for MDR/XDR-TB.

Little difference between minimum inhibitory concentrations of Mycobacterium tuberculosis wild-type organisms determined with BACTEC MGIT 960 and Middlebrook 7H10.

The MIC wild-type (WT) distribution for Mycobacterium tuberculosis in BACTEC 960 MGIT is not defined, which may result in poor reproducibility for drug susceptibility testing (DST), as several DST methods with different breakpoints are in use. In a comparison between MGIT and Middlebrook 7H10 medium of seven first- and second-line drugs, including 133 MIC determinations of 15 WT isolates, we found an agreement of 91.7% within ± one MIC dilution step. The results confirm the agreement in MIC testing between 7H10 and MGIT and indicate that breakpoints could be harmonized in order to avoid misclassification.