A multicentre evaluation of the NG-test DetecTool OXA-23 for the rapid detection of OXA-23 carbapenemase directly from blood cultures.

Objectives: A multicentre study evaluating NG-Test DetecTool OXA-23 for the detection of OXA-23 carbapenemase directly from positive blood cultures (PBCs). Methods: The NG-Test DetecTool OXA-23 is an immunoassay that integrates a sample preparation device. We evaluated NG-Test DetecTool OXA-23 on 189 spiked and 126 clinical PBCs. The clinical samples' standard-of-care procedure consisted of bacterial identification from the first day of positivity by MALDI-TOF MS, conventional culture and antimicrobial susceptibility testing. The immunoassay results were verified molecularly. The strains used for the spiked samples consisted of well-characterized Acinetobacter baumannii and Proteus mirabilis strains. Results: The NG-Test DetecTool OXA-23 was evaluated on 315 PBCs and revealed sensitivity of 100% (95% CI: 98.21%-100.00%) and specificity of 100% (95% CI: 96.73%-100.00%). It provided 204 true-positive results for OXA-23 in 196 bottles with carbapenem-resistant A. baumannii (CRAB) and 8 bottles with carbapenem-resistant P. mirabilis and also provided 111 true-negative results. There were no false-positive and no false-negative results. Among the 315 PBCs studied, 83 clinical blood cultures collected in the ICU of a Greek university hospital, which were tested prospectively, all yielded CRAB, and OXA-23 was correctly detected in all samples from the first day of positivity using the NG-Test DetecTool OXA-23. Conclusions: The NG-Test DetecTool OXA-23 has exhibited excellent sensitivity and specificity for OXA-23 detection in PBCs and can provide valuable information for appropriate selection of antibiotic therapy and early implementation of infection control measures.

Multidrug-resistant organism bloodstream infection and hospital acquisition among inpatients in three tertiary Greek hospitals during the COVID-19 era.

From 2019 (pre-COVID-19) to 2022 (COVID-19 years), three tertiary Greek hospitals monitored MDRO bloodstream infection (BSI) and hospital acquisition relying on laboratory data. Surveillance covered carbapenem-resistant Enterobacterales (CRE), Acinetobacter baumannii (CRAB), Pseudomonas aeruginosa (CRPA), vancomycin-resistant enterococci (VRE), and methicillin-resistant Staphylococcus aureus (MRSA), in intensive care units (ICUs) and non-ICUs. Non-ICUs experienced significant increases in CRE, CRAB and VRE during the pandemic. In ICUs, CRE increased in 2021, CRAB in 2020 and 2021, and VRE in 2021 and 2022. KPC predominated among CRE. MDRO BSI and hospital acquisition incidence rates increased, driven by CRE and CRAB.

Assessing Clinical Potential of Old Antibiotics against Severe Infections by Multi-Drug-Resistant Gram-Negative Bacteria Using In Silico Modelling.

In the light of increasing antimicrobial resistance among gram-negative bacteria and the lack of new more potent antimicrobial agents, new strategies have been explored. Old antibiotics, such as colistin, temocillin, fosfomycin, mecillinam, nitrofurantoin, minocycline, and chloramphenicol, have attracted the attention since they often exhibit in vitro activity against multi-drug-resistant (MDR) gram-negative bacteria, such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. The current review provides a summary of the in vitro activity, pharmacokinetics and PK/PD characteristics of old antibiotics. In silico modelling was then performed using Monte Carlo simulation in order to combine all preclinical data with human pharmacokinetics and determine the probability of target (1-log kill in thigh/lung infection animal models) attainment (PTA) of different dosing regimens. The potential of clinical efficacy of a drug against severe infections by MDR gram-negative bacteria was considered when PTA was >95% at the epidemiological cutoff values of corresponding species. In vitro potent activity against MDR gram-negative pathogens has been shown for colistin, polymyxin B, temocillin (against E. coli and K. pneumoniae), fosfomycin (against E. coli), mecillinam (against E. coli), minocycline (against E. coli, K. pneumoniae, A. baumannii), and chloramphenicol (against E. coli) with ECOFF or MIC90 ≤ 16 mg/L. When preclinical PK/PD targets were combined with human pharmacokinetics, Monte Carlo analysis showed that among the old antibiotics analyzed, there is clinical potential for polymyxin B against E. coli, K. pneumoniae, and A. baumannii; for temocillin against K. pneumoniae and E. coli; for fosfomycin against E. coli and K. pneumoniae; and for mecillinam against E. coli. Clinical studies are needed to verify the potential of those antibiotics to effectively treat infections by multi-drug resistant gram-negative bacteria.

Can bronchial secretion cultures identify the etiologic agent of COVID-19-associated pulmonary aspergillosis in ICU patients? Comparison with a species-specific Aspergillus PCR in serum.

Aspergillus spp. isolated from non-BAL cultures of coronavirus disease 2019 (COVID-19)-associated pulmonary aspergillosis (CAPA) patients may reflect colonization rather than infection. Sera (n = 181) from 49 adult ICU CAPA patients (24 probable and 25 possible CAPA) with bronchial secretions (BS) culture positive for Aspergillus spp. were collected and tested for Aspergillus DNA detection by species-specific real-time PCR. Overall, 30/49 (61%) patients were PCR positive. BS culture/serum PCR agreement was moderate (21/30; 70%). Based on serum PCR positive patients, all CAPAs were due to A. fumigatus (80%), A. flavus (10%), and A. terreus (10%). No A. niger/A. nidulans or mixed infections were found despite positive BS cultures.

Discordant results were observed between bronchial secretion cultures and species-specific serum PCR (30%) with A. fumigatus being by far the most common etiological agent of CAPA (80%). No A. niger/A. nidulans or mixed infections were found despite positive cultures.

Comparative Evaluation of Vitek 2 and Etest versus Broth Microdilution for Ceftazidime/Avibactam and Ceftolozane/Tazobactam Susceptibility Testing of Enterobacterales and Pseudomonas aeruginosa.

Ceftazidime/avibactam (CZA) and ceftolozane/tazobactam (C/T) are novel antibiotics with activity against multidrug-resistant Gram-negative pathogens. Nevertheless, resistance to both agents has been reported emphasizing the need for accurate and widely accessible susceptibility testing. In the present study, Vitek 2 and Etest CAZ and C/T MIC results for 100 non-repetitive clinical isolates (83 Enterobacterales and 17 P. aeruginosa, whereof 69 challenge isolates) were compared to the standard broth microdilution (BMD) method. EUCAST breakpoints were used for assessing the categorical (CA) and essential (EA) agreement between the methods along with the corresponding error rates. The Vitek 2 performance was comparable to that of BMD for testing both antimicrobial agents exceeding the ISO requirements (CA 98-99%, EA 96-100%, major errors (MEs) 0-1%, very major error (VMEs) 1%). Likewise, the Etest provided accurate results for CZA and C/T testing against Enterobacterales and P. aeruginosa, respectively (CA 100%, EA 97-100%, MEs 0%, VMEs 0%). On the contrary, EA of 85% and 6% VME rate were found for CZA Etest and P. aeruginosa. Overall, Vitek 2 measurements of CZA and C/T susceptibility correlated closely with the reference BMD, indicating that it can represent a suitable alternative to BMD for susceptibility testing of Enterobacterales and P. aeruginosa. The Etest did not fulfill the ISO performance criteria of EA and VME for CZA and P. aeruginosa. Further studies are needed to assess whether the Etest allows a reliable assessment of CZA and C/T EUCAST MICs.

Field Evaluation of the New Rapid NG-Test® SARS-CoV-2 Ag for Diagnosis of COVID-19 in the Emergency Department of an Academic Referral Hospital.

Background: As the COVID-19 pandemic resurges affecting large numbers of patients, rapid, and accurate diagnosis using point-of-care tests is very important. Objectives: To evaluate the NG-Test® SARS-CoV-2 Ag (NG-Test) immunoassay for qualitative detection of SARS-CoV-2 antigen in nasopharyngeal (NP) and oropharyngeal (OP) samples compared with RT-PCR, in patients attending the Emergencies of an academic referral hospital. Methods: All adult ambulatory patients presenting to the Emergencies of "Attikon" University hospital (Athens, Greece) within three consecutive hours per day between December 2020 and March 2021 and for whom SARS-CoV-2 PCR testing was requested were included. Two NP and one OP samples obtained from each participant were analyzed to determine the diagnostic performance [sensitivity, specificity, positive/negative predictive values (PPV/NPV)] of the NG-Test (NP/OP swabs) in comparison to the reference RT-PCR (NP swab). Results: Overall, 134/263 (51%) patients tested were RT-PCR positive, whereof 108 (overall sensitivity 81%, 95% CI 73-87%) were NP NG-Test positive (PPV 99%, NPV 83%) and 68 (overall sensitivity 51%, 95% CI 42-59%) were OP NG-Test positive (PPV 100%, NPV 66%). The test's specificity (95% CI) was 99% (95-100%) and 100% (96-100%) for NP and OP swabs, respectively. The assay's sensitivity (95% CI) for high viral load (Ct ≤25) was 99% (92-100%) and 71% (60-81%) for NP and OP swabs, respectively. Conclusions: NG-Test using NP swabs detected almost all patients with high viral loads, showing satisfactory performance as a point-of-care test for NP samples obtained from patients with acute infection.

COVID-19 and Antimicrobial Resistance: Data from the Greek Electronic System for the Surveillance of Antimicrobial Resistance-WHONET-Greece (January 2018-March 2021).

Changes in hospitals' daily practice due to COVID-19 pandemic may have an impact on antimicrobial resistance (AMR). We aimed to assess this possible impact as captured by the Greek Electronic System for the Surveillance of Antimicrobial Resistance (WHONET-Greece). Routine susceptibility data of 17,837 Gram-negative and Gram-positive bacterial isolates from blood and respiratory specimens of hospitalized patients in nine COVID-19 tertiary hospitals were used in order to identify potential differences in AMR trends in the last three years, divided into two periods, January 2018-March 2020 and April 2020-March 2021. Interrupted time-series analysis was used to evaluate differences in the trends of non-susceptibility before and after the changes due to COVID-19. We found significant differences in the slope of non-susceptibility trends of Acinetobacter baumannii blood and respiratory isolates to amikacin, tigecycline and colistin; of Klebsiella pneumoniae blood and respiratory isolates to meropenem and tigecycline; and of Pseudomonas aeruginosa respiratory isolates to imipenem, meropenem and levofloxacin. Additionally, we found significant differences in the slope of non-susceptibility trends of Staphylococcus aureus isolates to oxacillin and of Enterococcus faecium isolates to glycopeptides. Assessing in this early stage, through surveillance of routine laboratory data, the way a new global threat like COVID-19 could affect an already ongoing pandemic like AMR provides useful information for prompt action.

Epidemiology and Incidence of COVID-19-Associated Pulmonary Aspergillosis (CAPA) in a Greek Tertiary Care Academic Reference Hospital.

INTRODUCTION: Invasive pulmonary aspergillosis is an emerging complication among intensive care unit (ICU) patients with COVID-19 (CAPA). In the present study, all CAPA cases during the first year of the pandemic were reviewed in critically ill patients at a 650-bed tertiary Greek COVID-19 reference hospital. METHODS: Data regarding patients admitted to the ICU of Attikon Hospital in Athens, Greece, between 22 March 2020 and 28 February 2021 with a positive PCR for SARS-CoV-2 infection were reviewed. Clinical and microbiological records were analysed including demographic, clinical, laboratory and radiological features, treatment and outcomes. CAPA was determined according to the recent 2020 ECMM/ISHAM definitions. RESULTS: A total of 179 patients were admitted in the ICU and 6 (3.3%) patients were diagnosed with CAPA (4 probable and 2 possible CAPA) with 5/6 with co-infection with multidrug-resistant (MDR) gram-negative pathogens. No patient had a history of immunosuppression. All suffered from acute respiratory distress syndrome. The median (range) time from intubation to diagnosis was 6 (1-14) days. Five patients had positive Aspergillus cultures in bronchial secretions (1 A. fumigatus, 1 A. flavus, 1 A. fumigatus + A. flavus, 1 A. fumigatus + A. terreus and 1 A. terreus) while culture was negative in one patient. All isolates were susceptible to antifungal drugs. Serum galactomannan (GM), pan-Aspergillus PCR and (1,3)-ß-D-glucan (BDG) were positive in 4/6 (67%), 5/6 (83%, 3/5 in two consecutive samples) and 4/6 (67%, in consecutive samples) patients, respectively. GM and PCR positive bronchial secretions had GM indices > 9.95 and PCR Ct < 34. All were treated with antifungal drugs with 5 out of 6 receiving isavuconazole. Mortality was 67% (4/6) with 1/4 attributed to CAPA (two died as a result of bacterial septic shock and one as a result of multiorgan failure). CONCLUSION: The incidence of CAPA in ICU patients was 3.3% and it was associated with approximately a 17% attributable mortality in the setting of MDR gram-negative pathogen co-infections.

Phenotypic/Genotypic Profile of OXA-10-Like-Harboring, Carbapenem-Resistant Pseudomonas aeruginosa: Using Validated Pharmacokinetic/Pharmacodynamic In Vivo Models To Further Evaluate Enzyme Functionality and Clinical Implications.

In vitro MICs and in vivo pharmacodynamics of ceftazidime and cefepime human-simulated regimens (HSR) against modified carbapenem inactivation method (mCIM)-positive Pseudomonas aeruginosa isolates harboring different OXA-10-like subtypes were described. The murine thigh model assessed ceftazidime (2 g every 8 h [q8h] HSR) and cefepime (2 g and 1 g q8h HSR). Phenotypes were similar despite possessing OXA-10-like subtypes with differing spectra. Ceftazidime produced ≥1-log10 killing in all isolates. Cefepime activity was dose dependent and MIC driven. This approach may be useful in assessing the implications of ß-lactamase variants.

Detection of KPC, NDM and VIM-Producing Organisms Directly from Rectal Swabs by a Multiplex Lateral Flow Immunoassay.

We report a preliminary evaluation of the NG-Test CARBA 5 immunochromatographic assay for detecting carbapenemases directly from rectal swabs on the same day of sampling. Thirty fecal swabs were examined for carbapenemase-producing organisms (CPOs) by conventional culture, PCR, and NG-Test CARBA 5. Each sample was tested by the immunochromatographic assay five times, including direct testing and incubation in trypticase soy broth for 1, 2, 3, and 4 h. Twenty patients yielded CPOs by culture. Immunochromatographic and PCR results were concordant and detected the same 25 carbapenemases (11 KPC, 8 VIM, and 6 NDM). In five cases, we detected co-carriage of KPC and VIM. Compared with PCR, the sensitivity of NG-Test CARBA 5 for the detection of KPC, VIM, and NDM was 80% without incubation, 88% with one hour, 92% with two, and 100% with three hours incubation, while specificity was 100% for all time points. All samples containing adequate fecal content were detected by NG-Test CARBA 5 concordantly with PCR, without incubation. NG-Test CARBA 5 is a reliable test that rapidly detects the presence of carbapenemases at the same day of sampling, directly from rectal swabs. It thus provides early information to guide antimicrobial treatment and infection control interventions.

Activity of Sulbactam-Durlobactam and Comparators Against a National Collection of Carbapenem-Resistant Acinetobacter baumannii Isolates From Greece.

BACKGROUND: Acinetobacter baumannii is a leading cause of healthcare-associated infections worldwide, due to both its persistence in the hospital setting and ability to acquire high levels of antibiotic resistance. Carbapenem-resistant A. baumannii isolates (CRAB) limit the activity of current antimicrobial regimens and new alternatives or adjuncts to traditional antibiotics are urgently needed. Durlobactam is a novel broad-spectrum inhibitor of serine-type ß-lactamases that restores sulbactam (SUL) activity against A. baumannii. The sulbactam-durlobactam (SD) combination has recently completed Phase 3 testing in the global ATTACK trial. OBJECTIVES: The aim of this study is to evaluate the in vitro activity of SD versus comparators against a representative nationwide collection of CRAB isolates. METHODS: One hundred ninety CRAB isolates were collected from clinical samples of patients hospitalized in 11 hospitals throughout Greece during 2015. In vitro activities of SD and comparators (SUL alone, amikacin, minocycline, imipenem, meropenem, colistin, SD and imipenem combined with SD) were determined by broth microdilution. RESULTS: Durlobactam restored sulbactam activity against the majority of the strains tested, with SD exhibiting the lowest MIC90 (8 µg/ml) relative to the other single comparators tested; 87.9% of the isolates had SD MICs ≤4/4 µg/ml. The most active comparator was colistin (MIC90 = 16 µg/ml). The addition of imipenem further lowered the MIC90 of SD by one two-fold dilution. CONCLUSIONS: This study demonstrated the potential utility of SD for the treatment of infections caused by A. baumannii. If its clinical efficacy is confirmed, SD may be an important therapeutic option for CRAB infections.

Use of point-of-care molecular tests reduces hospitalization and oseltamivir administration in children presenting with influenza-like illness.

Influenza is associated with increased morbidity, healthcare costs, hospitalization rates, and mortality in children. Rapid immunochromatography assay (ICA), a test with low sensitivity, is often used as point-of-care (POC) test. Recently, the rapid syndromic molecular test FilmArray has become available. This observational study aims to evaluate whether the use of FilmArray would decrease the use of antivirals and hospitalization rates among children presenting to the emergency room (ER) with influenza-like illness (ILI) symptoms. Nasopharyngeal swabs were prospectively collected from children, aged 0-16 years, presenting with ILI at the ER of a tertiary hospital during the peak endemic period. Patients were allocated to be tested by either FilmArray or ICA. The use of antivirals and hospitalization rates were noted. Logistic regression models were used to investigate the impact of testing methods on decision-making. Overall, 80 children were included (mean age: 5 years). Admissions were more likely to occur if an ICA test was performed (OR, 3.16; 95% CI, 1.01-9.82; p = .046). Oseltamivir administration was more likely among children who had undergone the ICA test (OR, 4.67; 95% CI, 1.06-20.43; p = .041). The implementation of rapid molecular test had no impact on complementary diagnostic testing or antibacterial prescription. The use of FilmArray significantly reduced both hospitalization and oseltamivir administration in children. Further knowledge on the use of POC tests is required to improve current management of children presenting with ILI and decrease associated healthcare costs.

Enterococcus casseliflavus Bacteraemia in a Patient with Chronic Renal Disease.

Enterococcus casseliflavus is a rare pathogen that usually causes urinary tract and abdominal infections. Its main characteristics are positive motility, yellow colonies and constitutive low-level resistance to vancomycin. We present a case of E. casseliflavus bacteraemia due to thrombophlebitis at the site of the central venous catheter used for hemodialysis in a renal patient. The biochemical identification of the microorganism was further corroborated by molecular detection of the vanC gene. The patient received antibiotic therapy initially with daptomycin and gentamicin, and then with ampicillin and ceftriaxone. The outcome was cure, and he was released from the hospital after seven weeks afebrile with negative blood cultures.

Gastrointestinal Carriage of Vancomycin-Resistant Enterococci and Carbapenem-Resistant Gram-Negative Bacteria in an Endemic Setting: Prevalence, Risk Factors, and Outcomes.

Background: Gastrointestinal carriage of vancomycin-resistant enterococci (VRE) and carbapenem-resistant Gram-negative bacteria (CRGN) constitutes a major public health concern as it may be followed by clinical infection development or lead to intra-hospital dissemination. Detection of carriers and implementation of infection control measures are essential in every hospital. In this study we determined the point prevalence of VRE and CRGN in the fecal flora of the inpatients of a tertiary university hospital in Greece. We determined risk factors for carriage and examined the impact of carriage on hospital outcomes. Materials/Methods: A point prevalence study of VRE/CRGN rectal carriage of inpatients was conducted on March 2018. Specimens were selectively cultured for VRE/CRGN, microorganisms were biochemically identified, submitted to antibiotic susceptibility testing, and tested for carbapenemase production. Data on potential risk factors and hospital outcomes were collected at the time of culture and until hospital discharge. Multivariable logistic and linear regression models were used, adjusting for confounders. Results: Four hundred ninety-one patients were enrolled in the study. Of them, 64 (13.0%) were positive for VRE carriage, 40 (8.2%) for CRGN, and 10 patients (2.1%) for both VRE and CRGN. VRE carriage was independently associated with age over 65 years (adjusted OR: 2.4 [95%CI: 1.3, 4.5]) and length of stay (LOS) before rectal sampling (OR: 1.1 [95%CI: 1.0, 1.1]). Carriage of CRGN was associated with 11 days increase of LOS after rectal sampling (ß-coef: 11.4 [95%CI: 1.6, 21.2]), with a 3.5-fold increased risk of acquiring a resistant pathogen after rectal swabbing (RR: 3.5 [95%CI 1.2, 9.9]) and with a 6-fold increased risk of mortality (RR: 6.1 [95%CI: 2.1, 17.9]), after adjusting for sex, age, and comorbidity index. Conclusions: High prevalence rates were found for VRE and CRGN carriage among the inpatients of our hospital. Prolonged hospitalization and age were independent risk factors for VRE carriage, while CRGN carriage was associated with increased risk of acquiring a resistant pathogen, prolonged hospital stay, and increased mortality.

Epidemiological Trends of Fungemia in Greece with a Focus on Candidemia during the Recent Financial Crisis: a 10-Year Survey in a Tertiary Care Academic Hospital and Review of Literature.

Updated information on the epidemiology of candidemia, particularly during severe socioeconomic events, is important for proper management of these infections. A systematic literature review on candidemia in Greece and a retrospective surveillance study were conducted in a tertiary university hospital during the years of the recent financial crisis (2009 to 2018) in order to assess changes in incidence rates, patient characteristics, species distribution, antifungal susceptibilities, and drug consumption. The average annual incidence of 429 candidemic episodes was 2.03/10,000 bed days, with 9.88 in adult intensive care units (ICUs), 1.74 in surgical wards, and 1.81 in internal medicine wards, where a significant increase was observed (1.15, 1.85, and 2.23/10,000 bed days in 2009 to 2011, 2012 to 2014, and 2015 to 2018, respectively; P = 0.004). Candida albicans was the most common species (41%), followed by Candida parapsilosis species complex [SC] (37%), Candida glabrata SC (11%), Candida tropicalis (7%), Candida krusei (1%), and other rare Candida spp. (3%). Mixed infections were found in 20/429 (4.7%) cases, while 33 (7%) cases were due to non-Candida spp. Overall, 44/311 (14%) isolates were resistant/non-wild type (WT) to the nine antifungals tested, with 23/113 (20%) C. parapsilosis SC and 2/34 (6%) C. glabrata SC isolates being resistant to fluconazole (1 panechinocandin and 2 panazole resistant). All isolates were susceptible/WT to amphotericin B and flucytosine. While the overall consumption of antifungals diminished (P = 0.02), with a mean of 17.93 defined daily doses (DDD)/100 bed days, increased micafungin use was correlated with the rise in C. parapsilosis SC (P = 0.04). A significant increase of candidemia in internal medicine wards and of C. parapsilosis SC infections was found during the years of financial crisis. Although resistance rates remain low (<14%), fluconazole-resistant C. parapsilosis SC and multidrug-resistant C. glabrata SC isolates are of major concern.

An update on polymyxin susceptibility testing methods for Acinetobacter baumannii.

Introduction: Carbapenem-resistant Acinetobacter baumannii (CRAB) currently comprises >50% of A. baumannii isolates in Europe and the USA and commonly are extensively or pandrug resistant. They cause severe hospital infections, which according to CDC have very high mortality. Polymyxins are universally recognized as the last-line choice against CRAB infections. The role of polymyxin susceptibility testing (ST) for these pathogens remains a subject of debate, although it is critical for selection of appropriate antimicrobial therapy. There are significant discrepancies between in vitro ST methods and important shortcomings for diffusion and automated methods have been repeatedly verified. The joint CLSI-EUCAST Working Group has recently recommended broth microdilution (BMD) without additives as the reference method for polymyxin ST. Areas covered: This review, focused on this threatening pathogen, summarizes the current available ST methods for polymyxins and discusses the challenges encountered by clinical microbiological laboratories in obtaining and interpreting valid susceptibility results. Studies on polymyxin ST methods for Acinetobacter spp., retrieved from Pubmed database until May 2019, were evaluated. Expert opinion: Currently, no single commercial ST method for polymyxins is providing fully accurate results. Further optimization and standardization of the ST methods and international harmonization of guidelines should be achieved to facilitate the accurate detection of polymyxin-resistant A. baumannii.

Triple combination of meropenem, colistin and tigecycline was bactericidal in a dynamic model despite mere additive interactions in chequerboard assays against carbapenemase-producing Klebsiella pneumoniae isolates.

Background: Combination schemes are commonly used for the treatment of infections due to carbapenemase-producing Klebsiella pneumoniae (CP-Kp). We therefore investigated the in vitro effectiveness of double and triple combinations of meropenem, colistin and tigecycline against CP-Kp isolates with different resistance mechanisms in a static broth microdilution model and a pharmacokinetic-pharmacodynamic model. Methods: One WT isolate and seven CP-Kp isolates with different carbapenem resistance mechanisms and increasing MICs of meropenem (4-512 mg/L), colistin (0.5-32 mg/L) and tigecycline (0.25-4 mg/L) were tested with a 3D chequerboard microdilution method. Combinations were then assessed in an in vitro pharmacokinetic-pharmacodynamic model simulating 50 and 100 mg of tigecycline q12h as a 1 h infusion, 4.5 million units of colistin q12h as a 1 h infusion and 1 g of meropenem q8h as 1 and 0.5 h infusions for 2 days. Results: In the chequerboard assay, interactions within the triple combination were mainly additive with a median (range) fractional inhibitory index of 0.66 (0.22-1.26). In the dynamic model, meropenem alone was bactericidal against isolates with MICs up to 4 mg/L, whereas bactericidal activity was found with the double combination meropenem + colistin and the triple combination meropenem + colistin + tigecycline against CP-Kp isolates with meropenem MICs of 16 and 256 mg/L, respectively. A high dose (100 mg) of tigecycline and a prolonged infusion (1 h) of meropenem increased the efficacy of the triple combination. Conclusions: Despite the merely additive interactions in the chequerboard assay, the triple combination of meropenem, tigecycline and colistin was bactericidal in the dynamic model against highly resistant CP-Kp isolates. This effect was more pronounced if prolonged infusion of meropenem and high tigecycline dosing were used.

Exploring colistin pharmacodynamics against Klebsiella pneumoniae: a need to revise current susceptibility breakpoints.

Objectives: Because the pharmacokinetic/pharmacodynamic (PK/PD) characteristics of colistin against Enterobacteriaceae are not well explored, we studied the activity of colistin against K. pneumoniae in an in vitro PK/PD model simulating different dosing regimens. Methods: Three clinical isolates of K. pneumoniae with MICs of 0.5, 1 and 4 mg/L were tested in an in vitro PK/PD model following a dose-fractionation design over a period of 24 h. A high and low inoculum of 107 and 104 cfu/mL with and without a heteroresistant subpopulation, respectively, were used. PK/PD indices associated with colistin activity were explored and Monte Carlo analysis was performed in order to determine the PTA for achieving a bactericidal effect (2 log kill). Results: The fAUC/MIC (R2 = 0.64-0.68) followed by fCmax/MIC (R2 = 0.55-0.63) best described colistin's 24 h log10 cfu/mL reduction for both low and high inocula. Dosing regimens with fCmax/MIC ≥6 were always associated with a bactericidal effect (P = 0.0025). However, at clinically achievable concentrations, usually below fCmax/MIC = 6, an fAUC/MIC ≥25 was more predictive of a bactericidal effect. Using a dosing regimen of 9 MU/day, the PTA for this pharmacodynamic target was 100%, 5%-70% and 0%, for isolates with MICs of ≤0.5, 1 and ≥2 mg/L, respectively. Dosing regimens that aim for a trough level of 1 mg/L achieve coverage of strains up to 0.5 mg/L (target trough/MIC = 2 mg/L). Conclusions: Characterization of the pharmacodynamics of colistin against Enterobacteriaceae in an in vitro model of infection indicates that a revision of current susceptibility breakpoints is needed. Therapeutic drug monitoring of colistin to achieve pharmacodynamic targets in individual patients is highly recommended.

Dissemination of linezolid-dependent, linezolid-resistant Staphylococcus epidermidis clinical isolates belonging to CC5 in German hospitals.

Objectives: Linezolid-resistant Staphylococcus epidermidis (LRSE) and linezolid-dependent ST22 strains have been shown to predominate in tertiary care facilities all over Greece. We report herein the dissemination of ST22 but also ST2, ST5 and ST168 linezolid-dependent LRSE clones in four unrelated German hospitals. Methods: Fourteen LRSE clinical isolates recovered during 2012-14 from five distantly located German hospitals were tested by for MIC determination broth microdilution and Etest, PCR/sequencing for cfr and for mutations in 23S rRNA, rplC, rplD and rplV genes, MLST, PFGE and growth curves without and with linezolid at 16 and 32 mg/L. Results: Most (11, 78.6%) isolates had linezolid MICs >256 mg/L. Five isolates carried the cfr gene. Eight isolates belonged to ST22, two isolates each to ST168 and ST2 and one isolate each to ST5 and ST23. Ten isolates [seven belonging to ST22 and one to each of ST2, ST5 and ST168; all these STs belong to clonal complex (CC) 5] exhibited linezolid-dependent growth, growing significantly faster in linezolid-containing broth. Four isolates were non-dependent (one belonging to each of ST22, ST2, ST23 and ST168). Four isolates came from three different hospitals, whereas four and six isolates were recovered during outbreaks of LRSE in two distinct hospitals. Conclusions: The multi-clonal dissemination of CC5 linezolid-dependent LRSE throughout German hospitals along with the clonal expansion of ST22 linezolid-dependent LRSE in Greek hospitals is of particular concern. It is plausible that this characteristic is inherent and provides a selective advantage to CC5 LRSE under linezolid pressure, contributing to their dissemination throughout hospitals in these countries.