Tigecycline MIC Research Articles

In vitro activity of imipenem-relebactam against non-MBL carbapenemase-producing Klebsiella pneumoniae isolated in Greek hospitals in 2015-2016.

Relebactam is a β-lactamase inhibitor of class A and class C β-lactamases, including carbapenemases. We evaluated the ability of relebactam to restore imipenem susceptibility against a collection of Klebsiella pneumoniae isolates from Greek hospitals. We tested 314 non-MBL carbapenemase-producing K. pneumoniae consecutive clinical strains isolated from unique patients at 18 hospitals in Greece, between November 2014 and December 2016. Susceptibility testing of imipenem, imipenem-relebactam, meropenem, doripenem, gentamicin, and colistin was performed using broth microdilution. Additionally, MICs of ceftazidime-avibactam, fosfomycin, and tigecycline were determined by MIC Test Strips. MICs were interpreted per EUCAST breakpoints. Imipenem-relebactam MICs were interpreted using the breakpoints proposed for imipenem. Carbapenemase genes were detected using PCR. Whole genome sequencing was performed for selected isolates. Imipenem-relebactam inhibited 98.0% of the KPC-producing isolates at ≤ 2mg/L (MIC50/90, 0.25/1mg/L) and was considerably more active than imipenem (MIC50/90, 32/> 64mg/L). Reduced activity of imipenem-relebactam was rarely detected (2%) and was associated with chromosomal factors (ompK35 disruption and/or mutated ompK36). Only ceftazidime-avibactam showed in vitro activity comparable to imipenem-relebactam (99.6% susceptible). Relebactam provided only weak potentiation of imipenem activity against K. pneumoniae with class D OXA-48-like enzymes. Relebactam exhibited strong potential for restoring the in vitro activity of imipenem against KPC-producing K. pneumoniae, lowering the imipenem MIC50 and MIC90 from 32 to 0.25mg/L, and from > 64 to 1mg/L, respectively. Production of KPC carbapenemase represents the main cause of carbapenem resistance among K. pneumoniae in Greek hospitals (66.5%), and this carbapenemase appears to be very well inhibited by relebactam.

Once-a-week tigecycline for the treatment of drug-resistant TB.

MDR-TB and XDR-TB have poor outcomes. To examine the efficacy of tigecycline monotherapy in the hollow fibre system model of TB. We performed pharmacokinetic/pharmacodynamic studies using tigecycline human-like concentration-time profiles in the hollow fibre system model of TB in five separate experiments using Mycobacterium tuberculosis in log-phase growth or as semi-dormant or intracellular bacilli, as monotherapy. We also compared efficacy with the isoniazid/rifampicin/pyrazinamide combination (standard therapy). We then applied extinction mathematics, morphisms and Latin hypercube sampling to identify duration of therapy with tigecycline monotherapy. The median tigecycline MIC for 30 M. tuberculosis clinical and laboratory isolates (67% MDR/XDR) was 2 mg/L. Tigecycline monotherapy was highly effective in killing M. tuberculosis in log-phase-growth and semi-dormant and intracellular M. tuberculosis. Once-a-week dosing had the same efficacy as daily therapy for the same cumulative dose; thus, tigecycline efficacy was linked to the AUC0-24/MIC ratio. Tigecycline replacement by daily minocycline after 4 weeks of therapy was effective in sterilizing bacilli. The AUC0-24/MIC ratio associated with optimal kill was 42.3. Tigecycline monotherapy had a maximum sterilizing effect (day 0 minus day 28) of 3.06 ± 0.20 log10 cfu/mL (r2 = 0.92) compared with 3.92 ± 0.45 log10 cfu/mL (r2 = 0.80) with optimized standard therapy. In our modelling, at a tigecycline monotherapy duration of 12 months, the proportion of patients with XDR-TB who reached bacterial population extinction was 64.51%. Tigecycline could cure patients with XDR-TB or MDR-TB who have failed recommended therapy. Once-a-week tigecycline could also replace second-line injectables in MDR-TB regimens.

Synergy Testing by E-Test and Microdilution Checkerboard for Fosfomycin Combined with Tigecycline against KPC-Producing Klebsiella pneumoniae

KPC-producing Klebsiella pneumoniae (KPC-Kp) has become a serious threat to patients worldwide, as the treatment options are limited. The combination of fosfomycin with other antibiotics has been reported but with inconsistent results. Thus, we performed synergy testing of fosfomycin combined with tigecycline by E-test, which was easy to perform and to determine results, compared with microdilution checkerboard, which is considered to be the "gold standard", to evaluate the agreement between the two methods. Thirty non-repetitive KPC-Kp isolates from different patients were included in this study. Bacterial identification and routine antibiotic susceptibility testing were performed by a VITEK 2 Compact automated system. The KPC producing isolates were identified by modified Carbapenem Inhibitory Method (mCIM) and PCR amplification of carbapenemase genes. Synergy testing of fosfomycin combined with tigecycline was performed by E-test (E-test stripes were placed at 90° angle), with microdilution chequerboard performed in parallel. Fractional inhibitory concentration index (FICI) was calculated. Statistical analyses were performed by SPSS 18.0 software. All 30 KPC-Kp were mCIM test positive and KPC-2 producing. The susceptibility rates of fosfomycin and tigecycline were 36.7% (11/30) and 63.3% (19/30), respectively. Both checkerboard and E-test results showed that most MICs of fosfomycin and tigecycline decreased in the combination group. FICI showed 13.3% - 16.7% isolates were synergistic, 30.0% - 36.7% were additive, and 50.0% - 53.3% were indifferent. No antagonism was found. There was no significant difference between the two groups (p > 0.05), and the overall agreement (with FICI difference ≤ 0.25 in each isolate) between the two methods was 76.7% (23/30). The synergy testing results determined by E-test correlated well with microdilution checkerboard. Thus E-test synergy testing has the potential to be used in routine clinical laboratory.

Detection and characterization of tigecycline heteroresistance in E. cloacae: clinical and microbiological findings

ABSTRACT Tigecycline is regarded as a last-resort treatment for carbapenem-resistant Enterobacteriaceae (CRE), however, the emergence of tigecycline heteroresistance has posted the therapeutic challenge to combat this “nightmare bacteria”. The primary purpose of this study was to demonstrate the existence of tigecycline heteroresistance in carbapenem-resistant E. cloacae (TH-CRECL) and further to explore the epidemiological characteristics and underlying molecular mechanisms. Our study identified a relative low prevalence of carbapenem-resistant E. cloacae (CRECL) isolates, about 20.0% (28/140), as heteroresistance to tigecycline. Molecular genetic relatedness of these heteroresistant isolates were characterized epidemiologically sporadic. In addition, mechanistic analysis revealed that Phe-Arg-β-naphthylamide (PAβN) significantly reversed tigecycline MIC levels of resistant colonies in heteroresistant strains, as primarily related to the marked overproduction of efflux pump genes acrAB and oqxAB, as well as overexpression of transcriptional regulators (soxS and ramA). Moreover, logistic regression analysis showed that previous fluoroquinolone therapy was identified as the only potential independent risk factor for the acquisition of TH-CRECL. Most importantly, our data indicated that patients with TH-CRECL infection might lead to a remarkably prolonged hospital stay and deterioration in functional status. These findings emphasized the necessity of timely detection and intervention of patients infected with TH-CRECL.

Antimicrobial susceptibility among gram-positive and gram-negative blood-borne pathogens collected between 2012-2016 as part of the Tigecycline Evaluation and Surveillance Trial

BackgroundAntimicrobial activity of tigecycline and comparator agents was assessedin vitroagainst 27857 isolates source from blood samples collected between 2012 and 2016 as part of the Tigecycline Evaluation and Surveillance Trial (TEST).MethodsThe broth microdilution methods was used to determine minimum inhibitory concentrations (MIC) of blood-borne isolates according to guildlines of the Clinical and Laboratory Standards Institute (CLSI). Antimicrobial susceptibility breakpoints from CLSI guidelines were used as standards to determine susceptibility against comparator agents, whereas tigecycline breakpoints were provided by the US Food and Drug Administration (FDA).ResultsMore than 91% Enterobacteriaceae isolates, belonging to Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacaeandSerratia marcescens, were susceptible to amikacin, meropenem, and tigecycline. Meropenem resistance was observed in 8% ofK.pneumoniae isolates worldwide. Extended-spectrum β-lactamase (ESBL) was produced in 15.9 and 20.9%E.coli and K.pneumoniaeisolates, respectively. MIC90 of tigecycline against Acinetobacter baumannii was 2 μg/ml. The highest proportion of susceptible A.baumanniiisolates was 70.8% for minocycline. Among P.aeruginose isolates worldwide, 71.1–94.9% were susceptible to six antibiotics. Almost all Staphylococcus aureusisolates were susceptible to linezolid(100%), vancomycin(100%), and tigecycline (99.9%). The proportion of methicillin-resistant S.aureus (MRSA) was 33.0% among S.aureusisolates worldwide; it was highest in Asia with 46.6%, followed by North America and Latin America with 37.7 and 34.2%, respectively. Vancomycin-resistant (VR) isolates represented 1.4% ofEnterococcus faecalis (VR.E.faecalis) and 27.6% of Enterococcus faecium(VR.E.faecium). Highest percentages of VR.E.faeciumwere found in North America and Latin America, with 61.6 and 58.1% of the isolates, respectively. Production of penicillin-resistant Streptococcus pneumoniae(PRSP) represented 9.0% of S. pneumoniae isolates worldwide; the PRSP proportion was 25.8% in Asia, 13.0% in Africa, and 11.8% in Latin America.ConclusionsIn our study, tigecycline was the only antibiotic that was active against over 90% of all major blood-borne pathogens. A global comparison revealed that antimicrobial resistance was higher in Africa, Asia and Latin America than in Europe and North America.

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.

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. 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. 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. 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.

In vitro activity of tigecycline and comparators (2014–2016) among key WHO ‘priority pathogens’ and longitudinal assessment (2004–2016) of antimicrobial resistance: a report from the T.E.S.T. study

We report contemporary (2014-2016) Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) global data on activity of tigecycline and comparators against WHO 'priority pathogens', and global trends (2004-2016) in antimicrobial resistance. MICs were determined using CLSI broth microdilution methodology. Antimicrobial resistance was determined using CLSI breakpoints (FDA breakpoints for tigecycline). Data are reported for Africa, Asia, Europe, North America and South America. From 2014-2016, Africa, Asia and South America reported highest resistance rates among Acinetobacter baumannii; North America lowest (all antimicrobials tested). The tigecycline MIC90 against A. baumannii was 2 mg/L in all regions except South America (1 mg/L). Among Enterobacteriaceae, meropenem resistance was low and tigecycline resistance was ≤1.3% in all regions (Escherichia coli, 0.0-0.3%; Klebsiella pneumoniae 0.0-1.3%; Enterobacter spp. 0.5-1.1%; Serratia marcescens 0.0-1.3%). Ceftriaxone resistance among E. coli ranged from 14.5% (North America) to 54.7% (Asia), and among K. pneumoniae from 9.1% (North America) to 54.0% (South America). North America reported highest rates of vancomycin-resistant Enterococcus faecium (64.6%); Europe lowest (17.7%). The tigecycline MIC90 against methicillin-resistant Staphylococcus aureus (MRSA) ranged from 0.12 mg/L (Africa and North America) to 0.5 mg/L (Asia). From 2004-2016, carbapenem resistance increased among A. baumannii (all regions), reaching 92.3% in Africa and 85.7% in South America (2016). Rates of ceftriaxone-resistant E. coli increased in all regions except Asia. Ceftriaxone resistance in K. pneumoniae increased in Europe. Rates of vancomycin-resistant E. faecium and MRSA were highest in North America and South America (and Asia for MRSA); lowest in Europe.

Overexpression of OqxAB and MacAB efflux pumps contributes to eravacycline resistance and heteroresistance in clinical isolates of Klebsiella pneumoniae

This study investigated the characteristics and mechanisms of eravacycline resistance and heteroresistance in clinical Klebsiella pneumoniae isolates. A total of 393 clinical K. pneumoniae isolates were collected and subjected to eravacycline and tigecycline MIC determinations using the agar dilution method. Eravacycline heteroresistance was assessed by a population analysis profile (PAP). The expression levels of efflux pumps and their regulators were determined by quantitative reverse-transcription PCR (qRT-PCR). This study identified 67 eravacycline-nonsusceptible isolates; among the extended-spectrum β-lactamase (ESBL)-positive isolates, eravacycline-nonsusceptible isolates were detected more frequently than tigecycline-nonsusceptible isolates (21.7% vs. 9.4%, p = 0.001). The study sample was observed to include 20 K. pneumoniae isolates with eravacycline heteroresistance. Compared to the reference strain, oqxA or oqxB overexpression was observed in nine eravacycline-nonsusceptible isolates (range, 35.64–309.02-fold) and 13 eravacycline-heteroresistant isolates (8.42–296.34-fold). The overexpression of macA or macB was detected in 12 eravacycline-heteroresistant isolates (3.23–28.35-fold). Overexpression of the efflux pump regulator gene ramA was observed in 11 eravacycline-nonsusceptible isolates (3.33–94.05-fold) and 18 eravacycline-heteroresistant isolates (3.89–571.70-fold). The eravacycline MICs were increased by one–fourfold by overexpression of oqxAB or macAB in three eravacycline-sensitive isolates. In conclusion, the overexpression of OqxAB and MacAB efflux pumps and the transcriptional regulator RamA were suggested to be involved in K. pneumoniae eravacycline resistance and heteroresistance.

Antibiotic susceptibility and resistance profiles of Romanian Clostridioides difficile isolates

Abstract This study investigated the antibiotic susceptibility patterns and genetic resistance markers of 35 C. difficile strains isolated from patients with C. difficile infection. Vancomycin, metronidazole, tigecycline, teicoplanin, rifampicin, moxifloxacin, cefotaxime, tetracycline, erythromycin, clindamycin, chloramphenicol, linezolid and imipenem MICs were determined for toxigenic strains belonging to PCR ribotypes (PR) 012 (2), 014 (4), 017 (3), 018 (2), 027 (17), 046 (2), 087 (3) and 115 (2). Results showed vancomycin, metronidazole, tigecycline and teicoplanin to be active against all isolates. High resistance rates were noticed against cefotaxime (n = 35), clindamycin (n = 33), imipenem (n = 31), moxifloxacin (n = 25), erythromycin (n = 25) and rifampicin (n = 22). Linezolid-resistance was found in three isolates (PR 017/2, PR 012/1), showing complex resistance (7-9 antibiotics). PR 012, 017, 018, 027 and 046 isolates (n = 26) were resistant to 5-9 antibiotics. Twelve resistance profiles (2-9 antibiotics) were detected. Rifampicin-moxifloxacin-cefotaxime-erythromycin-clindamycin-imipenem-resistance was predominant, being expressed by 18 strains (PR 027/17, PR 018/1). PCR results suggested tetracycline-resistance to be induced by the gene tetM. Three tetM-positive isolates (PRs 012, 046), were also tndX-positive, suggesting the presence of a Tn5397-like element. Only two MLSB-resistant strains (PR 012) had the ermB gene and chloramphenicol-resistance determinant catD was not detected, leaving room for further investigating resistance mechanisms. Multidrug resistance could be attributed to most analysed strains, underlining, once more, the impact of wide-spectrum antimicrobial over prescription, still a tendency in our country, on transmission of antimicrobial resistance and emergence of epidemic C. difficile strains generating outbreaks.

Diversity of mutations in regulatory genes of resistance-nodulation-cell division efflux pumps in association with tigecycline resistance in Acinetobacter baumannii.

To investigate the mechanisms of tigecycline resistance in isogenic Acinetobacter baumannii isolate pairs as well as 65 unique clinical A. baumannii isolates obtained during the MagicBullet clinical trial from Greece, Italy and Spain. A. baumannii isolates were subjected to WGS and the regulatory genes of resistance-nodulation-cell division (RND)-type efflux pumps were analysed. MICs were determined by agar dilution and the expression of RND-type efflux pumps was measured by semi-quantitative RT-PCR. In isolate pairs, disruption of adeS or adeN by ISs increased adeB or adeJ expression and conferred increased resistance to at least three antimicrobial classes, respectively. The insertion of ISAba1 in adeN was observed in more than 30% of tested isolates and was the most prevalent IS. Furthermore, the insertion of ISAba125 and ISAba27 into adeN was observed for the first time in A. baumannii isolates. Besides ISs, several different mutations were observed in adeN (e.g. deletions and premature stop codons), all of which led to increased tigecycline MICs. Moreover, several amino acid substitutions were detected in AdeRS, AdeN and AdeL. Of note, the substitutions D21V, G25S and D26N in AdeR were found in multiple sequences and suggest a mutational hotspot. This study provides an insight into the different mechanisms associated with tigecycline resistance using a genomic approach and points out the importance of considering adeRS and adeN as markers for tigecycline-resistant A. baumannii isolates.

Use of Monte Carlo simulation to evaluate the efficacy of tigecycline and minocycline for the treatment of pneumonia due to carbapenemase-producing Klebsiella pneumoniae

Background: Pneumonia caused by carbapenemase-producing Klebsiella pneumoniae (CP-KP) are increasingly encountered in hospitals worldwide, causing high mortality due to lack of treatment options. The goal of this study was to assess the efficacy of tigecycline and minocycline for CP-KP hospital-acquired pneumonia (HAP) by using Monte Carlo simulation.Methods: A total of 164 non-duplicated CP-KP strains were collected from sputum or blood in patients with HAP. The MICs for antimicrobials were determined by the agar dilution method. A 10,000-patient Monte Carlo Simulation based on a PK/PD model incorporating the MICs and population pharmacokinetic parameters were conducted to calculate probability of target attainment (PTA) at each MIC value and total cumulative fraction of response (CFR).Results: The susceptibility rate of tigecycline and minocycline were 79.9% and 41.5%, respectively. At recommended doses, an optimal PTA of 90% was obtained for treating HAP caused by CP-KP with MICs of tigecycline ≤0.5 mg/L or minocycline ≤4 mg/L. The CFR of tigecycline at the recommended dose and double dose (100 mg q12h) were 71.2% and 90.2%, respectively. The CFR of minocycline at recommended dose and double dose (200 mg q12h) was 53.4% and 77.2%, respectively.Conclusions: The findings of this study suggest that the recommended dose of tigecycline was not effective in HAP caused by CP-KP, and a higher CFR indicating a better clinical efficacy can be gained by doubling the dose (100 mg q12h). minocycline (200 mg q12h) might be a potential alternative of tigecycline to against strains with MICs ≤ 8 mg/L.

Antibiotic susceptibility of Francisella tularensis subsp. holarctica strains isolated from tularaemia patients in France between 2006 and 2016.

To determine the in vitro susceptibility to 18 antibiotics of human strains of Francisella tularensis isolated in France between 2006 and 2016, to check the absence of acquired resistance and to evaluate potential therapeutic alternatives. Fifty-nine clinically unrelated F. tularensis subsp. holarctica strains identified at the French National Reference Centre for Francisella as belonging to the phylogenetic subclade B.FTNF002-00 were used. MICs were determined in CAMHB medium supplemented with 2% PolyViteX®, using the CLSI broth microdilution method. All strains were susceptible to fluoroquinolones (ofloxacin, ciprofloxacin, levofloxacin and moxifloxacin; MIC range: 0.016-0.25 mg/L), aminoglycosides (gentamicin and tobramycin; MIC range: ≤0.03-0.25 mg/L), doxycycline (MIC range: 0.125-0.25 mg/L) and chloramphenicol (MIC range: 0.5-2 mg/L). The erythromycin MIC range (0.5-2 mg/L) confirmed that all isolates belonged to biovar I of F. tularensis subsp. holarctica. Azithromycin and telithromycin displayed lower MIC ranges (0.25-1 and 0.03-0.5 mg/L, respectively). The tigecycline MIC range (0.25-1 mg/L) was slightly higher than that of doxycycline. All strains were resistant to ampicillin, meropenem, daptomycin, clindamycin and linezolid. F. tularensis strains isolated in France remain susceptible to antibiotic classes recommended for tularaemia treatment. Because fluoroquinolones display the lowest MIC90, have bactericidal activity and have lower therapeutic failure rates compared with doxycycline, they may be advocated as first-line treatment of mild cases of tularaemia, predominant in Europe. MIC data also indicate that azithromycin or telithromycin may be possible therapeutic options against biovar I strains from Western Europe in case of contraindication to first-line antibiotics.

Role of insertion sequence Aba-1 and AdeS in reduced tigecycline susceptibility in MDR-Acinetobacter baumannii clinical isolates from Cairo, Egypt

Infections caused by multidrug resistant (MDR) Acinetobacter baumannii (A. baumannii) especially in intensive care units have limited therapeutic options. Overexpression of the adeABC efflux pump may be caused either by the ISAba-1 insertion or by specific point mutations in adeR and adeS, therefore, plays a major role in conferring MDR-A. baumannii. We aimed in our study to monitor the tigecycline (TGC) susceptibility and to study the role of ISAba-1 and the adeS regulator within the AdeABC efflux pump among MDR-A. baumannii clinical isolates. MDR-A. baumannii (63) isolated from ICU patients were identified by detection of OXA-51-like gene. TGC MIC was determined by E-test and broth microdilution. PCR analysis of adeR, adeS, adeB and ISAba1 genes were done with further sequencing of adeS gene. Reduced susceptibility to TGC (MIC: 3–4 mg/L) was noticed in 6/63 (9.5%) MDR-A. baumannii isolates, ISAba-1 was detected in three isolates that two of which showed amino acid substitutions in the adeS operon. We concluded that the amino acids mutations in the adeS gene in presence of insertion ISAba-1 may play a role in conferring reduced TGC susceptibility of MDR-A. baumannii.

Antimicrobial activity among gram-positive and gram-negative organisms collected from the Asia-Pacific region as part of the Tigecycline Evaluation and Surveillance Trial: Comparison of 2015 results with previous years

We report the in vitro activity of tigecycline and comparators against Gram-negative and Gram-positive organisms collected from Asia-Pacific during 2004–2010 and 2015. MICs were determined by broth microdilution using CLSI guidelines. Antimicrobial susceptibility was assessed using CLSI breakpoints, except for tigecycline FDA breakpoints. For Acinetobacter baumannii, multidrug-resistant (MDR) rates were 81.8% in 2015 and 48.5% during 2004–2010. Among Escherichia coli and Klebsiella pneumoniae respectively, rates of extended-spectrum β-lactamase-producers in 2015 were 24.6% and 15.8%, and during 2004–2010, 21.6% and 23.8%. Pseudomonas aeruginosa MDR rates were 12.7% in 2015 and 18.5% during 2004–2010. For Staphylococcus aureus, 57.1% were methicillin-resistant in 2015 and 46.3% between 2004 and 2010. For Streptococcus pneumoniae, 32.1% were penicillin-resistant in 2015 and 29.9% between 2004 and 2010. Tigecycline MIC90 values were ≤2mg/L against all species except P. aeruginosa, against which tigecycline is inactive. Antimicrobial resistance in Asia-Pacific is widespread, including a concerning increase in MDR A. baumannii.

Do bacteria isolated from ICU patients 'ESKAPE' antibiotic treatment? In vitro susceptibility of the Enterobacteriaceae family to tigecycline.

Enterobacteriaceae are currently causing the majority of healthcare-associated infections (HAI) and simultaneously expressing increasing levels of antibiotic resistance. The purpose of this study is to assess the in vitro sensitivity of MDR strains from the family Enterobacteriaceae to tigecycline in relation to their origin from patients hospitalized in intensive care units (ICUs) and non-ICUs. The study involved 156 clinically significant strains of the Enterobacteriaceae family isolated from patients with complicated intraabdominal infections (cIAIs) and/or complicated skin and skin structure infections (cSSSIs) hospitalized in ICUs and other surgical departments. Tigecycline MICs were determined by Etest. The highest percentage of tigecycline non-susceptible (intermediate + resistant strains) in vitro strains among the Enterobacteriaceae species were observed for Serratia spp. 77.3%, followed by Citrobacter spp. (76.9%) and Enterobacter spp. (70%); whereas K. pneumoniae and E. coli showed 73-73.8% tigecycline susceptibility rates. Tigecycline demonstrates a high level of antimicrobial in vitro activity when tested against E. coli and K. pneumoniae, even those with the ESBL-phenotype. Tigecycline retained activity against merely 22-30% of Enterobacter, Citrobacter and Serratia genera.

Roles of ramR and tet(A) Mutations in Conferring Tigecycline Resistance in Carbapenem-Resistant Klebsiella pneumoniae Clinical Isolates.

Tigecycline is regarded as a last-resort treatment for carbapenem-resistant Klebsiella pneumoniae (CRKP) infections, but increasing numbers of tigecycline-resistant K. pneumoniae isolates have been reported. The tigecycline resistance mechanisms in CRKP are undetermined. This study aimed to elucidate the mechanisms underlying tigecycline resistance in 16 tigecycline- and carbapenem-resistant K. pneumoniae (TCRKP) isolates. Mutations in tigecycline resistance determinant genes [ramR, acrR, oqxR, tet(A), tet(L), tet(X), tet(M), rpsJ] were assessed by PCR amplicon sequencing, and mutations in ramR and tet(A) exhibited high prevalences individually (81%) and in combination (63%). Eight functional ramR mutation profiles reducing tigecycline sensitivity were verified by plasmid complementation of wild-type and mutant ramR Using a site-specific mutant, the most frequent RamR mutation, A19V (60%), had no significant effect on tigecycline susceptibility or the upregulation of ramA and acrA Two tet(A) variants with double frameshift mutations, type 1 and type 2, were identified; type 2 tet(A) is novel. A parent strain transformed with a plasmid carrying type 1 or type 2 tet(A) increased the tigecycline MIC by 8-fold or 4-fold, respectively. Synergistic effects were observed in strains harboring no ramR gene and a mutated tet(A), with an 8-fold increase in the tigecycline MIC compared with that in strains harboring only mutated tet(A) being seen. Overall, mutations in the ramR and tet(A) efflux genes constituted the major tigecycline resistance mechanisms among the studied TCRKP isolates. The identification of strains exhibiting the combination of a ramR deficiency and widespread mutated tet(A) is concerning due to the possible dissemination of increased tigecycline resistance in K. pneumoniae.

Tigecycline resistance among carbapenem-resistant Klebsiella Pneumoniae: Clinical characteristics and expression levels of efflux pump genes

ObjectivesTigecycline is a treatment option for infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP). Emerging tigecycline resistance in CRKP represents a growing threat. Knowledge of the clinical, microbiological, and molecular characteristics of tigecycline- and carbapenem-resistant Klebsiella pneumoniae (TCRKP) is limited.MethodsPatients infected with TCRKP were identified from a Taiwanese national surveillance study. Clinical data were collected from medical records. We performed susceptibility tests, carbapenemase gene detection, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Furthermore, we performed quantitative real-time polymerase chain reaction (qRT-PCR) analyses to assess the expression levels of the efflux pump genes acrB and oqxB.ResultsWe identified 16 patients infected with TCRKP, with urinary tract infection (UTI) being the most common type of infection (63%). The all-cause 30-day mortality rate was 44% in patients with TCRKP infection. Patients with a site of infection other than the urinary tract had a significantly higher mortality rate than patients with UTIs (83% vs. 20%, p = 0.035). PFGE and MLST revealed no dominant clone or sequence type. Using qRT-PCR, overexpression of both the acrB and oqxB genes was identified in seven isolates, and overexpression of the oqxB gene was observed in another seven. There was poor correlation between acrB or oqxB expression and tigecycline MICs (r = -0.038 and -0.166, respectively).ConclusionsThe mortality rate in patients infected with TCRKP in this study was 44% and this is an important subset of patients. The absence of a linear relationship between efflux pump genes expression and MICs indicates that tigecycline resistance may be mediated by other factors. Continuous monitoring of tigecycline resistance among CRKP isolates and resistance mechanisms are necessary.

In vitro susceptibility to 19 agents other than β-lactams among third-generation cephalosporin-resistant Enterobacteriaceae recovered on hospital admission.

As part of the multicentre Antibiotic Therapy Optimisation Study, MIC values of 19 non-β-lactam agents were determined for third-generation cephalosporin-resistant Escherichia coli , Klebsiella species and Enterobacter species (3GCREB) isolates collected in German hospitals. A total of 328 E. coli , 35 Klebsiella spp. (1 Klebsiella oxytoca and 34 Klebsiella pneumoniae ) and 16 Enterobacter spp. (1 Enterobacter aerogenes and 15 Enterobacter cloacae ) isolates were submitted to broth microdilution antimicrobial susceptibility testing with the MICRONAUT system. MICs of fluoroquinolones (levofloxacin and moxifloxacin), aminoglycosides (gentamicin, tobramycin, amikacin, streptomycin, neomycin and paromomycin), tetracyclines (tetracycline, minocycline and tigecycline), macrolides (erythromycin, clarithromycin and azithromycin) and miscellaneous agents [trimethoprim/sulfamethoxazole, chloramphenicol, nitrofurantoin, colistin and fosfomycin intravenous (iv)] were determined and reviewed against 2016 EUCAST breakpoints. The MIC of levofloxacin was >2 mg/L for 128 of 328 E. coli and 8 of 35 Klebsiella spp., but only 1 of 16 Enterobacter spp. Rates of resistance to trimethoprim/sulfamethoxazole were high (>70%), except for Enterobacter spp. Rates of resistance to colistin and fosfomycin iv were still low. About 20% of the tested isolates were resistant to chloramphenicol. Only 1 (of 328) E. coli isolate had an MIC of amikacin >16 mg/L and only 33 of 328 E. coli and 1 of 35 Klebsiella spp. had an MIC of tobramycin >4 mg/L, whereas average gentamicin MICs were in general more elevated. A tigecycline MIC >2 mg/L was only found for 1 of 16 Enterobacter spp., but in none of the E. coli or Klebsiella spp. isolates. Our study gives insight into previously unreported non-β-lactam MIC distributions of 3GCREB isolates.

Assessment of the In Vivo Efficacy of Plazomicin (PLZ) Alone or in Combination with Meropenem (MEM) or Tigecycline (TGC) against Enterobacteriaceae (EB) Isolates Exhibiting Various Resistance Mechanisms in an Immunocompetent (I+) Murine Septicemia Model

BackgroundPLZ is a next-generation aminoglycoside with potent in vitro activity against multidrug- and carbapenem-resistant EB. The objective of this study was to assess the efficacy of PLZ human-simulated exposure, alone and in combination with MEM or TGC, against EB in the I+ murine septicemia model.MethodsICR mice were inoculated intraperitoneally with bacterial suspensions of 10 6.5 CFU/mL. Eight EB isolates with PLZ, MEM and TGC MICs ranging from 2 to 16, ≤0.015 to >32, and ≤0.06 to 2 mg/L, respectively, were utilized to assess the efficacy of PLZ alone or in combination against isolates at the upper end of PLZ MIC distribution. PLZ, MEM and TGC doses in mice that mimic the human plasma exposures following the administration of the clinical doses summarized in the table were utilized. Drug Human Dose PLZ 15 mg/kg Q24H, 0.5 h infusion MEM 2 g Q8H, 3 hours infusion TGC 50 mg Q12HTreatment mice were administered PLZ, MEM or TGC human-equivalent doses alone or in combinations of PLZ/MEM and PLZ/TGC, while control mice were administered vehicle. Treatments were initiated 1 hours post-infection and continued for 24 hours. Efficacy was assessed by survival through 96 hours. Survival was compared using Kaplan-Meier analysis and log-rank test.ResultsCompared with controls, human-simulated exposure of PLZ monotherapy produced significant improvement in survival for all isolates (P < 0.05) and resulted in overall survival percentages of 86 (n = 50) and 53.3 (n = 30) for isolates with MIC ≤4 and ≥8 mg/L, respectively (P < 0.05). Survival of MEM and TGC groups correlated well with their respective susceptibilities, with incremental increase in survival observed at lower MIC values. For isolate KP 561 (PLZ, MEM and TGC MICs of 8, >32 and 2 mg/L, respectively), PLZ/MEM and PLZ/TGC showed significant reduction in mortality compared with any of the single agents (P < 0.05) (Fig 1).ConclusionPLZ monotherapy resulted in improved survival in the I+ murine septicemia model, notably for isolates with MIC ≤4. Moreover, some evidence suggests that co-administration of MEM or TGC could potentially lead to further improvement in survival. These preclinical data utilizing clinically relevant exposures support a role for PLZ in the management of septicemia due to EB, including carbapenem-resistant isolates.Disclosures A. Kim, Achaogen, Inc.: Employee, Salary and Stock; K. M. Krause, Achaogen, Inc: Employee, Salary; D. P. Nicolau, Achaogen, Inc.: Grant Investigator, Research grant and Research support

Evaluating Polymyxin B-Based Combinations against Carbapenem-Resistant Escherichia coli in Time-Kill Studies and in a Hollow-Fiber Infection Model.

Polymyxin B-based combinations have emerged as a mainstay treatment against carbapenem-resistant Escherichia coli (CREC). We investigated the activity of polymyxin B-based two-antibiotic combinations against CREC using time-kill studies (TKS) and validated the findings in a hollow-fiber infection model (HFIM). TKS were conducted using 5 clinical CREC strains at 5 log10 CFU/ml against 10 polymyxin B-based two-antibiotic combinations at maximum clinically achievable concentrations. HFIMs simulating dosing regimens with polymyxin B (30,000U/kg/day) and tigecycline (100 mg every 12 h) alone and in combination were conducted against two CREC strains at 5 log10 CFU/ml over 120 h. Emergence of resistance was quantified using antibiotic-containing media. Phenotypic characterization (growth rate and stability of resistant phenotypes) of the resistant isolates was performed. All five CREC strains harbored carbapenemases. Polymyxin B and tigecycline MICs ranged from 0.5 mg/liter to 2 mg/liter and from 0.25 mg/liter to 8 mg/liter, respectively. All antibiotics alone did not have bactericidal activity at 24 h in the TKS, except for polymyxin B against two strains. In combination TKS, only polymyxin B plus tigecycline demonstrated both bactericidal activity and synergy in two out of five strains. In the HFIM, polymyxin B alone was bactericidal against both CREC strains before regrowth was observed at 8 h. Phenotypically stable polymyxin B-resistant mutants were observed for both strains, with a reduced growth rate observed in one strain. Tigecycline alone resulted in a slow reduction in bacterial counts. Polymyxin B plus tigecycline resulted in rapid and sustained bactericidal killing up to 120 h. Polymyxin B plus tigecycline is a promising combination against CREC. The clinical relevance of our results warrants further investigations.