Tigecycline activity tested against 26,474 bloodstream infection isolates: a collection from 6 continents

Advances in Diagnostic Approaches and Therapeutic Management in Bovine Mastitis

Mastitis causes huge economic losses to dairy farmers worldwide, which largely negatively affects the quality and quantity of milk. Mastitis decreases overall milk production, degrades milk quality, increases milk losses because of milk being discarded, and increases overall production costs due to higher treatment and labour costs and premature culling. This review article discusses mastitis with respect to its clinical epidemiology, the pathogens involved, economic losses, and basic and advanced diagnostic tools that have been used in recent times to diagnose mastitis effectively. There is an increasing focus on the application of novel therapeutic approaches as an alternative to conventional antibiotic therapy because of the decreasing effectiveness of antibiotics, emergence of antibiotic-resistant bacteria, issue of antibiotic residues in the food chain, food safety issues, and environmental impacts. This article also discussed nanoparticles'/chitosan's roles in antibiotic-resistant strains and ethno-veterinary practices for mastitis treatment in dairy cattle.

A two-year retrospective study of multidrug-resistant Acinetobacter baumannii respiratory infections in critically Ill patients: Clinical and microbiological findings

BACKGROUND

Acinetobacter baumannii infection is a serious public health problem because it is highly resistant to antimicrobial therapy and causes a high fatality rate in critically ill patients. The aim of the study is to examine the demographics, microbiological findings, clinical presentation, and outcomes of multi-drug-resistant Acinetobacter baumannii respiratory infections in adult ICU intubated patients during COVID-19 pandemic.

METHODS

This study included 115 mechanically ventilated adult ICU patients who had multi-drug-resistant Acinetobacter baumannii retrieved from respiratory samples during the COVID-19 pandemic in Albaha, Saudi Arabia. The information was obtained from medical and laboratory files. Univariate analysis was used to compare gender, COVID-19 infection, and outcomes.

RESULTS

The rate of Acinetobacter baumanni respiratory infections among adult ICU patients was 6.2 %. Almost 93 % developed ventilator-associated pneumonia, and five of them developed bacteremia. The isolates had significant antibiotic resistance patterns, of which 3 % were pandrug-resistant bacteria. The death rate was 74 %, with major risk factors including sepsis, septic shock, VAP, liver diseases, and the use of inappropriate antibiotic therapy that lacked both colistin and tigecycline. Patients with COVID-19 coinfection had worse outcomes compared to non-COVID-19 patients.

CONCLUSIONS

The identification of MDR-AB as a threat highlights the importance of surveillance studies in this region.

Convergence of Biofilm Formation and Antibiotic Resistance in Acinetobacter baumannii Infection

Acinetobacter baumannii (A. baumannii) is a leading cause of nosocomial infections as this pathogen has certain attributes that facilitate the subversion of natural defenses of the human body. A. baumannii acquires antibiotic resistance determinants easily and can thrive on both biotic and abiotic surfaces. Different resistance mechanisms or determinants, both transmissible and non-transmissible, have aided in this victory over antibiotics. In addition, the propensity to form biofilms (communities of organism attached to a surface) allows the organism to persist in hospitals on various medical surfaces (cardiac valves, artificial joints, catheters, endotracheal tubes, and ventilators) and also evade antibiotics simply by shielding the bacteria and increasing its ability to acquire foreign genetic material through lateral gene transfer. The biofilm formation rate in A. baumannii is higher than in other species. Recent research has shown how A. baumannii biofilm-forming capacity exerts its effect on resistance phenotypes, development of resistome, and dissemination of resistance genes within biofilms by conjugation or transformation, thereby making biofilm a hotspot for genetic exchange. Various genes control the formation of A. baumannii biofilms and a beneficial relationship between biofilm formation and "antimicrobial resistance" (AMR) exists in the organism. This review discusses these various attributes of the organism that act independently or synergistically to cause hospital infections. Evolution of AMR in A. baumannii, resistance mechanisms including both transmissible (hydrolyzing enzymes) and non-transmissible (efflux pumps and chromosomal mutations) are presented. Intrinsic factors [biofilm-associated protein, outer membrane protein A, chaperon-usher pilus, iron uptake mechanism, poly-β-(1, 6)-N-acetyl glucosamine, BfmS/BfmR two-component system, PER-1, quorum sensing] involved in biofilm production, extrinsic factors (surface property, growth temperature, growth medium) associated with the process, the impact of biofilms on high antimicrobial tolerance and regulation of the process, gene transfer within the biofilm, are elaborated. The infections associated with colonization of A. baumannii on medical devices are discussed. Each important device-related infection is dealt with and both adult and pediatric studies are separately mentioned. Furthermore, the strategies of preventing A. baumannii biofilms with antibiotic combinations, quorum sensing quenchers, natural products, efflux pump inhibitors, antimicrobial peptides, nanoparticles, and phage therapy are enumerated.

Genomic and Phenotypic Evolution of Tigecycline-Resistant Acinetobacter baumannii in Critically Ill Patients

Acinetobacter baumannii is an important opportunistic pathogen of nosocomial infections. A. baumannii presently exhibits increasing antibiotic resistance, which poses great challenges to public health. The occurrence of tigecycline-resistant A. baumannii is related to tigecycline treatment and the within-host evolution of bacteria. We analyzed isogenic A. baumannii isolates from two critically ill patients who underwent tigecycline treatment. Whole-genome sequencing and comparative analyses were performed to determine the characteristics of genomic evolution. We conducted phenotypic studies, including in vitro antibiotic sensitivity tests, biofilm formation tests, growth curve determination, serum bactericidal determination, and Galleria mellonella lethality assays. In vivo emergent tigecycline resistance was observed after tigecycline treatment. After the withdrawal of tigecycline pressure, tigecycline-resistant isolates were not isolated from one patient. Four tigecycline-resistant isolates exhibited lower growth rates. The biofilm formation and virulence characteristics of tigecycline-resistant isolates were reasonably different between the two patients. A special phenotype appeared after tigecycline treatment in both patients, accompanied by reduced serum tolerance, enhanced biofilm formation ability, and reduced virulence of Galleria mellonella. Most of the genomic variation occurred after the tigecycline treatment, primarily involving transcription-, signal transduction-, translation-, ribosomal biogenesis-, and cell wall biogenesis-related genes. We determined that the genomic variations in baeR, wzc, aroQ, rluC, and adeS and acquisition of ISAba1 were associated with tigecycline resistance in vivo. Capsular polysaccharide-related genes, wzc, and itrA2, and aroQ, were the key genes related to the virulence evolution of A. baumannii within the host.

IMPORTANCE Multidrug-resistant Acinetobacter baumannii poses a huge challenge to clinical treatment, and tigecycline is considered a last-line drug for the treatment of multidrug-resistant A. baumannii. However, the mechanism of tigecycline resistance in vivo has not been elucidated. This study analyzed the genomic and phenotypic evolution of tigecycline-resistant A. baumannii in two critically ill patients. In this study, after treatment with tigecycline, tigecycline-resistant A. baumannii emerged with higher fitness costs. After the withdrawal of tigecycline pressure, tigecycline-resistant isolates were not isolated from one patient. The in vivo and in vitro virulence of the isolates exhibited diametrically opposite results in the two patients. Genomic variations in baeR, wzc, aroQ, rluC, and adeS and acquisition of ISAba1 were associated with tigecycline resistance in vivo. The capsular polysaccharide-related genes, wzc, itrA2, and aroQ, were the key genes related to the virulence of A. baumannii in hosts. Our research provides a theoretical basis for elucidating the mechanism of tigecycline resistance and presents new clues for future surveillance and treatment of multidrug-resistant A. baumannii.

Stenotrophomonas maltophilia bacteremia in children: risk factors and mortality rate

Purpose

Stenotrophomonas maltophilia (S. maltophilia) is an opportunistic and nosocomial pathogen that can cause an invasive and fatal infection, particularly in hospitalized and immunocompromised patients. However, little is known about the impact of S. maltophilia bacteremia in pediatric patients. Therefore, we aimed to identify risk factors for mortality, antibiotics susceptibility to S. maltophilia, and mortality rates in pediatric patients with S. maltophilia bacteremia.

Methods

We conducted a retrospective cohort study by identifying all S. maltophilia positive blood cultures in the microbiology laboratory database between January 2007 and December 2018 from hospitalized pediatric patients (age 1–14 years). After identifying patients with S. maltophilia bacteremia, medical charts were reviewed for demographics, clinical data, and outcomes within seven days of bacteremia diagnosis. Risk factors associated with mortality in S. maltophilia bacteremia patients were determined using univariate and multivariate analyses.

Findings

Sixty-eight pediatric patients with S. maltophilia bacteremia were identified. All infections were nosocomial infections, and (88.2%) bacteremia cases were catheter-related bloodstream infections. On multivariate analysis, ICU admission prior to bacteremia episode and neutropenia were the major risk factors associated with mortality. S. maltophilia was the most susceptible to trimethoprim and sulfamethoxazole (TMP/SMX, 94.1%), followed by levofloxacin (85.7%). The overall mortality rate within seven days of S. maltophilia bacteremia diagnosis was 33.8%.

Conclusion

S. maltophilia bacteremia is a devastating emerging infection associated with high mortality among hospitalized children. Therefore, early diagnosis and prompt management based on local susceptibility data are crucial. Various risk factors, especially ICU admission prior to bacteremia episode and neutropenia, are associated with S. maltophilia bacteremia mortality.

The global prevalence of Daptomycin, Tigecycline, Quinupristin/Dalfopristin, and Linezolid-resistant Staphylococcus aureus and coagulase-negative staphylococci strains: a systematic review and meta-analysis

OBJECTIVE

Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) are among the main causes of nosocomial infections, which have caused major problems in recent years due to continuously increasing spread of various antibiotic resistance features. Apparently, vancomycin is still an effective antibiotic for treatment of infections caused by these bacteria but in recent years, additional resistance phenotypes have led to the accelerated introduction of newer agents such as linezolid, tigecycline, daptomycin, and quinupristin/dalfopristin (Q/D). Due to limited data availability on the global rate of resistance to these antibiotics, in the present study, the resistance rates of S. aureus, Methicillin-resistant S. aureus (MRSA), and CoNS to these antibiotics were collected.

METHOD

Several databases including web of science, EMBASE, and Medline (via PubMed), were searched (September 2018) to identify those studies that address MRSA, and CONS resistance to linezolid, tigecycline, daptomycin, and Q/D around the world.

RESULT

Most studies that reported resistant staphylococci were from the United States, Canada, and the European continent, while African and Asian countries reported the least resistance to these antibiotics. Our results showed that linezolid had the best inhibitory effect on S. aureus. Although resistances to this antibiotic have been reported from different countries, however, due to the high volume of the samples and the low number of resistance, in terms of statistical analyzes, the resistance to this antibiotic is zero. Moreover, linezolid, daptomycin and tigecycline effectively (99.9%) inhibit MRSA. Studies have shown that CoNS with 0.3% show the lowest resistance to linezolid and daptomycin, while analyzes introduced tigecycline with 1.6% resistance as the least effective antibiotic for these bacteria. Finally, MRSA and CoNS had a greater resistance to Q/D with 0.7 and 0.6%, respectively and due to its significant side effects and drug-drug interactions; it appears that its use is subject to limitations.

CONCLUSION

The present study shows that resistance to new agents is low in staphylococci and these antibiotics can still be used for treatment of staphylococcal infections in the world.

Temporal and Geographic Variation in Antimicrobial Susceptibility and Resistance Patterns of Enterococci: Results From the SENTRY Antimicrobial Surveillance Program, 1997-2016

Background

The SENTRY Antimicrobial Surveillance Program was established in 1997 and presently encompasses more than 750 000 bacterial isolates from over 400 medical centers worldwide. Among these pathogens, enterococci represents a prominent cause of bloodstream (BSIs), intra-abdominal (IAIs), skin and skin structure, and urinary tract infections (UTIs). In the present study, we reviewed geographic and temporal trends in Enterococcus species and resistant phenotypes identified throughout the SENTRY Program.

Methods

From 1997 to 2016, a total of 49 491 clinically significant enterococci isolates (15 species) were submitted from 298 medical centers representing the Asia-Pacific (APAC), European, Latin American (LATAM), and North American (NA) regions. Bacteria were identified by standard algorithms and matrix-assisted laser desorption ionization–time of flight mass spectrometry. Susceptibility (S) testing was performed by reference broth microdilution methods and interpreted using Clinical and Laboratory Standards Institute/US Food and Drug Administration and European Committee on Antimicrobial Susceptibility Testing criteria.

Results

The most common Enterococcus species in all 4 regions were Enterococcus faecalis (64.7%) and E. faecium (EFM; 29.0%). Enterococci accounted for 10.7% of BSIs in NA and was most prominent as a cause of IAIs (24.0%) in APAC and of UTIs (19.8%) in LATAM. A steady decrease in the susceptibility to ampicillin and vancomycin was observed in all regions over the 20-year interval. Vancomycin-resistant enterococci (VRE) accounted for more than 8% of enterococcal isolates in all regions and was most common in NA (21.6%). Among the 7615 VRE isolates detected, 89.1% were the VanA phenotype (91.0% EFM) and 10.9% were VanB. Several newer antimicrobial agents demonstrated promising activity against VRE, including daptomycin (99.6–100.0% S), linezolid (98.0%–99.6% S), oritavancin (92.2%–98.3% S), tedizolid (99.5%–100.0% S), and tigecycline (99.4%–100.0% S).

Conclusions

Enterococci remained a prominent gram-positive pathogen in the SENTRY Program from 1997 through 2016. The overall frequency of VRE was 15.4% and increased over time in all monitored regions. Newly released agents with novel mechanisms of action show promising activity against VRE.

Insight into Acinetobacter baumannii: pathogenesis, global resistance, mechanisms of resistance, treatment options, and alternative modalities

Acinetobacter baumannii, once considered a low-category pathogen, has emerged as an obstinate infectious agent. The scientific community is paying more attention to this pathogen due to its stubbornness to last resort antimicrobials, including carbapenems, colistin, and tigecycline, its high prevalence of infections in the hospital setting, and significantly increased rate of community-acquired infections by this organism over the past decade. It has given the fear of pre-antibiotic era to the world. To further enhance our understanding about this pathogen, in this review, we discuss its taxonomy, pathogenesis, current treatment options, global resistance rates, mechanisms of its resistance against various groups of antimicrobials, and future therapeutics.

Vancomycin-resistant enterococcus infection in the hematopoietic stem cell transplant recipient: an overview of epidemiology, management, and prevention

Vancomycin-resistant enterococcus (VRE) is now one of the leading causes of nosocomial infections in the United States. Hematopoietic stem cell transplantation (HSCT) recipients are at increased risk of VRE colonization and infection. VRE has emerged as a major cause of bacteremia in this population, raising important clinical questions regarding the role and impact of VRE colonization and infection in HSCT outcomes as well as the optimal means of prevention and treatment. We review here the published literature and scientific advances addressing these thorny issues and provide a rational framework for their approach.

Antimicrobial activity against a global collection of skin and skin structure pathogens: results from the Tigecycline Evaluation and Surveillance Trial (T.E.S.T.), 2010-2014

BACKGROUND

As part of the Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) we report antimicrobial resistance among Gram-positive and Gram-negative isolates collected globally from integumentary sources between 2010 and 2014.

METHODS

Minimum inhibitory concentrations and antimicrobial resistance were determined according to Clinical and Laboratory Standards Institute guidelines (US Food and Drug Administration breakpoints against tigecycline). The Cochran-Armitage trend test was used to identify statistically significant changes in resistance.

RESULTS

Global rates of methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Acinetobacter baumannii were 38% and 43%, respectively. No S. aureus isolates were resistant to linezolid or vancomycin; all isolates were susceptible to tigecycline. Two percent of Enterococcus faecalis and 28% of Enterococcus faecium were vancomycin-resistant. Extended-spectrum β-lactamase (ESBL) producers accounted for 22% of Klebsiella pneumoniae and 16% of Escherichia coli. Resistance to minocycline among E. faecalis, E. faecium, K. pneumoniae, and E. coli decreased significantly (p<0.0001). There were significant increases (p<0.0001) in A. baumannii resistance to cefepime, ceftazidime, ceftriaxone, levofloxacin, meropenem, and piperacillin-tazobactam.

CONCLUSIONS

Among isolates from integumentary sources, rates of MRSA and ESBL-producing Enterobacteriaceae are stabilizing. Carbapenems and tigecycline have retained their in vitro activity against Gram-positive and Gram-negative organisms. Few agents were active against A. baumannii; its increasing resistance is cause for concern.

Theoretical approach to local infusion of antibiotics for infected pancreatic necrosis

BACKGROUND/OBJECTIVES

Infected pancreatic necrosis is a major complications of acute pancreatitis. If drainage is required, local administration of antibiotics through transmural nasocystic or percutaneous catheter may allow increasing local antibiotic concentrations. Drug diffusion becomes the main factor influencing local drug tissue penetration. The present study aims at providing the rationale for the design of new research protocols evaluating the efficacy of local antibiotics for infected pancreatic necrosis.

METHODS

A review of microbiological data was performed for the most common organisms causing the infection, antibiotics spectrum and minimum inhibitory concentrations (MIC). A search of the physico-chemical properties of antibiotics was performed to calculate the diffusion coefficients. An estimation of the antibiotic concentrations in pancreatic tissue was obtained using a mathematical model. Efficacy factors (EF) were calculated and the stability of the antibiotic solutions were evaluated to optimize the dosing regimen.

RESULTS

Piperacillin, vancomycin and metronidazole achieve high concentrations in the surrounding tissue very fast. Imipenem, ceftriaxone, ciprofloxacin, gentamicin, linezolid and cloxacillin achieve intermediate concentration values. Tigecycline, showed the lowest concentration values (<2 mg/L). Calculated EF is highest for piperacillin and imipenem short after administration and near to surface diffusion area (0.5 cm), but EF of imipenem is higher at deeper areas and longer time after administration.

CONCLUSIONS

Considering obtained results, some solutions are proposed using saline as diluent and 25 °C of temperature during administration. Imipenem has the best theoretical results in empiric local treatment. Linezolid and tigecycline solutions are not recommended.

Update on infections caused by Stenotrophomonas maltophilia with particular attention to resistance mechanisms and therapeutic options

Stenotrophomonas maltophilia is a Gram-negative, biofilm-forming bacterium. Although generally regarded as an organism of low virulence, S. maltophilia is an emerging multi-drug resistant opportunistic pathogen in hospital and community settings, especially among immunocompromised hosts. Risk factors associated with S. maltophilia infection include underlying malignancy, cystic fibrosis, corticosteroid or immunosuppressant therapy, the presence of an indwelling central venous catheter and exposure to broad spectrum antibiotics. In this review, we provide a synthesis of information on current global trends in S. maltophilia pathogenicity as well as updated information on the molecular mechanisms contributing to its resistance to an array of antimicrobial agents. The prevalence of S. maltophilia infection in the general population increased from 0.8-1.4% during 1997-2003 to 1.3-1.68% during 2007-2012. The most important molecular mechanisms contributing to its resistance to antibiotics include β-lactamase production, the expression of Qnr genes, and the presence of class 1 integrons and efflux pumps. Trimethoprim/sulfamethoxazole (TMP/SMX) is the antimicrobial drug of choice. Although a few studies have reported increased resistance to TMP/SMX, the majority of studies worldwide show that S. maltophilia continues to be highly susceptible. Drugs with historically good susceptibility results include ceftazidime, ticarcillin-clavulanate, and fluoroquinolones; however, a number of studies show an alarming trend in resistance to those agents. Tetracyclines such as tigecycline, minocycline, and doxycycline are also effective agents and consistently display good activity against S. maltophilia in various geographic regions and across different time periods. Combination therapies, novel agents, and aerosolized forms of antimicrobial drugs are currently being tested for their ability to treat infections caused by this multi-drug resistant organism.

Origin of de novo daptomycin non susceptible enterococci

The emergence of daptomycin non-susceptible enterococci (DNSE) poses both treatment and infection control challenges. Clinicians should be vigilant that DNSE may be isolated from patients with or without (de novo DNSE) prior use of daptomycin. Recent epidemiological data suggest the presence of a community reservoir for DNSE which may be associated with environmental, foodborne and agricultural exposures. The mechanisms of nonsusceptibility to daptomycin have not been well characterized and may not parallel those for Staphylococcus aureus. The identification of daptomycin resistance genes in anaerobes, in farm animals and in an ecosystem that has been isolated for million years, suggest that the environmental reservoir for de novo DNSE may be larger than previously thought. Herein, the limited available scientific evidence regarding the possible origin of de novo DNSE is discussed. The current existing evidence is not sufficient to draw firm conclusions on the origin of DNSE. Further studies to determine the mechanisms of de novo daptomycin nonsusceptibility among enterococci are needed.

In vitro susceptibility of tigecycline against multidrug-resistant gram-negative strains: Etest versus agar dilution

BACKGROUND AND AIM

Tigecycline is a semi-synthetic tetracycline with activity against most multidrug-resistant (MDR) bacteria.

METHODS

We studied in vitro activity of tigecycline by agar dilution (AD) and Etest methods to evaluate their correlation. The study included 206 isolates of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli, Klebsiella pneumoniae and MDR Acinetobacter baumannii recovered from blood cultures of patients of Baskent University between 2008 and 2010.

RESULTS

ESBL-producing E. coli had MIC50/MIC90 values of 0.5/0.5 µg/ml by AD and 0.25/0.5 µg/ml by Etest. ESBL-producing K. pneumoniae had MIC50/MIC90 values of 1/2 µg/ml by AD and 0.75/2 µg/ml by Etest, whereas MDR A. baumannii had MIC50/MIC90 values of 4/4 µg/ml by AD and 2/4 µg/ml by Etest. The correlation between AD and Etest was weak for ESBL-producing E. coli and strong for ESBL-producing K. pneumoniae and MDR A. baumannii. Tigecycline MIC values for ESBL-producing E. coli were lower than the tigecycline concentration, while they were higher than the concentrations attainable by treatment doses for A. baumannii.

CONCLUSION

Tigecycline is an appropriate agent in the treatment of E. coli bacteremia, but it is not for treating A. baumannii bacteremia. Tigecycline could be used for K. pneumoniae bacteremia treatment after determining its MIC value. Determining the MIC value by gold-standard methods is more appropriate due to the correlation between Etest and AD at high MIC values.

Vancomycin-Resistant Enterococcal Bacteremia Pharmacotherapy

Objective: To review the literature on the pharmacotherapy of bloodstream infections (BSI) caused by vancomycin-resistant enterococci (VRE). Data Sources: A MEDLINE literature search was performed for the period 1946 to May 2014 using the search terms Enterococcus, enterococci, vancomycin-resistant, VRE, bacteremia, and bloodstream infection. References were also identified from selected review articles. Study Selection and Data Extraction: English-language case series, cohort studies, and meta-analyses assessing the options in the pharmacotherapy of VRE BSIs in adult patients were evaluated. Data Synthesis: Studies were identified that utilized linezolid, quinupristin/dalfopristin (Q/D), and daptomycin. In all, 8 comparative retrospective cohort studies, 2 meta-analyses of daptomycin and linezolid, and 3 retrospective comparisons of linezolid and Q/D were included for review. Mortality associated with VRE BSIs was high across studies, and the ability to determine differences in outcomes between agents was confounded by the complex nature of the patients included. Two meta-analyses comparing daptomycin with linezolid for VRE BSIs found modest advantages for linezolid, but these conclusions may be hampered by heterogeneity within the included studies. Conclusions: VRE BSIs remain a difficult-to-treat clinical situation. Differences in toxicity between the agents used to treat it are clear, but therapeutic differences are more difficult to discern. Meta-analyses suggest that a moderate advantage for linezolid over daptomycin may exist, but problems with the nature of studies that they included make definitive conclusions difficult.

Tigecycline: a novel glycylcycline antibiotic

Tigecycline, the first-in-class glycylcycline, was developed to recapture the broad spectrum of activity of the tetracycline class and to treat patients with difficult-to-treat bacterial infections. Tigecycline's in vitro spectrum of activity encompasses aerobic, facultative and anaerobic Gram-positive and -negative bacteria, including antimicrobial-resistant bacteria such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis and Enterococcus faecium, and extended-spectrum beta-lactamase-producing Enterobacteriaceae. Clinical trials involving patients with complicated skin and skin-structure infections and complicated intra-abdominal infections, including patients infected with methicillin-resistant S. aureus, demonstrated that tigecycline was bacteriologically and clinically effective with mild-to-moderate gastrointestinal adverse events (i.e., nausea, vomiting and diarrhea) the most commonly reported. Tigecycline is a promising new broad-spectrum parenteral monotherapy for the treatment of patients with Gram-positive and -negative bacterial infections.

Potential role of tigecycline in the treatment of community-acquired bacterial pneumonia

Tigecycline is a member of the glycylcycline class of antimicrobials, which is structurally similar to the tetracycline class. It demonstrates potent in vitro activity against causative pathogens that are most frequently isolated in patients with community-acquired bacterial pneumonia (CABP), including (but not limited to) Streptococcus pneumoniae (both penicillin-sensitive and -resistant strains), Haemophilus influenzae and Moraxella catarrhalis (including β-lactamase-producing strains), Klebsiella pneumoniae, and ‘atypical organisms’ (namely Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila). Comparative randomized clinical trials to date performed in hospitalized patients receiving tigecycline 100 mg intravenous (IV) × 1 and then 50 mg IV twice daily thereafter have demonstrated efficacy and safety comparable to the comparator agent. Major adverse effects were primarily gastrointestinal in nature. Tigecycline represents a parenteral monotherapy option in hospitalized patients with CABP (especially in patients unable to receive respiratory fluoroquinolones). However, alternate and/or additional therapies should be considered in patients with more severe forms of CABP in light of recent data of increased mortality in patients receiving tigecycline for other types of severe infection.

Daptomycin nonsusceptible enterococci: an emerging challenge for clinicians

Daptomycin is the only antibiotic with in vitro bactericidal activity against vancomycin-resistant Enterococcus (VRE) that is approved by the Food and Drug Administration (FDA). Data on the potential emergence of daptomycin nonsusceptibility among enterococci remain limited. We systematically reviewed the published literature for reports of isolates of enterococci that were daptomycin nonsusceptible and assessed the clinical significance and outcome of therapy. Based on susceptibility breakpoints approved by the Clinical Laboratory Standards Institute (CLSI), daptomycin has in vitro activity against >90% of enterococcal isolates. Less than 2% of enterococcal isolates were daptomycin nonsusceptible, with minimum inhibitory concentrations (MICs) >4 μg/mL. The prevalence of nonsusceptibility of VRE isolates to daptomycin may be overestimated due to the spread of clonally related isolates in health care settings. Clinicians should be aware of the possibility of the emergence of daptomycin nonsusceptibility and should closely monitor daptomycin MICs of enterococci isolated during treatment.

National surveillance of antimicrobial susceptibility of CTX-M-positive and -negative clinical isolates of Escherichia coli from Kuwait government hospitals

Antibiotic resistance in Escherichia coli is becoming a complex therapeutic problem. Surveillance programs are valuable tools and offer important information on bacterial resistance trends. This study was undertaken to determine the susceptibility of clinically significant isolates of E. coli obtained from patients admitted to 8 Kuwait government hospitals and to examine how this was influenced by the production of CTX-M extended-spectrum beta-lactamases (ESBLs). The susceptibility of 876 consecutive clinically significant strains of E. coli to 13 antibiotics was determined by Etest. ESBL production was assessed by ESBL-Etest method and the presence of CTX-M beta-lactamases was confirmed by PCR technique. Of the 876 isolates, 604 (69%) were highly non-susceptible to ampicillin with MIC(90 )of >256 microg/ml. Resistance to the 3(rd)-generation cephalosporins ranged from 7.5% in the Maternity hospital to 29% in the Ibn Sina hospital; ciprofloxacin resistance rates ranged from 14% and 40%, respectively. Carbapenems and amikacin demonstrated excellent activity. The minimum inhibitory concentrations (MIC(90)) of cefotaxime, ceftazidime, cefepime and ciprofloxacin were >256, 64, >256 and >32 microg/ml, respectively for CTX-M-positive isolates versus 0.5, 1, 025 and 0.125 microg/ml for CTX-M-negative strains. Frequencies of CTX-M-positive isolates within the cefotaxime MIC ranges of 1-2, 3-8, 9-16 and >16 microg/ml were 0, 4, 15 and 81%, respectively. In conclusion, the susceptibility of E. coli to the 3(rd )generation cephalosporins and ciprofloxacin was influenced by the presence of CTX-M ESBL and a high proportion of the CTX-M-producing isolates were in the susceptibility ranges of cefotaxime.

An update on pharmacological interventions for diabetic foot ulcers

Diabetic foot ulcers are the most common lower extremity complications of diabetes. Peripheral neuropathy and peripheral vascular disease are the underlying risk factors for diabetic foot ulcers, subsequently leading to infections and requiring antimicrobial therapy for the management of the disease. Each risk factor is a target for clinical intervention, with the intent to delay or prevent disease progression to amputation. The effective therapy includes interdisciplinary care, which involves optimized pharmacological interventions in concert with other treatments such as debridement strategies and specialized wound dressings. The pharmacological therapy alone cannot lead to successful therapy, and therefore, these supplementary techniques/modalities should not be overlooked. It is therefore the aim of this report to review various pharmacological interventions, specific to the diabetic foot and wound healing, along with incorporation of advanced therapies required to achieve a multifaceted treatment of diabetic foot ulcers and provide basis for superior drugs as well as drug delivery systems.

In vitro activity of tigecycline against 2423 clinical isolates and comparison of the available interpretation breakpoints

MICs to tigecycline and 12 antimicrobials were performed by microdilution method, against 2423 nonduplicate pathogens recently isolated in 17 Greek hospitals. The Food and Drug Administration (FDA) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria were used comparatively for interpretation of tigecycline MICs. Tigecycline exhibited potent in vitro activity against the majority of the isolates tested. (MIC(90) values of 0.5, 1, 2, 0.125, 1, 0.25, 0.125, and 1 mg/L were observed for Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., Moraxella catarrhalis, Acinetobacter spp., Staphylococcus aureus, Enterococcus spp., and Streptococcus pneumoniae isolates, respectively.) Tigecycline activity was the same, irrespective of the resistance profile to other antimicrobials (Gram-negative pathogens susceptible or resistant to imipenem, Enterococcus spp., S. aureus, or S. pneumoniae isolates, susceptible or resistant to vancomycin, methicillin or penicillin, respectively). Interpretation using EUCAST and FDA breakpoints differed among isolates of K. pneumoniae and Enterobacter spp. having tigecycline MICs of 2 to 4 mg/L. In conclusion, tigecycline exhibited potent activity against pathogens recently isolated in a region that experiences high antimicrobial resistance rates. Indications that the available criteria might categorize differently tigecycline susceptibility status in K. pneumoniae and Enterobacter spp. isolates were also detected.

The in vitro evaluation of tigecycline tested against pathogens isolated in eight countries in the Asia-Western Pacific region (2008)

OBJECTIVES

To determine the in vitro activity of tigecycline and comparator common use antimicrobial agents tested against contemporary bacterial pathogens from the Asia-Western Pacific region.

METHODS

As part of the SENTRY Antimicrobial Surveillance Program, a total of 5759 Gram-positive and Gram-negative isolates were collected from 28 medical centers in eight Asia-Western Pacific countries during 2008. Minimum inhibitory concentrations (MICs) were determined using Clinical and Laboratory Standards Institute (CLSI) broth microdilution method and interpreted using CLSI breakpoints. United States Food and Drug Administration (US-FDA) breakpoints were used to interpret tigecycline susceptibility.

RESULTS

Antimicrobial resistance was found to be widespread and prevalence varied considerably between the eight countries. Against pathogens for which breakpoints were available, >98% of all isolates were susceptible to tigecycline. Against all Gram-positive isolates, including methicillin (oxacillin)-resistant Staphylococcus aureus, penicillin- and multidrug-resistant pneumococci, and vancomycin-resistant enterococci, the highest tigecycline MIC found was 1 microg/ml. Against all Enterobacteriaceae, including extended-spectrum beta-lactamase phenotypes, tigecycline susceptibility was 97.5%. Tigecycline had good activity against Acinetobacter spp. but was much less active against Pseudomonas aeruginosa.

CONCLUSION

Tigecycline demonstrated excellent sustained in vitro activity against a wide spectrum of contemporary Gram-positive and -negative pathogens from Asia-Western Pacific countries.

In vitro activity of tigecycline against patient isolates collected during phase 3 clinical trials for hospital acquired pneumonia

The in vitro activity of tigecycline was evaluated against 819 baseline pathogens isolated from 383 patients enrolled in the phase 3 clinical trial investigating the efficacy of tigecycline in hospital acquired pneumonia (HAP). The trials were global, enrolling patients in 27 countries. Tigecycline was active against the most prevalent pathogens in HAP, including gram-positive and gram-negative strains (90% of MICs ≤2 µg/mL for the entire collection). The spectrum of activity of tigecycline included important pathogens such as Staphylococcus aureus (including methicillin-resistant S. aureus), Enterococcus faecalis, Streptococcus pneumoniae, Acinetobacter baumannii/calcoaceticus complex, Escherichia coli, Klebsiella pneumonia, and Enterobacter cloacae. As reported previously, a few genera, such as Pseudomonas aeruginosa and the Proteeae, were generally less susceptible to tigecycline by comparison to other gram-negative pathogens. The excellent in vitro, expanded, broad-spectrum activity of tigecycline in the clinical isolates confirmed the potential utility of tigecycline for pathogens associated with with hospital acquired pneumonia infections.

Tigecycline for the treatment of patients with community-acquired pneumonia requiring hospitalization

Pneumonia, along with influenza, is the leading cause of mortality associated with infectious diseases in the USA. Tigecycline is a novel antimicrobial agent that is active against a broad spectrum of pathogens. Our objective is to review the literature about the efficacy of tigecycline in community-acquired pneumonia (CAP). Data from various sources, including Pubmed, the European Medicines Agency (EMEA) and the US FDA were appraised. Tigecycline was found to be noninferior compared with levofloxacin for the treatment of patients with bacterial CAP requiring hospitalization. Recently, the drug was approved for the treatment of these patients by the FDA, but owing to some concerns, its application in the EMEA has been withdrawn. In addition, in a recent study concerns were expressed about the efficacy of tigecycline in the lungs using the current dosage. More data are needed about the pharmacokinetics of tigecycline in the lungs and its efficacy in severe CAP.

In vitro activities of moxifloxacin and tigecycline against bacterial isolates associated with intraabdominal infections at a medical center in Taiwan, 2001-2006

A total of 569 nonduplicate isolates recovered from patients with community-onset or hospital-onset intraabdominal infections (IAIs) from 2001 to 2006 were studied. These included 28 Staphylococcus aureus and 541 Gram-negative isolates (33.6% Escherichia coli, 29.0% Klebsiella pneumoniae, 8.1% Acinetobacter baumannii, and 6.3% Pseudomonas aeruginosa). Minimum inhibitory concentrations (MICs) of the isolates to moxifloxacin, imipenem, and ciprofloxacin were determined using the agar dilution method and to tigecycline using the broth microdilution method. Extended-spectrum beta-lactamase (ESBL) producers were found in 15.5% (29 out of 182) of E. coli, 15.3% (24 out of 157) of K. pneumoniae, and 15.4% (2 out of 13) of K. oxytoca isolates. More than 85% of Enterobacteriaceae were susceptible to moxifloxacin, but this percentage was lower among E. coli (78%). The percentage of E. coli (K. pneumoniae) isolates that were not susceptible to moxifloxacin was 6% (0%) in 2001, 39% (17%) in 2003, and 21% (14%) in 2006. Tigecycline exhibited good in vitro activities against all S. aureus and >95% of all Enterobacteriaceae tested. Among the 24 isolates of ESBL-producing K. pneumoniae, 4 had tigecycline MICs > or = 2 microg/ml. Eighty percent of A. baumannii isolates exhibited tigecycline MICs of < or = 2 microg/ml. This study found that moxifloxacin and tigecycline exhibited good in vitro activity against bacterial isolates causing IAIs.

In vitro activity of tigecycline and comparator agents against a global collection of Gram-negative and Gram-positive organisms: tigecycline Evaluation and Surveillance Trial 2004 to 2007

The Tigecycline Evaluation and Surveillance Trial began in 2004 to monitor the in vitro activity of tigecycline and comparator agents against a global collection of Gram-negative and Gram-positive pathogens. Against Gram negatives (n = 63 699), tigecycline MIC(90)'s ranged from 0.25 to 2 mg/L for Escherichia coli, Haemophilus influenzae, Acinetobacter baumannii, Klebsiella oxytoca, Enterobacter cloacae, Klebsiella pneumoniae, and Serratia marcescens (but was > or =32 for Pseudomonas aeruginosa). Against Gram-positive organisms (n = 32 218), tigecycline MIC(90)'s were between 0.06 and 0.25 mg/L for Streptococcus pneumoniae, Enterococcus faecium, Streptococcus agalactiae, Staphylococcus aureus, and Enterococcus faecalis. The in vitro activity of tigecycline was maintained against resistant phenotypes, including multidrug-resistant A. baumannii (9.2% of isolates), extended-spectrum beta-lactamase-producing E. coli (7.0%) and K. pneumoniae (14.0%), beta-lactamase-producing H. influenzae (22.2%), methicillin-resistant S. aureus (44.5%), vancomycin-resistant E. faecium (45.9%) and E. faecalis (2.8%), and penicillin-resistant S. pneumoniae (13.8%). Tigecycline represents a welcome addition to the armamentarium against difficult to treat organisms.

Use of a clinically derived exposure-response relationship to evaluate potential tigecycline-Enterobacteriaceae susceptibility breakpoints

Potential tigecycline-Enterobacteriaceae susceptibility breakpoints were evaluated using 2 approaches, which differed in the nature of the probabilities assessed by MIC value. Using a previously derived tigecycline population pharmacokinetic model and Monte Carlo simulation, a probability density function of steady-state area under the concentration-time curve for 24 h (AUC(SS(0-24))) values for 9999 patients was generated. AUC(SS(0-24)) values were divided by clinically relevant fixed MIC values to derive AUC(SS(0-24))/MIC ratios, which were used to calculate the clinical response expectation by MIC value based upon a logistic regression model for efficacy (1st approach). For the 2nd approach, the probability of pharmacokinetic-pharmacodynamic (PK-PD) target attainment was calculated as the proportion of patients with AUC(SS(0-24))/MIC ratios greater than the threshold value of 6.96, the PK-PD target associated with optimal clinical response. Probabilities of clinical response and PK-PD target attainment were poorly correlated at MIC values >0.25 mg/L. For instance, the median probability of clinical success was 0.76, whereas the probability of PK-PD target attainment was 0.27 at an MIC value of 1 mg/L, suggesting that the probability of PK-PD target attainment metrics underestimates the clinical performance of tigecycline at higher MIC values.

Four cases of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections treated with tigecycline

We report 4 cases of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections who received treatment with tigecycline after unsuccessful treatment attempts with conventional drugs. All 4 patients were eventually cured although 1 experienced a relapse of her bacteremia while on treatment due to inadequate dosing.

Management of complicated infections in the era of antimicrobial resistance: the role of tigecycline

BACKGROUND

Increasing antimicrobial resistance and infection complications pose challenges to optimal antibiotic therapy. Paucity of new antibiotics (and the eventual bacterial resistance they face) highlights the critical need for more appropriate use of broadly effective agents, which may help to thwart the dramatic rise in global resistance. Single agents that can be combined effectively with others, if needed, promise the simplest overall utility. Approved in 2005 to treat complicated skin and intra-abdominal infections, tigecycline is a novel extended-spectrum minocycline derivative that circumvents bacterial resistance, as it is unaffected by efflux pumps and ribosomal protection. However, tigecycline should not be used as empiric monotherapy for treatment of health-care associated infections known or suspected to be owing to Pseudomonas aeruginosa or Proteus spp.

OBJECTIVE

This article summarizes the demonstrated clinical utility of tigecycline so far.

METHODS

A MEDLINE search examined authoritative published clinical studies, reviews and case reports detailing the clinical record of tigecycline since 2004.

RESULTS/CONCLUSION

Tigecycline continues to maintain satisfactory profiles of safety, efficacy and antimicrobial resistance avoidance. Regardless, continued surveillance is needed to detect reduced susceptibility and resistance against both community and nosocomial pathogens. Judicious use of agents reserved for multidrug resistant pathogens is vital to preserve their effectiveness.

Update on antimicrobial susceptibility rates among gram-negative and gram-positive organisms in the United States: results from the Tigecycline Evaluation and Surveillance Trial (TEST) 2005 to 2007

BACKGROUND

The Tigecycline Evaluation and Surveillance Trial (TTEST) is a global surveillance study initiated in 2004.Its goal is to assess the in vitro activity of the glycylcycline, tigecycline, and comparator antimicrobials.

OBJECTIVE

The aim of this study was to measure the in vitro activity of a panel of antimicrobial agents against gram-negative and gram-positive organisms collected in the United States in 2005, 2006, and 2007.

METHODS

Isolates were collected from 172 centers across the United States.In vitro activity was assessed using Clinical and Laboratory Standards Institute (CLSI) guidelines and CLSI or US Food and Drug Administration interpretive criteria.

RESULTS

Overall, data on 20,897 gram-negative and 8949 gram-positive isolates were collected. For the majority of organisms, percentage susceptibilities were unchanged over the 3 years of collection. One exception was Acinetobacter baumannii; rates of susceptibility to the majority of agents in the panel decreased by approximately 10% over the 3 years. Rates of resistant phenotypes were relatively unchanged with mean percentages over the 3 years of: 8.9% (337/3787) for extended beta-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae; 2.1% (17/801) for ESBL-producing Klebsiella oxytoca; 2.3% (111/4861) for ESBL-pproducing Escherichia coli; 56.2% (2564/4560) for methicillin-resistant Staphylococcus aureus; 5.1% (97/1903) for vancomycin-resistant Enterococcus faecalis; and 67.2% (487/725) for vancomycin-resistant Enterococcus faecium. The minimum inhibitory concentration required to inhibit the growth of 90% of organisms (MIC(90)) for tigecycline was stable over the 3 years and was < or = 22 mg/L against non-ESBL-producing K pneumoniae, K oxytoca, E coli, Enterobacter aerogenes, Enterobacter cloacae, Serratia marcescens, and A baumannii. Against methicillin susceptible and -resistant S aureus, E faecalis, E faecium, and Streptococcus agalactiae tigecycline MIC(90)s were < or = 0.25 mg/L.

CONCLUSIONS

This report of 3 years of data from the TEST study suggests stable susceptibility rates among gram-negative and gram-positive organisms, with the exception of decreased susceptibility rates for A baumannii. Tigecycline continued to have good activity against Enterobacteriaceae, A baumannii, S aureus, E faecalis, E faecium, and S agalactiae.

Nationwide surveillance in Taiwan of the in-vitro activity of tigecycline against clinical isolates of extended-spectrum beta-lactamase-producing Enterobacteriaceae

Tigecycline In-vitro Surveillance in Taiwan (TIST), initiated in 2006, is a nationwide surveillance programme designed to monitor longitudinally the in-vitro activity of tigecycline against commonly encountered resistant bacteria. This study compared the in-vitro activity of tigecycline against clinical isolates of resistant Gram-negative bacteria determined by the broth microdilution and Etest methods. A total of 622 isolates were collected from patients treated at 20 teaching hospitals. Tigecycline had excellent in-vitro activity against extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli (N = 275) with MIC(90) 0.5 microg/mL and a 99.6% susceptibility rate, and also against ESBL-producing Klebsiella pneumoniae (N = 324) with MIC(90) 2 microg/mL and a 98.5% susceptibility rate. For ESBL-producing Proteus mirabilis (N = 15) the MIC(90) was 4 microg/mL with a 73.3% susceptibility rate. For ESBL-producing Klebsiella oxytoca (N = 8) the MIC(50) and MIC(90) were 0.5 and 1 microg/mL, respectively, with a 100% susceptibility rate. Limited agreement (<80%) was found between the broth microdilution and the Etest methods when determining the in-vitro activity of tigecycline against ESBL- producing K. pneumoniae and K. oxytoca.

AmpC beta-lactamases

SUMMARY

AmpC beta-lactamases are clinically important cephalosporinases encoded on the chromosomes of many of the Enterobacteriaceae and a few other organisms, where they mediate resistance to cephalothin, cefazolin, cefoxitin, most penicillins, and beta-lactamase inhibitor-beta-lactam combinations. In many bacteria, AmpC enzymes are inducible and can be expressed at high levels by mutation. Overexpression confers resistance to broad-spectrum cephalosporins including cefotaxime, ceftazidime, and ceftriaxone and is a problem especially in infections due to Enterobacter aerogenes and Enterobacter cloacae, where an isolate initially susceptible to these agents may become resistant upon therapy. Transmissible plasmids have acquired genes for AmpC enzymes, which consequently can now appear in bacteria lacking or poorly expressing a chromosomal bla(AmpC) gene, such as Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Resistance due to plasmid-mediated AmpC enzymes is less common than extended-spectrum beta-lactamase production in most parts of the world but may be both harder to detect and broader in spectrum. AmpC enzymes encoded by both chromosomal and plasmid genes are also evolving to hydrolyze broad-spectrum cephalosporins more efficiently. Techniques to identify AmpC beta-lactamase-producing isolates are available but are still evolving and are not yet optimized for the clinical laboratory, which probably now underestimates this resistance mechanism. Carbapenems can usually be used to treat infections due to AmpC-producing bacteria, but carbapenem resistance can arise in some organisms by mutations that reduce influx (outer membrane porin loss) or enhance efflux (efflux pump activation).

Tigecycline in combination with other antimicrobials: a review of in vitro, animal and case report studies

Tigecycline has been investigated in combination with other antibacterials against a wide range of susceptible and multiresistant Gram-positive and Gram-negative bacteria. Combinations have been analysed in vitro, in animal models and in human case reports. In vitro, tigecycline combined with other antimicrobials produces primarily an indifferent response (neither synergy nor antagonism). Nevertheless, synergy occurred when tigecycline was combined with rifampicin against 64-100% of Enterococcus spp., Streptococcus pneumoniae, Enterobacter spp. and Brucella melitensis isolates. Combinations of tigecycline with amikacin also showed synergy for 40-100% of Enterobacter spp., Klebsiella pneumoniae, Proteus spp. and Stenotrophomonas maltophilia isolates. Moreover, bactericidal synergisms occurred with tigecycline plus amikacin against problematic Acinetobacter baumannii and Proteus vulgaris, and with colistin against K. pneumoniae. Data from animal experiments and case reports, although limited, displayed consistent beneficial activity of tigecycline in combination with other antibacterials against multiresistant organisms, including vancomycin against penicillin-resistant S. pneumoniae in experimental meningitis, gentamicin against Pseudomonas aeruginosa in experimental pneumonia, daptomycin against Enterococcus faecium endocarditis, and colistin against K. pneumoniae bacteraemia and P. aeruginosa osteomyelitis. Antagonism was extremely rare in vitro and was not reported in vivo. Thus, tigecycline may be combined with a second antimicrobial as part of a combination regimen.