Tigecycline: in-vitro performance as a predictor of clinical efficacy

Identification of a mepR mutation associated with tigecycline resistance in a clinical Staphylococcus aureus isolate

OBJECTIVES

To identify the role and function of mepR variants in conferring resistance to tigecycline in clinical Staphylococcus aureus.

METHODS

The identification of the mepR and mepA variants in S. aureus DMB26a was performed by whole-genome sequencing and Blast alignment. The effects of the mepRD and mepAD variants of DMB26a on tigecycline susceptibility were evaluated through deletion and complementation analyses, as well as the determination of gene expression levels by RT-qPCR. Minimal inhibitory concentrations (MICs) for DMB26a and its mutants were determined by antimicrobial susceptibility testing.

RESULTS

A mepR variant, designated mepRD, and a mepA variant, designated mepAD, were identified in the clinical tigecycline-resistant S. aureus isolate DMB26a, which showed 78.72% and 84.92% amino acid identity to the MepR and MepA proteins of S. aureus NCTC 8325-4, respectively. Our findings revealed that deletion of mepA in the tigecycline-susceptible S. aureus RN4220 did not lead to a decrease in the MIC of tigecycline, and that there was also no change in the tigecycline MIC after the complementation with mepAD. Furthermore, we constructed a mepR + mepA deletion strain of S. aureus RN4220 and complemented it with mepRD + mepAD. In that case, a 4-fold increase in the tigecycline MIC was observed in S. aureus RN4220ΔmepR + mepA-pLI50_mepRD + mepAD compared with S. aureus RN4220ΔmepR + mepA. In addition, the relative expression of mepAD was increased 6-fold under the regulation of mepRD.

CONCLUSIONS

This study provides the identification of a mepR variant contributing indirectly to tigecycline resistance via mediating increased expression of mepA in a clinical S. aureus isolate.

Serum concentration threshold and risk factors of tigecycline-induced hypofibrinogenaemia in critically ill patients

OBJECTIVES

Hypofibrinogenaemia is a serious adverse reaction associated with tigecycline (TGC) therapy and may lead to the discontinuation of the treatment. This study aimed to explore the relevant factors of TGC-induced hypofibrinogenaemia and determine the thresholds of serum concentration as a predictive indicator of TGC-induced hypofibrinogenaemia.

METHODS

A retrospective single-centre study was conducted on patients with severe infection who were treated with TGC. Clinical data and serum concentration parameters were extracted from the electronic medical records of these patients. Patients were divided into the hypofibrinogenaemia group (< 2.0 g/L) and the normal fibrinogen group (≥ 2.0 g/L) in order to evaluate risk factors associated with TGC-induced hypofibrinogenaemia. Logistic regression analysis and receiver operating characteristic curves were utilized to identify the risk factors associated with TGC-induced hypofibrinogenaemia and to establish plasma concentration thresholds as predictive indicators.

RESULTS

A total of 114 patients were enrolled in this study, with 59.6% experiencing hypofibrinogenaemia. The multivariate regression analysis indicated that baseline fibrinogen level, trough concentration (Cmin), peak concentration (Cmax), the concentration at 6 h after the dosing (C6h) and the area under the concentration-time curve over a 24-h period (AUC0-24) were significantly associated with hypofibrinogenaemia (P < 0.05). Furthermore, it was found that AUC0-24 is the optimal predictor of TGC-induced hypofibrinogenaemia. The optimal cut-off for the AUC0-24 of TGC in ICU patients was determined to be 17.03 mg h/L.

CONCLUSIONS

TGC exposure is highly predictive of TGC-induced hypofibrinogenaemia. We recommend closely monitoring plasma concentrations of TGC in patients to ensure patient efficacy and safety.

Toxicity of tigecycline on the freshwater microalga Scenedesmus obliquus: Photosynthetic and transcriptional responses

Tigecycline (TGC) is a new tetracycline antibiotic medication against multidrug-resistant bacteria. However, the toxicity of TGC to microalgae remains largely unknown. In this study, the toxicity of TGC on Scenedesmus obliquus was examined, focusing on changes in algal growth, photosynthetic activity, and transcriptome. According to an acute toxicity test, the IC10 and IC50 values were 0.72 mg/L and 4.15 mg/L, respectively. Analyses of photosynthetic efficiency and related parameters, such as light absorption, energy capture, and electron transport, identified a 35% perturbation in the IC50 group, while the IC10 group remained largely unaffected. Transcriptomic analysis showed that in the IC10 and IC50 treatment groups, there were 874 differentially expressed genes (DEGs) (220 upregulated and 654 downregulated) and 4289 DEGs (2660 upregulated and 1629 downregulated), respectively. Gene Ontology enrichment analysis showed that TGC treatment markedly affected photosynthesis, electron transport, and chloroplast functions. In the IC50 group, a clear upregulation of genes related to photosynthesis and chloroplast functions was observed, which could be an adaptive stress response. In the IC10 group, significant downregulation of DEGs involved in ribosomal pathways and peptide biosynthesis processes was observed. Kyoto Encyclopedia of Gene and Genomes enrichment analysis showed that treatment with TGC also disrupted energy production, protein synthesis, and metabolic processes in S. obliquus. Significant downregulation of key proteins related to Photosystem II was observed under the IC10 TGC treatment. Conversely, IC50 TGC treatment resulted in substantial upregulation across a broad array of photosystem-related proteins from both Photosystems II and I. IC10 and IC50 TGC treatments differentially influenced proteins involved in the photosynthetic electron transport process. This study emphasizes the potential risks of TGC pollution to microalgae, which contributes to a better understanding of the effects of antibiotic contamination in aquatic ecosystems.

IS257-mediated amplification of tet(L) variant as a novel mechanism of enhanced tigecycline resistance in Staphylococcus cohnii

The mechanism of enhanced tigecycline MIC in Staphylococcus cohnii after in vitro tigecycline exposure was investigated. S. cohnii 11-B-312 was exposed to incremental concentrations of tigecycline (2-32 mg/L) and the mutants growing at 8, 16 and 32 mg/L were determined by AST and WGS. Copy number and relative transcription level of the tet(L) gene were determined by quantitative PCR. The fitness cost was evaluated by growth kinetics and competition assays. The results revealed that enhanced tigecycline MIC was identified in S. cohnii mutants. Copy number and relative transcription level of tet(L) in the mutants increased 8-, 20-, and 23-fold and 20-, 34-, and 39-fold in the presence of 8, 16, and 32 mg/L tigecycline, respectively. The read-mapping depth ratio analysis indicated that a multidrug resistance region carrying the tet(L) variant has a gradually increased copy number, correlating with the tigecycline selection pressure. S. cohnii strain 11-B-312_32 had a fitness cost, and enhanced tigecycline MIC can revert to the initial level in the absence of tigecycline. In summary, enhanced tigecycline MIC develops with extensive amplification of an IS257-flanked tet(L)-carrying segment in S. cohnii. IS257 seems to play a vital role in the gain and loss of the amplification product.

Novel Tet(L) Efflux Pump Variants Conferring Resistance to Tigecycline and Eravacycline in Staphylococcus Spp

Tigecycline is regarded as one of the few important last-resort antibiotics to treat complicated skin and intra-abdominal infections. Members of the genus Staphylococcus are zoonotic pathogens and pose a serious threat to public health. Tigecycline resistance in this species appears to be a rare phenomenon, and the mechanisms underlying tigecycline resistance have not been fully elucidated. Here, we report two novel variants of the tet(L) gene in Staphylococcus spp. from swine in China, designed as tet(L)_F58L and tet(L)_A117V. The tet(L)_F58L was located within a 18,720 bp chromosomal multidrug resistance gene cluster flanked by two copies of IS257 in Staphylococcus cohnii 11-B-312, while the tet(L)_A117V was located on a 6,292 bp plasmid in S. haemolyticus 11-B-93, which could be transferred to S. aureus by electrotransformation. Cloning of each of the two tet(L) variants into S. aureus RN4220 showed 16- or 8-fold increases in the minimal inhibition concentrations (MICs), which can fully confer the resistance to tigecycline (MICs from 0.125 to 2 mg/liter) and eravacycline (MICs from 0.125 to 1 or 2 mg/liter), but no increase in the MICs of omadacycline, compared with the MICs of the recipient strain S. aureus RN4220. In the in vivo murine sepsis and in the murine pneumonia models, an increase in CFU of S. aureus 29213_pT93 carrying the tet(L)_A117V was seen despite tigecycline treatment. This observation suggests that the tet(L)_A117V and its associated gene product compromise the efficacy of tigecycline treatment in vivo and may lead to clinical treatment failure. Our finding, that novel Tet(L) efflux pump variants which confer tigecycline and eravacycline resistance have been identified in Staphylococcus spp., requires urgent attention.

IMPORTANCE Tigecycline and eravacycline are both important last-resort broad spectrum antimicrobial agents. The presence of novel Tet(L) efflux pump variants conferring the resistance to tigecycline and eravacycline in Staphylococcus spp. and its potential transmission to S. aureus will compromise the efficacy of tigecycline and eravacycline treatment for S. aureus associated infection in vivo and may lead to clinical treatment failure.

Tigecycline antibacterial activity, clinical effectiveness, and mechanisms and epidemiology of resistance: narrative review

Tigecycline is unique glycylcycline class of semisynthetic antimicrobial agents developed for the treatment of polymicrobial infections caused by multidrug-resistant Gram-positive and Gram-negative pathogens. Tigecycline evades the main tetracycline resistance genetic mechanisms, such as tetracycline-specific efflux pump acquisition and ribosomal protection, via the addition of a glycyclamide moiety to the 9-position of minocycline. The use of the parenteral form of tigecycline is approved for complicated skin and skin structure infections (excluding diabetes foot infection), complicated intra-abdominal infections, and community-acquired bacterial pneumonia in adults. New evidence also suggests the effectiveness of tigecycline for the treatment of severe Clostridioides difficile infections. Tigecycline showed in vitro susceptibility to Coxiella spp., Rickettsia spp., and multidrug-resistant Neisseria gonnorrhoeae strains which indicate the possible use of tigecycline in the treatment of infections caused by these pathogens. Except for intrinsic, or often reported resistance in some Gram-negatives, tigecycline is effective against a wide range of multidrug-resistant nosocomial pathogens. Herein, we summarize the currently available data on tigecycline pharmacokinetics and pharmacodynamics, its mechanism of action, the epidemiology of tigecycline resistance, and its clinical effectiveness.

Best tigecycline dosing for treatment of infections caused by multidrug-resistant pathogens in critically ill patients with different body weights

Background

The intensive care unit (ICU) is a center of multidrug-resistant (MDR) pathogens. This is due to overuse of antibiotics in the treatment of critically ill patients. Tigecycline is a broad-spectrum antibiotic that belongs to the glycylcycline group. Tigecycline has been indicated in treatment of complicated intra-abdominal infections (cIAIs) and complicated skin and soft-tissue infections (cSSTIs).

Objective

This study was done to discover the best dose regimen of tigecycline in treatment of cSSTIs and cIAIs, especially in patients who are critically ill and obese, for clinical outcomes and safety.

Setting

The study was conducted in an adult ICU that consists of 25 beds in a general hospital and was conducted within 2 years. A total of 954 patients were screened in this study.

Methods

This was a retrospective cohort study that compared the clinical outcomes of patients: mortality, ICU stay, and safety of using two different dose regimens of tigecycline between patients with different body weight who were treated for infections caused by MDR pathogens in the ICU. The study was conducted within 2 years. All results were collected from patients’ files and were analyzed with SPSS version 20.

Main outcome

The study was implemented to figure out the best dose regimen of tigecycline to achieve a reduction in mortality, ICU stay, treatment duration, and secondary septic-shock incidence with minimum side effects in treatment of cSSTIs and cIAIs in patients with different body weight.

Results

There was a significant improvement in mortality, ICU stay, recurrent infection by the same organism, duration of tigecycline treatment, number of patients who had first negative culture after starting treatment, secondary bacteremia, and secondary septic shock with patients who used high-dose regimens of tigecycline in different subgroups of body weight, with no significant difference in side effects.

Conclusion

The use of high-dose tigecycline resulted in a significant enhancement in all clinical outcomes, especially mortality and ICU stay when used in treatment of overweight and obese patients with cSSTIs and cIAIs.

Tigecycline resistance among Klebsiella pneumoniae isolated from febrile neutropenic patients

Febrile neutropenic patients are at a high risk of life-threatening bacterial infections. Tigecycline was developed to treat multidrug-resistant isolates, however resistance to tigecycline in Klebsiella pneumoniae has been reported. Here, we investigated tigecycline resistance among K. pneumoniae isolated from febrile neutropenic patients admitted to Hematology ICU, Egypt. Out of 75 enrolled febrile neutropenic patients, 48 cases showed bacteriologically confirmed infection. The majority of cases were infected with K. pneumoniae, of which nine were tigecycline non-susceptible. Expression levels of the efflux pump genes acrB and oqxB and their regulatory genes ramA and rarA were analysed. Six isolates had overexpression of the four efflux-related genes while one showed baseline expression. This study emphasizes the importance of growing tigecycline resistance in K. pneumoniae infecting febrile neutropenic patients. Concerning the mechanism of resistance, it was clear that the ramA gene plays the major role, although alternative resistance mechanisms may also exist.

Surveillance of tigecycline activity tested against clinical isolates from a global (North America, Europe, Latin America and Asia-Pacific) collection (2016)

Tigecycline and comparators were tested by the reference broth microdilution method against 33 348 non-duplicate bacterial isolates collected prospectively in 2016 from medical centres in the Asia-Pacific (3443 isolates), Europe (13 530 isolates), Latin America (3327 isolates) and the USA (13 048 isolates). Among 7098 Staphylococcus aureus isolates tested, >99.9% were inhibited by ≤0.5 mg/L tigecycline (MIC_50/90, 0.06/0.12 mg/L), including >99.9% of methicillin-resistant S. aureus and 100.0% of methicillin-susceptible S. aureus. Tigecycline was slightly more active against Enterococcus faecium (MIC_50/90, 0.03/0.06 mg/L) compared with Enterococcus faecalis (MIC_50/90, 0.06/0.12 mg/L) and its activity was not adversely affected by vancomycin resistance when tested against these organisms. Tigecycline potency was comparable for Streptococcus pneumoniae (MIC_50/90, 0.03/0.06 mg/L), viridans group streptococci (MIC_50/90, 0.03/0.06 mg/L) and β-haemolytic streptococci (MIC_50/90, 0.06/0.06 mg/L) regardless of species and penicillin susceptibility. Tigecycline was active against Enterobacteriaceae (MIC_50/90, 0.25/1 mg/L; 97.8% inhibited at ≤2 mg/L) but was slightly less active against Enterobacteriaceae isolates expressing resistant phenotypes: carbapenem-resistant Enterobacteriaceae (MIC_50/90, 0.5/2 mg/L; 98.0% susceptible); multidrug-resistant (MIC_50/90, 0.5/2 mg/L; 93.1% susceptible); and extensively drug-resistant (MIC_50/90, 0.5/4 mg/L; 87.8% susceptible). Tigecycline inhibited 74.4% of 888 Acinetobacter baumannii isolates at ≤2 mg/L (MIC_50/90, 2/4 mg/L) and demonstrated good in vitro activity against Stenotrophomonas maltophilia (MIC_50/90, 1/2 mg/L; 90.6% inhibited at ≤2 mg/L) Tigecycline was active against Haemophilus influenzae (MIC_50/90, 0.12/0.25 mg/L) regardless of β-lactamase status. Tigecycline represents an important treatment option for resistant Gram-negative and Gram-positive bacterial infections.

The In Vitro Evaluation of Tigecycline and the In Vivo Evaluation of RPX-978 (0.5% Tigecycline) as an Ocular Antibiotic

PURPOSE

The goals of the current study were to determine the in vitro antibacterial activity of tigecycline against multiple clinically relevant ocular pathogens and to evaluate the in vivo ocular tolerability and efficacy of 0.5% tigecycline in a methicillin-resistant Staphylococcus aureus (MRSA) keratitis model.

METHODS

In vitro: Minimum inhibitory concentrations (MICs) were determined for 110 clinical conjunctivitis isolates, 26 keratitis isolates of Pseudomonas aeruginosa, and 10 endophthalmitis isolates each of MRSA, methicillin-susceptible S. aureus (MSSA), MR, and MS coagulase-negative Staphylococcus.

TOLERABILITY

Six uninfected rabbits were topically treated in both eyes with 0.5% tigecycline, vehicle, or saline every 15 min for 3 h.

EFFICACY

Thirty-two rabbits were intrastromally injected with 700 Colony Forming Units (CFU) of MRSA in both eyes and were separated into 4 groups (n = 8): tigecycline 0.5%; vancomycin 5%; saline; and no treatment (euthanized before treatment for baseline CFU). Four hours after MRSA challenge, topical treatment of 1 drop every 15 min for 5 h was initiated. One hour after treatment, the corneas were harvested for CFU. The data were analyzed nonparametrically.

RESULTS

In vitro: Tigecycline demonstrated lower MICs than the other tested antibiotics against gram-positive organisms, especially MRSA, while MICs against gram-negative pathogens, including fluoroquinolone-resistant P. aeruginosa, appeared to be in the treatable range with aggressive topical therapy.

TOLERABILITY

0.5% tigecycline was graded as minimally irritating.

EFFICACY

0.5% tigecycline and vancomycin produced similar reductions in CFU and were less than saline (P < 0.05). Tigecycline and vancomycin demonstrated 99.9% reductions compared with baseline CFU.

CONCLUSIONS

Tigecycline is a potential candidate for a topical ocular antibiotic.

Bloodstream infections in intensive care unit patients: distribution and antibiotic resistance of bacteria

Bloodstream infections (BSIs) are among the leading infections in critically ill patients. The case-fatality rate associated with BSIs in patients admitted to intensive care units (ICUs) reaches 35%–50%. The emergence and diffusion of bacteria with resistance to antibiotics is a global health problem. Multidrug-resistant bacteria were detected in 50.7% of patients with BSIs in a recently published international observational study, with methicillin resistance detected in 48% of Staphylococcus aureus strains, carbapenem resistance detected in 69% of Acinetobacter spp., in 38% of Klebsiella pneumoniae, and in 37% of Pseudomonas spp. Prior hospitalization and antibiotic exposure have been identified as risk factors for infections caused by resistant bacteria in different studies. Patients with BSIs caused by resistant strains showed an increased risk of mortality, which may be explained by a higher incidence of inappropriate empirical therapy in different studies. The molecular genetic characterization of resistant bacteria allows the understanding of the most common mechanisms underlying their resistance and the adoption of surveillance measures. Knowledge of epidemiology, risk factors, mechanisms of resistance, and outcomes of BSIs caused by resistant bacteria may have a major influence on global management of ICU patients. The aim of this review is to provide the clinician an update on BSIs caused by resistant bacteria in ICU patients.

Emerging broad-spectrum resistance in Pseudomonas aeruginosa and Acinetobacter baumannii: Mechanisms and epidemiology

Multidrug resistance is quite common among non-fermenting Gram-negative rods, in particular among clinically relevant species including Pseudomonas aeruginosa and Acinetobacter baumannii. These bacterial species, which are mainly nosocomial pathogens, possess a diversity of resistance mechanisms that may lead to multidrug or even pandrug resistance. Extended-spectrum β-lactamases (ESBLs) conferring resistance to broad-spectrum cephalosporins, carbapenemases conferring resistance to carbapenems, and 16S rRNA methylases conferring resistance to all clinically relevant aminoglycosides are the most important causes of concern. Concomitant resistance to fluoroquinolones, polymyxins (colistin) and tigecycline may lead to pandrug resistance. The most important mechanisms of resistance in P. aeruginosa and A. baumannii and their most recent dissemination worldwide are detailed here.

In vitro antimalarial activity of tigecycline against Plasmodium falciparum culture-adapted reference strains and clinical isolates from the Brazilian Amazon

INTRODUCTION

We evaluated the in vitro antimalarial activity of tigecycline as an alternative drug for the treatment of severe malaria.

METHODS

A chloroquine-sensitive Plasmodium falciparum reference strain, a chloroquine-resistant reference strain, and three clinical isolates were tested for in vitro susceptibility to tigecycline. A histidine-rich protein in vitro assay was used to evaluate antimalarial activity.

RESULTS

The geometric-mean 50% effective concentration (EC50%) of tigecycline was 535.5 nM (confidence interval (CI): 344.3-726.8). No significant correlation was found between the EC50% of tigecycline and that of any other tested antimalarial drug.

CONCLUSIONS

Tigecycline may represent an alternative drug for the treatment of patients with severe malaria.

Tigecycline activity against metallo-β-lactamase-producing bacteria

Backgound:

Treatment of serious life-threatening multi-drug-resistant organisms poses a serious problem due to the limited therapeutic options. Tigecycline has been recently marketed as a broad-spectrum antibiotic with activity against both gram-positive and gram-negative bacteria. Even though many studies have demonstrated the activity of tigecycline against ESBL-producing Enterobacteriaceae, its activity is not well-defined against micro-organisms producing metallo-β-lactamases (MBLs), as there are only a few reports and the number of isolates tested is limited.

Aims:

The aim of the present study was to evaluate the activity of tigecycline against MBL-producing bacterial isolates.

Materials and Methods:

The isolates were tested for MBL production by (i) combined-disk test, (ii) double disc synergy test (DDST), (iii) susceptibility to aztreonam (30 μg) disk. Minimum inhibitory concentration to tigecycline was determined according to agar dilution method as per Clinical Laboratory Standards Institute (CLSI) guidelines. Disc diffusion susceptibility testing was also performed for all these isolates using tigecycline (15 μg) discs.

Results:

Among the total 308 isolates included in the study, 99 were found to be MBL producers. MBL production was observed mostly in isolates from pus samples (40.47%) followed by urine (27.4%) and blood (13.09%). MBL production was observed in E. coli (41.48%), K. pneumoniae (26.67%), Proteus mirabilis (27.78%), Citrobacter spp. (41.67%), Enterobacter spp. (25.08%), and Acinetobacter spp. (27.27%). The result showed that tigecycline activity was unaffected by MBL production and it was showed almost 100% activity against all MBL-producing isolates, with most of the isolates exhibiting an MIC ranging from 0.25-8 μg/ml, except 2 MBL-producing E. coli isolates who had an MIC of 8 μg/ml.

Conclusion:

To conclude, tigecycline was found to be highly effective against MBL-producing Enterobacteriaceae and acinetobacter isolates, but the presence of resistance among organisms, even before the mass usage of the drug, warrants the need of its usage as a reserve drug. The study also found that the interpretative criteria for the disc diffusion method, recommended by the FDA, correlates well with the MIC detection methods. So, the microbiology laboratories might use the relatively easier method of disc diffusion, as compared to the comparatively tedious method of MIC determination.

Therapy of intracellular Staphylococcus aureus by tigecyclin

Background

In the fields of traumatology and orthopaedics staphylococci are the most frequently isolated pathogens. Staphylococcus aureus and Staphylococcus epidermidis are known to be the major causative agents of osteomyelitis. The increasing number of multiresistant Staphylococcus aureus and resistant coagulase-negative staphylococci as a trigger of complicated osteomyelitis and implant-associated infections is a major problem. Antibiotic therapy fails in 20% of cases. Therefore the development of novel antibiotics becomes necessary.

Methods

This study analyses tigecyclin, the first antibiotic of the glycylines, as a potential therapy for osteomyelitis caused by multiresistant Staphylococcus aureus. Therefore its intracellular activity and the potential use in polymethylmetacrylate-bone cement are examined. The intracellular activity of tigecyclin is determined by a human osteoblast infection model. The investigation of the biomechanical characteristics is conducted concerning the ISO 5833-guidelines.

Results

Tigecyclin shows in vitro an intracellular activity that ranges between the antimicrobial activity of gentamicin and rifampicin. A significant negative effect on the biomechanical characteristics with an impaired stability is detected after adding tigecyclin to polymethylmetacrylate-bone cement with a percentage of 1.225% per weight.

Conclusions

This study shows that tigecyclin might be a potent alternative for the systemic therapy of osteomyelitis and implant-associated infections whereas the local application has to be reconsidered individually.

Identification and characterization of antigens as vaccine candidates against Klebsiella pneumoniae

Nosocomial infections, also called "hospital acquired infections," occur worldwide and affect both developed and resource-poor countries, thus having a major impact on their health care systems. Klebsiella pneumoniae, which is an opportunistic Gram-negative pathogen, is responsible for causing pneumonia, urinary tract infections and septicemia in immune compromised hosts such as neonates. Unfortunately, there is no vaccine or mAb available for prophylactic or therapeutic use against K. pneumoniae infections. For this reason, we sought for a protein-based subunit vaccine capable of combating K. pneumoniae infections, by applying our ANTIGENome technology for the identification of potential vaccine candidates, focusing on conserved protein antigens present in strains with different serotypes. We identified numerous novel immunogenic proteins using genomic surface display libraries and human serum antibodies from donors exposed to or infected by K. pneumoniae. Vaccine candidate antigens were finally selected based on animal protection in a murine lethal-sepsis model. The protective and highly conserved antigens identified in this study are promising candidates for the development of a protein-based vaccine to prevent infection by K. pneumoniae.

Clinical and microbiological characterization of KPC-producing Klebsiella pneumoniae infections in Brazil

In 2008 isolates of KPC-producing Klebsiella pneumoniae (KPC-KPN) were detected for the first time at Hospital Heliópolis, São Paulo, Brazil. The aim of this study was to characterize the clinical and microbiological outcomes of infections caused by KPC-KPN. A historical cohort of patients from whom KPC-KPN strains were isolated was performed. Isolates were identified as resistant to ertapenem by automated broth microdilution system and screened as carbapenemase producers by the modified Hodge test. The beta-lactamase resistance gene blaKPC was detected by PCR. The genetic relatedness of isolates was determined by PFGE. The study provides early clinical experience in treating KPC-KPN infections in a Brazilian tertiary center.

Genotypic characterization and in vitro activities of tigecycline and polymyxin B for members of the Enterobacteriaceae with decreased susceptibility to carbapenems

Carbapenem resistance in members of the Enterobacteriaceae is increasing. To evaluate the effects of tigecycline and polymyxin B against carbapenem-non-susceptible pathogens, 89 representative clinical carbapenem-non-susceptible Enterobacteriaceae isolates were recovered from seven hospitals from four cities in China during 2006-2009: 30 Serratia marcescens, 35 Klebsiella pneumoniae, seven Enterobacter cloacae, six Enterobacter aerogenes, five Escherichia coli, four Citrobacter freundii and two Klebsiella oxytoca isolates. Twenty-eight S. marcescens isolates were indistinguishable. The 35 K. pneumoniae isolates belonged to 12 clonal strains. Among the 89 Enterobacteriaceae isolates, 82 produced KPC-2, seven produced IMP (three produced KPC-2 simultaneously), three did not produce any carbapenemases and nine were deficient in porins. Polymyxin B was much more active than tigecycline against carbapenem-non-susceptible Enterobacteriaceae. The MIC(50) and MIC(90) of imipenem, meropenem, ertapenem, polymyxin B and tigecycline were 8 and 32 µg ml(-1), 8 and 32 µg ml(-1), 16 and 128 µg ml(-1), 0.5 and 16 µg ml(-1), and 4 and 16 µg ml(-1), respectively. Rates of susceptibility to imipenem, meropenem, ertapenem and polymyxin B were 30.0%, 27.5%, 2.5% and 89.2% by CLSI criteria. The rate of susceptibility to tigecycline was 40% and 17.5% by Food and Drug Administration (MIC ≤2 µg ml(-1)) and European Committee on Antimicrobial Susceptibility Testing (MIC ≤1 µg ml(-1)) criteria, respectively. KPC-2- or IMP-producing E. coli transconjugants exhibited reduced susceptibility to carbapenems but were susceptible to polymyxin B and tigecycline with an MIC range of 0.5-2 µg ml(-1), 0.25-2 µg ml(-1), 0.5-4 µg ml(-1), 0.5 µg ml(-1) and 0.5-1 µg ml(-1). In conclusion, carbapenem resistance in Enterobacteriaceae is mainly due to production of KPC-2, and polymyxin B is active for the carbapenem-resistant Enterobacteriaceae.

Tigecycline use in serious nosocomial infections: a drug use evaluation

Background

Tigecycline is a novel antibiotic with activity against multidrug resistant bacteria. The aim of this study was to assess the efficacy of tigecycline use in serious hospital-acquired infections (HAI)

Case presentation

Prospective observational study of tigecycline use was conducted in a 1500 beds university hospital. From January 1, 2007 and January 31, 2010, 207 pts were treated with tigecycline for the following indications: intra-abdominal, pneumonia, bloodstream and complicated skin and soft tissue infections and febrile neutropenia. The therapy was targeted in 130/207 (63%) and empirical in 77/207 (37%) patients. All bacteria treated were susceptible to tigecycline. Median duration of tigecycline therapy was 13 days (range, 6-28). Clinical success was obtained in 151/207 (73%) cases, with the highest success rate recorded in intra-abdominal infections [81/99 (82%)]. Microbiological success was achieved in 100/129 (78%) treated patients. Adverse clinical events were seen in 16/207 patients (7.7%):

Conclusions

Considering the lack of data on tigecycline for critically ill patients, we think that the reported data of our clinical experience despite some limitations can be useful for clinicians.

Antibiotic optimization in the difficult-to-treat patient with complicated intra-abdominal or complicated skin and skin structure infections: focus on tigecycline

Complicated intra-abdominal and skin and skin structure infections are widely varied in presentation. These infections very often lead to an increase in length of hospital stay, with a resulting increase in costs and mortality. In addition, these infections may be caused by a wide variety of bacteria and are often polymicrobial with the possibility of the presence of antimicrobial-resistant strains, such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, extended-spectrum β-lactamase strains (Escherichia coli, Klebsiella pneumoniae), and K. pneumoniae carbapenemase-producing strains. In combination with patients’ immunosuppression or comorbidities, the treatment and management options for initial therapy success are few. Tigecycline, a new glycylcyline antimicrobial from the tetracycline drug class, represents a viable option for the successful treatment of these infections. It has been shown to have activity against a wide variety of bacteria, including the antimicrobial-resistant strains. As with all tetracycline drugs, it is not recommended for pregnant or nursing women. The potential side effects are those typical of tetracycline drugs: nausea, vomiting, and headaches. Drug–drug interactions are not expected, and renal function monitoring is not necessary.

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.

ramR mutations in clinical isolates of Klebsiella pneumoniae with reduced susceptibility to tigecycline

Five Klebsiella pneumoniae isolates with reduced susceptibility to tigecycline (MIC, 2 microg/ml) were analyzed. A gene homologous to ramR of Salmonella enterica was identified in Klebsiella pneumoniae. Sequencing of ramR in the nonsusceptible Klebsiella strains revealed deletions, insertions, and point mutations. Transformation of mutants with wild-type ramR genes, but not with mutant ramR genes, restored susceptibility to tigecycline and repressed overexpression of ramA and acrB. Thus, this study reveals a molecular mechanism for tigecycline resistance in Klebsiella pneumoniae.

Comparative in vitro activity of tigecycline and nine other antibiotics against gram-negative bacterial isolates, including ESBL-producing strains

The enterobacteriaceae, especially Escherichia coli and Klebsiella spp., as well as Acinetobacter spp., are important agents of nosocomial infections in hospitalized patients. A total of 460 Gram-negative bacteria (GNb), were investigated for their susceptibility to tigecycline and 9 other antibiotics by the etest. ESBL production was inferred from ESBL etest phenotypes. All the GNb, including the ESBL-producers, were susceptible to tigecycline with MIC(90 )ranges of 0.25 to 2 microg/ml. Imipenem and meropenem were very active against ESBL and non-ESBL producers; mean MIC(90)s of 0.19 and 0.09 microg/ml and 0.05 microg/ml and 0.02 microg/ml, respectively. The MIC(90)s of imipenem and meropenem for the Acinetobacter spp. were 16 and >32 microg/ml, respectively with resistance rates of 64.3 and 66.1%. ESBL production was detected in 62% and 82.1% of the E. coli and K. pneumoniae isolates, respectively. Resistance to ciprofloxacin was higher among the ESBL-producing strains of E. coli and K. pneumoniae than the non-ESBL producers. Comparatively, tigecycline had excellent in vitro activities against ESBL-producing enterobacteriaceae and demonstrated superior activity against Acinetobacter spp. Increasing ESBL production and resistance to ciprofloxacin and gentamicin in enterobacteriaceae require careful selection of empirical therapy. Tigecycline holds promise as an alternative choice of therapy for infections caused by ESBL-producing isolates and multi-drug resistant Acinetobacter spp.

Antimalarial activity of tigecycline, a novel glycylcycline antibiotic

Tigecycline is a novel glycylcycline antibiotic with a broad antibacterial spectrum. Tigecycline was tested with 66 clinical isolates of Plasmodium falciparum from Bangladesh using the histidine-rich protein 2 in vitro drug susceptibility assay. The 50% and 90% inhibitory concentrations of tigecycline were 699 (95% confidence interval, 496 to 986) and 5,905 nM (4,344 to 8,028). Tigecycline shows no activity correlation with traditional antimalarials and has substantial antimalarial activity on its own.

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.

Non-susceptibility trends among Enterobacteriaceae from bacteraemias in the UK and Ireland, 2001-06

BACKGROUND

Enterobacteriaceae are common agents of bacteraemia, with Escherichia coli accounting for 20% of the cases. Reflecting this importance, members of the family constitute 4 of the 12 collection groups in the British Society for Antimicrobial Chemotherapy (BSAC) Bacteraemia Surveillance Programme.

METHODS

MICs from the BSAC surveillance programme were reviewed, along with bacteraemia reports received by the Health Protection Agency (HPA) via its CoSurv/LabBase system. Isolates with unusual resistances were subjected to molecular analysis.

RESULTS

The BSAC and HPA systems both revealed dramatically increasing resistance to cephalosporins, ciprofloxacin and gentamicin among E. coli and Klebsiella spp., with cephalosporin resistance largely contingent on the spread of CTX-M extended-spectrum beta-lactamases (ESBLs); fluoroquinolone resistance also increased among Proteus mirabilis and ESBL-negative E. coli. Carbapenem resistance remained extremely rare, but two Enterobacter spp., from the same patient in different years, had KPC carbapenemases, while a few isolates had carbapenem resistance contingent upon combinations of beta-lactamase and impermeability, and ertapenem MICs for AmpC-derepressed Enterobacter spp. rose over time. Three new agents-ceftobiprole, doripenem and tigecycline-were tested. Ceftobiprole was broadly active, except against ESBL producers and Klebsiella oxytoca hyperproducing K1 enzyme, and was variable against AmpC-derepressed Enterobacter spp. and against Proteus vulgaris. Doripenem was more potent than imipenem. Tigecycline was almost universally active against E. coli, but low-level non-susceptibility (MIC 2 mg/L) was frequent among Klebsiella spp.

CONCLUSIONS

E. coli and Klebsiella spp. showed dramatic shifts, with sharply rising non-susceptibility to cephalosporins, ciprofloxacin and gentamicin. The rise in cephalosporin resistance reflected dissemination of CTX-M ESBLs. Carbapenems remain broadly active and new agents offer potential.

In vitro activity of tigecycline against multidrug-resistant Enterobacteriaceae isolates from a Belgian hospital

Bacterial resistance among Gram-negative pathogens is a challenging clinical problem. Tigecycline has been developed specifically to overcome resistance. The aim of this study was to assess the in vitro activity of tigecycline against ESBL-producing Escherichia coli, ESBL-producing Klebsiella spp., and multidrug-resistant Enterobacter spp. Between May 2007 and March 2008, 26 strains of ESBL-producing Escherichia coli, 10 strains of ESBL-producing Klebsiella spp., and 27 strains of multidrug-resistant Enterobacter spp. were isolated consecutively from inpatients with a documented infection in which the collected isolate was identified as the probable causative organism. The in vitro susceptibility against tigecycline was measured by the E-test method. MIC(50) values were 1 microg/ml, 2 microg/ml, and 3 microg/ml respectively. MIC(90) values were respectively 1.5 microg/ml, 4 microg/ml, and 12 microg/ml. Nonsusceptibility rates of 35%, 100%, and 96% respectively were found using EUCAST breakpoints. Despite the limited number of strains tested, our in vitro data suggest that tigecycline is unsuitable for the treatment of infections with multidrug-resistant Enterobacteriaceae in our setting. Therefore, we suggest that larger multicenter studies should be conducted to reconsider the value of tigecycline for the treatment of infections with multidrug-resistant, Gram-negative bacteria.

Tigecycline for the treatment of multidrug-resistant Enterobacteriaceae: a systematic review of the evidence from microbiological and clinical studies

OBJECTIVES

Antimicrobial drug resistance is spreading among Enterobacteriaceae, limiting the utility of traditionally used agents. We sought to systematically review the microbiological activity and clinical effectiveness of tigecycline for multidrug-resistant (MDR) Enterobacteriaceae, including those resistant to broad-spectrum beta-lactams due to the expression of extended-spectrum beta-lactamases (ESBLs), AmpC enzymes and carbapenemases (including metallo-beta-lactamases).

METHODS

PubMed was searched for articles including relevant data.

RESULTS

Twenty-six microbiological and 10 clinical studies were identified. Tigecycline was active against more than 99% of 1936 Escherichia coli isolates characterized by any of the above resistance patterns (including 1636 ESBL-producing isolates) using the US Food and Drug Administration (FDA) breakpoint of susceptibility (MIC < or = 2 mg/L). Findings were not different using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoint (< or = 1 mg/L). Susceptibility rates for Klebsiella spp. with any of the above resistance patterns were 91.2% for 2627 isolates by the FDA criteria and 72.3% for 1504 isolates by the EUCAST criteria (92.3% for 2030 and 72.3% for 1284 ESBL-producing isolates, by the FDA and EUCAST criteria, respectively). The degree of microbiological activity of tigecycline against 576 MDR Enterobacter spp. isolates was moderate. In clinical studies, 69.7% of the 33 reported patients treated with tigecycline achieved resolution of an infection caused by a carbapenem-resistant or ESBL-producing or MDR Enterobacteriaceae.

CONCLUSIONS

Tigecycline is microbiologically active against almost all of the ESBL or MDR E. coli isolates and the great majority of ESBL or MDR Klebsiella spp. isolates. Further evaluation of its clinical utility against such resistant Enterobacteriaceae, particularly regarding non-labelled indications, is warranted.

Molecular epidemiology of clinically significant antibiotic resistance genes

Antimicrobials were first introduced into medical practice a little over 60 years ago and since that time resistant strains of bacteria have arisen in response to the selective pressure of their use. This review uses the paradigm of the evolution and spread of beta-lactamases and in particular beta-lactamases active against antimicrobials used to treat Gram-negative infections. The emergence and evolution particularly of CTX-M extended-spectrum beta-lactamases (ESBLs) is described together with the molecular mechanisms responsible for both primary mutation and horizontal gene transfer. Reference is also made to other significant antibiotic resistance genes, resistance mechanisms in Gram-negative bacteria, such as carbepenamases, and plasmid-mediated fluoroquinolone resistance. The pathogen Staphylococcus aureus is reviewed in detail as an example of a highly successful Gram-positive bacterial pathogen that has acquired and developed resistance to a wide range of antimicrobials. The role of selective pressures in the environment as well as the medical use of antimicrobials together with the interplay of various genetic mechanisms for horizontal gene transfer are considered in the concluding part of this review.

Clinical and microbiological outcomes of serious infections with multidrug-resistant gram-negative organisms treated with tigecycline

Eighteen patients received tigecycline as treatment for infection due to multidrug-resistant gram-negative bacilli, including Acinetobacter baumannii and Klebsiella pneumoniae carbapenemase- and extended-spectrum beta-lactamase-producing Enterobacteriaceae. Pretherapy minimum inhibitory concentration values for tigecycline predicted clinical success. Observed evolution of resistance during therapy raises concern about routine use of tigecycline in treatment of such infections when other therapies are available.

Antimicrobial activities of tigecycline and other broad-spectrum antimicrobials tested against serine carbapenemase- and metallo-beta-lactamase-producing Enterobacteriaceae: report from the SENTRY Antimicrobial Surveillance Program

A total of 104 carbapenemase (serine- and metallo-beta-lactamase [MbetaL])-producing strains of the Enterobacteriaceae family collected from 2000 to 2005 in medical centers distributed worldwide were tested against tigecycline and 25 comparators by reference broth microdilution methods. The most frequent carbapenemase was KPC-2 or -3 (73 strains), followed by VIM-1 (14), IMP-1 (11), SME-2 (5), and NMC-A (1). All serine carbapenemases were detected in the United States, while MbetaL-producing strains were isolated in Europe. Carbapenemase-producing Enterobacteriaceae showed high rates of resistance to most antimicrobial agents tested. The rank order of in vitro activity against these strains was as follows: tigecycline (100.0% susceptible) > polymyxin B (88.1%) > amikacin (73.0%) > imipenem (37.5%). Tigecycline was very active (MIC(90), 1 microg/ml) against this significant, contemporary collection of well-characterized strains and appears to be an excellent option compared to the polymyxins for treatment of infections caused by these multidrug-resistant Enterobacteriaceae.