Clinical Experience with Tigecycline in the Treatment of Carbapenem-ResistantAcinetobacterInfections

Risk factors and mortality rates of carbapenem-resistant Gram-negative bacterial infections in intensive care units

Background

The prevalence of hospital-acquired infections caused by carbapenem-resistant gram-negative bacteria (CRGNB) is increasing worldwide. Several risk factors have been associated with such infections. The present study aimed to identify risk factors and determine the mortality rates associated with CRGNB infections in intensive care units.

Methods

This retrospective case-control study was conducted at Erciyes University Hospital (Kayseri, Turkey) between January 2017 and December 2021. Demographic and laboratory data were obtained from the Infection Control Committee data and record system. Patients who had CRGNB infection 48-72 h after hospitalization were assigned to the case group, while those who were not infected with CRGNB during hospitalization formed the control group. Risk factors, comorbidity, demographic data, and mortality rates were compared between the two groups.

Results

Approximately 1449 patients (8.97%) were monitored during the active follow-up period; of those, 1171 patients were included in this analysis. CRGNB infection developed in 14 patients (70.00%) who had CRGNB colonization at admission; in 162 (78.26%) were colonized during hospitalization, whereas 515 (54.56%) were not colonized. There was no significant difference in age, sex (male/female) or comorbidities. The total length of hospital stay was statistically significantly longer (P=0.001) in the case group (median: 24 [interquartile range: 3-378] days) than the control group (median: 16 [interquartile range: 3-135] days). The rates of colonization at admission (25.5%; vs. 10.6%, P=0.001) and mortality (64.4% vs. 45.8%, P=0.001) were also significantly higher in the cases than in the control group, respectively. In the univariate analysis, prolonged hospitalization, the time from intensive care unit admission to the development of infection, presence of CRGNB colonization at admission, transfer from other hospitals, previous antibiotic use, enteral nutrition, transfusion, hemodialysis, mechanical ventilation, tracheostomy, reintubation, central venous catheter, arterial catheterization, chest tube, total parenteral nutrition, nasogastric tube use, and bronchoscopy procedures were significantly associated with CRGNB infections (P <0.05). Multivariate analysis identified the total length of stay in the hospital (odds ratio [OR]=1.02; 95% confidence interval [CI]: 1.01 to 1.03; P=0.001), colonization (OR=2.19; 95% CI: 1.53 to 3.13; P=0.001), previous antibiotic use (OR=2.36; 95% CI: 1.53 to 3.62; P=0.001), intubation (OR=1.59; 95% CI: 1.14 to 2.20; P=0.006), tracheostomy (OR=1.42; 95% CI: 1.01 to 1.99; P=0.047), and central venous catheter use (OR=1.62; 95% CI: 1.20 to 2.19; P=0.002) as the most important risk factors for CRGNB infection.

Conclusions

Colonization, previous use of antibiotics, and invasive interventions were recognized as the most important risk factors for infections. Future research should focus on measures for the control of these parameters.

Genetic Determinants of Acinetobacter baumannii Serum-Associated Adaptive Efflux-Mediated Antibiotic Resistance

Acinetobacter baumannii is a nosocomial pathogen of serious healthcare concern that is becoming increasingly difficult to treat due to antibiotic treatment failure. Recent studies have revealed that clinically defined antibiotic-susceptible strains upregulate the expression of a repertoire of putative drug efflux pumps during their growth under biologically relevant conditions, e.g., in human serum, resulting in efflux-associated resistance to physiologically achievable antibiotic levels within a patient. This phenomenon, termed Adaptive Efflux Mediated Resistance (AEMR), has been hypothesized to account for one mechanism by which antibiotic-susceptible A. baumannii fails to respond to antibiotic treatment. In the current study, we sought to identify genetic determinants that contribute to A. baumannii serum-associated AEMR by screening a transposon mutant library for members that display a loss of the AEMR phenotype. Results revealed that mutation of a putative pirin-like protein, YhaK, results in a loss of AEMR, a phenotype that could be complemented by a wild-type copy of the yhaK gene and was verified in a second strain background. Ethidium bromide efflux assays confirmed that the loss of AEMR phenotype due to pirin-like protein mutation correlated with reduced overarching efflux capacity. Further, flow cytometry and confocal microscopy measures of a fluorophore 7-(dimethylamino)-coumarin-4-acetic acid (DMACA)-tagged levofloxacin isomer, ofloxacin, further verified that YhaK mutation reduces AEMR-mediated antibiotic efflux. RNA-sequencing studies revealed that YhaK may be required for the expression of multiple efflux-associated systems, including MATE and ABC families of efflux pumps. Collectively, the data indicate that the A. baumannii YhaK pirin-like protein plays a role in modulating the organism's adaptive efflux-mediated resistance phenotype.

Tigecycline-Containing Regimens and Multi Drug-Resistant Acinetobacter baumannii: A Systematic Review and Meta-Analysis

Introduction: The use of tigecycline (TG) for the treatment of Acinetobacter baumannii is controversial. In this systematic review and meta-analysis, we aimed to better explore the safety and efficacy of TG for the treatment of multi drug-resistant (MDR) Acinetobacter. Methods: We searched PubMed/MEDLINE, Scopus, Cochrane Central, and Web of Science to identify studies reporting the clinical and microbiological efficacy and safety of regimens containing TG in patients with drug susceptibility testing (DST)-confirmed MDR A. baumannii, published until December 30, 2022. Observational studies were included if they reported clinical and microbiological efficacy of TG-based regimens. The Newcastle-Ottawa Scale (NOS) and Joana Briggs Institute (JBI) critical appraisal tool were used to assess the quality of included studies. Results: There were 30 observational studies, of which 19 studies were cohort and 11 studies were single group studies. Pooled clinical response and failure rates in the TG-containing regimens group were 58.1 (95% confidence interval [CI] 49.2-66.6) and 40.2 (95% CI 31.1-50.0), respectively. The pooled microbiological response rate was 32.1 (95% CI 19.8-47.5), and the pooled all-cause mortality rate was 41.1 (95% CI 34.1-48.4). Pooled clinical response and failure rates in the colistin-based regimens group were 52.7 (42.7-62.5) and 43.1 (33.1-53.8), respectively. The pooled microbiological response rate was 42.9 (16.2-74.5), and the pooled all-cause mortality rate was 34.3 (26.1-43.5). Conclusions: According to our results, the efficacy of the TG-based regimen is the same as other antibiotics. However, our study showed a high mortality rate and a lower rate of microbiological eradication for TG compared with colistin-based regimen. Therefore, our study does not recommend it for the treatment of MDR A. baumannii. However, this was a prevalence meta-analysis of observational studies, and for better conclusion experimental studies are required.

Bacterial Genome Wide Association Studies (bGWAS) and Transcriptomics Identifies Cryptic Antimicrobial Resistance Mechanisms in Acinetobacter baumannii

Antimicrobial resistance (AMR) in the nosocomial pathogen, Acinetobacter baumannii, is becoming a serious public health threat. While some mechanisms of AMR have been reported, understanding novel mechanisms of resistance is critical for identifying emerging resistance. One of the first steps in identifying novel AMR mechanisms is performing genotype/phenotype association studies; however, performing these studies is complicated by the plastic nature of the A. baumannii pan-genome. In this study, we compared the antibiograms of 12 antimicrobials associated with multiple drug families for 84 A. baumannii isolates, many isolated in Arizona, USA. in silico screening of these genomes for known AMR mechanisms failed to identify clear correlations for most drugs. We then performed a bacterial genome wide association study (bGWAS) looking for associations between all possible 21-mers; this approach generally failed to identify mechanisms that explained the resistance phenotype. In order to decrease the genomic noise associated with population stratification, we compared four phylogenetically-related pairs of isolates with differing susceptibility profiles. RNA-Sequencing (RNA-Seq) was performed on paired isolates and differentially-expressed genes were identified. In these isolate pairs, five different potential mechanisms were identified, highlighting the difficulty of broad AMR surveillance in this species. To verify and validate differential expression, amplicon sequencing was performed. These results suggest that a diagnostic platform based on gene expression rather than genomics alone may be beneficial in certain surveillance efforts. The implementation of such advanced diagnostics coupled with increased AMR surveillance will potentially improve A. baumannii infection treatment and patient outcomes.

Pharmacokinetic and Pharmacodynamic Considerations of Antibiotics of Last Resort in Treating Gram-Negative Infections in Adult Critically Ill Patients

PURPOSE OF REVIEW

We provide an overview of antimicrobials that are considered last resort for the treatment of resistant gram-negative infections in adult critically ill patients. The role in therapy, pharmacodynamic (PD) goals, and pharmacokinetic (PK) changes in critical illness for aminoglycosides, polymyxins, tigecycline, fosfomycin, and fluoroquinolones are summarized.

RECENT FINDINGS

Altered PK in septic patients in the intensive care unit (ICU) is observed with many of our agents of last resort. Based on the available literature, dosage adjustments may be required to optimize PK parameters and meet PD targets for most effective bacterial killing. Data is limited, studies are conducted in heterogeneous patient populations, and conclusions are frequently conflicting. Strategic dosing regimens such as high-dose extended interval dosing of aminoglycosides or loading doses with colistin and polymyxin B are examples of ways to optimize antibiotic PK in critically ill patients. Benefits of these strategies must be balanced with risks of increased toxicity. Patients with resistant gram-negative infections may present with septic shock in the ICU. Sepsis can significantly alter the PK of antibiotics and require dosage adjustments to attain optimal drug levels. An understanding of PK and PD properties of these agents of last resort will help to maximize therapeutic efficacy while minimizing toxic effects.

In vitro assessment of cefoperazone-sulbactam based combination therapy for multidrug-resistant Acinetobacter baumannii isolates in China

Background

Multidrug-resistant Acinetobacter baumannii (MDRAB) has emerged as an important pathogen of nosocomial infections. Even though cefoperazone-sulbactam is frequently used to treat MDRAB infections, this single-drug therapeutic approach often results in antibiotic resistance. Thus, combination therapy is preferred over single-drug therapy, particularly in the case of carbapenemase-producing gram negative bacteria. The aim of this study was to investigate the efficacy of cefoperazone-sulbactam combined with either tigecycline or rifampicin against clinical isolates of MDRAB.

Methods

One hundred and three MDRAB bacteria were isolated from patients in two hospitals in China. The Epsilomer test (E test) was used to determine the minimum inhibitory concentration (MIC) values for amikacin, ceftazidime, cefepime, levofloxacin, rifampicin, cefoperazone-sulbactam, meropenem, tigecycline, and gentamicin against MDRAB isolates. In vitro effects of various antibiotic combinations were measured and the fractional inhibitory concentration index (FICI) was calculated for each drug combination.

Results

Approximately 17.5% of the isolates were resistant to tigecycline, whereas more than 84.2% isolates were resistant to other antimicrobial agents tested in this study. Cefoperazone-sulbactam revealed remarkable synergistic effects when used in combination with either tigecycline or rifampicin. However, for the isolates with MICs lower than blood peak concentration after combination therapy, the ratio was lower in highly resistant isolates compared to the least resistant bacteria.

Conclusions

In vitro cefoperazone-sulbactam in combination with tigecycline or rifampicin showed the highest synergistic or additive activity against MDRAB isolates. However, acquisition of highly antibiotic resistant bacteria may lessen the effectiveness of combination therapy.

New Insight on Epidemiology and Management of Bacterial Bloodstream Infection in Patients with Hematological Malignancies

Bloodstream infections (BSI) are a significant cause of morbidity and mortality in onco-hematologic patients. The Gram-negative bacteria were the main responsible for the febrile neutropenia in the sixties; their impact declined due to the use of fluoroquinolone prophylaxis. This situation was followed by the gradual emergence of Gram-positive bacteria also following the increased use of intravascular devices and the introduction of new chemotherapeutic strategies. In the last decade, the Gram-negative etiology is raising again because of the emergence of resistant strains that make questionable the usefulness of current strategies for prophylaxis and empirical treatment. Gram-negative BSI attributable mortality is relevant, and the appropriate empirical treatment significantly improves the prognosis; on the other hand the adequate delayed treatment of Gram-positive BSI does not seem to have a high impact on survival. The clinician has to be aware of the epidemiology of his institution and colonizations of his patients to choose the most appropriate empiric therapy. In a setting of high endemicity of multidrug-resistant infections also the choice of targeted therapy can be a challenge, often requiring strategies based on off-label prescriptions and low grade evidence.

In this review, we summarize the current evidence for the best targeted therapies for difficult to treat bacteria BSIs and future perspectives in this topic. We also provide a flow chart for a rational approach to the empirical treatment of febrile neutropenia in a multidrug resistant, high prevalence setting.

Surveillance and management of multidrug-resistant microorganisms

Multidrug-resistant organisms are an established and growing worldwide public health problem and few therapeutic options remain available. The traditional antimicrobials (glycopeptides) for multidrug-resistant Gram-positive infections are declining in efficacy. New drugs that are presently available are linezolid, daptomicin and tigecycline, which have well-defined indications for severe infections, and talavancin, which is under Phase III trial for hospital-acquired pneumonia. Unfortunately the therapies available for multidrug-resistant Gram-negatives, including carbapenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii and Enterobacteriaceae, are limited to only colistin and tigecycline. Both of these drugs are still not registered for severe infections, such as hospital acquired pneumonia. Consequently, as confirmed by scientific evidence, a multidisciplinary approach is needed. Surveillance, infection control procedures, isolation and antimicrobial stewardship should be implemented to reduce multidrug-resistant organism diffusion.

Clinical and microbiological efficacy of tigecycline for complicated skin-soft-tissue and intra-abdominal infections in a Turkish university hospital

OBJECTIVE

Tigecycline, a new glycylcycline antimicrobial agent, is indicated for the treatment of complicated skin structure infection (cSSTI), intra-abdominal infection (cIAI) and community acquired pneumonia. We aimed to evaluate the clinical and microbiological data together about tigecycline therapy.

METHODS

Patients with cIAIs and cSSTIs were included in a prospective, observational follow-up. Patient follow-up forms were developed and clinical and microbiological data were recorded.

RESULTS

Of the 107 patients, 67 had cSSTIs, 40 had cIAIs. Tigecycline was used empirically in 37.5% of cIAIs and in 50.7% of cSSTIs. In 85.0% of the patients with cIAI and in 73.1% of the patients with cSSTI, clinical and/or microbiological response could be achieved. A drug change was made in 26.9% and 7.5% of the patients with cSSTI and cIAI respectively. Superinfection was detected in 14.9% of the cSSTI and 7.5% of the cIAI patients.

CONCLUSION

As a result, tigecycline can be safely used in the treatment of different infections. Compared with cSSTIs, the treatment response is better and the duration of treatment is shorter in cIAIs. However, MIC value must be determined at any rate if tigecycline is to be used in the treatment of Acinetobacter (MDR Acinetobacter, in particular) infections. Clinical cure and microbiological eradication rate of tigecycline therapy changes according to different clinical diagnosis and microorganism.

Factors influencing the early mortality in haematological malignancy patients with nosocomial Gram negative bacilli bacteraemia: a retrospective analysis of 154 cases

Background

The aim of this study is to assess the factors influencing the early mortality (7-day after index blood culture) in haematological malignancy patients with Gram negative bacilli (GNB) bacteraemia.

Methods

Infection control committee records were reviewed to identify the cases between March 2006 and June 2011. Only one bacteraemic episode per patient was included in the study.

Results

A total of 154 patients with GNB bacteraemia were identified. The early mortality rate was 19.5% (30 out of 154). Blood cultures revealed Enterobacteriacea in 120 patients (Escherichia coli; 86, Klebsiella spp.; 28, Enterobacter cloacea; 6) and glucose non-fermenting GNB in 34 patients (Pseudomonas aeruginosa; 15, Acinetobacter baumannii; 11, Stenotrophomonas maltophilia; 7, Burkholderia cepacia; 1). Forty (33.3%) out of 120 Enterobacteriaceae were extended spectrum beta-lactamase (ESBL) producers and 18 (52.9%) out of 34 glucose non-fermenting GNB were multidrug resistant. Carbapenems were administered as first line therapy in 139 out of 154 patients. In univariate analysis Pitt's bacteraemia score, presence of aplastic anaemia, bacteraemia caused by glucose non-fermentating GNB, inappropriate empirical antibacterial treatment, presence of severe sepsis or septic shock, unable to achieve microbiological cure, and intensive care unit (ICU) acquired bacteraemia were associated with mortality. Multivariate analysis showed ICU acquired bacteraemia (OR, 12.55; 95% CI, 2.34–67.38, p = 0.003) as an independent factor associated with early mortality.

Conclusion

Haematological malignancy patients who require ICU care are at high risk for early mortality related to GNB bacteraemia. Based on the local findings pointing out high rate of multidrug resistance, carbapenems combined with colistin seems to be a reasonable approach as empirical treatment of these patients. However, increasing carbapenem resistance rate is of concern.

Intravitreal tigecycline treatment in experimental Acinetobacter baumannii endophthalmitis

PURPOSE

To investigate the clinical and microbiological effectivity of intravitreal tigecycline in an experimental rabbit endophthalmitis model caused by imipenem resistant Acinetobacter baumannii.

MATERIALS AND METHODS

Forty-eight eyes of 24 New Zealand white albino rabbits were divided into six groups (n=8 in each). The right eyes were divided into three groups and defined as infected group; left eyes were divided into three groups and defined as uninfected group. Infected group received 0.1 ml intravitreal A. baumannii suspension. Twenty-four hours after bacterial inoculation, group 1 received 1 mg/0.1 ml tigecycline and group 2 received 0.5 mg/0.1 ml tigecycline. Group 3 eyes received no treatment. In group 4, 0.1 ml of saline solution was injected. Groups 5 and 6 were received intravitreal tigecycline injection of 1 mg/0.1 ml and 0.5 mg/0.1 ml respectively. The eyes were enucleated for histopathological evaluation on the sixth day. Clinical and histological scoring systems were used to evaluate clinical and histological severity of the intraocular infection.

RESULTS

The mean clinical scores of the six groups at the sixth day were 11±1.92, 12.4±6.2, 8.5±2.7, 0, 3±1.3, and 3±1.4 respectively. Mean histopathological scores were 7.8±2.8, 7.0±1.5, 5.6±1.4, 0, 0, and 0 respectively. There was no significant difference in mean clinical and histopathological scores of infected group (groups 1, 2 and 3). There was significant difference in mean clinical scores of groups 5 and 6 compared with group 4. Groups 4, 5 and 6 showed normal histological structure in histopathological evaluation and showed no significant difference. Microbiological cure was achieved in all infected eyes.

CONCLUSIONS

Experimental rabbit endophthalmitis model caused by imipenem resistant A. baumannii was microbiologically cured by intravitreal tigecycline injection. However, a hypersensitivity-like reaction due to intravitreal application of tigecycline limits the use of this antimicrobial agent in A. baumannii endophthalmitis.

Impact of inappropriate empiric antimicrobial therapy on mortality of septic patients with bacteremia: a retrospective study

Background. Inappropriate empiric antimicrobials could be a major cause of unfavorable mortality rates in co-morbid patients. This study aimed to assess the prevalence and impact of first-dose and 24-hour inappropriate antimicrobials on mortality rates of bacteremic septic patients. Methods. A retrospective cohort study was employed. Case record forms of patients diagnosed as sepsis, severe sepsis, or septic shock with positive hemoculture during 2009 were retrieved from the medical wards, Siriraj Hospital. Demographic data, antimicrobial use, types of bacteria isolated from blood and susceptibilities, patients' comorbidities, 28-day and overall mortality rates were collected and analyzed. Results. There were 229 cases, mean age (SD) of 63.5 (17.2) years and mean (SD) APACHE II score of 24.7 (6.8). The prevalence of first-dose and 24-hour inappropriate antimicrobials was 29.7% and 25.3%, respectively. The 28-day and overall mortality rates between first-dose inappropriate and appropriate antimicrobial were 67.6% versus 60.2% (P = 0.301) and 75.0% versus 68.3% (P = 0.345), consequently. Patients with septic shock and inappropriate first-dose antimicrobials significantly had higher 28-day mortality rate (61.6% versus 41.9%; P = 0.017). Conclusion. Higher mortality rates in bacteremic septic patients were substantially associated with inappropriate first-dose antimicrobials and 3-hour delayed antimicrobial administration after sepsis diagnosis.

Global spread of drug-resistant Acinetobacter baumannii: molecular epidemiology and management of antimicrobial resistance

Acinetobacter baumannii is an opportunistic Gram-negative pathogen with increasing relevance in a variety of hospital-acquired infections especially among intensive care unit patients. Resistance to antimicrobial agents is the main reason for A. baumannii spread. A. baumannii outbreaks described worldwide are caused by a limited number of genotypic clusters of multidrug-resistant strains that successfully spread among hospitals of different cities and countries. In this article, we will focus on the mechanisms responsible for resistance to antimicrobials and disinfectants in A. baumannii and the epidemiology of drug-resistant A. baumannii in healthcare facilities. We will also discuss the therapeutic and infection control strategies for management of drug-resistant A. baumannii epidemics.

Outcomes in patients infected with carbapenem-resistant Acinetobacter baumannii and treated with tigecycline alone or in combination therapy

PURPOSE

Acinetobacter baumannii is a non-fermenting aerobic gram-negative bacteria and one of the important nosocomial pathogens, especially in intensive care units (ICUs). In recent years, multidrug-resistant (MDR) isolates have been an emerging problem, with limited therapeutic options. Tigecycline is a novel antimicrobial, with its in vitro activity against most gram-positive and gram-negative pathogens.

METHODS

This is a retrospective study that was conducted in a tertiary care hospital with 550 beds in Ankara, Turkey, from January 2009 to July 2010. Thirty-three patients who had carbapenem-resistant Acinetobacter spp. infections and received tigecycline alone or in combination with other antibiotics for at least 3 days were included.

RESULTS

The median age of the patients was 62 (18-87) years. All of the patients were diagnosed and treated in the ICU. Clinical responses were observed in 23 patients (69.7%). Ten patients (30%) had clinical failure. There was no significant difference between ventilator-associated pneumonia (VAP) and bloodstream infection (BSI) in terms of clinical or microbiological outcome (p > 0.05). The microbiological response rate was 50%. Superinfection was detected in 13 patients (43.3%) and Pseudomonas aeruginosa was the most frequently isolated pathogen. The 30-day overall mortality rate and attributable mortality rates were 57.6 and 24.2%, respectively. The attributable mortality rate was higher in the group in which microbiological eradication was not provided.

CONCLUSIONS

Although it is approved by the Food and Drug Administration (FDA) for the treatment of complicated intra-abdominal infections, complicated skin and soft tissue infections, and community-acquired bacterial pneumonia, emerged resistance of Acinetobacter spp. and limited therapeutic options left physicians no choice but to use tigecycline for off-label indications.

Pathogens resistant to antibacterial agents

Resistance to antimicrobial drugs is increasing at an alarming rate among both gram-positive and gram-negative bacteria. Traditionally, bacteria resistant to multiple antimicrobial agents have been restricted to the nosocomial environment. A disturbing trend has been the recent emergence and spread of resistant pathogens in nursing homes, in the community, and in the hospital. This article reviews the epidemiology, molecular mechanisms of resistance, and treatment options for pathogens resistant to antimicrobial drugs.

Comprehensive assessment of tigecycline activity tested against a worldwide collection of Acinetobacter spp. (2005-2009)

A total of 5127 Acinetobacter spp. were collected from 140 hospitals in 32 countries in North America (17.1%), Europe (22.9%), Latin America (25.2%), and the Asia-Pacific (APAC) region (34.8%). Tigecycline MIC distributions were bimodal against isolates from North America and APAC region, while a unimodal pattern was noted for strains from Latin America. A variable MIC distribution was noted in Europe. Only tigecycline (MIC(50/90), 0.5/2 μg/mL) and polymyxin B (MIC(50/90), 0.5/1 μg/mL; 98.6% susceptible) exhibited high activity against Acinetobacter spp. Overall, tigecycline inhibited at least 90.0% of Acinetobacter spp. isolates from all countries evaluated at ≤2 μg/mL, as well as 95.0% of those displaying multidrug resistance. Other tested agents showed limited activity and a significant (P < 0.001) trend toward decreased susceptibility during the study period.