Breakthrough bacteraemia with a susceptible Enterococcus faecalis during tigecycline monotherapy

Clinical and microbiological analysis of risk factors for breakthrough bloodstream infection during Tigecycline Therapy

BACKGROUND

Tigecycline is widely used to treat a variety of bacterial infections despite concerns regarding increased mortality in severe infections. Previous case reports have documented breakthrough bloodstream infections (BSI) during tigecycline therapy. This study aimed to investigate the incidence of, and risk factors for, breakthrough BSI during tigecycline monotherapy.

METHODS

A retrospective matched case-control study was conducted in a 2700-bed tertiary referral center, involving patients who received tigecycline monotherapy. Patients with breakthrough BSI (1:1) were matched with controls without breakthrough BSI based on age, sex, and date of tigecycline therapy.

RESULTS

Of 4505 patients treated with tigecycline, 115 (2.6%, 95% confidence interval 2.1 to 3.1%) developed breakthrough BSI. The most frequently identified pathogen in breakthrough BSI was Klebsiella pneumoniae (22.8%), followed by Candida species (17.1%), Pseudomonas aeruginosa (16.3%), and Acinetobacter baumannii (14.6%). Of the K. pneumoniae and A. baumannii isolates for which tigecycline susceptibility results were available, 50% and 23%, respectively, were tigecycline-resistant (MIC > 2 mg/L). Intraabdominal (33.9%), catheter-related (30.4%), and hepatobiliary (19.1%) infections were the main sources of breakthrough BSI. In multivariable analysis, independent risk factors for breakthrough BSI during tigecycline therapy were liver cirrhosis (adjusted odds ratio [aOR], 3.09), indwelling catheter (aOR, 3.42), previous Candida colonization (aOR, 14.95), and previous multi-drug resistant bacteria colonization (aOR, 10.30).

CONCLUSION

In cases where there is a high suspicion of breakthrough BSI during tigecycline therapy, meticulous management and prudent selection of empirical antibiotics are crucial due to the diverse range of causative microorganisms involved.

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.