Abstract
The effect of biofilm formation on bacteraemic pneumonia caused by A. baumannii is unknown. We conducted a 4-year multi-center retrospective study to analyze 71 and 202 patients with A. baumannii bacteraemic pneumonia caused by biofilm-forming and non-biofilm-forming isolates, respectively. The clinical features and outcomes of patients were investigated. Biofilm formation was determined by a microtitre plate assay. The antimicrobial susceptibilities of biofilm-associated cells were assessed using the minimum biofilm eradication concentration (MBEC) assay. Whole-genome sequencing was conducted to identify biofilm-associated genes and their promoters. Quantitative reverse transcription polymerase chain reaction was performed to confirm the expression difference of biofilm-associated genes. There was no significant difference in the clinical characteristics or the outcomes between patients infected with biofilm-forming and non-biofilm-forming strains. Compared with non-biofilm-forming isolates, biofilm-forming isolates exhibited lower resistance to most antimicrobials tested, including imipenem, meropenem, ceftazidime, ciprofloxacin and gentamicin; however, the MBEC assay confirmed the increased antibiotic resistance of the biofilm-embedded bacteria. Biofilm-associated genes and their promoters were detected in most isolates, including the non-biofilm-forming strains. Biofilm-forming isolates showed higher levels of expression of the biofilm-associated genes than non-biofilm-forming isolates. The biofilm-forming ability of A. baumannii isolates might not be associated with worse outcomes in patients with bacteraemic pneumonia.
Highlights
Acinetobacter baumannii is an important pathogen that causes nosocomial bloodstream infections and pneumonia, accounting for high morbidity and mortality rates[1,2]
This study aimed to investigate the correlation between the biofilm-forming ability of A. baumannii isolates and clinical outcomes of patients with A. baumannii bacteraemic pneumonia and to evaluate the microbiological features of biofilm-forming A. baumannii isolates
The present study demonstrated no significant differences in the clinical characteristics and 14-day and 28-day mortality between patients with A. baumannii bacteraemic pneumonia caused by biofilm-forming and non-biofilm-forming isolates
Summary
Acinetobacter baumannii is an important pathogen that causes nosocomial bloodstream infections and pneumonia, accounting for high morbidity and mortality rates[1,2]. A. baumannii is notorious for its multiple antimicrobials resistance. This multidrug resistance, along with its ability to form biofilms[3], increases the difficulties in treating infections caused by this microorganism[4]. Its prevalence in nosocomial outbreaks and device-related infections has been attributed to its ability to form biofilms in hospital environments and on medical devices attributes, respectively[4,5]. Whether biofilm-forming ability affects the clinical outcomes of A. baumannii pneumonia is largely unknown. This study aimed to investigate the correlation between the biofilm-forming ability of A. baumannii isolates and clinical outcomes of patients with A. baumannii bacteraemic pneumonia and to evaluate the microbiological features of biofilm-forming A. baumannii isolates
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