# Biofilm Formation in Clinical Acinetobacter baumannii Is Influenced by Isolate Source and Is Inversely Correlated With Antibiotic Resistance

## TL;DR

This study shows that Acinetobacter baumannii isolates from ICUs and those less resistant to antibiotics tend to form stronger biofilms, which could affect treatment decisions.

## Contribution

The study reveals a novel inverse correlation between antibiotic resistance and biofilm formation in clinical A. baumannii isolates.

## Key findings

- ICU isolates showed higher biofilm formation and greater antibiotic resistance compared to non-ICU isolates.
- Susceptible isolates had a significantly higher tendency to form strong biofilms.
- Biofilm formation varied by hospital and specimen type, with blood and cerebrospinal fluid isolates showing stronger biofilm formation.

## Abstract

Acinetobacter baumannii is a troublesome bacterium that is highly prevalent in hospital settings, particularly in intensive care units (ICUs). Biofilm is one of the main virulence factors that makes A. baumannii a successful pathogen, enabling it to survive the harshest environments. This study aimed to corrolate the biofilm‐forming capacity of clinical A. baumannii isolates with their antibiotic resistance phenotypes and isolation sources. A total of 327 clinical isolates originated from different hospitals, were recovered from diverse clinical specimens collected from patients admitted to the ICU and non‐ICU wards. The isolates were characterized for their resistance phenotypes and biofilm formation capacities. Most A. baumannii isolates showed high resistance patterns against all examined antibiotics. Based on the resistance profiles, 81.2% and 12.3% of isolates were classified into extensively resistant (XDR) and multidrug‐resistant (MDR), respectively. Moreover, the number of the ICU isolates exhibiting the XDR phenotype (86.7%) was higher than non‐ICU XDR isolates (76.4%). The biofilm‐forming capacity varied among the isolates, with most of the isolates forming either strong (44.3%) or weak biofilms (25.7%). Additionally, the fraction of ICU isolates with a strong capacity to form biofilms (60.7%, 91/150) was higher compared with the non‐ICU isolates (30.5%, 54/177). We found a significantly higher tendency to form biofilms in isolates that are susceptible to 10 out of the 17 antibiotics (p = 0.014–0.002), including three carbapenems. In addition, a significant difference in the ability to form biofilms was revealed between the isolates originating from different hospitals and clinical specimens. Notably, a higher tendency to form biofilms was associated with susceptible strains isolated from blood (p = 0.024–0.04) and cerebrospinal fluid (p = 0.001–0.009). Our findings indicate that investigating the biofilm formation capacity of clinical A. baumannii strains could help identify patients requiring short or extended therapeutic treatments.