# Phenotypic and Molecular Characterization of Pyomelanin-Producing Acinetobacter baumannii ST2Pas;ST1816/ST195Oxf Causing the First European Nosocomial Outbreak

## TL;DR

This paper reports the first European hospital outbreak caused by Acinetobacter baumannii strains that produce pyomelanin, a pigment linked to increased virulence.

## Contribution

The study documents the first European nosocomial outbreak by pyomelanin-producing A. baumannii and provides its phenotypic and molecular characterization.

## Key findings

- Pyomelanin-producing A. baumannii strains caused an outbreak in a hospital in Pisa, Italy.
- Phenotypic and molecular analyses confirmed the presence of pyomelanin and its potential role in virulence.
- The strains belonged to specific sequence types (ST2Pas; ST1816/ST195Oxf).

## Abstract

Acinetobacter baumannii is one of the most successful and feared nosocomial pathogens. A. baumannii is considered a global threat in the healthcare setting, mainly owing to its ability to acquire multidrug resistance phenotypes. The A. baumannii pathogenesis is guided by its environmental persistence, as well as the production of numerous virulence factors. In several bacteria, the production of pigments, such as melanin, has indeed been linked with virulence and pathogenicity. Melanin is a brownish pigment, rarely observed in A. baumannii, that potentially reduces the susceptibility of the bacteria to host defense mechanisms and environmental insults. This study reports the first outbreak in Europe by pyomelanin-producing A. baumannii strains, in a tertiary-care university hospital in Pisa, Italy. Phenotypic and molecular analyses were performed.