Molecular characterization of acinetobacter isolates collected in intensive care units of six hospitals in Florence, Italy, during a 3-year surveillance program: a population structure analysis

Abstract

The strain diversity and the population structure of nosocomial Acinetobacter isolated from patients admitted to different hospitals in Florence, Italy, during a 3-year surveillance program, were investigated by amplified fragment length polymorphism (AFLP). The majority of isolates (84.5%) were identified as A. baumannii, confirming this species as the most common hospital Acinetobacter. Three very distinct A. baumannii clonal groups (A1, A2, and A3) were defined. The A1 isolates appeared to be genetically related to the well-characterized European EU II clone. A2 was responsible for three outbreaks which occurred in two intensive care units. Space/time population dynamic analysis showed that A1 and A2 were successful nosocomial clones. Most of the A. baumannnii isolates were imipenem resistant. The genetic determinants of carbapenem resistance were investigated by multiplex PCR, showing that resistance, independently of hospital origin, period of isolation, or clonal group, was associated with the presence of a bla (OXA-58-like) gene and with ISAba2 and ISAba3 elements flanking this gene. bla (OXA-58) appeared to be horizontally transferred. This study showed that the high discriminatory power of AFLP is useful for identification and typing of nosocomial Acinetobacter isolates. Moreover the use of AFLP in a real-time surveillance program allowed us the recognition of clinically relevant and widespread clones and their monitoring in hospital settings. The correlation between clone diffusion, imipenem resistance, and the presence of the bla(OXA-58-like) gene is discussed.

FIG. 1.

AFLP analysis dendrogram. Thick bar, Acinetobacter sp. isolates; thin bars, A1, A2, and A3 clonal groups of A. baumannii isolates. For IN/C (infection/colonization), black boxes indicate patient infection, gray boxes indicate patient colonization, and white boxes indicate that data are not available. For R/S, black boxes indicate resistance (≥16), gray boxes indicate susceptibility to imipenem, and white boxes indicate that data are not available. For the OXA genes, black boxes indicate the contemporary presence of OXA-51 and OXA-58, gray boxes indicate the presence of OXA51 (gray), and white boxes indicate the absence of both OXA-51 and OXA-58. White dots at the end of the corresponding tree branches represent (from top to bottom) the EU I, EU II, and EU III clones, and black boxes represent the ATCC reference strains of A. baumannii, gen. sp. 13TU, and A. coalcaceticus, gen. sp. 3. Shaded boxes 1, 2, and 3 within the dendrogram define groups of isolates involved in outbreak events (Table 1).

FIG. 2.

Time distribution of A. baumannii clones A1 (gray bars), A2 (black bars), and A3 (striped bar) and isolates with a unique AFLP profile (white bars) in hospital settings.

FIG. 3.

Principal component analysis of the AFLP profiles of A. baumannii isolates: A1 (gray circles), A2 (black circles), and A3 (striped circles) clones and isolates with a unique profile (white circles).