Molecular epidemiology of a clonal outbreak of multidrug-resistant Acinetobacter baumannii in a university hospital in Italy

Authors: Zarrilli, R.; Casillo, R.¹; Di Popolo, A.²; Tripodi, M.-F.³; Bagattini, M.²; Cuccurullo, S.⁴; Crivaro, V.²; Ragone, E.¹; Mattei, A.⁵; Galdieri, N.⁶; Triassi, M.²; Utili, R.¹

Source: Clinical Microbiology & Infection, Volume 13, Number 5, May 2007 , pp. 481-489(9)

Publisher: Wiley-Blackwell

Abstract:

This study investigated the molecular epidemiology of a clonal outbreak of multidrug-resistant Acinetobacter baumannii that occurred between June 2003 and June 2004 in a tertiary-care hospital in Naples, Italy. A. baumannii was isolated from 74 patients, of whom 38 were infected and 36 were colonised. Thirty-three patients had ventilator-associated pneumonia, three had hospital-acquired pneumonia, and two had sepsis. Genotypic analysis of 45 available A. baumannii isolates revealed two distinct pulsed-field gel electrophoresis (PFGE) patterns. Of these, PFGE pattern 1 was represented by isolates from 44 patients and was identical to that of an epidemic A. baumannii clone isolated in another hospital of Naples during 2002. All A. baumannii isolates of PFGE type 1 showed identical multiresistant antibiotypes, characterised by resistance to all antimicrobial agents tested, including carbapenems, with the exception of colistin. In these isolates, inhibition of OXA enzymes by 200 mM NaCl reduced the imipenem MIC by up to four-fold. Molecular analysis of antimicrobial resistance genes showed that all A. baumannii isolates of PFGE type 1 harboured a class 1 integron containing the aacA4, orfX and bla_OXA-20 gene cassettes, an ampC gene and a bla_OXA-51-like allele. Moreover, a bla_OXA-58-like gene surrounded by the regulatory elements ISAba2 and ISAba3 was identified in a 30-kb plasmid from A. baumannii isolates of PFGE type 1, but not PFGE type 2. Thus, selection of a single A. baumannii clone producing an OXA-58-type carbapenem-hydrolysing oxacillinase was responsible for the increase in the number of A. baumannii infections that occurred in this hospital.

Keywords: Acinetobacter baumannii; carbapenem resistance; molecular epidemiology; nosocomial infection; outbreak; OXA-58

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1469-0691.2006.01675.x

Affiliations: 1: Department of Cardiorespiratory Sciences, Division of Infectious and Transplant Medicine 2: Department of Preventive Medical Sciences, Hygiene Section, University of Naples `Federico II' 3: Department of Medicine, Division of Internal Medicine and Hepatology, Second University of Naples 4: Division of Microbiology and Virology 5: Division of Intensive Care 6: Division of Anaesthesiology, Hospital V. Monaldi, Naples, Italy

Publication date: 2007-05-01

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• By this author: Zarrilli, R. ;  Casillo, R. ;  Di Popolo, A. ;  Tripodi, M.-F. ;  Bagattini, M. ;  Cuccurullo, S. ;  Crivaro, V. ;  Ragone, E. ;  Mattei, A. ;  Galdieri, N. ;  Triassi, M. ;  Utili, R.

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