International Journal of Antimicrobial Agents 13 (2000) 175 – 182 Original article Outer-membrane proteins pattern and detection of -lactamases in clinical isolates of imipenem-resistant Acinetobacter baumannii from Brazil S.F. Costa a, *, J. Woodcock b , M. Gill b , R. Wise b , A.A. Barone a , H. Caiaffa a , A.S.S. Levin a a Hospital das Clı ´nicas da Faculdade de Medicina da Uniersidade de Sa ˜o Paulo, Brazil b Department of Microbiology, City Hospital, Birmingham, UK Received 25 February 1999; accepted 29 July 1999 Abstract In order to compare imipenem-sensitive and -resistant Acinetobacter baumannii strains isolated from three patients, ribotyping, plasmid, -lactamase detection and outer-membrane analysis were performed. Ribotyping and the use of a -lactam during the period when the strains were isolated suggested that they had a common origin and that resistance occurred in vivo. Outer membrane analysis showed no difference between susceptible and resistant strains with the exception of an A2 imipenem-resistant strain that lost a protein band of 31 – 36 kDa. Beta-lactamases were detected using isoelectric focusing in all strains (p I of 7.4). In addition, two -lactamases (p I of 5.9 and 6.7) were found in imipenem-resistant isolates. The double-disc technique demonstrated the presence of a -lactamase capable of imipenem inactivation in resistant strains. Plasmid analysis showed that all susceptible strains had the same pattern, one resistant strain did not have any plasmid, one had the same plasmid pattern of its susceptible pair and only one had a different pattern when compared with its susceptible pair. © 2000 Elseveir Science B.V. and International Society of Chemotherapy. All rights reserved. Keywords: Acinetobacter baumannii ; Resistance; Imipenem www.elsevier.com/locate/isc 1. Introduction In recent years nosocomial infections caused by Acinetobacter spp. have increased [1–3]. The genus Acinetobacter includes at least 19 DNA-DNA hy- bridization groups (genomic species); but four groups: group 1 (A. calcoaceticus ), group 2 (A. baumannii ), group 3 and group 13 cannot be reliably separated phenotypically so they are collectively referred to as the ‘A. baumannii – A. calcoaceticus complex’ [4,5]. This nosocomial pathogen is known to exhibit resis- tance to a large number of antibiotics including many -lactams [6 – 8] and carbapenem-resistant Acinetobacter baumannii is an emerging worldwide problem. Several case reports and outbreaks due imipenem resistant A. baumannii have been published recently [9 – 14]. Resistance to imipenem may be mediated by one of four mechanisms: alteration of outer-membrane proteins [15 – 17], specific drug efflux pumps [18,19], penicillin-binding protein (PBP) alterations [20] and enzymatic inactivation by -lactamase [21,22]. The small number and size of porins could explain the decrease of A. baumannii outer-membrane perme- ability (less than 5%) when compared with other Gram- negatives [15]. In fact, -lactam resistance of Acinetobacter has been associated with a decrease of band intensity of the two outer membrane proteins previously recognized as porins and designated protein I (44.5 kDa) and protein II (46.5 kDa) [16]. Resistance to imipenem in A. baumannii has also been associated * Corresponding author. Present address: 6424, Central City Blvd 432, Galveston, TX, 77551, USA. Fax: +1-409-7722337. E-mail address: josem.vieira@prodigy.net (S.F. Costa) 0924-8579/00/$ - see front matter © 2000 Elsevier Science B.V. and International Society of Chemotherapy. All rights reserved. PII:S0924-8579(99)00123-5