Multidrug-Resistant Acinetobacter baumannii Harboring OXA-24 Carbapenemase, Spain

In February 2006, a patient colonized with a multidrug-resistant sequence type 56 Acinetobacter baumannii strain was admitted to a hospital in Madrid, Spain. This strain spread rapidly and caused a large outbreak in the hospital. Clinicians should be alert for this strain because its spread would have serious health consequences.

quinolones, and aminoglycosides (gentamicin, tobramycin, amikacin). Isolates were classifi ed on the basis of antimicrobial susceptibility patterns: antibiotype 1, MDR isolates; antibiotype 2, isolates resistant to carbapenems but not MDR; and antibiotype 3, isolates susceptible to carbapenems. Colonization was defi ned as isolation of A. baumannii from >1 clinical specimen in the absence of clinical symptoms consistent with infection. Bacteremia was determined by application of criteria proposed by the Centers for Disease Control and Prevention (Atlanta, GA, USA) (7).
Clonal relatedness between clinical isolates was determined by using pulsed-fi eld gel electrophoresis (PFGE) and the CHEF DRIII system (Bio-Rad Laboratories, Hercules, CA, USA) according to reported techniques (8). Migration of DNA fragments was normalized, and computer-assisted analysis of PFGE patterns was conducted by using Bionumerics software (Applied Maths, Sint-Martens-Latem, Belgium). Multilocus sequence typing (MLST) was performed according to published protocols (9). Isolates were assigned to a sequence type according to the allelic profi les database (http://pubmlst.org/ abaumannii/). Univariate analysis was performed by using the t test for continuous variables and the χ 2 or Fisher exact tests for categorical variables. Adjusted odds ratios (ORs) were calculated by using logistic regression analysis. Data were analyzed by using SPSS software (SPSS Inc., Chicago, IL, USA). A p value <0.05 was considered signifi cant.
Two genes with a putative role in virulence were detected in plasmids from clones AbH12O-A2 and AbH12O-CU3 upstream of bla OXA-24 : a septicolysin-like gene coding for a pore-forming toxin (12), and a TonB-dependent receptor gene coding for an outer membrane protein involved in iron uptake and virulence (13)(14)(15). Insertion sequence 4, which provided an additional promoter sequence, was detected upstream from the septicolysin gene in plasmid pMMA2;  this sequence was absent in plasmid pMMCU3 ( Figure  2). Two nucleotide changes detected in promoter regions provided an additional promoter region for the TonBdependent receptor gene in plasmid pMMA2.
The septicolysin gene showed 2× overexpression caused by insertion of IS4, which provided an additional promoter. Although the exact role of septicolysin is unknown, it has been designated a cholesterol-dependent cytolysin, which has been reported to be produced by pathogenic bacteria such as Clostridium perfringens, Bacillus anthracis, and Streptococcus pneumoniae to aid invasion of tissues or cells (12).
The protein produced by the TonB-dependent receptor gene has been associated with virulence and iron uptake in A. baumannii (13) and may be involved in survival of bacteria in the lungs and blood. This characteristic may explain the large rate of bacteremia caused by clone AbH12O-A2. Thus, clinicians should be alert for the MDR ST56 A. baumannii clone because its spread would have serious health consequences.