Evidence of diversity among epidemiologically related carbapenemase-producing Acinetobacter baumannii strains belonging to international clonal lineage II.
Carbapenem-resistant Acinetobacter baumannii strains belonging to international clonal lineage II (ICL-II) have become predominant in intensive care units (ICUs) throughout Italy. Between 2005 and 2009, the carbapenem-hydrolyzing class D β-lactamase (CHDL) bla(OXA-23) gene became more prevalent than bla(OXA-58) among epidemic ICL-II strains showing extensive genetic similarity. These findings posed the question of whether CHDL gene replacement occurred in the homogeneous ICL-II population or a new OXA-23 clone(s) emerged and spread in ICUs. In this study, the changes in the ICL-II A. baumannii population and CHDL gene carriage were investigated in 30 genetically related isolates collected during the bla(OXA-58)-to-bla(OXA-23) transition period. Pulsotyping, randomly amplified polymorphic DNA (RAPD) analysis, and multilocus sequence typing (MLST) results were combined with multilocus variable-number tandem-repeat (VNTR) analysis (MLVA-8), siderotyping, and plasmid profiling to improve genotype-based discrimination between isolates. Pulsotyping, RAPD analysis, and MLST clustered isolates into a single type. MLVA-8 identified 19 types that clustered into three complexes. All OXA-23-producing isolates formed a single complex, while OXA-58 producers were split into two complexes. Southern blot analysis of the physical localization and genetic context of the CHDL genes showed that bla(OXA-58) was invariably located on plasmids, while bla(OXA-23) was present within Tn2006 on the chromosome or both the chromosome and plasmids. These data indicate that the apparently homogeneous population of CHDL-producing ICL-II strains was composed of several independent strains and that, between 2005 and 2009, distinct OXA-23 producers displaced the preexisting OXA-58 producers. Thus, MLVA-8 appears to be a suitable tool not only for investigating A. baumannii population structure but also for high-resolution epidemiological typing.
Dipartimento di Biologia, Universita` Roma Tre,a and Istituto Nazionale per le Malattie Infettive Lazzaro Spallanzani IRCCS.
Fabrizia
F
Minandri
Silvia
S
D'Arezzo
Luísa C S
LC
Antunes
Christine
C
Pourcel
Luigi
L
Principe
Nicola
N
Petrosillo
Paolo
P
Visca
D000151:Acinetobacter Infections / Q000453:epidemiology* / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000145:classification* / Q000201:enzymology / Q000235:genetics* / Q000302:isolation & purification; D001426:Bacterial Proteins / Q000235:genetics*; D016000:Cluster Analysis; D016521:Electrophoresis, Gel, Pulsed-Field; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D007558:Italy / Q000453:epidemiology; D018598:Minisatellite Repeats; D058885:Multilocus Sequence Typing; D010957:Plasmids / Q000032:analysis; D019105:Random Amplified Polymorphic DNA Technique; D017262:Siderophores / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics*
D001426:Bacterial Proteins; D017262:Siderophores; D001618:beta-Lactamases; C063912:carbapenemase