Chromosome-encoded AmpC and CTX-M extended-spectrum β-lactamases in clinical isolates of Proteus mirabilis from Korea

Among 222 Proteus mirabilis clinical isolates collected from 17 hospitals in Korea in 2008, 28 (12.6%) and 8 (3.6%) isolates exhibited extended-spectrum β-lactamase (ESBL) and AmpC phenotypes, respectively. The most common type of ESBL gene identified by PCR and sequencing experiments was bla _CTX-M-14a (n = 12). The bla_CTX-M-90 (n = 4), bla _CTX-M-15 (n = 3), bla_CTX-M-12 (n = 3), bla _CTX-M-2 (n = 2), bla_CTX-M-14b (n = 1), bla _TEM-52 (n = 5), and bla_SHV-12 (n = 1) genes were also detected. Eight isolates carried an AmpC β-lactamase gene, such as bla _CMY-2 (n = 6) or bla_DHA-1 (n = 2). All bla genes encoding CTX-M-1- and CTX-M-9-type enzymes and all bla_CMY-2 genes were preceded by ISEcp1-like elements. The bla_CTX-M-2 gene found in two isolates was located on a complex class 1 integron. The bla_DHA-1 gene was preceded by a transcriptional regulator gene and was followed by phage shock protein genes. The bla_CTX-M genes were located on the chromosome in 21 isolates. A plasmid location for the bla_CTX-M gene was found in only four isolates: the bla_CTX-M-14a gene was located on ∼150-kbp IncA/C plasmids in three isolates and on a ∼50-kbp IncN plasmid in one isolate. The bla_TEM-52 gene was located on ∼50-kbp IncN plasmids in all five isolates. The AmpC β-lactamase genes were located on the chromosome in seven of eight isolates; one isolate carried the bla_CMY-2 gene on a ∼150-kbp IncA/C plasmid. Our results show that a chromosomal location of CTX-M ESBL and AmpC β-lactamase genes in P. mirabilis is no longer an unusual phenomenon in hospital environments.