Environmental Shewanella xiamenensis Strains That Carry bla_OXA-48 or bla_OXA-204 Genes: Additional Proof for bla_OXA-48-Like Gene Origin

LETTER

The chromosome-encoded beta-lactamases of Shewanella spp. have been recognized as progenitors of bla_OXA-48-like genes (1). The analysis of available genome sequences of Shewanella spp. showed the presence of bla_OXA-48-like genes in their chromosome with at least 80% identity to bla_OXA-48 (2). Although initially considered geographically restricted, it has now been demonstrated that the spread of the bla_OXA-48 gene is one of the greatest concerns in terms of antibiotic resistance (3). In fact, since its first description less than a decade ago (4), bla_OXA-48-like genes have been reported worldwide (1, 3). Several variants of bla_OXA-48 genes have been identified in Enterobacteriaceae strains, mostly isolated from clinical settings. So far, bla_OXA-181 (5) and bla_OXA-48b and bla_OXA-199 (2) have been reported in Shewanella xiamenensis strains.

The OXA-204 enzyme was recently described in Klebsiella pneumoniae clinical isolates in Tunisia. Its substrate profile is similar to that of OXA-48, from which differs by only two amino acids (6). The origin of bla_OXA-204 was not identified before. Here we report the isolation from river water in Portugal of three S. xiameniensis strains, one of which carried the bla_OXA-204 gene. Strains IR24, IR33, and IR34 were isolated from rivers (7) in MacConkey agar plates supplemented with 8 μg/ml of imipenem and identified by 16S rRNA gene sequencing as S. xiamenensis. Sequencing of the bla_OXA-48-like genes amplified by PCR using previously described primers (2) revealed that these strains carried either a bla_OXA-48b gene (IR24 and IR33) or a bla_OXA-204 gene (IR34). Antimicrobial susceptibility and MICs were determined in Mueller-Hinton agar plates at 37°C and interpreted according to the CLSI guidelines (8). Results are shown in Table 1. All three isolates were resistant to penicillins and carbapenems but susceptible to expanded-spectrum cephalosporins and fluoroquinolones. MICs of ertapenem, imipenem, and meropenem for the OXA-204-producing strain were at least 4 times higher than those determined for the OXA-48-producing strains. Moreover, MICs for carbapenems were also higher than those previously described for K. pneumoniae carrying bla_OXA-204 (6).

Table 1.

Resistance phenotype and MICs of carbapenems for S. xiamenensis strains^a

Strain::blaOXA-48-like gene	Resistance phenotype	MIC in μg/ml (resistance status)
		ERT	IPM	MER
S. xiamenensis IR24::blaOXA-48-like	AML, AMC, IPM, ERT, ATM	8 (R)	4 (R)	2 (I)
S. xiamenensis IR33::blaOXA-48	AML, AMC, CTX, IPM, ERT, ATM	8 (R)	4 (R)	1 (S)
S. xiamenensis IR34::blaOXA-204	AML, AMC, IPM, ERT, NAL	>32 (R)	>32 (R)	8 (R)

^aAML, amoxicillin; AMC, amoxicillin plus clavulanic acid; ATM, aztreonam; CTX, cefotaxime; ERT, ertapenem; IPM, imipenem; MER, meropenem; NAL, nalidixic acid; I, intermediate; S, susceptible; R, resistant.

To investigate the genetic context, primers were designed targeting regions commonly described as flanking bla_OXA-48-like genes in Shewanella spp. (2): upstream, a gene encoding peptidase C15 (C15_fwd [5′-TTACGGCCTGGGAAGTGTTC-3′]), and downstream, the lysR gene (lysR_rev [5′-AAGGGATTCTCCCAAGCTGC-3′]), which codes for a putative LysR transcriptional regulator. Sequencing of the amplified region revealed identical contexts for both bla_OXA-204 and the bla_OXA-48 genes, presenting upstream the C15 gene and downstream the lysR gene. This constitutes the first report on S. xiamenensis strains carrying a bla_OXA-204 gene, suggesting that the emergence of different bla_OXA-48-like genes probably had its origin in different S. xiamenensis strains. It also suggests the participation of diverse mobilization events and mechanisms in the transfer of bla_OXA-48-like genes from Shewanella spp. to Enterobacteriaceae. Whereas ISEcp1 has been identified preceding the bla_OXA-204 and bla_OXA-181 gene, IS1999 has been found upstream of bla_OXA-48 genes (1). Moreover, it is of great relevance to acknowledge that these genetic events may have occurred in natural environments, reinforcing the idea of the importance of aquatic systems in the evolution and spread of antibiotic resistance.

Nucleotide sequence accession numbers.

The nucleotide sequence data determined in this work have been deposited in GenBank under accession numbers KC902850, KC902851, and KC902852.