No abstract

The present work describes the abrupt emergence of Klebsiella pneumoniae carbapenemase (KPC) and characterizes the first 79 KPC-producing enterobacteria from Argentina (isolated from 2006 to 2010). The emergence of bla(KPC-2) was characterized by two patterns of dispersion: the first was the sporadic occurrence in diverse enterobacteria from distant geographical regions, harbouring plasmids of different incompatibility groups and bla(KPC-2) in an unusual genetic environment flanked by ISKpn8-Δbla(TEM-1) and ISKpn6-like. bla(KPC-2) was associated with IncL/M transferable plasmids; the second was the abrupt clonal spread of K. pneumoniae ST258 harbouring bla(KPC-2) in Tn4401a.

cWe studied a collection of 105 clinical enterobacteria with unusual phenotypes of quinolone susceptibility to analyze the occurrence of plasmid-mediated quinolone resistance (PMQR) and oqx genes and their implications for quinolone susceptibility. The oqxA and oqxB genes were found in 31/34 (91%) Klebsiella pneumoniae and 1/3 Klebsiella oxytoca isolates. However, the oqxAand oqxB-harboring isolates lacking other known quinolone resistance determinants showed wide ranges of susceptibility to nalidixic acid and ciprofloxacin. Sixty of the 105 isolates (57%) harbored at least one PMQR gene [qnrB19, qnrB10, qnrB2, qnrB1, qnrS1, or aac(6=)-Ib-cr)], belong to 8 enterobacterial species, and were disseminated throughout the country, and most of them were categorized as susceptible by the current clinical quinolone susceptibility breakpoints. We developed a disk diffusionbased method to improve the phenotypic detection of aac(6=)-Ib-cr. The most common PMQR genes in our collection [qnrB19, qnrB10, and aac(6=)-Ib-cr] were differentially distributed among enterobacterial species, and two different epidemiological settings were evident. First, the species associated with community-acquired infections (Salmonella spp. and Escherichia coli) mainly harbored qnrB19 (a unique PMQR gene) located in small ColE1-type plasmids that might constitute its natural reservoirs. qnrB19 was not associated with an extended-spectrum ␤-lactamase phenotype. Second, the species associated with hospital-acquired infections (Enterobacter spp., Klebsiella spp., and Serratia marcescens) mainly harbored qnrB10 in ISCR1-containing class 1 integrons that may also have aac(6=)-Ib-cr as a cassette within the variable region. These two PMQR genes were strongly associated with an extended-spectrum ␤-lactamase phenotype. Therefore, this differential distribution of PMQR genes is strongly influenced by their linkage or lack of linkage to integrons.

No abstract

The first allele of a 16S rRNA methyltransferase gene, rmtD2, conferring very high resistance to all clinically available aminoglycosides, was detected in 7/1,064 enterobacteria collected in 2007. rmtD2 was located on a conjugative plasmid in a Tn2670-like element inside a structure similar to that of rmtD1 but probably having an independent assembly. rmtD2 has been found since 1996 to 1998 mainly in Enterobacter and Citrobacter isolates, suggesting a possible reservoir in these genera. This presumption deserves monitoring by continuous surveillance.Posttranscriptional methylation of the 16S rRNA aminoglycoside binding site, common in aminoglycoside-producing microorganisms, has been described in nosocomial isolates highly resistant to all clinically available aminoglycosides. Currently, seven plasmid-mediated 16S rRNA methyltransferase (16S-methylase) genes have been identified: armA, npmA, rmtA, rmtB, rmtC, rmtD (named rmtD1 herein), and very recently, rmtE, from bovine origin (3,4,19). To date, only Klebsiella pneumoniae harboring rmtD1 has been reported in Argentina (7). Herein, a nationwide survey of aminoglycoside resistance mediated by 16S-methylases among enterobacteria in Argentina was performed.(Preliminary data were presented in abstract form at the 109th General Meeting, American Society for Microbiology, 2009, and at the 50th Interscience Conference on Antimicrobial Agents and Chemotherapy, American Society for Microbiology, 2010.) Susceptibility and molecular detection of resistance mechanisms. To determine the prevalence of the 16S-methylases, a collection of 1,064 consecutive, nonduplicate enterobacterial isolates was analyzed. This sample set was collected during a 5-day period in 2007 from 66 hospitals belonging to the WHONET-Argentina Resistance Surveillance Network and submitted to the Servicio Antimicrobianos (the Argentinian National Reference Laboratory). Initial screening of 16S-methylase activity was performed using the disc diffusion susceptibility method for amikacin and gentamicin (inhibition zones of Յ10 mm) (1, 4). Although almost 80% of the collection was made up of Escherichia coli and Klebsiella spp., only 12 isolates belonging to other species (4 Enterobacter cloacae, 1 Enterobacter aerogenes, 3 Serratia species, 2 Citrobacter freundii, 1 Morganella morganii, and 1 Proteus mirabilis isolate) met the screening criteria used. Of these, 5 showed inhibition zones of Ն7 mm to amikacin, and 7 (all of the Enterobacter species and C. freundii isolates) showed an absence of inhibition zones for both aminoglycosides. Only these last 7 isolates gave positive results when tested for 16S-methylase genes by PCR (Table 1), and only the primers against rmtD genes rendered amplicons (Table 2). Complete gene amplification and DNA sequencing showed a unique 16S-methylase gene in these 7 isolates. This gene displayed 97.3% nucleotide identity (20 nucleotides of difference) and 96.4% amino acid identity (9 residues of difference) with rmtD1. Since this is the first description of a 16S-methylase ...