Outbreak of a cluster with epidemic behavior due to Serratia marcescens after colistin administration in a hospital setting.

Serratia marcescens causes health care-associated infections with important morbidity and mortality. Particularly, outbreaks produced by multidrug-resistant isolates of this species, which is already naturally resistant to several antibiotics, including colistin, are usually described with high rates of fatal outcomes throughout the world. Thus, it is important to survey factors associated with increasing frequency and/or emergence of multidrug-resistant S. marcescens nosocomial infections. We report the investigation and control of an outbreak with 40% mortality due to multidrug-resistant S. marcescens infections that happened from November 2007 to April 2008 after treatment with colistin for Acinetobacter baumannii meningitis was started at hospital H1 in 2005. Since that year, the epidemiological pattern of frequently recovered species has changed, with an increase of S. marcescens and Proteus mirabilis infections in 2006 in concordance with a significant decrease of the numbers of P. aeruginosa and A. baumannii isolates. A single pulsed-field gel electrophoresis (PFGE) cluster of S. marcescens isolates was identified during the outbreak. When this cluster was compared with S. marcescens strains (n = 21) from 10 other hospitals (1997 to 2010), it was also identified in both sporadic and outbreak isolates circulating in 4 hospitals in Argentina. In132::ISCR1::blaCTX-M-2 was associated with the multidrug-resistant cluster with epidemic behavior when isolated from outbreaks. Standard infection control interventions interrupted transmission of this cluster even when treatment with colistin continued in several wards of hospital H1 until now. Optimizing use of colistin should be achieved simultaneously with improved infection control to prevent the emergence of species naturally resistant to colistin, such as S. marcescens and P. mirabilis.

Spreading of AbaR-type genomic islands in multidrug resistance Acinetobacter baumannii strains belonging to different clonal complexes.

In order to determine the occurrence of AbaR-type genomic island in multidrug resistant Acinetobacter baumannii (MDRAb) strains circulating in Argentina, Uruguay, and Chile, we studied 51 MDRAb isolates recovered from several hospitals over 30 years. AbaR-type genomic resistance islands were found in 36 MDRAb isolates since 1986 till now. MLST technique allowed us to identify the presence of four different Clonal Complexes (109, 104, 119, 113) among the positive AbaR-type island positive strains. This is the first description of AbaR-type islands in the CC104 and CC113 that are the most widespread Clonal Complexes in Argentina. In addition, PCR mapping exposed different arrays to those previously described, evidencing the plasticity of this island. Our results evidence a widespread distribution of the AbaR-type genomic islands along the time in the MDRAb population, including the epidemic global clone 1 (GC1) as well as different clonal complexes to those already described in the literature.

Distribution of allelic variants of the chromosomal gene bla OXA-114-like in Achromobacter xylosoxidans clinical isolates.

Achromobacter xylosoxidans is increasingly being documented in cystic fibrosis patients. The bla(OXA-114) gene has been recognized as a naturally occurring chromosomal gene, exhibiting different allelic variants. In the population under study, the bla(OXA-114)-like gene was found in 19/19 non-epidemiological-related clinical isolates of A. xylosoxidans with ten different alleles including 1 novel OXA-114 variant.

Acinetobacter baumannii is able to gain and maintain a plasmid harbouring In35 found in Enterobacteriaceae isolates from Argentina.

The aim of this study was to determine the presence of bla (CTX-M-2) in our A. baumannii population and their putative role as an alternative mechanism of resistance to third-generation cephalosporins in this species. The bla (CTX-M-2) gene is widespread among the Enterobacteriaceae isolates from our country; however, it was not found in 76 isolates A. baumannii non-epidemiologically related clinical isolates resistant to third-generation cephalosporins isolated since 1982 in hospitals from Buenos Aires City. A plasmid isolated from Proteus mirabilis that possesses the complex class 1 integron In35::ISCR1::bla (CTX-M-2) was used to transform the natural competent A. baumannii clinical strain A118. PCR, plasmid extraction, DNA restriction, and susceptibility test confirmed that A118 could gain and maintain the plasmid possessing In35::ISCR1::bla (CTX-M-2), the genetic platform where the bla (CTX-M-2) gene is dispersing in Argentina.

Achromobacter xylosoxidans: an emerging pathogen carrying different elements involved in horizontal genetic transfer.

In the last few years, numerous cases of multidrug-resistant Achromobacter xylosoxidans infections have been documented in immunocompromised and cystic fibrosis patients. To gain insights into the molecular mechanisms and mobile elements related to multidrug resistance in this bacterium, we studied 24 non-epidemiological A. xylosoxidans clinical isolates from Argentina. Specific primers for plasmids, transposons, insertion sequences, bla(ampC), intI1, and intI2 genes were used in PCR reactions. The obtained results showed the presence of wide host range IncP plasmids in ten isolates and a high dispersion of class 1 integrons (n = 10) and class 2 integrons (n = 3). Four arrays in the variable region (vr) of class 1 integrons were identified carrying different gene cassettes as the aminoglycoside resistance aac(6')-Ib and aadA1, the trimethoprim resistance dfrA1 and dfrA16, and the ß-lactamase bla(OXA-2). In only one of the class 2 integrons, a vr was amplified that includes sat2-aadA1. The bla(ampC) gene was found in all isolates, confirming its ubiquitous nature. Our results show that A. xylosoxidans clinical isolates contain a rich variety of genetic elements commonly associated with resistance genes and their dissemination. This supports the hypothesis that A. xylosoxidans is becoming a reservoir of horizontal genetic transfer elements commonly involved in spreading antibiotic resistance.

Dissemination of multiple drug resistance genes by class 1 integrons in Klebsiella pneumoniae isolates from four countries: a comparative study.

A comparative genetic analysis of 42 clinical Klebsiella pneumoniae isolates, resistant to two or more antibiotics belonging to the broad-spectrum ß-lactam group, sourced from Sydney, Australia, and three South American countries is presented. The study focuses on the genetic contexts of class 1 integrons, mobilizable genetic elements best known for their role in the rapid evolution of antibiotic resistance among Gram-negative pathogens. It was found that the class 1 integrons in this cohort were located in a number of different genetic contexts with clear regional differences. In Sydney, IS26-associated Tn21-like transposons on IncL/M plasmids contribute greatly to the dispersal of integron-associated multiple-drug-resistant (MDR) loci. In contrast, in the South American countries, Tn1696-like transposons on an IncA/C plasmid(s) appeared to be disseminating a characteristic MDR region. A range of mobile genetic elements is clearly being recruited by clinically important mobile class 1 integrons, and these elements appear to be becoming more common with time. This in turn is driving the evolution of complex and laterally mobile MDR units and may further complicate antibiotic therapy.

bla(OXA-51)-type beta-lactamase genes are ubiquitous and vary within a strain in Acinetobacter baumannii.

We investigated the spread of bla(OXA-51)-type beta-lactamase genes in 200 Acinetobacter spp. clinical strains isolated in Argentina from 1982 to 2005. bla(OXA-51)-type genes were present in all Acinetobacter baumannii isolates tested (n=194), whereas they were not detected in two Acinetobacter haemolyticus, two genomic species 10 or two Acinetobacter lwoffii isolates. The bla(OXA-51)-type alleles varied within a strain and were found in six different A. baumannii pulsed-field gel electrophoresis clones that were susceptible or resistant to imipenem, suggesting a controversial role in imipenem resistance. Our findings agree with previous reports showing that bla(OXA-51)-type genes are naturally harboured by A. baumannii isolates from various geographical origins and support the presence of a direct reservoir of beta-lactam resistance genes within the nosocomial environment.

"Distribution and functional identification of complex class 1 integrons".

The emergence of extended-spectrum ß-lactamases and plasmid-mediated resistance to quinolones has been previously found to be associated with the dissemination of complex class 1 integrons in Argentina. In this study, we analyzed their distribution through time and evaluated the functionality of the Orf513 protein, which is the putative recombinase of the ISCR1 mobile element. We investigated the presence of the orf513, blaCTX-M-2, dfrA3b, qnrB10 and blaDHA-1 genes by PCR and DNA sequencing as well as their linkage to class 1 integrons in 451 non-epidemiologically related nosocomial strains resistant to at least one expanded-spectrum cephalosporin and to one aminoglycoside, isolated between 1989 and 2010 from 7 hospitals from Buenos Aires City. The epidemiology of complex class 1 integrons was found to be notably different among fermenting (94/171) and non-fermenting clinical bacilli isolates (1/280). The ISCR1::qnrB10 positive isolates were found since 1993, confirming its presence in clinical isolates more than a decade before its first description. As expected, In35::ISCR1::blaCTX-M-2 was the most common complex class 1 integron among Enterobacteriaceae isolates, particularly in Proteus mirabilis. Experimental analysis corroborated the activity of the Orf513 protein, which was found to bind specific DNA sequences containing the previously suggested oriIS region. These findings showed the high dispersion and maintenance of complex class 1 integrons across time in our nosocomial isolates. The contribution of the ISCR1 mobile element to multidrug resistant phenotypes is significant due to its sustained association to class 1 integrons.

Transposons and integrons in colistin-resistant clones of Klebsiella pneumoniae and Acinetobacter baumannii with epidemic or sporadic behaviour.

Multiple transposons, integrons and carbapenemases were found in Klebsiella pneumoniae colistin-resistant isolates as well as a genomic resistance island of the AbaR type in Acinetobacter baumannii colistin-resistant isolates from different hospitals from Buenos Aires City. PFGE analysis showed a polyclonal dissemination of antimicrobial resistance mechanisms among K. pneumoniae isolates, while in A. baumannii isolates the epidemic clone 1 from South America was found. Resistance determinants associated with horizontal gene transfer are contributing to the evolution to pandrug resistance in both epidemic and sporadic clones.

Polyclonal spread of bla(OXA-23) and bla(OXA-58) in Acinetobacter baumannii isolates from Argentina.

BACKGROUND: In order to study the enzymatic carbapenem resistance mechanisms in Acinetobacter baumannii isolates from Argentina, we performed molecular characterization on 41 epidemiologically unrelated strains isolated from 1995 to 2006 with diminished susceptibilities to imipenem and meropenem. METHODOLOGY: Acinetobacter baumannii isolates were identified with the ARDRA technique. The total genomic DNA was used to detect each carbapenem beta-lactamase gene described so far in this species and those insertion sequences usually associated to carbapenem beta-lactamase genes (ISAba1, 2, 3, 4 and IS18) by the PCR technique with specific primers. RESULTS: 26 out of 41 Acinetobacter baumannii isolates with diminished susceptibilities to carbapenems harboured the bla(OXA-23) gene. The bla(OXA-58) was detected in 13 out of 41 isolates. ISAba1 was always located upstream bla(OXA-23). All isolates containing the bla(OXA-58) gene showed ISAba3 downstream of the carbapenemase, while 4 isolates had a second copy of the ISAba3 upstream of the gene. CONCLUSION: Enzymatic carbapenem resistance in Acinetobacter baumannii was found in 88% of 41 non-epidemiologically-related strains mediated by the polyclonal spread of the bla(OXA-23) and bla(OXA-58) genes. The genetic structures surrounding the oxacillinase genes found in our bacterial isolates revealed a particular epidemiology in our geographical region. This data suggests the need of local molecular surveillance to help control multirresistance Acinetobacter baumannii infections.

Analizan la diseminación de determinantes de resistencia a antibióticos del género Shewanella en el ambiente hospitalario / Analysis of antimicrobial resistance determinants associated with antibiotics of the genus Shewanella in a hospital environment

La alta frecuencia de diseminación de estos determinantes pone de manifiesto la capacidad de este género para actuar como reservorio y a su vez vector de la resistencia antibiótica