María Soledad Ramírez

Aminoglycoside Modifying Enzymes

Aminoglycosides have been an essential component of the armamentarium in the treatment of life-threatening infections. Unfortunately, their efficacy has been reduced by the surge and dissemination of resistance. In some cases the levels of resistance reached the point that rendered them virtually useless. Among many known mechanisms of resistance to aminoglycosides, enzymatic modification is the most prevalent in the clinical setting. Aminoglycoside modifying enzymes catalyze the modification at different -OH or -NH₂ groups of the 2-deoxystreptamine nucleus or the sugar moieties and can be nucleotidyltransferases, phosphotransferases, or acetyltransferases. The number of aminoglycoside modifying enzymes identified to date as well as the genetic environments where the coding genes are located is impressive and there is virtually no bacteria that is unable to support enzymatic resistance to aminoglycosides. Aside from the development of new aminoglycosides refractory to as many as possible modifying enzymes there are currently two main strategies being pursued to overcome the action of aminoglycoside modifying enzymes. Their successful development would extend the useful life of existing antibiotics that have proven effective in the treatment of infections. These strategies consist of the development of inhibitors of the enzymatic action or of the expression of the modifying enzymes.

Plasmid-Mediated Antibiotic Resistance and Virulence in Gram-Negatives: the Klebsiella pneumoniae Paradigm.

Plasmids harbor genes coding for specific functions including virulence factors and antibiotic resistance that permit bacteria to survive the hostile environment found in the host and resist treatment. Together with other genetic elements such as integrons and transposons, and using a variety of mechanisms, plasmids participate in the dissemination of these traits, resulting in the virtual elimination of barriers among different kinds of bacteria. In this article we review the current information about the physiology of plasmids and their role in virulence and antibiotic resistance from the Gram-negative opportunistic pathogen Klebsiella pneumoniae. This bacterium has acquired multidrug resistance and is the causative agent of serious community- and hospital-acquired infections. It is also included in the recently defined ESKAPE group of bacteria that cause most U.S. hospital infections.

Novel insights about class 2 integrons from experimental and genomic epidemiology.

ABSTRACT In order to contribute to the knowledge of the architecture and epidemiology of class 2 integrons, we performed a class 2 integron molecular survey in which we analyzed 726 isolates in two bacterial populations from environmental and nonepidemiologically related clinical samples, respectively, collected from 1982 to 2007. We recovered the intI2 gene from 130 of 726 isolates, most of which were clinical isolates, and only 1 (a psychrophilic Pseudomonas sp.) was from a water sample. Unlike the widespread distribution of class 1 integrons within Gram-negative bacilli, only Acinetobacter baumannii and Enterobacter cloacae harbored class 2 integrons at a high frequency in our collection. Class 2 integrons with six novel cassette arrays were documented. Characterization of the transposition module of Tn7, the genetic platform in which class 2 integrons have always been reported, showed tns modules with a mosaic genetic structure. A bioinformatic analysis performed with the tns genes present in sequence databases, the finding of intI2 not associated with tns genes, and the genetic examination of novel tns-like genes found in three isolates indicated the possibility of the independent evolution of the two components related to horizontal gene transfer, the class 2 integrons and the Tn7 transposons.

Rise and dissemination of aminoglycoside resistance: the aac(6′)-Ib paradigm

Enzymatic modification is a prevalent mechanism by which bacteria defeat the action of antibiotics. Aminoglycosides are often inactivated by aminoglycoside modifying enzymes encoded by genes present in the chromosome, plasmids, and other genetic elements. The AAC(6′)-Ib (aminoglycoside 6′-N-acetyltransferase type Ib) is an enzyme of clinical importance found in a wide variety of gram-negative pathogens. The AAC(6′)-Ib enzyme is of interest not only because of his ubiquity but also because of other characteristics, it presents significant microheterogeneity at the N-termini and the aac(6′)-Ib gene is often present in integrons, transposons, plasmids, genomic islands, and other genetic structures. Excluding the highly heterogeneous N-termini, there are 45 non-identical AAC(6′)-Ib related entries in the NCBI database, 32 of which have identical name in spite of not having identical amino acid sequence. While some variants conserved similar properties, others show dramatic differences in specificity, including the case of AAC(6′)-Ib-cr that mediates acetylation of ciprofloxacin representing a rare case where a resistance enzyme acquires the ability to utilize an antibiotic of a different class as substrate. Efforts to utilize antisense technologies to turn off expression of the gene or to identify enzymatic inhibitors to induce phenotypic conversion to susceptibility are under way.

Naturally Competent Acinetobacter baumannii Clinical Isolate as a Convenient Model for Genetic Studies

ABSTRACT Acinetobacter baumannii A118 was isolated from a patients blood culture. It is susceptible to several antibiotics, is naturally competent, and supports replication and stable maintenance of four plasmid replicons. A. baumannii A118 took up a fluorophore-labeled oligonucleotide analog. These characteristics make this isolate a convenient model for genetic studies.

Novel Rearrangement of a Class 2 Integron in Two Non-Epidemiologically Related Isolates of Acinetobacter baumannii

ABSTRACT Tn7::In2-8 contains sat2-aadB-catB2(ΔattC)-dfrA1-sat2-aadA1-orfX in the variable region of a class 2 integron embedded in the Tn7-like transposon. This novel transposon was inserted in its preferred site downstream of the glms gene in Acinetobacter baumannii. Acquisition of the pseudocassette catB2 could have arisen by a secondary-site integrase-mediated intermolecular recombination event.

Acinetobacter baumannii extensively drug resistant lineages in Buenos Aires hospitals differ from the international clones I-III.

As a way to contribute to the assessment of Acinetobacter baumannii clinical population structure, multi-locus sequence typing (MLST) was performed in a collection of 93 isolates from Buenos Aires (1983-2012) and Rosario (2006-2009) hospitals. Sequence types (STs) were achieved by Bartual (B) and Institut Pasteur (P) schemes. PFGE typing, antimicrobial susceptibility assays, and the amplification of the OXA carbapenemase genes most prevalent in our region, were also performed. e-Burst clustered the 25 STs(B) (15 novels) into 5 clonal complexes (CC) and 5 singletons, and grouped the 18 STs(P) (12 novels) into 3 CC and 4 singletons. Bartual scheme divided the CC79(P) into two groups. CC113(B)/CC79(P) prevailed in Buenos Aires at least in 1992-2009, being responsible for epidemic and for endemic infections and acquiring the XDR (extensively drug-resistant) pattern throughout the years. While, CC119(B)/CC79(P) was apparently present before the CC113(B)/CC79(P)domain. CC103(B)/CC15(P) was the second most prevalent CC. Interestingly, CC110(B)/ST25(P) apparently increased over the last years. Conversely, CC109(B)/CC1(P) (international clone I) predominated in Rosario, although the presence of CC113(B)/CC79(P), CC103(B)/CC15(P) and CC110(B)/ST25(P) was observed. Nineteen novel STs clustered in CC79(P), CC15(P), CC113(B), CC109(B) and CC103(B), suggesting their clonal expansion during persistence. PFGE typing proved transmission of strains intra- and inter-hospitals in each city. Except for one, all the recent isolates (2007-2012) harboured the blaOXA-23-like. All isolates were susceptible to colistin. Tigecycline MIC(90) was 1mg/L and the rifampicin MIC>512mg/l was found among isolates in three hospitals. In conclusion, the international clone II (CC92(B)/CC2(P)) was not found among our isolates. CC113(B)/CC79(P), CC103(B)/CC15(P), and ST25(P), suggested also as major components in the A. baumannii population together with the international clone I, were present in Buenos Aires and Rosario with different prevalence rate. Their recent isolates showed high distribution of the blaOXA-23-like as well as the XDR pattern.

Recovery of a Functional Class 2 Integron from an Escherichia coli Strain Mediating a Urinary Tract Infection

ABSTRACT A class 2 integron was found in an Escherichia coli isolate mediating a urinary tract infection. Unlike other class 2 integrons from pathogens, the encoded IntI2 protein was functional. The integron possessed a dfrA14 cassette, and a second novel cassette in which a lipoprotein signal peptidase gene is predicted.

Class 2 Integron with a Novel Cassette Array in a Burkholderia cenocepacia Isolate

Burkholderia cepacia complex (BCC) organisms are gram-negative opportunistic emerging pathogens associated with a poor prognosis for patients with cystic fibrosis (CF) ([10][1]). Carbapenems and ceftazidime are administered to patients suffering from BCC infections, and trimethoprim-sulfamethoxazole

Class 1 Integrons in Environments with Different Degrees of Urbanization

Background Class 1 integrons are one of the most successful elements in the acquisition, expression and spread of antimicrobial resistance genes (ARG) among clinical isolates. Little is known about the gene flow of the components of the genetic platforms of class 1 integrons within and between bacterial communities. Thus it is important to better understand the interactions among “environmental” intI1, its genetic platforms and its distribution with human activities. Methodology/Principal Findings An evaluation of two types of genetic determinants, ARG (sul1 and qacE1/qacEΔ1 genes) and lateral genetic elements (LGE) (intI1, ISCR1 and tniC genes) in a model of a culture-based method without antibiotic selection was conducted in a gradient of anthropogenic disturbances in a Patagonian island recognized as being one of the last regions containing wild areas. The intI1, ISCR1 genes and intI1 pseudogenes that were found widespread throughout natural communities were not associated with urbanization (p>0.05). Each ARG that is embedded in the most common genetic platform of clinical class 1 integrons, showed different ecological and molecular behaviours in environmental samples. While the sul1 gene frequency was associated with urbanization, the qacE1/qacEΔ1 gene showed an adaptive role to several habitats. Conclusions/Significance The high frequency of intI1 pseudogenes suggests that, although intI1 has a deleterious impact within several genomes, it can easily be disseminated among natural bacterial communities. The widespread occurrence of ISCR1 and intI1 throughout Patagonian sites with different degree of urbanization, and within different taxa, could be one of the causes of the increasing frequency of multidrug-resistant isolates that have characterized Argentina for decades. The flow of ARG and LGE between natural and clinical communities cannot be explained with a single general process but is a direct consequence of the interaction of multiple factors operating at molecular, ecological, phylogenetic and historical levels.