Acquisition Of Resistance Determinants Research Articles

Ultrastructural, metabolic and genetic characteristics of determinants facilitating the acquisition of macrolide resistance by Streptococcus pneumoniae

AimsTo investigate the molecular events associated with acquiring macrolide resistance genes [mefE/mel (Mega) or ermB] in Streptococcus pneumoniae (Spn) during nasopharyngeal colonization. Methods and resultsGenomic analysis of 128 macrolide-resistant Spn isolates revealed recombination events in genes of the conjugation apparatus, or the competence system, in strains carrying Tn916-related elements. Studies using confocal and electron microscopy demonstrated that during the transfer of Tn916-related elements in nasopharyngeal cell biofilms, pneumococcal strains formed clusters facilitating their acquisition of resistance determinants at a high recombination frequency (rF). Remarkably, these aggregates comprise both encapsulated and nonencapsulated pneumococci that span extracellular and intracellular compartments. rF assessments showed similar rates regardless Mega was associated with large integrative and conjugative elements (ICEs) (>23 kb) or not (∼5.4 kb). The rF for Mega Class IV(c) insertion region (∼53 kb) was three orders of magnitude higher than the transformation of the capsule locus. Metabolomics studies of the microenvironment created by colonization of human nasopharyngeal cells revealed a link between the acquisition of ICEs and the pathways involving nicotinic acid and sucrose. ConclusionsPneumococcal clusters, both extracellular and intracellular, facilitate macrolide resistance acquisition, and ICEs were acquired at a higher frequency than the capsule locus. Metabolic changes could serve as intervention targets.

Aerobactin Synthesis Proteins as Antivirulence Targets in Hypervirulent Klebsiella pneumoniae.

Hypervirulent Klebsiella pneumoniae (hvKp) is an underrecognized pathotype of K.pneumoniae since the majority of cases have occurred in East Asia. However, hvKp is a public health threat due to its ability to infect healthy individuals, ongoing dissemination, and acquisition of resistance determinants. hvKp-directed antivirulence therapy is appealing since it has the potential to minimize resistance selection. The discovery that aerobactin is a critical hvKp-specific virulence factor has made its biosynthetic enzymes attractive targets for the development of small molecule inhibitors. However, identification of additional high value targets is needed to enable a robust countermeasure program for this evolving superbug.

Prevalence of plasmid-borne benzalkonium chloride resistance cassette bcrABC and cadmium resistance cadA genes in nonpathogenic Listeria spp. isolated from food and food-processing environments

The sixty-seven nonpathogenic Listeria spp. strains isolated from food and food processing environments in Poland were examined for the presence of benzalkonium chloride (BC) resistance cassette (bcrABC) and four different variants of cadmium resistance determinants (cadA1-cadA4). All the strains were phenotypically resistant to cadmium and 22 among them were also resistant to BC. PCR-based analysis revealed that bcrABC cassette was harbored by 95.5% of the strains phenotypically resistant to BC. All of them harbored also either cadA1 or cadA2 genes (none carried cadA3 or cadA4), which corresponded to the presence of plasmids with two restriction patterns. The strains resistant to cadmium but susceptible to BC harbored only the cadA1 gene variant. DNA-DNA hybridization analysis showed that all the identified bcrABC, cadA1 and cadA2 genes were located within plasmids, classified into 11 groups of RFLP profiles. Only one of the plasmids – pLIS1 of Listeria welshimeri (carrying bcrABC and cadA2) – was capable of efficient conjugal transfer from nonpathogenic Listeria isolates to a pathogenic Listeria monocytogenes strain. Analysis of the complete nucleotide sequence of pLIS1 (the first sequenced plasmid of L. welshimeri species) revealed the presence of genes involved in plasmid replication, stabilization and transfer as well as genes conferring resistance phenotypes. Comparative analysis showed that pLIS1 genome is highly similar to a group of plasmids originating from L. monocytogenes strains. A common feature of pLIS1 and its relatives, besides the presence of the resistance genes, is the presence of numerous transposable elements (TEs). The analysis revealed the important role of TEs in both promoting genetic rearrangements within Listeria spp. plasmids and the acquisition of resistance determinants.

Impact of the colistin resistance gene mcr-1 on bacterial fitness

A Klebsiella pneumoniae isolate harbouring a 217 kb IncHI2-type plasmid (pKP2442) encoding the colistin resistance gene mcr-1 was isolated from a leukaemia patient. pKP2442 was mobilised by intragenus and intergenus transconjugation from the clinical isolate to Escherichia coli J53 (transconjugation frequency 6.86 × 10−8 ± 5.57 × 10−8) and K. pneumoniae PRZ (transconjugation frequency 4.04 × 10−8 ± 3.03 × 10−8), respectively. Since acquisition of resistance determinants often results in a loss of fitness, the impact of mcr-1 on the fitness of E. coli and K. pneumoniae was investigated. Escherichia coli J53 and K. pneumoniae PRZ transformants harbouring the TOPO expression vector encoding mcr-1 displayed significantly decreased growth rates compared with isogenic parental strains and controls. In contrast, competitive growth experiments revealed equal growth rates between E. coli J53 pKP2442 transconjugants (TcpKP2442) and the parental strain, whereas K. pneumoniae PRZ TcpKP2442 showed significantly reduced growth rates compared with their parental strain (selection rate constant −1.62 ± 0.49), indicating a decrease in fitness. Infection of A549 human lung epithelial cells with TcpKP2442 or mcr-1 transformants and controls revealed equal lactate dehydrogenase activities, indicating no significant impact of mcr-1 on cytotoxicity. Likewise, survival of Galleria mellonella larvae infected with mcr-1-expressing strains and isogenic controls was similar. These data indicate that expression of mcr-1 is able to cause a fitness cost when encoded on expression vectors and that acquisition of natural plasmid-borne mcr-1 does not impair fitness in E. coli J53 but negatively influences growth rates in K. pneumoniae PRZ.

ISCR2 and IS26: Two Insertion Sequences Highly Dispersed among Acinetobacter spp. Clinical Strainss

Fil: Montana, Sabrina Daiana. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones en Microbiologia y Parasitologia Medica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiologia y Parasitologia Medica; Argentina

Regulation of antibiotic resistance in Staphylococcus aureus

Staphylococcus aureus has a formidable ability to adapt to varying environmental conditions and an extraordinary capacity to rapidly become resistant to virtually all antibiotics. Resistance develops either through mutations and rearrangements within the staphylococcal genome, or by the acquisition of resistance determinants. Antibiotic resistances often impose a fitness burden on the host. Such biological costs can be reduced by tight regulation and antibiotic-inducible expression of resistance genes, or by compensatory mutations. Resistance induction by antibiotics can be mediated by dedicated, antibiotic-recognizing signal transducers or by mechanisms relieving translational attenuation. Antibiotic tolerance and the expression of resistance phenotypes can also be strongly influenced by the genetic backgrounds of strains and several other factors. Modification and indirect regulation of resistance levels can occur by mutations that alter gene expression or substrate specificity of genes contributing to resistance. Insertion elements can alter resistance profiles by turning relevant genes on or off. Environmental conditions and stress response mechanisms triggered by perturbation of the cell envelope, DNA damage, or faulty intermediary metabolism can also have an impact on resistance development and expression. Clinically relevant resistance is often built up through multiple steps, each of which contributes to an increase in resistance. The driving force behind resistance formation is antibiotic stress, and under clinical conditions selection for resistance is continuously competing with selection for bacterial fitness.

Evaluation of genetic determinants involved in β-lactam- and multiresistance in a surgical ICU

Antibiotic resistance is a major and well-known problem in intensive care units (ICUs) world-wide and previously susceptible isolates become resistant through the acquisition of resistance determinants from other bacteria or the development of mutations, as is the case in β-lactam resistance. We evaluated the presence of resistance determinants involved in β-lactam resistance and multi-resistance in order to establish the contribution of horizontal gene transfer to the spread of resistance in a surgical ICU during an antibiotic rotation study. Pseudomonas aeruginosa and Enterobacteriaceae isolates were selected and iso-electric focusing (IEF), DNA-typing methods such as specific β-lactamase and specific integron PCRs were performed to determine the presence of β-lactamases. The PCRs specific for IMP-1, OXA-1, and VIM-type β-lactamases performed on the selected P. aeruginosa and Enterobacteriaceae isolates with MICs for cephalosporins >1 mg/l did not demonstrate any of these β-lactamases. IEF for 14 pseudomonads, representing 7 genotypes from 9 patients, showed a β-lactamase with a p I larger than 8.5 in 13 of the isolates. The integrase PCR was positive for only five isolates from three patients and conserved segment PCR showed integrons of variable sizes (700, 900, 1400 and 1500 bp). Each patient had its own integron types. It can be concluded that integrons and associated resistance determinants played only a minor role in the surgical ICU and β-lactam resistance among P. aeruginosa isolates was most likely due to the derepression of its AmpC gene.

Resistance mechanisms of Gram-positive bacteria

AbstractThe introduction and increasing use of antibiotics for antibacterial therapy has initiated a rapid development and expansion of antibiotic resistance in microorganisms, particularly in human pathogens. Additionally, a shift to an increase in number and severity of Gram-positive infections has been observed the last decades. Common to these pathogens is their tendency to accumulate multiple resistances under antibiotic pressure and selection. Methicillin-resistant Staphylococcus aureus (MRSA), that have acquired multiresistance to all classes of antibiotics, have become a serious nosocomial problem. Recently, the emergence of the first MRSA with reduced vancomycin susceptibility evoked the specter of a totally resistant S. aureus. Problems with multiresistance expand also to penicillin-resistant Streptococcus pneumoniae that are partially or totally resistant to multiple antibiotics, and to vancomycin-resistant Enterococcus ssp., completely resistant to all commonly used antibiotics. The rapid development of resistance is due to mutational events and/or gene transfer and acquisition of resistance determinants, allowing strains to survive antibiotic treatment.

Basic Aspects of Antibiotic Resistance in the Multiresistant Staphylococcus: An Overview

Analysis of staphylococcal resistance to antimicrobial agents has revealed three main biochemical mechanisms of resistance that are common to other bacteria: (1) inactivation of the antimicrobial by enzymes modifying or hydrolysing the agent, (2) target receptor alteration – by acquisition of a target with reduced affinity for the antimicrobial, acquisition of enzymes converting a native target, or mutation of genes encoding the native target, (3) limiting access of the antimicrobial, mainly by active efflux of the antibiotic. Often, several mechanisms confer resistance to the same antimicrobial agent. Staphylococcal resistance has evolved by acquisition of resistance determinants and by mutation or recombination events in existing staphylococcal DNA. Effective horizontal distribution of DNA among staphylococci is possible via transformation, transduction, plasmid-mediated conjugation or phage-mediated conjugation. Plasmid-mediated DNA mobilization and the location of R determinants on transposable elements are important genetic features of Staphylococcus, allowing versatility of resistance.