Positive R plasmid mutator effect on chromosomal mutation to nalidixic acid resistance in nalidixic acid-exposed cultures of Escherichia coli

Resistance and integron characterization of Acinetobacter baumannii in a teaching hospital in Chongqing, China

A total of 189 Acinetobacter baumannii isolates were collected in 2011 from a teaching hospital in Chongqing, China. Susceptibility data showed strains carrying integrons were significantly more resistant to all tested antibiotics that strains lacking integrons. Five types of gene cassettes belonging to class I integrons were identified in this study, and for the first time two types of gene cassettes belonging to class II integrons are reported. Most of the cassettes belong to a class I integron (136/144) encoding arr3, aacA4, dfrA17, aadA5, aadB, cat, blaOXA10 , aadA1, aadA2, dfrA and aacC1. Isolates contained a class I gene cassette; AadA2-HP-dfrA was the prevalent strain in this hospital. A class II integron was detected in eight strains, which contained the type IV fimbriae expression regulatory gene pilR and sulfate adenylyltransferase, suggesting a possible role in multidrug resistance. The major epidemic strains from intensive care unit patients belong to international clone 2. In conclusion, the presence of integrons was significantly associated with multiple drug resistance of A. baumannii in this hospital, and class I integron isolates bearing AadA2-HP-dfrA were the prevalent strain in this hospital.

Development of a High-Throughput Human HepG2 Dual Luciferase Assay for Detection of Metabolically Activated Hepatotoxicants and Genotoxicants

Hepatic toxicity remains a major concern for drug failure; therefore, a thorough examination of chemically induced liver toxicity is essential for a robust safety evaluation. Current hypotheses suggest that the metabolic activation of a drug to a reactive intermediate is an important process. In this article, we describe a new high-throughput GADD45β reporter assay developed for assessing potential liver toxicity. Most importantly, this assay utilizes a human cell line and incorporates metabolic activation and thus provides significant advantage over other comparable assays used to determine hepatotoxicity. Our assay has low compound requirement and relies upon 2 reporter genes cotransfected into the HepG2 cells. The gene encoding Renilla luciferase is fused to the CMV promoter and provides a control for cell numbers. The firefly luciferase gene is fused to the GADD45β promoter and used to report an increase in DNA damage. A dual luciferase assay is performed by measuring the firefly and Renilla luciferase activities in the same sample. Results are expressed as the ratio of the 2 luciferase activities; increases over the control are interpreted as evidence of stress responses. This mammalian dual luciferase reporter has been characterized with, and without, metabolic activation using positive and negative control agents. Our data demonstrate that this assay provides for an assessment of potential toxic metabolites, is adaptable to a high-throughput platform, and yields data that accurately and reproducibly detect hepatotoxicants.

Mechanisms of resistance to quinolones

The increased use of fluoroquinolones has led to increasing resistance to these antimicrobials, with rates of resistance that vary by both organism and geographic region. Resistance to fluoroquinolones typically arises as a result of alterations in the target enzymes (DNA gyrase and topoisomerase IV) and of changes in drug entry and efflux. Mutations are selected first in the more susceptible target: DNA gyrase, in gram-negative bacteria, or topoisomerase IV, in gram-positive bacteria. Additional mutations in the next most susceptible target, as well as in genes controlling drug accumulation, augment resistance further, so that the most-resistant isolates have mutations in several genes. Resistance to quinolones can also be mediated by plasmids that produce the Qnr protein, which protects the quinolone targets from inhibition. Qnr plasmids have been found in the United States, Europe, and East Asia. Although Qnr by itself produces only low-level resistance, its presence facilitates the selection of higher-level resistance mutations, thus contributing to the alarming increase in resistance to quinolones.

Better control of antibiotic resistance

This text summarizes the conclusions of the French Working Party to Promote Research to Control Bacterial Resistance, initiated by the French Institute for Public Health Surveillance. The goal was to identify and prioritize the research areas most pertinent to the evolution of antibiotic resistance. The working group was part of a nationwide consultation of experts in the field of bacterial resistance and was coordinated with 2 other groups addressing (1) the use and surveillance of resistance to antibiotics and (2) the control and prevention of resistance to antibiotics. The proposals were discussed at a meeting held on 13 January 1999 by a large group of French microbiologists and clinicians who specialize in infectious diseases. The expert panel stressed that the determinants of evolution of antimicrobial resistance and the possibility of reversing this evolution are not completely known or understood. It emphasized the need for efforts to anticipate emergence of new resistances, to analyze the consequences of bacterial resistance, to develop rapid tests for determination of susceptibility to antibiotics, and to develop new antibiotics.

Cefuroxime resistance in Escherichia coli. Resistance mechanisms and prevalence

In order to characterize cefuroxime resistance in Escherichia coli 22 clinical isolates were investigated for susceptibility to different beta-lactam antibiotics and ciprofloxacin. The production of beta-lactamases, the pattern of the major outer membrane proteins (OMPs), and the plasmid profiles were determined for these isolates. Ten of the isolates were resistant to ceftazidime, two to cefotaxime, and none was resistant to imipenem or ciprofloxacin. The dominating resistance mechanism was hyperproduction of the chromosomally encoded beta-lactamase to some extent accompanied by alterations of the OMP's. Two isolates with low ampicillin MIOs seemed solely to have alteration of the OMPs. None of the isolates produced plasmid-mediated extended-spectrum beta-lactamases. In addition, the prevalence of cefuroxime resistance was investigated. The prevalence as attained in 8704 clinical isolates of E. coli collected from Copenhagen County during a 5-year period (1990-1994) was 4.4%, but there was considerable variation among specimens from different sites of the body. Isolates from blood were much less resistant (2.5%) than isolates from the respiratory tract (9.7%).

Post-UV survival of Escherichia coli strains carrying more than one UV-sensitising plasmid

The post-UV phenotypes conferred by wild-type plasmids R391 and pYD1, which increase UV-induced mutagenesis but sensitise Escherichia coli AB1157 umuC+ uvrB+ to UV, were compared, alone and in combination with that of plasmid pGW16, which sensitises AB1157 to low, but protects against high UV doses. All three plasmids increased UV resistance when present in Shigella sonnei. No plasmid significantly affected the UV sensitivity of E. coli TK501 umuC uvrB, in which pKM101, the parent of pGW16 increases UV resistance up to 1000-fold. Both pYD1 and R391 reduced the UV protective effect of pKM101, and increased UV-sensitisation conferred by pGW16. UV-sensitisation conferred by pYD1 and R391 was additive when the plasmids were together in strain AB1157, and both pKM101 and pGW16 reduced this additive sensitisation.