CPOP: An open source C++ cell POPulation modeler for radiation biology applications.

Purpose: Multicellular tumor spheroids are realistic in-vitro systems used in radiation biology research to study the effect of anticancer drugs or to evaluate the resistance of cancer cells under specific conditions. When combining the modeling of spheroids together with the simulation of radiation using Monte Carlo methods, one could estimate cell and DNA damage to be compared with experimental data. We developed a Cell Population (CPOP) modeler combined to Geant4 simulations in order to tackle how energy depositions are allocated to cells, especially when enhancing radiation outcomes using high-Z nanoparticles.

Fitness of Escherichia coli strains carrying expressed and partially silent IncN and IncP1 plasmids.

Background: Understanding the survival of resistance plasmids in the absence of selective pressure for the antibiotic resistance genes they carry is important for assessing the value of interventions to combat resistant bacteria. Here, several poorly explored questions regarding the fitness impact of IncP1 and IncN broad host range plasmids on their bacterial hosts are examined; namely, whether related plasmids have similar fitness impacts, whether this varies according to host genetic background, and what effect antimicrobial resistance gene silencing has on fitness.

Results: For the IncP1 group pairwise in vitro growth competition demonstrated that the fitness cost of plasmid RP1 depends on the host strain.

Persistence of a wild type Escherichia coli and its multiple antibiotic-resistant (MAR) derivatives in the abattoir and on chilled pig carcasses.

The aim of this study was to evaluate the ability of an Escherichia coli with the multiple antibiotic resistance (MAR) phenotype to withstand the stresses of slaughter compared to an isogenic progenitor strain. A wild type E. coli isolate (345-2RifC) of porcine origin was used to derive 3 isogenic MAR mutants.

Evidence of antibiotic resistance gene silencing in Escherichia coli.

The possibility that unexpressed antibiotic resistance genes are carried by bacterial genomes is seldom investigated. Potential silencing of the resistance genes bla(OXA-2), aadA1, sul1, and tetA carried on the plasmid pVE46 in a recent porcine isolate of Escherichia coli was investigated following oral inoculation of the strain into organic piglets. A small proportion of isolates recovered from feces did not express one or more resistance genes, despite retaining the pVE46 plasmid.

Assessment of the fitness impacts on Escherichia coli of acquisition of antibiotic resistance genes encoded by different types of genetic element.

Objectives: Little is known of the fitness cost that antibiotic resistance exerts on wild-type bacteria, especially in their natural environments. We therefore examined the fitness costs that several antibiotic resistance elements imposed on a wild-type Escherichia coli isolate, both in the laboratory and in a pig gut colonization model.

Methods: Plasmid R46, Tn1 and Tn7 and a K42R RpsL substitution were separately introduced into E.

Effect of the growth promoter avilamycin on emergence and persistence of antimicrobial resistance in enteric bacteria in the pig.

Aim: To assess the effect of the growth promoter avilamycin on emergence and persistence of resistance in enteric bacteria in the pig.

Methods And Results: Pigs (treated with avilamycin for 3 months and controls) were challenged with multi-resistant Salmonella Typhimurium DT104 and faecal counts were performed for enterococci, Escherichia coli, S. Typhimurium and Campylobacter (before, during and 5 weeks post-treatment).

Determination of avilamycin A and B in pig faeces by solid phase extraction and reverse-phase HPLC assay.

A HPLC method is described for the simultaneous determination of avilamycin A and B in pig faeces, following extraction using acetonitrile and normal-phase solid phase extraction. The HPLC stationary phase was Kromosil 5 micro C-18 with a mobile phase of 48% acetonitrile and 52% 0.01N ammonium acetate buffer, pumped at a flow rate of 1 ml/min.

A reverse-phase HPLC assay for the simultaneous determination of enrofloxacin and ciprofloxacin in pig faeces.

A reverse-phase HPLC assay is described for the simultaneous assay of enrofloxacin (ENR) and ciprofloxacin (CPX) in pig faeces. Extraction used dichloromethane, 2-propanol and 0.3M ortho-phosphoric acid (1:5:4 v/v/v).

Emergence of fluoroquinolone resistance in the native Campylobacter coli population of pigs exposed to enrofloxacin.

Objective: The effect of a single 5 day enrofloxacin treatment on the native Campylobacter coli population in conventionally weaned 5-week-old pigs was investigated.

Materials: Twelve pigs were split into two groups of six: one group was treated with a therapeutic dose (15 mg/pig/day) of enrofloxacin and the other remained untreated to act as the control. Campylobacter coli were isolated from faecal samples and tested for ciprofloxacin resistance by measuring MIC values.

Effect of a 5 day enrofloxacin treatment on Salmonella enterica serotype Typhimurium DT104 in the pig.

Objectives: There are concerns that the use of enrofloxacin in livestock production may contribute to the development of fluoroquinolone resistance in zoonotic bacteria. The objective of our study was to investigate the effect of a single 5 day enrofloxacin treatment on Salmonella enterica serotype Typhimurium DT104 in a pig model.

Results: Our results showed that a single treatment failed to eradicate S.

Rifampicin resistance and its fitness cost in Enterococcus faecium.

Objectives: The genetic basis of rifampicin resistance and the associated fitness cost in Enterococcus faecium were investigated.

Methods: Twelve spontaneous rifampicin-resistant E. faecium mutants were selected from four parent strains recently isolated from porcine faecal material.

The effect of chlortetracycline treatment and its subsequent withdrawal on multi-resistant Salmonella enterica serovar Typhimurium DT104 and commensal Escherichia coli in the pig.

Aims: To investigate the effect of a therapeutic and sub-therapeutic chlortetracycline treatment on tetracycline-resistant Salmonella enterica serovar Typhimurium DT104 and on the commensal Escherichia coli in pig.

Methods And Results: Salmonella Typhimurium DT104 was orally administered in all pigs prior to antibiotic treatment, and monitored with the native E. coli.

Determination by HPLC of chlortetracycline in pig faeces.

An HPLC assay used to determine chlortetracycline (CTC) in pig faeces is reported. Prodigy ODS3 (4.6 x 150 mm) was used for the stationary phase, whereas the mobile phase comprised oxalic acid, sodium oxalate and sodium decane sulfonate (66%)--each of 4 mM, and 34% acetonitrile.