Emergence of resistance after therapy with antibiotics used alone or combined in a marine model

A murine model of peritonitis allowing detection and quantification of in-vivo acquired resistance during short term therapy has been used in order to evaluate the capacity of antimicrobial combinations to limit emergence of resistance, as compared to individual components of the regimens. Mice were challenged intraperitoneally with 108 cfu of bacteria. Two hours later, a single antibiotic dose was injected subcutaneously: amikacin (15 mg/kg), ceftriaxone (50 mg/kg), pefloxacin (25 mg/kg), amikacin + ceftriaxone, amikacin + pefloxacin or ceftriaxone + pefloxacin. Escherichia coli and Staphylococcus aureus never became resistant. Single drug therapy yielded resistant mutants in Enterobacter cloacae, Serratia marcescens, Klebsiella pneumoniae and Pseudomonas aeruginosa as follows: 74% of ceftriaxone-treated animals, 57% of pefloxacin treated animals and 27% of amikacin treated animals. All the tested combinations reduced the frequency of in-vivo acquired resistance produced by single drugs, and no combination selected resistance when the separate agents of the combination did not. Combining antimicrobial agents limits the risk of emergence of resistance during antibiotic therap

In vitro evaluation of antibiotics' combinations for empirical therapy of suspected methicillin resistant Staphylococcus aureus severe respiratory infections

<p>Abstract</p> <p>Background</p> <p>Methicillin resistant <it>Staphylococcus aureus </it>(MRSA) is an increasingly common cause of nosocomial infections, causing severe morbidity and mortality worldwide, and accounting in some hospitals for more than 50% of all <it>S. aureus </it>diseases. Treatment of infections caused by resistant bacterial pathogens mainly relies on two therapeutic modalities: development of new antimicrobials and use of combinations of available antibiotics.</p> <p>Combinations of antibiotics used in the empiric treatment of infections with suspected methicillin resistant <it>Staphylococcus aureus </it>etiology were investigated.</p> <p>Methods</p> <p>Double (vancomycin or teicoplanin with either levofloxacin or cefotaxime) and triple (vancomycin or teicoplanin + levofloxacin + one among amikacin, ceftazidime, cefepime, imipenem, piperacillin/tazobactam) combinations were evaluated by means of checkerboard assay and time kill curves. Mutational rates of single and combined drugs at antimicrobial concentrations equal to the resistance breakpoints were also calculated.</p> <p>Results</p> <p>Vancomycin or teicoplanin + levofloxacin showed synergy in 16/50 and in 9/50 strains respectively, while vancomycin or teicoplanin + cefotaxime resulted synergic for 43/50 and 23/50 strains, respectively. Triple combinations, involving teicoplanin, levofloxacin and ceftazidime or piperacillin/tazobactam gave synergy in 20/25 strains. Teicoplanin + levofloxacin gave synergy in triple combinations more frequently than vancomycin + levofloxacin.</p> <p>For single antibiotics, mutational frequencies ranged between 10^-5and <10^-9for levofloxacin, cefotaxime, amikacin and imipenem, and <10^-9for vancomycin and teicoplanin. When tested in combinations, mutational frequencies fell below 10^-9for all the combinations.</p> <p>Conclusion</p> <p><it>In vitro </it>evidence of synergy between glycopeptides, fluoroquinolones (levofloxacin) and β-lactams and of reduction of mutational frequencies by combinations are suggestive for a potential role in empirical therapy of severe pneumonia with suspected MRSA etiology.</p

Tracking of sea level impact on Caspian Ramsar sites and potential restoration of the Gorgan Bay on the southeast Caspian coast

The situation of Ramsar sites along the Caspian Sea coast has deteriorated over the past decades, and this is more noticeable in the narrow coastal strip of the south Caspian Sea. In this study we investigate how the Caspian Sea level changes affect the coastal Ramsar sites. Particularly, we focus on the Gorgan Bay in the southeast corner of the Caspian Sea, which is experiencing extensive water level decline, even desiccation. We used satellite images from three periods corresponding to periods of two sea level falls and one sea level rise, in order to decipher spatio-temporal changes of the wetlands. We conducted field campaign in the Gorgan Bay for sampling and measurement of physical, chemical and biological parameters. We simulated water circulation for the past, current and future conditions of the Gorgan Bay, which is essential to sustain better water exchange between the Bay and the Caspian Sea. We applied dust simulation in the case of a total desiccation of the Gorgan Bay. The result shows that the total area of the Caspian coastal Ramsar sites during the two periods of the sea level fall is almost the same; however, the aerial changes in the southern wetlands are more visible. Nutrient and plankton analysis of the Gorgan Bay display mainly mesotrophic conditions, in some areas close to eutrophic ones. The average current velocity in the main inlet is 2.5 cms−1. Dust simulation indicates that in case of the Gorgan Bay desiccation, it will become a dust source for the surrounding area up to 60 km. Simulation of the water circulation with dredging of inlets (future scenario), indicates that the water exchange velocity doubles compared to the current scenario. A recommended inlet maintenance would accelerate water circulation and reduce residence time, which will lead to better trophy and prevent bay desiccation. © 202

Differential Selection of Multidrug Efflux Mutants by Trovafloxacin and Ciprofloxacin in an Experimental Model of Pseudomonas aeruginosa Acute Pneumonia in Rats

The ability of trovafloxacin and ciprofloxacin to select efflux mutants in vivo was studied in a model of acute Pseudomonas aeruginosa pneumonia in rats. Twelve hours after intratracheal inoculation of 10(6) CFU of P. aeruginosa strain PAO1 enmeshed in agar beads, two groups of 12 rats were treated by three intraperitoneal injections of each antibiotic given every 5 h. Dosing regimens were chosen to obtain a comparable area under the concentration-time curve from 0 to infinity/MIC ratio of 27.9 min for trovafloxacin (75 mg/kg of body weight) and of 32.6 min for ciprofloxacin (12.5 mg/kg). Twelve rats were left untreated and served as controls. Rats were sacrificed 12 h after the last injection (34 h after infection) for lung bacteriological studies. Selection of resistant bacteria was determined by plating lung homogenates on Trypticase soy agar plates containing antibiotic. In untreated animals, the frequency of resistant colonies was 10-fold higher than in agar beads. Compared to controls, both treatment regimens resulted in a 2-log reduction of lung bacterial load. The frequency of resistant colonies was 10-fold less with trovafloxacin than with ciprofloxacin at twice the MIC (7.4 × 10(−5) versus 8.4 × 10(−4), respectively) (P < 0.05) and at four times the MIC (6.2 × 10(−4) versus 5.0 × 10(−5), respectively) (P < 0.05). A multidrug resistance phenotype typical of efflux mutants was observed in all 41 randomly tested colonies obtained from treated and untreated rats. In agreement with in vitro results, trovafloxacin and ciprofloxacin preferentially selected MexCD-OprJ and MexEF-OprN overproducers, respectively. These results demonstrate the differential ability of trovafloxacin and ciprofloxacin to select efflux mutants in vivo and highlight the rapid emergence of those mutants, even without treatment