Emergence and maintenance of multidrug-resistant Escherichia coli of canine origin harbouring a blaCMY-2-IncI1/ST65 plasmid and topoisomerase mutations

OBJECTIVES

To characterize the mechanisms implicated in fluoroquinolone (FQ) and expanded-spectrum cephalosporin (ESC) resistance in three clinical and seven faecal multidrug-resistant (MDR; resistant to at least three antimicrobial classes) Escherichia coli isolates from a dog with atopic dermatitis, also suffering from recurrent otitis, that had already been exposed to prolonged antimicrobial treatment and colonized for a long period.

METHODS

MICs of FQs, ESCs and other antimicrobials were determined by the broth microdilution method. Phenotypic tests (efflux pump inhibition and combination disc tests) and isoelectric focusing were combined with genotypic analyses [PCRs, sequencing, conjugation, S1 nuclease PFGE, PCR-based replicon typing, plasmid multilocus sequence typing (pMLST) and PCR mapping] to characterize the molecular basis of FQ and ESC resistance. Isolates were further characterized by MLST and PFGE.

RESULTS

Three otitis and five faecal isolates with enrofloxacin MICs of 32 to >128 mg/L displayed the GyrA:S83L+D87N/ParC:E62K/ParE:G545D pattern harbouring novel ParC and ParE substitutions, whereas the two remaining faecal isolates were susceptible or borderline resistant single-step mutants (GyrA:S83L pattern) and carried qnrS1. Efflux pump overexpression also contributed to FQ resistance and the MDR phenotype. The three otitis and five faecal isolates also exhibited cefoxitin/ceftazidime MICs of 32-64 mg/L and harboured blaCMY-2, adjusted to ISEcp1, on an IncI1/ST65 conjugative plasmid, previously described in Salmonella Heidelberg from poultry. Interestingly, all isolates shared an identical MLST type (ST212), with the otitis isolates showing indistinguishable patterns with the high-level resistant faecal E. coli isolates.

CONCLUSIONS

The long-term maintenance of FQ- and ESC-resistant clones harbouring topoisomerase mutations and a blaCMY-2-IncI1/ST65 plasmid in canine commensal flora after prolonged antimicrobial use may contribute to the dissemination of multidrug resistance.

Pharmacokinetic interaction between losartan and Rhodiola rosea in rabbits

AIM

The study investigates the potential interaction of the herbal medicinal product of Rhodiola rosea on the pharmacokinetics of losartan and its active metabolite EXP3174 after concurrent oral administration to rabbits.

MATERIALS AND METHODS

We conducted a randomized, single-dose, two-treatment, two-period, two-sequence, cross-over pharmacokinetic study on 6 healthy female New Zealand rabbits, after concurrent oral administration of losartan (5 mg/kg) and the herbal medicinal product of R. rosea (50 mg/kg). Quantification of losartan and its main active metabolite EXP3174 was achieved using a validated HPCL/UV method. Pharmacokinetic and statistical analysis was performed using the EquivTest/PK software.

OBSERVATIONS

Administration of the herbal medicinal product of R. rosea resulted in a statistically significant increase of the following pharmacokinetic parameters for losartan: the maximum plasma concentration (C(max)), the area under the curve (AUC) and the apparent total body clearance (CL/F). An almost 2-fold increase in the AUC of losartan was observed after concurrent administration of the herbal medicinal product of R. rosea. No statistically significant alteration was observed in the pharmacokinetic parameters of the active metabolite of losartan EXP3174.

CONCLUSION

The data of this study suggest that R. rosea significantly alters the pharmacokinetic properties of losartan after concurrent oral administration to rabbits. A study in humans should be conducted to assess the clinical significance of a possible herb-drug interaction between the herbal medicinal products of R. rosea and drugs such as losartan, which are substrates of both CYPs and P-gp.

Influence of the injection site on the pharmacokinetics of amoxicillin after intramuscular administration of a conventional and a long-acting formulation in sheep

The pharmacokinetics of amoxicillin (AMX) were investigated in sheep following intravenous (i.v.) and intramuscular (i.m) injection, comparing two different drug formulations, a conventional and a long-acting AMX-trihydrate suspension. For the i.m. application two different injections sites, the neck area and the hind limb were used to identify possible differences in the kinetic parameters related to the site of injection. A three-compartment open model could best describe AMX disposition after i.v. administration. Data analysis after i.m. administration of the conventional suspension at both injection sites revealed the occurrence of a flip-flop phenomenon, clearly indicating that absorption of AMX is the rate-limiting step of its overall disposition. A moderate effect of the injection site was observed with a tendency for the neck area to be advantageous, mainly in terms of rate rather than extent of absorption. Injection of the long-acting formulation led to a focal depot formation, thus yielding lower but remarkably prolonged serum AMX levels reflected in the respective terminal half-lives. The concentration-time profile of AMX after administration of the long-acting formulation was less affected by the injection site, but the low serum levels justify its use only in cases in which a high susceptibility of the involved bacterial population is confirmed.

Cisapride counteracts the anticholinergic effect of disopyramide on the guinea pig isolated small but not large intestine

This study examines the influence of the prokinetic agent cisapride on the disopyramide's effect on the isolated duodenum and ileum, as well as on the ascending colon of the guinea pig. Acetylcholine produced the well known stimulatory effect on the intestinal parts with EC50 values 9.6 x 10(-8), 7 x 10(-9) and 1.1 x 10(-6) M for the duodenum, ileum and ascending colon, respectively. Disopyramide inhibited, in a concentration-dependent manner, the contractile responses of the intestinal parts to acetylcholine. Cisapride, at concentrations ranging from 5 x 10(-9) M to 10(-6) M, significantly reversed the above inhibitory effect of disopyramide on the guinea pig duodenum and ileum and produced a parallel leftward shift of the concentration-response curve for acetylcholine in the presence of disopyramide. However, cisapride was not found able to reverse the inhibitory effect of disopyramide on the ascending colon. In conclusion, cisapride may counteract the inhibitory effect of disopyramide on the guinea pig duodenum and ileum, probably by facilitating the cholinergic neurotransmission, while it is not able to reverse the disopyramide's inhibitory effect on the guinea pig ascending colon.

Effect of cisapride on the isolated guinea pig gall bladder and common bile duct

1. In this study, the effect of cisapride on the isolated guinea pig gall bladder (GB) and common bile duct (CBD) motility was investigated. 2. Cisapride, up to a certain concentration, produced an increase in tone of the GB (EC50 1.35 x 10(-8) M) and the CBD (EC50 2.75 x 10(-9) M), whereas, at concentrations higher than 3 x 10(-5) M for the GB and 5 x 10(-6) M for the CBD, it produced a transient increase in tone followed by a sustained decrease in tone or in the contraction amplitude or in both. 3. The cisapride-induced increase in tone was antagonized by atropine on both the GB and the CBD. 4. Cisapride up to 2 x 10(-5) M for the GB and 3 x 10(-6) M for the CBD did not modify, whereas, at concentrations higher than 2.8 x 10(-5) M for the GB and 4 x 10(-6) M for the CBD, it antagonized, noncompetitively, the concentration-response curve to exogenously applied acetylcholine. The IC50 values for cisapride on the EC50 of acetylcholine on the GB and the CBD were 9.4 x 10(-5) M and 8.2 x 10(-6) M, respectively. 5. In conclusion, on the guinea pig GB and CBD, low concentrations of cisapride produce a stimulating effect, probably of cholinergic origin, whereas higher concentrations produce a transient stimulating effect, probably of cholinergic origin, followed by a sustained relaxing effect, which may involve both cholinergic and noncholinergic pathways.

Influence of naproxen on the zinc, copper, magnesium and calcium content of guinea pig tissues

The effect of the administration of chronic doses of naproxen on the zinc, copper, magnesium and calcium concentrations in guinea pig tissues was studied. One hundred mg naproxen/kg body weight/week were administered intraperitoneally to adult female guinea pigs in two doses twice a week for eight weeks. A statistically significant decrease was found of the zinc content in the brain, lung, heart, liver, kidney, spleen and adrenals, of the copper content in the liver, kidney and adrenal and of the magnesium content in the spleen and heart. A significant increase was observed of the calcium content in the adrenals, heart, spleen and uterus of the treated animals, while no significant changes were observed in the thigh bone concentrations of the various ions tested.