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BACKGROUND: Respiratory pathogens are becoming increasingly resistant to antimicrobials. A new group of drugs, called respiratory quinolones have been synthesized to overcome this problem. AIM: To study the in vitro susceptibility of respiratory pathogens to old and new antimicrobials. MATERIALS AND METHODS: Forty five strains of S pneumoniae, 44 strains of H influenzae, 21 strains of M catarrhalis, 10 strains of methicillin susceptible S aureus and 20 strains of methicillin resistant S aureus were studied. All were isolated from community acquired respiratory infections during 1999. Minimal inhibitory concentrations of moxifloxacin, amoxicillin, amoxicillin/clavulanic acid, clarithromycin, azithromycin, ciprofloxacin and levofloxacin were determined using the Etest method. Beta-lactamase production by H influenzae and M catarrhalis was also studied. RESULTS: S pneumoniae strains were 100% susceptible to quinolones and cotrimoxazole, 2% were resistant to macrolides, 11% were resistant to amoxicillin/clavulanic acid and 47% were resistant to cefuroxime. H influenzae was 100% susceptible to quinolones, azithromycin and amoxicillin/clavulanic acid. There was a 53% resistance to cotrimoxazole, 21% to amoxicillin, 9% to clarithromycin and 7% to cefuroxime. M catarrahalis was 100% susceptible to quinolones and 100% resistant to amoxicillin, 5% resistant to macrolides, 14% resistant to amoxicillin/clavulanic acid, 20% to cefuroxime and 30% to cotrimoxazole. Methicillin susceptible S aureus was susceptible to all antimicrobials and methicillin resistant S aureus was resistant to all. CONCLUSIONS: Maxifloxacin and the new respiratory quinolones can be useful in the treatment of respiratory infections.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11227240&dopt=Abstract
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The potential for antibiotic residues in calves from consuming milk containing penicillin G or amoxicillin was investigated. Six calves were fed milk replacer, 6% body weight twice daily, containing 0.293, 2.92, or 5.85 microg of penicillin/ml (ppm) G or 0.25, 1.0, or 2.0 microg of amoxicillin/ml for three consecutive feedings. Urine and blood samples were collected after each feeding. Serum and urine samples were tested with a microbial receptor assay and a microbial growth inhibition assay to indicate potential drug residues. Penicillin G and amoxicillin were detected in the serum and urine of several calves 3 h after drinking spiked milk replacer. Possible violative drug residues in the calves were detected by the microbial growth inhibition assay up to 15 h after drinking spiked milk replacer. Penicillin G, but not amoxicillin, could be detected in urine 24 h after the final feeding of spiked milk replacer. Subsequently, six calves were fed milk replacer containing 11.7 microg of penicillin G/ml (ppm) twice daily, 6% body weight per feeding. Calves were slaughtered 3 h after the final feeding. Mean (+/-SD) concentrations of penicillin G measured by high-pressure liquid chromatography in liver, kidney, muscle, and serum were 0.409 (+/-0.167) microg/g, 0.031 (+/-0.012) microg/g 0.008 (+/-0.002) microg/g, and 0.013 (+/-0.006) mg/ml, respectively. This study indicates that calves fed milk with amoxicillin or penicillin G could possibly have violative residues if slaughtered within 24 h after feeding. Violative drug residues in liver tissue were found in calves slaughtered 3 h after consuming milk replacer containing 11.7 microg of penicillin G/ml (ppm).
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11210024&dopt=Abstract
Antimicrob Agents Chemother. 2001 Mar;45(3):727-33.
Spontaneous mutations that confer antibiotic resistance in Helicobacter pylori.
Wang G, Wilson TJ, Jiang Q, Taylor DE.
Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada.
In this study, we systematically examined in vitro frequencies and spectra of the spontaneous mutations in Helicobacter pylori that confer resistance to clarithromycin (Cla(r)), metronidazole (Mtz(r)), amoxicillin (Amx(r)), ciprofloxacin (Cip(r)), and rifampin (Rif(r)). The mutation rate of Rif(r) or Cip(r) determined in a fluctuation assay is 1 x 10(-8) to 2 x 10(-8) per cell per division. In contrast, the mutation rates of Cla(r), Mtz(r), and Amx(r) are much lower (<10(-9)). However, Mtz(r) mutants could be readily selected in vitro by using the serial passage method, suggesting that the mutagenic effect and selective effect of a sublethal dose of metronidazole contribute to the rapid development of Mtz(r). Analysis of spontaneous Rif(r), Cla(r), and Cip(r) mutants confirmed previous results indicating that mutations within the rpoB gene, the 23S rRNA gene, and the gyrA gene, respectively, are responsible; also, several new mutant alleles were identified. Mtz(r) mutants resulted most frequently, but not always, from mutations in the rdxA gene. DNA fragments containing each mutant allele could readily transform susceptible H. pylori strains to resistance, confirming that each mutant allele is responsible for the resistance phenotype.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11181351&dopt=Abstract
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