Effect of Fluoroquinolone Resistance Selection on the Fitness of Three Strains of Clostridium perfringens

Antimicrobial Resistance in Clostridium and Brachyspira spp. and Other Anaerobes

This article describes the antimicrobial resistance to date of the most frequently encountered anaerobic bacterial pathogens of animals. The different sections show that antimicrobial resistance can vary depending on the antimicrobial, the anaerobe, and the resistance mechanism. The variability in antimicrobial resistance patterns is also associated with other factors such as geographic region and local antimicrobial usage. On occasion, the same resistance gene was observed in many anaerobes, whereas some were limited to certain anaerobes. This article focuses on antimicrobial resistance data of veterinary origin.

In Vivo Toxicity of Solasonine and Its Effects on cyp450 Family Gene Expression in the Livers of Male Mice from Four Strains

Solasonine was reported to inhibit tumour cell growth in several different models. The in vivo toxicity of solasonine, the effects of genetic background on its toxicity, and its possible roles in regulating the expression of cyp450 family genes were still unclear and required characterisation. Here, Horn’s assays were performed on male mice from four different strains, and the expression of cyp450 family genes in their livers was examined by RT-PCR and ELISA. Mice treated by intraperitoneal injection with high levels of solasonine showed immediate post-excitatory depression, intraperitoneal tissue adhesion, and dissolving of cells in the liver. Furthermore, these four mouse strains showed different toxicological sensitivity to solasonine. The strains, in decreasing order of LD50 value, rescuing speed of body weight, and more severe pathological symptoms, were KM, ICR, C57BL/6, and BALB/c. Interestingly, more cyp450 genes were downregulated at the mRNA and/or protein level in the livers of male mice from C57BL/6 or BALB/c strains than those from KM or ICR strains. These results suggest that (1) Solasonine has hepatic toxicity and downregulates cyp450 genes expression at transcriptional and/or post-transcriptional levels; (2) Genetic background is an important factor which can affect the in vivo toxicity; (3) Downregulation of cyp450 gene expression in the liver may be a clue to help understand whether or not a given strain is sensitive to solasonine; (4) Influences on the expression of cyp450 genes should be considered when using solasonine alone, or in combination with other drugs.

The effect of a commercial competitive exclusion product on the selection of enrofloxacin resistance in commensal E. coli in broilers

The effect of a competitive exclusion product (Aviguard®) on the selection of fluoroquinolone resistance in poultry was assessed in vivo in the absence or presence of fluoroquinolone treatment. Two experiments using a controlled seeder-sentinel animal model (2 seeders: 4 sentinels per group) with one-day-old chicks were used. For both experiments, as soon as the chicks were hatched, the birds of two groups were administered Aviguard® and two groups were left untreated. Three days later, all groups were inoculated with an enrofloxacin-susceptible commensal E. coli strain. Five days after hatching, two birds per group were inoculated with either a bacteriologically fit or a bacteriologically non-fit enrofloxacin-resistant commensal E. coli strain. In experiment 2, all groups were orally treated for three consecutive days (days 8-10) with enrofloxacin. Throughout the experiments, faecal excretion of all inoculated E. coli strains was determined on days 2, 5, 8, 11, 18 and 23 by selective plating (via spiral plater). Linear mixed models were used to assess the effect of Aviguard® on the selection of fluoroquinolone resistance. The use of Aviguard® (P < 0.01) reduced the excretion of enrofloxacin-resistant E. coli when no enrofloxacin treatment was administered. However, this beneficial effect disappeared (P = 0.37) when the birds were treated with enrofloxacin. Similarly, bacterial fitness of the enrofloxacin-resistant E. coli strain used for inoculation had an effect (P < 0.01) on the selection of enrofloxacin resistance when no treatment was administered, whereas this effect was no longer present when enrofloxacin was administered (P = 0.70). Thus, enrofloxacin treatment cancelled the beneficial effects from administrating Aviguard® in one-day-old broiler chicks and resulted in an enrofloxacin-resistant flora. RESEARCH HIGHLIGHTS The effect of Aviguard® on the selection of enrofloxacin resistance was assessed in vivo. Without enrofloxacin, Aviguard® reduced the selection of enrofloxacin resistance. When enrofloxacin was administered, it cancelled the beneficial effect of Aviguard®.

Effect of Trehalose and Trehalose Transport on the Tolerance of Clostridium perfringens to Environmental Stress in a Wild Type Strain and Its Fluoroquinolone-Resistant Mutant

Trehalose has been shown to protect bacterial cells from environmental stress. Its uptake and osmoprotective effect in Clostridium perfringens were investigated by comparing wild type C. perfringens ATCC 13124 with a fluoroquinolone- (gatifloxacin-) resistant mutant. In a chemically defined medium, trehalose and sucrose supported the growth of the wild type but not that of the mutant. Microarray data and qRT-PCR showed that putative genes for the phosphorylation and transport of sucrose and trehalose (via phosphoenolpyruvate-dependent phosphotransferase systems, PTS) and some regulatory genes were downregulated in the mutant. The wild type had greater tolerance than the mutant to salts and low pH; trehalose and sucrose further enhanced the osmotolerance of the wild type to NaCl. Expression of the trehalose-specific PTS was lower in the fluoroquinolone-resistant mutant. Protection of C. perfringens from environmental stress could therefore be correlated with the ability to take up trehalose.

Diversity of Clostridium perfringens isolates from various sources and prevalence of conjugative plasmids

Clostridium perfringens is an important pathogen, causing food poisoning and other mild to severe infections in humans and animals. Some strains of C. perfringens contain conjugative plasmids, which may carry antimicrobial resistance and toxin genes. We studied genomic and plasmid diversity of 145 C. perfringens type A strains isolated from soils, foods, chickens, clinical samples, and domestic animals (porcine, bovine and canine), from different geographic areas in the United States between 1994 and 2006, using multiple-locus variable-number tandem repeat analysis (MLVA) and/or pulsed-field gel electrophoresis (PFGE). MLVA detected the genetic diversity in a majority of the isolates. PFGE, using SmaI and KspI, confirmed the MLVA results but also detected differences among the strains that could not be differentiated by MLVA. All of the PFGE profiles of the strains were different, except for a few of the epidemiologically related strains, which were identical. The PFGE profiles of strains isolated from the same domestic animal species were clustered more closely with each other than with other strains. However, a variety of C. perfringens strains with distinct genetic backgrounds were found among the clinical isolates. Variation was also observed in the size and number of plasmids in the strains. Primers for the internal fragment of a conjugative tcpH gene of C. perfringens plasmid pCPF4969 amplified identical size fragments from a majority of strains tested; and this gene hybridized to the various-sized plasmids of these strains. The sequences of the PCR-amplified tcpH genes from 12 strains showed diversity among the tcpH genes. Regardless of the sources of the isolates, the genetic diversity of C. perfringens extended to the plasmids carrying conjugative genes.

A Severe Accident Caused by an Ocellate River Stingray (Potamotrygon motoro) in Central Brazil: How Well Do We Really Understand Stingray Venom Chemistry, Envenomation, and Therapeutics?

Freshwater stingrays cause many serious human injuries, but identification of the offending species is uncommon. The present case involved a large freshwater stingray, Potamotrygon motoro (Chondrichthyes: Potamotrygonidae), in the Araguaia River in Tocantins, Brazil. Appropriate first aid was administered within ~15 min, except that an ice pack was applied. Analgesics provided no pain relief, although hot compresses did. Ciprofloxacin therapy commenced after ~18 h and continued seven days. Then antibiotic was suspended; however, after two more days and additional tests, cephalosporin therapy was initiated, and proved successful. Pain worsened despite increasingly powerful analgesics, until debridement of the wound was performed after one month. The wound finally closed ~70 days after the accident, but the patient continued to have problems wearing shoes even eight months later. Chemistry and pharmacology of Potamotrygon venom and mucus, and clinical management of freshwater stingray envenomations are reviewed in light of the present case. Bacterial infections of stingray puncture wounds may account for more long-term morbidity than stingray venom. Simultaneous prophylactic use of multiple antibiotics is recommended for all but the most superficial stingray wounds. Distinguishing relative contributions of venom, mucus, and bacteria will require careful genomic and transcriptomic investigations of stingray tissues and contaminating bacteria.

Global Phenotypic Characterization of Effects of Fluoroquinolone Resistance Selection on the Metabolic Activities and Drug Susceptibilities of Clostridium perfringens Strains

Fluoroquinolone resistance affects toxin production of Clostridium perfringens strains differently. To investigate the effect of fluoroquinolone resistance selection on global changes in metabolic activities and drug susceptibilities, four C. perfringens strains and their norfloxacin-, ciprofloxacin-, and gatifloxacin-resistant mutants were compared in nearly 2000 assays, using phenotype microarray plates. Variations among mutant strains resulting from resistance selection were observed in all aspects of metabolism. Carbon utilization, pH range, osmotic tolerance, and chemical sensitivity of resistant strains were affected differently in the resistant mutants depending on both the bacterial genotype and the fluoroquinolone to which the bacterium was resistant. The susceptibilities to gentamicin and erythromycin of all resistant mutants except one increased, but some resistant strains were less susceptible to amoxicillin, cefoxitin, ceftriaxone, chloramphenicol, and metronidazole than their wild types. Sensitivity to ethidium bromide decreased in some resistant mutants and increased in others. Microarray analysis of two gatifloxacin-resistant mutants showed changes in metabolic activities that were correlated with altered expression of various genes. Both the chemical structures of fluoroquinolones and the genomic makeup of the wild types influenced the changes found in resistant mutants, which may explain some inconsistent reports of the effects of therapeutic use of fluoroquinolones on clinical isolates of bacteria.