Quality control guidelines for disk diffusion and broth microdilution antimicrobial susceptibility tests with seven drugs for veterinary applications

Multifunctional Hydrogel Dressing That Carries Three Antibiotics Simultaneously and Enables Real-Time Ultrasound Bacterial Colony Detection

We have developed a multifunctional hydrogel that can carry three synergistic antibiotics commonly used in clinical practice. This hydrogel was discovered to have drug encapsulation efficiencies of 94% for neomycin, 97% for bacitracin, and 88% for polymyxin B. Drug release data indicated that the release profiles of these three antibiotics were different. A swelling test demonstrated that the hydrogel absorbed liquid after the release of its antibiotics until it became saturated, which occurred within 48 h. Moreover, this hydrogel exhibited excellent antibacterial effects against Escherichia coli and Pseudomonas aeruginosa and biocompatibility; it can thus protect a wound from microbial invasion. When the alginate hydrogel is used to cover a wound, the wound can be checked for colonization at any time using ultrasound imaging; this can thus enable the prevention of wound biofilm formation in the early stages of infection. We evaluated the hydrogel against commercially available wound dressings and discovered that these wound dressings did not have the aforementioned desirable features. In conclusion, our multifunctional hydrogel can carry three types of antibiotics simultaneously and is a suitable medium through which an ultrasound can be performed to detect the growth of colonies in wounds. The hydrogel is expected to make a valuable contribution to the prevention of wound infections in the future.

Wild-type cutoff for Apramycin against Escherichia coli

Background

Apramycin is used exclusively for the treatment of Escherichia coli (E.coli) infections in swine around the world since the early 1980s. Recently, many research papers have demonstrated that apramycin has significant in vitro activity against multidrug-resistant E.coli isolated in hospitals. Therefore, ensuring the proper use of apramycin in veterinary clinics is of great significance of public health. The objectives of this study were to develop a wild-type cutoff for apramycin against E.coli using a statistical method recommended by Clinical and Laboratory Standards Institute (CLSI) and to investigate the prevalence of resistance genes that confer resistance to apramycin in E. coli.

Results

Apramycin susceptibility testing of 1230 E.coli clinical isolates from swine were determinded by broth microdilution testing according to the CLSI document M07-A9. A total number of 310 E.coli strains from different minimum inhibitory concentration (MIC) subsets (0.5–256 μg/mL) were selected for the detection of resistance genes (aac(3)-IV; npmA; apmA) in E. coli by PCR. The percentage of E. coli isolates at each MIC (0.5, 1, 2, 4, 8, 16, 32, 64, 128, and 256 μg/mL) was 0.08, 0.08, 0.16, 2.93, 31.14, 38.86, 12.85, 2.03, 1.46, and 10.41%. The MIC₅₀ and MIC₉₀ were 16 and 64 μg/mL. All the 310 E.coli isolates were negative for npmA and apmA gene, and only the aac(3)-IV gene was detected in this study.

Conclusions

The wild-type cutoff for apramycin against E.coli was defined as 32 μg/mL. The prevelance of aac(3)-IV gene mainly concentrated in these MIC subsets ‘MIC ≥ 64 μg/ mL’, which indicates that the wild-type cutoff established in our study is reliable. The wild-type cutoff offers interpretion criteria of apramycin susceptibility testing of E.coli.

Environmental superbugs: The case study of Pedobacter spp

The environment is one of the main reservoirs of antibiotic resistance genes (ARGs) but multidrug resistant (MDR) environmental isolates are barely characterised. As suggested by the name, Pedobacter species have been predominantly isolated from soils, but are also recovered from water (including drinking water), chilled food, fish, compost, sludge, glaciers and other extreme environments. The susceptibility phenotype of Pedobacter lusitanus NL19 (isolated from a deactivated uranium mine), its closely related species and the genus type strain were investigated. All strains are MDR bacteria, resistant to β-lactams, colistin, aminoglycosides and ciprofloxacin. Therefore, Pedobacter spp. are likely intrinsically resistant to β-lactams (including ertapenem) and to other three classes of antibiotics. 6%-8% of their total protein-encoding genes encode a diverse collection of putative ARGs, including β-lactamases. These enzymes are highly abundant in all the other Pedobacter strains with sequenced genomes, especially class C, class B3 and class A. LUS-1 and PLN-1 were further characterised in E. coli. LUS-1 is a class A β-lactamase and it conferred an increase in the MIC of cefotaxime, albeit very low. PLN-1 is a class B3 β-lactamase with carbapenemase activity, conferring resistance to ertapenem and a 66x and 16x increase in the MIC of imipenem and meropenem, respectively. PLN-1 also hydrolyses ampicillin, 1st and 3rd generation cephalosporins, and at a lower extent cephamycins and 4th generation cephalosporins. Therefore, Pedobacter spp. encode a large and diverse arsenal of resistance mechanisms that make them environmental superbugs.

Synergistic Activity of Colistin-Containing Combinations against Colistin-Resistant Enterobacteriaceae

Resistance to colistin, a polypeptide drug used as an agent of last resort for the treatment of infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacteria, including carbapenem-resistant Enterobacteriaceae (CRE), severely limits treatment options and may even transform an XDR organism into one that is pan-resistant. We investigated the synergistic activity of colistin in combination with 19 antibiotics against a collection of 20 colistin-resistant Enterobacteriaceae isolates, 15 of which were also CRE. All combinations were tested against all strains using an inkjet printer-assisted digital dispensing checkerboard array, and the activities of those that demonstrated synergy by this method were evaluated against a single isolate in a time-kill synergy study. Eighteen of 19 combinations demonstrated synergy against two or more isolates, and the 4 most highly synergistic combinations (colistin combined with linezolid, rifampin, azithromycin, and fusidic acid) were synergistic against ≥90% of strains. Sixteen of 18 combinations (88.9%) that were synergistic in the checkerboard array were also synergistic in a time-kill study. Our findings demonstrate that colistin in combination with a range of antibiotics, particularly protein and RNA synthesis inhibitors, exhibits synergy against colistin-resistant strains, suggesting that colistin may exert a subinhibitory permeabilizing effect on the Gram-negative bacterial outer membrane even in isolates that are resistant to it. These findings suggest that colistin combination therapy may have promise as a treatment approach for patients infected with colistin-resistant XDR Gram-negative pathogens.

Invitro Apramycin Activity against multidrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa

The in vitro activity of apramycin was compared to that of amikacin, gentamicin, and tobramycin against multidrug-resistant, extensively drug-resistant, and pandrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa. Apramycin demonstrated an MIC₅₀/MIC₉₀ of 8/32μg/ml for A. baumannii and 16/32μg/ml for P. aeruginosa. Only 2% of A. baumannii and P. aeruginosa had an MIC greater than an epidemiological cutoff value of 64μg/ml. In contrast, the MIC₅₀/MIC₉₀ for amikacin, gentamicin, and tobramycin were ≥64/>256μg/ml for A. baumannii with 57%, 95%, and 74% of isolates demonstrating resistance, respectively, and the MIC₅₀/MIC₉₀ were ≥8/256μg/ml for P. aeruginosa with 27%, 50%, and 57% of strains demonstrating resistance, respectively. Apramycin appears to offer promising in vitro activity against highly resistant pathogens. It therefore may warrant further pre-clinical study to assess potential for repurposing as a human therapeutic and relevance as a scaffold for further medicinal chemistry exploration.

Evaluation of apramycin activity against carbapenem-resistant and -susceptible strains of Enterobacteriaceae

We evaluated activity of apramycin, a non-ototoxic/non-nephrotoxic aminocyclitol against 141 clinical Enterobacteriaceae isolates, 51% of which were non-susceptible to carbapenems (CRE). Among CRE, 70.8% were apramycin susceptible, which compared favorably to aminoglycosides in current clinical use. Our data suggest that apramycin deserves further investigation as a repurposed, anti-CRE therapeutic.

Antibiotic susceptibility of Brachyspira hyodysenteriae isolates from Czech swine farms: a 10-year follow-up study

Brachyspira hyodysenteriae is the causative agent of swine dysentery. Loss of clinical efficacy of some antimicrobial agents authorized for treating swine dysentery was observed on certain Czech pig farms. The aim of the present study was to evaluate the antimicrobial sensitivity of six antibiotics using a set of 202 randomly selected B. hyodysenteriae isolates obtained from farms in the Czech Republic between years 1997 and 2006. Minimum inhibitory concentration of antibiotics tylosin, lincomycin, tylvalosin, chlortetracyclin, tiamulin and valnemulin were tested, using an agar dilution method. All antibiotics tested showed an increase in minimal inhibitory concentrations. Continual decrease in susceptibility of B. hyodysenteriae isolates to tiamulin and valnemulin was observed. Multiresistant B. hyodysenteriae were isolated more frequently in the past years. Only a careful use of antibiotics can ensure their efficacy, especially in case of pleuromutilins, in the strategic therapy of swine dysentery. This rare study demonstrates the minimal inhibitory concentration changes of selected antidysenterics among Czech isolates of Brachyspira hyodysenteriae during a ten-year period.

Susceptibility of bacteria isolated from pigs to tiamulin and enrofloxacin metabolites

Susceptibilities to metabolites of tiamulin (TIA) and enrofloxacin (ENR) were tested using selected bacteria with previously defined minimal inhibitory concentrations (MIC). The TIA metabolites tested were: N-deethyl-tiamulin (DTIA), 2beta-hydroxy-tiamulin (2beta-HTIA) and 8alpha-hydroxy-tiamulin (8alpha-HTIA), and the ENR metabolites were: ciprofloxacin (CIP) and enrofloxacin N-oxide (ENR-N). Bacteria, all of porcine origin, were selected as representatives of bacterial infections (Staphylococcus hyicus and Actinobacillus pleuropneumoniae), zoonotic bacteria (Campylobacter coli) and indicator bacteria (Escherichia coli and enterococci). Furthermore the effects of these compounds were tested on the microbial community of active sludge to test any negative effect on colony forming units (CFU). DTIA had a potency of 12.5-50% of the potency of TIA. 2beta-HTIA and 8alpha-HTIA had potencies less than 1% of the potency of TIA. ENR-N had a potency of 0.75-1.5% of the potency of ENR, while CIP and ENR had similar potencies. Results obtained here indicate that CIP and DTIA could contribute to the selective pressure for upholding antimicrobial resistant bacteria in animals under ENR or TIA treatment. The most potent metabolites CIP and DTIA showed considerable potencies against activated sludge bacteria compared to the parent compounds. EC(50) (microg/ml) for ENR, CIP, TIA and DTIA were 0.018 [95% CI: 0.028-0.149], 0.064 [95% CI: 0.007-0.046], 6.0 [95% CI: 3.6-9.8], and 9.7 [95% CI: 5.8-16.3], respectively. This indicates that the compounds can change the bacterial population in the sludge, and hereby alter the properties of the sludge.

Pulmonary disposition of tilmicosin in foals and in vitro activity against Rhodococcus equi and other common equine bacterial pathogens

The objectives of this study were to determine the serum and pulmonary disposition of tilmicosin in foals and to investigate the in vitro activity of the drug against Rhodococcus equi and other common bacterial pathogens of horses. A single dose of a new fatty acid salt formulation of tilmicosin (10 mg/kg of body weight) was administered to seven healthy 5- to 8-week-old foals by the intramuscular route. Concentrations of tilmicosin were measured in serum, lung tissue, pulmonary epithelial lining fluid (PELF), bronchoalveolar lavage (BAL) cells, and blood neutrophils. Mean peak tilmicosin concentrations were significantly different between sampling sites with highest concentrations measured in blood neutrophils (66.01+/-15.97 microg/mL) followed by BAL cells (20.1+/-5.1 microg/mL), PELF (2.91+/-1.15 microg/mL), lung tissue (1.90+/-0.65 microg/mL), and serum (0.19+/-0.09 microg/mL). Harmonic mean terminal half-life in lung tissue (193.3 h) was significantly longer than that of PELF (73.3 h), bronchoalveolar cells (62.2 h), neutrophils (47.9 h), and serum (18.4 h). The MIC90 of 56 R. equi isolates was 32 microg/mL. Tilmicosin was active in vitro against most streptococci, Staphylococcus spp., Actinobacillus spp., and Pasteurella spp. The drug was not active against Enterococcus spp., Pseudomonas spp., and Enterobacteriaceae.

Decreased susceptibility to tiamulin and valnemulin among Czech isolates of Brachyspira hyodysenteriae

The agar dilution method was used to investigate the sensitivity to pleuromutilins of 100 isolates of Brachyspira hyodysenteriae isolated from 63 pig farms between 1997 and 2001. In the period under investigation, MICs to both tiamulin and valnemulin increased, with differences between the periods 1997-98 and 1999-2001 being statistically significant (P < 0.001 for tiamulin and P < 0.0001 for valnemulin). Between 1997 and 2001, the MIC50 and MIC90 of tiamulin increased from 0.062 and 0.25 microg ml, respectively, to 1.0 and 4.0 microg ml. Valnemulin MIC50 and MIC90 were < or = 0.031 microg ml in 1997 and by 2001 were respectively, 2.0 and 8.0 microg ml. The increase in MICs of tiamulin and valnemulin demonstrated in this study reflect the intensity of pleuromutilin use in the treatment of swine dysentery in the Czech Republic.

Comparison of in vitro activities of ketolides, macrolides, and an azalide against the spirochete Borrelia burgdorferi

Two ketolides, three macrolides, and one azalide were tested in vitro against 17 isolates of the B. burgdorferi s.l. complex. As measured in micrograms per milliliter, activity was highest for cethromycin (MIC at which 90% of the tested isolates were inhibited [MIC(90)], 0.0019 micro g/ml) and telithromycin (MIC(90), 0.0078 micro g/ml). Electron-microscope analysis and time-kill studies also supported enhanced effectiveness of both ketolides.

Antimicrobial susceptibility testing of porcine Brachyspira (Serpulina) species isolates

No standardized method for susceptibility testing of Brachyspira spp. is currently available. A broth dilution procedure was evaluated and used to test the activities of six antimicrobial agents for 108 isolates of Swedish porcine Brachyspira spp. representing biochemical groups I, II, and III. Group I corresponds to Brachyspira hyodysenteriae, group II corresponds to B. intermedia, and group III corresponds to B. murdochii and B. innocens. A panel was designed with the antimicrobial agents dried in tissue culture trays with wells that allowed a liquid volume of 0.5 ml in each and agitation of the broth when incubated on a shaker. The MICs were determined by using brain heart infusion broth with 10% fetal calf serum. For 10 isolates, the results obtained in broth were compared to the MICs obtained on two different types of agar. Different inoculum densities and incubation times were also compared. The concentrations at which 90% of the B. hyodysenteriae isolates (n = 72) were inhibited in the broth dilution test by tiamulin (0.25 micro g/ml), tylosin (>256 micro g/ml), erythromycin (>256 micro g/ml), clindamycin (>4 micro g/ml), virginiamycin (4 micro g/ml), and carbadox (0.06 micro g/ml) were determined. The MICs tended to be lower in broth than on agar. Differences in inoculum densities and incubation times had little influence on the MICs. The evaluated broth dilution test was simple to perform, the end points were easily read, and the results were reproducible and reliable. No isolates with decreased susceptibility to tiamulin were found among the Swedish isolates tested.

In vitro activity of eight oral cephalosporins against Borrelia burgdorferi

Oral cephalosporins have not previously been extensively tested against larger numbers of Borrelia burgdorferi isolates derived from different clinical and geographical sources. This study investigated the in vitro activity of eight oral cephalosporins in addition to ceftriaxone and apramycin, against 17 isolates of the B. burgdorferi complex, including one B. valaisiana and one B. bissettii tick isolate. Minimal inhibitory concentrations and minimal borreliacidal concentrations providing 100% killing of the final inoculum were determined by a standardised methodology in Barbour-Stoenner-Kelly-medium after 72 h of incubation. The rank order of potency was ceftriaxone>cefuroxime-axetil>cefixime, cefdinir>cefpodoxime>cefaclor >ceftibuten, loracarbef>cefetamet-pivoxil, apramycin. Our study demonstrates the superior in vitro effectiveness of ceftriaxone with good to excellent activity with the oral agents cefuroxime-axetil, cefixime and cefdinir against B. burgdorferi under strictly standardised test conditions.