Antibiotic residues and their recovery from animal tissues

Bioactivity-based screening of antibiotics and hormones

Bioactivity-based screening methods are relatively cheap, quick and easy to use tools. Especially with respect to antimicrobial residues and compounds with hormonal activity, they form a very cost-effective alternative to physical chemical methods in large-scale surveillance and monitoring programs, where their main purpose is to identify samples that require additional chemical confirmation. A major advantage is their intrinsic capability to detect unknown compounds and new hazards. This review shows an overview of the available methods and their potential and limitations for regulatory control.

The effect of some antibiotics on Enterococcus faecium SF 68 inoculated in germ-free mice

A strain of Enterococcus faecium SF 68 (sensitive to penicillin, tetracycline, virginiamicin and tylosin, but resistant to streptomycin) was administered to five groups of germ-free mice. Each group was subsequently given 40 micrograms/ml and then 80 micrograms/ml of a single antibiotic. The following determinations were made: a) colonization of the bacterial strain before and after administration of the antibiotic and b) the MICs in the original strain and after administration of the antibiotic (80 micrograms Iml). The results show that in the mice treated with streptomycin, colonization is not influenced by the antibiotic treatment; in mice treated with antibiotics to which the strain is sensitive, the colonization increases in proportion to the level of the antibiotic resistance (tylosin and tetracycline).

Chromatographic methods of analysis for penicillins in food-animal tissues and their significance in regulatory programs for residue reduction and avoidance

Chromatographic methods for penicillin analysis in animal tissues play a significant role in the regulation of the use of these drugs in livestock production. Regulatory agencies rely on data generated from these methods to establish withdrawal times and to determine whether presumptive positive tissue samples from slaughtered animals intended for human consumption contain violative levels of penicillins to necessitate regulatory action. The need to develop sensitive, accurate, and reliable methods to support regulatory programs is examined together with emerging techniques that could be taken advantage of to improve the sensitivity and usefulness of current chromatographic methods for tomorrow's regulatory agency.

Minimum antibiotic levels for selecting a resistance plasmid in a gnotobiotic animal model

The minimum antibiotic concentrations for selecting an R plasmid in vivo were determined in germfree mice colonized by two isogenic strains of Escherichia coli, one of which carried an R plasmid. Seventy groups of three gnotobiotic mice were given low doses of ampicillin, colistin, flumequin, gentamicin, tetracycline, or streptomycin via drinking water for 2 weeks. The equilibrium between susceptible and resistant populations of bacteria was monitored daily in feces and compared with that of control mice given pure water. This model yielded reproducible data, and dose and response were strongly correlated. The minimum selecting doses ranged from 0.9 to 12.8 micrograms/ml of water, depending on the antibiotic and the R plasmid. The use of mathematical models and complementary in vitro experiments accounted for the effect of the low antibiotic levels.

Antibiotic residues and drug resistance in human intestinal flora

The effect of residual levels of ampicillin on the drug resistance of fecal flora was studied in human volunteers given 1.5 mg of ampicillin orally per day for 21 days. This treatment failed to have any significant reproducible effect on the number of resistant Escherichia coli in their feces. The effect of continuous administration of small doses of ampicillin, chlortetracycline, or streptomycin in the drinking water was studied in gnotobiotic mice inoculated with a human fecal flora. In this animal model, which is free of many interfering factors, an increase in the fecal concentration of resistant E. coli was observed when the mice were given 0.5 microgram of ampicillin or chlortetracycline per ml of water. This model is therefore a sensitive system for testing the effect of antimicrobial drugs on the resistance characteristics of the intestinal flora.

Determination of penicillin G and cloxacillin residues in beef and pork tissue by high-performance liquid chromatography

Tissues were homogenized and then deproteinized with acetonitrile. The acetonitrile extract was partitioned between dichloromethane and pH 2.2 buffer and then extracted with pH 7 buffer. After addition of ammonium sulfate to the aqueous solution, it was mixed with acetonitrile. The acetonitrile extract was separated and evaporated, and the residue was taken up in water. The aqueous solution was analyzed by high-performance liquid chromatography (HPLC) on a C18, 10-microns particle size, reversed-phase column using gradient elution with 0.01 M orthophosphoric acid-acetonitrile (from 80:20 to 40:60 in 20 min) at a flow-rate of 1 ml/min and UV absorbance detection at 220 nm. Recoveries were generally greater than 90% with all tissues. Data on incurred residues from a treated cow showed recoveries of penicillin which were frequently several times higher by HPLC than by bioassay. Sensitivity limits in muscle were about 0.05 ppm for both penicillin G and cloxacillin, but higher in liver and kidney because of interferences. The method is suitable for other monobasic penicillins but not for dibasic or amphoteric penicillins.

Effect of cooking and cold storage on biologically active antibiotic residues in meat

An investigation was undertaken to see if cooking or cold storage would destroy or decrease the level of biologically active antibiotic in tissues from animals given therapeutic doses of antibiotic on three occasions prior to slaughter. The effects of cooking and cold storage on the biological activity of the residues of ampicillin, chloramphenicol, oxytetracycline, streptomycin and sulphadimidine were varied; in some instances the effects were minimal, in others nil.