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Biomedical subjects

H S Ragheb

Publications and source records attributed to H S Ragheb.

At least 19 recordsLinked to original sources
PubMed1989

Determination of virginiamycin in combination with chlortetracycline in feeds by anion-exchange chromatography.

Standard additions experiments for chlortetracycline hydrochloride and virginiamycin at a ratio of 16:1 showed a positive bias for both the plate and turbidimetric methods. The bias was eliminated by anion-exchange chromatography in both the presence and absence of feed components. When chlortetracycline and virginiamycin pre-mixes were used for fortification of laboratory-prepared feeds at chlortetracycline to virginiamycin ratios of 8 or 16:1, the recovery of virginiamycin, without treatment, was 93-100% using the plate assay and 181-236% with the turbidimetric method. The corresponding values obtained using anion-exchange chromatography were 89-99 and 85-91%, respectively. The anion-exchange technique is necessary if the turbidimetric method is used for the assay.

Animal Feed↗
PubMed1981

Bacitracin determination in feeds: evaluation of methods.

Assay of bacitracin activity in feeds is subject to many sources of variation. Bacitracin standards are complex mixtures and may contain various amounts of less active forms of bacitracin. Test organisms may respond differently to these mixtures. Collaborative studies should involve the use of one standard, perhaps USP zinc bacitracin. The use of different types of bacitracin standards (regular or zinc) in a laboratory may contribute to variation in sample potency. The pyridine extraction method is subject to serious operational difficulties. Among the contributing factors are incomplete evaporation of pyridine (causing positive bias), allowing the temperature to increase too much during evaporation (causing negative bias), and the numerous manipulative steps in the technique (causing large variability). Because of these factors and the toxic properties of pyridine, the method finds little use. Methanol extraction offers a better substitute for determining zinc or methylene disalicylate bacitracin in premixes and complete feeds by the plate method.

Animal Feed↗
PubMed1980

Evaluation of methanol extraction for determination of bacitracin in feeds.

Five laboratories evaluated methanol extraction for the determination of zinc and methylene disalicylate (MD) bacitracn in swine and poultry feeds at 100 g/ton and 2 premixes labeled 50 g/lb (MD bacitracin) and 40 g/lb (zinc bacitracin). Bacitracin activity was determined on each of 2 days with 2 dilutions on each day. No significant difference was found between dilutions within a day or between days for each sample. The kind of bacitracin or type of feed did not significantly affect results.

Animal Feed↗
PubMed1980

Some factors affecting assay variability in the determination of chlortetracycline in premix feeds.

There are many sources of error in the microbiological determination of high levels of chlortetracycline in premix. Among the critical factors that can be controlled by the analyst are careful weighing of the reference standard and careful dosing of cylinders. A spectrophotometric approach and automatic filling of cylinders are suggested to ensure proper monitoring of these operations. Among factors that cannot be controlled by the analyst is the assay design. A 3-point design which is a modified version of the (3+3) design is considered, and its advantages are illustrated.

Animal Feed↗
PubMed1979

Microbiological assays for antibiotics and vitamins: considerations for assuring accuracy.

Factors that may influence the accuracy and precision of microbiological manual and semiautomated turbidimetric methods as well as diffusion assays are discussed. Influence of kind of equipment, media, test bacteria, sample preparation, form of dose response lines, operations, and personnel on quality of assays is examined with the objective of reducing to insignificance those factors under control of the analyst that are responsible for low quality assays.

Anti-Bacterial Agents↗
PubMed1979

Determination of virginiamycin in feeds.

Virginiamycin was extracted from the feed by ethanol-pH 2.5 phosphate buffer (1 + 1). The pH during extraction was adjusted (when necessary) to between 4 and 5. Sample dilutions and the standard dose response line were prepared to contain ethanol pH 6 phosphate buffer (2 + 8), and the test organism was Sarcina lutea. Three feeds (a poultry ration, a swine finishing ration, and a swine starter ration) showed virginiamycin recovery of 88.8--108.9% when standard solutions were added at concentrations of 4.54--90.8 g/ton. The coefficient of variation (4--20%) was larger for low potency feeds (10 g/ton) compared to the higher feeds (100 g/ton). Similarly, excellent recovery was obtained when the swine starter feed was fortified by a commercial premix. Amprolium, roxarsone, and monensin can be present at 20 times the concentration of virginiamycin with little or no interference in the antibiotic determination. Lasalocid at 10 times the concentration of virginiamycin caused a slightly positive bias (recovery, 107.4%).

Animal Feed↗
PubMed1979

Pyridine extraction method for determination of bacitracin in feeds: collaborative evaluation.

Seventeen laboratories evaluated the pyridine extraction method and neomycin-sensitized agar for the determination of zinc and MD bacitracin in swine and broiler rations at 10 and 100 g/ton. The method was also applied to the analysis of 2 premixes labeled 50 g/lb (MD bacitracin) and 40 g/lb (zinc bacitracin). Bacitracin activity was determined on each of 2 days with 2 dilutions on each day. No significant difference was found between dilutions within a day or between days for each sample. The type of bacitracin or type of feed did not significantly affect results. The difference in results between MD and zinc bacitracin in premixes approached significance. The large coefficients of variation for premixes (ca 13%) and complete feeds (ca 15--30%) indicate operational problems. The main difficulty was evaporation of pyridine. Some laboratories were not able to evaporate it completely, whereas others lost bacitracin activity, probably due to high temperature of drying. The pyridine extraction method as in 42.200 and 42.204 should be discontinued.

Animal Feed↗
PubMed1977

Microbiological plate and turbidimetric assays of chlortetracycline in feeds: collaborative study.

The manual and automated turbidimetric assays and a modified official plate assay for chlortetracycline (CTC-HCl) in feed were collaboratively studied. Three feed samples (swine feed, 100 g CTC-HCl/ton; premix I, 20 g each of CTC-HCl and sulfamethazine/lb, and 10 g penicillin/lb; and premix II, 50 g CTC-HCl/lb) were analyzed at 2 dilutions. Twelve laboratories conducted the plate assay; 8 laboratories the manual turbidimetric method; and 7 laboratories, the Autoturb analysis. Within a method, there was no significant difference between dilutions. Between methods, there was a significant difference between the manual turbidimetric plate assays only for swine feed. However, the same sample dilutions or the average values of the 2 dilutions for both methods showed no statistical difference. Among the collaborators, the slope of CTC-HCl standard curve varied between about 2.0 and 3.0 for the plate method. The turbidimetric assay has been adopted as official first action for feeds containing larger than or equal to 20 g CTC-HCl/lb.

Animal Feed↗
PubMed1976

Turbidimetric and diffusion assay of bacitracin in feeds.

A manual turbidimetric method for determining zinc or methylene disalicylate bacitracin in feeds was developed. When zinc ions (10-4M) were added to the medium and the phosphate ion concentration in standard solutions was decreased to 1%, the median response of Streptococcus faecalis was about 0.038 unit. Feeds analyzed by the turbidimetric assay should be prewashed with petroleum ether and extracted with pyridine as in 42.204. Zinc bacitracin standards added to swine and broiler rations were recovered at 93.1-102.6% by the turbidimetric method. Excellent agreement between the manual turbidimetric method and the plate assay was also obtained for finished feeds containing the zinc or methylene disalicylate salt of the antibiotic. The turbidimetric method appears to have high accuracy and precision. It is more rapid and less costly than the plate assay.

Animal Feed↗
PubMed1976

Modified assay medium for the turbidimetric assay of chlortetracycline in feeds.

In previous experiments, the turbidimetric method for determining chlortetracycline-HCI (CTC-HCI) in feeds showed lower recovery than the AOAC plate method. Although the addition of vitamins to the turbidimetric medium improved results, values by the turbidimetric method remained about 10% lower than by the plate method. A modified (1.7X the weight recommended by the manufacturer) turbidimetric assay medium decreased assay sensitivity but did not significantly change the slope of S. aureus response to CTC-HCI. There was no evidence that vitamin fortification of the modified medium had any significant effect on the growth rate of test organism. Examination of about 100 samples of commercial feeds containing CTC-HCI showed excellent agreement in results between the turbidimetric and plate methods.

Animal Feed↗
PubMed1975

Microbiological turbidimetric analysis of low chlortetracycline concentrations in feeds.

Recovery studies in which chlortetracycline hydrochloride (CTC-HCI) standard was added to cattle and swine feed supplements at 4.09-9.99 g/ton showed lower antibiotic recovery turbidimetrically (80.6-98.7%) than by the AOAC modified standard as in 38.179(d) (91.2-98.7%) and the plain buffer as in 38.179(b) (93.8-133.0%) methods. Three feeds fortified with a commercial premix at the levels of 5.0 and 10.0 g CTC-HCI/ton showed an overall CTC-HCI recovery of 87.6-110.6% by manual turbidimetric assay. Results were 89.1-108.7% by the AOAC inactivated feed diluent standard and 95.4-125.4% by the plain buffer methods. For some sample extracts (as in cattle feed) the use of heat to stop bacterial growth in the turbidimetric method caused formation of a precipitate. Cooling of cultures to room temperature and rapid reading of sample turbidity followed by standard curve concentrations minimized this interference. The manual turbidimetric assay of low levels of CTC-HCI in feeds appears to offer advantages over other methods.

Animal Feed↗
PubMed1968

Cellular fatty acid composition and identification of rumen bacteria.

The fatty acid compositions of 21 pure cultures of rumen bacteria, representing 12 genera and 14 species, were compared as methyl esters. Each organism possessed a consistent and reproducible fatty acid profile. Overlapping similarities and differences in composition did not allow differentiation between families or genera. Although species differentiation was possible, fatty acid composition appeared to be only an aid in the identification of bacteria.

Animals↗