Microbiological methods of assay in clinical medicine with particular reference to the investigation of deficiency of vitamin B12 and folic acid

THE URINARY EXCRETION AND TISSUE RETENTION OF CYANOCOBALAMIN BY SUBJECTS GIVEN REPEATED PARENTERAL DOSES

The urinary excretion of injected cyanocobalamin was studied in 30 previously untreated vitamin B(12)-deficient patients by measuring the urinary radioactivity after repeated injections of (58)Co vitamin B(12). The dose range used was 54 to 30,000 mug., each patient receiving the same dose at each injection. The results show that there is no constant trend to the excretion of greater or smaller proportions of the amount injected. It is also shown that there is a wide variation in the amounts excreted by each individual and between individual patients and that the capacity of the tissues to retain injected cyanocobalamin is very great, the amounts retained often being greatly in excess of the normal body stores. The excretion of radioactivity after parenteral infections of (58)Co vitamin B(12) was usually complete within 24 hours but exceptions to this were seen. The significance and value of the results is discussed.

INVESTIGATIONS INTO THE EUGLENA METHOD FOR THE ASSAY OF THE VITAMIN B12 IN SERUM

Details are given of a modified Euglena method for the assay of B(12) in serum. Serum in very small quantities is usually inhibitory to the growth of the Euglena. In general, this inhibition is most marked when the organism is growing prolifically. For estimating serum B(12) values, a standard curve is used from B(12) standards containing 0.01 ml. of serum of low B(12) content, so that growth in test serum solutions is compared with growth in serum-containing standards. The recovery of B(12) added to serum, incomplete when estimated from aqueous standards, is now complete and the variation in results from batch to batch is markedly reduced. Various factors-such as medium, light, and inoculum-can affect growth in aqueous and serum solutions differently and are an important cause of variations between batches and laboratories. Optimal conditions were studied and they are essential for the most sensitive and accurate assay, but if the results are estimated from serum-containing standards accurate values can be obtained even under less than optimal conditions. Subnormal serum B(12) concentrations can be detected visually as early as 24 hours after the start of assay. For diagnostic purposes the assay can be read at three days, provided that appropriate dilutions are used, conditions are optimal, and growth is measured in a 1 cm. cell.

Vitamin B12 in human colostrum and milk. Quantitation of the vitamin and its binder and the uptake of bound vitamin B12 by intestinal bacteria

The concentration of vitamin B12 was measured by microbiological assay in 229 samples of normal human colostrum and milk taken at various stages of lactation. Colostrum obtained within 48 hours of delivery contains high concentrations of vitamin B12 (mean 2 431 pg/ml), but within a few days the levels fall to a range similar to the levels in normal serum. The vitamin B12 binding capacity of 111 samples of colostrum and milk was estimated by gel filtration or charcoal binding. Colostrum samples have a mean binding capacity of 72 ng/ml, while the binding capacity in milk is only one third of this value. The ability of a range of intestinal bacteria to take up colostrum-bound vitamin B12, was assessed. All the organisms took up free vitamin B12, but when the vitamin was bound in colostrum, there was little or no uptake even after 24 hours incubation.

An automated microbiological method for the measurement of vitamin B12

An automated method for the microbiological assay of vitamin B(12) is described. A chloramphenicol-resistant strain of Lactobacillus leichmannii is used as the test organism and this eliminates the need for sterilization or aseptic addition. Precipitation of the serum protein is avoided by dilution of the serum with a glutamic/malic acid solution before heating the preparation to free the vitamin B(12). Tests can be set up at a rate of 80 an hour and after incubation they can be read at 160 an hour. By interfacing a programmed electronic calculator directly with the Mecolab M which is used for the assays, results are printed directly in ng/l.

Long-term trimethoprim-sulphamethoxazole in the management of recurrent urinary infection

Nineteen patients with recurring urinary infections were treated with trimethoprim-sulphamethoxazole in full dosage for 6 months. In 14 (Group I) the upper urinary tract was structurally abnormal and in 5 (group II), the I.V.P. showed no abnormality. In Group I the response rate was initially 70 per cent but had fallen to 30 per cent by the end of the treatment period. In group II all patients responded initially and 4 out of the 5 maintained sterile cultures over the period of treatment. Side effects were not serious and in particular, no haematological anomalies were noted in any patient throughout the 6 months of treatment.

The folate status of alcoholics

Plasma and erythrocyte folate levels and plasma vitamin B12 levels have been studied in a group of 50 well motivated alcholics admitted to a psychiatric unit for the treatment of alcoholism. Sixty-six per cent of the patients had abnormal liver function tests and 12 per cent had neurological complications. The folate status of the alcoholics did not differ significantly from that of 40 healthy blood donors, and was unrelated to the degree of impairment of liver function.

Sulphamethoxazole-trimethoprim therapy in urinary tract infection with reference to its haematological effects

The bacteriological and haematological effects of 7 days' treatment with trimethoprim and sulphamethoxazole in a combination of 1 : 5 (13 patients) or 1 : 10 (12 patients) has been investigated in 25 women with significant urinary tract infection. The organisms were Escherichia col***l (23 patients), Klebsiella aerogenes (1 patient) and Proteus mirabilis (1 patient). All 18 primary isolates tested were sensitive to the drug combination in vitro although 3 were resistant to sulphatriad. Twenty-four out of 25 (96%) had sterile urine at 5 days and 80 per cent remained sterile 7 days after therapy. At least 30 per cent recurred within 6 weeks. No significant change was seen in haemoglobin levels, platelet counts or in the percentage of neutrophil polymorphonuclear leucocytes. Sixty-five per cent of patients had low serum folate levels prior to therapy, a finding which may be related to the presence of significant bacteriuria. Following treatment, however, there was a reduction in serum folate levels in both groups which was significant at the 5 per cent level 3 to 7 days after treatment with the 1 : 10 regime and 3 days after treatment with the 1 : 5 regime. It is suggested that it might be advisable in any patient in whom the drug is given on a long-term basis to consider the possibility of haematological side effects.

Gastroenterostomy and vagotomy for chronic duodenal ulcer

Images

Results with radioisotopic assay of serum B12 using serum binding agent

Results obtained with a radioisotope method for assay of serum vitamin B(12) (Ekins and Sgherzi, 1965) are described. This method, which uses serum as binding agent, is simple, easy to set up, and suitable for routine diagnostic use. It gives results extremely similar to those obtained with standard microbiological assays.

Chromatography and microbiological assay of vitamin B12 in smokers

Images

Rapid microbiological assay of serum vitamin B 12 by electronic counter

A new method of measuring the growth of Lactobacillus leichmannii is reported. Its adoption for the estimation of serum vitamin B(12) levels shortens the incubation period required to five hours at 45 degrees C. The method is compared statistically with a standard method of estimation, requiring incubation at 37 degrees C., by duplicate determinations on 106 hospital patients. The significance of the apparently decreased accuracy of the new method at low serum levels is discussed, and a re-appraisal of the optimum growth temperature of Lactobacillus leichmannii suggested.