346
Correspondence
activity than the preparation from the other culture and activity losses were lower for this lower activity enzyme at the undiluted and ten-fold diluted levels. In addition, the solutions of TEM enzyme contained the most protein and had the lowest specific activity; this enzyme suffered the lowest activity losses, although this might have been related to the enzyme structure rather than to specific activity. Changing the buffer concentration to 0-15, 005 or 001 M had relatively little effect on losses. Addition of 0 1 % (w/v) gelatin helped to reduce loss of activity both on sterile filtration and on freeze-drying. The results summarized above show that solutions of p-lactamases of at least three different Gram-negative bacteria can be sterile filtered or freeze-dried to give preparations of P-lactamase that are still highly effective and can have both penicillinase and cephalosporinase activity. M. G. BOULTON G. W. ROSS Microbiology Department Glaxo Research Ltd Greenford, Middlesex, England References Datta, N. & Richmond, M. H. Purification and properties of penicillinase whose synthesis is mediated by an R-factor in Escherichia colt. BlochemicalJournal 98: 204-9 (1966). Hamilton-Miller, J. M. T. & Brumfitt, W. Contaminated P-lactamase and blood cultures. British Medical Journal Hi: 410 (1974). Lynn, R. & Eykyn, S. Contamination of blood cultures from a commercial P-lactamase preparation. British Medical Journal Hi: 46 (1974). Marshall, M. J., Ross, G. W., Chanter, K. V. & Harris, A. M. Comparison of the substrate specificities of the P-lactamases from Klebsiella aerogenes 1082E and Enterobacter cloacae P99. Applied Microbiology 23: 765-9 (1972). O'Callaghan, C. H., Muggleton, P. W. & Ross, G. W. Effects of P-lactamases from Gramnegative organisms on cephalosporins and penicillins. In Antimicrobial Agents and Chemotherapy Ed. Hobby, G. L. American Society for Microbiology (1968), pp. 57-63. Richmond, M. H. & Sykes, R. B. The P-lactamases of Gram-negative bacteria and their possible physiological role. Advances in Microbial Physiology 9: 31-88 (1973). Ross, G. W. & Boulton, M. G. Purification of Plactamases on QAE-Sephadex. Blochimica et Biophysica Acta 309: 430-9 (1973).
Long-term co-trimoxazole and folate depletion Dear Sir, D. T. D. Hughes and his colleagues (Journal of Antimicrobial Chemotherapy 1, 55) have
shown clearly that folate depletion is a risk in patients taking co-trimoxazole for 3 months or longer. The mean serum folate during treatment was lower than the mean pre-treatment level in 6 of their 11 patients, but only 3 of these showed other changes which taken together suggested that some folate deficiency had developed. The authors therefore recommend that the drug should be used cautiously in patients with borderline folate deficiency, such as pregnant women, alcoholics, the elderly and the undernourished, and that the haemoglobin, white blood count, polymorph lobe count and serum folate should be monitored monthly in all patients taking co-trimoxazole for longer than 3 months. These recommendations are logical, but I wonder whether it is necessary or desirable to burden haematological laboratories with the work that the second one entails. It would surely be simpler and cost far less if haematological measurements were made initially (perhaps of Hb and serum folate), and thereafter a modest regular folic acid supplement were given as long as treatment with cotrimoxazole continued. This would not impair the antimicrobial activity of the drug, since bacteria cannot utilize folic acid. There is an obvious analogy with the prophylactic use of folic acid together with oral iron in pregnancy. However, it might be desirable to measure the serum-Bn level at the start of treatment with co-trimoxazole and a folic acid supplement, to minimize the risk of harming a patient with vitamin B u deficiency. A. HERXHEIMER Department of Pharmacology and Therapeutics London Hospital Medical College London El 2AD, England
Chemical detection of p-lactamase activity on Haemophilus influenza* Dear Sir, Because of the importance of rapidly determining whether Haemophilus influenzae Type
B infections are likely to respond to ampicillin therapy, chemical methods have been used to demonstrate the presence of p-lactamase and thereby predict resistance to ampicillin.
Correspondence
activity than the preparation from the other culture and activity losses were lower for this lower activity enzyme at the undiluted and ten-fold diluted levels. In addition, the solutions of TEM enzyme contained the most protein and had the lowest specific activity; this enzyme suffered the lowest activity losses, although this might have been related to the enzyme structure rather than to specific activity. Changing the buffer concentration to 0-15, 005 or 001 M had relatively little effect on losses. Addition of 0 1 % (w/v) gelatin helped to reduce loss of activity both on sterile filtration and on freeze-drying. The results summarized above show that solutions of p-lactamases of at least three different Gram-negative bacteria can be sterile filtered or freeze-dried to give preparations of P-lactamase that are still highly effective and can have both penicillinase and cephalosporinase activity. M. G. BOULTON G. W. ROSS Microbiology Department Glaxo Research Ltd Greenford, Middlesex, England References Datta, N. & Richmond, M. H. Purification and properties of penicillinase whose synthesis is mediated by an R-factor in Escherichia colt. BlochemicalJournal 98: 204-9 (1966). Hamilton-Miller, J. M. T. & Brumfitt, W. Contaminated P-lactamase and blood cultures. British Medical Journal Hi: 410 (1974). Lynn, R. & Eykyn, S. Contamination of blood cultures from a commercial P-lactamase preparation. British Medical Journal Hi: 46 (1974). Marshall, M. J., Ross, G. W., Chanter, K. V. & Harris, A. M. Comparison of the substrate specificities of the P-lactamases from Klebsiella aerogenes 1082E and Enterobacter cloacae P99. Applied Microbiology 23: 765-9 (1972). O'Callaghan, C. H., Muggleton, P. W. & Ross, G. W. Effects of P-lactamases from Gramnegative organisms on cephalosporins and penicillins. In Antimicrobial Agents and Chemotherapy Ed. Hobby, G. L. American Society for Microbiology (1968), pp. 57-63. Richmond, M. H. & Sykes, R. B. The P-lactamases of Gram-negative bacteria and their possible physiological role. Advances in Microbial Physiology 9: 31-88 (1973). Ross, G. W. & Boulton, M. G. Purification of Plactamases on QAE-Sephadex. Blochimica et Biophysica Acta 309: 430-9 (1973).
Long-term co-trimoxazole and folate depletion Dear Sir, D. T. D. Hughes and his colleagues (Journal of Antimicrobial Chemotherapy 1, 55) have
shown clearly that folate depletion is a risk in patients taking co-trimoxazole for 3 months or longer. The mean serum folate during treatment was lower than the mean pre-treatment level in 6 of their 11 patients, but only 3 of these showed other changes which taken together suggested that some folate deficiency had developed. The authors therefore recommend that the drug should be used cautiously in patients with borderline folate deficiency, such as pregnant women, alcoholics, the elderly and the undernourished, and that the haemoglobin, white blood count, polymorph lobe count and serum folate should be monitored monthly in all patients taking co-trimoxazole for longer than 3 months. These recommendations are logical, but I wonder whether it is necessary or desirable to burden haematological laboratories with the work that the second one entails. It would surely be simpler and cost far less if haematological measurements were made initially (perhaps of Hb and serum folate), and thereafter a modest regular folic acid supplement were given as long as treatment with cotrimoxazole continued. This would not impair the antimicrobial activity of the drug, since bacteria cannot utilize folic acid. There is an obvious analogy with the prophylactic use of folic acid together with oral iron in pregnancy. However, it might be desirable to measure the serum-Bn level at the start of treatment with co-trimoxazole and a folic acid supplement, to minimize the risk of harming a patient with vitamin B u deficiency. A. HERXHEIMER Department of Pharmacology and Therapeutics London Hospital Medical College London El 2AD, England
Chemical detection of p-lactamase activity on Haemophilus influenza* Dear Sir, Because of the importance of rapidly determining whether Haemophilus influenzae Type
B infections are likely to respond to ampicillin therapy, chemical methods have been used to demonstrate the presence of p-lactamase and thereby predict resistance to ampicillin.
