- Email: [email protected]
MAGIC SHOTGUN PELLETS
1414
predictable event" which, as I stressed at the start of my letter, is responsible for a high proportion of myocardial in farcts. Foster suggests that phenothiazines might benefit myocardial infarction by protecting against the deleterious effects of hypoxia on mitochondria. This is perfectly possible, as is yet another mechanism-namely, that a membrane-stabilising effect diminishes the incidence of arrhythmias. The purpose of my letter was to point out the connection between the antihxmolytic action of chlorpromazine-like drugs and the associated inhibition of platelet thrombosis which can be demonstrated, even in conditions such as those in artificial blood-vessels, in which thrombogenic constituents such as collagen of arterial walls cannot be involved. Department of Pharmacology, King’s College,
G. V. R. BORN
London WC2R 2LS
CHLORIURETIC OR NATRIURETIC HORMONE?
SIR,-Dr Grekin and colleagues (May 26, p. 1116) propose that hyposecretion or hypersecretion of a hypothetical chloriuretic hormone might account for Bartter’s syndrome, Gordon’s syndrome, and hyporeninxmic hypoaldosteronism. This’ is an interesting hypothesis, although the chloriuretic hormone concept is by no means new. What we find surprising is their proposal that chloriuretic hormone is identical to natriuretic hormone. Although one would expect a chloriuretic hormone to act on the ascending limb of the loop of Henle, as they suggest, most evidence points to a more distal site of action for natriuretic hormone-e.g., the direct demonstration of inhibition of active sodium transport in the collecting tubule.2 Indirect evidence would also suggest a distal site of action, the inhibition of sodium reabsorption during volume expansion, a potent stimulus to natriuretic hormone production, occurring also chiefly in the collecting duct. 3,4 Furthermore, several groups have shown that natriuretic hormone directly inhibits the sodium-transporting enzyme sodium-potassium A.T.p.ase,s-’ suggesting that any effect on chloride transport would be a secondary effect. Although chloriuretic and natriuretic hormones may well both exist, we see little reason to propose that "natriuretic hormone be renamed chloriuretic hormone". Liver Unit,
it into 50 ml of Robertson’s cooked-meat medium. The resulting cultures are incubated at 37°C for 48 h, then subcultured onto 5% horse-blood agar plates which are in turn incubated (one aerobically and the other anaerobically) at 37°C for 24 h. During the past three years, one student in each pair has been asked to replace the needle used for venepuncture with a fresh sterile one before injecting the blood collected into the culture medium. The number of cultures made in this way each year and the number found to be contaminated are shown in the table. The use of a second sterile needle to inoculate the culture medium
ject
significantly reduced Changing the needle ture technique.
the number of contaminated cultures. should be a standard part of blood-cul-
I thank the students who took part in this
investigation.
Bacteriology Department, Ninewells Hospital, Dundee DD1 9SY
A. C. SCOTT
MAGIC SHOTGUN PELLETS
SIR,-When teaching about the molecular actions and toxicities of antibiotics, I regularly have to contend with the "magic bullet" aura which surrounds the use of these drugs -i.e., the misbegotten notion that an on-rushing bacterium can be felled in its tracks by a single molecule, or at most a few, delivered marksmanlike to a vital organelle. This wildly inaccurate picture fosters a cavalier attitude to antibiotic toxi-
city.
S. P. WILKINSON LUCILLA POSTON ROGER WILLIAMS
Department of Medicine, King’s College Hospital, London SE5 9RS
BLOOD-CULTURE
EFFECT OF NEEDLE-CHANGING ON CONTAMINATION OF CULTURES
TECHNIQUE: TWO NEEDLES OR ONE?
SIR,-Standard textbooks of clinical bacteriology express of the value, in reducing contamination .by skin bacteria when setting up blood cultures, of replacing the
differing opinions
needle used for venepuncture with a fresh sterile one before delivering the blood into culture medium. The same conflict of opinion was voiced during a meeting of medical bacteriologists held in Edinburgh in 1976. Students attending a class in practical medical microbiology are instructed in the techniques of venepuncture and blood culture and thereafter, working in pairs, are invited to prepare blood cultures from each other. This is the first venepuncture that many of them have done. Weak solution of iodine B.P. and sterile swabs are provided for disinfection of the skin; each student is instructed to withdraw 5-10 ml of blood and to in1.
Watlington, C., King, R., Baldwin, G., Grossman, S., Estep,
H. Lancet,
1977, ii, 169. 2. Fine, L., Bourgoignie, J. J., Hwang, K. H., Bricker, N. S. J. clin. 1976, 58, 590. 3. Sonnenberg, H. Am. J. Physiol. 1972, 223, 916. 4. Stein, J. H, Osgood, R. W., Boonjarern, S., Ferns, T. F. J. clin. 1973, 52, 2313 5. Kramer, H. J., Gonick, H. C. Nephron, 1974, 12, 281. 6. Hillyard, S. D., Lu, E., Gonick, H. C. Circ. Res. 1976, 38, 250. 7. Poston, L., Wilkinson, S. P., Williams, R. Clin. Sci. 1979, 56, 25P.
Invest.
Invest.
Hand
exposed to 10’ female Aedes agypti mosquitoes/m3.
All commonly used antibiotics have molecular weights of between 300 and 800, (e.g., penicillin G, erythromycin, tetracycline, chloramphenicol, cephalothin, and gentamicin). With almost all a therapeutic concentration in serum of between 2 and 8 ug/ml is sought, which is 0-2-1-0x10’" molecules;1. A bacterium will on average measure 1 x 1 x1 sum ( 10-’S 1 or 1 fl) and the average length of an antibiotic molecule might be 1 nm so, at therapeutic concentrations, each bacterium will be exposed to 103-10’ antibiotic molecules, every one 1/1000 of the bacterial length. This is rather like a man sitting in a room with 104-105 mosquitoes/m3 (see figure). Once students have been exposed to this simple analogy, they are generally more receptive to learning about toxicity of antibiotics for mammalian cells (which really are not so much
larger than bacteria). Armed Forces Research Institute of Medical Sciences, Bankok, Thailand
DONALD S. BURKE
predictable event" which, as I stressed at the start of my letter, is responsible for a high proportion of myocardial in farcts. Foster suggests that phenothiazines might benefit myocardial infarction by protecting against the deleterious effects of hypoxia on mitochondria. This is perfectly possible, as is yet another mechanism-namely, that a membrane-stabilising effect diminishes the incidence of arrhythmias. The purpose of my letter was to point out the connection between the antihxmolytic action of chlorpromazine-like drugs and the associated inhibition of platelet thrombosis which can be demonstrated, even in conditions such as those in artificial blood-vessels, in which thrombogenic constituents such as collagen of arterial walls cannot be involved. Department of Pharmacology, King’s College,
G. V. R. BORN
London WC2R 2LS
CHLORIURETIC OR NATRIURETIC HORMONE?
SIR,-Dr Grekin and colleagues (May 26, p. 1116) propose that hyposecretion or hypersecretion of a hypothetical chloriuretic hormone might account for Bartter’s syndrome, Gordon’s syndrome, and hyporeninxmic hypoaldosteronism. This’ is an interesting hypothesis, although the chloriuretic hormone concept is by no means new. What we find surprising is their proposal that chloriuretic hormone is identical to natriuretic hormone. Although one would expect a chloriuretic hormone to act on the ascending limb of the loop of Henle, as they suggest, most evidence points to a more distal site of action for natriuretic hormone-e.g., the direct demonstration of inhibition of active sodium transport in the collecting tubule.2 Indirect evidence would also suggest a distal site of action, the inhibition of sodium reabsorption during volume expansion, a potent stimulus to natriuretic hormone production, occurring also chiefly in the collecting duct. 3,4 Furthermore, several groups have shown that natriuretic hormone directly inhibits the sodium-transporting enzyme sodium-potassium A.T.p.ase,s-’ suggesting that any effect on chloride transport would be a secondary effect. Although chloriuretic and natriuretic hormones may well both exist, we see little reason to propose that "natriuretic hormone be renamed chloriuretic hormone". Liver Unit,
it into 50 ml of Robertson’s cooked-meat medium. The resulting cultures are incubated at 37°C for 48 h, then subcultured onto 5% horse-blood agar plates which are in turn incubated (one aerobically and the other anaerobically) at 37°C for 24 h. During the past three years, one student in each pair has been asked to replace the needle used for venepuncture with a fresh sterile one before injecting the blood collected into the culture medium. The number of cultures made in this way each year and the number found to be contaminated are shown in the table. The use of a second sterile needle to inoculate the culture medium
ject
significantly reduced Changing the needle ture technique.
the number of contaminated cultures. should be a standard part of blood-cul-
I thank the students who took part in this
investigation.
Bacteriology Department, Ninewells Hospital, Dundee DD1 9SY
A. C. SCOTT
MAGIC SHOTGUN PELLETS
SIR,-When teaching about the molecular actions and toxicities of antibiotics, I regularly have to contend with the "magic bullet" aura which surrounds the use of these drugs -i.e., the misbegotten notion that an on-rushing bacterium can be felled in its tracks by a single molecule, or at most a few, delivered marksmanlike to a vital organelle. This wildly inaccurate picture fosters a cavalier attitude to antibiotic toxi-
city.
S. P. WILKINSON LUCILLA POSTON ROGER WILLIAMS
Department of Medicine, King’s College Hospital, London SE5 9RS
BLOOD-CULTURE
EFFECT OF NEEDLE-CHANGING ON CONTAMINATION OF CULTURES
TECHNIQUE: TWO NEEDLES OR ONE?
SIR,-Standard textbooks of clinical bacteriology express of the value, in reducing contamination .by skin bacteria when setting up blood cultures, of replacing the
differing opinions
needle used for venepuncture with a fresh sterile one before delivering the blood into culture medium. The same conflict of opinion was voiced during a meeting of medical bacteriologists held in Edinburgh in 1976. Students attending a class in practical medical microbiology are instructed in the techniques of venepuncture and blood culture and thereafter, working in pairs, are invited to prepare blood cultures from each other. This is the first venepuncture that many of them have done. Weak solution of iodine B.P. and sterile swabs are provided for disinfection of the skin; each student is instructed to withdraw 5-10 ml of blood and to in1.
Watlington, C., King, R., Baldwin, G., Grossman, S., Estep,
H. Lancet,
1977, ii, 169. 2. Fine, L., Bourgoignie, J. J., Hwang, K. H., Bricker, N. S. J. clin. 1976, 58, 590. 3. Sonnenberg, H. Am. J. Physiol. 1972, 223, 916. 4. Stein, J. H, Osgood, R. W., Boonjarern, S., Ferns, T. F. J. clin. 1973, 52, 2313 5. Kramer, H. J., Gonick, H. C. Nephron, 1974, 12, 281. 6. Hillyard, S. D., Lu, E., Gonick, H. C. Circ. Res. 1976, 38, 250. 7. Poston, L., Wilkinson, S. P., Williams, R. Clin. Sci. 1979, 56, 25P.
Invest.
Invest.
Hand
exposed to 10’ female Aedes agypti mosquitoes/m3.
All commonly used antibiotics have molecular weights of between 300 and 800, (e.g., penicillin G, erythromycin, tetracycline, chloramphenicol, cephalothin, and gentamicin). With almost all a therapeutic concentration in serum of between 2 and 8 ug/ml is sought, which is 0-2-1-0x10’" molecules;1. A bacterium will on average measure 1 x 1 x1 sum ( 10-’S 1 or 1 fl) and the average length of an antibiotic molecule might be 1 nm so, at therapeutic concentrations, each bacterium will be exposed to 103-10’ antibiotic molecules, every one 1/1000 of the bacterial length. This is rather like a man sitting in a room with 104-105 mosquitoes/m3 (see figure). Once students have been exposed to this simple analogy, they are generally more receptive to learning about toxicity of antibiotics for mammalian cells (which really are not so much
larger than bacteria). Armed Forces Research Institute of Medical Sciences, Bankok, Thailand
DONALD S. BURKE