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CHLORAMPHENICOL RESISTANCE IN HÆMOPHILUS SPECIES
696 MORTALITY* AMONG MICE TREATED BACTERIA
AND
ANAESTHETISED
WITH WITH
ANAEROBIC CORYNEPENTOBARBITONE
and chemotherapeutic susceptibility of this and other members of the Haemophilus group; there are also plans to extend to a larger geographical area our present investigation of the relation between drug susceptibility and previous treatment. Public Health Laboratory, Central Pathology Laboratory, Hartshill Road, Hartshill, Stoke-on-Trent ST4 7PX.
Public Health Laboratory,
Shrewsbury. *
Number of deaths
over
we used were lower than those given by Mrs Mosedale and Mr Smith, and by Castro. Although our results differ, they do not preclude the possibility of a potential risk in giving anaesthetics, or other drugs which depend on the liver for catabolism, to patients treated with C. parvum. More investigations, however, are needed with different animal species. Also, it is necessary to test the effect of doses of C. parvum which are comparable to those which can be safely used for clinical studies. Doses of C. parvum given to patients usually do not exceed 5 mg. per sq.m.,2 the dose which corresponds to 0-04 mg. per 25 g. mouse, assuming equivalency on the basis of mg. per sq.m.3. It is obvious then that the doses which we, Castro, and Mosedale and Smith have used in mice were much higher. Many clinical trials of tumour immunotherapy with C. parvum are being conducted in U.S.A. and in Europe. It would be helpful to know whether if patients previously receiving this bacterium and undergoing surgery tolerate anaesthetics or other agents normally.
Section of Experimental Radiotherapy, M. D. Anderson Hospital and Tumor
Institute, Houston, Texas 77025, U.S.A.
C. A. MORRIS N. J. MITCHELL.
total number of mice.
HYGIENE OF BABIES’ INCUBATORS
granulosum
-
PETER CAVANAGH.
SIR,-Dr Kelsey (Feb. 22, p. 455) highlights the potential infection hazards within infant incubators due to cleaning procedures. These problems point to the need for redesign of incubators to produce an acceptable bacteriological and thermal environment. Some time ago we studied the environmental conditions within commercial incubators. We were interested in defining the convective air-flows generated by the infant itselfand in determining their interaction with the ventilating air-flows within the incubator. The study showed that, with a 1-2°C temperature difference between the infant and the surrounding air, the natural convective air-streams generated by the baby had velocities of some 3-4 cm. per second, giving an upward volume flow of about 1 litre per second in still air. These air velocities were found to be capable of lifting microorganisms that may be carried on skin particles released from the infant’s
body. Within the incubator the ventilating air recirculated and there was no particle filter within the air-circuit. When the infant was nursed in the customary posture the air-flow moved from the feet towards the head. This suggested that pathogens generated from the perineum or lower limbs could become airborne to sediment subsequently in the region of the respiratory tract and cause autogenous infection. In addition, any airborne particles not sedimenting on the infant would become entrained within the circulating air, whence they might contaminate all other parts of the incubator, including the humidifier. Should they not be removed during cleaning and again become airborne these could create a cross-infection hazard for infants
continuously, LUKA MILAS.
CHLORAMPHENICOL RESISTANCE IN HÆMOPHILUS SPECIES SIR,-We have isolated a chloramphenicol-resistant strain of Hcemophilus parainfiuenzae from the pharynx of a cooperative patient who has had numerous attacks of sinusitis for several years. He has been treated, on various and separate occasions, with ampicillin, tetracycline, and co-trimoxazole. Chloramphenicol has not been prescribed except in the form of eye-drops for the treatment, 2 years ago, of an attack of conjunctivitis. Growth of this strain was inhibited only by a concentration of 31 jjtg. per ml. chloramphenicol (sensitive strains are usually inhibited by less than 0-5 (1.g. per ml. of the drug). We have not yet recovered a wild strain of H. influenza which is chloramphenicol resistant; our experience so far suggests that such strains are rare. Nevertheless, we are concerned by the apparently " natural *’ state of resistance to chloramphenicol in a wild strain of H. parainfluenzce. We are not aware of any reason why such resistance should not be transferable to H. infiuenzae; transfer of ampicillin resistance under laboratory conditions has already been reported from the U.S.A.4 We consider that the mere possibility of chloramphenicol resistance in H. influenza, heightens current interest in the search for alternative drugs for the treatment of H. influenza meningitis; it also justifies the continued, careful examination of the antibiotic 2. Medical Department, Burroughs Wellcome Company, Triangle Research Park, North Carolina. J. K. Whisnant, 1975. Personal communication. 3. Freireich, E. J., Gehan, E. A., Rall, D. P., Schmidt, L. H., Skipper, H. E. Cancer Chemother. Rep. 1966, 50, 219. 4. Thornsberry, C. Personal communication.
the device later. Smoke tests showed that very little " make up " air was drawn into the canopy. The air-change rates were extremely low and, without the addition of oxygen, the concentration of carbon dioxide could rise to unacceptable levels. The flow within the canopy was disordered and very far from laminar or linear. Vertical and horizontal temperature gradients of up to 3-5 °C were recorded and showed the difficulty of assessing the exact temperature to which the infant was subjected. We were able to improve matters by redesigning various parts of the air-circuit to produce a linear air-flow over the infant, with smaller velocity and temperature variations within the canopy. Filters capable of removing pinicles down to 0-5 .rn. were incorporated into the air-stream. These ensured that sterile air was delivered to the canopy and that inaccessible parts of the air-circuit were not contaminated. These modifications are covered in a patent supported by the National Research Development Corporation, in which it is suggested that new incubator
using
1.
Lewis, H. E., Foster, A. R., Mullan, B. J., Cox, R. N., Clark, R. P. Lancet, 1969, i, 1273.
AND
ANAESTHETISED
WITH WITH
ANAEROBIC CORYNEPENTOBARBITONE
and chemotherapeutic susceptibility of this and other members of the Haemophilus group; there are also plans to extend to a larger geographical area our present investigation of the relation between drug susceptibility and previous treatment. Public Health Laboratory, Central Pathology Laboratory, Hartshill Road, Hartshill, Stoke-on-Trent ST4 7PX.
Public Health Laboratory,
Shrewsbury. *
Number of deaths
over
we used were lower than those given by Mrs Mosedale and Mr Smith, and by Castro. Although our results differ, they do not preclude the possibility of a potential risk in giving anaesthetics, or other drugs which depend on the liver for catabolism, to patients treated with C. parvum. More investigations, however, are needed with different animal species. Also, it is necessary to test the effect of doses of C. parvum which are comparable to those which can be safely used for clinical studies. Doses of C. parvum given to patients usually do not exceed 5 mg. per sq.m.,2 the dose which corresponds to 0-04 mg. per 25 g. mouse, assuming equivalency on the basis of mg. per sq.m.3. It is obvious then that the doses which we, Castro, and Mosedale and Smith have used in mice were much higher. Many clinical trials of tumour immunotherapy with C. parvum are being conducted in U.S.A. and in Europe. It would be helpful to know whether if patients previously receiving this bacterium and undergoing surgery tolerate anaesthetics or other agents normally.
Section of Experimental Radiotherapy, M. D. Anderson Hospital and Tumor
Institute, Houston, Texas 77025, U.S.A.
C. A. MORRIS N. J. MITCHELL.
total number of mice.
HYGIENE OF BABIES’ INCUBATORS
granulosum
-
PETER CAVANAGH.
SIR,-Dr Kelsey (Feb. 22, p. 455) highlights the potential infection hazards within infant incubators due to cleaning procedures. These problems point to the need for redesign of incubators to produce an acceptable bacteriological and thermal environment. Some time ago we studied the environmental conditions within commercial incubators. We were interested in defining the convective air-flows generated by the infant itselfand in determining their interaction with the ventilating air-flows within the incubator. The study showed that, with a 1-2°C temperature difference between the infant and the surrounding air, the natural convective air-streams generated by the baby had velocities of some 3-4 cm. per second, giving an upward volume flow of about 1 litre per second in still air. These air velocities were found to be capable of lifting microorganisms that may be carried on skin particles released from the infant’s
body. Within the incubator the ventilating air recirculated and there was no particle filter within the air-circuit. When the infant was nursed in the customary posture the air-flow moved from the feet towards the head. This suggested that pathogens generated from the perineum or lower limbs could become airborne to sediment subsequently in the region of the respiratory tract and cause autogenous infection. In addition, any airborne particles not sedimenting on the infant would become entrained within the circulating air, whence they might contaminate all other parts of the incubator, including the humidifier. Should they not be removed during cleaning and again become airborne these could create a cross-infection hazard for infants
continuously, LUKA MILAS.
CHLORAMPHENICOL RESISTANCE IN HÆMOPHILUS SPECIES SIR,-We have isolated a chloramphenicol-resistant strain of Hcemophilus parainfiuenzae from the pharynx of a cooperative patient who has had numerous attacks of sinusitis for several years. He has been treated, on various and separate occasions, with ampicillin, tetracycline, and co-trimoxazole. Chloramphenicol has not been prescribed except in the form of eye-drops for the treatment, 2 years ago, of an attack of conjunctivitis. Growth of this strain was inhibited only by a concentration of 31 jjtg. per ml. chloramphenicol (sensitive strains are usually inhibited by less than 0-5 (1.g. per ml. of the drug). We have not yet recovered a wild strain of H. influenza which is chloramphenicol resistant; our experience so far suggests that such strains are rare. Nevertheless, we are concerned by the apparently " natural *’ state of resistance to chloramphenicol in a wild strain of H. parainfluenzce. We are not aware of any reason why such resistance should not be transferable to H. infiuenzae; transfer of ampicillin resistance under laboratory conditions has already been reported from the U.S.A.4 We consider that the mere possibility of chloramphenicol resistance in H. influenza, heightens current interest in the search for alternative drugs for the treatment of H. influenza meningitis; it also justifies the continued, careful examination of the antibiotic 2. Medical Department, Burroughs Wellcome Company, Triangle Research Park, North Carolina. J. K. Whisnant, 1975. Personal communication. 3. Freireich, E. J., Gehan, E. A., Rall, D. P., Schmidt, L. H., Skipper, H. E. Cancer Chemother. Rep. 1966, 50, 219. 4. Thornsberry, C. Personal communication.
the device later. Smoke tests showed that very little " make up " air was drawn into the canopy. The air-change rates were extremely low and, without the addition of oxygen, the concentration of carbon dioxide could rise to unacceptable levels. The flow within the canopy was disordered and very far from laminar or linear. Vertical and horizontal temperature gradients of up to 3-5 °C were recorded and showed the difficulty of assessing the exact temperature to which the infant was subjected. We were able to improve matters by redesigning various parts of the air-circuit to produce a linear air-flow over the infant, with smaller velocity and temperature variations within the canopy. Filters capable of removing pinicles down to 0-5 .rn. were incorporated into the air-stream. These ensured that sterile air was delivered to the canopy and that inaccessible parts of the air-circuit were not contaminated. These modifications are covered in a patent supported by the National Research Development Corporation, in which it is suggested that new incubator
using
1.
Lewis, H. E., Foster, A. R., Mullan, B. J., Cox, R. N., Clark, R. P. Lancet, 1969, i, 1273.