Estimating surface soil moisture from SMAP observations using a Neural Network technique

A Neural Network (NN) algorithm was developed to estimate global surface soil moisture for April 2015 to March 2017 with a 2-3 day repeat frequency using passive microwave observations from the Soil Moisture Active Passive (SMAP) satellite, surface soil temperatures from the NASA Goddard Earth Observing System Model version 5 (GEOS-5) land modeling system, and Moderate Resolution Imaging Spectroradiometer-based vegetation water content. The NN was trained on GEOS-5 soil moisture target data, making the NN estimates consistent with the GEOS-5 climatology, such that they may ultimately be assimilated into this model without further bias correction. Evaluated against in situ soil moisture measurements, the average unbiased root mean square error (ubRMSE), correlation and anomaly correlation of the NN retrievals were 0.037 m³m^-3, 0.70 and 0.66, respectively, against SMAP core validation site measurements and 0.026 m³m^-3, 0.58 and 0.48, respectively, against International Soil Moisture Network (ISMN) measurements. At the core validation sites, the NN retrievals have a significantly higher skill than the GEOS-5 model estimates and a slightly lower correlation skill than the SMAP Level-2 Passive (L2P) product. The feasibility of the NN method was reflected by a lower ubRMSE compared to the L2P retrievals as well as a higher skill when ancillary parameters in physically-based retrievals were uncertain. Against ISMN measurements, the skill of the two retrieval products was more comparable. A triple collocation analysis against Advanced Microwave Scanning Radiometer 2 (AMSR2) and Advanced Scatterometer (ASCAT) soil moisture retrievals showed that the NN and L2P retrieval errors have a similar spatial distribution, but the NN retrieval errors are generally lower in densely vegetated regions and transition zones.

Sulphate preconcentration by anion exchange resin in flow injection and its turbidimetric determination in water

A preconcentration procedure was established for sulphate determination in rain waters at the mg/l level, employing a small column packed with the AG1-X8 (200-400 mesh) anionic resin inserted into a flow injection system. Sulphate determination was performed by using the turbidimetric method based on reaction with barium. For concentrations within 0.10 and 2.0 MgSO(2-)(4)/l, a throughput of 50 determinations/hr was achieved, and the relative standard deviation of results was better than 2%.

Chromosomal instability at a mutational hotspot in polyoma middle T-antigen affects its ability to activate the ARF-p53 tumor suppressor pathway

We have isolated spontaneous mutants of polyoma virus middle T-antigen (PyMT) that do not activate the ARF-p53 pathway based on their inability to block REF52 cell division. The REF52 cells containing these mutants have a flat untransformed morphological phenotype and do not express the ARF protein. The PyMT mutations in the different cell isolates so far analysed occur at a mutational hotspot in the PyMT sequence between nucleotides 1241 and 1249, which contains nine consecutive cytosines. In one set of mutants a single cytosine was deleted, while in another mutant set an additional cytosine was inserted. Both these mutations result in frameshifts, generating altered PyMT proteins containing amino-acid sequences derived from each of the two other alternative reading frames of the polyoma virus early region. Both types of mutations result in the loss of the C-terminal PyMT region containing the membrane-binding hydrophobic region and result is mislocalization of the PyMT mutant proteins. Revertant wild-type PyMT (containing nine cytosines) was easily detected in transformants generated after infection of REF52 cells expressing high amounts of dominant negative p53 with retroviruses containing either mutation. We demonstrate that wild-type PyMT revertants are derived from mutations in the hotspot sequence of the integrated mutant PyMT sequences.

Microbiological safety cabinets: selection, installation, testing and use

In the last quarter of the 20th century, there was much confusion and uncertainty amongst microbiologists and managers about the choice, installation, testing and use of the various types of microbiological safety cabinet. This review clarifies these issues, with reference to the latest standards and safe procedures.

The bovine tubercle bacillus

The bovine tubercle bacillus has always been eclipsed by the much higher incidence and the social and economic importance of its human cousin, as well as by the clinical unimportance of differentiating between the two. Nevertheless, in view of the resurgence of tuberculosis generally, the increase in the number of immunosuppressed individuals (i.e. the AIDS epidemic) and the 'great badger debate', there is renewed interest in it. Briefly, this review explores the history of Mycobacterium bovis and its potential for transmission between cattle and humans.

Biosafety: future priorities for research in health care

Currently the public interest in biosafety issues has focussed on the discussions surrounding the use of genetically modified organisms, very specifically on the use of transgenic plants in agriculture. Although many of the questions raised in connection with genetically modified organisms are of legitimate scientific interest, attention should be drawn back to a number of other more classical biosafety research areas, namely the problem of control of new and reemerging infectious diseases, the need for new vaccines, control of transport and routes of dissemination, biosafety information exchange and networking, where research results are dearly needed. In the area of modern biotechnology new applications such as gene therapy and transgenic animals will be on the list of future priorities for biosafety related activities and research.

Evolution of microbiological safety cabinets

Microbiological safety cabinets have had a chequered history, often being confused with chemical fume cupboards and cabinets intended to protect cultures from contamination rather than workers from infection. They have suffered from incorrect and inapt names. Much work has been required to determine the levels of air flow necessary to contain infectious particles and to prevent the exhaust of those particles to the environment, and this is considered in historical sequence. Warnings are given about the shortcomings of portable and home-made cabinets. This review traces the evolution of these cabinets, from the time of Robert Koch to the development of good national standards.

Effects in high-performance liquid chromatography of a high pH in the mobile phase on poly(methyloctylsiloxane) immobilized by gamma-radiation on titanium-grafted silica

Effects of high-pH environments on a stationary phase prepared by gamma-radiation immobilization of poly(methyloctylsiloxane) on titanium-grafted silica were investigated by HPLC testing with standard sample mixtures. The HPLC parameters indicate good stationary phase stability to 10000 column volumes each of mobile phases with pH of 7, 9 and 12. At pH 13, the efficiency decreases slowly, although reasonably good separations are still possible until increasing flow resistance no longer allows easy passage of the mobile phase.

Stability of high-performance liquid chromatography columns packed with poly(methyloctylsiloxane) sorbed and radiation-immobilized onto porous silica and zirconized silica

Reversed-phase packing materials were prepared from HPLC silica and from zirconized HPLC silica support particles having sorbed poly(methyloctylsiloxane) (PMOS) as the stationary phase. Portions of zirconized material were subjected to 80 kGy of ionizing radiation. Columns prepared from these packing materials were subjected to 5000 column volumes each of neutral and alkaline (pH 10) mobile phases, with periodic tests to evaluate chromatographic performance. It was shown that the PMOS stationary phase sorbed onto zirconized silica requires an immobilization treatment (such as gamma irradiation) for long term stability while prior surface zirconization of the silica support surface greatly improves the chromatographic stability of the stationary phase when using alkaline mobile phases.

Tuberculosis acquired in laboratories and necropsy rooms

The resurgence of tuberculosis, and the increasing number of cases that are HIV-related and/or multidrug resistant, has renewed interest in the occupational hazards posed by tuberculosis to staff in laboratories and necropsy rooms. A search undertaken using Medline and Pre-Medline identified few comprehensive reviews: the last was published in 1982. Staff may acquire pulmonary infection by inhalation of aerosols and skin lesions through cuts and abrasions. Particular hazards for laboratory staff include specimen containers contaminated on the outside, unfixed sputum smears, and the generation of aerosols during examination procedures. Examination of patients with tuberculosis not diagnosed during life constitutes a particular risk to necropsy room staff. Staff of laboratories and necropsy rooms are estimated to be between 100 and 200 times more likely than the general public to develop tuberculosis. Training in good laboratory practice is the most important aspect of staff protection, especially in resource-poor countries where well-maintained safety cabinets are rarely available. This article summarises requirements and recommendations for safe handling of tuberculous material and the available guidelines for work in developed and resource-poor countries.

Confidential inquiry into quality of care before admission to intensive care

OBJECTIVE

To examine the prevalence, nature, causes, and consequences of suboptimal care before admission to intensive care units, and to suggest possible solutions.

DESIGN

Prospective confidential inquiry on the basis of structured interviews and questionnaires.

SETTING

A large district general hospital and a teaching hospital.

SUBJECTS

A cohort of 100 consecutive adult emergency admissions, 50 in each centre.

MAIN OUTCOME MEASURES

Opinions of two external assessors on quality of care especially recognition, investigation, monitoring, and management of abnormalities of airway, breathing, and circulation, and oxygen therapy and monitoring.

RESULTS

Assessors agreed that 20 patients were well managed (group 1) and 54 patients received suboptimal care (group 2). Assessors disagreed on quality of management of 26 patients (group 3). The casemix and severity of illness, defined by the acute physiology and chronic health evaluation (APACHE II) score, were similar between centres and the three groups. In groups 1, 2, and 3 intensive care mortalities were 5 (25%), 26 (48%), and 6 (23%) respectively (P=0.04) (group 1 versus group 2, P=0.07). Hospital mortalities were 7 (35%), 30 (56%), and 8 (31%) (P=0.07) and standardised hospital mortality ratios (95% confidence intervals) were 1.23 (0.49 to 2.54), 1.4 (0.94 to 2.0), and 1.26 (0.54 to 2.48) respectively. Admission to intensive care was considered late in 37 (69%) patients in group 2. Overall, a minimum of 4.5% and a maximum of 41% of admissions were considered potentially avoidable. Suboptimal care contributed to morbidity or mortality in most instances. The main causes of suboptimal care were failure of organisation, lack of knowledge, failure to appreciate clinical urgency, lack of supervision, and failure to seek advice.

CONCLUSIONS

The management of airway, breathing, and circulation, and oxygen therapy and monitoring in severely ill patients before admission to intensive care units may frequently be suboptimal. Major consequences may include increased morbidity and mortality and requirement for intensive care. Possible solutions include improved teaching, establishment of medical emergency teams, and widespread debate on the structure and process of acute care.

Safe biotechnology. 8. Transport of infectious and biological materials. Working Party "Safety in Biotechnology" of the European Federation of Biotechnology

The transport of infectious and biological material is regulated by a number of international organizations. This mini-review has been compiled to increase awareness within the scientific community of problems caused by differences in terminology (such as infectious materials/substances, biological products, diagnostic specimens, genetically modified microorganisms) and certain technical aspects of the main international guidelines, and to assist policy makers in the creation of harmonized guidelines. A list of relevant Internet resources has been compiled.

Safe biotechnology. 7. Classification of microorganisms on the basis of hazard. Working Party "Safety in Biotechnology" of the European Federation Biotechnology

The current systems for classifying human pathogens on the basis of hazard are well developed and their basic criteria are in general agreement one with another. Of more importance, the safety practices based on these classifications have generally been successful. They have enabled extensive research activities, medical practice and industrial production to be conducted on an ever-increasing scale, involving dangerous microorganisms (e.g. in vaccine production and treatment of infected patients) with a very low incidence of adverse effects on the workers involved and the general public. Although the EU has adopted a harmonised list of agents in groups 1-4 there is as yet no complete agreement among member states and individual microbiologists. The purpose of this paper is to present a historical survey and to discuss the current processes for identifying and classifying the hazards posed by the use of microorganisms in research and technology. This is essential in the design of appropriate methods of counteracting potential risks.

Formaldehyde disinfection in laboratories: limitations and hazards

Formaldehyde is a substance hazardous to health, specified in Schedule 1 to the British Control of Substances Hazardous to Health Regulations 1988 but still used in laboratories as a preservative and for disinfection of surfaces and spaces. In this paper we review the properties and hazards of formaldehyde and its common laboratory uses, and suggest some precautions and ways of minimising risk from those fumigation procedures that carry the greatest risk of exposure to high levels of the gas.

Safe biotechnology. Part 6. Safety assessment, in respect of human health, of microorganisms used in biotechnology

The assessment of microorganisms in respect to human health is an important step for the introduction of new natural and genetically modified production strains to biotechnology. This report outlines the potential hazards posed by industrial microorganisms, important considerations related to pathogenicity, such as routes and portals of entry into the human body, mechanisms of spread of biological material and a definition of pathogenicity. Furthermore the most important steps in the assessment of pathogenicity of unknown strains are described. A short overview on characterization and in vitro and in vivo tests is presented. The hazard related to allergens and toxic metabolites is reviewed and the choice of methods and the handling of strains with unknown potential are discussed.

Safe biotechnology (5). Recommendations for safe work with animal and human cell cultures concerning potential human pathogens

The benefits of using animal or human cell cultures have been clearly demonstrated in diagnostic and therapeutic research and in their application for manufacturing. Cell cultures serve as a tools for the production of vaccines, receptors, enzymes, monoclonal antibodies and recombinant DNA-derived proteins. They represent an integral part of drug development for which corresponding facilities, equipment and manufacturing processes are required. Although the cells themselves offer no particular risk to workers in laboratories and production areas or to the environment, the cell cultures may be contaminated with viruses, mycoplasma, bacteria, yeast and fungi or might contain endogenous viruses. The containment level for animal and human cells is therefore determined by the risk class of these agents. The history of animal and human cell cultures has proved that they can be handled safely. The recommendations in this publication concern the safe handling of cell cultures (tissue explants, primary cell cultures) and permanent cell lines of animal and human origin. A classification system of safety precautions has been elaborated according to the potential for contamination with the pathogenic agents involved.

Safe biotechnology (4). Recommendations for safety levels for biotechnological operations with microorganisms that cause diseases in plants

The Working Party on Safety in Biotechnology of the European Federation of Biotechnology has proposed a classification of microorganisms that cause diseases in plants. In this paper appropriate safety levels are proposed for these classes of microorganisms in order to ensure that research, development and industrial fermentation work with plant pathogens will limit the risk of outbreaks of diseases in crops that could result from work with such microorganisms when they are cultivated in laboratories, glasshouses and biotechnology installations.

Treatment and disposal of clinical and laboratory waste

There are no entirely satisfactory definitions of clinical waste; nor are there methods in general use that are safe and environmentally acceptable for the storage, transport and final disposal of the ever-increasing volume of such waste that is generated by the health services. Hazardous, potentially infectious and aesthetically objectionable waste has been found on beaches and exposed on domestic refuse landfill sites, causing public disquiet about health hazards and environmental pollution. Landfill is officially discouraged, where not illegal, and many older-type incinerators can not now be used because their effluent pollutes the atmosphere. Modern and efficient incinerators are expensive and the parochial nature of health service management and accounting mitigates against their installation and use. Laboratory waste, however, can be rendered safe and unobjectionable, aesthetically and environmentally, if the requirements and recommendations of the several Codes of Practice and technical advice, which are simple and inexpensive, are implemented by laboratory and hospital managers.

A comparison of APACHE II and a clinical sickness score. A study of 97 consecutive admissions to a district general hospital intensive care unit

The aim of this study was to compare the predictive power of a simple illness severity score (Clinical Sickness Score) to that of APACHE II in a District General Hospital intensive therapy unit. A prospective comparison was carried out on 97 consecutive adult patients whose severity of illness was scored one hour after admission using both the Clinical Sickness Score and APACHE II. Intensive Therapy Unit and hospital outcomes were recorded for each patient. The Clinical Sickness Score and APACHE II identified survivors and nonsurvivors with similar power (p less than 0.001). There was a highly significant correlation between the two scoring systems for hospital survivors and nonsurvivors together (r = 0.5418, r2 = 0.28, p = less than 0.0001) and for hospital survivors alone (r = 0.6102, r2 = 0.37, p = 0.0001). Correlation for hospital nonsurvivors was not significant (r = 0.1629, r2 = 0.027, p = 0.3134). The positive predictive values of APACHE II were between 5% and 10% more sensitive than the Clinical Sickness Score for hospital outcome. Admission Clinical Sickness Score and APACHE II scores had similar predictive power in this study.

Protocol for increasing organ donation after cerebrovascular deaths in a district general hospital

In a district general hospital serving 303,000 people, deaths from cerebrovascular incidents over 12 months were analysed retrospectively. 8 patients who died in general wards were identified as potential organ donors. A working party then devised a protocol for managing such donors by transfer to the intensive care unit for support until organ retrieval could be arranged. In the first 19 months with the protocol, organs (1 heart, 2 sets of heart valves, 2 livers, and 16 kidneys) were retrieved from 8 patients who would not otherwise have become donors. If these results were replicated nationally a further 16.7 donors per million per year would be added to the current annual UK rate of 14.6 donors per million.

Comparison of propofol and midazolam for sedation in critically ill patients

101 critically ill patients admitted to five intensive-care units were allocated randomly to receive a continuous intravenous infusion of either propofol or midazolam for sedation for up to 24 h. In addition, morphine was given to provide analgesia. The mean duration of infusion was 20.2 h (range 3.0-24.5) in the propofol group and 21.3 h (4.0-47.0) in the midazolam group and infusion rates were 1.77 mg/kg/h (range 0.40-5.00) and 0.10 mg/kg/h (0.01-0.26), respectively. The infusion rates were adjusted as necessary, and the desired level of sedation was achieved easily in most patients in both groups. There were slight falls in arterial pressure, but there were no significant differences between the groups. Heart rate was lower in patients who received propofol. Some small changes occurred in biochemical and haematological variables in both groups, but they were not clinically significant. There was no indication that either drug substantially impaired adrenal steroidogenesis. When the infusion was discontinued, there was less variability in recovery of consciousness in patients who had received propofol. In a subgroup of patients, weaning from mechanical ventilation was achieved significantly faster after discontinuation of propofol than of midazolam. Propofol proved to be a satisfactory agent for sedation of these critically ill patients and compared favourably with midazolam.

Heat stroke--an uncommon presentation

A case of heat stroke is reported in which there was a delayed diagnosis and a fatal outcome. Recent literature is reviewed.

High-level vancomycin-resistant enterococci causing hospital infections

Nosocomial infection or colonization due to enterococci with high-level resistance to vancomycin (minimal inhibitory concentrations [MICs] between 64 and greater than 2000 mg/L) has occurred in 41 patients with renal disease. These vancomycin-resistant enterococci were cultured from many sources including blood. All but one strain contained one or more plasmids ranging in molecular weight from 1.0 to 40 Megadaltons (MDa). Vancomycin resistance was transferable by conjugation to a susceptible recipient strain of Enterococcus faecalis but this was not always associated with plasmid DNA. The emergence of transferable high-level vancomycin resistance in enterococci causing significant clinical infections is of particular importance since vancomycin is widely regarded as a reserve drug for the management of infections with multi-resistant Gram-positive organisms.

In-vitro activity of seventeen antimicrobial compounds against seven species of mycobacteria

Within attainable serum concentrations, quinolones, especially ciprofloxacin, inhibited strains of Mycobacterium tuberculosis, M. xenopi, M. kansasii, M. fortuitum and M. marinum; vancomycin inhibited M. tuberculosis, the M. avium-intracellulare-scrofulaceum complex. M. kansasii, M. xenopi and M. chelonei; erythromycin was active against M. kansasii, M. xenopi and M. fortuitum, minocycline against M. kansasii and M. marinum and netilmicin and cefuroxime against M. xenopi. Aztreonam showed some activity against M. tuberculosis but little or no effect was shown by five cephalosporins or imipenem.

In vitro activity of ciprofloxacin in combination with standard antituberculous drugs against mycobacterium tuberculosis

Chequer-board titrations show that the in vitro activity of ciprofloxacin against Mycobacterium tuberculosis is independent of that of streptomycin, isoniazid, ethambutol and pyrazinamide and confirm that there is antagonism between ciprofloxacin and rifampicin.

Presumptive identification of nocardias in a clinical laboratory

One hundred and thirty-six cultures of aerobic streptomycetes were examined by simple cultural and microscopical methods. Nocardia spp. were recognized by their resistance to lysozyme and identified to the three important species by casein, xanthine and tyrosine hydrolysis tests.

Bovine tubercle bacilli and disease in animals and man

In 1882 Robert Koch reported the isolation oftuberkelbazillenfrom human and bovine sources. Sixteen years later, Theobald Smith (1898) demonstrated that strains of Koch's tubercle bacilli from these two hosts differed in cell morphology, cultural characteristics and virulence in rabbits. He did not believe that these variants were limited to the hosts from which they were isolated nor that the differences resulted from adaptations to a given host. Indeed, he remarked that ‘It might be better to omit the host designation of such varieties in order to anticipate assumptions that they are necessarily limited to the host whose name they bear.’ Nevertheless, heedless of his own misgivings he termed them the ‘human’ and ‘bovine’ types.

The nature of mycobacterial disease in south east England, 1977-84

The nature and incidence of bacteriologically confirmed mycobacterial disease in south east England over the eight year period 1977-84 has been determined by a study of cultures received by the PHLS Regional Centre for Tuberculosis Bacteriology at Dulwich. The number of cases of tuberculosis in the ethnic European population has shown a decline, more so among males than females, but there has not been a significant decline in cases among ethnic Asians. Most tuberculosis is due to the classical human tubercle bacillus but cases due to the Asian human type, the bovine type (M. bovis), and the African types (M. africanum) also occur. The number of cases of disease due to 'atypical' mycobacteria has doubled over the eight year period, and these now account for about 5% of bacteriologically diagnosed mycobacterial disease in this region. The continuing role of reference facilities for the surveillance of tuberculosis and the diagnosis and management of the growing numbers of other mycobacterial infections is stressed.

Differentiation of Mycobacterium chelonei from M. fortuitum by ciprofloxacin susceptibility

Seventy-five strains of Mycobacterium fortuitum were inhibited by 3.0 mg/l ciprofloxacin but 36 strains of M. chelonei were resistant. The results correlated well with those obtained by the nitratase test. The ciprofloxacin sensitivity test is a useful supplement to the tests used to identify these two species.

In-vitro susceptibility of mycobacteria to ciprofloxacin

Two hundred and seventy-six strains of mycobacteria were tested for susceptibility to ciprofloxacin (Bay 0 9867), a 4-quinolone antimicrobial agent. Most strains of Mycobacterium tuberculosis, Myco. fortuitum, Myco. kansasii, Myco. marinum and Myco. xenopi were sensitive to minimum inhibitory concentrations (MICs) of 0.78-1.56 mg/l, equivalent to resistance ratios of 1 or 2. Most strains of Myco. avium-intracellulare and Myco. chelonei required MICs of 12.5 mg/l or more, giving resistance ratios of 8.

Mycobacterium xenopi and Mycobacterium kansasii in a hospital water supply

A steady rise in the number of isolations of Mycobacterium xenopi from patients in a general hospital led to an examination of water taps. Most patients had been accommodated in a group of wards which had a common water supply. This organism was recovered from 35 of 69 outlets, mostly from hot and mixer taps in those wards. Mycobacterium kansasii was also isolated from 14, mostly cold and mixer taps. Ten strains of Myco. xenopi were recovered from 131 taps sampled at 10 other locations. We conclude that colonization of water supplies by mycobacteria is a likely source of contamination of clinical specimens.

Mycobacterium marinum infections in man

Mycobacterium marinum, formerly known as ‘Mycobacterium balnei’, is a free-living organism which causes disease in fish and occasionally in man. When such infections occur in man they are usually associated with some aquatic activity, e.g. swimming, fishing, boating and keeping tropical fish. For this reason, the organism has been called a ‘leisure-time pathogen’ by Feldman, Long & David (1974) and the disease a ‘hobby hazard’ by Heineman, Spitzer & Pianphongsant (1972).

Subdivision of Mycobacterium tuberculosis for epidemiological purposes: a seven year study of the "Classical' and 'Asian' types of the human tubercle bacillus in South-East England

Human strains of Mycobacterium tuberculosis were divided into the 'Classical' and 'Asian' types according to their sensitivity to thiophen-2-carboxylic acid hydrazide. The isolation of these two types in South-East England was studied during a seven-year period (1977-1983). The 'Asian' type was more prevalent among ethnic Asian patients than among ethnic Europeans. Among Europeans there was a decline in the isolation rate of 'Classical' strains and a small but significant increase in 'Asian' strains during the study period, so that the proportion of the latter type in this group is increasing. The type of bacillus was unrelated to the site of isolation except that the incidence of lymphadenitis due to the 'Asian' type among European females was significantly higher than expected. In general, European patients tended to be older than Asian patients, and the differences in age distribution according to site of isolation and type of bacillus in each ethnic group were small. A notable exception occurred with European females infected with the 'Asian' type, whose age distribution was similar to the Asians. In view of the differences in behaviour of the two types of human tubercle bacilli in this country there is a need to continue a bacteriological surveillance and also to determine whether the nature of the host-pathogen interaction varies according to the type of bacillus.

A study of the relationship between the resistance of Mycobacterium tuberculosis to isonicotinic acid hydrazide (isoniazid) and to thiophen-2-carboxylic acid hydrazide

Thiophen-2-carboxylic acid hydrazide (TCH) is used to distinguish TCH-sensitive bovine, 'Asian human' and 'African' strains from TCH-resistant 'classical' human strains of Mycobacterium tuberculosis. It has been claimed that this test cannot be applied to isoniazid-resistant strains as these also become resistant to TCH. Although such cross-resistant mutants were readily isolated in vitro, a study of the incidence of TCH resistance in a large series of INH-sensitive and -resistant strains isolated from patients indicated that the emergence of this type of mutant is the exception rather than the rule in vivo. Thus, the use of TCH for subdividing the species M. tuberculosis remains valid for epidemiological purposes, irrespective of the occurrence of isoniazid resistance.