The Eflqciency of Disinfectants in Tuberculous Sputa

By A L F R E D AI)AMS, M.D., D.P.H.

~IEDIOAL SUPERINTENDENT, LIVERPOOL SANATORIU.M, I)ELA.MERE FOREST

The selection of a safe and efficient chemical agent for the sterilization of sputum containing the Mycobacteriunl tuberculosis is a problem in the treatment of pulmonary tuberculosis concerning particularly heads of institutions, officers in charge of tuberculosis clinics and general practitioners. Recently many new disinfectants and antiseptics have been placed on the market with strong recommendations as to their efficacy as germicides ; and tile Rideal-Walker co-efficient of these has been quoted as proof of this. Rideal-Walker tests are usually carried out on such organisms as B. coli, B. typhosus and Staphylococcus aureus ; but little work seems to have been done on the effects of these preparations on the tubercle bacillus.

It is well known that this organism in sputum with its albuminous and mucous content shows a resistance to bactericides. Even when these extraneous matters are removed its lipoid envelope is highly resistant to the penetration of dyes and germicides. Probably sterilization by heat is best, either by boiling or destruction in an incinerator; but even in an institution this is an objectioxmble process; the hands and clothing of the attendant are liable to be fouled and tim sterilization may fail for many reasons. The use of the standard sputum flask has largely added to the difficulty, as many are broken in the sterilizing process, the bulk to be treated is large and often the contents are spilled where heat sterilization is impossible. In institutions, the treatment of the cups is accompanied by the same disadvantages, trot the greatest difficulty exists with the patient on his return home ; here sterilization by heat is impracticable and chemical sterilization must be the main defence against the spread of infection. An attempt has therefore been made to compare the value of some of the more recently introduced disinfectants with those in general use, and to find those most efficient.

Phenol, the standard basis in the Rideal-Walker test for the organisms quoted, is of little use for penetrating either the albuminous content of the sputum or the lipoid coating of the tubercle bacillus, owing to its tendency to coagulate the albumins and form an impenetrable mass in which the organisms remain viable ; and it is the general experience that a saponaceous solution helps to disintegrate the mass and is more effective as a tubercle bactericide.

For purposes of the test a quantity of infected sputum was collected from a number of patients, intimately mixed and centrifi~ged to obtain a high concentration of various types of this organism. This concentrate was used in each experiment, an equal quantity being mixed with the disinfectant in o ! per cent and 5 per cent dilutions for periods of 3 ~ minutes, I hour, and 4 hours, centrifi~ged for 2o minutes

February I938 T U B E R C L E 0_09

(the time occupied in the centrifuge being included in the contact time), then washed with sterile distilled water to remove all traces of the disinfectant, again centrifuged, and the resultant residue seeded out on three tubes of a modified Lowenstein-Jensen medium. For controls the original concentrate was treated with 5 per cent solution of caustic potash for half an hour, centrifuged, the deposit neutralized with normal solution of HCI and also seeded out on the same media. Readings of the resultant growths were taken on the x8th and 3oth days, and the results are shown in tables A and B, the sign + denoting growth of the tubercle organism. In each case the result obtained in the three tubes used for each individual test was identical, and in no case was there any secondary infection of the media, showing that in the controls as well as with the different chemicals tested the growth of other organisms had been inhibited.

The chemicals tested were a high grade lysol (liquor cresol saponatus BP), a solution of sodium hypochlorite, NaOCl, containing 14 to x 5 per cent available chlorine by weight, and D, Za, and Ze. D is a widely advertised disinfectant said to be a halogen derivative of xylenol dissolved in a saponified mixture of essential oils. Za is a proprietary preparation said to be a combination of para-chlor-meta-xylenol emulsified with pine and other essential oils by a suitable soap. Ze is stated to be a water solution of a mixture of alkyl-dimethyl-benzyl-ammonium chlorides faintly perfumed and of alkaline reaction.

From table A it will be seen that the controls all produced viable cultures

TABLE A

Results obtahzed after 18 days' incubation.

Y l m c of exposure to Controls

antiseptic 30 minutes + I hour + 4 hours +

Chlorine solution

~�89 5% + ,-4-

D 2�89

+ + +

Lysol 5% ~�89 5% 3 V - - - -

Z z t

2�89

+

Z e

5% 2~% 5% + + + - - + + - - + +

of the tubercle organism. When lysol was used, however, a contact of 3 ~ minutes in a 2�89 per cent dilution was sufficient to prevent the growth of the tubercle bacillus, and a similar result was obtained in one hour when Za and chlorine solutions were used, but 5 per cent solutions of D and Ze failed even in four hours to prevent a luxurious growth of the organism.

TABLE B

Results obtained after 3 ~ days' incubation.

T i n l e

of exposure to antiseptic

30 minutes I hour 4 hours

Controls Chlorine solution

2�89 5%

D ~�89

Z a

2�89 Lysol

5% 2�89 5% - [ - - - _ _ + + + + _I_

-t- + + + + - - _ +

Z e

5% 2t% 5% + + + - - + + - - + -?

The readings were unchanged after 4 ~ days' incubation.

~2IO TUBERCLE February i938

When, however, the inctibation was carried to 3 ~ days (see table B), the organisms treated with lysol still failed to grow. Za showed no growth after one, as also after four hours' contact ; whilst those treated with chlorine in both 2-12 . per cent and 5 per cent dilutions after one hour's contact showed growth, it being clear that the organisms were not killed but only partially inhibited, but the four hours' contact still showed no sign of growth. It is therefore evident that lysol in a strength of 2�89 per cent with a contact of half an hour kills the tubercle bacillus, Za is similarly effective in a contact for one hour in 2�89 per cent solution, whilst chlorine requires four hours' contact for the same result, but D and Ze appear to have no effect whatever on the viability of the tubercle bacillus in sputum, and may give a false sense of security to those using them.

That the menstruum in which a chemical germicide is dissolved has a direct influence on its efficiency cannot be doubted, but to estimate this would be exceedingly difficult; the capacity to dissolve and penetrate the mucus and albumens contained in a viscid sputum and also the lipoid capsule of the organism must be considered, as also its effect on surface tension. The tWO solutions giving the best germicidal readings were highly saponaceous, and this may account for at least part of their superiority ; in the other solutions this was much less evident or lacking.

Another point of practical interest arises from the table. For the detection of the presence of tubercle bacilli by cultural or biological methods in specimens of sputa, faeces, or sewage, the material can safely be exposed to the action of chlorine in 5 per cent solution for an hour without interfering with the viability of the organism, and contamination by secondary organisms is prevented.

The questions of cost, toxicity, absence of irritating effects on tim skin and mucous membranes, and unpleasant odour have not been taken into consideration. Lysol is definitely toxic and irritating, and it was hoped that some other solution could be found which would replace i t ; Za seems to offer the next maximum safety as a germicide with fewer of the disadvantages.