Alexander Fleming (1881-1955)

226

ON THE ANTIBACTERIAL ACTION OF CULTURES OF A
PENICILLIUM, WITH SPECIAL REFERENCE TO THEIR
USE IN THE ISOLATION OF B. INFLUENZÆ.

                    ALEXANDER FLEMING, F.R.C.S.

From the Laboratories of the Inoculation Department, St Mary’s Hospital, London.

                                      Received for publication May 10th, 1929.

WHILE working with staphylococcus variants a number of culture-plates
were set aside on the laboratory bench and examined from time to time. In
the examinations these plates were necessarily exposed to the air and they
became contaminated with various micro-organisms. It was noticed that
around a large colony of a contaminating mould the staphylococcus colonies
became transparent and were obviously undergoing lysis (see Fig. 1).

Subcultures of this mould were made and experiments conducted with a
view to ascertaining something of the properties of the bacteriolytic substance
which had evidently been formed in the mould culture and which had diffused
into the surrounding medium. It was found that broth in which the mould
had been grown at room temperature for one or two weeks had acquired
marked inhibitory, bactericidal and bacteriolytic properties to many of the
more common pathogenic bacteria.

                         CHARACTERS OF THE MOULD.

The colony appears as a white fluffy mass which rapidly increases in size
and after a few days sporulates, the centre becoming dark green and later in
old cultures darkens to almost black. In four or five days a bright yellow
colour is produced which diffuses into the medium. In certain conditions a
reddish colour can be observed in the growth.

In broth the mould grows on the surface as a white fluffy growth changing
in a few days to a dark green felted mass. The broth becomes bright yellow
and this yellow pigment is not extracted by CHCl₃. The reaction of the broth
becomes markedly alkaline, the pH varying from 8·5 to 9. Acid is produced
in three or four days in glucose and saccharose broth. There is no acid
production in 7 days in lactose, mannite or dulcite broth.

Growth is slow at 37°C. and is most rapid about 20°C. No growth is
observed under anaerobic conditions.

In its morphology this organism is a penicillium and in all its characters
it most closely resembles P. rubrum. Biourge (1923) states that he has never
found P. rubrum in nature and that it is an “ animal de laboratoire.” This
penicillium is not uncommon in the air of the laboratory.