608 STAPH YLOCCOCUS 



Habitat. — There are but few situations from wliich staphylococci may not be 

 isolated. In the animal body they are normally found in the nose, on the skin, 

 in saliva, in the intestinal contents, and in faeces ; they are frequently isolated 

 from suppurative processes (see Pathogenicity) ; and they are present in varying 

 numbers in air, water, milk, sewage, and on all articles liable to come in contact 

 with these substances. Their main habitat appears to be the nose. Several 

 workers (see Hallman 1937, McFarlan 1938, Gillespie et al. 1939) have shown that 

 they are present in the anterior nares of a high proportion of normal persons and 

 that 30 to 60 per cent, of persons are nasal carriers of potentially pathogenic 

 staphylococci. Relatively harmless members of the albus species are commonly 

 present on the skin, but the more dangerous aureus species is found on the hands 

 of only a small proportion of healthy persons who are usually shown, on investiga- 

 tion, to be heavy nasal carriers (Gillespie et al. 1939, Miles et al. 1944). Staph, aureus 

 has been reported in the milk of a high proportion of nursing mothers (Report 1942, 

 Duncan and Walker 1942), but whether this is a normal condition or whether it 

 occurs only in infected maternity wards is not clear. Ubiquitous as staphylococci 

 are their natural habitat is the animal body, and it is the animal body that furnishes 

 the main supply to the outside world. 



Morphology. — The staphylococci consist of round or somewhat oval cells, 

 having an average diameter of 0-8-1 -0^. The size is variable, not only from 

 one species to another, but in members of the same species ; it depends partly 

 on the age of the culture and the nature of the medium on which it is grown. 

 Some species are generally smaller than others ; thus the average diameter of 

 Staphylococcus aureus is 0-7-0 -9 jn, whereas the salivary staphylococci are said 

 to be larger, 1-0-1-2 /n. All the members of the group are non-motile, non- 

 flagellated, and non-sporing. They are usually described as non-capsulated. 



Lyons (1937), however, states that 



...^ •• capsules are demonstrable in 3-hour 



,;: ■ broth cultures, but disappear as 



•;' ,,'a\ .•■■ f the culture gets older. 



,. - ■• ■'■ '•' -■'"" ■ i.. The true staphylococci are 



,.f ' M ^' '■ arranged in grape-like clusters, 



" _ ;. ••• . \ A " ,^"" ^ that is to say they form groups, 



■•.A ■ ■•'•-"■*'■■■=?;:, „. ^'- • ■ the members of which are disposed 



./' "" .,;. , *. ■ ^ • * ^ '' in three planes of space without 



;' .• ' . ..* . ,.» f -t .„■'''''''' ::'.'*■ : regard to any definite configura- 



'.:'■■ '^ *. . ' tion. This distribution is best 



- .j^ •.... • • ,{. % J ' appreciated when a hanging drop 



.-f / / J^^" y\ . '•' preparation is examined — especi- 



\. ally if a stereoscopic microscope 



^^ ..••■■* .-• .. '"" J- is employed. The characteristic 



* .•;.. '■ ••■-<. ^ • grouping into clusters is more evi- 



* ^v. ** dent on solid than in liquid media. 



Fig. \25.— Staphylococcus aureus. Indeed in broth it is common to 



From an agar culture, 24 hours, 37° C. ( X 1000). find the COCci occurring, not only 



in groups, but in pairs and in 

 short chains ; they are then liable to be mistaken for streptococci. This con- 

 fusion may be accentuated owing to the fact that streptococci on soUd media tend 

 to lose their capacity for forming chains, and may develop in small clusters. 



