Most of the organisms, which make up the intestinal flora

in man belong to the family enterobacteriaceae. These may

include the intestinal commensals (the coliform bacilli

and Proteus species) as well as the enteric pathogens of

Salmonella and Shigella, intestinal streptococci, clostridia

and various yeasts including Candida albicans may be

present. The cholera vibrio may also be isolated.

Samples of feces should be sent to the laboratory in

disposable containers, e.g. cartons of waxed cardboard, which

are incinerated after use. Since feces contain innummerable

bacteria, and since selective media for enteric (intestinal)

pathogens are almost invariably used, aseptic precautions

are rather futile and unnecessary. It should be remembered,

however, that where blood and mucus are present in the

stool, this part should be especially selected for culture, since

the pathogens are most likely to be found there.

The feces are inoculated into a solid bile salt medium

such as MacConkey agar or deoxycholate-citrate-agar

(DCA) and also onto Wilson and Blair’s bismuth sulfite

medium. Liquid media such as Selenite F which will

inhibit the growth of the coliform bacilli or brilliant green

broth, which will enhance the growth of the pathogens: are

also inoculated. These are all incubated at 37oC over-night.

A Gram stain of the feces is of little value except in cases of

fungi and staphylococci infections.

Sputum

The commonly isolated organisms from sputum

are pneumococci, beta-hemolytic streptococci and

836 Concise Book of Medical Laboratory Technology: Methods and Interpretations

Mycobacterium tuberculosis. If the culture for organisms

other than M. tuberculosis is needed, all possible care

has to be taken while doing so. Rinse the mouth with an

antiseptic or clean water to avoid contamination from the

oral cavity. The specimen should be collected in a wide

mouthed sterile jar with a screw-cap lid. If the sample has

to be concentrated when culturing for M. tuberculosis,

there is less need for a sterile jar, in fact, disposable waxed

cartons are preferable since they and their contents can

safely be incinerated.