CHAPTER XIII 

 MICROCOCCUS TETRAGENUS AND SARCINA 



Micrococcus tetragenus is found occasionally in the mouth and sputum of 

 healthy people. It is frequently present in the cavities and sputum of pul- 

 monary tuberculosis and in the pus from abscesses and suppurative lesions 

 of the mouth or naso-pharynx. 



Morphology. Micrococcus tetragenus is recognized by its arrangement in 

 fours forming a square. These groups of four are usually surrounded by a 

 capsule, but a capsule is not always visible. Each coccus is about the size of 

 the staphylococcus. Micrococcus tetragenus is non-motile, stains with all the 

 usual dyes and is Gram positive. 



Growth. All conditions favorable to growth of staphylococcus on culture 

 media suffice for cultivation of micrococcus tetragenus. 



On agar, potato and blood serum a luxuriant, thick, confluent, white growth 

 appears in 24 to 48 hours at 37C. Small, shiny white round colonies form on 

 gelatin; it is not liquefied. 



Milk is not coagulated. 



When cultured on artificial media micrococcus tetragenus usually loses its 

 capsule and very frequently loses its characteristic arrangement in fours so that 

 the appearance of stained smears from cultures is often indistinguishable from 

 staphylococci. 



Hay infusion culture medium is said to favor the preservation of the arrange- 

 ment in fours. 



Resistance. High and low temperatures and chemical germicides have the 

 same effect on this organism as on staphylococci. Oral administration of 

 sodium sulphite will cause the disappearance of sarcina in stomach contents. 



Pathogenesis. Micrococcus tetragenus is primarily a saprophyte. It 

 usually enters diseased areas as a secondary invader, after some virulent organ- 

 ism has injured or destroyed tissue. It can cause abscess formations and pus 

 either as a primary or secondary invader, usually the latter. At least one in- 

 stance is on record of this organism having entered the blood-stream and causing 

 septicemia. Its pathogenic properties and virulence are slight. 



Injected into white mice a fatal septicemia may result. Injected into rabbits 

 and other animals it causes an inflammation with or without pus formation, 

 followed by rapid recovery in most cases. 



Diagnosis. The characteristic arrangement of micrococcus tetragenus 

 suffices for its recognition in sputum, stomach contents, pus and other body 

 tissues or fluids. 



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