Microbial Structures and Staining Reactions 91 



call the resulting formation a tetrad. Micrococcus tetragemis is a 

 common skin contaminant. 



Sarcina 



If a tetrad divides to form four spheres back to back with four 

 other spheres, this packet of eight cocci is a sarcina. An organism 

 commonly found floating on dust particles in the atmosphere is 

 Sarcina Jiitea. The specific name lutea is derived from the yellow 

 color this organism produces when grown on a solid medium under 

 aerobic conditions. 



Staphylococcus 



Haphazard multiplication in all planes resulting in masses of 

 cocci in grape-like clusters gives us an arrangement called a 

 staphylococcus. Representative members of this group include 

 Micrococcus pyogenes variety alhus (formerly called Staphylo- 

 coccus albus), a pus-producing inhabitant of normal skin, and its 

 golden-colored cousin Micrococcus pyogenes var. aureus, the 

 common cause of pimples, boils, carbuncles, osteomyelitis (a bone 

 disease), and blood poisoning. Both the albus and the aureus 

 varieties of this organism may be implicated in cases of food poison- 

 ing, but the golden variety is more often the causative agent. 

 Many workers in the field of microbiology, probably from force of 

 habit, prefer the term Staphylococcus food poisoning to Micro- 

 coccus food poisoning. 



The typical arrangement of mature cultures of bacteria is 

 characteristic of the species and aids in the identification process. 

 While it is true that a single sphere placed in a liquid medium must 

 first pass through the diplococcus stage before it can become a 

 tetrad, a streptococcus, a sarcina, or a staphylococcus, if that 

 single sphere was destined to be a staphylococcus, it will eventually 

 mature and have that arrangement. If a coccus is destined to 

 be a diplococcus, it will stop at the diplo stage. However, a diplo- 

 coccus may temporarily appear as a tetrad just at the time that it 

 is dividing into another diplococcus, but the characteristic arrange- 



