CHAPTER XV. 



MICROCOCCUS MELITENSIS. 



Historical. The organism was discovered by Bruce. 1 



Morphology. Micrococcus melitensis is a very small oval coccus, 

 occurring singly or in pairs, rarely in short chains; the individual 

 cells measure about 0.3 to 0.4 micron in diameter. Some observers 

 declare the organism to be a short bacillus, a view which is perhaps 

 based upon its appearance in old cultures, where various involution 

 forms are readily observed. The coccus form almost invariably pre- 

 dominates in fresh material. The organism is non-motile, possesses 

 no flagella and forms no capsule. Spore formation has never been 

 observed. It stains readily with ordinary anilin dyes, and is Gram- 

 negative. 



Isolation and Culture. One of the noteworthy cultural characters 

 of Micrococcus melitensis is its slow growth on artificial media, even 

 at 37 C. Suspected material, either blood, urine, milk, or material 

 from splenic puncture, should be spread upon the surface of slightly 

 acid agar and examined after three or four days' incubation for very 

 minute white colonies which have a darker center. The organism 

 grows slowly in gelatin, without producing liquefaction, and it pro- 

 duces a slight turbidity in broth. Milk appears to be a good medium 

 for its development, goats' milk being better than cows', milk for this 

 purpose. 



The coccus is aerobic, facultatively anaerobic. The minimum tem- 

 perature of growth is about 8 C., the optimum 37 C., and the 

 maximum about 44 C. Direct sunlight kills it in a few hours; an 

 exposure to 55 C. is usually fatal within an hour; 1 per cent, carbolic 

 acid kills it in ten to fifteen minutes. 2 It resists drying in the cold 

 and in the dark for several weeks. 



Products of Growth. Micrococcus melitensis is culturally inert; 3 it 

 produces no proteolytic enzymes and it produces neither acid nor gas 

 in any sugars. Milk, particularly goats' milk, becomes progressively 

 alkaline in reaction. No toxins have been demonstrated. 



1 Practitioner, September, 1887, xxxix, 161. 



2 Mohler and Eichhorn, Bureau of Animal Industry, 1911, xxviii, 125. 



3 Kendall, Day and Walker, Jour. Am. Chem. Soc., 1913, xxxv, 1247. 



