General Microbiology - Schlegel, H. G. 1987

Prokaryotes: Systematic Review
Gram-negative cocci (groups 10 and 11)

This group brings together Gram-negative non-motile cocci and short rods. They can be aerobic and

anaerobic (some are pathogens of infectious diseases). Among them are inhabitants of the soil, mucous membranes, and the mammalian intestinal tract.

Aerobic cocci (Group 10). The genus Neisseria gives a positive oxidase reaction and includes Bacteria pathogenic to animals and humans. N. gonorrhoeae is the CAUSATIVE AGENT OF Gonorrhea, a sexually transmitted disease that is now almost forgotten due to the extremely high sensitivity of this bacterium to penicillin (bacteriostatic concentration of 1 µg/ml). N. gonorrhoeae is difficult to cultivate, requiring 10% CO₂ in the air; it is very sensitive to light and desiccation, which is why infection can only occur through intimate contact. N. meningitidis is found in the nasopharynx, but can also invade the bloodstream and cause meningitis. Moraxella also yields a positive oxidase reaction and is very sensitive to penicillin. There are coccobacilli that are unable to utilize CARBOHYDRATES. Acinetobacter is an oxidase-negative bacterium found in soil and Water. An enrichment culture can be obtained in a nutrient medium at pH 5.5–6.0 containing 0.2% acetate and easily isolated; as a rule, it does not utilize glucose, di- and Polysaccharides, but otherwise resembles Pseudomonas in its versatile substrate utilization capabilities. Genetic exchange via transformation is possible between strains of Acinetobacter calcoaceticus.

Important for the Cytology/practical/136.html">Differential Diagnosis OF this group, the oxidase reaction is based on The conversion of dimethyl-p-phenylenediamine (N,N-dimethyl-1,4-diaminobenzene) into a colored compound under the action of soluble cytochrome c. Drops of the reagent are applied to colonies grown on Agar, and the appearance of a red color is observed.

Anaerobic cocci (Group 11). The best-known Gram-negative strictly anaerobic cocci are Veillonella alcalescens (formerly Micrococcus lactilyticus) and Megasphaera (Peptostreptococcus) elsdenii. Both are incapable of fermenting carbohydrates. V. alcalescens is found in the saliva of humans and animals and in the rumen of ruminants. They ferment organic acids, particularly lactate, converting them into propionate, acetate, CO₂, and H₂ (see sections 8.3 and 14.1). Megasphaera elsdenii ferments glutamic acid and Other Amino Acids; apparently, it is a common inhabitant of the animal digestive tract.