Gramnegative Coccus

Artificial (practical) group of bacteria comprising Gram-negative coccoid bacteria of various sizes (approximately 0.3-0.5 to 2.5 μm).

The gram-negative cocci are divided into the families:

Neisseriaceae with the genera:

• Neisseria
• Eikenella
• Kingella

Moraxellaceae with the genera:

• Moraxella
• Acinobacter

_________________________________________________________________________________

Neisseriaceae

The classic and best known representatives of this family are the gonococci and meningococci. These characteristically occur as diplococci, also as single cells, in clumps or (short) chains. The staining behavior is typically gram-negative. In the family Neisseriaceae, the following genera are of human pathological importance:

Neisseria genus:

• Neisseria gonorrhoea (aerobic diplococci, causative agent of gonorrhoea).
• Neisseria menigitis (gram-negative diplococci, nasopharynx - causative agent of epidemic meningitis and Waterhouse-Friderichsen syndrome)
• Neisseria lactamica (nasopharynx - causative agent of epidemic meningitis)
• Neisseria cinerea (nasopharynx - causative agent of epidemic meningitis)
• Neisseria sicca (nasopharynx - causative agent of epidemic meningitis)
• Neisseria flavescens (nasopharynx - causative agent of epidemic meningitis)
• Neisseria elongata (urogenital mucosa)

Genus: Eikenella

• Eikenella corrodens (single species; part of the mucosal flora of the oral cavity; coccoid gram-negative, aerobic short rods (Eikenella corrodens are part of the normal body flora of humans and may occasionally participate in infections; the pathogens belong to the HACEK group of bacteria: HACEK is the acronym for a group of gram-negative, bacterial endocarditis pathogens that, because of their special growth conditions, grow in the laboratory only after prolonged incubation; they account for approx. 3 % of all endocarditis).

Genus: Kingella (aerobic, gram-negative, coccoid, rod-shaped bacteria, colonizers of the oral cavity; belongs to the family Neisseriaceae and is counted among the so-called "fastidious gram-negative rods").

• Kingella kingae (part of the normal pharyngeal flora; infections of the oral mucosa or upper respiratory tract; like Eikenella, Kingella kingae belongs to the HACEK group and is thus a potential causative agent of endocarditis).

Family of the Moraxellaceae

The members of this family are gram-negative cocci resembling Neisseria spp. However, they can be distinguished by routine biochemical tests after cultural isolation from infected fluids or tissues.

Genus Moraxella

• Moraxella catarrhalis (colonizer of the nasopharynx in healthy individuals - causative agent of sinusitis, otitis media, bronchitis, and severe pneumonia).

Genus Acinobacter (coccoid gram-negative, aerobic, coccoid short rods with occurrence in the environment. As pathogens of nosocomial infections they represent a medical problem)

• Acinobacter baumannii (pathogen of nosocomial infections, risk of occurrence of 3-MRGN and 4-MRGN - strict isolation)
• Acinobacter calcoaceticus
• Acinobacter lwoffii

1. Hof H et al (2019) Oral streptococci. In: Hof H, Schlüter D, Dörries R, eds Duale Reihe Medizinische Mikrobiologie. 7th, completely revised and expanded edition. Stuttgart: Thieme p 386-394