diplococos

Diplococci are bacteria that appear as pairs of spherical cells after division in one plane. This is a morphological description rather than a formal taxonomic grouping, and many different bacterial species can form diplococci in culture or in tissues. Diplococci can be Gram-positive or Gram-negative depending on the genus.

Notable diplococci include Streptococcus pneumoniae (Gram-positive, lancet-shaped diplococcus) and Neisseria species such as Neisseria meningitidis and Neisseria gonorrhoeae (Gram-negative diplococci). Moraxella catarrhalis is another Gram-negative diplococcus associated with respiratory infections. These examples illustrate the diversity of diplococci in terms of physiology and disease potential.

Ecology and transmission of diplococci vary by species. They commonly colonize human mucosal surfaces, especially the nasopharynx. Transmission occurs via respiratory droplets, close contact, or sexual contact (as with Neisseria gonorrhoeae). While many diplococci are commensals, several are important pathogens.

Clinical relevance arises from infections caused by diplococci, including pneumonia and meningitis (notably by Streptococcus pneumoniae and Neisseria species), meningococcemia, gonorrhea, and conjunctivitis, among others. Host factors and bacterial virulence determinants influence disease severity and presentation.

Laboratory identification relies on morphological and biochemical tests. On Gram stain, diplococci present as paired cocci. Neisseria and Moraxella are oxidase-positive; Neisseria are catalase-positive, often require enriched media and CO2 for growth. Streptococcus pneumoniae is catalase-negative, optochin-sensitive, and bile-soluble, with alpha-hemolysis on blood agar. Molecular methods can provide definitive species confirmation.

Prevention strategies include vaccines targeting pneumococcal, meningococcal, and gonococcal infections, which have reduced disease burden in many settings.