Moraxells

The genus Moraxella includes gram-negative bacteria, usually in the form of very short round rods with typical dimensions of 1.0-1.5 x 1.5-2.5 µm, often acquiring the form of cocci, located mainly in pairs or short chains. Some cultures retain a distinct shape, others are pleomorphic: the size and shape of the cells vary, sometimes they form threads and long chains. Polymorphism increases with a lack of oxygen and at temperatures above the optimum for growth (32-35 °C). They do not form spores and do not have flagella. Some strains exhibit "twitching" motility on a dense surface. Capsules and fimbriae may or may not be present. Moraxella are chemoorganotrophs with oxidative metabolism, the optimum pH is 7.0-7.5. Strict aerobes. Most strains are demanding of nutrient media, but specific growth factors are poorly known. A small number of organic acids, sterols and amino acids are used as a source of carbon and energy. They do not consume carbohydrates. They have oxidase and usually catalase. They do not form indole, acetoin and H2S. They are highly sensitive to penicillin. The G+C content in DNA is 40-46 mol%.

Moraxella are parasites of the mucous membranes of humans and warm-blooded animals; saprophytes may also exist. The genus Moraxella includes two subgenera: Moraxella proper and Branhamella. The key features of the main species of Moraxella are as follows.

• They do not grow on mineral media with acetate and ammonium salts.
• The curdled whey is liquefied.
• They cause hemolysis on chocolate agar.
• Usually form nitrites.
• Hemolysis is not observed on blood agar.
  • M. lacunata.
• Nitrites are not formed. Hemolysis is usually observed on blood agar.
  • M. bovis.
• The coagulated serum is not liquefied. Hemolysis is not given on "chocolate" agar.
• Phenylalanine deaminase is absent.
  • M. nonliquefaciens.
• Phenylalanine deaminase is present.
  • M. phenylpyruvica.
• They grow on a mineral medium with acetate and ammonium salts.
  • M. osloensis.

The subgenus Branhamella includes 4 species, including Moraxella catarrhalis, previously called Micrococcus catarrhalis. Usually has the form of gram-negative cocci, located in pairs. Does not form spores, has no flagella, forms a capsule, does not ferment carbohydrates, does not form polysaccharides from sucrose. Grows on nutrient agar and on a medium containing amino acids, mineral salts, biotin and lactate or succinate as a source of energy and carbon. Does not form urease, H2S and indole. Forms lipase, cytochrome oxidase, catalase and DNase. Reduces nitrates to nitrites. Aerobe, temperature optimum 37 °C, but grows at 22 °C. The content of G + C in DNA is 40-45 mol %. Sensitive to penicillin. It is a parasite of the mucous membranes of humans and mammals. It is often found on the mucous membrane of the cervix and urethra in healthy women. It can cause inflammation of the mucous membranes independently or in association with other bacteria. There is a report that it can cause meningitis. The pathogenicity of many Moraxella for humans has not been sufficiently studied, but they cause inflammatory diseases of the mucous membranes on which they parasitize. For example, M. lacunata, M. bovis often cause conjunctivitis in people living in poor sanitary and hygienic conditions. Some species, such as M. osloensis and M. phenylpyruvica, are potential pathogens of septicemia, meningitis or pyogenic diseases.