Commensalism

Competition Predation Commensalism Mutualism Synergism Antibiosis A race for nutrients and space One feeds on another One lives off another with negligible help or barm Each benefits the other Combination has cooperative metabolism One excretes a factor harmful to the other... 

Commensalism When two organisms coexist, one organism benefits, the other is not affected. 

P. acnes is an anaerobic diphteroid that populates the androgen-stimulated sebaceous follicles and is a normal constituent of the cutaneous microflora even if acne is not infectious, the commensal P. acnes acts in acne pathogenesis. Three pieces of evidence support the role of P. acnes in acne 1) higher counts of P. acnes in individuals with acne than in those without acne 2) correlation between the reduction of P. acnes counts and the clinical improvement of the disease and 3) correlation between development of acne and presence of antibiotic-resistant P. acnes organisms. P. acnes products mediate the formation of comedones and contribute to their rupture, leading to extrusion of... 

The optimum temperature varies widely from species to species but in general the common moulds will grow better at 22-25 °C than most human pathogenic and commensal bacteria. It is customary, therefore, to incubate mould cultures at lower temperatures than bacterial cultures. 

Lactic acid in the vagina gives it an acidic pH (5.0) which together with other products of metabohsm inhibits colonization by most bacteria, except some lactobacilli, which constitute the commensal flora. Other types of baeteria are unable to establish themselves in the vagina unless they have become extremely specialized. These species of microorganism tend to be associated with venereal infeetions. 

HOOPER L V, WONG M H, THELIN A, HANSSON L, FALK P G, GORDON J I (2001) Molecular analysis of commensal host-microbial relationships in the intestine. Science. 291 881—4. 

Commensal or environmental fungi that are typically harmless can become invasive mycoses when the host immune defenses are impaired. Host immune suppression and risk for opportunistic mycoses can be broadly classified into three categories (1) quantitative or qualitative deficits in neutrophil function, (2) deficits in cell-mediated immunity, and (3) disruption of mechanical/and or microbiologic barriers. 

Macpherson A.J., Geuking M.B. and McCoy K.D. (2005). Immune responses that adapt the intestinal mucosa to commensal intestinal bacteria . Immunology, 115, 153-163. 

Christensen BB, Haagensen JAJ, Heydom A, Molin S (2002) Metabolic commensalism and competition in a two-species microbial consortium. Appl Environ Microbiol 68 2495-2502... 

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