Preclinical Paediatrics · MU Sofia

34. Microbial interactions. Interactions between micro- and macroorganisms.

Covers how oral microbes interact with one another, including coaggregation, competition, communication and collaborative invasion, then sets out the neutral, synergistic and antagonistic relationships with the mechanisms and an example of antagonism. It goes on to the host-microorganism links (symbiosis, commensalism, mutualism, parasitism). A closing summary traces plaque formation by stage and the ecological plaque hypothesis, with a table of interaction types and examples.

Inside: 2 sections · 1 table · 16 flashcards · 5 min

Topic 34 of 40 in the MU Sofia syllabus for Preclinical Paediatrics (Dental Medicine, Year 3). The free AceMed note covers it in 2 sections, about 645 words (5 min of reading), with 16 flashcards.

In this note

  1. MICROBIAL INTERACTIONS. INTERACTIONS BETWEEN MICRO- AND MACROORGANISMS
  2. Summary and extra points

MICROBIAL INTERACTIONS. INTERACTIONS BETWEEN MICRO- AND MACROORGANISMS

MICROBIAL INTERACTIONS:

INTERSPECIES COLLABORATION: some anaerobic species (e.g. fusobacterium or P.gingivalis) need to coaggregate to survive in the presence of O₂

INTERSPECIES COMPETITION: many oral species produce substances that can kill closely related competitors (e.g. Wild Type S.mutans)

INTERSPECIES COMMUNICATION: bacteria sense other species based on their characteristics (e.g. streptococci ferment CHO and excrete lactic acid and veillonella uses this for nutrition)

COLLABORATIVE INVASION: mainly coaggregation (e.g. F.nucleatum) invades epithelial cells but S.crisatus cant after coaggregation so S.crisatus is carried inside by F.nucleatum

BACTERIAL COAGGREGATION: process that helps in development and maintenance of mixed spp. Biofilm communities

MICROBIAL RELATIONSHIPS

NEUTRAL: between 2 species living together w/o affecting each other, neither favourable nor unfavourable

SYNERGY: between 2 species living together where both are mutually favoured, leading to enhancement of these effects of these

  • E.g. various MOs may cooperate to use substances that aren’t able to metabolise themselves, P.gingivalis & F.nucleatum unite to hydrolyse casein

ANTAGONISM: between 2 species living together where they inhibit their function or reduces the effect on the independent operation of each one of them

  • Mechanism of Microbial Antagonism:
  • Competition for adhesion receptors
  • Competition for nutrients
  • Production of inhibitory substances: Organic fatty acids, H₂O₂, dairy complexes, antibiotics, enzymes, bacteriocins
  • Example of Microbial Antagonism:
  • S.mutans & Lactobacillus produce lactic acid, causing an acidic environment
  • Inhibits growth of S.sanguis & S.oralis and Gram (-ve) microorganisms
  • Separation bacteriocum inhibit Gram (+ve) MOs

HOST (MACROORGANISM)- MICROORGANISM RELATIONSHIPS

SYMBIOTIC: includes association in which 1 organism lives on/in another or partner lives within the other

COMMENSALISM: between 2 organisms where one benefits and other is not significantly harmed or helped

  • May involve 1 organism using another for transportation or housing, or may also involve 1 organism using something another created after its death

MUTUALISM: individuals of different species both benefit. Host cell lacks some of the nutrients which are provided by the endosymbiont

  • Host favours endosymbiont’s growth processes within itself by producing some specialised cells
  • These cells affect genetic composition of the host in order to regulate the increasing population of endosymbionts and ensure that these genetic changes are passed onto offspring via vertical transmission
  • Mutualistic Relationship: allows each to grow in an environment where neither grow alone

PARASITISM: one member of the association benefits whislt the other is harmed; aka Antagonistic or Antipatheic symbiosis

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