II - Microbiology & Infection - Symbiosis Flashcards
What is a symbiotic microorganism?
A symbiotic organism is one that we have a beneficial relationship too. In a healthy body there is a balance formed between us and microorganisms in our body.
- Direct benefits include the microbes breaking down nutrients for us
- Indirect benefit is that they grow and overcrowd the environment creating competition for pathogenic microbes.
The body does not always differentiate between a pathogen and a symbiotic organism, so they are subject to attack by the immune system. They do have mechanisms to protect themselves.
What would disrupt a symbiotic complex community?
- Changes in the number of microorganisms in the gut. This is subjective to different individuals.
- Pathogen invasion from the external environment and when they colonise the host
- Inflammation: IBS and colitis. Changes in the environment of the gut effects colonising symbiotic microorganisms
- Disease which causes infection. These can have side effects such as diarrhoea and cramps
- Taking antibiotics or synthetic drugs like chemotherapy, if they target pathogens, it may change the gut microbiota.
Antimicrobials are not given for a long duration (3-5 days) as to not affect the gut microbiota and allow pathogens to colonise the gut.
Restoration and maintenance of a healthy gut microbiota is needed and requires effective therapies to reduce and prevent colonisation of pathogens whilst simultaneously promoting growth of beneficial bacteria.
What are the different form of a symbiotic relationship?
Symbiotic relationship:
- Mutualism is a type of symbiosis that benefits both organisms. E.g., e-coli in the gut uses nutrients and in turn produced vitamins K and B.
- Commensalism is an association between two organisms in which one benefits and the other derives neither benefit nor harm. E.g., bacteria colonising an area and preventing pathogens colonisation – an indirect benefit
- Parasitism is habitual reliance on or exploitation of others.
How unique and organism is will show whether it is mutualistic or commensalic. If it is interchangeable, another organism can replace it and the relationship will not be affected, it is commensalic. If it is specific like E. coli in the gut, then that is mutualistic.
How is Peristalsis a challenge to bacterial survival?
- Peristalsis: the involuntary constriction and relaxation of the muscle of the intestines that helps food move along. As a result 10^10 bacteria are lost every day. This means the microorganisms need to divide through binary fission rapidly to make up the loss.
How is Oxidative stress a challenge to bacterial survival?
Oxidative stress: reactive oxygen and nitrogen species are indiscriminate so they can target host cells. Oxidative stress happens when there is a major infection/injury.
How are Antimicrobial peptides a challenge to bacterial survival?
Antimicrobial peptides, also called host defence peptides are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for antimicrobial peptides. These peptides are potent, broad-spectrum antibiotics which demonstrate potential as novel therapeutic agents. Antimicrobial peptides have been demonstrated to kill Gram negative and Gram-positive bacteria, enveloped viruses, fungi and even transformed or cancerous cells. Unlike most conventional antibiotics it appears that antimicrobial peptides frequently destabilize biological membranes, can form transmembrane channels, and may also enhance immunity by functioning as immunomodulators. They do however also affect good bacteria.
How is Microbe to microbe competition a challenge to bacterial survival?
Microbe to microbe competition: some microbes are bad at colonisation but live in the gut well and some microbes are the other way around
How is niche specificity a challenge to bacterial survival?
Niche specificity: e.g., there are different pH environments in the gut, so different organisms live in different pH. Another specificity is oxygen tolerance.
What are the problems with antibiotics?
- Human gut microbiota can be exposed to anthropogenic antibiotics
- Antibiotic therapy can result in drastic changes to gut microbiota composition
- Rapid evolution and expansion of antibiotic resistance
- Rise in antibiotic resistance matched development of new antibiotics
What are some strategies implemented to keep the current arsenal of antibiotics relevant?
Three major strategies to keep current arsenal of antibiotics relevant:
- Synthetic tailoring of antibiotic side groups. This is where the main mode of action is maintained by keeping the core structure the same, but the side groups are changed to prevent the resistant mechanism from taking place.
- Antibiotic combination. Different antibiotics have a synergistic (combined) activity so lower concentrations are used to achieve the same effect. The different drugs may target different biosynthetic pathways e.g., one can target a resistance mechanism and the other can target the actual bacteria
- Antibiotic cycling. This is when a person is given an antibiotic, they are resistant too, to increase their resistance then they are given another class of drug to treat the infection. This is because if there is one bacterium that is resistant to one antimicrobial agent then it tends to be more susceptible to another class of antimicrobial. The problem with this is that we are encouraging our resistance to occur and so is only clinically applied in extreme cases.
Each strategy aims to eliminate pathogens but has collateral damage to gut microbial community.
How can we promote beneficial bacteria?
Probiotics: Can treat variety of diseases including IBD, atopic disease (eczema), lactose intolerance, pathogen-associated diarrhoea, and necrotizing enterocolitis. I have the potential for stable integration into microbiota without the need for continue with ministration however they cannot colonise well, so they need to be constantly taken.
Prebiotics: (e.g. oligofructose) or addition of nondigestible carbohydrates to diet. They encourage good bacterial growth.
Using a combination of both probiotics and prebiotics is good to use to encourage gut microbiota to grow.
How does the spread of resistance occur?
The healthy gut bacteria will be invaded by a pathogen. Some of the healthy gut bacteria may carry a plasmid that has a resistant factor to it. If an antibiotic is applied only the organism that has resistance will survive. At this stage the good bacteria will share its resistance to other microbiota (a bit like evolution).
The resistance spreads too many different healthy gut bacteria. Now when a pathogen invade, it will be exposed to more bacteria that has the resistance. The resistance bacteria will now spread to the bad bacteria. This happens naturally.
Antibiotics do not cause resistance as they are not mutagenic, but they encourage resistance to emerge and spread.
What process helps us produce beneficial probiotics?
The good bacteria is taken from the poo. This is the gut coloniser. DNA is taken from the bacteria and the colonisation enhancing factors are looked at specifically. These factors are things like adhesions. Operon model is a set of genes that code for a specific biosynthetic pathway. It is this operon that is extracted from bacterial cells.
This allows us to bioengineer better probiotics
When do opportunistic microorganisms invade cells?
Under normal circumstances normal microbiota does not cause disease. Unless:
- There is introduction of a normal microbiota into an unusual site of the body
- There is an immune suppression
- There are changes in normal microbiota due to use of antimicrobials that affect it
How do we get persistent infections occurring from a commonsalic organism living on the surface of our skin?
Fungal microorganisms live on the surface of the skin and often they do not cause infections. They are regulated by commonsalic organisms that regulate them from over growing. If antibacterial treatment is given for an unrelated condition that may kill off commonsalic bacteria, allowing the fungus to overgrow and cause a systemic disease. an example of a fungus that can do this is candida.
Once they overgrow there is mucosal damage and neutropenia (lower than normal number of neutrophils) occurring. This results in the invasion of the epithelium. The fungus is now in the blood stream and it is spread around the body. The formation of biofilms may occur. Biofilms are protective polysaccharides that are very hard to penetrate. An example of a biofilm is plaque on teeth.
The reduction of neutrophils adds to the escalation of events. We can give antibiotics but biofilm will still exist. So a person may be cured form the current infection but the infectious material is still laying dormant in the biofilm. Once we stop antibiotic treatment the fungal microbe can regrow and re cause an infection.
In this instant the application of antibiotics has encouraged a fungal infection to grow.
