microbiology- biological science

intoduction to mircobiology

what are infectious diseases caused by?

microorganisms

what are the different criteria which must be met in order that a condition falls under the remit of an infectious disease called

koch’s postulates (4 conditions)

what are the 4 koch’s postulates conditions? (theory of germ disease)

1. The organism responsible MUST be present in EVERY case

2. It MUST be possible to isolate the organism from a diseased individual and grow it in pure culture

  – not always the easiest thing to achieve!

3. It MUST be able to cause the disease when a healthy animal is infected with the pure culture

4. The organism MUST be recoverable from an animal which has been experimentally infected

name types of microbes?

• bacteria

• fungi

• protozoa

• viruses

• algae

what are general properties of bacteria?

• prokaryotes

• lack organelles

• no nucleus

what are general properties of fungi?

• eukaryotes

• contains a nucleus- may even contain multiple nuclei

• contains organelles- e.g. mitochondria

what are general properties of protozoa?

• eukaryotes

• contains a nucleus- may contain multiple

• contains organelles- e.g. mitochondria

what are general properties of viruses?

• incapable of independent life- requires a host for replication

what are general properties of algae?

• multi and unicellular

• eukaryotes

• photosynthetic

• capable of causing potent toxins

examples of bacteria which can cause human diseases?

Escherichia coli – found in digestive tract

Neisseria gonorrhoeae – causes gonorrhoea

Clostridium tetani – causes tetanus

Mycobacterium tuberculosis – causes tuberculosis

Borrelia burgdorferi – causes Lyme disease

examples of fungi relevant to humans?

Trichophyton rubrum – involved in athlete’s foot

Penicillium chrysogenum  - source of penicillin

Aspergillus nidulans – involved in farmer’s lung

Saccharomyces cerevisiae – brewing and baking industries

examples of protozoa associated with diseases?

Giardia lamblia – giardiasis (digestive tract infection)

Trypanosoma brucei – sleeping sickness

Entamoeba histolytica - amoebiasis (digestive tract infection)

Trichomonas vaginalis – trichomoniasis (STI)

exapmles of viruses associated with diseases?

Human Immunodeficiency Virus

Ebolavirus

Hepatitis Viruses

West Nile Virus

Corona Virus

examples of algae associated with diseases?

Gambierdiscus toxicus – ciguatera fish poisoning

Various – amnesic, paralytic, diarrheal, neurotoxic shellfish poisoning

Raphidiopsis raciborskii – Palm Island Mystery disease

Alexandrium catenella – Saxitoxin (nerve agent – classed as WMD)

what are internal organs generally free of?

mircoorganisms

(digestive/urinary tracts are outside the body therefore they have lots of mircoorganisms)

Collectively the microbiota (microbial community ) associated with an organism is called its?

mircobiome

how is the human microbiome distributed?

found in different places, some outside the body and other inside the body

(it also introduces the idea of different levels of diversity)

what are most species of microbe in the human body mircobiome?

bacteria

(these colonise from birth onwards and the population changes overtime)

early bacteria colonisers are known as?

commensal bacteria

what type of relationship does (commensal) bacteria have with its host and describe features?

mutualistic/symbiotic

Access to nutrients

Defence

Multiple factors influence early colonisers

Diet

Environmental factors

Geographic location

Use of antibiotics

what does Healthy (intact) skin acts as a reliable barrier to?

most bacterial attacks

(however many microbes will adhere to the surface of the skin)

Some bacteria can attach to surfaces and grow (biofilms) which often involves?

attachment of bacterial adhesins to glycoproteins of the skin surface

describe bacterial distribution on the skin (external)?

although bacteria can colonise much of the skin, distribution is not even.

certain areas have more mircobes than others and different species in different places

factors influencing skin distribution?

• nutrients

• moisture

• temperature

• pH

• skin shedding

• fluid osmolarity

• potential inhibitors

where do the largest number of bacteria tend to be found in on the skin?

regions with most apocrine sweat glands

what are the two groups of skin associated mircobes?

• resident microbes

• transient microbes

resident population tend to have evolved to preserve?

nutrients in this niche

resident populations produce bacteriocins to kill?

transient species, or help the resident species outcompete the transient species

exposed areas of the skin tend to have high numbers of which microbal species?

transient species

(face, neck, hands, ect.)

conditions are often not favourable for transient species, so what often happens to them?

they cannot replicate and multiply so they die off

transient mircobes come in contact with skin and may attach due to which conditions/factors

environmental

domestic

occupational

what do The digestive tract, respiratory tract and urogenital tract have direct contact with?

the outside of the body

(they also have their own microbial community)

what does the oral cavity provide an excellent environment for?

mircobal growth

why is the oral cavity an excellent environment for mircobal growth?

• constant temperature

• moist environment

• ready supply of nutrients

• range of surfaces for attachment

due to food and drink being ingested, what is there a risk of?

mircobes being washed away

(therefore microbes attach to surfaces and also form biofilms)

what are the attachment sites for microbes on the oral cavity?

• tongue

• teeth

• corners of mouth/ lips

• gums

• epithelial cells

why does the nasal cavity provide favourable conditions for microbal growth?

• moist conditions

• relatively constant temperature

• nutritional sources from secretions

how do microbes enter nasal cavity?

during inhalation

(In more distal areas of the respiratory tract this can also be true, but the mouth provides a point of contact via pharynx)

what is the stomachs pH?

very acidic

pH 1.5-2.0

(however there are still organisms in this area, passed from person to person or from food)

many probiotic mircobes act best in which region of the stomach?

lower gut

• however have to survive the acidic condtions of the stomach to get there

an example of an organism that prefers to live in the environment of the stomach?

Helicobacter pylori

This is a major source of gastric ulcers

(Once into the stomach Helicobacter can colonise the mucosal surfaces. Once attached it can cause inflammation and then ulceration)

mircobal community of the small intestine changes due to several variables such as?

• age

• diet

• geographical distribution

• antibiotic exposure

• health

• pH

the number of mircobes in the figure are expressed in terms of what?

numbers per gram of digesta

(Examples of organisms present here are species from the genera Enterococcus, Bacteroides and Lactobacillus)

the hindgut population contains numerous species (very diverse), many of them are?

obligate anaerobes - oxygen is toxic to them

(pH in this area is relatively neutral, 4-7)

what does bacteria do in the large intestine?

helps to break down foods and synthesizes molecules such as some vitamins

what is the relationship between bacteria and the large intestine?

symbiotic

human supplies nutrients

what do microbial numbers and composition in the large intestine change with?

changes with age

(Potential links to increased predisposition to diarrhoea in the elderly)

what can also influence the composition and distribution of the microbial community in the large intestine?

diet

(Vegetarian diet versus those that eat meat

Differences in those eating red meat versus those eating white meat)

Why are probiotics sold?

to enhance digestive efficiency

RECTUM

why is the rectal bacterial population very dense?

due to water being reabsorbed

what metabolites do bacterial population produce in the rectum?

• hydrogen sulphide

• methane

• hydrogen

• volatile fatty acids (vfa)