The human microbiota, normal health and infection

Question 1

Definition of Microbiota

Answer 1

The entire collection of microorganisms in a specific niche

Question 2

Definition of microbiome

Answer 2

Comprises all the genetic material within a microbiota

Question 3

Definition of Commensals

Answer 3

Microorganisms that reside on or in the body without causing harm

Question 4

Definition of normal flora

Answer 4

all the microorganisms associated with a healthy individual

Question 5

Definition of translocation

Answer 5

Movement of microorganisms from their usual location in the body to sterile body sites

Question 6

What is a biofilm

Answer 6

A thick layer pf bacteria which has formed aggregates on a surface along with extracellular material.

The bacteria within a biofilm can communicate with each other using quorum sensing.

Biofilms have an important role in protecting our body from invasion of other microbes

Question 7

The Importance of the microbiome

Answer 7

• protecting from invading microbes
• immune stimulation
• human nutrition and metabolism
  -linked to a number of diseases
• opportunistic pathogens
• translocation

Question 8

Circumstances which affect the the microbiome

Answer 8

• antibiotics
• lifestyle
• environment
• mother child inheritance

Question 9

Location of the microbiotas

Answer 9

• skin
• oral cavity
• gut
• urogenital tract
• upper respiratory tract

Question 10

Skin microbiota

Answer 10

• important role in the cutaneous immune system
• associated with an altered microbial state
• ## acts as a physical barrier to prevent invasion of pathogens

Question 11

Oral microbiota

Answer 11

• saliva is a source of nutrients but also contains antibacterial enzymes

DENTAL CARIES = as plaque accumulates, bacteria produce lactic acid which damage tooth enamel leading to tooth decay and cavities . Streptococcus sobrinus and streptococcus mutans are key species responsible

Question 12

Gut microbiota

Answer 12

• gut microbiota is affected by food and drink, medicines, exercise and sleep

DYSBIOSIS OF THE GUT MICROBIOME CAN LEADE TO NUMBEROUS DISORDERS :

• overgrowth and infection
• IBS
• Neurological disorders

Question 13

The urogenital tract

Answer 13

Mucous membraned support growth of specific microorganisms which can prevent colonisation by pathogens.

UTIS- epithelial cells lining the urethra are colonised by gran negative bacteria. Opportunistic pathogens present in the small amounts can multiply and cause infection

Bacterial Vaginosis - LACTOBACILLUS SP. dominate species in healthy vaginal microbiome and a reduction in LACTOBACILLUS SP. and an increase in anaerobic microorganisms leads to BV

Question 14

The respiratory tract

Answer 14

Some bacteria can colonise the host mucus layer :
- staphylococci and streptococci sp.
- gram negative cocci
- diphtheroid bacteria

COPD - associated with a change in species dynamic. Inflammation results in impairment of lung inmate immune response and increase in bacteria.

Asthma - studies have showed a link between microbiome development and wheezing.

Cystic Fibrosis - mucus builds up which can be colonised by resistant bacteria causing chronic and persistent infections

Question 15

Define of pathogenicity

Answer 15

the ability of a pathogen to infect a host and cause disease.

Pathogenicity is composed of 3 stages :
- exposure and adherence
- invasion, colonisation and infection
- host damage and disease

Question 16

Define Virulence

Answer 16

degree of damage or harm a pathogen can cause to a host

Question 17

Stage 1 of pathogenicity
(EXPOSURE AND ADHERENCE)

Answer 17

Microorganisms needs to penetrate the skin or mucous membranes.
Some microorganisms use blood and lymphatic system to move to site or cause systemic infection. Others use flagella, pili , fimbriae to move through the body.
Microorganisms often adhere to epithelial cells to initiate infection. Adherence is selective.

Question 18

Adherence factors

Answer 18

CAPSULE/SLIME LAYER
- pathogenic E coli = promotes adherence to the brush border of the intestinal microvilli
- Streptococcus mutans = slime layer promotes binding to tooth surfaces

ADHERENCE PROTEINS
- streptococcus pyogenes = M protein on the cell binds to receptors on respiratory mucosa
- neisseria gonorrhoea = opa proteins on the cell binds to CD66 receptors on epithelium

LIPOTEICHIOC ACID
-streptococcus pyogenes = lipoteichoic acid facilitates binding to respiratory mucosal receptor.

FIMBRIAE - PILI
- neisseria gonorrohoea - Pili facilitate binding to epithelium
- salmonella species = type 1 fimbriae facilitate binding to epithelium of small intestine
- pathogenic E. Coli = Fimbral colonisation factor antigens facilitate binding to epithelium of small intestine

Question 19

Stage 2 of pathogenicity (COLONISATION AND INFECTION)

Answer 19

• first the pathogen must multiply and colonise the tissue
• biofilms often form which are advantageous to the microbial cell in terms of attachment and colonisation

Question 20

Stage 3 of pathogenicity (TISSUE DAMAGE AND DISEASE)

Answer 20

Virulence is due to toxicity and invasiveness of the pathogen resulting in tissue damage. Invasion is ability to enter host cells/tissue, spread to other sites and cause disease. Toxicity is the ability to cause disease by means of a pre-formed toxin that inhibits host cell function or kills host cells

Question 21

EXOTOXINS

Answer 21

• proteins which are excreted by gram positive and negative bacteria.
• travel from site of infection and cause damage at distant sites
• highly toxin and specific in their action
• highly immunogenic stimulating the production of neutralising antibodies.
• easily inactivated and converted into toxoids

CYTOLYTIC = degrade the cytoplasmic membrane integrity

SUPER ANTIGEN = stimulate large numbers of immune cells leading to extensive inflammation and tissue damage
Toxic shock syndrome toxin of S. aureus

Question 22

ENDOTOXINS

Answer 22

• heat associated with cell envelope of certain gram negative bacteria.
• not secreted and are only released when cells are disrupted
• Induce illness, causing symptoms such as diarrhoea and vomiting
• cannot be destroyed by the sterilisation process and remain toxic to cells

SMALL QUANTITIES OF TOXINS :
. mild fever
- stimulation of the immune response

LARGE QUANTITIES OF TOXIN :
- high fever
- low bp
- increase heart/respiratory rate
- organ failure
- systemic inflammatory response
- tissue necrosis and death