The human microbiota, normal health and infection Flashcards
Definition of Microbiota
The entire collection of microorganisms in a specific niche
Definition of microbiome
Comprises all the genetic material within a microbiota
Definition of Commensals
Microorganisms that reside on or in the body without causing harm
Definition of normal flora
all the microorganisms associated with a healthy individual
Definition of translocation
Movement of microorganisms from their usual location in the body to sterile body sites
What is a biofilm
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
The Importance of the microbiome
- protecting from invading microbes
- immune stimulation
- human nutrition and metabolism
-linked to a number of diseases - opportunistic pathogens
- translocation
Circumstances which affect the the microbiome
- antibiotics
- lifestyle
- environment
- mother child inheritance
Location of the microbiotas
- skin
- oral cavity
- gut
- urogenital tract
- upper respiratory tract
Skin microbiota
- important role in the cutaneous immune system
- associated with an altered microbial state
- ## acts as a physical barrier to prevent invasion of pathogens
Oral microbiota
- 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
Gut microbiota
- 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
The urogenital tract
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
The respiratory tract
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
Define of pathogenicity
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
Define Virulence
degree of damage or harm a pathogen can cause to a host
Stage 1 of pathogenicity
(EXPOSURE AND ADHERENCE)
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.
Adherence factors
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
Stage 2 of pathogenicity (COLONISATION AND INFECTION)
- 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
Stage 3 of pathogenicity (TISSUE DAMAGE AND DISEASE)
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
EXOTOXINS
- 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
ENDOTOXINS
- 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
