Bacterial Disease Flashcards
Describe bacteria?
Small, unicellular, prokaryotic, diverse and ubiquitous
Tend to lack membrane organelles
They outnumber humans by 6 x 10^9
Human/media terms
Friendly bacteria - ecosystem (nitrification), source of useful compounds (gut - vitamin K and biotin as well as clinical antibiotics) and food production
Bad bugs - disease in animals and humans, food spoilage and biofouling/corrosion
Why do bacteria cause disease?
To ensure continued survival, microbes need to:
Find a suitable habitat
Exploit that habitat - extract resources
Disperse to a new (suitable) habitat
In humans - to exploit habitat they will break down tissue to try to exploit its resources
Conditionally pathogenic - can cause infection in immunocompromised organisms
Give an overview of bacterial disease?
538 human pathogen species
Causes of death by bacteria has dramatically decreased e.g. Pneumonia/influenza
Therefore things like heart disease, cancer and strokes are now much higher
However, bacterial infection is still rife - 100 million cases per year in western Europe
e.g. acute respiratory infections, HIV/AIDs, diarrhoeal diseases, TB, malaria and measles
Give some examples of bacterial disease?
All surfaces/organs are susceptible to bacteria disease
Examples:
Impetigo - superficial infection of the skin
Pneumonia - affects the lungs
They can spread throughout the body be moving into the blood
Describes Koch’s ‘guidelines’ to link organisms to disease?
The microorganism must be present in every case of the disease (not in healthy animals)
The microorganism must be isolated from the diseased host and grown in pure culture
The specific disease must be reproduced when a pure culture of the microorganism is inoculated into a healthy susceptible host
The microorganism must be recoverable from the experimentally infected host and shown to be identical to the original causative agent
Most aren’t able to fufil all these
Describe the human microbiomes involvment in disease?
All body surfaces possess a rich normal flora
Mouth, nose, GI, urogenital tract, skin
Provides colonisation resistance
This coats our epithelial surfaces blocking receptors that infection/viruses may want to infect
Includes numerous conditional pathogens - complicates recovering specimens in a medical workup
Is a major source of disease
Can contaminate specimens
What is endogenous infection?
This is infection originating from the microbiome (within)
Skin infections, urinary tract infections, bacteria meningitis, pneumonia etc…
In many different infections around the body staphylococcus aureus - a major cause of infection
Human commensal bacteria
Carried by 1/3 of people - often living in your nose
Kills more people than HIV
If you go in for surgery you have a 1/50 chance of getting a staff orious infection
It causes a wide range of infection types/toxin mediated syndromes
What is exogenous infection?
Infection caused by the acquisition of infection from your outside environment - including sexually transmitted diseases
Acquiring these diseases:
Respiratory route - e.g. tuberculosis, pneumonia
Faecal-oral route - e.g. cholera
Venereal spread - e.g. syphilis, gonorrhoea
Vector-mediated - e.g. Plague (fleas)
What is zoonosis?
Infectious disease can be transmitted animal to human
May or may not cause disease in the animal host
60% of known human pathogens are zoonotic Anthrax Campylobacteriosis/ salmonellosis E. coli 0157:H7 Plague (Yersinia pestis)
Reverse zoonosis – disease transmission from human to animal
Give an overview of tuberculosis (TB)?
Caused by Mycobacterium tuberculosis
Primarily an infection of the lungs
Very non-specific symptoms - cough, chest pain, weight loss, bloody sputum
Latent vs. active infection
Symptoms are only present in the active disease
Granuloma formation - types: necrosis and fibrosis
Granuloma is a spherical mass of immune cells - which are seen on x-rays of TB patients
1/3 world’s population latently infected
1/10 latent infections become active disease
Untreated active TB kills 1/2
What is MDR and XDR in relation to TB?
These organisms are harder to eradicate as they don’t respond to the first line of treatment
MDR - multidrug resistant
Around 5% of cases of TB are multi-drug resistant
MDR can take up to 20 months to cure this cases of TB with a 70% cure rate (this is in a western world)
XDR - extensively drug resistant
A smaller portion fall in this category
What is bacterial pneumonia?
Affects alveoli in the lungs
Most common cause is Streptococcus pneumoniae
Also caused by: staphylococcus aureus, haemophilus influenzae, klebsiella pneumoniae and pseudomonas aeruginosa
Cough, fever, chest pain
O2 transport through alveoli compromised - affecting all gaseous exchange
Leakage of bacteria into bloodstream
What is synergy between viral and bacterial disease?
Major causes of human death
Influenza + bacterial pneumonia
Most deaths in 1918 flu pandemic due to pneumonia
Viral disruption of bronchial and lung cells
Variety of bacterial species, most endogenous
COVID + bacterial pneumonia
Critically ill patients had the highest percentage of bacterial coinfection
HIV and TB
High prevalence of latent TB infection
HIV+ individuals 800x more likely to develop active TB
TB major cause of death in HIV patients
What is food borne bacterial disease?
AKA “food poisoning”
Bacteria are a major cause of food-borne illness
1 million cases per year in the UK
20,000 hospital admissions and 500 deaths
Infectious vs. toxin-mediated
Infectious - you ingest the organism, it grows and causes symptoms (zoonotic)
Toxin - the organism has grown and caused a toxin within the food it grew in, the toxin then infects you and not the organism
Describe exotoxin mediated disease?
They are secreted by bacteria - toxic proteins
Toxin is ingested and causes disease:
Botulism caused by Clostridium botulinum
Food poisoning caused by Staphylococcus aureus
You ingest the organism and the toxin is produced once inside you
Cholera, anthrax, dysentry, typhoid, tetanus and E. coli infection
