Microbial Infections Flashcards
What bacteria causes TB?
Mycobacterium tuberculosis
What are Koch’s postulates?
1- Bacteria must be present in every case of the disease
2- Bacteria must be isolated from the host with the disease and grown in pure culture
3- The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host
4- The bacteria must be recoverable from the experimentally infected host
What are two different ways in which the body resists infection?
1- Innate immune system
2- Normal flora
What does the innate immune system consist of?
1- Normal microbiota
2- Physical barriers
3- Chemical barriers
4- Phagocytic cells
There are more ____ cells than human cells in the body?
Prokaryotic
What is normal microbiota?
1- An ecological community of microorganisms- both ‘good’ and ‘bad’- present on or in the body
2- These offer protection by competing with pathogens for colonisation sites
3- Produce either antibiotic substances called bacteriocins or toxic metabolix substances to suppress growth of competing organisms
4- May alter pH (e.g. Lactobacilli)
5- Can be suppressed by antibiotics
What are the physical barriers of the immune system?
1- Skin: secretes sebum and fatty acids to inhibit growth of pathogens, however some microbes have evolved mechanisms to help them penetrate the skin
2- Mucomuciliary clearance: particles settle/are trapped on sticky mucus of respiratory epithelium, debris is transported by cilia to oropharynx where it is swallowed
3- Flushing: urinary tract, bacteria is flushed out
4- Peristalsis: GI tract, helps remove infective agents
What are the chemical barriers of the immune system?
1- Mucus: traps infective agents
2- Antimicrobial proteins: e.g. lysozyme, lactoferrin, defensins
3- Gastric acid: low pH helps destroy harmful pathogens
4- Plasma proteins: complement, C-reactive protein (CRP), Mannose-binding lectin (MBL), transferrin
What is phagocytosis?
1- Ingestion of foreign cell
2- Process used by the human body to destroy dead or foreign cells
What are the five different types of phagocytes?
1- Macrophages 2- Neutrophils 3- Monocytes 4- Dendritic cells 5- Mast cells
When does an infection occur?
When a micro-organism causes ill health
In what two ways can infection occur?
1- Invading host tissue
2- Exerting effect from mucosal surfaces
Define commensal
1- A micro-organism which forms part of the normal host microbiota
2- Benefits from others without affecting them
Define pathogen
A micro-organism capable of causing infection
Define pathogenicity
The capacity to cause disease
Define virulence
1- Measure of the capacity to cause disease
2- Degree of pathogenicity
What are the three types of pathogens?
1- Obligate pathogen
2- Conditional pathogen
3- Opportunistic pathogen
What is an obligate pathogen?
1- A type of pathogen that is almost always associated with disease
2- E.g. HIV
What is a conditional pathogen?
1- A pathogen which may cause disease if certain conditions are met
2- E.g. Bacteroides fragilis, Staphylococcus aureus
What is an opportunistic pathogen?
1- A pathogen which usually only infects an immunocompromised host
2- E.g. Pneumocytis jiroveci
What are the six steps of infection?
1- Recognition 2- Attachment and entry 3- Multiplication 4- Evasion of host defences 5- Shedding 6- Damage
How can an otherwise healthy host be infected?
1- Microbes with specific mechanisms for attachment and penetration of host’s body surfaces
2- Microbes introduced into host by anthropods (e.g. insects) that bite
3- Microbes introduced into host via skin wounds or animal bites
4- Microbes which are able to infect only when host is immunocompromised or their defences are impaired
Waht is tissue tropism?
1- The affinity for a specific tissue
2- This defines the cells and tissues of a host which support the growth of a particular microbe
3- Some microbes have broad tissue tropism, affecting many different types of tissue
4- Others may infect a certain type of tissue
5- Influencing factors include: presence of cell receptors, transcription factors, local temperature, physical defences, efficiency of barriers, and pH levels.
What are the two levels of tissue tropism?
1- Broad tissue tropism
2- Specific tissue tropism
What are the influencing factors in tissue tropism?
1- Presence of cell receptors 2- Presence of transcription factors 3- Local temperature 4- Physical defences 5- Efficiency of barriers 6- pH levels
Which tissue does Varicella zoster virus (VZV) have a high affinity to?
Nerve cells
Which tissue does rhinovirus have a high affinity to?
Upper respiratory tract cells
What tissue does Hep B have a high affinity to?
Liver cells
What tissue does helicobacter pylori have a high affinity to?
Gastric mucosa cells
What tissue does Campylobacter jejuni have a high affinty to?
Intestinal epithelial cells
What tissue does Epstein Barr virus have a high affinity to?
B lymphocyte cells
What tissue does HIV have a high affinity to?
T lymphocyte cells
What tissue does Neisseria gonorrhoeae have a high affinity to?
Urethral epithelial cells
What does Vibrio cholerae have a high affinity to?
Intestinal epithelial cells
What seven factors contribute to virulence?
1- Toxin secretion (toxigenesis) which are produced by bacteria and fungi
2- Antibiotic resistance
3- Pilus formation
4- Capsule strength and efficiency
5- Iron transport systems
6- Adhesion factors called adhesins
7- Enzymes e.g. proteases, DNAses and lipases
What are the two types of bacterial toxins?
Endo and Exo
Describe endotoxins
1- Highly toxic
2- Secreted from both Gram-positive and Gram-negative bacteria
3- Can be converted to toxoids for vaccine use
4- E.g. tetanus toxin, cholera toxin, botulinum toxin
Where can antibiotic resistance genes be found?
On plasmids
How can bacteria be resistant to antibiotic?
1- Production of enzymes such as β-lactamase
2- Impermeability
3- Efflux mechanisms
4- Alteration of target site
What are important examples of antibiotic resistance?
1- Meticillin-resistant Staphylococcus aureus (MRSA)
2- Vancomycin-resistant Staphylococcus aureus (VRSA)
3- Multi-resistant Mycobacterium tuberculosis
4- HIV
5- Malaria
What is MRSA?
Meticillin-resistent Staphylococcus aureus
What is VRSA?
Vancomycin-resistent Staphylococcus aureus
What three factors is transmission dependent on?
1- Number of micro-organisms shed
2- Number of micro-organisms required to infect a ‘fresh’ host i.e. the efficiency of the infection
3- The micro-organisms stability in the environment
In what two pathways can transmission occur?
1- Horizontal
2- Vertical
What is horizontal transmission?
Transmission from one individual to another in the same generation (not parent-child)
What is vertical transmission?
Transmission from parent to offspring
What are the nine different routes to human-to-human transmission?
1- Respiratory 2- Faeco-oral 3- Veneral 4- Skin 5- Perinatal 6- Semen 7- Blood 8- Breast milk 9- Saliva
What route are TB, influenza and the common cold all transmitted by?
Respiratory
What route are cholera and shigellosis both transmitted by?
Faeco-oral
What route are chlamydia, HIV and HPV all transmitted by?
Venereal
What route are the ringworm and S. aureus both transmitted by?
Skin
What route are HIV, meningitis
Perinatal
What route are HIV, HBV, and cytomegalovirus all transmitted by?
Semen
What route are HIV, HBV and malaria transmitted by?
Blood
What route can HIV be transmitted by from mother to child?
Breast milk
What route can EBV and herpes simplex virus both be transmitted by?
Saliva
What are the two routes of animal-to-human transmission (zoonoses)?
1- Invertebrate vectors e.g. anthropods and shellfish
2- Vertebrate vectors e.g. mammals and birds
What is fomite transmission?
Transmission via inanimate objects e.g. door handles, cutlery, etc.
What are nosocomial infections?
nosocomial infections?
1- Infections acquired during a hospital stay
2- Major public health concern
