Bacterial pathogenicity Flashcards
What is a pathogen
An organism capable of causing disease
What is a commensal
An organism that is part of the normal flora
What is pathogenicity
The ability to cause disease
What is virulence
The ability to cause severe disease
What is the simple life cycle of a parasite
Enter
Attach
Colonise
Evade host immunity
Produce harmful proteins
Disseminate
Release from host
What are the subdivisions of microorganisms
Bacteria
Fungi
Viruses
Prions
Parasites
What is microbiology
The study of microscopic organisms; sub-disciplines include virology, mycology, parasitology, and bacteriology
What are some flora found in the nasopharynx
Streptococci
Candida
Neisseria
What normal flora are found on skin
Streptococci
Staphylococci
Yeasts
What flora are found in the lower bowel
Bacteroides
Clostridium
What flora are found within the vagina
Candida
Lactobacilli
Corynebacteria
What is colonisation
When microbes find a new host and start to multiply
What is an endogenous infection
An infection caused by the patient’s own flora
What is an exogenous infection
Infection from external flora
What is the difference between primary and opportunistic pathogens
Microbes that always cause disease in a new susceptible human are called primary pathogens while microbes that cause disease only in immunocompromised patients are called opportunistic pathogens
What is the carrier state
The continued presence of an organism (bacteria, virus, or parasite) in the body that does not cause symptoms, but is able to be transmitted and infect other persons
What is bacterial colonisation
The presence of bacteria on a body surface (like on the skin, mouth, intestines or airway) without causing disease in the person
What is the germ theory of disease
The microbe must be present in every case of the disease
The microbe must be isolated from the diseased host and grown in pure culture
The disease must be reproduced when a pure culture is introduced into a susceptible host
The microbe must be recovered from an experimentally infected host
Who created the germ theory of disease
KOCH’S POSTULATES (1890)
How can diseases be spread
Person-to-person
-Contaminated blood or other bodily fluids
-Touch
-Saliva
-Air
Fomites
Insects
Water
Food
What features pf a prokaryotic cell are usual
Cell envelope
DNA
Cytoplasmic membrane
Ribosomes
What MAY be present in a prokaryotic cell
Capsule
Inclusion granules
Frimbriae (pilli) (gram -ve)
Flagellum
Membranous invagination
Defence against UTIs
Main defence is flushing action of urine
Tamm-Horsfall protein helps bind specific Escherichia coli strains and remove them
What are some encapsulated infections
Meningitis, pneumonia, otitis media and sinusitus
What is the function of a bacterial capsule
Mediate adhesion
Immune evasion
Protection from desiccation
Reserves of carbohydrate
Encapsulated bacteria give rise to smooth colonies
Capsule material gives rise to ‘capsular antigens’ - strep infections
What are endotoxins
Produced inside mostly Gram -ve bacteria as part of their growth and metabolism
They are secreted and released following lysis into the surrounding medium
What are endotoxins
Part of the outer portion of the cell wall or Gram -ve bacteria
They are liberated when bacteria die and the cell wall breaks apart
What is the point of LPS (endotoxin)
Promotes production of platelets, clotting factors, mast cells, macrophages, inflammatory response etc
These responses when uncontrolled can lead to hypertension and toxic shock which can result in death
Lethal bacterial proteins (exotoxins)
Botulinum 0.6x10-8 (mouse)
Tetanus 4x10-8 (mouse)
Shigella toxin 2.3x10-6 (rabbit)
Difference between endo and exo toxins
ENDO
Lipopolysaccharide
Outer membrane
Not very potent
Low specificity
Pyrogenic
EXO
Protein
Extracellular (diffusible)
Highly potent
Very specific
Occasionally pyrogenic
Virulence factors
Fimbriae (pilli)
-adhesion
Capsule
-protection/camouflage
Flagella
-Chemotaxis, Penetration
LPS/Endotoxin
-endotoxic shock/ inflammation
