Microbial Infection Flashcards
What are Koch’s Postulates?
+ The bacteria must be present in every case of disease
+ The bacteria must be isolated from the host with the disease and grown in pure culture
+ The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host
+ The bacteria must be recoverable from the experimentally infected host
What does the innate immune system consist of?
+ Normal macrobiota
+ Physical barriers
+ Chemical barriers
+ Phagocytic Cells
What are features of normal microbiota?
+ More prokaryotic cells than human cells in the body
+ Offers protection by competing with pathogens for colonisation sites
+ Produce antibiotic substances suppressing growth of competing organisms (bacteriocins)
+ May produce toxic metabolic products to inhibit other micro-organisms
+ May alter pH e.g Lactobacilli
+ Suppressed by antibiotics
What are the physical barriers of the body?
+ Skin
+ Mucomuciliary clearance
+ Flushing (urinary tract)
+ Peristalsis (GI tract)
What are the features of skin as a physical barrier?
+ Secretes sebum and fatty acids to inhibit growth
+ Microbes have evolved mechanisms to penetrate skin
What are the features of mucomuciliary clearance as a physical barrier?
+ Particles settle on sticky mucus of respiratory epithelium
+ Debris transported by cilia to oropharynx where it is swallowed
What are some of the chemical barriers within the body?
+ Mucus
+ Antimicrobial proteins
- lysozyme
- lacroferrin
- defensins
+ Gastric acid
+ Plasma proteins
- complement
- C-reactive protein
- Mannise-binding lectin (MBL)
- transferrin
Name different types of phagocytes
\+ Macrophages \+ Neutrophils \+ Monocytes \+ Dendritic cells \+ Mast cells
What are the two ways that a micro-organism can an cause infection by causing ill-health?
+ Invading host tissues
+ Exerting effects from mucosal surfaces
What is a commensal?
A micro-organism which forms part of the normal host microbiota
What is a pathogen?
A micro-organism capable of causing an infection
What is pathogenicity?
The capacity to cause disease
What is virulence?
Measure of the capacity to cause disease i.e degree of pathogenicity
What are the different types of pathogens?
+ Obligate
+ Conditional
+ Opportunistic
What is an obligate pathogen?
+ Almost always associated with disease
+ E.g HIV
What is a conditional pathogen?
+ May cause disease of certain conditions are met
+ E.g Bacteroides fragilis, Staphylococcus aureus
What is an opportunistic pathogen?
+ Usually only infects immunocompromised hosts
+ E.g Pneumocystis jiroveci
What are the steps of infection?
> Recognition > Attachment & entry > Multiplication > Evasion of host defences > Shedding > Damage
What are ways that infection can be established in normally healthy hosts?
+ Microbes with specific mechanisms for attachment and penetration of host’s body surfaces
+ Microbes introduced into host by biting arthropods
+ Microbes introduced into host via skin wounds or animal bites
+ Microbes able to infect only when host defences are impaired
What is tissue tropism?
+ Affinity for a specific tissue
+ Defines the cells and tissues of a host which support the growth of a particular microbe
+ Some microbes have a broad tissue tropism, infecting many types of cells and tissues
+ Others may primarily infect a single tissue
What are factors that may influence tissue tropism?
\+ Presence of cell receptors \+ Transcription factors \+ Local temperature \+ Physical barriers \+ pH
What microbe targets nerve cells?
Varicella zoster virus (VZV)
What microbe targets the upper respiratory tract?
Rhinovirus
What microbe targets the liver cells?
Hepatitis B virus (HBV)
What microbe targets the gastric mucosa?
Helicobacter pylori
Wha microbe targets the intestinal epithelium?
Campylobacter jejuni
What microbe targets B lymphocyte cells?
Epstein Barr virus (EBV)
What microbe targets T lymphocyte cells?
Human Immunodeficiency virus (HIV)
What microbe targets urethral epithelium?
Neisseria gonorrhoeae
What microbe targets nasopharyngeal epithelium?
Neisseria meningitidis
What microbe targets intestinal epithelium?
Vibrio cholerae
Name virulence factors
+ Toxin secretion (toxigenesis)
- produced by bacteria and fungi
\+ Antibiotic resistance \+ Pilus formation \+ Capsule \+ Iron transport systems \+ Adhesion factors (adhesins)
+ Enzymes
- e.g proteases, DNAses, lipases
What are the two types of bacterial toxins?
+ Endotoxins
+ Exotoxins
What are features of endotoxins?
+ Low toxicity
+ Part of the cell wall of Gram negative bacteria
+ Lipopolysaccharide
+ Low specificity
What are features of exotoxins?
+ Highly toxic
+ Secreted from bacterial cells
+ Produced by both Gram positive and negative bacteria
+ Can be converted into toxoids for vaccine use
+ E.g tetanus toxin, cholera toxin, botulinum toxin
What are the features of microbes/bacteria with antibiotic resistance?
\+ Resistance genes on plasmids \+ Production of enzymes e.g β-lactamase \+ Impermeability \+ Efflux mechanisms \+ Alteration of target site
What are some important examples of antibiotic resistance?
+ Methicillin-resistant Staphylococcus aureus (MRSA)
+ Vancomycin-resistant Staphylococcus aureus (VRSA)
+ Multi-resistant Mycobacterium tuberculosis
+ HIV
+ Malaria
Upon what factors does transmission depend?
+ The number of micro-organisms shed
+ The number of micro-organisms required to infect a fresh host (the efficiency of the infection)
+ The micro-organism’s stability in the environment
What is horizontal transmission?
Transmission of an infectious agent, such as bacterial, fungal, or viral infection between members of the same species that are not in a parent-child relationship
What is vertical transmission?
Passage of a disease-causing agent (pathogen) from mother to baby (during the period immediately before and after birth)
What are examples of diseases transmitted via the respiratory route?
+ TB
+ Influenza
+ Common cold
What are examples of diseases transmitted via the faeco-oral route?
+ Cholera
+ Shigellosis
What are examples of diseases transmitted via the venereal route?
+ Chlamydia
+ HIV
+ Human papilloma virus (HPV)
What are examples of diseases transmitted via the skin?
+ Ringworm
+ S. aureus
What are examples of diseases transmitted via the perinatal route?
+ HIV
+ Meningitis
+ Conjunctivitis
What are examples of diseases transmitted via the semen?
+ HIV
+ Hepatitis B
+ Cytomegalovirus
What are examples of diseases transmitted via the blood?
+ HIV
+ Hepatitis B
+ Malaria
What are examples of diseases transmitted via the breast milk
+ HIV
What are examples of diseases transmitted via the saliva?
+ EBV
+ Herpes simplex virus (HSV)
What are the different vector categories for animal - human transmission (zoonoses)?
+ Invertebrate
+ Vertebrate
What are examples of invertebrate vectors?
+ Arthropods: e.g malaria, sleeping sickness, yellow fever
+ Shellfish: e.g hepatitis A, cholera
What are examples of vertebrate vectors?
+ Mammals: e.g rabies, leptospirosis, tapeworm
+ Birds: e.g psittacosis, salmonella
What are fomites?
Objects or materials which are likely to carry infections
What are some examples of fomite transmission?
\+ Door handles \+ Cutlery \+ Computer keyboards \+ Clothing \+ Phones \+ Pens
What are nosocomial infections?
+ Infections acquired during a hospital stay/originating in a hospital
+ Major public health concern
What are examples of nosocomial antibiotic resistance?
+ Clostridium difficile
+ Staphylococcus aureus
