Microbes 2 Flashcards
What is commensal flora?
Organisms found in ecological niches of the body which generally have a symbiotic relationship
What is a pathogen?
Microorganisms which cause disease
What is a primary pathogen?
Pathogens which overcome host defences to cause disease
What is an opportunistic pathogen?
Normal flora causing disease when normal host defences are broken down
What is infection?
Process of microbial invasion of the body
What is infectious?
A pathogen which can be spread from person to person
What is pathogenicity?
Capacity of a microbe to cause damage in a host
What is virulence?
Degree of pathology caused by an organism
What are the 6 stages of pathogenesis?
- Entry
- Attachment
- Multiplication
- Evasion of host defences
- Causes damage
- Release and spread
What is the main difference between gram-positive and gram-negative bacteria?
Gram-positive organisms have a thick peptidoglycan layer and no lipopolysaccharide and lipoprotein
What is a mycobacteria?
Bacteria containing a mycolic acid layer and arabinogalactan
Where is genetic material found in viruses?
Capsid
What does the genetic material and capsid make up?
Nucleocapsid
What 5 things are viruses classified by?
- Symmetry
- Enveloped or not
- Nucleic acid type
- Number of nucleic acid strands
- Polarity
Give 5 steps of infection of host cells by viruses
- Virus attaches to target cell epithelium
- Cell engulfs virus by endocytosis
- Viral contents are released and viral RNA enters nucleus
- Viral mRNA is used to make viral proteins
- New viral proteins are made and released into ECF
How does a virus attach to a target cell epithelium?
Attaches to a specific receptor cell through attachment proteins in capsid or glycoproteins in virus envelope
What 2 ways can a vrius enter the cell?
- Endocytosis
2. Fusion of viral envelope and cell membrane
Describe the replication mechanism for a DNA virus
Use host proteins and enzymes to transcribe DNA into mRNA to make proteins
Describe the replication mechanism for a RNA virus
Use RNA core to directly synthesise mRNA which directs host cells to synthesise viral enzymes and proteins
What are 4 effects of viruses on host cells?
- Lytic infection
- Persistent infection
- Latent infection
- Transforming infection
What is lytic infection?
Death of host cell and release of new viral particles
What is an example of lytic infection?
Polio virus or influenza virus
What is persistent infection?
Cells remain alive and continue to release viral particles, where an infected person can act as a symptomless carrier
What is an example of persistent infection?
Hepatitis B
What is latent infection?
Virus remain quiescent and nucleic acid persists in the cell but mature viral particles are undetected. No viral replication occurs unless triggers
What is an example of latent infection?
Herpes viruses or retroviruses
What is transforming infection?
Cells show changes in morphology, behaviour and biochemistry which can lead to loss of control growth patterns or tumours
What is an example of transforming infection?
Epstein Barr virus or Papillomavirus 16
Name 3 types of fungi
- Yeast
- Moulds
- Dimorphic
What characterises yeast fungi?
Cells form buds which detaches to form new cells
What characterises mould fungi?
Grow by producing hypae - forms an intertwining mass called a mycelium
What characterises dimorphic fungi?
Can form hypae at room temperature but occur as yeast at body temperature
Name an example of dimorphic fungi
Histoplasma
Name an example of a yeast fungi
Candida albicans
Name an example of a mould fungi
Trichophyton rubrum
What are 3 types of fungal infections?
- Superficial mycoses
- Cutaneous and subcutaneous mycoses
- Systemic or deep mycoses
What is a superficial mycoses?
Fungal infection of skin or hair
What is cutaneous or subcutaneous mycoses?
Infection of nails or deeper skin layers
What is systemic or deep mycoses?
Fungal infection involving internal organs
What is the difference between systemic fungal pathogens and opportunistic fungi?
Systemic fungal pathogens can cause serious disease in healthy individuals whereas opportunistic fungi cause disease in compromised hosts
What are protozoa?
Parasites of humans prevalant in tropical and subtropical regions
Name 2 examples of protozoans
- Malaria
2. Toxoplasma
What are helminths?
Parasitic worms, prevalent in tropical and subtropical climates
In what 3 ways can the helminths enter the body?
- Ingestion
- Penetration of skin
- Vector bite
What are 3 examples of helminths
- Tapeworms
- Flukes
- Roundworms
What are prions?
Small infectious proteins
Name 8 factors of an ideal antimicrobial agent
- Selective toxicity against microorganism
- Minimal toxicity to host
- Ability to kill microorganism
- Long plasma half life
- Good tissue distribution
- Low binding to plasma proteins
- Oral and intravenous preparations
- No adverse interactions with other drugs
What is a bactericidal agent?
Agent which kills bacteria
What is a bacteriostatic agent?
Agents which inhibit the growth of bacteria to allow immune system to respond
Name 4 classes of antibacterial agents
- Beta-lactams
- Lincosamides
- Nitroimidazoles
- Polymyxins
What is the function of beta-lactams?
Inhibitors of cell wall synthesis
What is the function of lincosamides?
Inhibitors of protein synthesis by preventing peptide bond formation
What is the function of nitroimidazoles?
Inhibitors of nucleic acid synthesis by breakdown of bacterial DNA
What is the function of polymyxins?
Inhibitors of cytoplasmic membrane function
How to beta-lactams carry out their function?
Bind to penicillin binding proteins
Name 3 examples of beta-lactams?
- Penicillins
- Cephalosporins
- Monobactams
What type of bacteria do lincosamides act against?
Gram positive aerobes and gram positive and negative anaerobes
What type of bacteria do nitroimidazoles act against?
Anaerobic bacteria
What is the most common antiviral agent used in dentistry?
Aciclovir
What type of drug is aciclovir?
Nucleoside analogue
How does aciclovir work?
It inhibits herpes simplex virus DNA polymerase enzyme so inhibits viral DNA replication
What are 2 main types of antifungal agents?
- Polyenes
2. Azoles
How do polyenes work?
Bind to sterols in fungal cell membranes causing cell leakage
Name 2 examples of polyenes
- Nystatin
2. Amphotericin B
How do azoles work?
Interfere with the synthesis of ergosterol in cell membrane
Name 2 examples of azoles
- Fluconazole
2. Itraconazole