Microbes 2 Flashcards by Peter Duncan

What is commensal flora?

Organisms found in ecological niches of the body which generally have a symbiotic relationship

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What is a pathogen?

Microorganisms which cause disease

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What is a primary pathogen?

Pathogens which overcome host defences to cause disease

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What is an opportunistic pathogen?

Normal flora causing disease when normal host defences are broken down

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What is infection?

Process of microbial invasion of the body

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What is infectious?

A pathogen which can be spread from person to person

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What is pathogenicity?

Capacity of a microbe to cause damage in a host

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What is virulence?

Degree of pathology caused by an organism

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What are the 6 stages of pathogenesis?

Entry
Attachment
Multiplication
Evasion of host defences
Causes damage
Release and spread

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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

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What is a mycobacteria?

Bacteria containing a mycolic acid layer and arabinogalactan

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Where is genetic material found in viruses?

Capsid

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What does the genetic material and capsid make up?

Nucleocapsid

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What 5 things are viruses classified by?

Symmetry
Enveloped or not
Nucleic acid type
Number of nucleic acid strands
Polarity

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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

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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

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What 2 ways can a vrius enter the cell?

Endocytosis

2. Fusion of viral envelope and cell membrane

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Describe the replication mechanism for a DNA virus

Use host proteins and enzymes to transcribe DNA into mRNA to make proteins

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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

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What are 4 effects of viruses on host cells?

Lytic infection
Persistent infection
Latent infection
Transforming infection

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What is lytic infection?

Death of host cell and release of new viral particles

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What is an example of lytic infection?

Polio virus or influenza virus

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What is persistent infection?

Cells remain alive and continue to release viral particles, where an infected person can act as a symptomless carrier

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What is an example of persistent infection?

Hepatitis B

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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

1. Yeast 2. Moulds 3. 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?

1. Superficial mycoses 2. Cutaneous and subcutaneous mycoses 3. 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

1. Malaria | 2. Toxoplasma

What are helminths?

Parasitic worms, prevalent in tropical and subtropical climates

In what 3 ways can the helminths enter the body?

1. Ingestion 2. Penetration of skin 3. Vector bite

What are 3 examples of helminths

1. Tapeworms 2. Flukes 3. Roundworms

What are prions?

Small infectious proteins

Name 8 factors of an ideal antimicrobial agent

1. Selective toxicity against microorganism 2. Minimal toxicity to host 3. Ability to kill microorganism 4. Long plasma half life 5. Good tissue distribution 6. Low binding to plasma proteins 7. Oral and intravenous preparations 8. 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

1. Beta-lactams 2. Lincosamides 3. Nitroimidazoles 4. 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?

1. Penicillins 2. Cephalosporins 3. 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?

1. Polyenes | 2. Azoles

How do polyenes work?

Bind to sterols in fungal cell membranes causing cell leakage

Name 2 examples of polyenes

1. Nystatin | 2. Amphotericin B

How do azoles work?

Interfere with the synthesis of ergosterol in cell membrane

Name 2 examples of azoles

1. Fluconazole | 2. Itraconazole