Infection Introduction to Microbials Flashcards
What is an infection?
When a group of microorganisms invade host tissue and cause disease by multiplication, toxins and the host response
3 ways people get infections
Transfer from another- vector, airborne, physical agent Contaminated environment- food or water, surface, inhalation Microbiota- commensals
Define a Pathogen and Pathogenicity
A microorganism which is capable of causing a disease
The ability to cause disease
Define commensals
An organism which is part of the normal bacterial flora
Define Virulence
The ability to cause SEVERE disease
How do microorganisms cause disease?
1) Exposure
2) Adherence
3) Invasion
4) Multiplication
5) Dissemination
Give some Virulence Factors
Exotoxins- AB Toxins, Superantigens, Enzymes (Proteins) -Toxic substances released by the organism into the cell
Endotoxins- Part of the Cell, made of lipid
Both damage the host
Disease Determinants
Pathogens- Virulence factors, innoculation size, antimictobial resistance
Patient- Site and Co-morbidities
Investigating an Infection: What do we do and Why?
1) History- severity, duration, potential exposures
2) Full Blood Count- neutrophils and lymphocytes
3) C Reactive Protein - acute phase protein is a measure of inflammation
4) Blood Chemistry- LFT KFT
5) Imaging
6) Histopathology
7) Examination
8) Bacteriology- grow specimen, microscopy, culture, succeptability, antigen/nucleic acid detection
9) Virology- antigen, antibody, viral nucleic acid detection
How can we classify Bacteria?
Gram stain
Shape- cocci, bacilli, spirals
Do they have an endospore? shape and position
An/aerobes, Enzymes, Serology, DNA Sequencing
Which bacteria are always Gram Positive?
Streptococci,
Staphylococci,
Listeria,
Clostridium,
Bacillus
Describe Gram Staining
Cells are stained with crystal violet dye. Iodine is added to create a complex with the violet (larger than original stain) Ethanol is added to dehydrate the peptidoglycan layer (shrinks and tighten) As positive bacteria have a thick peptidogylcan layer it is trapped. Negative Bacteria have a thinner P layer and the outside is mainly lipopolysaccharide so can be counter-stained red
What are the main features of a Virus?
Nucleic Acid- allow replication, can be DNA or RNA
Protein Coat
Envelope
Virus proteins- allow to bind and enter cells
What is a Bacteriophage?
A virus that invades and replicates inside bacteria
They transfer DNA to Bacteria, can transfer antibiotic resistance from B to B
Mechanism of Bacterial Pathogenesis
Host Entry - Capsule
Invasive - Specific enzymes to get into cells (e.g. Collagenase)
Adherence - Pili and Fimbrae
Iron Sequestration
Types of Fungi?
Yeast- single celled Moulds- multicellular
Types of Parasite?
Protozoa- single-celled Helminths- multicellular, worms and flukes
Describe the Infection Model
1) Patient and Pathogen meet 2) Mechanism of Infection 3) Infection 4) Management 5) Outcome
Define the Mechanisms of Infection
Contiguous Spread- direct e.g from skin into a wound Inoculation- trauma carries bacteria into site Haematogenous- via blood stream Ingestion- usually Faecal to Oral transmission Inhalation- Droplets or Aerosols Vector Vertical- Mother to Baby
What do Antibacterials aim at?
1) DNA Synthesis Quinolones, Antifolates 2) Protein Synthesis Aminoglycosides, Tetracycline, Macrolides 3) Cell Wall Synthesis - Most Common Beta Lactams, Glycopeptides
Give 3 ways that Antibiotic Resistance can occur
1) Drug Inactivation 2) Alteration of the Target 3) Altered Uptake
How does resistance occur?
Chromosomal Gene Mutation Horizontal Gene Transfer- Conjugation, Transduction or Transformation
Name one Qualatative and one Quantitative way of measuring the activity of antibacterials
Disc Sensitivity Testing Minimum Inhibitory Concentration
Name some gram negative bacteria
Neisseria
E Coli
Salmonella typhi
Haemophilus influenza
Proteus
Give some examples of Cocci?
Are they Gram + or - ?
Streptococcus pneumoniae (+)
Coagulase negative Staph (+)
Staph aureus (+)
Neisseria (-)
Enterococcus faecilis (+)
Give some examples of bacilli?
Are they Gram + or - ?
E Coli (-)
Salmonella typhi (-)
Listeria (+)
Bacillus … (+)
Give some examples of encapsulated bacteria
Are they Gram + or - ?
Neisseria (-)
Salmonella typhi (-)
Strep pneumoniae (+) Haemophilus influenzae (-)
Describe Staphylococcus aureus
Shape
Gram Stain
Virulence Factors
Diseases it causes
Relevence?
Cocci, Aerobe
Gram Positive Bacteria
Capsule to evade phagocytosis, Exotoxins
Causes Hospital Acquired Pneumonia and Cellulitis
Normal Skin Commensal
Resistant Strains (enzyme cleaves B lactam ring)
Describe Clostrium Difficile
Shape
Gram Stain
Virulence Factors
Diseases it causes
Spore Forming Anaerobe
Gram Positive
Part of Intestinal Flora, F to O transmission
It becomes pathogenic following drug (amoxicillin) treatment as flora is disrupted
Secretes Toxins A and B (cytotoxic and enterotoxic)
Causes Colitis
Hospital Acquired Infections
Describe Streptococcus pneumoniae
Shape
Gram Stain
Virulence Factors
Diseases it causes
Cocci, Encapsulated Bacteria
Gram Positive
Increased risk in Asplenic patients
Causes Community Acquired Pneumonia, Meningitis and Bone infections
Describe Neisseria meningitidis
Shape
Gram Stain
Virulence Factors
Diseases it causes
Gram Negative, Diplococci, Encapsulated
Causes Meningitis
Secrete Endotoxins, Pili, Polysaccharide, Capsule
Can be present in nasopharynx flora (10% adult carriers)
Spread: Aerosols
Describe E coli
Shape
Gram Stain
Virulence Factors
Diseases it causes
Gram Negative, Bacilli
Part of Intestinal Flora (Coliform)
Causes UTIs, Diarrhoea
Describe Helicobacter pylori
Shape
Gram Stain
Virulence Factors
Diseases it causes
Helical
Gram Negative
Secreates Urease, Has Flagellum, Releases Cytotoxins
Can be part of Stomach Flora
Speads O to O or F to O
Causes Gastritis and Ulceration
Describe Influenza A
Shape
Gram Stain
Virulence Factors
Diseases it causes
Single Stranded
RNA Virus
No Gram Stain
Direct, Surface Contamination or Aerosol
Describe Legionella pneumoniae
Shape
Gram Stain
Virulence Factors
Diseases it causes
Gram Positive, Coccobacillus
Has Flagellum, Aerobic
Spread: Infected water aerosols
Causes Legionnaires
Immunocompromised more at risk
Describe Salmonella typhi
Shape
Gram Stain
Virulence Factors
Diseases it causes
Gram Negative, Aerobe
Encapsulated, Has invasin and fimbrae
Bacilli
Travel Related Infections
From F to O (food and water contaminated)
Causes Headache, Constipation.. Typhoid Fever
