Infectious Disease Flashcards
1
Q
Infectious Disease
A
- Caused by pathogenic or infectious agents - etiological agent
- Factors in disease process: infectious agents, disease reservoirs, mode of transmission, body’s defenses, host resistance and susceptibility
2
Q
Infectious Agents
A
- Bacteria
- Protozoa
- Fungi/Yeast
- Helminths
- Rickettsia
- Viruses
- Prions
- Staphylococcus auerus: bacteria, humans, domesticated animals
- E.coli: bacteria, cattle
- Salmonella: bacteria, birds, reptiles, mammals
- Listeria: bacteria, soil, water
- Shigella: bacteria, humans, water, flies
3
Q
Symbiotic Relationship Between Microbes and Host
A
- Normal microbiota in hosts: also termed normal flora, organisms that colonize body’s surface without normally causing disease
- Two types: resident microbiota and transient microbiota
- Resident is in us when born, transient happens periodically over time
4
Q
Resident microbiota
A
- Part of normal microbiota through life
- Mostly commensal/mutualism
5
Q
Symbiotic relationships between microbes and hosts
A
- Mutualism: Organism 1 and 2 benefit, eg. bacteria in human colon
- Commensalism: Organism 1 benefits, organism 2 neiter benefit or harm, eg. staphylococcus on skin
- Parasitism: Organism 1 benefits, organism 2 is harmed, eg. tuberculosis in lung
6
Q
How normal microbiota become opportunistic pathogen
A
- Opportunistic pathogen: normal microbiota that cause disease under certain circumstances
- Conditions that provide opportunities for pathogens -> introduction of normal microbiota into unusual sites of body
- Immune suppression
- Changes in normal microbiota, changes in relative abundance may allow opportunity for a member to thrive and cause disease
7
Q
Exposure to Microbes: Contamination and Infection
A
- Contamination: mere presence of microbes in or on body
- Colonization: conditions are right for bacterial growth, they grow without causing infection
- Infection: when organism evades body’s external defenses, multiplies, and becomes established in body
8
Q
Role of Adhesion in Infection
A
- Process by which microorganisms attach themselves to cells
- Required to successfully establish colonies within host
- Uses adhesion factors: specialized structures, attachment proteins
- Attachment proteins found on viruses and many bacteria, viral or bacterial ligands bind host cell receptors, interaction can determine host cell specificity
- Changing/blocking ligand or receptor can prevent infection
- Inability to make attachment proteins renders microorganisms avirulent
- Some bacterial pathogens attach to each other to form a biofilm -> attach to each other
9
Q
Nature of Infectious Diseases
A
- Symptoms: subjective characteristics of disease felt only by patient(pain, nausea, headache)
- Signs: objective manifestations of disease observed or measured by others(swelling, vomiting, shivering)
- Syndrome: Symptoms and signs that characterize a disease of abnormal condition
- Asymptomatic or subclinical infections lack symptoms but may still have signs of infection
10
Q
Koch’s Postulate
A
- Suspected agent must be present in every case of disease
- Agent must be isolated and grown in pure culture
- Cultured agent must cause disease when inoculated into a healthy, suspectible individual
- Same agent must be reisolated from diseases experimental host
11
Q
Exceptions to Koch’s postulates
A
- Some pathogens can’t be cultured in laboratory
- Diseases caused by a combination of pathogens and other cofactors
- Ethical considerations prevent applying Koch’s postulate to human pathogens
- Pathogens that are ignored as potential causes of disease
12
Q
Virulence Factors of Infectious Agents
A
- Pathogenicity: ability of a microorganism to cause disease
- Virulence: degree of pathogenicity
- Virulence factors contribute to virulence
- Adhesion factors
- Biofilms
- Extracellular enzymes
- Toxins
- Antiphagocytic factors(allow cell to kill/evade WBC)
- Antibiotic resistance
13
Q
Most to less virulent pathogens
A
- Francisella tularensis: rabbit fever
- Yersinia pestis: plague
- Bordetella pertussis: whooping cough
- Pseudomonas aeruginosa: infections of burns
- Clostridium difficile: Antibiotic induced colitis
- Candida albicans: vaginitis, thrush
- Lactobacilli, diphtheroids
14
Q
Extracellular enzymes
A
- Secreted by pathogen
- Dissolve structural chemicals in body
- Help pathogen maintain infection, invade, and avoid body defenses
15
Q
Virulence factors
A
- Hyaluraonidase and collagenase: invasive bacteria reach epithelial surface, bacteria produce hyaluronidase and collagenase, bacteria invade deeper tissue
- Coagulase and kinase: bacteria produce coagulase, clot forms, bacteria later produce kinase to dissolve clot and release bacteria
16
Q
Toxins
A
- Chemicals that harm tissues or trigger host immune responses that cause damage
- Toxemia refers to toxins in bloodstream that are carried beyond site of infection
- Two types: exotoxins and endotoxins
17
Q
Exotoxin and Endotoxin
A
Exotoxin: bacteria secrete exotoxins -> kills host cells
- Endotoxin: Dead gram negative bacteria release endotoxin(lipid A) which induces effects such as fever, inflammation, etc.
18
Q
Comparison of Exotoxins and Endotoxins
A
- Exotoxins: mainly gram negative and positive, metabolic producted secreted from cell, high toxicity, not fever producing, eg. botulism, tetanus, diphteria
- Endotoxin: gram negative, portion of cell wall released after death, low toxicity but fatal in high dose, fever, blood coagulation, eg. typhoid fever, urinary tract infections
19
Q
Antiphagocytic factors
A
- Factors that prevent phagocytosis by host phagoytic cells
- Bacterial capsule: composed of chemical recognized as non-foreign, difficult for phagocytes to engulf bacteria
- Antiphagocytic chemicals: Prevent fusion of lysosome and phagocytic vesicles, leukocidins destroy phagocytic white blood cells
20
Q
Stages of infectious disease
A
- Incubation period: no signs/symptoms
- Prodromal period: vague, general symptoms
- Illness; most severe symptoms
- Decline: declining symptoms
- Convalescence: no signs/symptoms
21
Q
Mechanisms of Pathogenesis
A
- Exposure to pathogen -> Adherence to skin or mucosa -> Invasion through epithelium -> Colonization and growth of virulence factors -> Toxicity (toxin effects are local or systemic) or Invasiveness (further growth at original site and distant sites) -> tissue damage/disease
22
Q
Listeria monocytogenes
A
- Gram positive, non spore forming coccobacillus
- Found in soil, water, mammals, bird, fish, and insects
- Enters body in contaminated food and drink
- Does not produce toxins/enzymes
- Virulence directly related to bacterium’s ability to live within cells
- Can cause meningitis
23
Q
How listeria avoids immune system
A
- Enters through phagocytosis, use our actin to form actin tail and push itself into other cells
- “Zipper mechanism” : process where a phagocytes membrane engages a particles surface through receptor and ligands
24
Q
Listeria
A
- Diagnosis: presence of bacteria in cerebrospinal fluid, rarely seen in gram stain
- Treatment: most antimicrobial drugs
- Prevention: difficult becaue organism is ubiquitous, avoid certain foods
25
Pathogenic gram negative vibrios
- Helicobacter pylori: slightly helical, motile bacteria that colonizes stomach of hosts
- Cause gastritis and peptic ulcers
- Produce numerous virulence factors that enable it to colonize stomach
26
Role of helicobacter pylori in formation of peptic ulcers
- Bacteria invade mucus and attach to gastric epithelial cells, helicobacter cause mucus layer to become thin, gastric acid destroys epithelial cells and underlying tissues
27
Enterobacteriaceae
- Intestinal microbiota of most animals and humans
- Ubiquitous in water, soil, and decaying vegetation
- Enteric bacteria are most common gram-negative pathogens of humans
28
Antigens and virulence factors of enteric bacteria
- Antigens: Outer membrane (common antigen, O antigen, lipid A), Type 3 secretion system, Capsular antigens (K: Vi in salmonella), Flagellar antigens (H)
- Virulence factors: fimbria, exotoxin, adhesin, plasmid(virulence gene), iron binding protein, hemolysin
29
Coliform Opportunistic Enterobacteriaceae
- Coliforms: Aerobic or facultatively anaerobic, gram negative, rod shaped that ferment lactose to form gas on lactose broth
- Commonly found in soil, on plants, and on decaying vegetation
- Colonize intestinal tracts of animals and humans
- Coliforms in water indicate impure water and poor sewage treatment
- doesn't affect cows
30
Escherichia coli
- Most common and important of coliform
- Virulent strains have virulence plasmids
- Gastroenteritis is most common disease (mediated by exotoxins)
- Common cause of non-nosocomial urinary tract infections
- E. coli 0157:H7
- Most prevalent pathogenic E.coli in developed countries
- Causes diarrhea, hemorrhagic colitis, hemolytic uremic syndrome
