Microbiology & Infectious Diseases Flashcards
What are microbes?
Single cell organisms
What are prokaryotes?
Simple organisms, no organelles
What are eukaryotes?
Complex organisms, have organelles and nucleus
What is pathogenicity?
Measure how easily a bug can make you sick
What are virulence factors?
Factors that enhance the bugs ability to make you sick
What is a virus?
One strand of DNA or RNA, no cell wall therefore antibiotics are ineffective
What is the lifestyle of viruses?
1) Attachment
2) Penetration & uncoating
3) mRNA synthesis
4) Protein synthesis
How do you kill viruses?
- Sunlight
- Bleach
- Antiviral drugs
What are fomites?
Inanimate objects that can transmit disease
What is active & passive protection?
- First line protection - natural host protection/barriers
- Second line protection - Inflammation, fever
What is innate immunity?
- Preformed, non-specific, immediate
- Humoral → complement & neutrophils
- Cell mediated → macrophages & natural killers
- No memory
What is adaptive immunity?
- Highly specific, several days to activate
- Humoral → B-cells & antibodies
- Cell mediated → Helper T-cells & cytotoxic T-cells
- Memory → faster next time
What is the difference between the primary and secondary response?
Both involve immune cells and antibodies but the secondary response is 10 fold stronger
What are macrophages?
- Apart of the innate immune system
Compared to neutrophils - Live longer, larger, phagocyte more pathogens, dominate later (1-2 days), large round nucleus
What are neutrophils?
- Apart of the innate immune system
- Dominate early, multi lobed nucleus
What do dendritic cells do?
Capture and present protein antigens to naive T-lymphocytes
What do mast cells do?
Found in connective tissue, release histamine, promoting inflammation
What are the 5 antibodies/immunoglobulins?
- IgG - Main serum antibody, resolution of infection
- IgA - Secretory antibody
- IgM - Indicates current infection
- IgE - Allergies
- IgD - Attached to B cells, antigen receptor
What are the meninges layers?
- Dura mater
- Arachnoid space mater
- Subarachnoid space → cerebrospinal fluid
- Pia mater
Why is cerebral spinal fluid vulnerable?
Due to lack of defences
What is meningitis?
Inflammation of meninges
What is encephalitis?
Inflammation of the brain
What is meningitis’ causative agent?
Neisseria meningitidis
What is the epidemiology of meningitis?
- A, B, C, X, Y and W are most likely
- Group B most common in NZ
What is the transmission of meningitis?
- Meningococcal bacteria commonly carried in nose and throat, does not cause disease
- Transferred person to person through saliva contact, fomites with saliva
- In rare cases bacteria invade rapidly leading to disease→ reason why not understood
What increases risks of meningitis?
- Tobacco smoke, binge drinking, respiratory infection
- Living in close proximity to others
- Living with people with the disease
- Impaired immune system
- Age and ethnicity’
What are symptoms of meningitis?
- Flu-like symptoms in first 24 hours
- Infants → gradual onset, fever, cry, unsettled, feed poorly, vomit, dislike bright lights, rash, bulging fontanelle
- Older children → fever, malaise, nausea, vomiting, muscle aches & pains, drowsiness, headache, dislike bright lights, neck stiffness, rash
- Atypical symptoms → GI symptoms, pneumonia, septic arthritis, endocarditis, epiglottitis, supraglottitis
What is a petechial rash?
- Small red or purple spots on skin caused by minor bleed from broken capillary blood vessels
- Use glass test to confirm
How to test for meningitis?
- Lumbar puncture → cloudy shows infection
- Diagnosis depends on gram stain of CSF
- More neutrophils in fluid indicate bacterial infection
- More lymphocytes or monocytes in fluid indicate viral infection
How to treat bacterial meningitis?
Antibiotics
What are complications of meningitis?
- Inflammation of membranes around brain (meningitis)
- Blood infection → septicaemia
- Pneumonia - lung infection
- Long-term damage - skin scarring, limb amputation, hearing loss and brain injury (in 1-2 of 10 survivors)
- Death of 1-2 out of 10 people even with rapid treatment
How to prevent meningitis?
- Preventative antibiotics of people patient has been in contact with
- Vaccines for several strands → no vaccines against B which is most common in NZ
What are defences against upper respiratory tract infections?
- Mucous
- Cilla
- Hair
- Antimicrobial molecules (defensins, lysozyme)
- Lymph nodes
What are defences against lower respiratory tract infections?
- Macrophages
- Antimicrobial molecules
What is MALT?
Mucosa associated lymphoid tissues
Why do babies have high infection rates?
Since they have no immunisation and an immature immune system
What is the causative agent for whooping cough?
Bordetella pertussis, a gram negative coccobacillus
How is whooping cough diagnosed?
PCR test from aspirated mucus
What is the pathogenesis of whooping cough?
- Bacteria have specific adhesions allowing to attach to ciliated respiratory mucosa
- Multiples in epithelial cells
- Produces toxins which increase respiratory secretions and mucus production, inducing inflammatory response
- “Tracheal cytotoxin” is cell wall component that appears to kill tracheal epithelial cells, immobilising mucociliary escalator causing accumulation of mucus in airways
What are whooping cough symptoms in adults?
1) Flu-like symptoms
2) Intense coughing, high pitched whooping sound, cough lasting ~ 12 weeks
3) Chronic cough lasting for weeks to months
What is treatment for whooping cough?
- Antimicrobials to reduce number of microorganisms → lowering severity
- Oxygen
- Suctioning secretions
- Bed rest
- Small frequent meals
- Isolation
- IVF
What prevents whooping cough?
- Immunisations
- Preventive antibiotics for individuals in contact with patient
How is whooping cough transmitted?
Air droplets, direct contact with infected throat/nasal discharges
What is food poisoning?
- Disease that results from ingestion of foods containing preformed microbial toxins
- The microorganisms that produced the toxins do not have to grow in the host
What is food infection?
Microbial infection resulting from ingestion of pathogen-contaminated food followed by growth of pathogen in the host
What is clostridial food poisoning & what is it caused by?
- A form of serious food poisoning
- Caused by Clostridium perfringens & Clostridium botulinum
- Exotoxin
- Botulinum toxin
- Produce tough endospores
What is clostridium difficile associated disease (CDAD)?
- Disease whereby infection damages colitis causing “pseudomembrane” from a collection of inflammatory cells, fibrin & necrotic cells
- Antibiotics disrupts normal intestinal flora → leading to overgrowth of C. difficile
- Heat resistant spores transmitted via fecal oral route
- Survive in clinical setting and stomach acid → activated in acid to germinate and multiply in the colon
How is clostridium difficile associated disease (CDAD) treated?
Faecal transplant
What is salmonellosis and what is it caused by?
- A gastrointestinal illness caused by food borne Salmonella infection
- Food infection
- Onset of the disease occurs 8-48 hours after digestion
- Disease normally resolves in 2-5 days but can cause septicaemia
What is the salmonella infection?
- Gram negative rods which can cause enterocolitis, enteric fevers and septicaemia
- Two categories
1) Typhoidal Species (S. typhi, S. paratyphi)
2) Non-typhoidal or enterocolitis species (S. enterica and nauseum) - Enterocolitis - invasion between mucosal cells causing inflammation and diarrhoea, usually self limiting
- Septicaemia - 5-10% of infections. May cause distant tissue infection. IV Ceftriaxone or ciprofloxacin
What is typhoid fever?
- Enteric fever caused by infection with Salmonella enterica serotype Typhi
- Fecal oral route cause
- Travelers illness, prevalent in areas with poor sanitation
- Vaccine preventable
- Chronic asymptomatic carriers are a risk to others especially if involved in food preparation
What is the clinical manifestation of typhoid fever?
- 1st week - stepwise rising fever, bacterium
- 2nd week - abdomen pain develops and “rose spots” on trunk and abdomen
- 3rd week - liver and spleen inflammation, intestinal bleeding, peritonitis, septic shock and death
- Or resolves over weeks to months
- 15% mortality without antibiotics
- Other clinical manifestations include constipation, intestinal perforation, neurological manifestations, & cough
Diagnosis of typhoid fever?
- Culture (blood, stool, urine, bone marrow)
- Susceptibility
- Serology
How to test for salmonella?
Blood test:
- Positive test - agglutination within a minute
- Negative test - no agglutination
Treatment for salmonella?
- Fluoroquinolones
- 3rd generation Cephalosporins such as Ceftriaxone
- Azithromycin
- Ideally base on specific results of susceptibility
Why is the norovirus so easily spread?
- Highly contagious
- Trigger little immune response
- Constantly evolving
What is cystitis?
Infection of the urinary tract
What is pyelonephritis?
Infection of the kidneys
How do you analyse urine in the lab?
- Collect midstream urine with no menstrual blood or epithelial cells
- Observe colour, blood content, devris, unusual material
- Perform dipstick analysis
- May perform microscopic exam
- Culture, incubate at 37 degrees for 18 hours
- Examine, select “significant” isolate for identification
- Perform antibiotic susceptibility tests
What does microscopy analysis look at?
WBC, RBC, casts, crystals, bacteria
How to treat a UTI?
- Trimethoprim → drug of choice for uncomplicated UTIs (300mg nocte for 3 days)
- Amoxicillin
- Antibiotic susceptibility testing is essential for best treatment
What is diagnosis and treatment for pyelonephritis?
- Diagnosis dpends on UTI symptoms along with symptoms of an upper UTI including fever, chills, flank pain, nausea, vomiting, costovertebral angle tenderness.
- Urine culture should always be performed
- Perform dipstick analysis
- Antibiotics should be started before results are available
Do you screen for UTI’s in longterm care facilities?
- Screening in UTIs not recommended since elderly have bacteria in their bladder
- Symptomatic UTIs are investigated
- Keep record of results to outbreak strains with unusual susceptibility
What is the causative agent for syphilis?
Treponema pallidum
How is syphilis transmitted?
- Sexually transmitted
- Spreads via skin or mucous membrane contact with these sores
What are the signs and symptoms of syphilis and how does it progress?
Stage 1 - 3-90 days after exposure → A painless sore - typically on genitals, rectum or mouth
Stage 2 - 4-10 weeks after initial infection → Body rash
Stage 3 - 3-15 years after initial infection (Can lie dormant in body for decades before activating) → Affects internal organ, damaging heart, brain or other organs → life threatening
How is syphilis treated?
Early syphilis can be cured with penicillin
What are congenital and perinatal infections?
- Congenital infections must cross the placenta to infect the foetus e.g Treponema pallidum (congenital syphilis)
- Perinatal infections are acquired at birth e.g. herpes
What is congenital syphilis?
- Congenital infection
- Screened at antenatal visit during first trimester by blood test
- Can be obtained later during the pregnancy
- Infection can result in stillbirth, prematurity, or a wide spectrum of clinical manifestations
What is the complement system?
- Part of the immune system which enhances recognition of pathogen identification
- Protein circulating blood, produced by liver, when binding to pathogen causes lysis
What occurs in the hypersensitivity reaction of anaphylaxis?
- IgE antibodies activate mast cells in response to antigen, activating B cells to release histamine
What occurs in the hypersensitivity reaction of cytotoxic?
- Involves activation of complement by combination of IgG or IgM with antibodies with an antigenic cell, lysing of foreign or host cell that carry foreign antigenic determinant on its surface, excessive reaction damages on tissues, commonly in blood transfusion
What occurs in the hypersensitivity reaction of immune complex?
1) Immune complexes are deposited in wall of blood vessel
2) Presence of immune complexes activates complement and attracts inflammatory cells such as neutrophils
3) Enzymes released from neutrophils cause damage to endothelial cells of basement membrane
What occurs in the hypersensitivity reaction of delayed?
Reaction takes a day or more to occur since T-cells and macrophages migrate to and accumulate near foreign antigens. Sensitisation occurs when foreign antigens are phagocytosed by macrophages and presented to receptors in the T-cell surface
What does autoimmune mean?
Cells attack own body
What does immunodeficiency mean?
Lack of immune response
What is the Stevens-Johnson Syndrome?
- Delayed type cell-mediated hypersensitivity reaction
- Causes separation of epidermis from dermis and +++ inflammation, necrolysis
- 4 etiologic categories:
1) Infectious
2) Drug induced
3) Malignancy-related
4) Idiopathic (25-50%)
What are causes of autoimmunity?
- Molecular mimicry
- Release of sequestered antigens
- Epitope spreading
- Failure of regularly T cells
- Impaired maturation of B or T cells
What are primary immunodeficiency diseases?
When there is a defect in any one of the many steps during lymphocyte development
What is selective antibody deficiency (SAD)?
An inadequate antibody response to polysaccharide antigens in individuals with otherwise normal immune responses
What causes acquired immunodeficiency?
- Severe malnutrition
- Cancers and chemotherapy
- Radiotherapy
- Immunosuppressive therapy in transplant patients
- Corticosteroid drugs for anti-inflammatory treatment in autoimmunity
- Viral infections e.g. HIV, HTLV
