Microbiology Flashcards
(118 cards)
1
Q
What is a pathogen
A
Organism that causes or is capable of causing disease
2
Q
What is a commensal
A
Organism which colonises the host but causes no disease in normal circumstances
3
Q
What is opportunist pathogen
A
microbe that only causes disease if host defences are compromised
4
Q
What is virulence/pathogenicity
A
The degree to which a given organism is pathogenic
5
Q
What is asymptomatic
A
When a pathogen is carried harmlessly at a tissue site where it causes no disease
6
Q
What is an endotoxin
A
Component of the outer membrane of bacteria e.g lipopolysaccharide in Gram negative bacteria
7
Q
What is an exotoxin
A
Secreted proteins from gram positive and gram negative bacteria
8
Q
Give the virulence factors, normal habitat, spread, resistant strain and resistant medication for Staphylococcus Aureus
A
virulence factors;pore-forming toxins (alpha-haemolysin and Pantone-valentine leucocidin (PVL)), protease (exfoliatin), toxic shock syndrome toxin (TSST) which stimulates cytokines release, protein A (surface protein which binds Ig’s in wrong orientation)
Normal habitat; nose and skin
Spread; aerosol and touch
Resistant strain; MRSA
Resistant medication; B-lactams, Gentamicin, Erythromycin, Tetracycline
9
Q
Staphylococcus are divided into coagulase positive and negative. How can are coagulate positive bacteria tested for
A
Coagulase positive bacteria release coagulate enzymes which clot blood plasma. The fibrin clot formation around the bacteria may protect from phagocytosis.
10
Q
What is the most important coagulase positive bacteria
A
Staphylococcus Aureus
11
Q
Give 2 examples of coagulase-negative Staphylococci
A
Staphylococci epidermidis; in prostheses, catheters and debilitated patients. Main virulence factor is the ability to form persistent bio films
Staphylococcus Saprophyticus; causes acute cystitis (inflammation of urinary bladder). Main virulence factor are haemagglutinin for adhesion, urease causing kidney stones
12
Q
Give the 3 classifications of Streptococci
A
- Haemolysis
- Lancefield typing
- Biochemical properties
13
Q
Give 3 classes of Haemolysis Streptococcus Pyogenes
A
Alpha-partial, greening e.gStreptococcus intermedius which releases H2O2 that reacts with haemoglobin
Beta-complete lysis e.g Streptococcus pyogenes
Non(or gamma) so lysis e.g some streptococcus mutans
14
Q
What is lancefield grouping
A
A method of grouping catalase negative, coagulase negative bacteria based on bacterial carbohydrate cell surface antigens
Lancefield A-H and K-V
15
Q
Most important Lancefield Group B bacteria
A
Streptococcus Agalactiae for neonatal infections
16
Q
Most important Lancefield Group A bacteria
A
Streptococcus Pyogenes
17
Q
What type of bacteria is Enterobacter
A
Gram-negative rod-shaped (bacillus) bacteria
18
Q
What infections are enterobacter bacteria most associated with
A
Respiratory and urinary symptoms
19
Q
Which enterobacter bacteria are the most common opportunistic pathogens
A
Enterobacter cloacae
Enterobacter Aerogenes
20
Q
Give 6 characters of Enterobacter
A
- motile
- non-spore forming
- facultative anaerobic (can only survive in oxygen)
- oxidase negative (doesn’t produce oxidase)
- urease positive (urease enzyme that converts urea to CO2 and ammonia)
- grows well on macconkey agar (identifies if lactose fermenters or not)
21
Q
Gives 3 gram negative lactose fermenting bacteria
A
- Enterobacter
- Klebsiella
- Escherichia Coli
Pink colonies on agar
22
Q
Give 2 gram negative bacteria that can’t ferment lactose
A
Salmonella
Shigella
Colourless colonies on agar
23
Q
Gives some virulence factors of Enterobacter
A
Fimbriae (secrete Haemolysis which put holes in cells)
24
Q
Give examples of respiratory conditions caused by Enterobacter
A
Inflammation of Trachea and Bronchi
Pneumonia
Lung Abscesses
Pleural Empyema (collection of pus in the pleura cavity)
25
What would diagnosis of Enterobacter include
Blood test, sputum, urine and pus test
Urinary tract infections urine
- alkaline urine pH>7
- pyuria (white blood cells in urine)
- bacteriuria (bacteria in urine)
X-ray for respiratory infections
CT or ultrasound for abdominal infections
Endocardiogram for endocarditis
26
What medications are used to endobacter
- carbapenems
- aminoglycosides
- fluoroquinolones
- polymyxins
27
What type of bacteria is Escherichia coli (E.Coli)
Rod-shaped gram negative bacteria
28
Gives 4 characteristics of Escherichia Coli
- catalase positive (produces catalase)
- lactose fermenter
- facultative anaerobe (lives with or without oxygen)
29
How to test for catalase enzyme
- Few drops of hydrogen peroxide are added to bacteria
- A foamy appearance shows dissociation to water and oxygen
- encapsulated
- motile
30
How are Escherichia coli classified
- by stereotypes based on antigens
| - pathotypes (same virulence factors)
31
Give the 4 types of antigens located on E.coli
Somatic (O)
Capsular (K)
Fimbrial (F)
Flagellar (H)
32
What are pathotypes
group of organisms of the same species that cause disease in the same way (same virulence factors)
33
What are the 5 E.Coli pathotypes
1) shiga-like toxin-producing E.coli (STEC)
2) enterotoxigenic E.coli (ETEC)
3) enteroinvasive E.coli (EIEC)
4) enteropathogenic E.coli (EPEC)
5) Uropathogenic E.Coli (UPEC)
34
How does shiga-like toxin-producing E.coli work
- makes toxin similar to the one called shiga toxin by shigella
- attaches to host’s intestinal cells an d releases toxins
- causing inflammation and bloody diarrhoea so sometimes referred to as enterohemorrhagic E.coli (EHEC)
- can cause haemolytic uremic syndrome (HUS) which leads to proteinuria, thrombocytopenia, anaemia from microangiopathic hemolysis, uremia
35
How does enterotoxigenic E.coli work
- E.coli releases two enterotoxins
- heat stable enterotoxin (not easily destroyed by heat) and heat-labile enterotoxin (destroyed by heat) causing loss of water from intestine and watery diarrhoea
- unlikely to damage cell walls so no bloody diarrhoea
36
How does enteroinvasive E.coli work
- destroys intestinal cells, enters the cells and multiplies
- this triggers inflammation leading to damage of cells
- so might be bloody diarrhoea
37
How does enteropathogenic E.coli work
Causes disease in children under 2 years of age
- invades intestinal cells and destroys cell cytoskeleton
- makes intestinal cells flatten and inhibits ability to absorb water and nutrients
38
How does uropathogenic E.coli work
- Commensal pathogen which can become opportunistic pathogen when around urinary tract
- produce alpha and beta hemolysins which cause lysis of urinary cells
- cystitis and polynephritis
- dysuria (pain during urination)
39
Give 4 characteristics of Staphylococcus Aureus
- gram positive
- facultative anaerobes
- non-motile
- no spores
- catalase positive (produces catalase)
- coagulase positive (converts fibrinogen into fibrin)
40
What is a superficial impetigo
Infection of the epidermis
41
What is cellulitis
Infection of the dermis
42
Give the 5 superantigens (toxins) associated with Straphylcoccus Aureus
- pore-forming toxins (alpha-haemolysin (in red blood cells) and Pantone-valentine leucocidin (PVL)(in white blood cells))
- protease (exfoliatin)
- toxic shock syndrome toxin1 (TSST1) which stimulates cytokines release
- protein A (surface protein which binds Ig’s in wrong orientation)
43
Give 5 characteristics of Staphylococcus Epidermidis
- gram-positive
- non-motile
- doesn’t spore
- facultative anaerobe
- catalase positive
- urease positive
- coagulase negative
- novobiocin sensitive
- dominant bacteria on normal skin flora
- most common complication with prosthetics
44
Which bacteria does the novobiocin test differentiate
Staphylococcus epidermidis (novobiocin sensitive)
Staphylococcus saprophyticus (novobiocin resistant)
45
Give 5 characteristics of streptococcus pneumoniae
- gram positive
- non-motile
- no spores
- catalase negative
- facultative anaerobes
- alpha hemolysis (green ajar) and optochin sensitive
- bile soluble
46
Which species of bacteria does the optochin test differentiate
Streptococcus pneumoniae (optochin sensitive)
Streptococcus viridans (optochin resistant)
47
Which species does the bile solubility test
Streptococcus pneumoniae (bile dissolves)
Other alpha haemolytic streptococcus (bile insoluble)
48
Virulence factors of streptococcus pneumoniae
- fimbria
- biofilm
- pneumococcal surface protein A (PSPA) which inhibits complement activation and avoid opsonisation
- IgA protease
49
Give examples of different types of agar
Blood agar
Chocolate agar - heated to 80 degrees for 5 mins
Cysteine Lactose electrolyte deficient (CLED) agar - used to examine microorganisms in urine and differentiate between lactose fermenting (yellow) and non-lactose fermenting (blue) gram negative bacilli
MacConkey Agar - helps to differentiate lactose fermenting (pink) and non-lactose fermenting (yellow/colourless) gram negative bacilli
Gonococcus agar - used to grow Neisseria Gonorrhea
XLD agar - xylose lysine deoxycholate agar (XLD), shigella is red and salmonella is red with black Centers
Sabouraud’s agar - used for fungi
50
Give 5 characteristics of Mycobacteria
- rod-shaped (bacillus)
- strict aerobes
- waxy cell wall (made from mycolic acid)
- acid fast (red with Ziehl-Neelsen stain)
51
What is caseous necrosis
Necrosis associated with Tuberculosis (ghon focus)
| Where the inner part of the granuloma dies off and looks like cheese
52
What is a ranke complex
Fibrosed and calcified granuloma found on an X-ray
53
What complications are associated with systemic military TB?
- sterile pyuria in the kidneys
- meningitis in the meninges of the brain
- pott disease in the lumbar vertebrae
- Addison’s disease in the adrenal glands
- hepatitis in the liver
- lymphadenitis in the neck (scrofula)
54
How to test for TB
- purified protein derivative (PPD) Intradermal skin test (also called tuberculin test, mantoux test, TB test). Positive is when a bump and redness shows after being injected with some TB
- interferon gamma release assay (IGRA), evidence in the blood and more specific than PPD
- chest X-ray after positive result on any of the test
55
Give 5 characteristics of Epstein-Barr Virus (EBV)
- also known as Human Herpes Virus-4 (HHV-4)
- linear, double-stranded DNA
- enveloped
- most common cause of infectious mononucleosis (mono)
56
Which cells does EPV infect
- epithelial cells
| - b lymphocytes
57
What is a virus
An infectious obligate intracellular parasite compromising genetic material (DNA or RNA) surrounded by a protein coat and or a membrane
58
Are viruses living
No they are not
59
How do virus replicate
- Attachment to specific receptor
- cell entry (uncoating of virion within the cell)
- host cell interaction + replication
- assembly of virion
- release new virus particles (bursts out e.g rhinovirus or exocytosis e.g HIV/Influenza)
60
How do virus cause disease
- direct destruction of host cells e.g poliovirus
- modification of host cell e.g rotavirus (which atrophies villi and flattens epithelial cells
- over-reactivity of immune system e.g hepatitis B (jaundice)
- damage through cell proliferation e.g human papilloma virus (causes cervical cancer)
- evasion of host defences e.g herpesviridae
61
Give examples of anti-penicillin treatments that MRSA is resistant too
Nafcillin
Oxacillin
Cloxacillin
Dicloxacillin
62
What is spongiform encephalopathy and what causes it
- brain degeneration that turns healthy tissue into cysts and makes the brain look like a sponge
- caused by misfolded proteins called prions (which make other prions misfolded to cause cell apoptosis)
- caused by Creutzfeldt-Jakob Disease (CJB)
- caused by mutation in prion protein gene (PRNP)
- caused by kuru (cannibalism of infected human flesh)
63
What does a prion protein do
- contains 230 amino acids longs
| - found in neurone cytoplasm and used in neurones for uptake of copper in cells
64
How does variant Creutzfeldt-Jakob disease cause prions in people
Prions in cows = bovine spongiform encephalopathy (also known as mad cow disease)
Prions in sheep = scrapie
When human eats animal with prions, the prions enter human brain through absorptive endocytosis
65
Give the 5 plasmodium species that cause malaria in humans
```
Plasmodium falciparum (invades RBCs of all ages)
Plasmodium vivas (invades reticulocytes)
Plasmodium malarial (invades older RBCs)
Plasmodium ovale (invades RBCs of all ages)
Plasmodium knowlesi (invades older RBCs)
```
66
Which conditions offer protection against malaria
- Sickle cell anemia (no Duffy antigen)
- Thalassemia (makes parasite infected erythrocytes more susceptible to dying from oxidative stress)
- G6PD deficiency
67
How is malaria contracted in a human from a mosquito
- plasmodium-infected female anopheles mosquito looking for a blood meal
- mosquito are attracted to CO2 and human smells
- developing plasmodium (called sporozoite) is in mosquitoe’s salivary gland
- mosquito’s proboscis (needle mouth) pierce skin, sporozoites spill into bloodstream and go to the liver and reproduces asexually (called schizogony)
- next 2 weeks, these species become merozoites (p.faciparum, p.malaria, p.knowlesi)
- next months to years, these species become hypnozoites and don’t divide (p.vivax, p.ovale)
68
What is the exoerythrocytic phase of plasmodium
- next 2 weeks, these species become merozoites (p.faciparum, p.malaria, p.knowlesi)
- next months to years, these species become hypnozoites and don’t divide (p.vivax, p.ovale)
- usually asymptomatic
69
What is the erythrocytic phase
- merozoite inside the red blood cell
- lasts 2 to 3 days
- stage 1= early trophozoite (a ring)
- stage 2 = late trophozoite
- stage 3 = schizont (replicative stage with hemozoin - a brown smudge)
70
Describe sporogony of plasmodium
- merozoites becomes gametocytes through gametogony
- gametocytes in blood are sucked up by another female mosquito
- gametocytes become zygote and then ookinete and then oocyst which rupture into sporozoites
- the sporozoites then move to the salivary glands of the mosquito
71
What causes chagas disease (American trypanosomiasis)
- caused by protozoan called trypanosome Cruzi which transmitted through the feaces of triatominae
- triatominae is a reduviid bug that bites people on the face when they are sleeping (also called the kissing bug)
72
Describe the life cycle of trypomastigote
- starts as epimastigote in gut of reduviid’s midgut
- multiplies through binary fission
- becomes typomastigote which can no longer divide and can now enter human cells
- become amastigote (loses flagellum) and infects cells and divides through binary fission
- becomes trypomastigote and enters lymph and blood
- becomes amastigote when in cells again
73
Symptoms of Chagas’ disease
- Romana’s sign (swollen eye)
- chagoma (swelling at bite site)
- local inflammation
- hepatosplenomegaly
- meningoencephalitis
- pericardial effusion
74
Symptoms of chronic Chagas’ disease
- can be asymptomatic
- cardiomyopathy
- nerve damage
- gastrointestinal tract symptoms (megaesophagus, megacolon)
75
Medication for acute phase of Chagas’ disease
Anti-parasitic medication
- benznidazole
- nifurtomox
76
Give 5 characteristics of Streptococcus Pyogenes
- gram positive
- non-motile
- no spores
- facultative anaerobe
- catalase negative
- pyrrolidonyl arylamidase positive (produces this enzyme)- turns red
- beta-hemolysis (complete hemolysis) on blood agar - releases streptolysins which hydrolyses hemoglobin
- bacitracin sensitive
77
Virulence factors of streptococcus pyogenes
- encapsulated
- hyaluronidase (destroys hyaluronic acid)
- streptolysin S & O (destroys red blood cells)
- streptococcal pyrogenic exotoxins (Spe) - SpeA, SpeB and SpeC (triggers cytokine storm that can lead to toxic shock syndrome)
78
Where can streptococcus pyrones be found as commensal flora
- skin
- mucosa of pharynx or throat
- vagina
79
Conditions that can be caused by streptococcus pyogenes
- strep throat (pharyngeal mucosa, tonsils)
- scarlet fever (bright skin rash and tongue has sandpaper feel)(intracapillary hemolysis)
- impetigo (epidermis)
- erysipelas (upper dermis)
- cellulitis (lower dermis)
- necrotising fasciitis (muscle fascia)
Complications
- type 2 sensitivity after bacteria eliminated from body (post-infectious sequelae) - M protein on bacteria mimics myosin and glycogen on heart
- post-streptococcal glomerulonephrotis (Acute inflammation of of kidneys after impetigo due to type 3 sensitivity reaction)
80
What are the symptoms of acute rheumatic fever
JONES
Joint inflammation
Heart damage (new murmurs)
Nodules (on elbows, knees and forearm)
Erythema marginatum (rash with thick margins)
Sydenham’s Chorea (rapid involuntary movements of the face and hands
81
Give some bacteria that increase risk of C. Difficile
The ones that start with C
- cephalosporins
- carbapenems
- ciprofloxacin
82
In which situations would you be cautious giving antibiotics
- allergies, anaphylaxis
- pregnancy
- liver and Renal function
- drug interactions
83
How do antibiotics kill bacteria
- inhibits cell wall synthesis
- inhibits of protein synthesis
- inhibitors of nuclei acid synthesis
- anti-metabolites
- inhibitors of membrane function
84
Give 5 characteristics of streptococcus agalactiae (group B strep - GBS)
- gram positive
- non-motive
- non-spores forming
- facultative anaerobe
- catalase negative
- beta hemolysis (uses beta-hemolysin enzyme)
- bacitracin resistant
- only hippurate positive strep (hippuricase)
- camp positive
85
Who does streptococcus agalactiae (GBS) infect normally
- commonly affects pregnant women and newborns
| - infects cattle involved in milk production (cows)
86
Where can streptococcus agalactiae be found in the body
- GI tract
| - vagina
87
What can an infection of streptococcus agalactiae lead to
- miscarriage or premature delivery
- intrauterine death
- cystitis
- pneumonia in newborns
- neonatal sepsis
- neonatal meningitis
- septic arthritis
88
Give 5 groups within the streptococcus viridans group
```
Streptococcus Anginous
Streptococcus Mitis
Streptococcus Sanguinis
Streptococcus Salivarius
Streptococcus Mutans
```
89
Give 5 characteristics of streptococcus viridans
- gram positive
- catalase negative
- alpha, beta and gamma hemolytic
- optochin resistant
- bile insoluble
- no capsule
90
Where can viridans streptococcus be found
- oral cavity
- teeth
- skin
- GI tract
- genitourinary tracts
91
Which species of streptococcus encourages dental caries and gum disease
Streptococcus Mutans
| Streptococcus Mitis
92
Which bacteria is the most common cause of subacute bacterial endocarditis
- streptococcus sanguinis
93
Which streptococcus species is found to be most commonly responsible for brain abscesses
Streptococcus Intermedius
94
which disease conditions are streptococcus viridans associated with causing
- dental plaques
- dental caries
- periodontal disease
- brain and liver abscesses
- bacterial endocarditis
- viridans group streptococcal shock
95
Give the two types of herpes simplex virus
- HS1 (above waist lesions)
| - HS2 (below waist lesions)
96
What type virus are the herpesviridae
- enveloped
| - double-stranded DNA virus
97
Where do the herpes virus usually reside after infection permanently
- trigeminal ganglia (face)
- sacral ganglia (genitalia)
- herpes sores develop on the same side as affected ganglia
98
With herpes simplex virus (HSV), what is prodrome
- a tingling and burning sensation felt a few days before herpes symptom flair up
99
Give symptoms of herpes simplex virus
- Fluid filled small painful blisters found on the vermillion border, gums, palate, tongue, lip, tongue and facial area
- blisters on females and males genitalia
- herpetic whitlow (herpes on fingers
- keratoconjunctivitis (inflammation of cornea and conjunctivitis) - branching dendritic lesion (like thunder branch in eye)
- meningitis or encephalitis (usually temporal lobe)
100
What does varicella zoster (a type of herpes virus) cause
- varicella (chickenpox)
| - herpes zoster (shingles)
101
What tests are used to test for chickenpox and shingles
- tzanck test (multinucleated giant cells in skin)
- blood test for varicella antibodies
- PCR to look for viral DNA
102
What medication should not be given to people with chicken pox and why
- aspirin
- because it might trigger Reye syndrome which when varicella zoster virus and aspirin affect the liver causing toxic buildup of ammonia in the body
103
Give an example of an oncovirus (cancer causing virus)
- human herpesvirus 8 (HHV-8)
- also called the Kaposi’s sarcoma - associated herpesvirus (KSHV)
- in the family of human gamma herpesviruses
104
Give 5 characteristics of the kaposi’s sarcoma-associated herpesvirus (KSHV)
- icosahedral capsid
- double stranded linear DNA
- protein tegument
- viral glycoproteins
105
How is kaposi sarcoma-associated herpesvirus transmitted
- through sexual contact
106
What are the two stages of viral infection in the body
- lytic phase (DNA transcribed and translated into viral proteins)
- latent phase
107
Which virus is usually associated with causing roseola infantum (also called exanthema subitum or 6th disease)
- human herpesvirus 6 (HHV-6)
| - roseolovirus
108
What conditions are associated with adenoviruses
- respiratory (sore throat, common cold, pneumonia)
- gastrointestinal (diarrhoea)
- genitourinary infections (cystitis)
- conjunctivitis (pink eye)
109
How does the herpesvirus differ from the adenovirus
- Naked as no lipid membrane
| - fibres like projections from each of the vertices of the virus
110
How does adenovirus get into epithelial cells
- binds to the coxsacki adenovirus receptor on the cell
111
How does the adenovirus cause cell death
- Prevent synthesis of cellular DNA
| - Prevents production of proteins
112
What is the smallest known DNA animal virus
Parvovirus B19 (18-28nm)
113
What is parvovirus associated with causing in children
- fifth disease (slapped cheek syndrome)
114
Give 5 characteristics of parvovirus
- single stranded linear DNA
- icosahedral capsid
- naked (no lipid membrane)
115
Which cells are parvovirus attracted to and why
- proerythroblasts
- parvovirus need P- antigen and cells within the S phase
- the proerythroblasts has lots of P antigens and usually were in the S phase (DNA duplication stage)
- the parvovirus uses cells to produce non-structural protein 1 (NS1) which are toxic and cause apoptosis
- this leads to less new red blood cells being released into the blood stream
116
What is the first line HIV test given at Sheffield teaching hospital
- Roche COBAS assay
117
What are the two second line HIV tests given at Sheffield teaching hospitals
- Liason X
| - a line assay
118
What is the fourth HIV test given if the previous ones were inconclusive
- Rescreen Ultra (an ELISA assay)
