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STEP 1 > Microbiology and Infectious Diseases > Flashcards

Microbiology and Infectious Diseases Flashcards

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1
Q

What are the structural differences between Gram-positive and Gram-negative bacteria?

A
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2
Q

What color do Gram +ve vs Gram -ve stain on Gram stains, respectively?

A

Gram positive = purple
Gram negative = red

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3
Q

What kind of agar does Haemophilus influenzae type b (Hib) require to grow?

A
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4
Q

What is the satellite phenomenon in microbiology?

A

Satellite phenomenon: Hib can also grow near Staphylococcus aureus colonies on blood agar because S. aureus secretes NAD+, supplying Factor V.

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5
Q

What are anaerobes, and why are they medically important?

A

Anaerobes are bacteria that do not require oxygen for growth and may be harmed or killed by its presence.

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6
Q

What are the types of anaerobes, and how do they differ?

A

Anaerobes are classified based on how they tolerate or use oxygen:

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7
Q

What are the main anaerobes we need to know (5)?

A

Anaerobes Can’t Breathe Fresh Air

Clostridioides
Clostridium
Bacteroides
Fusobacterium
Actinomyces

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8
Q

Are all anaerobic bacteria Gram-negative?

A

No, anaerobic bacteria can be Gram-positive or Gram-negative, and they can be rods or cocci.

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9
Q

What are intracellular bacteria, and why are they significant?

A

Intracellular bacteria are bacteria that survive and replicate inside host cells, often to evade immune detection and persist within the body. They can be obligate intracellular or facultative intracellular.

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10
Q

What are the encapsulated bacteria? (8)

A

Haemophilus influenzae b
Neisseria meningitidis
Strep pneumo
Pseumodomas aeruginosa
E coli
Salmonella
Klebsiella
Group B strep

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11
Q

What are urease-positive organisms, and why are they clinically important?

A

Urease-positive organisms produce the enzyme urease, which hydrolyzes urea into ammonia and CO₂. This increases local pH (alkalinity), helping the organism survive acidic environments (e.g., stomach, urinary tract).

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12
Q

What kind of test can be used to diagnose H pylori?

A

Urease breath test

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13
Q

What are the urease-positive organisms?

A

Mnemonic: “Pee CHUNKSS”

Proteus
Cryptococcus
Helicobacter pylori
Ureaplasma
Nocardia
Klebsiella
Staphylococcus saprophyticus
Staphylococcus epidermidis

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14
Q

What kind of kidney stones do urease-positive organisms predispose their host to?

A

Struvite (magnesium ammonium phosphate), particularly Proteus

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15
Q

What are catalase-positive organisms, and why are they clinically significant?

A

Catalase-positive organisms produce the enzyme catalase, which breaks down hydrogen peroxide (H₂O₂) into water and oxygen. This helps them evade oxidative killing by neutrophils.

Patients with chronic granulomatous disease (CGD) are especially susceptible to these organisms because they lack NADPH oxidase, so they can’t generate enough reactive oxygen species to kill catalase-positive microbes.

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16
Q

4 examples of spore-forming bacteria

A

Clostridioides difficile
Clostridium botulinum
Clostridium tetani

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17
Q

Are clostridioides and clostridium bug families related?

A

Yes — Clostridioides is a genetic subgroup reclassified from the Clostridium genus. They are closely related and part of the same bacterial family. They are both gram-positive.

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18
Q

What is the virulence factor produced by staph aureus?

A

Protein A: a surface protein that binds the Fc region of IgG, preventing opsonization and phagocytosis.

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19
Q

What is IgA protease, and which bacteria secrete it?

A

IgA protease is an enzyme that cleaves secretory IgA, allowing bacteria to colonize mucosal surfaces by evading mucosal immune defenses.

Strep pneumo
Hib
Neisseria
(SHiN)

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20
Q

What is M protein, which bacterium produces it, and what disease is it associated with?

A

Acute rheumatic fever: antibodies against M protein can cross-react with human tissues (molecular mimicry), especially in the heart, joints, and CNS

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21
Q

Is Streptococcus pyogenes the same as Group A Streptococcus (GAS)?

A

Yes — Streptococcus pyogenes is the bacterium classified as Group A Streptococcus (GAS) based on Lancefield grouping, which categorizes beta-hemolytic streptococci by their cell wall carbohydrates.

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22
Q

What are the differences between exotoxins and endotoxins?

A

Exotoxins = actively secreted
Endotoxins = G(-) LPS membrane that is shed

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23
Q

What are the bacteria with exotoxins that inhibit protein synthesis and how do they manifest?

A

corynebacterium diphtheriae: pharyngitis with pseudomembranes in throat and severe lymphadenopathy

pseudomonas aeruginosa: host cell death

shigella species and EHEC: shiga toxin. Damage to the GI mucosa = cytokine release = hemolytic uremic syndrome

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24
Q

Which bacteria produce exotoxins that increase fluid secretion?

A

ETEC: increased cAMP (heat labile) or cGMP (heat stable).

Vibrio cholerae: cholera toxin = overactivation of cAMP = voluminous rice-water diarrhea.

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25
Which bacterium produces an exotoxin that increase fluid secretion?
Bordetella pertussis. = whooping cough
26
Which bacteria produce exotoxins that inhibit the release of a neurotransmitter?
Clostridium botulinum = infant botulism. Caused by ingestion of spores (e.g. raw honey, soil) Clostridium tetani = tetanus, spastic paralysis due to blockade of GABA.
27
MoA of bacteria producing exotoxins that inhibit the release of a neurotransmitter
Proteases that cleave the SNARE protein which is normally required for NT release via vesicular formation
28
Which bacterium produces an exotoxin that lyses cell membranes?
Group A strep Lyses RBCs = beta-hemolysis.
29
What is the ASO test, and how is it related to Streptococcus pyogenes?
The ASO test (Anti-Streptolysin O test) measures host antibodies against Streptolysin O, a toxin produced by Streptococcus pyogenes (Group A Strep / GAS). Elevated ASO titers indicate recent GAS infection. **Useful to diagnose rheumatic fever** when the original strep infection is no longer detectable
30
Which bacteria produce exotoxins that are superantigens causing shock?
**Staph aureus**: toxic shock syndrome. Associated with prolonged tampon use. **GAS**: toxic-like shock syndrome. More invasive, higher mortality rate.
31
What are the three "main" effects of endotoxins?
1. Macrophage activation 2. Complement activation 3. Tissue factor activation
32
Describe the lab algorithm for gram-positive bacteria
1. Bacilli, cocci or branching filaments? 2. If bacilli or branching filaments, aerobic or anaerobic? 3. If cocci --> catalase-positive or negative? 4. If catalase-positive, coagulase positive or negative? 5. If catalase-negative, hemolysis alpha, beta or gamma?
33
How would you classify listeria and bacillus?
Gram-positive aerobic bacilli
34
How would you classify clostridium?
Gram-positive anaerobic bacilli
35
How would you classify the streptococcus family?
Gram-positive cocci that are catalase **negative**, in pairs or chains.
36
How would you classify the staphylococcus family?
Gram-positive cocci that are catalase **positive**, in clusters
37
Are all catalase-positive organisms Gram-positive?
No — catalase-positive organisms include both Gram-positive and Gram-negative bacteria, as well as fungi.
38
How would you classify streptococcus pneumoniae?
Catalase-negative alpha hemolytic gram positive cocci
39
How would you classify groups A and B strep.
Catalase-negative beta hemolytic gram positive cocci
40
What are other names for Group A Strep and Group B Strep?
GAS: Strep pyogenes GBS: Strep agalactiae
41
What does beta hemolysis mean?
Complete hemolysis; the agar is clear.
42
What does alpha hemolysis mean?
Partial hemolysis; the agar is green.
43
How would you classify staph aureus?
Coagulase positive, catalase positive and gram-positive cocci in clusters. *It is also beta hemolytic
44
How would you classify staph saphrotycus and epidermidis?
Coagulase negative, catalase positive and gram-positive cocci in clusters.
45
How does TSST-1 (Toxic Shock Syndrome Toxin-1) from Staphylococcus aureus work?
46
Which bacteria are part of the normal skin microbiota?
**Staphylococcus epidermidis (most common)** Staphylococcus aureus (some individuals, especially in the nares, opportunistic) Corynebacterium species (generally harmless) Propionibacterium (Cutibacterium) acnes (contributes to acne, in hair follicles)
47
Where is Staphylococcus saprophyticus normally found, and what is its clinical relevance?
Part of the normal flora of the female genital tract and perineum Second most common cause of urinary tract infections (UTIs) in sexually active young women (after E. coli)
48
What are the diseases in which strep pneumo is the #1 causative agent?
MOPS: Meningitis Otitis media in children Pneumonia (lobar) Sinusitis
49
What is Scarlet fever?
Scarlet fever is a disease caused by Streptococcus pyogenes (Group A Strep) that produces erythrogenic (pyrogenic) exotoxins, which act as superantigens. Fine, blanching, generalized sandpaperlike rash sparing the palms and soles, strawberry tongue and circumoral pallor. In the setting of **GAS pharyngitis**
50
What is the clinical relevance of Group B Streptococcus (GBS / Streptococcus agalactiae)?
Group B Streptococcus is a Gram-positive, β-hemolytic cocci that is part of the normal vaginal and rectal flora in many women, but it can cause serious infections in newborns.
51
What prophylactic measures are taken to prevent Group B Streptococcus (GBS) neonatal infections?
Pregnant women are screened for GBS colonization via vaginal and rectal swab at 35–37 weeks gestation If screening positive: give intrapartum antibiotic prophylaxis (during labor)
52
What are Enterococci, and what is their clinical significance?
53
Distinguish between the types of paralyses seen in botulin toxin administration vs tetanus
54
What are the classic symptoms of botulism (the 5 D’s)?
Botulism, caused by the botulinum toxin from Clostridium botulinum, leads to descending flaccid paralysis. 5 Ds:
55
What are the possible natural courses of a tuberculosis (TB) infection?
56
What is the gram-negative lab algorithm?
1. Diplococci, coccobacilli, bacilli or curved rods? 2. If diplococci --> maltose fermentation? 3. If bacilli --> lactose fermentation? 4. If no lactose fermentation, oxidase positive or negative?
57
How would you distinguish between Neisseria Gonorrhoeae and Neisseria Meningitidis?
They are both gram-negative diplococci. Distinguished by maltose fermentation: negative = gono, positive = meningitidis.
58
How would you describe HiB and Bordetella Pertussis?
Gram-negative coccobacilli.
59
How would you sub-categorize gram-negative bacilli?
Do they ferment lactose? If so, fast = E Coli and Klebsiella. If not, are they oxidase positive or negative? positive = pseudonomas aeruginosa negative = shigella, yersinia, salmonella
60
How would you describe salmonella, shigella and yersinia?
Gram negative bacilli that do not ferment lactose and that are oxidase negative.
61
How would you describe E Coli and Klebsiella?
Gram negative bacilli that ferment lactose fast.
62
Are curved rods oxidase positive or negative?
Positive
63
What are the 3 curved rods to know?
Campylobacter jejuni Vibrio cholerae H Pylori
64
Which organism causes epiglottitis and what is the X Ray sign?
Hib Thumb sign
65
Which organisms are commonly found in bronchiectasis secondary to cystic fibrosis?
Burkholderia cepacia complex Pseudomonas aeruginosa
66
What is ecthyma gangrenosum?
Rapidly progressive necrotic cutaneous lesion caused by Pseudomonas bacteremia. Typically seen in immunocompromised patients.
67
Are rods the same as bacilli in bacteriology?
Yes — in bacteriology, "rods" and "bacilli" are interchangeable terms that describe the shape of bacteria.
68
What is the clinical relevance of campylobacter jejuni?
Campylobacter jejuni is a curved, Gram-negative rod that is a major cause of bacterial gastroenteritis, especially in children and travelers. It is also associated with Guillain Barré Syndrome.
69
What are the features of Lyme disease (Stages 1, 2 and 3)
70
Compare Syphilis stages (primary, secondary, tertiary, latent) in terms of features, contagiousness, time from infection
71
Treatment for Lyme disease?
Doxycycline first line
72
What is the cause of walking pneumonia?
Mycoplasma pneumoniae
73
What are the 4 types of endemic mycoses?
1. Histoplasmosis 2. Blastomycosis 3. Coccidioidomycosis 4. Para-coccidioidomycosis
74
What are the characteristics are systemic mycoses?
Dimorphic fungi - Cold (20C) = mold - Heat (37C) = yeast Except coccidioides which is not a yeast.
75
Which of the four mycoses is found in Canada and what are its features
Blastomycosis Inflammatory lung disease Disseminates to bone/skin
76
What is the vector responsible for transmitting all types of malaria?
The female Anopheles mosquito is the exclusive vector for all species of Plasmodium that cause malaria.
77
What varies between different types of malaria if the vector is always the same?
The species of Plasmodium varies, affecting disease severity, fever pattern, risk of relapse, and geographic distribution.
78
What are the 4 different types of Plasmodium species and how do their disease differ?
79
What are the common presentations of Toxoplasma gondii in immunocompetent vs. immunocompromised individuals?
Immunocompetent: Mononucleosis-like symptoms AIDS patients: Reactivation leads to brain abscesses
80
What is the characteristic imaging finding in cerebral toxoplasmosis?
Multiple ring-enhancing lesions on MRI of the brain
81
How is Toxoplasma gondii transmitted and why should pregnant women be cautious?
ransmission occurs via cysts in undercooked meat, oocysts in cat feces, and transplacentally. Pregnant women should avoid cat litter to prevent congenital toxoplasmosis.
82
What is the classic triad of congenital toxoplasmosis?
Chorioretinitis Hydrocephalus Intracranial calcifications
83
What is the pathophysiology of scabies?
Sarcoptes scabiei mites burrow into the stratum corneum, causing intense pruritus (especially at night) and serpiginous burrows, often between the fingers and toes.
84
What are common risk factors and populations for scabies outbreaks?
Scabies is common in children and in crowded populations such as jails and nursing homes.
85
How is scabies transmitted?
Scabies is transmitted via skin-to-skin contact (most common) and also through fomites (e.g., bedding, clothing).
86
What are the main diseases caused by Schistosoma mansoni and Schistosoma japonicum?
They cause hepatosplenic schistosomiasis, leading to liver and spleen enlargement, fibrosis, portal hypertension, and intestinal symptoms like diarrhea, abdominal pain, and iron-deficiency anemia.
87
What are the complications of chronic infection with Schistosoma haematobium?
It can cause painless hematuria, squamous cell carcinoma of the bladder, and pulmonary hypertension.
88
How is Schistosoma transmitted to humans?
Humans become infected when cercariae from freshwater penetrate the skin during activities like swimming or bathing; snails are the intermediate hosts.
89
Name 5 important families of DNA viruses
Herpesviruses Poxvirus Adenovirus Papillomavirus Parvovirus
90
Which families of DNA viruses have an envelope?
Herpesviruses Poxvirus
91
Which families of DNA viruses are double stranded?
Herpesviruses Poxviruses Adenoviruses Papillomavirus
92
What is parvovirus B19 associated with, clinically?
*Children: Erythema infectiosum ("slapped cheek" rash) *Adults: Arthralgia/arthritis *Hemolytic anemia patients: Aplastic crisis *Pregnancy: Hydrops fetalis (fetal anemia) *Immunocompromised: Chronic pure red cell aplasia
93
What are the most common clinical features of HSV-1 infection?
HSV-1 is transmitted through respiratory droplets or the saliva.
94
What are the most common clinical features of HSV-2 infection?
Transmitted through sexual contact and perinatally Causes genital herpes and neonatal herpes
95
What are the main features of EBV?
HHV-4
96
Why should patients avoid contact sports if they have EBV?
Risk of splenic rupture
97
How does EBV infect B cells?
Through CD21
98
How do CMV and EBV mononucleosis differ?
99
Name 4 families of RNA viruses
Picornaviruses Flaviviruses Retroviruses Coronaviruses They are all single stranded and linear
100
Name the kinds of picornaviruses
Poliovirus Hepatitis A Coxsackie virus Rhinovirus
101
What is the cause of the common cold?
Rhinoirus
102
Are picornaviruses enveloped?
No
103
Is influenza enveloped?
Yes
104
What is the difference between antigenic shift and antigenic drift in influenza viruses?
105
Threshhold CD4+ count for AIDS
<200
106
How do oral candidiasis and oral hairy leukoplakia differ in cause and appearance?
107
Describe the diagnostical pattern for HIV testing
108
What are AIDS-defining conditions?
They are illnesses that signal severe immunosuppression in HIV and include:
109
How do we prevent resistance in HIV treatment?
110
Describe the cerebrospinal fluid findings in meningitis for fungal/TB vs bacterial vs viral meningitis
111
What are 7 common rashes of childhood?
112
Compare and contrast the three most common vaginal infections.
113
What are the treatments for the three most common vaginal infections?
BV = metronidazole or clindamycin TV = metronidazole Candida = azoles (fluconazole)
114
3 most common culprits of uncomplicated UTIs, in order of frequency
1. E Coli 2. Staph saphrotycus 3. Klebsiella
115
Which rash of childhood presents in the following manner, what what is its causative agent?
Hand-foot-mouth disease Coxsackievirus type A
116
Which rash of childhood presents in the following manner, what what is its causative agent?
Roseola Human herpesvirus 6
117
Which rash of childhood presents in the following manner, what what is its causative agent?
Measles ("rougeole") Measles virus
118
Which rash of childhood presents in the following manner, what what is its causative agent?
erythema infectiosum (fifth disease) Parvovirus B19
119
Which rash of childhood presents in the following manner, what what is its causative agent?
Rubella Rubella virus
120
Which rash of childhood presents in the following manner, what what is its causative agent? Sore throat, circumoral pallor, sandpaper-like rash, lymphadenopathy, strawberry tongue
Scarlet fever Strep pyogenes (GAS)
121
What complication does parvovirus B19 cause in utero?
Hydrops fetalis
122
What are common nonspecific signs of TORCH infections
hepatosplenomegaly jaundice thrombocytopenia growth restriction
123
What are the TORCH infections we should know about
ToRCHHeS: Toxoplasma gondii Rubella CMV HIV HSV-2 Syphilis
124
How is toxoplasma gondii acquired
Cat feces Ingestion of undercooked meat
125
How does toxoplasma gondii present in the newborn?
Triad: Chorioretinitis Hydrocephalus Intracranial calcifications +/- blueberry muffin rash
126
How is rubella acquired
Respiratory droplets
127
How does a maternal rubella infection present in the newborn?
Congenital cataracts Deafness CHD (PDA)
128
How does a maternal CMV infection present in the newborn?
Hearing loss Seizures Blueberry muffin rash Chorioretinitis Periventricular calficiations
129
How is CMV acquired
Sexual contact, organ transplant
130
How does HIV present in the newborn
Recurrent infections Chronic diarrhea
131
How does Syphilis present in the newborn
Stillbirth/hydrops fetalis If child survives: facial anomalies (notched teeth, saddle nose, rhinitis, short maxilla), saber shins, CN VIII deafness
132
What are the symptoms of a mumps infection
Parotitis Orchitis Aseptic meningitis Pancreatitis Sterility (especially after puberty)
133
What are the most common causes of meningitis in newborns?
GEL: GBS E coli Listeria
134
What are the most common causes of meningitis in children 6mo-6y?
Strep pneumo Neisseria meningitidis Hib GBS Enteroviruses
135
What are the most common causes of meningitis in patients 6-60y?
Strep pneumo Neisseria meningitidis Enteroviruses HSV
136
What are the most common causes of meningitis in patients 60+?
Strep pneumo Neisseria meningitidis Hib GBS Listeria
137
What organism should be suspect as a causative agent of meningitis in HIV patients?
Cryptococcus neoformans
138
Which viruses are common culprits of meningitis?
Enteroviruses (especially coxsackievirus), HSV-2, HIV, West Nile virus, VZV
139
HSV-1 vs HSV-2 as brain infections
HSV-1 = encephalitis HSV-2 = meningitis
140
Empirical management of meningitis
Ceftriaxone and vancomycin + ampicillin if Listeria suspected + acylclovir if viral encephalitis suspected
141
Most common causative agent of osteomyelitis
Staph aureus
142
What are the 3 most common causative agents of encephalitis?
143
What is the difference in symptoms between meningitis and encephalitis?
Meningitis: Fever, headache, neck stiffness, photophobia, nausea/vomiting Encephalitis: Altered mental status (confusion), seizures, personality changes, ± fever and headache
144
What is the risk of transmission from a needlestick injury involving a known positive patient for Hep B, Hep C and HIV respectively?
Hepatitis B: 30% Hepatitis C: 3% HIV: 0.3%
145
How does the heat-labile (LT) toxin of enterotoxigenic E. coli resemble cholera toxin?
Like cholera toxin, heat-labile toxin activates adenylate cyclase, leading to increased intracellular cyclic AMP, which causes watery diarrhea due to loss of water and electrolytes.
146
Compare viral vs bacterial LP findings for meningitis

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