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MBBS VI - SpC - Medicine > Microbiology - Medically important microbes > Flashcards

Microbiology - Medically important microbes Flashcards

1
Q

Outline the classification scheme for gram positive cocci

A

Gram positive rods

Gram positive cocci:

  • Catalase positive GPC in clusters - Staphylococcus sp.
  • Catalase negative GPC in chains - Streptococci and Enterococcus
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2
Q

S. aureus

List types of infections

A

Infections:

  • Skin/ soft tissue
  • Abscesses
  • Native or prosthetic joint septic arthritis
  • Osteomyelitis
  • Pneumonia
  • Infective endocarditis
  • Endovascular infection
  • Surgical site infection

Toxin-mediated:

  • Food poisoning by staphylococcal enterotoxin
  • Toxic shock syndrome
  • Scalded skin syndrome
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3
Q

4 subtypes of S. aureus with varying antibiotics resistance

List the antibiotics resistance

A

MSSA: Sensitive to most B-lactams

HA- MRSA: Resistant to B-lactams and others e.g. clindamycin

CA- MRSA (may carry PVL toxin for necrotizing infection): Resistant to B-lactams, less resistant to non-B-lactams e.g. clindamycin

VISA/ VRSA: Immediate or full resistance to glycopeptides

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4
Q

Antibiotics of choice for MSSA, MRSA, VRSA

A

MSSA: Cloxacillin

HA- MRSA: Vancomycin, Linezolid, Daptomycin, Ceftaroline

CA-MRSA: Vancomycin, Linezolid, Daptomycin, Ceftaroline + any susceptible antibiotics

VISA/VRSA: Linezolid, Daptomycin, Ceftaroline

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5
Q

Function of coagulase test for gram positive cocci?

A

Catalase positive GPC in clusters:

  • Coagulase positive = S. aureus
  • Coagulase negative = Staphylococci spp.
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6
Q

Coagulase negative staphylococcus

  • Nature source of bacteria
  • Infections
  • Collection method
A

Natural skin commensals, benign

Exceptions:

  • Genuine infection of prosthesis
  • S. saprophyticus = UTI
  • S. lugdunensis = Virulent
  • S. epidermidis = prosthesis/ catheter-related infection

Collection:
Take at least two sets of blood culture if GPC in clusters
Single blood culture isolate may be contamination due to improper blood taking technique

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7
Q

Alpha hemolytic streptococci

Types of infection caused by Strep. pneumoniae

A

Streptococcus pneumoniae

Pneumonia 
Meningitis 
Otitis media 
Sinusitis 
Septicaemia
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8
Q

List 5 medically important alpha-hemolytic streptococci

List infections these cause

A
  1. Streptococcus pneumoniae: pneumonia, meningitis, otitis media, sinusitis, speticaemia
  2. Viridans streptococci- infective endocarditis, dental carries, oral infections
  3. Streptococcus anginosus/ S. milleri - Abscess formation in abdominal, pelvic cavities
  4. Streptococcus bovis - bacteremia, IE, GI malignancies (CRC)
  5. Streptococcus suis - meningitis, bacteremia
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9
Q

Which alpha-hemolytic streptococcus is related to colorectal cancer and IE

A

Strep. bovis

Major biotype in HK is type 2, associated with cholangitis
Biotype 1 is associated with IE and CRC

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10
Q

Beta-hemolytic streptococci

S. pyogenes infections

A

S. pyogenes (GAS in Lancefield grouping)

  • Local skin Infections: impetigo, cellulitis, necrotizing fasciitis
  • Respiratory: pneumonia, pharyngitis
  • Systemic infections: Toxic shock syndrome, Scarlet fever, lymphadenitis
  • Post-infectious syndrome: PSGN, acute rheumatic fever
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11
Q

Outline scheme for differentiating Catalase negative GPC/ Streptococci spp.

A

First: Alpha/ Gamma hemolysis or Beta hemolysis pattern

Alpha/ Gamma group:

  • Optochin susceptible and bile soluble, PYR +ve and VP -ve = Streptococcus pneumoniae
  • Optochin resistant and bile Insoluble = Viridans streptococci, Strep. bovis and Enterococci

Beta groups:
- Lancefield grouping, Bacitracin susceptibility, Biochemical reactions
GAS = Strep. pyogenes
GBS (Bacitracin resistant, CAMP _ve, Hippurate hydrolysis +ve) = Strep. agalactiae
GCS or GGS = Strep. dysgalactiae
Streptococcus anginosus group/ Strep. milleri

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12
Q

Virulent mechanisms of group A strep.

A

Invasion and spread through tissue via Streptokinase, Hyaluronidase

Systemic toxin: Streptolysin O, superantigen and other Streptococcal pyrogenic exotoxins

Anti-phagocytosis and adhere to epithelial cells/ mucosa : M protein, capsule

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13
Q

Scarlet fever

  • Presentation
A

Rash:

  • Facial flushing with peri-oral pallor
  • Diffuse, centrifugally spreading rash over face and upper chest
  • Blanchable

Strawberry tongue

Eosinophilia

Preceding pharyngitis or any GAS infection

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14
Q

Diagnostic criteria of Streptococcal toxic shock syndrome

Treatment options

A

Lab: Isolation of Group A Streptococcus

Clinical: 
- Hypotension 
- Multiorgan involvement with at least 2 of 
Renal impairment 
Coagulopathy 
Liver involvement 
ARDS 
Generalized, erythematous macular rash 
Soft tissue necrosis

Tx: Penicillin + Clindamycin or linezolid

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15
Q

Diagnostic criteria for acute rheumatic fever

A 
Jone's criteria 
Major: 
- Carditis 
- Arthritis 
- Sydenham's chorea 
- Subcutaneous nodules 
- Erythema marginatum

Minor:

  • Fever
  • Arthralgia
  • High ESR or CRP
  • Long PR interval

Supportive:

  • High Anti-streptolysin O titer (ASO)
  • Positive throat culture for GAS

Dx: 2 major or 1 major + 2 minor

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16
Q

Treatment of acute rheumatic fever

A

Penicillin x 10 days
Anti-inflammatory: Aspirin, Corticosteroids
Surgery for mitral valve involvement

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17
Q

S. agalactiae infections

Biochemical tests

A

S. agalactiae (GBS in Lancefield grouping)&raquo_space;> Raw fish!
Major infections: Meningitis, Pneumonia, Sepsis, Skin, Septic arthritis, Osteomyelitis, Female genital tract infections

  • Neonatal sepsis, meningitis, peripartum infections , pneumonia
  • Pregnant women: UTI, genital tract infection, placenta infection, post-partum sepsis
  • Elderly/ immunocompromised: skin infection, septic arthritis, osteomyelitis, pneumonia, endocarditis, meningitis, sepsis

Bacitracin resistant
CAMP positive
Hippurate hydrolysis positive

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18
Q

S. dysgalactiae Infections

Biochemical tests

A

Infections: Very similar to S. agalactiae
Same as S. agalactiae: Meningitis, Pneumonia, Sepsis, Skin infection, Septic arthritis, Osteomyelitis
Add-on: Pharyngitis, PSGN, Endocarditis
No pregnancy/ female genital infections

Lancefield group C/G
Bacitracin resistant
PYR -ve
VP -ve

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19
Q

S. anginosus/ S. milleri

Infections
Biochemical tests

A

Abscess formation
- Dental, brain, liver, pelvic, lung, empyema
Endocarditis
Bacteremia in neutropenic patients - ARDS, Toxic shock

Bacitracin resistant
PYR -ve 
VP +ve
Alpha/ Gamma hemolysis 
Lancefield non-groupable

(Caramel smell)

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20
Q

Viridans streptococci

Source of bacteria
Types of infections

A

Common oral flora

Infections:
Dental carries
Infective Endocarditis

Bacteremia in neutropenic patients
Meningitis
Pneuomonia

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21
Q

Enterococci

Examples
Lancefield grouping and special biochemical tests, growth environment
Types of infections

A

Example: E. faecium and E. faecalis

Lancefield group D
Grows in 6.5% NaCl and 40% bile salt (similar to gut environment)
PYR +ve, Hydrolyzes bile esculin

Normal gut flora, causes mainly opportunistic infections

-Catheter-associated UTI, Line sepsis
-Endocarditis
- Component of polymicrobial intra-abdominal/ biliary infections

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22
Q

Outline the classification scheme for gram positive rods

A

Aerobic GPR: BCLNM

  • Bacillus
  • Corynebacterium
  • Listeria monocytogenes
  • Norcardia, Rhodococcus
  • Mycobacteria: MTB complex and non-tuberculosis mycobacteria

Anaerobic GPR:

  • Spore forming: Clostridium spp.
  • Non-spore forming
23
Q

Bacillus spp.

List examples and types of infection
Source of bacteria

A

Widely distributed in environment

B. anthracis = anthrax
B. cereus = Food poisoning (rice products)

Bacillus in blood culture is most likely contamination

24
Q

Listeria monocytogenes

Source of bacteria
Types of infections
Antibiotic resistance
Tx

A

Source: Milk, Chicken and poultry products

Infections:

  • Neonatal meningitis and pregnancy infections
  • CNS infections in elderly/ immunocompromised
  • Resistant to cephalosporins, sensitive to ampicillin

Tx: Ampicillin, (ceftriaxone)

25
Q

Corynebacterium

Example
Type of infection
Presentation
Source of bacteria

A

Respiratory and cutaneous diphtheria infection

Sore throat with grey pseudo-membrane in oropharynx
Cervical lymphadenopathy, toxin-mediated cardiac and neurological complications

Source: Skin, oral mucosal commensals, mostly cause opportunistic infections

26
Q

Nocardia and Rhodococcus

  • Type of infection
  • Biochemical test
A

Infection: Opportunistic infection, chronic in immunocompromised pt.

Test: Weakly/ Modified acid-fast

Nocardia: Pulmonary abscess, CNS abscess and cutaneous nocardiosis
(Lung and brain abscess > think Nocardia)

Rhodococcus: Pneumonia, lymphadenopathy, wound infections
(Zoonotic)

27
Q

List anaerobic gram positive rods and related infections

A

Spore-forming; Clostridium spp.

  • C. perfringens: gas gangrene, food poisoning, biliary sepsis
  • C. tetani: tetanus
  • C. botulinum: Botulism
  • C. difficile: Pseudomembranous colitis, Antibiotics associated diarrhea

Non-spore forming: Actinomyces

  • GI and genital tract colonizer
  • Pelvic (IUCD use), abdominal, cervicofacial actinomycosis
  • Infection across tissue planes, invasive
28
Q

Outline classification scheme for Gram negative bacteria

A

Gram negative rods
- Anaerobes: oral flora - Fusobacterium; Gut flora - bacteroides
- Aerobes/ facultative anaerobes: Enterobacteriaceae, Vibrionaceae, Non-fermenters
- Other Aerobes: e.g. H.influenzae, Legionella pneumophilia, Campylobacter, H. pylori, HACEK group, brucella

Gram negative cocci
- Neisseria
- Moraxella catarrhalis

29
Q

Enterobacterales

List examples under this group

A

Think inflammatory gastroenteritis:
E. coli
Klebsiella
Proteus
Enterobacter
Citrobacter
Morganella
Serratia
Salmonella
Shigella
Yersinia
~~~

30
Q

Enterobacterales

Types of infections

A

UTI
Inflammatory Diarrhoea syndromes: E.coli, Non-typhoidal salmonella, shigella
Specific syndromes: Bacillary dysentry (Shigella), Typhoid fever (Salmonella typhi/ paratyphi)

31
Q

Enterobacterales

Antibiotics resistant subtypes

A

ESBL-producers = resistant to B-lactams except carbapenems, so use carbepenems!

CPE (Carbapenemase-producing Enterobacteriaceae) = Resistant to carbapenems

32
Q

Vibrionaceae

Examples and related infections
Biochemical tests

A

Vibrio:

  • V. cholerae: Cholera epidemics (O1, O139); Watery diarrhea (Non-O1, Non-O139)
  • V. vulnificus: Necrotizing fasciitis
  • V. parahaemolyticus: Food poisoning

Aeromonas
Plesiomonas

Tests: Glucose fermenters, oxidase positive

33
Q

List non-fermenters and related infections

A

Most are environmental

- Pseudomonas aeruginosa
- Acinetobacter baumannii
- Stenotrophomonas maltophilia
- Burkholderia cepacia complex

Nosocomial infections: pneumonia, wound infections, prosthesis-related

Chronic infection e.g. P. aeruginosa, Burkholderia spp. in cystic fibrosis pt.

Burkholderia pseudomallei = cause of severe community-acquired pneumonia and bacteremia

34
Q

Anaerobic gram negative rods

Source of bacteria
Type of infection
2 examples

A

Normal flora in oral cavity and GIT
Causes polymicrobial infections and abscess

  • Fusobacterium spp.: Lemierre’s disease (IJV thrombophlebitis; - high fever with acute neck pain), Brain abscess
  • Bacteroides fragilis: GI colonizer, complicated intra-abdominal infections
35
Q

Gram negative cocci

Examples and related infections

A
36
Q

List bacteria that are unculturable/ unstainable by gram smear

A
  1. Spirochaetes:
    - Treponema pallidum (Syphilis)
    - Borrelia recurrentis (recurring fever)
    - Borrelia burgdorferi (Lyme disease)
    - Leptospira (Leptospirosis)
  2. Mycoplasma and Ureaplasma
  3. Chlamydia and Chlamydophilia (STD)
  4. Coxiella burnetii (Q fever)
  5. Bartonella quintana (Trench fever) and B. henselae (Cat-scratch disease)
  6. Rickettsia spp. and Orientia tsutsugamushi: Typhus, spotted mountain fever
37
Q

Fungi

Classification and examples

A

Yeast - unicellular

  • Candida
  • Cryptococcus
  • Trichophyton
  • Malassezia

Mould - Pro-mycelial

  • Dermatophytes
  • Aspergillus
  • Zygomycetes
  • Fusarium

Dimorphic fungi

Pneumocystis jiroveci

38
Q

Candida spp

Type of infection
Examples according to sensitivity to Azoles

A

Mucosal candidiasis, Thrush, systemic infection in immunocompromised and ICU pt.

Azole sensitive:

  • C. albicans
  • C. parapsilosis

Azole resistant:

  • C. krusei
  • C. glabrata
  • C. auris
39
Q

Types of infection caused by crytococcus, trichosporon, malassezia

A

All yeasts cause opportunistic infections in immunocompromised

Cryptococcus: opportunistic meningitis, opportunistic pneumonia, systemic infections in immunocompromised

Trichosporon spp: piedra, systemic infection in immunocompromised

Malassezia: pityriasis versicolor, systemic infection

40
Q

Moulds

List examples and types of infection

A

Dermatophytes: Tinea pedis, Tinea cruris, Tinea corporis, Onychomycosis

  • Trichophyton spp.
  • Microsporum spp.
  • Epidermophyton floccosum

Severe systemic infections in immunocompromised:
Aspergillus:
- A. fumigatus
- A. falvus
- A. niger
Zygomycetes: Rhizopus spp. Mucor
Fusarium: F. solani, F. oxysporum

41
Q

Examples of dimorphic fungi

A

Sporothrix schenckii

Blastomyces dermatitidis

Histoplasma capsulatum

Penicillium marneffei

42
Q

Examples of fungal disease according to skin layers

A

Superficial mycoses: Tinea, Onychomycosis (thrush), Cutaneous candidiasis, Pityriasis verisolor

Subcutaneous mycoses: mycetoma (gardener)

Deep mycoses

43
Q

3 classes of parasites and examples

A
44
Q

List viruses with high propensity to cause lower respiratory tract illness

A

Decreasing propensity to cause LRTI

Rhinovirus/ Enterovirus
Coronavirus
Parainfluenza (CROUP or bronchoiolitis)

45
Q

List viruses that cause URTI

A 
Bocavirus 
Adenovirus 
Influenza A,B (URTI or bronchiolitis)
Enterovirus D68
Rhinovirus
46
Q

Viruses that cause hepatitis

A

Hepatitis A virus, HBV, HCV, HDV, HEV

cytomegalovirus (immunocompromised), primary EBV (also causes infectious mononucleosis),
primary HHV-6 (human herpesvirus), adenovirus,
enterovirus

47
Q

Viruses that cause gastroenteritis

A

Rotavirus (children, vaccine-preventable), Norovirus (any age group), Sapovirus, Adenovirus, Astrovirus

Others:
Hepatitis A virus, CMV, Coronavirus, HIV, Influenza, Torovirus, Aichi virus, Picobirnavirus, Bocavirus

48
Q

Viruses that cause meningoencephalitis/ encephalopathy

A

Herpes simplex virus (HSV) and Other herpesviruses: Primary EBV, Primary CMV, Primary HHV-6

Varicella zoster virus (VZV)

Exanthematous disease viruses: Measles (but mainly cough, rash), rubella, parvovirus B19

Japanese encephalitis (JE), Animal contact: Rabies, Herpes B, LCMV, Hendra, Nipah

Enterovirus

Influenza-associated encephalopathy: Influenza, adenoviruses

49
Q

First-line investigation for viral meningoencephalitis

A 
 Brain scans (CT/MRI)
 Lumbar puncture
 PCR for specific viral pathogens
 Antibodies against specific viral pathogens
 Electroencephalogram
50
Q

Viruses that cause myocarditis

A 
 Adenovirus
 Enterovirus
 HSV/ VZV
 Cytomegalovirus
 Influenza
51
Q

4 viral rashes

A

Chickenpox:
 Varicella zoster virus: reactivation as herpes zoester/ shingles

Measles

Rubella

Enterovirus

Parvovirus B19: ‘slapped cheek rash’, ‘fifth disease’

HHV-6: Roseola infantum

52
Q

Arboviruses

Examples and related infections

A

 Japanese encephalitis (JE): meningoencephalitis

 Dengue (登革熱): hemorrhagic fever if severe

 Zika (Zika infection during pregnancy - microcephaly)

 West Nile virus: meningoencephalitis

 Yellow Fever virus

53
Q

Major cancers associated with viral infections

A

Nasopharyngeal carcinoma, lymphoma: Epstein-Barr virus (EBV)

Hepatocellular carcinoma: Hepatitis B virus (HBV), HCV

Cervical cancer, anal cancer, oropharyngeal cancer: 
Human papillomavirus (HPV), high-risk genotypes (16, 18)
54
Q

Transmissible spongiform encephalopathies

Pathogenesis
Causative pathogen
Types

A

proteinaceous infectious particle (no DNA or RNA):
 Autocatalytic conversion of normal prion protein to abnormally folded prion protein: Chain reaction: PrPC&raquo_space; PrPSc
 Accumulation of abnormal prion protein causes spongiform changes and vacuolation in the
brain (looks like cheese)&raquo_space; fatal, no effective treatment

Types of TSE:
- Sporadic CJD (sCJD)
- Variant CJD (vCJD):Transmission of BSE (bovine spongiform encephalopathy) agent from cows to
humans (consumption of beef)
- Iatrogenic CJD (iCJD): prion exposure due to surgical procedures and blood transfusion
(vCJD)
- Genetic CJD (gCJD)

MBBS VI - SpC - Medicine (80 decks)

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