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MICR2209 > 17 - Direct Contact Bacterial Diseases > Flashcards

17 - Direct Contact Bacterial Diseases Flashcards

1
Q

Direct contact transmission

A

Physical interaction with the infectious source

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2
Q

Indirect contact transmission

A

Pathogen is transferred between hosts via intermediary (e.g. doorknob, food, dust)

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3
Q

Types of direct contact

A
  1. Horizontal contact (touching - handshaking, kissing)
  2. Vertical contact (mother to child)
  3. Droplet (cough, sneeze)
  4. Vector (mosquitoes, flies)
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4
Q

Direct contact skin diseases

A
  • Gas gangrene
  • Group B streptococcal disease
  • Staphylococcal infections
  • Mycobacterial skin infections (e.g. leprosy)
  • Cutaneous anthrax
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5
Q

Direct contact mucous membrane examples

A
  • STIs (Gonorrhoea, chlamydia, syphilis)
  • Peptic ulcer disease
  • Trachoma (chlamydial eye infection)
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6
Q

Clostridial infections

A
  • Gram +ve endospore forming anaerobic bacillus
  • Most are saprophytes in soil, water, decomposing plant and animal matter
  • Few opportunistic pathogens (Gas gangrene, Tetanus, Botulism)
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7
Q

Gas gangrene

A
  • Commonly caused by Clostridium perfringens
  • Results from soil contamination of deep wound
  • Must be impairment of blood supply for infection (anaerobes)
  • Bacterial toxins allow spread to adjacent tissues and then finally myonecrosis occurs (tissue death)
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8
Q

Gas gangrene transmission

A

Direct contact with soil (infectious source)

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9
Q

Tetanus

A
  • Clostridium tetani
  • Common in soil, dust, horse manure
  • Enters bloodstream via skin wound
  • Disease is toxin mediated (causes tetanospasm)
  • Vaccine preventable
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10
Q

Transmission of Tetanus

A

Direct contact with soil/dust/manure

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11
Q

Tetanospasm

A
  • Toxin prevents release of inhibitory neurotransmitters (Muscles cannot relax)
  • Lockjaw and muscles spasms
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12
Q

Staphylococcus aureus infection

A
  • Gram positive cocci, facultative anaerobes
  • Infections range from superficial skin infections
    to life-threatening osteomyelitis (bones) and septicaemia (blood)
  • Commonly found in hospitals
  • Multiple antibiotic resistance a major problem worldwide
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13
Q

Staphylococcus aureus pathogenesis

A
  • More virulent strains cause infection in absence of breakdown, others cause infection when skin is broken
  • May be carried asymptomatically
  • Transmission in health care settings in via hands (direct)
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14
Q

Staphylococcus aureus virulence factors

A
  • Coagulase positive
  • Many strains are strongly toxigenic
  • Some toxins are superantigens (stimulate large immune response)
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15
Q

Examples of S. aureus superantigens

A
  • Enterotoxins (heat stable: types A,B,C,D,E,G)
  • Toxic shock syndrome toxin (TSST-1)
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16
Q

Group B Streptococcal (GBS) disease

A
  • Streptococcus agalactiae
  • Gram positive cocci
  • Cause a range of different diseases
  • Leading cause of sepsis and meningitis in newborns
17
Q

Early onset GBS disease in newborns

A
  • Infant acquires GBS from mother during delivery (vertical transmission)
  • Severe diseases include: septicemia, meningitis, pneumonia
18
Q

Group A Streptococcal disease

A
  • Streptococcus pyogenes
  • Gram positive cocci
  • Causes pharyngitis, scarlet fever, Necrotising fasciitis
  • Multiple episodes of infection may lead to autoimmune complications
19
Q

Streptococcus pyogenes pathogenesis

A
  • Capsular polysaccharide
  • Surface proteins: mainly adhesins (M protein, Fimbrial proteins)
20
Q

S. pyogenes invasins (extracellular)

A
  • Streptolysin S (oxygen stable)
  • Streptolysin O (oxygen labile)
21
Q

S. pyogenes exotoxins (extracellular)

A
  • 3 pyrogenic exotoxins (A,B,C) which are superantigens
  • Degrade host factors thus facilitating spread
22
Q

Chlamydia

A
  • Chlamydia trachomatis
  • Gram negative-like, coccoid in shape
  • Obligately intracellular: can’t synthesise their own ATP
  • Infection may be asymptomatic
23
Q

Chlamydia transmission

A
  • By oral, vaginal or anal sex (horizontal)
  • From mother to infant during birth (vertical)
24
Q

Male chlamydia

A

Symptoms usually mild (urethritis)

25
Q

Female chlamydia

A
  • Pelvic inflammatory disease, and eye infections
  • Chronic infection can lead to scarring and infertility
  • Increased risk of cervical cancer (in association with HPV)
26
Q

Gonorrhoea infection

A
  • Caused by Neisseria gonorrhoea
  • Gram negative diplococci
  • High prevalence due to increasing resistance to antibiotics and asymptomatic carriers
27
Q

Male gonorrhoea

A

Acute urethritis

28
Q

Female gonorrhoea

A

More complicated, primary site of infection in the endocervix

29
Q

Gonorrhoea transmission

A
  • Transmitted sexually (horizontal)
  • Transmitted vertically (acquired during birth)
  • Other sites: rectal and oropharyngeal gonorrhoea
30
Q

Neisseria gonorrhoea

A
  • Fastidious Gram negative bacterium, obligate human pathogen
  • Highly susceptible to extreme temps and drying)
31
Q

Gonorrhoea virulence factors

A

Adhesion and invasion:
- Use pili to adhere to mucosal cells
- phagocytosed by mucosal cells
- survive intracellularly (avoid immune response)

32
Q

Antibiotic resistant gonorrhoea

A

β-lactams (e.g. penicillin) and tetracyclines

33
Q

Two types of β-lactam resistance

A
  1. Chromosomal genes encoding a modified penicillin binding protein (PBP)
  2. plasmid genes which code for β-lactamases
34
Q

Syphilis

A
  • Caused by spirochete Treponema pallidum
  • Gram negative-like, microaerophilic
  • Organism enters body through mucous membranes,
    breaks in skin, abrasions (horizontal contact)
35
Q

Three stages of syphilis

A

Primary: ulcer forms at site of infection about 3 weeks after contact (replicates locally –> moves to regional lymph nodes)
Secondary: Skin rash then latent disease
Tertiary: Many years later, central nervous system involvement

36
Q

Syphilis transmission

A
  • Transmitted by sexual contact
  • May be acquired congenitally (vertical)
  • Organism can not be cultured in the
    laboratory (obligate intracellular pathogen)
  • Tertiary stage: organism destroyed bone and cartilage of nose

MICR2209 (26 decks)

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