17 - Direct Contact Bacterial Diseases Flashcards
Direct contact transmission
Physical interaction with the infectious source
Indirect contact transmission
Pathogen is transferred between hosts via intermediary (e.g. doorknob, food, dust)
Types of direct contact
- Horizontal contact (touching - handshaking, kissing)
- Vertical contact (mother to child)
- Droplet (cough, sneeze)
- Vector (mosquitoes, flies)
Direct contact skin diseases
- Gas gangrene
- Group B streptococcal disease
- Staphylococcal infections
- Mycobacterial skin infections (e.g. leprosy)
- Cutaneous anthrax
Direct contact mucous membrane examples
- STIs (Gonorrhoea, chlamydia, syphilis)
- Peptic ulcer disease
- Trachoma (chlamydial eye infection)
Clostridial infections
- Gram +ve endospore forming anaerobic bacillus
- Most are saprophytes in soil, water, decomposing plant and animal matter
- Few opportunistic pathogens (Gas gangrene, Tetanus, Botulism)
Gas gangrene
- 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)
Gas gangrene transmission
Direct contact with soil (infectious source)
Tetanus
- Clostridium tetani
- Common in soil, dust, horse manure
- Enters bloodstream via skin wound
- Disease is toxin mediated (causes tetanospasm)
- Vaccine preventable
Transmission of Tetanus
Direct contact with soil/dust/manure
Tetanospasm
- Toxin prevents release of inhibitory neurotransmitters (Muscles cannot relax)
- Lockjaw and muscles spasms
Staphylococcus aureus infection
- 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
Staphylococcus aureus pathogenesis
- 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)
Staphylococcus aureus virulence factors
- Coagulase positive
- Many strains are strongly toxigenic
- Some toxins are superantigens (stimulate large immune response)
Examples of S. aureus superantigens
- Enterotoxins (heat stable: types A,B,C,D,E,G)
- Toxic shock syndrome toxin (TSST-1)
Group B Streptococcal (GBS) disease
- Streptococcus agalactiae
- Gram positive cocci
- Cause a range of different diseases
- Leading cause of sepsis and meningitis in newborns
Early onset GBS disease in newborns
- Infant acquires GBS from mother during delivery (vertical transmission)
- Severe diseases include: septicemia, meningitis, pneumonia
Group A Streptococcal disease
- Streptococcus pyogenes
- Gram positive cocci
- Causes pharyngitis, scarlet fever, Necrotising fasciitis
- Multiple episodes of infection may lead to autoimmune complications
Streptococcus pyogenes pathogenesis
- Capsular polysaccharide
- Surface proteins: mainly adhesins (M protein, Fimbrial proteins)
S. pyogenes invasins (extracellular)
- Streptolysin S (oxygen stable)
- Streptolysin O (oxygen labile)
S. pyogenes exotoxins (extracellular)
- 3 pyrogenic exotoxins (A,B,C) which are superantigens
- Degrade host factors thus facilitating spread
Chlamydia
- Chlamydia trachomatis
- Gram negative-like, coccoid in shape
- Obligately intracellular: can’t synthesise their own ATP
- Infection may be asymptomatic
Chlamydia transmission
- By oral, vaginal or anal sex (horizontal)
- From mother to infant during birth (vertical)
Male chlamydia
Symptoms usually mild (urethritis)
Female chlamydia
- Pelvic inflammatory disease, and eye infections
- Chronic infection can lead to scarring and infertility
- Increased risk of cervical cancer (in association with HPV)
Gonorrhoea infection
- Caused by Neisseria gonorrhoea
- Gram negative diplococci
- High prevalence due to increasing resistance to antibiotics and asymptomatic carriers
Male gonorrhoea
Acute urethritis
Female gonorrhoea
More complicated, primary site of infection in the endocervix
Gonorrhoea transmission
- Transmitted sexually (horizontal)
- Transmitted vertically (acquired during birth)
- Other sites: rectal and oropharyngeal gonorrhoea
Neisseria gonorrhoea
- Fastidious Gram negative bacterium, obligate human pathogen
- Highly susceptible to extreme temps and drying)
Gonorrhoea virulence factors
Adhesion and invasion:
- Use pili to adhere to mucosal cells
- phagocytosed by mucosal cells
- survive intracellularly (avoid immune response)
Antibiotic resistant gonorrhoea
β-lactams (e.g. penicillin) and tetracyclines
Two types of β-lactam resistance
- Chromosomal genes encoding a modified penicillin binding protein (PBP)
- plasmid genes which code for β-lactamases
Syphilis
- Caused by spirochete Treponema pallidum
- Gram negative-like, microaerophilic
- Organism enters body through mucous membranes,
breaks in skin, abrasions (horizontal contact)
Three stages of syphilis
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
Syphilis transmission
- 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
