AIDS Defining Bacterial/Fungal Infections

Question 1

What is Mycoplasma pneumonia?

Answer 1

• Mycoplasma species are the smallest free living organisms (150-250 nm)
• Pleomorphic organism
  
  • Lacks cell wall
  • Does not need host cell for replication
• Prokaryotes: lack a cell wall, lack of a reaction to gram stain and lack of susceptibility to many antimicrobial agents
• Usually associated with mucosal surfaces, residing extracellularly in the respiratory and urogenital tracts
• Mycoplasma pneumoniae, hominis, genitalium, and Ureaplasma species

Question 2

What is the epidemiology of Mycoplasma pneumonia?

Answer 2

• M pneumoniae is transmitted from person to person by infected respiratory droplets during close contact
• The incubation period after exposure averages three weeks
• Infection occurs most frequently during the fall and winter but may always develop

Question 3

What is the pathogenesis of Mycoplasma pneumonia?

Answer 3

• M pneumoniae is a superantigen
  
  • Superantigen: antigen that provokes a massive T cell response by non specifically activating T cells with receptors carrying a particular variable region
  • Activates macrophages and stimulates cytokine production and lymphocyte activation
  • Can attract inflammatory cells and induce cytokine secretion
• Host factors contribute to pathogenesis

Question 4

What is Streptococcus pneumonia?

Answer 4

• S pneumoniae is of the Streptococcaceae family
• Gram positive
• Oval/lancet shaped cocci are often arranged in pairs, known as diplococcus (can be present in short chains)
• There are around 90 serotypes and its surface capsule (distinguishing trait of pneumococcus and is the major virulent factor)
• Culture grows on blood agar, where it forms round facultative anaerobic colonies surrounded by alpha hemolysis

Question 5

What is the epidemiology of S pneumonia?

Answer 5

• Host range: humans, mice, rats, guinea pigs, chimpanzees, rhesus monkeys, and mammals that live in association with humans
• Mode of transmission: Infectious cells can be disseminated via microaerosol droplets created by coughing or sneezing or oral contact (nasopharyngeal region)
• Incubation period: Not well determined as they are in the nasopharynx of healthy individuals, but it has been speculated about 1-3 days
• Communicability: Transmitted between humans by aerosol pathways via coughing or sneezing

Question 6

What is Treponema palladium?

Answer 6

• Also known as syphilis
• A very frail organism that cannot thrive outside the body and is crippled by simple physical and chemical elements such as heat, soap, and water

Treponemes: not yet cultured in vitro
• Treponemes are helically coiled, corkscrew shaped cells (6-15 micrometers longs and 0.1 to 0.2 micrometers wide- a spirochete)
• They have an outer membrane which surrounds the periplasmic flagella, a peptidoglycan cytoplasmic membrane complex, and a protoplasmic cylinder

Question 7

How do T palladium multiply?

Answer 7

Binary Transverse Fission

Question 8

Pathogenesis of T palladium

Answer 8

• Treponemes are highly invasive pathogens which often disseminate relatively soon after inoculation
• Evasion of host immune responses appears to be due to the unique structure of the treponemal outer membrane (low content of surface exposed proteins)
• Although treponemes lack classical lipopolysaccharides, they possess abundant lipoproteins which induce inflammatory processes

Question 9

Epidemiology of T palladium

Answer 9

• Primary Syphilis: Individual sores in adults around genitals
• Secondary Syphilis: General rash all over the body
• Latent Syphilis: The disease shows no symptoms by the organism continues to reproduce
• Tertiary Syphilis: major destruction to the skeletal system and nervous system (bones, heart, brain, NS)
• Congenital Syphilis: Disease spread through infection of the mother to the child through the blood supply to the womb

Question 10

What is Candida albicans?

Answer 10

• An opportunistic fungal pathogen that is responsible for candidiasis in human hosts
• Typically C albicans live as harmless commensals in the GI and genitourinary tract
• Overgrowth of these organisms leads to disease which usually occurs in the immunocompromised individuals, such as HIV infected victims, transplant recipients chemotherapy patients, and low birth-weighted babies

Question 11

What are the 3 major forms of C albicans disease?

Answer 11

• Oropharyngeal candidiasis: thrush
• Vulvovaginal candidiasis: yeast infection
• Invasive candidiasis: serious infection that can affect the blood, heart, brain, eyes, and bones
• Candidemia: bloodstream infection with candida is a common infection in hospitalized patients

Question 12

What is the epidemiology of C albicans?

Answer 12

• C albicans infections remain as the top source of fungal infections in immunocompromised people
• 90%+ of HIV patients
• Candidemia is the fourth most common bloodstream infection in the USA

Question 13

How is C albicans transmitted?

Answer 13

• Candida albicans is usually transmitted from mother to infant through childbirth and remains as part of a normal human’s microflora
• Overgrowth of this bacteria leads to symptoms of disease and it occurs when there are imbalances (Acidity of vagina)
• C albicans infections very rarely spread through sexual intercourse
• Typical reservoir is the normal human microflora and is not found in animal vectors