Neisseria, Spirochetes, and intracellular pathogens Flashcards
What are the morphologic and physiologic properties of Neisseria?
- Gram-negative bacteria, typically coccoid and found as diplococci
- Aerobic
- Are all oxidase positive and most produce catalase
- N. gonnorrhoeae is fastidious and only growns on chocolate agar and other supplemented media
Which Neisseria species can colonize the nasopharynx without producing disease?
N. meningitidis
What are the diseases produced by Neisseria gonorrhoeae?
- Gonorrhea
- Gonococcemia (disseminated infections)
- Ophthalmia neonatorum
What are the features of gonorrhea?
- Purulent discharge from the involved area (e.g. urethra, cervix, epidiymis, prostate, rectum) after 2- to 5-days of incubation
- Dysuria
- Virtually all men will have symptoms
- As many of half of all infected women have mild or no symptoms
What are the features of gonococcemia?
Disseminated infection with septicemia and infections of the skin and joints
What is the pathogenesis of gonorrhea?
- Pilins are used to attach to nonciliated human cells
- Opa (opacity) protein also mediates firm attachment
- Por (porin) protein: promotes intracellular survival by preventing phagosome–lysosome fusion
- The neutrophilic response causes the purulent discharge
- Transferrin-, lactoferrin-, and hemoglobin-binding proteins mediate acquisition of iron for the bacteria
- IgA1 protease destroys IgA in the mucosa
What are the diseases caused by Neisseria meningitidis?
- Meningitis
- Meningococcemia (septicemia)
What are the features of Neisseria meningitidis-caused meningitis?
- Begins abruptly with headache, meningeal signs, and fever
- Very young children may have only nonspecific signs, such as fever and vomiting
- Mortality is near 100% in untreated patients
What is the pathogenesis of meningitis caused by Neisseria meningitidis?
- Meningococci attach to mucosal cells, penetrate into them, and multiply
- They then pass through the cells into the subepithelial space where infection is established
- Antigenic differences in the polysaccharide capsule of N. meningitidis determines if the strain will cause disease
What is the epidemiology of Neisseria meningitidis?
- Meningococcal disease occurs in patients who lack specific antibodies directed against the capsule and other antigens
- Disease is greatest in children under 2 years (at which point maternal immunity is disappearing), patients with deficiencies in complement C5–8, and patients post splenectomy
What are the clinically significant spirochetes?
- Treponema pallidum
- Borrelia burgdorferi
What are the morphologic and physiologic properties of Treponema pallidum?
- Thin, helical, Gram-negative bacteria
- Too thin to be seen with brightfield microscopy—fluorescent microscopy is used instead
- Highly fastidious and extremely sensitive to oxygen (microaerophilic or anaerobic)
What is the epidemiology of syphilis?
- A common and increasing STD
- Patients are at increased risk for acquiring and transmitting HIV when genital lesions are present
- Syphilis cannot be spread through fomites, as the bacteria are very fragile
- The most common route of transmission is sexual, although congenital and blood transfusion routes also exist
What are the features and course of syphilis infection?
- Primary phase: skin lesions (painless chancres) at the site where the spirochete penetrated
- Secondary phase: disseminated disease, involving skin lesions all over the body, fever, and headache
- Late phase: severe damage to organs involved, e.g. neurosyphilis, cardiovascular syphilis, leading to various symptoms (e.g. dementia, blindness)
What are the morphologic and physiologic properties of Borrelia burgdorferi?
- Spirochete in shape, Gram-negative
- Stain well with dyes such as Giemsa but poorly with Gram stain
- Culture is generally unsuccessful, so diagnosis is via serology of microscopy
How is lyme disease transmitted?
Hard ticks transfer borreliae present in saliva or feces via bites
What are the features of lyme disease?
- Erythema migrans (two concentric areas of redness)
- Severe fatigue, headache, fever, malaise due to hematogenous dissemination
- Approximately 60% of patients develop arthritis
What are the most common symptoms of tick-related illnesses?
- Fever/chills
- Aches and pains
- Rash
What are the morphologic features of Rickettsia?
- Obligate intracellular, grow only in the cytoplasm
- Gram-negative rods
- Aerobic
- Stain best with Giemsa
What is the pathogenesis of Rickettsia infections?
- The rickettsiae bind to the cell and are internalized by induced phagocytosis
- The rickettsiae escape from the phagosome and replicate in the cytosol
- The rickettsiae lyse the cell and infect other cells, especially by attracting immune cells
What are the disease caused by Rickettsia rickettsii?
- Rocky Mountain spotted fever
- Typhus (not typhoid fever)
How is Rickettsia rickettsii transmitted?
Hard ticks transfer borreliae present in saliva or feces via bites
What are the features of Rocky Mountain spotted fever?
- Abrupt onset
- Fever, headache, malaise, myalgias, nausea, vomiting, abdominal pains
- Macular (spotted) rash
What is the causative agent of epidemic typhus?
Rickettsia prowazekii
What are the features of epidemic typhus?
- Abrupt onset
- Fever, headache, chills, myalgias, photophobia
- Macular (spotted) rash
What are the morphologic features of Bartonella?
- Gram-negative coccobacillary or bacillary rods
- Fastidious growth requirements
- Very slow growth
- Facultative intracellular
How are Bartonella transmitted?
- By vectors, e.g. ticks, fleas, flies, and mosquitoes
- B. henselae is transmitted by exposure to infected cats
What are the features of cat-scratch disease?
- Non-painful bump or blister at the site of injury
- Swollen lymph nodes
What are the morphologic and physiologic properties of Chlamydia?
- Obligate intracellular parasites with dependence on host ATP
- Possess inner and outer membranes similar to Gram-negative bacteria
- Form emtabolically inactive but infectious forms (elementary bodies, EBs) or metabolically active but noninfectious forms (reticulate bodies, RBs)
What is the tropism of Chlamydia?
Epithelial cells of the mucous membranes of the:
- urethra,
- endocervix,
- endometrium,
- fallopian tubes,
- anorectum,
- respiratory tract, and
- conjunctivae
What is the pathogenesis of Chlamydia infections?
Damage is caused by intracellular replication and destruction of infected cells upon release
What is the most common bacterial STD in humans?
Chlamydia
How is Chlamydia trachomatis diagnosed?
- Cytologic, serologic, or culture findings
- Detection of antigen in specimens
- Nucleic acid–based tests
What are the features of chlamydia?
- Trachoma: chronic granulomatous inflammation of the eye surface leading to corneal ulceration, scarring, pannus formation, and blindness
- Urogenital infections: mucopurulent discharge with asymptomatic infection in women
- Cervicitis in women and urethritis and proctitis (inflammation of anorectal region) in men and women
How is Chlamydia trachomatis transmitted?
- Eye-to-eye transmission by droplets, hands, fomites, flies
- Sexual transmission
