Medical Microbiology: Mycoplasma, Ureaplasma, Spirochetes, Chlamydia, and Rickettsiae

Flashcards covering Mycoplasma, Ureaplasma, Spirochetes (Leptospira, Borrelia, Treponema), Chlamydia, Rickettsia, and Ehrlichia based on the clinical microbiology lecture notes.

What are the smallest known self-replicating bacteria?

Mycoplasma (along with Ureaplasma).

Why were Mycoplasma species historically mistaken for viruses?

Because of their extremely small size and ability to pass through bacterial filters.

What cellular structure is permanently absent in all Mycoplasma and Ureaplasma species?

A cell wall.

What are the three most significant human pathogens among the mycoplasmas and ureaplasmas?

Mycoplasma pneumoniae, Mycoplasma hominis, and Ureaplasma urealyticum.

How can Mycoplasma and Ureaplasma be differentiated using a biochemical test?

Ureaplasma possesses urease activity ($+$), whereas Mycoplasma lacks urease activity ($-$).

Why are Mycoplasma and Ureaplasma naturally resistant to penicillin and other beta-lactam antibiotics?

They lack a peptidoglycan cell wall, which is the cellular target of beta-lactam antibiotics.

What two essential lipid components must be provided in media to cultivate Mycoplasma species?

Cholesterol and fatty acids.

What characteristic colony morphology is shown here, which is typical of some Mycoplasma species on solid agar?

A "fried egg" appearance.

What respiratory tract illnesses are primarily caused by Mycoplasma pneumoniae?

Bronchitis, pharyngitis, and primary atypical pneumonia ("walking pneumonia").

Approximately what percentage of reported pneumonias in the general population are caused by Mycoplasma pneumoniae?

$\sim 20\%$ of reported pneumonias.

What is the typical incubation period of a Mycoplasma pneumoniae infection?

$2\text{--}3\text{ weeks}$.

What four upper genitourinary tract complications can Mycoplasma hominis cause in females?

Salpingitis, pyelonephritis, pelvic inflammatory disease (PID), and postpartum fevers.

What clinical condition in males is associated with Ureaplasma urealyticum?

Nongonococcal urethritis (NGU).

Name three specialized transport media recommended for clinical specimens suspected of containing Mycoplasma.

SP4, Shepard 10B broth, and 2SP.

At what temperature must clinical specimens for Mycoplasma testing be frozen if plating cannot occur within $24\text{ hours}$?

$-70^\circ\text{C}$.

What testing method serves as the gold standard for the laboratory diagnosis of Mycoplasma pneumoniae?

Serological diagnosis.

What two families are contained within the bacterial order Spirochaetales?

Leptospiraceae and Spirochaetaceae.

Which two human pathogenic genera belong to the family Spirochaetaceae?

Borrelia and Treponema.

What are the specialized motility organelles called that lie wound inside the flexible cell wall of spirochetes?

Periplasmic flagella.

What distinctive structural feature is visible at the terminal ends of the spirochete pictured below?

Hooked ends ("hooks"), characteristic of Leptospira.

What are the atmospheric/oxygen requirements of Leptospira species?

They are obligate aerobes.

Name three artificial culture media used to grow Leptospira in the laboratory.

Fletcher semisolid medium, Stuart-liquid medium, and EMJH semisolid medium.

How do leptospires shed into water or mud enter the human body?

Through small breaks in the skin or through intact mucous membranes.

What severe clinical complications characterize the second phase of leptospirosis, also known as Weil disease?

Kidney failure, liver failure, and meningitis.

What animal groups act as the primary reservoirs for Leptospira organisms?

Dogs, rats, and other rodents.

Which US state accounts for approximately $50\%$ of all leptospirosis cases reported annually in the nation?

Hawaii.

During which phase of leptospirosis should blood or CSF be collected, and when is urine the preferred clinical specimen?

Blood or CSF should be collected during the first week after exposure (acute phase); urine yields higher numbers of organisms later in the illness.

How do Borrelia coils and microscopy requirements compare to those of Leptospira?

Borrelia spirals are much less tightly coiled than leptospires and can be easily visualized using standard bright-field microscopy.

What is the name and appearance of the Stage 1 skin lesion pictured below in Lyme disease?

Erythema migrans, exhibiting a classic expanding "target" or bullseye appearance.

What is the most common clinical manifestation observed in Stage 3 (late stage) of Lyme disease?

Arthritis.

What biological vector is responsible for transmitting Borrelia burgdorferi to humans?

Ixodes ticks.

During what seasonal window do the majority of Lyme disease cases occur in the United States?

June through September.

Describe the two-tiered testing protocol used for the laboratory diagnosis of Borrelia burgdorferi infection.

Tier-one is an IFA or EIA screening test; if positive, Tier-two is performed via confirmation with IgM and/or IgG Western Blot.

What microscopic technique is recommended for directly visualizing the delicate, regular coils of Treponema pallidum?

Dark-field microscopy.

Name the four pathogenic Treponema species/subspecies that cause human disease.

Treponema pallidum subsp. pallidum, Treponema pallidum subsp. pertenue, Treponema pallidum subsp. endemicum, and Treponema carateum.

What is the primary skin lesion of syphilis called, and what are its physical characteristics?

A chancre: a single, firm, non-tender erythematous lesion with a clean surface and raised border.

What stage of syphilis is indicated by the rash on the palm pictured below?

Secondary stage of syphilis.

How is early latent syphilis distinguished from late latent syphilis?

Early latent syphilis occurs within $1\text{ year}$ of initial infection; late latent syphilis is latency lasting longer than $1\text{ year}$.

What specific granulomatous lesions and organ pathologies are associated with tertiary syphilis?

Gummas in the skin, bones, and liver; degenerative CNS changes; and cardiovascular lesions.

What direct finding under dark-field microscopy from chancre exudate is diagnostic of primary syphilis?

The demonstration of motile treponemes.

What organism causes yaws, and in what global environments is it endemic?

Treponema pallidum subsp. pertenue; endemic in humid, tropical regions of Africa, South America, India, Indonesia, and Pacific islands.

What disease is caused by Treponema pallidum subsp. endemicum, and how is it primarily spread?

Endemic syphilis (bejel); spread by direct skin-to-skin contact or by sharing contaminated eating utensils.

What organism causes pinta, and what is the typical progression of its skin lesions?

Treponema carateum; lesions start as scaling, painless papules, progress to an erythematous rash, and eventually become hypopigmented.

What are the two morphological forms in the Chlamydiaceae developmental cycle, and which form is infectious?

Elementary bodies (EBs), which are infectious, and Reticulate bodies (RBs), which are noninfectious.

What is trachoma, and what organism is its causative agent?

A chronic keratoconjunctivitis that is the leading cause of preventable blindness worldwide; caused by Chlamydia trachomatis.

What sexually transmitted syndrome caused by Chlamydia trachomatis presents with genital lesions followed by suppurative inguinal buboes?

Lymphogranuloma Venereum (LGV).

What is the most frequently reported sexually transmitted bacterial pathogen in the United States?

Chlamydia trachomatis.

Approximately how many new cases of Chlamydia trachomatis infection are estimated by the CDC to occur each year in the US?

$2\text{--}3\text{ million}$ new cases annually.

What is the most common clinical infection seen in neonates who pass through a Chlamydia-infected birth canal?

Inclusion conjunctivitis.

What prophylactic medication is routinely administered into the eyes of all newborn infants in the US to prevent neonatal conjunctivitis?

Erythromycin ophthalmic ointment/drops.

Which laboratory diagnostic methodology is considered the gold standard for the detection of Chlamydia trachomatis?

Nucleic Acid Amplification Tests (NAATs).

Where inside eukaryotic host cells do Rickettsia species replicate?

Exclusively inside the host cell cytoplasm.

What three major clinical/taxonomic groups comprise the genus Rickettsia?

The typhus group, the spotted fever group, and the transitional group.

What organism causes Rocky Mountain spotted fever (RMSF), and what are its primary tick vectors in the United States?

Rickettsia rickettsii; transmitted by Dermacentor andersoni (wood tick) and Dermacentor variabilis (dog tick).

What host cells do Rickettsia rickettsii organisms target, and what histopathologic condition do they induce in internal organs?

Endothelial cells lining blood vessels; they induce widespread vasculitis.

Describe the characteristic anatomical progression of the rash in Rocky Mountain spotted fever.

Erythematous macular patches appear first on the ankles and wrists, spreading inward and characteristically involving the palms and soles.

What is the mortality rate of untreated Rocky Mountain spotted fever?

$20\%$.

What organism causes murine (endemic) typhus, and how is it transmitted to humans?

Rickettsia typhi; transmitted when the oriental rat flea (Xenopsylla cheopis) defecates on the skin while feeding, and feces are rubbed into the bite wound.

What is Brill-Zinsser disease, and what organism causes it?

A recrudescent, milder form of epidemic typhus caused by the reactivation of dormant Rickettsia prowazekii in human lymphoid tissue.

What organism causes rickettsialpox, and what are its vector and animal reservoir?

Rickettsia akari; transmitted by the mouse mite, with the common house mouse serving as the reservoir.

What characteristic skin lesion forms at the initial bite site in a patient with rickettsialpox?

An indurated black eschar (following progression from a papule to a pustule).

What tick vector is shown here, which is the primary vector for Ehrlichia chaffeensis?

The Lone star tick (Amblyomma americanum).

What are the intracytoplasmic bacterial inclusion bodies indicated by the arrow called in this infected white blood cell?

Morulae (characteristic of Ehrlichia infection).

What classic laboratory hematologic and hepatic findings are associated with Human Monocytic Ehrlichiosis (HME)?

Leukopenia, neutropenia, thrombocytopenia, and elevated liver enzymes.

In the Case in Point, what infection should be suspected in the athlete who developed fever, chills, myalgia, and diarrhea after capsizing his kayak and swallowing freshwater in Borneo?

Leptospirosis (caused by Leptospira).