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Microbiology and immunology > Non–spore-forming Gram-positive bacteria > Flashcards

Non–spore-forming Gram-positive bacteria Flashcards

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1
Q

What are the non–spore-forming Gram-positive bacteria of clinical interest?

A

Anaerobic

  • Actinomyces
  • Lactobacillus
  • Cutibacterium (Proprionibacterium)
  • Mobiluncus
  • Bifidobacterium
  • Eubacterium
  • Poststreptococcus

Aerobic

  • Listeria
  • Nocardia
  • Corynebacterium
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2
Q

Which of the non–spore-forming Gram-positive bacteria are anaerobic?

A
  • Actinomyces
  • Lactobacillus
  • Cutibacterium (Proprionibacterium)
  • Mobiluncus
  • Bifidobacterium
  • Eubacterium
  • Poststreptococcus
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3
Q

Which of the non–spore-forming Gram-positive bacteria are aerobic?

A
  • Listeria
  • Nocardia
  • Corynebacterium
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4
Q

What are the features of Actinomyces?

A
  • Facultative anaerobic or obligate anaerobic
  • Gram-positive
  • Grow slowly in culture (up to 2 weeks) and produce delicate filamentous forms or hyphae that resemble fungi
  • Colonize the upper respiratory tract, upper GI tract, and female genital tract
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5
Q

How are Actinomyces transmitted?

A

Traumatic implantation or exposure to tissue during surgery

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6
Q

What disease is caused by Actinomyces?

A

Actinomycosis

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7
Q

What are the features of actinomycosis?

A
  • Development of chronic garnulomatous lesions that become suppurative and form abscesses connected by sinus tracts
  • The areas of suppuration are surrounded by fibrotic granulation tissue, giving the overlying surface a hard or woody consistency
  • Infections are typically cervicofacial, developing in patients with poor oral hygiene or who have undergone an invasive dental procedure
  • Infection can also happen thoracically or abdominopelvically (from abdominal surgery, tuboovarian abscesses, a ruptured appendix, or contaminated IUD)
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8
Q

How is actinomycosis treated?

A
  • Surgical debridement of the involved tissues
  • Prolonged administration of antibiotics
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9
Q

How is actinomycosis diagnosed?

A

Culture. This is difficult as there is often contamination with Actinomyces that are part of the normal bacterial population on mucosal surfaces

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10
Q

What are the features of Nocardia?

A
  • Obligate aerobic rods
  • Form branched filaments in tissues and culture, resembling fungi
  • Have a Gram-positive cell wall but stain poorly with the Gram stain; they are weakly acid-fast
  • Slow growth taking 3–5 days
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11
Q

How are Nocardia transmitted?

A
  • Exogenous infection from soil
  • Not normally part of the human microbiota
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12
Q

What is the pathogenesis of infections with Nocardia?

A
  • Pathogenic strains avoid phagocytic killing by secreting catalase and superoxide dismutase
  • Nocardiae are able to survive and replicate in macrophages by preventing phagosome–lysosome fusion (mediated by cord factor) and preventing acidification of the phagosome
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13
Q

What are the diseases caused by Nocardia?

A
  • Bronchopulmonary disease
  • Cutaneous infections, e.g. mycetoma
  • Disseminated brain infection causing brain abscesses
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14
Q

What are the features of bronchopulmonary disease due to Nocardia?

A
  • Slow development, usually in immunocompromised patients
  • Cough, dyspnea, and fever are usually present
  • Cavitation and spread to the pleura are common
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15
Q

What are the features of cutaneous infections with Nocardia?

A
  • May be primary infections (mycetoma, lymphocutaneous infections, cellulitis, subcutaneous abscesses) or secondary infections arising from a primary pulmonary infection
  • Mycetoma is a painless, chronic infection of the feet, characterized by localized subcutaneous swelling with inolvement of the underlying tissues, muscle, and bone; suppuration; and formation of sinus tracts
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16
Q

What are the features of lactobacilli?

A
  • Facultative anaerobic or obligate anaerobic
  • Found as part of the normal flora of the mouth, stomach, intestines, and genitourinary tract
17
Q

Why do lactobacilli rarely caused urinary tract infections?

A

Lactobacilli cannot grow in urine

18
Q

In which settings can lactobacilli colonize the blood?

A
  • Transient bacteremia from a genitourinary source (e.g. after childbirth or a gynecologic procedure)
  • Endocarditis
  • Opportunistic septicemia in immunocompromised patients
19
Q

What are the features of Cutibacterium (Proprionibacterium)

A
  • Small Gram-positive rods often arranged in short chains or clumps
  • Commonly found on the skin, conjunctiva, and external ear, and in the oropharynx and female genital tract
20
Q

What disease does Cutibacterium acnes (Proprionibacterium acnes) cause?

A

Acne (in susceptible individuals)

21
Q

What is the pathogenesis of acne caused by Cutibacterium acnes (Proprionibacterium acnes)?

A
  • Production of a low-molecular-weight peptide by the bacteria residing in sebaceous fillicles attracts leukocytes
  • The bacteria are phagocytosed and, after release of bacterial hydrolytic enzymes (lipases, proteases, neuraminidase, and hyaluronidase), stimulate a localized inflammatory response
  • The acne is treated through topical application of benozyl peroxide and antibiotics
22
Q

What diseases do Mobiluncus spp. cause?

A

Bacterial vaginosis (vaginitis)—M. curtisii

23
Q

What are the features of Mobiluncus?

A
  • Obligate anaerobic
  • Gram-variable or Gram-negative curved rods with tapered ends
24
Q

Mobiluncus stain poorly with the Gram stain, yet they are considered Gram-positive. Why is this?

A
  • They have a Gram-positive cell wall
  • They lack endotoxin (LPS)
  • They are susceptible to vancomycin, clindamycin, erythromycin, and ampicillin but resistant to colistin
25
Q

What are the clinical features of poststreptococci?

A
  • They colonize the oral cavity, GI tract, genitourinary tract, and skin
  • They produce infections when they move from these sites to normally sterile sites, e.g. causing sinusitis and pleuropulmonary infections in the upper airways
26
Q

What are the features of Listeria monocytogenes?

A
  • Short, non-branching, Gram-positive facultative anaerobic rod
  • Capable of growing at broad temperature ranges and in a high concentration of salt
  • The rods appear singly, in pairs, or in short chains and can thus be mistaken for Streptococcus pneumoniae
  • The organisms are motile at room temperature, but less so at 37ºC
  • Exhibits weak β-hemolysis
27
Q

What is the epidemiology of Listeria monocytogenes?

A
  • Human disease is uncommon and restricted to neonates, the elderly, pregnant women, and patients with defective cellular immunity
  • The primary source of infection is contaminated food, but vertical transmission is possible
28
Q

What is the pathogenesis of Listeria monocytogenes?

A
  • L. monocytogenes is a facultative intracellular pathogen
  • After ingestion into the GI tract, it survives proteolytic enzymes, stomach acid, and bile salts through stress-response genes
  • The bacteria adhere to host cells via the interaction of their cell-surface proteins (e.g. internalin A) with glycoprotein receptors on the host cells (e.g. E-cadherin)
  • After penetration into the cells, the acid pH of the phagolysosome activated a bacterial pore-forming cytolysin (listeriolysin O) and two different phospholipase C enzymes, leading to release into the cytosol
  • The bacteria proceed to replicate and then move to the cell membrane. This movement is mediated by the protein ActA, which coordinates assembly of actin
  • Cellular immunity is most important for this pathogen as it spends most of its time within the cell
29
Q

What diseases does Listeria monocytogenes cause?

A
  • Neonatal disease
  • Disease in pregnant women in the third trimester, when cellular immunity is most impaired
  • Mild influenza-like illness in healthy adults
30
Q

What are the features of neonatal Listeria monocytogenes disease?

A
  • Early-onset disease is acquired transplacentally and can result in abortion, stillbirth, or prematurity
  • Late-onset disease is acquired at or soon after birth and manifests as meningitis or meningoencephalitis with septicemia
31
Q

What are the features of Corynebacterium diphtheriae?

A
  • Possesses medium- and long-chain mycolic acids, but is not acid-fast
  • Aerobic or facultatively anaerobic
  • Nonmotile and catalase positive
  • Ubiquitous in plants and animals, and they normally colonize the skin, upper respiratory tract, GI tract, and genitourinary tract in humans
32
Q

What is the epidemiology of Corynebacterium diphtheriae?

A
  • Transmission occurs through respiratory droplets or skin contact
  • Humans are the only known reservoir
33
Q

What is the pathogenesis of diphtheria?

A
  • The diphtheria toxin is an A-B exotoxin
  • There are three functional regions: a catalytic region on the A subunit, a receptor-binding region on the B subunit, and a translocation region on the B subunit
  • The toxin binds to the heparin-binding epidermal growth factor receptor, which is present mostly on heart and nerve cells
  • After the toxin attaches to the host cell, the translocation region is inserted into the endosomal membrane, facilitating the movement of the catalytic region into the cell cytosol
  • The A subunit then terminates host cell protein synthesis by inactivating elongation factor-2, which is a factor required for the movement of nascent peptide chains on ribosomes
34
Q

What are the features of respiratory diphtheria?

A
  • The onset is sudden, with malaise, sore throat, exudative pharyngitis, and low-grade fever
  • The exudate evolves into a thick pseudomembrane compsoed of bacteria, lymphocytes, plasma cells, fibrin, and dead cells
  • The exudate covers the tonsils, uvula, and palate and can extend up into the nasopharynx or down into the larynx
  • Diphtheria has become uncommon due to vaccination—there have been no new cases in the US since 2003

Microbiology and immunology (33 decks)

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