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Flashcards in Micro 6: Examples of Bacteria Deck (119)
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61

What happens to the treatment regimen if you suspect meningitis in an elderly patient, an immunocompromised person, or neonates?

have to cover for Listeria with ampicillin

So you'll give vancomycin, ceftriaxone, and ampicillin

62

What are some characteristics of Strep. pneumo (aka pneumococcus)?

1. Gram positive lancet-shaped diplococcus
– Alpha-hemolytic
– Optochin (Taxo P) sensitive

• Respiratory route of transmission

63

What kinds of virulence factors does pneumococcus have?

– Capsule
– Secretory IgA protease
– Pneumolysin (helps lyse cells during infection)

64

How can infection via. Strep. pneumo be prevented?

vaccination with Prevnar (marketed to 60+ individuals and babies), a polyvalent capsular vaccine

65

Case 4
• A 33 y/o Hispanic male presents to his primary care provider with a 6-week history of low-grade fevers, night sweats, loss of appetite, unintended weight loss of 15 pounds, and cough productive of blood-streaked sputum. He moved to the U.S. from Mexico 5 years ago. He has no known medical problems.
• Family history: His father died 10 years ago of some type of pneumonia.
• Exam: vital signs normal. Patient appears mildly chronically ill. Lung exam reveals coarse sounds in right upper lobe.
• The patient is admitted to the hospital for further workup.
• Basic labs are unremarkable.
• Chest x ray shows a right upper lobe infiltrate and mediastinal lymphadenopathy.
• The doctor orders sputum Gram stain and culture as well as AFB (acid-fast bacillus) stain on the sputum.

• Gram stain is negative and routine culture is also negative at 48 hours. AFB smear is positive and a presumptive diagnosis of active pulmonary tuberculosis is made.
• The patient is immediately started on treatment consisting of 4 different drugs: Isoniazid, Rifampin, Pyrazinamide, and Ethambutol (PIRE).


• The pulmonologist decides to take the patient for bronchoscopy to get lung samples and also for a lymph node biopsy.
• Here is a picture of the biopsy specimen: This shows a caseating granuloma.

Case 4
• A 33 y/o Hispanic male presents to his primary care provider with a 6-week history of low-grade fevers, night sweats, loss of appetite, unintended weight loss of 15 pounds, and cough productive of blood-streaked sputum. He moved to the U.S. from Mexico 5 years ago. He has no known medical problems.
• Family history: His father died 10 years ago of some type of pneumonia.
• Exam: vital signs normal. Patient appears mildly chronically ill. Lung exam reveals coarse sounds in right upper lobe.
• The patient is admitted to the hospital for further workup.
• Basic labs are unremarkable.
• Chest x ray shows a right upper lobe infiltrate and mediastinal lymphadenopathy.
• The doctor orders sputum Gram stain and culture as well as AFB (acid-fast bacillus) stain on the sputum.

• Gram stain is negative and routine culture is also negative at 48 hours. AFB smear is positive and a presumptive diagnosis of active pulmonary tuberculosis is made.
• The patient is immediately started on treatment consisting of 4 different drugs: Isoniazid, Rifampin, Pyrazinamide, and Ethambutol.


• The pulmonologist decides to take the patient for bronchoscopy to get lung samples and also for a lymph node biopsy.
• Here is a picture of the biopsy specimen: This shows a caseating granuloma.

66

Why were the patient’s Gram stain and culture negative?

high mycolic acid content blocks the stain.

67

What is a granuloma?

macrophages (and other cells) containing the infection

68

Which part of the immune system is responsible for formation of a granuloma?

T-cell mediated

69

Do you think this could be a chronic infection? Latent?

yes it is both, he was probably infected in Mexico. This is an example of secondary TB

70

Antibiotic treatment of tuberculosis lasts for several (6-9) months. Why do you think that is, and why are 4 drugs needed to treat tuberculosis?

this prevents multi-drug resistance from arising and that granuloma is essentially walled-off and hard to get to easily

Also, an acid-fast culture takes up to 6 weeks to come positive for TB so it is a slow grower and there are metabolically-inactiving proteins in the granuloma so treatment takes a while

71

What is TB?

TB is a complex infection where initial infection is only apparent due to our immune response. The disease can progress, or more often, become latent for years before symptoms arise. Reactivation leads to a chronic pneumonia characterized by cough, fever, bloody sputum, night sweats, and weight loss.

A staggering number of TB cases occur each year, but most are confined to developing nations. AIDS patients have accounted for an increase in TB cases in industrialized nations.

• Individuals previously infected with TB (or who have received the BCG vaccine) will test positive in a tuberculin skin test. This is a DTH reaction that does not distinguish active vs latent infection. Newer interferon-based assays can do so.

• Because of the prolonged treatment regimen that is required, compliance is an issue and patients should be directly observed taking their medications ('direct-observed therapy is necessary).

72

What things are key to TB pathogenesis?

Key to TB pathogenesis is the formation of granulomas (tubercles), in which the latent bacteria reside.

73

Upon reactivation, where do sites of infection tend to be?

in well-oxygenated sites, such as the upper lobe of the lung (more oxygenated than the lower lobes)

74

What are some characteristics of Mycobacterium tuberculosis?

Acid-fast bacillus (single membrane like G+)
– Mycolic acid in cell wall
– MTB can inhibit phago-lysosome fusion,
survive in unactivated macrophages
• Transmission is respiratory route
– Infectivity is high

• AFB on sputum may reveal organism

• The bacillus Calmette-Guerin (BCG, a related mycobacterium) live vaccine is variably effective, but not used in US

• Skin test is based on a purified protein derivative (PPD) of a protein component of the cell wall, tuberculin (a cell wall protein component)

• Combination drug therapy is required because the mycolic acid excludes many conventional antibiotics and resistance is an issue, and it a slow metabolic organism so the drugs are not taken up quickly

– 6-9 months, susceptibility testing required

75

Mycobacterium TB diagnosis requires growth on what kind of agar?

Growth on Lowenstein-Jensen agar can take 3 weeks

76

Is MTB an extracellular or intracellular pathogen?

intracellular

77

Why is Rifampin very commonly given with other antibiotics?

because resistance to it occurs extremely fast in bacteria

78

Case 5
• An 18 y/o male currently in basic training in the army develops sore throat, headache, dry cough, low-grade fevers, and fatigue. He presents to the infirmary after 3-4 days and is prescribed amoxicillin. His symptoms do not improve. He goes back to the infirmary. Gram stain is performed on his sputum and shows white cells but no bacteria.

Case 5
• An 18 y/o male currently in basic training in the army develops sore throat, headache, dry cough, low-grade fevers, and fatigue. He presents to the infirmary after 3-4 days and is prescribed amoxicillin. His symptoms do not improve. He goes back to the infirmary. Gram stain is performed on his sputum and shows white cells but no bacteria.

79

Why was the Gram stain of the sputum negative? Was it a bad sample?

could have been a viral infection or Mycoplasma (no cell wall)

No, because of presence of WBCs

80

Why might the amoxicillin have been ineffective?

No cell wall to act on

81

Could this be a viral infection?

Could be

82

Can you think of a way to detect a bacterial infection rapidly besides Gram stain?

PCR that shit

83

Nasopharyngeal PCR for Mycoplasma pneumoniae is done and is positive. He is started on Azithromycin.

Why might Azithromycin be effective when amoxicillin was not in treating Mycoplasma infection?

Effective against ribosome function

84

What is atypical pneumonia?

Technically, any pneumonia that does not present like pneumococcal pneumonia, ie, abrupt onset of fever, chills

Atypical or “walking” pneumonia is a less severe, chronic form

Most courses of infection are benign but may still be treated

85

What three organisms cause atypical pneumonia?

Mycoplasma pneumoniae (young adults)

Chlamydia (Chlamydophila) pneumoniae (young and older adults)

Legionella pneumophila (Legionnaire’s disease) (elderly)-Legionnaire’s is a much more severe disease

86

What are some of the common symptoms of a mycoplasma induced atypical pneumonia?

Mycoplasma pneumonia usually includes a nonproductive cough, fever, and headache. Sore throat and otitis media are common. Patchy infiltrates on x-ray

87

What are some characteristics of mycoplasma pneumoniae?

• Aerobic, pleomorphic bacterium
– Lacks cell wall (no Gram stain)
– Contains sterol in membrane
– Can grow on synthetic medium

• Smallest free living organism

• Transmission is by respiratory route
– Pharyngitis
– Otitis media
– Atypical pneumonia

• Formation of cold agglutinins () in two- thirds of patients, can be diagnostic

• Treat with

88

What is an important virulence factor of mycoplasma pneumoniae?

P1 adhesion protein binds to ciliary cells, causing cell stasis and death

89

What are cold agglutinins?

IgM antibodies that bind RBCs, characteristic of this a mycoplasma pneumoniae infection

90

What is the preferred treatment of mycoplasma pneumoniae?

erythromycin or axithromycin – beta-lactams have no target