14 - Bacterial Infections of the Respiratory Tract

Question 1

What is in the upper respiratory tract? What about the lower respiratory tract?

Answer 1

It’s colonized by normal bacterial flora.

Lower respiratory tract is considered sterile.

Question 2

What are common bacteria that cause disease in the respiratory tract?

Answer 2

Pertussis, cornybacterium diptheria, neisseria meningitidis, strep pyogenes, strep pneumonia, staph aureus, haemophilus influenza, mycoplasma pneumonia, pseudomonas aeruginosa, legionella pneumophilla, and mycobacterium tuberculosis.

Question 3

How can the common bacteria that infect the respiratory tract be differentiated?

Answer 3

Based on their gram-staining patten, their shape, and their organization (clusters, chains, etc.)

Question 4

What are the general characteristics of mycobacterium tuberculosis that could be used to identify it?

Answer 4

Non-spore forming rod shaped organism.

Does not gram stain.

Identify with acid-fast staining.

Slow growing.

Question 5

Describe the complex cell envelop of mycobacterium tuberculosis? What is the treatment and how is this disease spread?

Answer 5

Contains long-chain lipids (trehalose dimycolate-cord factor) that make it resistant to determinants and antimicrobials.

Makes mycolic acids which are the target of anti-TB drugs isoniazid and ethambutol.

Human specific pathogen; transmitted from people with active disease.

Question 6

What is the epidemiology of tuberculosis?

Answer 6

High morbidity and mortality. Currently #1 killer due to infectious agent. 2 bil have latent infection.

Low incidence in US; majority of cases in the US are in foreign borne people (latent reactivating).

Higher incidence in developing countries where healthcare infrastructure is less.

Question 7

What is the mechanism of pathogenesis of TB?

Answer 7

Bacteria transmitted through air (droplets) from person with active TB.

In lung, bacteria ingested by alveolar macrophages and block phagolysosome fusion.

Bacteria multiply in macrophage.

Question 8

What occurs once mycobacterium tuberculosis multiply within macrophages?

Answer 8

If host immune response is good: cell-mediated response causes granulomas to form and contain the bacteria. Bacteria will enter a non-replicating state and cause latent infection.

If host response if poor: bacteria multiply and cause active infection.

Question 9

Describe an active TB infection? What are the symptoms?

Answer 9

Can transmit person-person. Requires extended contact, only takes a few to cause infection. Highly infectious.

Symptoms: malaise, weight loss, productive cough, and night sweats.

Usually causes dense lesion in lung on X-ray. Positive PPD skin test.

Question 10

Describe latent TB? What does their diagnostic testing show?

Answer 10

No symptoms; host will form granulomas at infection site which contain activated immune cells that wall off organism to prevent dissemination.

Few bacteria are present.

Sputum tests are negative, chest X-ray is normal, but PPD skin test is positive.

Question 11

Describe the reactivated disease associated with TB?

Answer 11

If latency-infected ppl become immunocompromised, bacteria can reactivate and begin replicating.

They will damage lung tissue and can lead to expiration of bacteria in sputum upon cough; this leads to transmission to others.

Thought that majority of TB cases are due to reactivated disease.

Question 12

What is the PPD skin test?

Answer 12

Purified protein derivative.

Skin test measures a delayed hypersensitivity reaction to bacterial proteins in the cell envelope.

Many types of mycobacterium will give a + PPD; a quantiferon test can confirm that the postitive PPD is from mycobacterium tuberculosis.

Question 13

What is a quantiferon test?

Answer 13

ELISA-based blood test that measures IFN gamma released from patient’s blood cells following incubation with 2 purified proteins only produced by mycobacterium tuberculosis: CFP10 and ESAT-6.

Question 14

How do you treat an active TB infection?

Answer 14

Active: 6 mo treatment: RIPE

• Rifampin: targets RNA pol
• Isoniazid: targets enzyme making mycolic acid
• Pyrazinamide: targets fatty acid synthase enzyme

Latent: 9 mo with isoniazid treatment

Question 15

What is the BCG vaccine? When is it given?

Answer 15

Given at birth in most other countries.

Not given in US as it would reduce ability to detect active or latent infection using PPD skin test.

Question 16

What are the characteristics of legionella pneumophila that would allow you to identify it in lab?

Answer 16

Gram-negative obligate aerobe with a single polar flagellum

Requires L-cysteine and ferric iron to glow

Generates energy by breaking down aas

Question 17

Legionella Pneumophila causes what two diseases?

Answer 17

Legionnaire’s disease or Pontiac Fever.

Question 18

What is legionnarie’s disease?

Answer 18

Acute respiratory infection characterized by high fever, cough, and chest pain. Hospitalization is common.

Question 19

What is pontiac fever? What dictates whether a person gets this or legionnaries?

Answer 19

Non-descript flu-like illness, usually self-limiting. Hospitalization is rare.

Unclear which bacterial and/or host factors will dictate whether infected individuals will develop legionnaires or pontiac fever.

Question 20

How are legionnare and pontiac fever spread?

Answer 20

Primary reservoir is within water sources like ponds and cooling towers where it lives within amoebas.

NOT transmitted person-to-person; only transmitted when infected water source is aerosolized and bacteria are inhaled.

Question 21

What is the epidemiology of legionella? Who is at risk of infection?

Answer 21

infects 10-20K people a year, many of which are nosocomial.

50% caused by serogroup 1

Disease only in immunocompromised individuals. Increased risk in elderly, smokers, and immunosuppressed.

Question 22

What is the mechanism of pathogenesis of legionella?

Answer 22

1. Intracellular pathogen of amoeba and macrophages, enters macrophages using coiling phagocytes.
2. Alters endocytic network following phagocytosis - phagosome doesn’t fuse with lysosome.
3. Bacteria replicates to high numbers until host cell bursts and releases bacteria into environment where it can infect neighboring macrophages

Question 23

What are the virulence factors used by legionella? What is the disease a result of?

Answer 23

Cytotoxins, hemolysins, proteases, endotoxins, and lipases.

Disease is a result of tissue damage in the lungs due to production of virulence factors and the accumulation of fluid.

Question 24

How would you diagnose Legionella pneumophila in the lab? What are some limitations to these?

Answer 24

Culture, urine antigen, serology, fluorescent Ab stain, PCR.

Culture: bacteria need special medium and grow slowly
Urinary test: current ELISA only can detect bacteria of serotype 1
Serology: detection requires waiting 3 weeks so that antibody titers are high enough to detect

Often few organisms in sputum and other specimens so direct detection can be hard.

Question 25

How are legionnaires and Pontiac fever treated? How would you remove legionella from the environment?

Answer 25

Legionnaires: antibiotic therapy
Pontiac fever: no therapy since self-limiting

Removal of legionella from the environment requires disinfection of water sources by chlorine treatment or superheating water supply.

Question 26

What are general characteristics of Pseudomonas Aeruginosa?

Answer 26

Gram negative bacteria with a single polar flagellum.

Forms biofilms on objects,

Oxidase + (bacteria oxidize carbs for energy).

Question 27

What is pseudomonas aeruginosa resistant to? Describe it’s growth.

Answer 27

Highly resistant to chemical disinfection and naturally resistant to many antibiotics.

They grow at elevated temps and on various carbon sources.

Growth is rapid so controlling infection early is important.

Question 28

What does pseudomonas aeruginosa produce?

Answer 28

Pigments including pyoverdin and pycocanin which are important virulence factors.

Strong hemolytic on blood agar medium.

Question 29

Where is pseudomonas aeruginosa found? Who does it infect?

Answer 29

Readily within the environment in soil and water.

Causes opportunistic infections (in compromised host), often seen in burn victims, puncture type wounds, but can enter any site if breached.

Question 30

Besides the environment, where else can pseudomonas aeruginosa be found?

Answer 30

Nosocomial infections; found on sinks, toilets, dialysis equiptment, catheters, respiratory devices, etc.

Can survive on these surfaces for long periods of time.

Question 31

Pseudomonas aeruginosa commonly effects patients with cystic fibrosis, why is this?

Answer 31

Host less able to clear bacteria due to defect in CFTR, causing build-up of mucus and difficulty in expelling organism through normal mechanisms.

Bacteria recovered from these pts has a mucoid looking appearance due to the presence of an alginate capsule.

Question 32

What type of infections can pseudomonas aeruginosa cause?

Answer 32

UTIs (due to catheters), ear infections, eye infections, bacteremia and endocarditis.

Question 33

What is the pathogenesis of pseudomonas aeruginosa?

Answer 33

They are very versatile and produce many virulence determinants:

Pili, LPS, flagellum, sidephores, exotoxins (A, S, T, U, and L) which damage cells and tissues, elastase, proteases, and phospholipases.

Question 34

Pseudomonas aeruginosa produces a capsule made of _____. What is the purpose of this? What else does it produce?

Answer 34

Alginate. This helps resist phagocytosis.

Also produces biofilms that protect the bacteria from antibacterial compounds in the environment and makes Abx treatment difficult because its hard for them to penetrate biofilm.

Question 35

How would you diagnose pseudomonas aeruginosa in the lab?

Answer 35

Culturing organism and looking for distinguishing characteristics including colony size, pigmentation, and hemolytic activity.

Question 36

What is the treatment for pseudomonas aeruginosa?

Answer 36

Infections treated with antibiotics can differ depending on the infection site and severity of infection.

Natural resistance to antibiotics is a problem.

Question 37

What is MDR, XDR, and TDR for mycobacterium tuberculosis?

Answer 37

MDR: resistant to isoniazid and rifampicin; Treatment for this is 2 years.

XDR: resistant to at least isoniazid and rifampicin among first line anti TB drugs, resistance to any fluoroquinone, and resistance to at least one second-line injectable. Treatment options are limited and prognosis is grim.

TDR: resistance to all known drugs