06 Normal Flora

Question 1

What are some functions of the normal flora?

Answer 1

Defense mechanism against infection. Source of potentially pathogenic organisms. Nutritional function (intestinal bacteria produce several B vitamins and vitamin K

Question 2

What are “Sterile” areas of the body?

Answer 2

Internal organs. CNS. Blood. Trachea, lower bronchi and alveoli. Sinuses, middle ear. Liver. Spleen. Kidneys. Bladder

Question 3

Where are normal flora located?

Answer 3

Skin. Oral cavity. Respiratory tract. Intestinal tract. Genitourinary tract

Question 4

What are the characteristics of the skin and the normal flora that live there?

Answer 4

Abundance depends on: number and activity of sebaceous and sweat glands. Most located superficially in the stratum corneum; some in hair follicles, deeper follicles in the dermis. Staph epidermidis > Propionibacterium, Staph aureus

Question 5

What are the normal flora that live in the oral cavity?

Answer 5

Streptococci Viridans. Peptostreptococcus. Prevotella sp. Fusobacterium. Neisseria sp. (non-gonorrheae). Candida albicans

Question 6

What can the normal flora in the oral cavity cause?

Answer 6

Peridontal abscess; aspiration pneumonia. Thrush, mucosal “candidiasis”

Question 7

What are the characteristics of the intestinal tract and the normal flora that live there?

Answer 7

Colon: most prolific flora in the body. Mixed flora, predominantly anaerobes (Bacteroides, Fusobacterium, Clostridium perfringens. E. coli, enterococci, Klebsiella, Enterobacter spp. Candida species (yeasts))

Question 8

What part of the intestinal tract are most anaerobes found?

Answer 8

Distal ileum. Colon

Question 9

What flora are found in the anterior nares?

Answer 9

S. aureus > S. epidermidis, various streptococci

Question 10

What are the characteristics of Mycobacteria?

Answer 10

Aerobic, acid-fast bacilli = stain poorly by the dyes used in Gram stain due to high content of lipids (mycolic acid) in the cell wall. M. tuberculosis - found only in humans

Question 11

What is Mycoplasma pneumoniae?

Answer 11

“Wall-less” 3-layer cell membrane containing cholesterol. Grow slowly (1 week to form a visible colony), complex nutritional requirements. Human pathogen only. Transmitted by respiratory droplets

Question 12

What does Mycoplasma pneumoniae cause?

Answer 12

“Atypical” pneumonia - most common type. Found in young, otherwise healthy people

Question 13

What is the diagnosis for Mycoplasma pneumoniae?

Answer 13

Serologic testing for cold-agglutinins; IgG, IgM serology. IgM autoantibodies against type O red blood cells that agglutinate these cells at 4C but not at 37C. Non-specific - only 1/2 patients with infection are positive; false-positive with influenza virus and adenovirus infection. Indicates recent infection. Culturing sputum sample on regular media reveals only normal flora. Some labs perform PCR assay on nasopharyngeal swab or sputum

Question 14

What is Chlamydiae?

Answer 14

Obligate intracellular parasites (lack the ability to produce sufficient energy to grow independently; grow only inside host cells). Rigid cell wall with NO peptidoglycan. Unique replicative cycle different from all of other bacteria

Question 15

What is the main target of Chlamydiae infection?

Answer 15

Infect primarily epithelial cells of the mucous membranes or the lungs; rarely invasive

Question 16

What are the 3 species of Chlamydiae that infect humans?

Answer 16

C. psittaci. C. trachomatis. C. pneumoniae. Inclusion bodies can be stained and visualized microscopically

Question 17

How is C. psittaci transmitted?

Answer 17

Inhaled organisms in dry bird feces

Question 18

How is C. trachomatis transmitted?

Answer 18

Sexual or passage thru birth canal

Question 19

How is C. pneumoniae transmitted?

Answer 19

Respiratory droplets

Question 20

How is Chlamydiae diagnosed?

Answer 20

Chlamydial antigens detected in exudates or urine. PCR-based urine test to diagnose STD. PCR-based test on nasopharyngeal swab and sputum

Question 21

What does Chlamydophila pneumoniae cause?

Answer 21

“Atypical” pneumonia in otherwise healthy adults

Question 22

What does C. psittaci cause?

Answer 22

Pneumonia

Question 23

What does C. trachomatis cause?

Answer 23

Most common STD bacterial pathogen in USA. Nongonococcal urethritis, epididymitis in males. Cervicitis, endometritis, salpingitis in females -=-> infertility, ectopic pregnancy. Pneumonia and conjunctival disease in newborn acquired from mother. Many patients are minimally symptomatic or asymptomatic

Question 24

What are the 3 Spirochetes?

Answer 24

Treponema pallidum. Borrelia burgdorferi. Leptospira

Question 25

What is the morphology of Treponema pallidum?

Answer 25

Spiral and thin, actively motile

Question 26

What is the transmission of Treponema pallidum?

Answer 26

Natural infection limited to human hosts. Sexual contact –> infectious lesions on the skin or mucous membranes of genitalia. Passage thru the placenta –> congenital syphilis. Kissing or other close contact with an active lesion. Transfusion of fresh human blood

Question 27

What is the Pathogenesis of Treponema pallidum?

Answer 27

Within hours to days after penetrating intact mucous membrane or gain access thru abranded skin, it enters the lymphatics or bloodstream and disseminates throughout the body. Incubation period is directly proportional to the size of the inoculum. Clinical lesions appear when a concentration is reached of ~10^7 organisms/gm of tissue

Question 28

What are the three clinical stages of infection for Syphilis caused by Treponema pallidum?

Answer 28

Natural course of infection follow these three clinical stages: 1) Incubation period lasting 3 weeks. 2) Primary stage - non-painful skin lesion (chancre). 3) Secondary bacteremic or disseminated stage (rash)

Question 29

40% of Syphilis cases lead to the tertiary stage, what can this cause?

Answer 29

Progressive disease involving the ascending aorta, CNS, granuloma-like lesion (gumma) in the skin, bone, liver

Question 30

What are the “early” stages of Congenital Syphilis clinical signs?

Answer 30

Osteochrondritis (nose, lower extremities), rhinitis, rash, anemia, hepatosplenomegaly from heavy infection of the liver, mucous patches

Question 31

What are the “late” stages of Congenital Syphilis clinical signs?

Answer 31

Interstitial keratitis, 8th nerve deafness, recurrent arthropathy

Question 32

What are some other causes of Congenital Syphilis?

Answer 32

Neonatal death is usually caused by liver failure, severe pneumonia or pulmonary hemorrhage. All neonates born to syphilitis mothers should be treated with penicillin

Question 33

What laboratory tests are done to diagnose Treponema pallidum infection?

Answer 33

Serologic tests: 1) Nonspecific, Nontreponemal tests (positive result needs to be confirmed), 2) Specific antireponemal antibody (positive for life). NOT seen on gram-stain or culture in the routine laboratory

Question 34

What is Borrelia burgdorferi?

Answer 34

Spirochete, highly motile. Grows most readily in complex liquid medium. Normally lives in mice, squirrels, and other small animals. It is transmitted among these animals – and to humans – through the bites of the blacklegged ticks (Ixodes genus). Most easily isolated from erythema migrans skin lesions. Organisms can also be cultured from ticks

Question 35

What is the Pathogenesis of Borrelia burgdorferi?

Answer 35

Transmitted to humans by injection of organism in tick saliva or by regurgitation of the ticks midgut contents. The organism then migrates out from the site, producing the characteristic skin lesion. Dissemination occurs by lymphatics or blood to other skin and musculoskeletal sites and other organs

Question 36

What are the early stages of Lyme Disease?

Answer 36

Nonpainful rash (erythema migrans) in 70-80% patients at the site of tick bite accompanied by flu-like symptoms

Question 37

What is the late stage of Lyme Disease?

Answer 37

60% of patients untreated developed intermittent bouts of arthritis after several months. Up to 5% develops chronic neurologic symptoms (HA, difficulty concentrating, numbness/tingling of hands and feet) months to years after infection

Question 38

How is Lyme Disease cured?

Answer 38

Curative with antibiotic therapy (2-4 weeks)

Question 39

What is the Diagnosis of Borrelia burgdorferi?

Answer 39

Based on symptoms, physical findings (e.g. rash), and the possibility of exposure to infected ticks. Laboratory testing is helpful in the later stages of disease based on measuring antibodies developed (may be falsely negative in early stages)