06 Normal Flora Flashcards
What are some functions of the normal flora?
Defense mechanism against infection. Source of potentially pathogenic organisms. Nutritional function (intestinal bacteria produce several B vitamins and vitamin K
What are “Sterile” areas of the body?
Internal organs. CNS. Blood. Trachea, lower bronchi and alveoli. Sinuses, middle ear. Liver. Spleen. Kidneys. Bladder
Where are normal flora located?
Skin. Oral cavity. Respiratory tract. Intestinal tract. Genitourinary tract
What are the characteristics of the skin and the normal flora that live there?
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
What are the normal flora that live in the oral cavity?
Streptococci Viridans. Peptostreptococcus. Prevotella sp. Fusobacterium. Neisseria sp. (non-gonorrheae). Candida albicans
What can the normal flora in the oral cavity cause?
Peridontal abscess; aspiration pneumonia. Thrush, mucosal “candidiasis”
What are the characteristics of the intestinal tract and the normal flora that live there?
Colon: most prolific flora in the body. Mixed flora, predominantly anaerobes (Bacteroides, Fusobacterium, Clostridium perfringens. E. coli, enterococci, Klebsiella, Enterobacter spp. Candida species (yeasts))
What part of the intestinal tract are most anaerobes found?
Distal ileum. Colon
What flora are found in the anterior nares?
S. aureus > S. epidermidis, various streptococci
What are the characteristics of Mycobacteria?
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
What is Mycoplasma pneumoniae?
“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
What does Mycoplasma pneumoniae cause?
“Atypical” pneumonia - most common type. Found in young, otherwise healthy people
What is the diagnosis for Mycoplasma pneumoniae?
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
What is Chlamydiae?
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
What is the main target of Chlamydiae infection?
Infect primarily epithelial cells of the mucous membranes or the lungs; rarely invasive
What are the 3 species of Chlamydiae that infect humans?
C. psittaci. C. trachomatis. C. pneumoniae. Inclusion bodies can be stained and visualized microscopically
How is C. psittaci transmitted?
Inhaled organisms in dry bird feces
How is C. trachomatis transmitted?
Sexual or passage thru birth canal
How is C. pneumoniae transmitted?
Respiratory droplets
How is Chlamydiae diagnosed?
Chlamydial antigens detected in exudates or urine. PCR-based urine test to diagnose STD. PCR-based test on nasopharyngeal swab and sputum
What does Chlamydophila pneumoniae cause?
“Atypical” pneumonia in otherwise healthy adults
What does C. psittaci cause?
Pneumonia
What does C. trachomatis cause?
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
What are the 3 Spirochetes?
Treponema pallidum. Borrelia burgdorferi. Leptospira
What is the morphology of Treponema pallidum?
Spiral and thin, actively motile
What is the transmission of Treponema pallidum?
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
What is the Pathogenesis of Treponema pallidum?
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
What are the three clinical stages of infection for Syphilis caused by Treponema pallidum?
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)
40% of Syphilis cases lead to the tertiary stage, what can this cause?
Progressive disease involving the ascending aorta, CNS, granuloma-like lesion (gumma) in the skin, bone, liver
What are the “early” stages of Congenital Syphilis clinical signs?
Osteochrondritis (nose, lower extremities), rhinitis, rash, anemia, hepatosplenomegaly from heavy infection of the liver, mucous patches
What are the “late” stages of Congenital Syphilis clinical signs?
Interstitial keratitis, 8th nerve deafness, recurrent arthropathy
What are some other causes of Congenital Syphilis?
Neonatal death is usually caused by liver failure, severe pneumonia or pulmonary hemorrhage. All neonates born to syphilitis mothers should be treated with penicillin
What laboratory tests are done to diagnose Treponema pallidum infection?
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
What is Borrelia burgdorferi?
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
What is the Pathogenesis of Borrelia burgdorferi?
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
What are the early stages of Lyme Disease?
Nonpainful rash (erythema migrans) in 70-80% patients at the site of tick bite accompanied by flu-like symptoms
What is the late stage of Lyme Disease?
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
How is Lyme Disease cured?
Curative with antibiotic therapy (2-4 weeks)
What is the Diagnosis of Borrelia burgdorferi?
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)
