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G+ Non-Spore-Formers (Irregular
-Named because of irregularities in…
G+ Non-Spore-Formers
Irregular -Named because of irregularities in morphology & staining properties (pleomorphic)-20 genera; most clinically significant are:
- Corynebacterium
- Mycobacterium
- Propionibacterium
- Nocardia
-All produce catalase, possess mycolic acids & a unique peptidoglycan
Mycobacterium
-Gram-Positive Irregular bacilli
-Acid-fast staining; high lipid content, resistant to drying, acids & various germicides
-Strict aerobes
-Produce catalase
-Possess mycolic acids in cell walls; a unique type of peptidoglycan
-Do not form capsules, flagella or spores
-Growth is slow but persistent
Mycobactarium Tuberculosis -Agent of tubercle bacillus -Produces no exotoxins/enzymes-Virulence factors include:
- High infectivity
- Cord factor & complex waxes (prevents lysosome action)
- Ability to escape phagocytosis
- Ability to stimulate host-delayed hypersensitivity response
- Multiple drug resistance
Epidemiology -Predisposing factors include: * Inadequate nutrition
- Debilitation of immune system
- Poor access to medical care
- Lung damage
- Genetics
-33% of world pop. & 15 mil. in US carry tubercle bacillus; highest rate in US occurring in recent immigrants-Bacillus is very resistant -Transmitted by airborne respiratory droplets
Course of Infection & Disease
-Only 5% of infected people develop clinical disease
-If untreated, the disease progresses slowly; majority of TB cases contained in lungs
Types of TB
Secondary TB -If patient doesn't recover from primary TB, reactivation of bacilli can occur-Tubercles expand & drain into the bronchial tubes & upper resp. tract-The patient gradually experiences more severe symptoms, including:
- Violent coughing
- Greenish/bloody sputum
- Fever
- Anorexia
- Weight loss
- Fatigue
-If untreated, has a 60% mortality rate
Extrapulmonary TB
-During secondary TB, bacilli disseminate into regional lymph nodes, kidneys, long bones, genital tract, brain & meninges
-Has grave complications; end result is damage to associated tissues
Primary TB
-Infectious dose = 10 cells -Phagoyctosed by alveolar macrophages & multiply intracellularly
-After 3-4 weeks, immune system attacks, forming tubercles (granulomas consisting of a central core containing bacilli surrounded by WBCS)
-If center of tubercle breaks down into necrotic caseous lesions, they gradually heal by calcification
Diagnosis -In vivo/TB testing
- Mantoux test: Local intradermal injection of purified protein derivative; looks for red wheal to form in 48-72 hrs (induration); established guidelines indicate interpretation of result based on size of wheal & specific population factors
-X rays-Direct identification of acid-fast bacilli in specimen-Cultural isolation from biochemical testing
Management & Prevention
-6-24 months of combined drug treatment (at least 2 drugs from a list of 11)
-Rifater pills (isoniazid, rifampin, pyrazinamide) are the standard prophlyactic treatment; 1 dose daily
-Vaccines based on attenuated bacilli Calmet-Guerin strain of M. bovis used in other countries
Mycobacterium Leprae
-AKA "The Leprosy Bacillus" -Causes leprosy/ Hansen's disease
-Strict parasite (does not grow on artificial media/tissue culture)
-Slowest growth of all species
-Multiplies within host cells in large packets known as "globi"
-Leprosy = Chronic disease that begins in the skin & mucous membranes then progresses into the nerves
Epidemiology & Transmission
-Endemic in certain regions throughout the world
-Spreads through direct contact from leprotics
-Not highly virulent; health & living conditions influence susceptibility & course of disease
-May be associated w/ specific genetic marker
Course of Infection & Disease
-Macrophages phagocytize the bacilli, but a weakened macrophage/slow T cell response may not kill the bacillus
-Incubation can last from 2-5 yrs.; if untreated, bacilli grow slowly in the skin macrophages & Schwann cells of peripheral nerves
-Has 2 possible forms
Tuberculoid Leprosy
-Superficial infection w/o skin disfigurement
-Causes damage to nerves & loss of pain perception
Lepromatous
-A deep, nodular infection that causes severe disfigurement of face & extremities
Treatment & Prevention
-Long-term combination drug therapy
-Prevention requires constant surveillance of high risk populations
-Only a trial vaccine is currently available
Diagnosis -Combination of symptomology, microscopic examination of lesions & patient history-Numbness in hands & feet, loss of heat & cold sensitivity-Muscle weakness, thickened earlobes, chronic stuffy nose-Detection of acid-fast bacilli in skin lesions, nasal discharge & tissue samples-Diagnosing Methods
- Skin assessment
- Checking for patches & no. of patches
- Testing sensations
- Assessment of nerve damage
Non-TB Mycobacteria (NTM)
-M.avium Complex: Third most common cause of death in AIDS patients
-M. kansaii: Causes pulmonary infections in adult white males w/ emphysema/bronchitis
-Mr. marinum: Water inhabitant; causes lesions after scraping on swimming pool concrete
-M. scrofulaceum: Infects cervical lymph nodes
-M. paratuberculosis: Found in raw cow's milk; recovered from 65% of individuals diagnosed w/ Crohn's disease
Actinomyces & Nocardia
-Both genera are nonmotile filamentous bacteria related to mycobacteria
-May cause chronic infection of skin & soft tissues
-Actinomyces israelii: Responsible for diseases of the oral cavity, thoracic cavity or intestines (actinomycoses)
-Nocardia brasiliensis: Causes pulmonary disease similar to TB
Proprionibacterium
-Propionibacterium acnes = Most common species
-Gram-Positive rods
-Can be aerotolerant or anaerobic
-Non-toxigenic
-Common resident of sebaceous glands
-Agent of acne vulgaris, an infection of pilosebaceous glands exacerbated by biochemical changes of adolescence
Corynebacterium (Diphtheria) -Gram-Positive irregular bacilli-Virulence factors assist in attachment & growth-Diphtherotoxin; an endotoxin w/ 2 parts
- Part A: Arrests protein synthesis
- Part B: Binds & induces endocytosis
Diagnostic Methods
-Presence of pseudomembrane & swelling = indication of Corynebacterium Diphtheria
-Staining
-Assessment of conditions & health history
-Serological assay
Treatment & Prevention
-Antitoxin treatment
-Antibiotic therapy through penicillin/erythromycin
-Toxoid vaccines & boosters
Epidemiology
-Reservoir of healthy carriers; potential for diphtheria is always present
-Most cases occur in non-immunized children living in crowded, unsanitary conditions
-Acquired vie respiratory droplets from carriers/actively infected individuals
Pathology -2 Stages of Disease 1) Local infection - Upper respiratory tract inflammation, characterized by:
- Sore throat
- Nausea
- Vomiting
- Swollen lymph nodes
- Pseudomembrane formation in pharynx; can lead to asphyxiation
2) Diphtherotoxin production & toxemia
- Toxin is absorbed from the throat
- Carried to heart & nerves
- Causes myocarditis & abnormal EKG patters (usually reversible)
Regular
-Named because of their consistent shape & staining properties
-Has 7 genera which are diverse in habitat, biochemical properties & size
-Lactobacillus species are important commercial producers of many dairy products
Listeria Monocytogenes
-Non-spore-forming & Gram-Positive
-Range from coccobacilli to long filaments
-1 to 4 flagella
-No capsules
-Resistant to cold, heat, salt, pH extremes & bile
-Virulence attributed to ability to replicate in the cytoplasm of cells after inducing phagocytosis; avoids humoral immune system
-Beta-hemolytic
Diagnosis & Control
-Culture requires lengthy cold enrichment process
-Rapid diagnostic tests using ELISA available for dairy products & cultures
-Ampicillin, penicillin & trimethoprimsulfamethoxazole are available antibiotic therapies
-Prevention can be done through pasteurization & cooking
Epidemiology & Pathology
-Primary reservoir is soil, H2O & animal intestines
-Can contaminate foods & grow during refrigeration
-Listeriosis: Most associated w/ dairy products, poultry & meat
-Often a mild/subclinical infection w/ non-specific symptoms of fever, diarrhea & sore throat (normal adults)
-Has a high morbidity & mortality rate in immunocompromised patients, neonates & fetuses; affects brain & meninges (20% death rate)
Erysipelothrix Rhysiopathiae
-Gram-Positive rod widely distributed in animals & the environment
-Primary reservoir = Tonsils of healthy pigs
-Enters through skin abrasion, multiplies to produce erysipeloid, a disease characterized by dark red lesions
-Antibiotic therapy involves penicillin/erythromycin
-Vaccine available for pigs