Chapter 19: Gram Positive, Pathogenic Bacteria Flashcards
What are some general characteristics of Gram positive pathogenic bacteria?
Stain purple when Gram-stained
Two major groups based on content of DNA
Low G+C bacteria:
Cocci (Staphylococcus, Streptococcus, and Enterococcus)
Bacilli (Bacillus, Clostridium, Listeria, and Mycoplasmas)
HIgh G + C Bacteria
Rod Shaped (Corynebacteria, Mycobacteria, Proponibacteria)
Filamentous (Nocardia, Actinomyces)
What are some general characteristics of the Staphylococcus genus?
Normal member of human’s microbiota
May be an opportunistic pathogen
What is the general structure and physiology of Staphylococcus?
Gram positive cocci, nonmotile, facultative anaerobes
Cells occur in grape-like clusters
Salt tolerant- Tolerate salt of human skin
Tolerant of dessication- survive on environmental surfaces
Synthesizes catalase
What are the two species of Staphylococcus are commonly associated with human disease?
Staphylococus aures: More virulent, variety of conditions depending on site of infection
Staphylococcus epidermidis: Normal microbiota of human skin, opportunistic infection
How does a bacterial species become virulent?
Infections result when staphylococci breach body’s physical barriers
Entry of only a few hundred bacteria can result in disease
Pathogenicity results from three factors: Production of toxins, enzymes, and antiphagocytic factors
What are some structural defences of Staphylococcus against phagocytosis?
Protein A- coats the surface of the cell, interferes with humoral immune responses by inhibiting opsonization, inhibit complement cascade
Bound coagulase enzyme- converts fibrinogen into fibrin molecules, fibrin clot hide the bacteria from phagocytic cells
Slime layers (capsules)- inhibit leukocyte chemotaxis and phagocytosis, facilitate attachment of Staphyloccous to surfaces
Define opsonization
Opsonization is the neutralization of an antigen by an antibody which allows it to be engulfed by a phagocyte
Define the complement cascade pathway
Proteins in blood serum that help the immune response
What are the pathogenic enzymes produced by Staphylococcus?
Cell free coagulase- triggers blood clotting
Hyaluronidase- break down hyaluronic acid, enables the bacteria to spread between cells
Staphylokinase- dissolves fibrin threads into blood clots, allows S. aureus to free itself from clots
Lipases- digest lipisd, allow Staphylococcus to grow on skin and in oil glands
Beta-lactamase- breaks down penicillin, allows bacteria to survive treatment with beta-lactam antimicrobial drugs
What are the toxins produced by Staphylococcus?
S. aureus produces toxins more frequently than S. epidermidis
Cytolytic toxins- alpha, beta, gamma, delta, and leukocidins (lyse leukocytes), disrupt the cytoplasmic membrane of a variety of cells
Exfoliative toxins- cause skin cells to separate and slough off
Toxin-shock syndrome toxin- causes toxic shock syndrome
Entertoxins: (A,B,C, D, and E), stimulate symptoms associated with food poisoning, are heat stable
What are the types of disease caused by Staphylococcus?
Three categories of disease:
Noninvasive- Food poisioning, due to ingestion of enterotoxin-contaminated food, consumed bacteria do not continue to produce the disease, less than 24 hours
Cutaneous- Various, Scalded skin syndrome, impetigo, follicultis, sty, furuncle, carbuncle
Systemic- variety of infections when bacteria invade deeper tissues
What are the effects of scalded skin syndrome?
Exfoliative toxin causes reddened pathches of the epidermis to slough off
Blisters contain clear fluid lacking bacteria or WBCs
What are the characteristics of impetigo?
Reddened patches of skin become pus filled vsicles that eventually curst over
Generally affects children (immune system not as developed)
What are the characteristics of toxic shock syndrome?
Occurs when TSS toxin is absorbed through the skin
Characterized by fever, vomiting, red rash, low BP, loss of sheets of skin (desquamation)
Correlated with tampon use and knowledge
What are the other systemic diseases caused by Staphylococcus aureus?
Bactermia- bacteria enter into bloodstream
Endocarditis- bacteria present in the lining of the heart
Pneumonia- an inflammation of lungs where alveoli and bronchioles become filled with fluid
Osteomyelitis- bacteria invades the bones causing inflammation of bone marrow and surrounding bone
How is a Staphylococci infection diagnosed?
Detect gram positive, cluster like arrangments of bacteria
If bacteria are able to clot blood, they are coagulase positive (characteristic to S. aureus)
How do you treat and prevent a Staphyloccocal infection?
Only 5% of strains are susceptible to penicilin
Methicillin (in MRSA must treat with vancomycin)
Hand antisepsis important to prevent nosocomial infections
What are the general characteristics of Streptococcus?
Gram positive cocci, facultative anaerobes
Arranged in pairs or chains, catalase negative
Classified on the basis of antigens, types of hemolysis, cell arrangment, or physiological properties
Often categorized based on Lancefield Classification
What is the Lancefield classification system?
Streptococci species are classified using the Lancefield system
Divided into serotypes based on bacteria’s antigens
Includes serotypes A through H and K through V
Lancefield groups A and B include the significant human pathogens
What is the species of Group A Streptococci?
Group A- Streptococcus pyogenes, forms white colonies surround by a large zone of beta hemolysis
What are the components that make S. pyogenes pathogenic?
Structural components- Protein M (analgoues in funcion to Protein A), Hyaluronic acid capsule (remain hidden from phagocytic cells)
Enzymes- Streptokinase, deoxyribonucleotides, C5A peptidase (complement breaking peptide), hyaluronidase
Pyrogenic toxins (Erythrogenic toxins)- stimulate the release of cytokines (proteins) that cause fever, toxin carried on bacteriophages (only lysogneized strains are able to cause disease)
Streptolysins- lyse red blood cells, WBCs, and platelets
What are the group A streptococcal diseases?
Pharyngitis “strep throat”- inflammation of pharynx
Scarlet fever- involves lysogenized strain of S. pyogenes (Due to pyrogenic toxins) Strawberry red tongue
Pyoderma (similar to impetigo) and erysipelas- pus-producing lesions involving lymph nodes, pain, and inflammation
Streptococcal toxinc shock like syndrome (TSLS)
Necrotizing fasciitis- caused by “flesh eating bacteria” bacteria spread deep within the body along the fascia
Rheumatic fever- autoimmune, antibodies cross-react with heart antigens, inflammation leads to damage of heart valves and msucle, leads to achy joints
Glomerulonephritis- autoimmune, antibodies against group A Streptococcus accumulate in the glomeruli and nephrons of the kidneys causing inflammation, causes tea-colored urine
How do you diagnose, treat, and prevent a Streptococcal Group A infection?
Diagnosis- Gram + pair or chain found in cutaneous specimens, streptococci normally in the pharynx (not diagnostic), immunological tests
Treatment- penicillin is effective, sensitive to erythromycin, cephalosporin, and bacitracin
Prevention- antibodies against M protein provide protection
What are the characteristics of Group B Streptococcal strains?
Group B- BABY, Streptococcus agalactiae
Beta-hemolysis zones that are smaller, gram positive cocci in chains
Group specific polysaccharide cell wall antigens, resistant to bacitracin
How is Streptococcus agalactiae pathogenic?
Capsule is not protective (unlike S. pyogenes)
Often infects newborns without specific antibodies
Produces enzymes (proteases, hemolysins, hyaluronidase, etc.) whose roles are not yet understood
What are the diseases caused by S. agalactiae?
Associated with neonatal bactermia, meningitis, and pneumonia
Older, immunocomprimised patients also at risk
How is S. agalactiae diagnosed, treated, and prevented?
Diagnosis- ELISA test used to identify group B streptococcus
Treatment-Penicilin G is the drug of choice
Prevention- immunization of women can protect future children
What is the Viridans Group?
Alpha-hemolytic Streptococci (incompletely break down RBCs, WBCs, etc.)
Lack group specific carbohydrates- cannot be classified using Lancefield system
Many produce a green pigment when grown on blood media
Inhabit mouth, pharynx, GI tract, genital tract, and urinary tract
One cause of dental caries and dental plaque- Stick to dental surfaces via dextarn
If enter the blood can cause meningitis and endocarditis
What is the other alpha-hemolytic Streptococcus species?
Streptococcus pneumoniae
Gram positive cocci that most commonly form pairs
Form unpigmented, alpha hemolytic colonies on blood agar
What are the virulence factors of Streptococcus pneumoniae?
Polysaccaride capsule (required for virulence)
Phosphorylcholine- stimulates cells to phagocytize the bacteria
Protein adhesin- mediates binding of cells to epithelial cells of pharynx
Secretory IgA protease- destroys IgA (anitbodies found in the pharynx)
Pneumolysin- binds to cholesterol in the cytoplasmic membranes of epithelial cells, producing pores that result in cell lysis
What are the pneumoccoal diseases caused by S. pneumoniae?
Pneumococcal pneumonia- bacteria multiply in the alveoli, damaging the alveolar lining, allowing fluid, RBCs, and leukocytes to enter the lunds
Sinusitis and otitis media- bacteria can invade the sinuses and middle ear causing pus and inflammation
Bacteremia and endocarditis- colonize in the blood and heart
Pneumococcal meningitis- spread to the meninges
How is a S. pneumoniae infection diagnosed, treated, and prevented?
Diagnosis- gram-stain of sputum smears, confirmed with Quellung reaction (anti-capsular antibodies cause the capsule to swell)
Treatment- penicillin
Prevention- vaccine made from purified capsular material
What are the characteristics of the Enterococcus genus?
Previously classified with group D streptococcus- reclassified as a separate genus
Gram positive, unencapsulated, catalase negative, non-hemolytic
Forms short chains and pairs
Can grow up to 45 degrees Celsius, pH 9.6, and can grow in the presence of salt and bile
Found in the human colon where it is rarely pathogenic- may introduce disease if found in a different area
Enterococcus faecalis and Enterococcus faecium
How is Enterococcus clinically relevant?
Important cause of nosocomial infections
Difficult to treat because enterococci often are resistant to antimicrobials
Prevention in health care setting is difficult- patients often have weakened immune systems
What are the characteristics of the Bacillus genus?
Gram positive bacilli that occur singly, in pairs, or in chains
Normally dwells in soil, is facultatively anaerobic
Form endospores and posess and protective capsule composed of polyglutamic acid which inhibits phagocytosis (not polysaccharides)
Pathogenic strains produce anthrax toxin containing three polypeptides: Edema factor, Protective antigen, and Lethal factor
What is the epidemiology of Bacillus?
Primarily a disease of herbivores (zoonoses)
Humans contract via one of three routes- inhalation of spores (most deadly), incoluation of spores through break in skin, ingestion of spores
Category A bioterror agent
What is the disease caused by Bacillus?
Bacillus anthracis only causes anthrax
Three clinical manifestations
Gastrointestinal anthrax- rare in humans, results in intestinal hemorraging and death
Cutaneous- produces a painless, swollen, black, crusty ulcer called an eschar which releases a toxin in blood
Inhalation- rare in fever, high fever, aches, labored breathing, high mortality rate
How is a Bacillus infection diagnosed, treated, and prevented?
Diagnosis- large, nonmotile Gram-positive bailli in lung or skin sample
Treatment- ciproflaxacin and many other antimicrobials
Prevention- control of disease in animals, effective vaccine available (requires multiple doses and boosters)
What are important characteristics of Clostridium?
Gram positive, anaerobic, endospore-forming bacillus
Ubiquitous in soil, water, and gastrointestinal tracts of animals and humans
Endospores allow for survival in harsh conditions
Ability to secrete potent toxins- histolytic, enterotoxins, and neurotoxins
4 important species- C.perfringens, C.difficile, C. botulinum, and C. tetani
What are characterisitics of Clostridium perfringens?
Produces toxins that can cause irreversible damage to body
Food poisioning- abdominal cramps and watery diarrhea, lasts for less than 24 hours, occurs through ingestion of contaminated meat
Gas gangrene- trauma introduces endospores into body where they germinate in anaerobic environment of deep tissues (extremities)
Endospores germinate and cause necrosis, produce gaseous watse (results in bubbling or crakcing cells)
How is a C.perfrigens infection diagnosed, treated, and prevented?
Diagnosis- presence of minimum bacterial load in food or feces, gas gangrene self diagnostic
Treatment- food poisoning is self limited, gas gangrene requires removel of dead tissue and administering antitoxins and antimicrobials
Prevention- dfficult to prevent because organism is so common, reheating food can destory toxin
What are important characterisics of C. difficule?
Very difficult to treat
Common member of intestinal microbiota
Opportunistic pathogen in patients taking broad-spectrum antimicrobial drugs
Minor infections result in self-limiting explosive diarrhea
May cause pseudomembranous colities (sections of colon wall slough off) which can follow the use of broad spectrum antibiotics
Toxin A causes diarrhea and Toxin B is cytotoxic to colon cells (life threatening)
How is C. difficile diagnosed, treated, and prevented?
Diagnosis- isolation of organism from feces of immnoassay
Treatment- discontinue causative antimicrobial drugs to resolve minor infections, serious cases treated with vancomycin or metronidazole
New, more pathogenic strain
Prevention- proper hygiene to limit nosocomial infections
What are important characterisics of Clostridium botulinum?
Common in soil or water
Botulism results when the endospore germiantes and produces potent neurotoxins
Seven known botulinum toxins, A through G
How does the botulism toxin work at the neuromuscular junction?
Acetylcholine is a neurotransmitter that mediates communication between neurons and othe cells
Botulism prevents the release of acetylcholine into the synaptic cleft, resulting in the prevention of muscular contraction (flaccid paralysis)
What are the diseases of C. botulinum and how are they spread?
Botulism in an intoxation, not an infection
3 Manifestations:
Foodborne botulism (canned food, preserved fish)- results from ingestion of toxins, death can result from asphyixation
Infant botulism (honey)- results from ingestion of endospores- “Failure to thrive”
Wound botulism- contamination of wound by endospores
How is a C. botulinum infection diagnosed, treated, and prevented?
Diagnosis- symptoms are diagnostic
Treatment- administer neutralizing antibodies against botulism toxin, administer antimicrobial durgs in infant botulism cases
Prevention- proper canning of food, infants under one year should not eat honey
What are important characteristics of Clostridium tetani?
Obligately anaerobic
Ubiquitious in soil, dust, and GI tract of animals and humans
Tetanus results when endospores germinate and produce tetanus toxin- tetanospasmin
How does tetanospasmin work?
Blocks the release of inhibitory neurotransmitters leading to constant contraction of muscles
How is a C. tetani infection diagnosed, treated, and prevented?
Diagnosis- characteristic muscle contraction
Treatment- administer immunoglobulin against tetanus toxin, administer antimicrobial drugs, active immunization with tetanus toxoid
Prevention- immunization with tetanus toxoid, five doses beginning at 2 months of age, followed by a booster every ten years of life
What are important characteristics of Listeria?
Gram positive, low G+C, non-spore-forming coccobacillus
Ubiquitous in nature; found in soil, water, mammals, birds, fish, and insects
Enters body in contaminated food and drink
Motility at lower temperatures through flagella and due to actin polymerization at 37 degrees Celsius within a human cell
Intracellular pathogen
What makes Listeria so pathogenic? (What are its virulence factors?)
Virulence is directly related to the bacteria’s ability to live and spread within cells
Unique ability to survive over a wide range of temperatures from 4 to 40 degrees Celsius
Causes an uncommon but potentially serious type of food-borne infection known as listeriosis
E.g.- Listeria monocytogenes
What are the motility characteristics of Listeria?
Listeria is acquired by ingestion, must find and adhere to the small intestine mucosa to infect it
Highly motile due to flagella at lower temperatures (20- 25°C)
Actin-based tumbling motility in human cells
Uses host cell actin to move within and between host cells
Polymerizes actin molecules into long stiff actin filament tails that propel the bacteria into cytoplasm
What does Listeria produce to help it spread intracellularly?
Listeria binds to the surface of a phagocytic cell and triggers its own endocytosis
Adherence and invasion is mediated by membrane proteins internalins
Once inside the human cell’s phagosome, Listeria synthesizes a pore-forming cytotoxin, called Listeriolysin O (LLO)
It also produces two other enzymes, phosphatidylinositol- specific phospholipase C (PI-PLC) and phospholipase C (PC-PLC)
All enzymes help Listeria to escape from phagosome
How does Listeria spread intracellularly?
Listeria is initially endocytized
The intracellular bacteria escapes the phagosome and reproduces within the phagocyte
The bacteria then polymerizes the host cell’s actin filaments at one end to form a “tail” that propels it through the cytoplasm into pseudopods
A neighboring cell then endocytizes the pseudopod
Listeria once again “tunnels” its way out of the phagosome and continues its intracellular existence
What are the diseases caused by Listeria and how are they spread?
L. monocytogenes is rarely pathogenic in healthy adults
Causes high mortality in individuals developing systemic infection
Most deaths involve fetuses, newborns, or immunocompromised adults
One of the few microbes that can cross the placenta and blood brain barrier, results in miscarriage, stillbirths, or severely infected newborn
Immunocompromised adults can develop meningitis, and death
Very difficult to control during food processing as it can multiply over wide range of temperatures
Incubation period very long from 11-70 days
How is a Listeria infection diagnosed, treated, and prevented?
Diagnosis- Presence of bacteria in the cerebrospinal fluid, characteristic tumbling motility (only at room temp.), Rarely seen in Gram stain
Can be cultured by cold enrichment technique
Treatment-Antimicrobial drugs like penicillin and erythromycin inhibit Listeria
Resistant to tetracycline and trimethoprim
Prevention-Difficult because organism is ubiquitousAt-risk individuals should avoid certain foods like raw vegetables, unpasteurized milk, soft cheeses, cole slaw, etc.
What are important characteristics of mycoplasmas?
Smallest free-living microbes, pleomorphic
Lack cytochromes, enzymes of the Krebs cycle, and cell walls
Most have sterols in their cytoplasmic membranes
Classified as low G+C, gram positive bacteria according to genetic classification, even though they stain pink with Gram stain
Require various growth factors from a host or supplied in laboratory media
Can colonize the mucous membranes of the respiratory and urinary tracts
What is the disease caused by Mycoplasma pneumoniae?
Attaches to epithelial cells lining the respiratory tracts of humans
Causes primary atypical pneumonia (walking pneumonia)
Early symptoms not typical of other types of pneumonia
Not usually severe enough to require hospitalization
Not seasonal
Spread by nasal secretions among people in close contact
Diagnosis difficult
Mycoplasmas are small and difficult to detect
Difficult to prevent
Patients often infectious without signs or symptoms
Erythromycin or tetracycline
No vaccine available
What are other mycoplasma species of importance?
Three other mycoplasma associated with human diseases
M. hominis, M. genitalium, and Ureaplasma urealyticum
Often colonize the urinary and genital tracts of newborn girls
M. genitalium and U. urealyticum cause inflammation of the urethra (urethritis), Treated by erythromycin or tetracycline
M. hominis can cause pelvic inflammatory disease in women, Treated by clindamycin
What are imporant characteristics of Corynebacterium?
High G+C, pleomorphic, non-endospore forming bacteria
Ubiquitous on plants, animals
Colonize on skin and respiratory, gastrointestinal, urinary, and genital tracts
Bacteria divide by binary fission (snapping division) to form characteristic V-shapes and palisade arrangements
Distinctive feature is presence of metachromatic granules
Corynebacterium diphtheriae causes diphtheria
What are the diseases caused by Corynebacterium diphtheriae and the how is the disease spread?
Corynebacterium diphtheriae is transmitted from person to person via respiratory droplets or skin contact
Bacteria contains a lysogenic bacteriophage that codes for diphtheria toxin
Toxin contains two polypeptides
One polypeptide binds to a growth factor receptor on cells triggering the endocytosis of the toxin
Inside the cell, proteolytic enzymes cleave the toxin, releasing the second polypeptide into the cytosol
Enzymatically destroys elongation factor, a protein required for the synthesis of polypeptides in eukaryotes
Results in complete stoppage of polypeptide synthesis and cell death
What are some characteristics of diphtheria?
Infections in immune and partially immune individuals are asymptomatic or result in mild respiratory disease
Disease most severe in non-immune patients resulting in diphtheria
Sore throat, fever, pharyngitis
Oozing of fluid composed of intracellular fluid, blood clotting factors, leukocytes, bacteria, and dead cells
This fluid thickens into a pseudomembrane
Adheres to tonsils, uvula, palate, pharynx, and larynx
Blocks the respiratory passages resulting in death by suffocation
Cutaneous diphtheria results in formation of pseudomembrane on skin
Toxin can get absorbed into the blood, leading to coma and death
How is Corynebacteria infection diagnosed, treated, and prevented?
Diagnosis
Initial diagnosis on the basis of presence of pseudomembrane
Elek test – immunodiffusion assay in which antibodies against toxin react with the toxin in the sample
Culture on Loffler’s medium reveals typical colonial morphology
Treatment
Antitoxin administration to neutralize the toxin
Penicillin or erythromycin
Prevention
By vaccination
Administered as part of DTaP vaccine
What are some important characteristics of Mycobacterium?
High G+C, non-endospore forming pathogen
Cell wall contains a way lipid called mycolic acid in cell wall, results in a number of unique characteristics
Slow growth
Protection from lysis after phagocytosis
Capacity for intracellular growth
Resistance to Gram statning, stain acid fast, detergents, many antimicrobial drugs, and dessication
What are some important characteristics of Mycobacterium (continued)?
Grows on differential medium Lowenstein-Jensen agar
Virulent strands of M. tuberculosis have a cell wall component called cord factor- produces strands of daughter cells that remain attached to one another in parallel alignment, inhibits migration of neutrophils
Pathogen not particularly virulent- only %5 of infected people develop disease, Kill 50% of untreated patients
Two main species: M. tuberculosis and M. leprae
What is the diseae caused by M.tuberculosis?
Tuberculosis- respiratory disease
Cases are declining in US due to better living conditions, pandemic in other regions of the world
Remains one of the top three killers of people worldwide today
Nearly 2 billion people are currently infected
What are the three types of TB?
Primary TB- results from initial infection, formation of tubercles
Secondary TB- reestablishment of active infection after period of dormancy
Disseminated TB- results when infection spreads throughout body
How are tubercles formed in primary tuberculosis?
85% of infections remain in lungs
Primary infection involves the formation of small, ahrd nodules in the lungs
5 Stages of Infection:
- Bacteria infects the respiratory tract via inhalation- minimum dose is 10 cells, baceteria have adhesive pili that attach to extarcellular human protein laminin
- Macrophages in the alveoli of ungs phagovytize the pathogens but unable to digest them as the bacteria prevents the fusion of phagosome and lysosome
- Bacteria replicate freely within the host cells, gradually killing them, release chemokines, bacteria are released from dead cells are phagocytized by other macrophages, asymptomatic stage
- Infected macrophages present antigen to T lymphocytes, which produce cytokines to trigger inflammation, tightly appressed macrophages surround site of infection, forming a tubercle
- Other cells deposit collagen fibers enclosing the infected macrophages within the tubercle, infected cells in the center die, releasing M. tuberculosis and producing caseous necrosis (liquid), center may become filled with air as a tuberculous cavity
If immune system able to kill all the mycobacteria, it subsequently deposits calcium around the tubercle, known as Ghon complexes
How is tuberculosis reactivated?
The bacteria ruptures the tubercle, and re-establishes active infection
Bacteria sperad through lungs via bronchioles
Reactived TB found commonly in immunosuppressed individuals
What are the effects of disseminated Tuberculosis?
Results when some macrophages carry the pathogens via the blood and lymph to variety of sites
Bone marrow, spleen, kidneys, spinal cord, brain
Common name for TB in the early 1900s-consumption-reflected wasting of body due to involvement of multiple sites
How is tuberculosis diagnosed?
Tuberculin skin test (PPD)
Inject 0.1mL of cell wall antigens into the skin, appearance of induration (swelling) within 24-72 hours is positive
Many false positives and false negatives
Chest X-rays identify individuals with active disease
Presence of acid-fast cells and cords in sputum
How is a tuberculosis infection treated?
Common antimicrobials (penicillin, erythromycin) are ineffective, mycobacterium grows so slowly taht drugs are cleared from body before being effective
Combination therapy used for months to treat disease- combination of Isoniazid, rifampin, pyrazinamide, and ethambutol for two months followed by isoniazid and rifampin alone for 4 months
Development of multi-drug resistant strins (MDR)- have to be treated with fluoroquinolones in combination with kanamucin for more than 2 yeras
Extensively drug resistant TB (XDR-TB)- resistant to all TB anti-microbials
How is tuberculosis spread and how can it be prevented?
Cases in US show a strong correlation with the age, sex, and recent immigration history of a patient
High rates in new immigrants from areas of South Asia, South America, and Africa, also in AIDS patients
Directly Observed Treatment, Shortcourse (DOTS)- ingestion of TB medications is observed by a responsible person, lowers rate of drug-resistant TB and the rate of tuberculosis relapse
Prevention- BCG vaccine (composed of attenuated M. bovis strain), administered to children in all developing countries, efficicay studies vary
What is the other type of disease caused by Mycoacterium?
Leprosy- caused by Mycobacterium leprae
Bacteria do not grow in cell-free culture, armadillos only other host
Bacteria grow best at 30 degrees Celsius, showing preference to grow in cooler regions of the body, like peripherlal nerve endings and skin in fingers, toes, etc.
Becoming relatively rare
Transmitted via person to person contact or break in skin
Two different forms: Tuberculoid leprosy, and lepromatous leprosy
What is tuberculoid leprosy?
Non-progressive form of disease
Strong cell-mediated immunity is able to kill infected cells
Regions of skin lose sensation due to nerve damage
What is lepramatous leprosy?
Develops in patients with weak CMI
Bacteria multiply in skin and nerve cells, gradually destroying tissue and leading to progressive loss of facial features, fingers, toes, etc.
Incubation period up to several years
Transmitted via person-to-person contact, not particularly virulent
How is leprosy diagnosed, treated, and prevented?
Diagnosis- based on signs and symptoms of disease, Leprosy antigen skin test
Treatment- combination of antimicrobial drugs (clofazimine, rifampin, or dapsone for 12 months), lifelong treatment is sometimes needed
Prevention- limiting exposure to the pathogen, BCG vaccine provides some protection
What are other possible mycobacerial infections?
Mycobacterium avium-intracellulare
Opportunistic pathogen
Most common mycobacterial infection among AIDS patients in the US
Infections result from ingestion of contaminated food or water
Can affect almost every organ and result in massive organ failuer
Treatment is difficult due to the dissmeinated nature of the infection
What is the Buruli ulcer and what bacterial species is it caused by?
Caused by M.ulcerans, an emerging pathogen present in swamps
Produces a potent toxin mycoalcton that destroys cells beow the skin
Treatment- Rifampina and Streptomycin
What are important characteristics of Propionibacterium?
Small, gram positive rods often found on the skin
Produce propionic acid as a by product of fermenation of carbohydrates
Propionibacterium acnes msot commonly involved in human infections- causes acne in 85% of adolescents and young adults
May be an opportunistic pathogen
Many cases require no treatment
Antimicrobial drugs help control bacterium
Retinoic acid- derivative of Vitamin A, can inhibit formation of oil
What are important characteristics of Nocardia asteroides?
Common inhabitant of soils rich in organic matter
Cell wall contains mycolic acid and stains acid-fast
Appear like long hyphal cells- diagnostic
Produces opportunistic infections in numerous sites
Pulmonay infections, Cutaneous infections (may produce a myceotma characterized by swelling, pus, and sores), CNS infections
Prevention involves avoiding exposure to bacterium in soil
What are important characteristics of Actinomyces?
Characterized by hypha-like, gram positive cells
Member of surface microbiota of human mucous membranes
Colonies form visible concretions resembling grains of sand known as “sulfur granules”- actually contain calcium phosphate
Opportunistic infections- respiratory, gastrointestinal, urinary, and female genital tracts, sometimes cause dental carries
Actinomycosis- results when bacteria enter breaks in the mucous membrane, formation of absecesses connected by channels in skin or mucous membranes
Diagnosis difficult as other orgniams cause similar symptoms
