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Gram-postive Cocci
Staphylococcus aureus “The golden Staph” The basics Characteristics Pathogenicity Epidemiology -tolerates dessication and heat -Faculative anaerobes -non-motile -salts tolerant -Infections result when Staphylococci breach bodys physical barrier -Entry of only a few hundred bacteria can result in disease -Found mostly on skin folds -can grow in the upper respiratory,GI, and urogenital tracts of humans -transmitted by direct contact or formites Three features that result in Pathogenicity Structural defenses against phagocytosis Protein A: -coats the cell surface -Binds to IgG -Inhibits opsonization and the complement cascade Bound coagulase: -Converts fibrinogen into fibrin molecules -fibrin clots hide the bacteria from phagocytic cells Synthesizes polysaccharides slime layer capsules: -Inhibit leukocyte chemotaxis and phagocytosis -Facilitate attachment of staphylococcus to surfaces Enzymes Cell-free coagulase: -Triggers blood clotting Hyaluronidase: -Breaks down hyaluronic acid -Enables the bacteria to spread between cells Staphylokinase: -Dissolves fibrin threads in blood clots -Allows S.aureus to free itself from clots Lipases: -Digest lipids -allow staphylococcus to grow on skin and in oil glands β-lactamase -Breaks down penicillin -Allows bacteria to survive treatment with β-lactam antimicrobial drugs Toxins (produced by S. aureus less frequently by S.epidermidids Cytolytic toxin: -Disrupt the cytoplasmic membrane of a variety of cells -Leukocidin can lyse leukocytes specifically Exfoliative toxins: -Cause skin cells to separate and slough off Toxic shock syndrome: -Causes TSS Enterotoxins: -Stimulate symptoms associated with food poisoning
Diseases Non-invasive diseases (bacteria produce Exotoxin on food) -food poisoning (intoxication) due to ingestion of enterotoxin- contaminated food Cutaneous Diseases -Various skin conditions -Scalded skin syndrome, impetigo, folliculitis Toxic-shock syndrome (nonstreptococcal) -Super absorbent tampons (rely 80’s) -Some staph strains produce TSS -TSS toxin absorbed into the blood: produces fever, vomiting, rash, and low BP Systemic Diseases Bacteremia -Presence of bacteria in blood Endocarditis -Damage to the lining of the heart Pneumonia -Inflammation of the lungs -Empyema occurs when pus fills the lungs Osteomyelitis -Inflammation of the bone and marrow Diagnosis, Treatment, and Prevention Diagnosis -Detect Gram-positive bacteria in grapelike arrangements -Catalase positive, coagulase positive Treatment -Nafcillin or Bactrim -Vancomycin used to treat MRSA infections Prevention -Handwashing important to prevent nosocomial infections -No vaccine available yet Streptococcus Pyogenes (group A) The Basics Characteristics Pathogenicity Epidemiology -Group A -Faculative anaerobes -Coccci in pairs or chains -Since it is a group A bacteria they are considered significant human pathogens -typicaly infects the pharynx or skin -Often causes disease when normal microbiota are depleted -Spreads via respiratory droplets
Diagnosis, Treatment, and Prevention Diagnosis -Beta hamolysis & Bacitracin susceptible -Skin infections diagnosed by the presence of gram-positive bacteria in short chains or pairs -Rapid strep test used to diagnose respiratory infections Treatment -Penicillin is effective Prevention -Prophylactic penicillin injections IM for high risk individuals Streptococcus agalactae (group B) The Basics Characteristics Pathogenicity Epidemiology -Group-specific cell wall antigens -Smaller zone of beta-hemolysis -Resistant to bacitracin -CAMP test positive -Often infects newborns without specific antibodies -Produces enzymes whose roles are not yet understood -Colonizes the GI, genital, and urinary tracts -Wound infections and childbirth cause most adult infections -Newborns often inoculated at birth Diseases Associated with: -neonatal bacteremia -meningitis -pneumonia Other -Older immunocompromise d patients are also at risk Diagnosis, Treatment, and prevention Diagnosis -ELISA test used to identify group B streptococcus Treatment -treat with penicillin or ampacillin -Prophylactic use of penicillin during childbirth reduces newborn infections Prevention -Immunization of women can protect future children
Streptococcus pneumoniae (Viridans Group) The basics Characteristics Pathogenicity Epidemiology -Cocci that most commonly form pairs (diplococci) -Form unpigmented, alpha-hemolytic colonies on blood agar -Optochin susceptible -Lacks lancfield antigens Polysaccharide capsule -Protein adhesin Mediates binding of cells to epithelial cells of pharynx -Secretory IgA protease Destroys IgA; mucosal antibody encountered during infection -Pneumolysin Lyses epithelial cells -present in the mouths and pharynges of most humans -Causes diseases when travel to the lungs or other parts of the body -Infections occur most often in children and the elderly Diseases Pneumococcal pneumonia -most common diseas caused by Strep. pneumoniae Sinusitis and otitis media -middle ear infections Bactermia and endocarditis -S. Pneumoniae can enter the blood through lacerations or tissue damage Pneumococcal meningitis -mortality rate higher that other causes of meningitis Diagnosis, Treatment, and Prevention Diagnosis -Alpha hemolytic -Susceptible to optochin test -gram stain of sputum smears (lancet-shaped, diplococci) Treatment -Penicillin -Resistant strains have emerged (use othe antibiotics) Prevention -Vaccine made from purified capsular material
Gram-positive rods
Bacillus Anthracis The Basics Characteristics Pathogenicity Epidemiology -Facultative anaerobes -Bacilli that occur singly, in pairs, or in chains -form endospores -Pathogenic strains produce anthrax toxins -humans contract from infected animals -Transmission occurs via one of three routes → Inhalation of spores → Inoculation of spores through break in the skin → ingestion of spores Diseases (only causes anthrax!) Gastrointestinal anthrax -Rare in humans Cutaneous anthrax -Produces ulcer called an eschar -Fatal in 20% of untreated patients Inhalation anthrax -Requires inhalation of airborne endospres -High mortality rate Diagnosis, treatment, and prevention Diagnosis -Large, nonmotile, gram-positive bacilli in lung or skin samples Treatment -Many antimicrobials are effective Prevention -Control of disease in animals by vaccine -Effective vaccine available for military →requires multiple doses and boosters
Bacillus cereus (the shits and runs of Dr.Fu Manchu) The basics Characteristics Epidemiology -gram-positive spore-forming rod -facultative anaerobe -commonly found in soil -found in animal GI tract as normal flora, competes with salmonella in chx -Common cause of “fried rice syndrome” →spores & toxins can survive at 100C, improper storage of food at room temp for some time →8-16 hour incubation period →emetic and diarrheal toxins Diagnosis, Treatment, and Prevention Diagnosis -Vomiting and explosive diarrhea, usually within hours of ingestion of contaminated food Culturing organisms from suspected food item Treatment -Symptomatic treatment for intoxication, no secondary cases, self-limiting. -More care for children and elderly Prevention -Proper food storage and cooking temperatures Clostridium Perfringens The basics Characteristics Pathogenesis Epidemiology -Large nonmotile bacillus -most frequently isolated from clinical specimens -Produces toxins that can cause irreversible damage to the body -Grows in the digestive tracts of animals and humans Diseases Food poisoning -abdominal cramps and watery diarrhea Gas gangrene -Trauma introduces endospores into body -Endospores germinate and cause necrosis
Clostridium botulinum The basics Characteristics Pathogenicity Epidemiology -anerobic -Endospore-forming bacillus -common in soil and water -Botulism results when the endospores germinate and produce botulism toxins (food poisoning) -Botulism toxins → C. Botulinum strains produce seven distinct toxins → among the deadliest known toxins → Bind neurons and prevent muscle contractions *remember to draw out the steps! -Botulism is an intoxication with three manifestations -Foodborne botulism -Infant botulism -Wound botulism Diseases Foodborne botulism -Death can result from asphyxiation -slow recovery from growth of new nerve cell endings Infant botulism -Results from the ingestion of endospores -Paralysis and death are rare Wound botulism -Contamination of a wound by endospores -Symptoms similar to foodborne botulism Diagnosis, Treatment, and prevention Diagnosis -Symptoms are diagnostic Treatment -Wash intestinal tract to remove Clostridium -Administer neutralizing antibodies against botulism toxin -Administer antimicrobial drugs in infant and wound botulism cases Prevention -Proper canning of food (beware of the “hissing cans”) -Infants under 1 year should not consume honey
Clostridium tetani The Basics Characteristics Pathogenicity Epidemiology -Motile -Obligately anaerobic -bacilli with a terminal endospore(looks like chx drumstick) -ubiquitous in soil, dirt, dust, and GI tract of animals and humans -Tetanus results when endospores germinate and produce tetanus toxin -Tetanospasmin toxin (tetanus toxin) →released by C. tetani cells when they die →potent neurotoxin →causes continuous muscle contractions -most cases occur in less-developed countries → due to inadequate medical care and lack of vaccination -Recovery requires growth of new neuronal terminals -Mortality rate about 50% *Diseases draw out action tetanus toxin Lockjaw -tightening of the jaw and neck muscles Spasms and contractions can spread to other muscles Unrelenting contraction of the diaphragm can cause death Diagnosis, Treatment, and Prevention Diagnosis -Characteristic muscular contraction Treatment -Cleansing of wounds to remove endospores -Administer immunoglobulin against tetanus toxin -Administer antimicrobial drugs -Active immunization with tetanus toxoid Prevention -Immunization with tetanus toxoid vaccine
