Gram Positive Bacteria Flashcards
What are the 3 groups of streptococci based on lysis of red blood cells?
1) beta-hemolytoc- completely lyse red blood cells
2) alpha-hemolytic- partially lyse red blood cells
3) gamma-hemolytic- unable to hemolyze RBCs
In addition to RBC lysis, what other characteristic is commonly used to classify strep?
Lancefield antigens (on c carbohydrate on cell wall). Lacefield group A, B, and D contain pathogens
Basic description strep pyogenes
Group A (lancefield group A) beta hemolytic
What diseases does strep pyogenes cause by local invasion/ exotoxon release?
Streptococcal pharyngitis
Strep skin infections
Scarlet fever
Strep toxic shock syndrome
What antibiotic is used for group a beta hemolytic strep or strep pyogenes?
Penicillin G + clindamycin (clindamycin shuts down protein synthesis if pyrogenic toxin)
What is the species name for group B strep?
Streptococcus agalactiae
Who does group B strep primarily impact?
Babies
3 most common pathogens associated with meningitis in infants
E coli, listeria monocytogenes, and group B strep
Organisms that cause meningitis after 3 months of age
Neisseria meningitis, haemophilus influenzae
Symptoms group B strep pregnant women
Bacteremia, sepsis, stillbirth, spontaneous abortion
Strep commonly part of GI tract, esp gingival crevices and nasopharynx
Viridans group strep
3 infections viridans streptococci cause
1) dental infections
2) endocarditis
3) abcessses
Describe strep bovis
Group D strep, lives in GI, often affiliated with colon cancer
Describe enterococcus (faecalis and faecium)
Normal flora in intestines, common HAI- UTI, wound infection, native and prosthestic valve endocarditis, bacteremia via intravenous catheters, sepsis. Drug resistant (VRE)
What illnesses does strep pneumo cause?
Bacterial pneumonia
Meningitis in adults
Otitis media in children
What does strep pneumo look like?
No lancefield antigens, lancet shaped grams positive diplococci
Strep pneumo virulence factor
Capsule with 83 capsule serotypes
Which gram positive organism is catalase positive?
Staph
What are the 3 pathogenic staph species?
Staphylococcus aureus
Staphylococcus epidermidis
Staphylococcus saprophyticus
How do staph hemolyze RBCs on sheep agar?
Beta hemolytic- lyse red blood cells
Which staph is coagulase positive (causes blood to clot)?
Staph aureus
What proteins does staph aureus have that disable our immune defenses?
- Protein A (protects from opsonization)
- Coagulase
- Hemolysins
- Leukocidins(mrsa- panton valentine leukocidin)
- Penicillinase (beta lactamase)
- Novel penicillin binding protein (transpeptidase)
Toxins associated with staph aureus
All exotoxins
1. enterotoxins (food poisoning)
2. Toxic shock syndrome toxin- super antigen
3. Exfoliatin
Staph diseases caused by exotoxon release
- Gastroenteritis
- Toxic shock syndrome
- Scalded skin syndrome
Staph aureus diseases from direct organ invasion
- Pneumonia
- Meningitis
- Osteomyelitis
- Acute bacterial endocarditis
- Septic arthritis
- Skin infections
- Bacteremia/ sepsis
- UTI
Symptoms of toxic shock syndrome
- high fever
- diffuse erythematous rash
- desquamation of palms and soles
- vomiting and diarrhea
- septic shock
Do antibiotics cure toxic shock syndrome?
No because it’s from toxin
Dif between endocarditis from staph aureus and strep
Staph very fast and aggressive, strep slow onset
Sites where people typically colonized with staph aureus
Nasopharynx and skin folds
What type of antibiotics are community mrsa typically susceptible to?
Clindamycin and trimethoprim-sulfamethoxaxole
First line defense antibiotic for HAI staph aureus? If mrsa?
Methecilin, nafacillin
Vancomycin
describe staph epidermidis
Part of normal skin flora, coagulase negative
What patients are at highest risk for staph epidermidis ?
Foley catheters and IV lines
Prosthetic devices
How many blood cultures are needed for staph epidermidis? Why?
2, regular contaminant from skin
How staph epidermidis causes bacteremia / infections from devices such as catheters
Forms biofilms, bacteria leeches out
Second leading cause of UTI in sexually active women
Staph saprophyticus
What is an aerobic gram positive spore forming rod?
Bacillus
What is an anaerobic gram positive spore forming rod?
Clostridium
What are the two pathogenic types of bacillus?
Bacillus anthracis and bacillus cereus
What is the most common route of entry for anthrax?
Cutaneous, releases exotoxin which causes tissue necrosis
Describe pulmonary anthrax
Concern for terrorism, taken into alveoli, gets into macrophages and lymphatic system
What are the antibiotics used for bacillus anthracis?
Doxy and cipro
Describe bacillus anthracis
Spore forming, gram positive rod, capsule made of protein which prevents phagocytosis, exotoxins
Describe bacillus cereus
Gram positive, spore forming rods, aerobic, motile, non-encapsilated, resistant to penicillin and causes food poisoning.
Describe clostridium botulinum
Gram positive, spore forming rod, anaerobic, spores enter food and neurotoxins block release of acetylcholine, causes flaccid muscle paralysis.
Describe clostridium tetani
Gram positive, spore forming rod, anaerobic, transmitted by spores on object entering into puncture wound, releases exotoxin tetanospasmin, causes sustained contraction of muscles
Describe clostridium perfringens
Gas gangrene, spores contaminate wounds, release exotoxins, anaerobic, gram positive spore forming rods
What can Clostridioides difficile cause?
Pseudomembranous colitis
What toxins does C. Diff release?
Toxin A- causes diarrhea, Toxin B- cytotoxic to colon cells
More pathogenic strain C. Diff since 2002
NAP1/BI/027
Dx for c. diff
Test for toxins, then PCR of stool, 3 or more liquid bowel movements in 24 hours
Risk c diff
Antibiotics in past month
Treatment c. Diff
Oral vacomycin, fidaxomicin
What are the gram positive, non spore forming rods? What age group do they impact?
Corynebacterium diphtheriae and Listeria monocytogenes
Pediatric
Describe clinical illness for corynebacterium diptheria
Forms grayish pseudomembrane in pharynx and releases exotoxin into bloodstream that damages heart and neural cells
Agar for diptheria
Potassium telluride and loefflers coagulated blood serum
Describe other non-diptheria corynebacterium, env and how they differ.
Normal inhabitants of water, soil, skin, mucous membranes. Common specimen contaminant.
Cause HAIs
Resistant to antibiotics, must be treated with IV vanco
What are common corynebacterium HAIs organisms? Infections?
Corynebacterium jeikeium
Corynebacterium urealyticum, corynebacterium amycolatum
Corynebacterium striatum
Surgical wound infections
catheter/prosthetic valve infections
native/ prosthetic endocarditis
Describe rhodococcus equi
Formerly corynbacterium (gram positive rod like, aerobic), but partially acid fast. Causes necrotizing pneumonia in immunocompromised and AIDS patients. Looks like TB or norcardia but lung imaging shows modules and cavities that form air fluid levels
Basics of listeria monocytogenes
Gram positive rod, facultative anaerobe, non spore forming, motile, grows at low temps
Virulence factor listeria
Listeriolysin O- avoids being killed by macrophages
Risks for listeria
- Third trimester pregnancy- sepsis, bacteremia, neonatal death or premature birth with active infection
- Fetus and neonates- meningitis
- Elderly and immunocompromised - second leading cause of meningitis in people over 50 (behind pneumococcus)
What is a facultative intracellular organism? Example?
Survives either outside or within cells
Listeria monocytogenes
CSF bacterial meningitis
High neutrophils, high protein, low glucose
What diseases can strep cause by delayed antibody mediated release?
Rheumatic fever
Glomerulonephritis
