Gram Positive Bacteria Flashcards
(23 cards)
Streptococcus Viridans
Gram Positive Coccus
Catalase Negative
Alpha hemolytic (green on agar = viridans-partial hemolysis)
Diseases: endocarditis
Virulence factors: teichoic acid???
Transmission/Pathogenesis: comes from oral cavity (commensal) after dental procedures
Streptococcus Pneumoniae (aka pneumococcus)
Gram Positive Coccus
Catalase Negative
Alpha hemolytic (green on agar-partial hemolysis)
Diseases: Pneumonia, Otitis Media, Sinusitis, Infant + Adult meningitis)
Epi: alcohol, smoking, asthma, splenectomy, immunocompromised, extremes of age
Virulence factors: capsule, IgA protease, phase variation, teichoic acid, pneumolysin, sialidase
Transmission/Pathogenesis: cell wall proteins bind to sialic acid, platelet activating factor receptors;
IgA protease inhibits IgA, removed via IgG-mediated opsonization in spleen
Signs/Symptoms: pleuritic chest pain and cough, rusty sputum, lobar pneumonia, empyema (collection of pus in natural anatomic cavity, ie pleural cavity)
Unique dx methods: blood/sputum culture (lancet-shaped chains), urine antigen, low glucose in CSF in meningitis
Treatment/Notes: Penicillin –> if resistance: 3G cephalasporin –> if high level resistance: vancomycin/levofloxacin (3G quinolone): 20x dose if CNS involved; 32-valent vaccine (pneumovax) for adults, conjugated (Prevnar) for children
Streptococcus pyogenes (Group A)
Gram positive coccus
Catalase negative
Beta hemolytic (clear on agar-full hemolysis)
Diseases: strep throat, toxic shock syndrome, impetigo, rheumatic fever
Epi: 5-15 year olds, winter, spring
Virulence factors: toxin, hyaluronic acid capsule, M proteins in pili
Transmission/pathogenesis: humans are reservoir, spread by droplets/nasal secretions, strains with M protein and hyaluronidate more easily transmitted, form colonies in oropharynx
Signs/symptoms: fever, erythematous pharynx with tonsillar exudates, palatal petechiae, sore throat, pain with swallowing, lymphadenitis, NO coryza (nasal congestion), cough, diarrhea; can lead to rheumatic fever, glomerulonephritis
Unique Dx methods: rapid strep specific but not sensitive, culture is gold standard; anti-streptolysin-O = past infection
Treatment/Notes: *Penicillin/Amoxicillin –> if allergy: macrolides/1G cephalosporin
Streptococcus agalactiae (Group B)
Gram Positive Coccus
Catalase negative
Beta hemolytic (clear on agar-total hemolysis)
Diseases: neonatal meningitis, sepsis
Virulence factor: capsule
Transmission/pathogenesis: often commensal in childbearing women, gets aspirated by baby; capsule mimics mammalian polysaccharide
Signs/symptoms: high grade bacteremia, sepsis, meningitis
Unique dx methods: screen colonized mothers, pre-term, multiple births
Treatment/Notes: *penicillin/amoxicillin –> if allergy: macrolides/1G cephalosporin
Enterococci
Gram positive coccus
Catalase negative
Gamma hemolytic (red on agar-no hemolysis)
Diseases: acute bacterial prostatitis, endocarditis, neonatal meningitis
Treatment/Notes: *Penicillin/ampicillin –> if penicillin-resistant: vancomycin –> if endocarditis, aminoglycoside for synergy
Vancomycin-Resistant Enterococcus
Gram positive coccus
Catalase negative
Gamma hemolytic (red on agar-no hemolysis)
Diseases: VRE
Transmission/Pathogenesis: D-Ala-D-Lac confers resistance
Treatment/Notes: Linez/Dapto/Streptogramin
Staphylococcus epidermidis
Gram positive coccus Catalase positive Coagulase negative Diseases: endocarditis Epi: prosthesis Virulence factors: polysaccharide Transmission/Pathogenesis: normal skin flora, but can form biofilms on prostheses Sigs/Symptoms: pain, device loosening Treatment/notes: frequently contaminates cultures
Staphylococcus saprophyticus
Gram-positive coccus Catalase positive Coagulase negative Diseases: UTI Transmission/Pathogenesis: second most common cause of uncomplicated UTI
Methicillin-Resistant Staphylococcus Aureus (MRSA)
Gram-positive coccus
Catalase positive
Coagulase positive
Diseases: endocarditis, skin lesions
Epi: saunas, football players
Transmission/Pathogenesis: mutated PBP (2a) results in resistance to all beta lactams, penicillin, cephalosporins
Treatment/notes: vancomycin > (linezolid, diaptomycin, streptogramin)
Staphylococcus Aureus
Gram-positive coccus
Catalase positive
Coagulase positive
Diseases: endocarditis, skin lesions, toxic shock syndrome
Epi: 20-40% of population has; IVDU, DM, HIV
Virulence factors: capsule, coagulase, hyaluronidase, beta-lactamase, TSST1, alpha toxin, exfoliative toxin, leukocidin
Transmission/Pathogenesis: human is reservoir, mostly caused by auto-inoculation from commensal s.aureus (anterior nares, skin), but hospital can be person-person, mechanical breach in skin –> tissue damage –> metastatic seeding; host response primarily PMN
Mycobacterium Tuberculosis
“Gram-positive rod” (impervious to gram stain)
Acid-fast positive
Diseases: tuberculosis
Transmission/pathogenesis: infected person coughs, sneezes, talks, TB enters your lungs; then replicates both extracellularly and in alveolar macrophages; gets metastatic foci in regional nodes and hematogenous spread; can also affect nodes, bones, kidneys
Signs/symptoms:
- primary infection with resolution*: 85% asymptomatic or viral syndrome with enlargement of hilar/peribronchial nodes and calcified granulomas
- primary infection with progression*: kids miliary TB, dissemination, CNS
- Tuberculous pleurisy*: hypersensitivity reaction
- primary infection in adolescents*: caviation of lungs, most infectious people fall into this category
- primary infection in AIDS*: outbreaks in 80s, 90s
- overwhelming TB*: rapid uncontrolled dissemination
- reactivation*: most cases; 10-15% of those infected will reactivate, due to immunosuppression/immunocompromise, malnutrition, old age, etc.; 85% of reactivation affects lungs
Unique dx methods: sputum smear; sputum culture in liquid media (gold standard) nucleic acid amplification, RFLP, CXR: upper lobe infiltrates +/- apical/sub-apical cavitations, or miliary pattern, biopsy if at risk (HIV, + CXR, etc.), test PPD, if positive (5 mm+ for HIV/close contacts/+CXR, 10 mm otherwise), then use ELISPOT assay (since PPD can turn positive from BCG vaccine)
Treatment/notes: *RIPE: *
- Rifampin* (cidal, kills solid caseous material, AE: GI upset, DDIs, orange urine/sweat/tears)
- Isoniazid*: (cidal, CNS penetration, AE: hepato/neurotoxicity),
- Pyrazinamide*: (cidal within macrophages, reduces Tx from 9 months to 6, AE: can’t use in pregnancy, hyperuricemia and abnormal LFTs)
- Ethamubtol*: (not cidal, used to prevent resistance, safe in pregnancy, AE: retroulbar neuritis)
Begin with all 4 while sensitivity testing, treat for 6-9 months; always use at least 2@
Mycobacterium avium intracellulare (MAI)
“Gram-positive rod” (impervious to gram stain)
Acid-fast positive
Disease: acute viral hepatitis
Bacillus cereus
Gram-positive rod Special features: aerobic, motile Disease: food poisoning Epi: fried rice Virulence factors: neurotoxin (emetic + diarrheal) Transmission/Pathogenesis: food poisoning associated with fried rice-more likely to elaborate toxins in starchy environment Signs/symptoms: watery diarrhea Treatment: none
Bacillus anthracis
Gram-positive rod
Special features: aerobic, non-motile
Disease: anthrax (skin, inhalation, intestinal)
Epi: inhalation-working with animal hides
Virulence factors: 3 exotoxins: EF, LF, PA
Transmission/Pathogenesis: no person-person spread, spores (viable for years) touch skin, get inhaled or get eaten; local necrosis, regional hemorrhagic lymphadenitis, anthrax septicemia, death
Signs/symptoms:
Cutaneous: vesicles –> ulcers –> painless black eschars
Inhalation: pleural effusion, necrotizing mediastinitis
Intestinal: local necrosis, hemorrhagic lymphadenitis
Unique diagnostic methods:
Cutaneous: skin biopsy/vesicular fluid aspiration,
Inhalation: CXR to assess for adenopathy/effusion
Treatment: Cipro + doxy; anthrax Ig for very sick patients, mortality very high
Clostridium botulinum
Gram-positive rod
Special features: anaerobic, motile
Diseases: Botulism
Epi: syrups, honeys, canned foods (A, B), preserved fish (E)
Virulence factors: neurotoxin (botulinum toxin)
Transmission/Pathogenesis:
foodborne: canned foods, preserved fish
infant: syrups, honeys contaminated with spores
wound botulism from skin popping, asymptomatic carriage
Signs/symptoms:
foodborne: 12-36 hours after ingesting toxin, muscle weakness, symmetric CN palsies (3,4,6,7 –> 4Ds: diplopia, dysphonia, dysarthria, dysphagia) –> respiratory failure
infant: muscle weakness (floppy baby)
Treatment/Notes: supportive care, gastric lavage, metronidazole, botulinum Ig (BIG)
Costridium difficile
Gram-positive rod
Special features: anaerobic, motile
Diseases: antibiotic-associated diarrhea, ulcerative colitis
Epi: clindamycin is classic causative antibiotic
Virulence factor(s): toxin
Transmission/Pathogenesis: asymptomatic colonization exacerbated by antibiotics eliminating endogenous gut flora
Signs/symptoms: diarrhea, pseudomembranous colitis
Treatment/notes: oral vancomycin, metronidazole, d/c other antibiotics, pooled IV Ig for severe disease
Clostridium tetani
Gram-positive rod
Special features: anaerobic, motile
Diseases: tetanus
Epi: unvaccinated
Virulence factors: tetanospasmin neurotoxin
Transmission/Pathogenesis: soils, animal GI tracts; spore gets into wound, neurotoxin travels in retrograde axonal transport to CNS, irreversibly blocks GABA
Signs/symptoms: muscle spasms (tetanus, risus sardonicus, bulbar/paraspinal muscles, trismus (lockjaw), opisthotonos, autonomic symptoms)
Unique diagnosis methods: clinical
Treatment/notes: wound debridement, metronidazole, tetanus Ig, vaccination with tetanus toxoid
Clostridium perfringens: gas gangrene
Gram-positive rod
Special features: anaerobic, non-motile
Disease: gas gangrene
Epi: poor prognosis
Virulence factor: alpha toxin has lecithinase which lyses endos and blood cells, beta toxin is necrotizing
Transmission/Pathogenesis: Type A in soil, feces, Types B-E in intestinal tracts of animals; happens after traumatic wounds with muscle damage
Signs/symptoms: rapidly progressing cellulitis, fasciitis, myonecrosis; gas is metabolic product of bacteria, get necrosis + gas, local swelling, bullae, muscle necrosis, shock
Treatment/notes: debridement, high dose penicillin, hyperbaric O2
Clostridium perfringens: diarrhea
Gram-positive rod
Special features: anaerobic, non-motile
Disease: diarrhea
Virulence factor: enterotoxin
Transmission/pathogenesis: Type A in soil, feces, Types B-E in intestinal tracts of animals
Signs/symptoms: self-limited gastroenteritis with diarrhea
Treatment/notes: self-limited
Actinomyces israelii
Gram-positive rod
Special features: anaerobic, non-motile
Disease: (Cervicofacial) Actinomycosis
Epi: oral trauma/poor dentition
Virulence factors: sulfur granules (but only when mucosal barriers disrupted)
Transmission/pathogenesis: no person-person spread, endogenous disease, found in poor oral hygiene, oral trauma, dental procedures
Signs/symptoms: chronic granulomatous lesions that become suppurative (pus-containing)
Unique diagnosis methods: infected fluid shows macroscopic colonies with grains of sand (= sulfur granules)
Listeria monocytogenes
Gram-positive rod
Special features: facultative anaerobic, motile
Disease: neonatal meningitis
Epi: soft, unpasteurized cheese
Transmission/Pathogenesis: immunocompromised mom eats cheese, gets flu-like illness, baby gets listeria
Signs/symptoms: early seizures, neurological deficits
Treatment/notes: don’t eat unpasteurized cheese while pregnant!
Corynebacterium diphtheriae
Gram-positive rod
Special features: Facultative anaerobic, non-motile
Disease: diphtheria (pharyngitis)
Epi: rare bc of TDAP vaccine
Virulence factor: toxin
Transmission/pathogenesis: conversion from phage that encodes toxin
Signs/symptoms: pharyngitis, low fever, pseudomembrane on tonsils/pharynx/nasal cavity, myocarditis (inflammation of heart muscle), peripheral neuropathy
Unique diagnosis methods: ELEK test
Mycoplasma pneumoniae
“Gram-positive rod” (won’t stain bc no cell wall but in this section)
Special features: no cell wall
Disease: “walking” pneumoniae
Epi: school-age children, young adults
Virulence factors: TLR-2, P1
Transmission/Pathogenesis: TLR-2 binds to respiratory epithelium, P1 facilitates attachment to sialic receptors on respiratory epithelium, remains extracellular but destroys cilia, incites cytokine storm!
Unique diagnostic techniques: serology
Treatment/notes: macrolides/azalides, quinolones +/- tetracycline, can’t use beta lactams
