Bacteria
Gram-Positive Bacteria
Staphylococcus spp. Cocci (grapes) / Catalase + / Facultative anaerobe / Pyogenic & Toxin-related diseases / Biofilm
Staphylococcus aureus* ● Coagulase + ● Nasal & skin
● Beta-hemolysis ● Hospital-acquired bloodstream infections; MRSA
● Protein A (prevents phagocytosis) ● Staphylococcal scalded skin syndrome (SSSS): exfoliative toxin A & B → stratum granulosum → skin peeling
(desmoglein); generalized form of bullous impetigo
● Staphylococcal toxic shock syndrome (TSS): superantigen TSST-1 (menstrual TSS) & enterotoxin B/C
(non-menstrual TSS) → fever, shock, multisystem involvement cuz too many T cell produced
● Staphylococcal food poisoning: enterotoxin A
● Infective endocarditis, osteomyelitis
Staphylococcus lugdunensis ● Coagulase - ● Skin
● Infective endocarditis, bone & prosthetic joint infections, peritonitis
● Skin & soft tissue infection: abscess, cellulitis, pustules
Staphylococcus epidermidis ● Coagulase - ● Skin; accidental pathogen → enter thru wound
● Urease + ● Biofilm formation (on devices); endocarditis
Staphylococcus saprophyticus ● Coagulase - ● Perineum, rectum, urethra, cervix, GI; young female
● Urease + ● Lower UTI: dysuria, urinary freq., cystitis
● Pyelonephritis, ureteritis, prostatitis
Streptococcus spp. Cocci (chains) / Catalase - / Facultative anaerobe
Streptococcus pneumoniae* ● Alpha-hemolysis ● Nasopharyngeal colonization
● Optochin sensitivity ● Pneumonia, meningitis, sinusitis, otitis media
● Diplococci (lancet-shaped) ● Pneumococcal pneumonia: enter alveolar & kill macrophages → purulent sputum, chestpain
● Polysaccharide capsule (prevent
phagocytosis)
Viridans Streptococcus ● Alpha-hemolysis ● Oropharynx, skin, GI tract → opportunistic
● Optochin resistant ● Abscess, meningitis, endocarditis (5 grps)
● Cocci chain ● S. mutans: dental caries; endocarditis
● S. sanguis: endocarditis
● S. anginosus: dental caries; abscess
● S. mitis: endocarditis
● S. salivarius (similar to S. bovis): endocarditis
Streptococcus pyogenes ● Beta-hemolysis ● Exotoxin-mediated
(Group A Streptococcus) ● M protein (prevent phagocytosis) 1) Scarlet fever: rash (neck → trunk → extremities) spares face, strawberry tongue
● Hyaluronic capsule 2) Streptococcal toxic shock syndrome
● Streptolysin O ● Direct invasion
1) Pharyngitis: tonsillar white exudates, enlarged lymph nodes, redness of pharynx
, 2) Skin infection: folliculitis/cellulitis, necrotizing fasciitis
● Antibody-mediated
1) Rheumatic fever (can follow pharyngitis): inflam of heart, joints, subcutaneous tissues & CNS; valvular
damage & cardiac failure
2) Post-streptococcal glomerulonephritis (can follow pharyngitis/skin infection): immune complex deposit
Streptococcus agalactiae ● Beta-hemolysis ● Genital area & lower GI
(Group B Streptococcus) ● Severe infection in newborn, elderly, immunocompromised
● Infection of female genital tract, infants pneumonia, endocarditis, osteomyelitis, skin & soft tissue infections,
arthritis, meningitis, UTI
● Vertical transmission
Streptococcus bovis ● Gamma hemolysis ● Formerly known as S. gallolyticus
(Group D Streptococcus) ● GI tract of humans & cows
● Bacteremia endocarditis
Streptococcus suis* ● Polysaccharide capsule ● Pigs; zoonotic disease thru close contact, eating of contaminated pork
● Acute bacterial meningitis
Enterococci spp. (Group D) Cocci (oval-shaped) / Facultative anaerobe
Enterococcus faecalis ● Gamma hemolysis ● GI tract, oval cavity, vagina
● Lower UTI in older man
Enterococcus faecium ● Uncomplicated cystitis in young women
● Bacteremia & endocarditis
● Healthcare-associated; biofilm
Clostridium spp. Bacilli / Anaerobic / Soil & marine sediments, intestinal tract of animals / Decompose protein or form toxins
Clostridium perfringens* ● Beta hemolysis ● Clostridial myonecrosis (gas gangrene): crepitation in subcutaneous tissue & muscles, foul-smelling
● Alpha toxin discharge, rapidly progressing necrosis, shock
● Food poisoning: enterotoxin; diarrhea w/o vomiting or fever
Clostridium tetani* ● Tetanospasmin ● Soil and animal feces; thru wound
● Degrade synaptobrevin (VAMP2) → inhibit glycine and GABA → muscle does not relax
● Muscular spasms; opisthotonus (backward arching of head; severe)
● Death from respiratory interference
Clostridium botulinum* ● Spores resistant to heat ● Eating food contaminated w/ toxin or spore (canned food, honey)
● Botulinum (heat-labile) toxin ● Proteolysis of SNARE protein → inhibit acetylcholine release → lack of muscle contraction
● Visual disturbances, inability to swallow, speech difficulty → respiratory paralysis, cardiac arrest
● Infant botulism: honey (spore)
● Floppy baby syndrome, flaccid paralysis
Clostridioides difficile* ● Obligate anaerobe (but can ● Ingest spores from healthcare setting (nosocomial); antibiotic use
survive in aerobic using spores) ● Acute diarrheal illness due to pseudomembranous colitis
● Toxins A & B ● Spore germination → bacteria proliferate in colon → erosion of mucosa and pseudomembrane formation
