staphylococcus and streptococcus

Staphylococcus Morphology?

Gram-positive cocci in clusters ("grape-like").

Staphylococcus Motility?

Non-motile; lack flagella.

Staphylococcus Oxygen requirement?

Facultative anaerobes. Can survive both with and without

Staphylococcus Catalase test result?

Catalase positive.

Staphylococcus Halotolerance?

Can grow in high-salt environments.

How are Staphylococcus species classified?

By coagulase production: S. aureus = coagulase positive; S. epidermidis, S. saprophyticus = coagulase negative.

Staphylococcus epidermidis Normal habitat?

Resident skin microbiota; transmitted via direct contact.

Staphylococcus epidermidis Pathogenesis?

Opportunistic; invades via medical/prosthetic devices; forms biofilm.

Staphylococcus epidermidis Diseases caused?

Nosocomial bloodstream infections; prosthetic valve endocarditis.

Staphylococcus epidermidis Resistance?

High resistance to beta-lactams, erythromycin, clindamycin, and Bactrim (~50% each).

Staphylococcus epidermidis Preferred treatment?

IV vancomycin; sometimes valve replacement and long antibiotic course.

Staphylococcus saprophyticus Normal habitat?

Genitourinary and gastrointestinal tracts.

Staphylococcus saprophyticus Common disease?

Uncomplicated UTI in young sexually active females.

Staphylococcus saprophyticus Treatment?

Nitrofurantoin or Bactrim (TMP-SMX).

Staphylococcus aureus Coagulase test result?

Positive.

Staphylococcus aureus Clinical importance?

Major pathogen causing wide variety of diseases; both community and hospital acquired.

Staphylococcus aureus Key resistant strain?

MRSA - methicillin-resistant S. aureus.

Staphylococcus aureus Virulence factors?

Protein A, leukocidins, superantigens (SEB, TSST-1), exfoliative toxins (A & B).

Staphylococcus aureus Function of Protein A?

Binds Fc of IgG (immune evasion) and Fab of B cell receptor (induces apoptosis).

Staphylococcus aureus Pore-forming toxins?

Leukocidins - lyse RBCs and WBCs.

Staphylococcus aureus Superantigen toxins?

Staphylococcal Enterotoxin B (SEB), Toxic Shock Syndrome Toxin (TSST-1).

Staphylococcus aureus Exfoliative toxins?

Exfoliative Toxin A & B → scalded skin syndrome.

S. aureus Diseases Most common cause of?

Skin and soft tissue infections (SSTIs): folliculitis, boils, carbuncles, impetigo, abscesses.

S. aureus Diseases Treatment of SSTIs?

Incision and drainage (I&D) essential; antibiotics if severe; avoid beta-lactams (CA-MRSA common).

S. aureus Diseases Bone infection?

Osteomyelitis - S. aureus is most common cause.

S. aureus Diseases Toxin-mediated diseases?

Scalded skin syndrome (exfoliative toxins), food poisoning (SEB), toxic shock syndrome (TSST-1).

Staphylococcal Food Poisoning Source?

Toxin-contaminated food (meat mixes, ham, dairy).

Staphylococcal Food Poisoning Toxin?

Staphylococcal Enterotoxin B (heat-stable superantigen).

Staphylococcal Food Poisoning Incubation period?

Rapid - 1-2 hours.

Staphylococcal Food Poisoning Symptoms?

Vomiting, diarrhea, stomach cramps (no fever).

Staphylococcal Food Poisoning Exam hint?

Rapid food poisoning (<2 hr) → S. aureus, not E. coli or Salmonella.

Toxic Shock Syndrome (TSS) Cause?

TSST-1 (superantigen toxin).

Toxic Shock Syndrome (TSS) Commonly seen in?

Women using superabsorbent tampons; post-surgical infections.

Toxic Shock Syndrome (TSS) Symptoms?

Fever, rash, hypotension, multi-organ failure.

Toxic Shock Syndrome (TSS) Treatment?

Clindamycin (inhibits toxin production) + supportive therapy.

Staphylococcal Laboratory Diagnosis Media types?

Blood agar (differential), Mannitol Salt Agar (selective + differential), Baird Parker agar (selective + differential).

Staphylococcal Laboratory Diagnosis Mannitol Salt Agar?

High salt inhibits most organisms; mannitol fermentation → yellow colonies (S. aureus).

Staphylococcal Laboratory Diagnosis Baird Parker Agar?

S. aureus produces black colonies with clear halos (lecithinase activity).

Staphylococcal Laboratory Diagnosis Coagulase test?

Positive for S. aureus; negative for S. epidermidis and S. saprophyticus.

Staphylococcal Laboratory Diagnosis Catalase test?

Positive for all Staphylococcus spp.

Staphylococcal Laboratory Diagnosis Oxidase test?

Negative for all Staphylococcus spp.

Streptococcus and Enterococcus General Traits Morphology?

Gram-positive cocci in chains.

Streptococcus and Enterococcus General Traits Catalase test result?

Negative (differentiates from Staphylococcus).

Streptococcus and Enterococcus General Traits Oxygen requirement?

Facultative anaerobes.

Streptococcus and Enterococcus General Traits Hemolysis types?

Alpha (partial, green), Beta (complete, clear), Gamma (none).

Hemolysis Patterns Streptococcus pyogenes?

Beta-hemolytic (complete, clear zone).

Hemolysis Patterns Streptococcus agalactiae?

Narrow zone of beta-hemolysis.

Hemolysis Patterns Streptococcus pneumoniae?

Alpha-hemolytic (greenish).

Hemolysis Patterns Enterococcus faecalis?

Gamma (non-hemolytic).

Streptococcus pyogenes (Group A Strep, GAS) Key virulence factors?

Capsule, M protein, lipoteichoic acid (LTA), pyrogenic exotoxins, streptolysins S/O, hyaluronidase, streptokinase, DNases.

Streptococcus pyogenes (Group A Strep, GAS) M protein function?

Binds factor H → prevents opsonization; highly antigenic.

Streptococcus pyogenes (Group A Strep, GAS) Diseases?

Pharyngitis, impetigo, cellulitis, necrotizing fasciitis, scarlet fever, rheumatic fever, glomerulonephritis.

Streptococcus pyogenes (Group A Strep, GAS) Necrotizing fasciitis?

Rapidly spreading soft-tissue infection → surgical debridement + penicillin/clindamycin.

Streptococcus pyogenes (Group A Strep, GAS) Scarlet fever?

Rash, "strawberry tongue"; delayed-type hypersensitivity to pyrogenic exotoxin A.

Streptococcus pyogenes (Group A Strep, GAS) Post-infectious diseases?

Rheumatic fever (autoimmune), glomerulonephritis (immune complex).

S. pyogenes Lab Diagnosis Blood agar?

Small, white, beta-hemolytic colonies.

S. pyogenes Lab Diagnosis Catalase?

Negative.

S. pyogenes Lab Diagnosis Oxidase?

Negative.

S. pyogenes Lab Diagnosis Bacitracin sensitivity?

Sensitive (differentiates from S. agalactiae).

Streptococcus agalactiae (Group B Strep, GBS) Normal habitat?

GI and genitourinary tract (20-30% of women).

Streptococcus agalactiae (Group B Strep, GBS) Transmission?

During childbirth → neonatal meningitis or sepsis.

Streptococcus agalactiae (Group B Strep, GBS) Hemolysis?

Narrow beta-hemolysis.

Streptococcus agalactiae (Group B Strep, GBS) Catalase?

Negative.

Streptococcus agalactiae (Group B Strep, GBS) CAMP test?

Positive.

Streptococcus agalactiae (Group B Strep, GBS) Bacitracin?

Resistant.

Streptococcus agalactiae (Group B Strep, GBS) Treatment?

Penicillin or ampicillin.

Streptococcus pneumoniae (Pneumococcus) Morphology?

Gram-positive, lancet-shaped diplococcus.

Streptococcus pneumoniae (Pneumococcus) Normal habitat?

Nasopharynx (10% adults, higher in children).

Streptococcus pneumoniae (Pneumococcus) Major virulence factors?

Capsule (anti-phagocytic, antigenic), pneumolysin (cytolytic toxin).

Streptococcus pneumoniae (Pneumococcus) Diseases?

Otitis media, sinusitis, lobar pneumonia, meningitis, sepsis (esp. in sickle cell disease).

Streptococcus pneumoniae (Pneumococcus) Lab findings?

Alpha-hemolytic, mucoid colonies; catalase negative; optochin sensitive; bile soluble.

Streptococcus pneumoniae (Pneumococcus) Treatment?

Beta-lactams, fluoroquinolones, vancomycin.

Streptococcus pneumoniae (Pneumococcus) Prevention?

Vaccines: Pneumovax and Prevnar (capsular polysaccharides).

Staphylococcus vs Streptococcus?

Staph = clusters, catalase positive; Strep = chains, catalase negative.

S. aureus vs S. epidermidis?

Coagulase positive vs negative.

S. pyogenes vs S. agalactiae?

Bacitracin sensitive vs resistant.

S. pneumoniae vs Viridans strep?

Optochin/bile sensitive vs resistant.