Gram Positive Cocci

What are common characteristics of gram positive cocci?

common normal flora, NOT endospore formers (vegetative cells)

Common characteristics of genus staphylococcus?

Flora on skin and mucous membranes (e.g. nose)

Catalase (+)

No flagella, capsules may

Some toxigenic, infection may be caused from distant site

Staphylococcus aureus colony characteristics

Large round opaque cluster colonies (golden yellow)

Characteristics of Staph. aureus (resistance, o2, growth, coagulase, hemolytic pattern)

Coagulase (+), beta on blood agar

Resistance to: high salt (MSA), extreme pH, high temperature

Facultative anaerobes

Mesophiles

What antibiotics are staph aureus mostly resistant to?

Beta lactams (95% make Beta lactamases)

What does mecA gene in methicillin resist. S. aureus do?

Encode penicillin-binding protein (helps with cross linking in peptidoglycan), not affected by beta lactams

What local skin infections can be caused by S. aureus?

Folliculitis, furuncle (boil), carbuncle, impetigo, and mastitis

Systematic infections of S. aureus from bacteremia

Osteomyelitis (children→affect long bone growth; adults →vertebrae)

endocarditis (heart valve infection)

pneumonia

septic arthritis (joint destruction)

How to treat S. aureus infections?

Clindanycin (protein synth. inhibitor)

Trimethoprim/sulfamethoxzole (inhibit folic acid→antimetabolites)

S. aureus toxin-mediated diseases (3)

Food intoxication (from consuming ST enterotoxin)

Staphylococcus Scalded Skin Syndrome (from exfoliative toxins → redness, blisters, peeling of skin)

Toxic Shock Syndrome (from superantigen→toxemia)

List of Staphylococi species that are coagulase negative, opportunistic, and cause wound infections

epidermidis (endocarditis, bacteremia, UTIs)

lugdunensis (normal flora of perineal region, similar to S. aureus)

hominis + haemophilus (apocrine sweat glands like armpits)

capitis (scalp, face, ear)

saprophyticus (2nd common cause of UTIs)

Where is Staphylococcus isolated from?

pus, tissue exudates, sputum, urine, blood

How to cultivate and differentiate Staphylococcus?

Blood Agar (Beta= S. aureus)

MSA (Yellow= S. aureus)

Catalase: (+) (Strepto./Enterococcus)

Coagulase: (+) for S. aureus

Notable virulence factors of S. aureus

Glycocalyx

Coagulase

Protein A (bind Fc of IgG →prevent opsonization + complement binding)

cytolysin (membrane dmg toxins)

exfoliative toxins (protease)

enterotoxin (super Ag)

“Toxic Shock Syndrome” toxin (super Ag)

Characteristics of Streptococci (morphology, structures, o2, catalase, culture needs, sensitivity)

cocci chains, small translucent colorless colonies

may have glycocalyx

facultative anaerobe

catalase (-); has peroxidase (breaks H2O2 no bubbles)

pathogenic species fastidious (enriched media)

sensitive to drying, heat, disinfectants

How can Streptococci be classified?

Hemolysis pattern on blood agar

Lancefield group (based on Ab recognition of cell wall Ags)

Characteristics of Lancefield group A Streptococcus pyogenes

B-hemolysis

Strict parasites

Most serious strepto. pathogens

Flora throat, nasopharynx, and some skin

Exotoxins of Strepto. pyogenes (4)

Streptolysins O and S —> dmg cell membrane

Strepto. pyogenic exotoxin (“Erythrogenic toxins) → sandpaper-like red rash + fever

Super Ags —> non specific T cell activation (cytokine storms)

Extracellular enzymes of Strepto pyogenes

Streptokinase (digest clots host barriers)

Hyaluronidase (break hyaluronic acid in connective tissue → invasion)

DNAse (degrade NETs trap neutrophils)

Surface structures of Strepto. pyogenes

C-carbohydrate (used Lancefield identity)

Fimbriae (attachment to epithelial cells)

M protein (block C3B binding → can't opsonize)

Hyaluronic acid capsule (looks like host protein)

ScpA (C5a protease; can't attract neutrophils)

What bacteria commonly causes Necrotizing fasciitis (flesh eating)

Streptococcal pyogenes (GAS)

What other infections does Strepto. pyogenes cause?

Skin, pharyngitis (strep throat)

What bacteria causes Scarlet fever? What virulence factor plays a role?

Strepto. pyogenes; Strepto. pyogenic exotoxin (sand paper rash)

Characteristics +infections of Lancefield Group B: Streptococcus agalactiae

B-hemolysis, cause neonatal infection during delivery (sepsis, meningitis)

nosocomial

in debilitated adults (wound/skin infection, endocarditis, UTIs)

Rheumatic fever (after overt or subclinical pharyngitis)

Who is at risk of GBS? How to prevent?

Pregn. women; screening and antibiotics as prophylaxis

• don't give antibiotics if have GBS

• Higher risk for the baby if long interval between membrane rupture and delivery, fever while in labor, or UTI during pregnancy

How to identify B-hemolytic Strep. species (e.g. GAS and GBS)

Blood Agar

Bacitracin sensitivity (GAS= (+); GBS= (-))

CAMP test (GBS=+)

Lancefield grouping test

How to treat GAS and GBS?

Penicillin

• for allergies: there are alternatives but usually have more resistance

• take long term if patient has history of rheumatic fever or reoccurring strep throat

Characteristics of Viridans Group?

Alpha hemolysis Streptococcus

Normal flora of oral, nasopharynx, genital tract, skin

e.g.) S. mutans, oralis, salivarius, etc.

Infections caused by Viridans group

dental caries or tooth abscesses (from dental procedure/surgery)

Subacute endocarditis (bacteria use biofilm to colonize → risk for those w heart disease)

Characteristics of Streptococcus pneumoniae

lancet shape (pointed oval) cells, diplococci + short chains

fastidious (blood or chocolate agar)

peroxidase negative

can't tolerate high o2 (micro-aerophilic)

caspules

normal flora 50% of people

What makes vaccine development for Strep. pneumoniae hard?

Has many capsule strains (each with specific soluble substance antigens)

Infections caused by S. Pneumoniae?

Pneumonia, otitis media, bacterial meningitis (#1 cause)

How to diagnose alpha hemolytic Streptococci?

Blood Agar (alpha)

Optochin sensitivity (Virdan resist; pneumoniae sensitive)

Bile solubility (Viridans -, pneumoniae +)

Insulin fermentation (Viridans -, pneumoniae +)

For S. pneumoniae

• Gram stain of sputum and CSF

• Quellung test (swelling reaction of capsule)

Treatment and prevention for Strep. pneumoniae

Vaccine (for high risk indv.)

• Capsular Ag: last 5 years, min. age above 2

• Conjugate: children 6weeks-71 mo; effective in reducing invasiveness for vaccine’s strains

Lancefield D characteristics

‘Enterococci’

normal flora of large intestine

Opportunistic

nosomical infections (2nd most after Staphylococci)

lot of antibiotic resistance

Enterococci diagnosis

bile solubility → resistant

bile esculin → (+) (vs. Streptococcus neg)

optochin sensitivity → resistant

PYR production test → (+) cherry red

What Genera are Gram positive coccis?

Staphylococcus and Streptococcus