LECTURE 2 GRAM POSITIVE

Characteristics of Staphylococcus aureus

Catalase and coagulase positive

B-hemolytic

Gold-yellow colonies (especially skin and anterior nares)

Virulence Factors of Staphylococcus aureus

Protein A: binds Fc portion of IgG → interferes with opsonization/phagocytosis

Coagulase: promotes fibrin clot formation

Exotoxins: Enterotoxins, TSST-1, Exfoliative toxins, Leukocidins

Pyogenic infections locations of Staphylococcus aureus

Skin/soft tissue

Bone/joint

Lungs

Heart

Surgical wounds

Toxin-mediated diseases of Staphylococcus aureus

Food poisoning (enterotoxins): Rapid onset nausea/vomiting +diarrhea

Toxic shock syndrome (TSST-1): fever, rash, hypertension, multiorgan involvement

Scalded skin syndrome (Exfoliative toxins): Blistering and skin peeling

Bullous impetigo: localized blistering

Prevention of Staphylococcus aureus

Hand hygiene

Decolonization (intranasal mupirocin)

Perioperative prophylaxis (cefazolin for surgical procedures)

No vaccine available

Characteristics of Staphylococcus epidermis

Catalase-positive, coagulase-negative

Novobiocin-sensitive

Part of normal skin flora

Pathogenesis of Staphylococcus epidermis

Forms biofilms on artificial surfaces

Opportunistic pathogen especially on implanted medical devices

Common infections of Staphylococcus epidermis

Prosthetic valve endocarditis

Prosthetic joint

IV/central line

CSF shunt

Peritonitis

Neonatal sepsis

Transmission of Staphylococcus epidermis

Enters through catheters, surgical wounds, or implanted devices

Nosocomial (healthcare-related)Pre

Prevention of Staphylococcus epidermis

Aseptic technique

Proper care

No vaccine available

Characteristics of Staphylococcus saprophyticus

Catalase positive, coagulase-negative

Novobiocin-resistant

Normal flora of genital mucosa

Common diseases of Staphylococcus saprophyticus

UTIs especially cystitis

Prevalant in young, sexually-active women

Pathogenesis of Staphylococcus saprophyticus

Ascends through urethra

Prevention of Staphylococcus saprophyticus

General hygiene and post-coital voiding

Characteristics of Streptococcus pyogenes

Catalase-negative

B-hemolyticP

Group A

Pyogenic Diseases of Streptococcus pyogenes

Pharyngitis (strep throat)

Tonsillitis

Otitis media, sinusitis

Sepsis

Skin infections: impetigo, erysipelas, cellulitis, necrotizing fasciitis

Toxin-mediated Diseases of Streptococcus pyogenes

Scarlet fever

Streptococcal toxic shock syndrome

Post-Streptococcal (Immunologic) Diseases of Streptococcus pyogenes

Acute rheumatic fever (in the heart)

Acute post-streptococcal glomerulonephritis (in the kidneys)

Transmission of Streptococcus pyogenes

Respiratory droplets

Direct contact with lesions

Characteristics of Streptococcus agalactiae

Catalase-negative

B-hemolytic

Encapsulated

Found in GI and genital tract flora

Group B

Diseases of Streptococcus agalactiae

Neonatal sepsis, meningitis, pneumonia

Postpartum endometritis

UTI

Transmission of Streptococcus agalactiae

Mother → newborn during birth

Characteristics of Streptococcus pneumoniae

Catalase-negative

a-hemolytic

Found in respiratory tract

Known as Pneomococcus

Encapsulated

Optochin-sensitive

Transmission of Streptococcus pneumoniae

Respiratory droplets

Prevention of Streptococcus pneumoniae

Vaccination available (esp. in asplenic patient)

Characteristics of Streptococcus viridans

A-hemolytic

Catalase-negative

Optochin-resistant

Part of normal oral flora

Diseases of Streptococcus viridans

Dental caries

Subacute endocarditis

Virulence of Streptococcus viridans

Biofilm formation adheres to teeth and damaged heart valves

Characteristics of Enterococcus species (Group D)

Catalase-negative

Non-hemolytic or weakly a-hemolytic

Part of normal gut flora (colon, urethra, female genital tract)

Two species: E. faecalis (virulent) and E. faecium (Vanco-resistant)

Causes nosocomial infections

Diseases of Enterococcus species

UTI

Endocarditis

Intra-abdominal/biliary and pelvic infections

Characteristics of Bacillus anthracis

Large rod-shaped

Spore-forming

Aerobic/facultatively anaerobic

Found in soil

Diseases of Bacillus anthracis

Cutaneous anthrax: painless black eschar

Inhalation anthrax: severe pneumonia (deadly)

Characteristics of Clostridium tetani

Rod-shaped

Terminal spore (tennis racket)

Obligate anaerobe

Found in soil and GI tract of animals

Cause of Tetanus from Clostridium tetani

Spores germinate in contaminated wounds

Tetanospasmin exotoxin produced and travels by retrograde axonal transport to CNS

Blocks GABA and glycine release in spinal cord

Inhibition of motor neurons lost in anterior horn

Trismus (lockjaw), risus sardonicus (facial spasm), Opisthotonos (severe back arching)

Prevention of tetanus from Clostridium tetani

Tetanus toxoid vaccine (active immunity)

Tetanus immune globulin (immediate passive antibodies for high-risk wounds)

Characteristics of Clostridium botulinum

Heat-resistant Spore-forming rod

Obligate anaerobe

Produces botulinum neurotoxin which is heat-sensitive

Toxin blocks ACh release leading to flaccid paralysis

Pathogenicity of Botulism

Foodborne: Ingestation of improperly preserved food (intoxicated not infection)

Leads to descending, symmetric flaccid paralysis

Infant: ingestion of spores that produce toxin in intestine (especially from honey)

Leads to constipation, poor feeding, lethargy, floppy baby

Characteristics of Clostridioides difficile

Rod-shaped

Spore-forming

Obligate anaerobe

Motile with flagella

Toxins associated with Clostridioides difficile

Toxin A (enterotoxin)

Toxin B (cytotoxin)

Damages intestinal epithelial cells and disrupts cytoskeleton

Causes inflammation, fluid secretion, diarrhea and pseudomembrane formation

Pathogenesis of Clostridioides difficile

Antibiotics disrupt normal gut microbiota allowing C. difficile to proliferate and produce toxins

Associated with clindamycin, cephalosporins, fluoroquinolones, and broad-spectrum penicillins

Characteristics of Clostridium perfringens

Spore-forming rod with blunt/square ends

Anaerobic

Found in soil and maybe human and animal GI tract

Virulence of Clostridium perfringens

Alpha toxin (phospholipase C)

Damages cell membranes leading to tissue destruction, hemolysis, and shock

Diseases of Clostridium perfringens

Gas Gangrene (myonecrosis)

Follows traumatic wound contamination

Rapid muscle and tissue necrosis

Gas production within tissue leading to severe pain, swelling, and shock

Characteristics of Corynebacterium diphtheriae

Club-shaped rod

Produces diphtheria toxin (A-B exotoxin)

Can be found in human throat and nasopharynx

Transmitted via respiratory droplets

Virulence/Toxin of Corynebacterium diphtheriae

Inhibits protein synthesis leading to cell death

Local effect can be seen via gray pseudomembrane in throat

Causes systemic myocarditis and nerve damage/paralysis

Causes bull neck and in severe cases airway obstruction

Characteristics of Listeria monocytogenes

Rod-shaped

B-hemolytic

Catalase-positive

Facultative anaerobe

Characteristic tumbling motility

Diseases of Listeria monocytogenes

Contaminates deli meats, unpasteurized dairy products, soft cheeses

Can also transmit from mother to fetus or during childbirth

Causes gastroenteritis or meningitis/sepsis (esp. in neonates, older adults, and immunocompromised patients)