Microbiology Gram positive organisms SEH study guide

What test is used to differentiate between gram positive cocci

Catalase test

What family of gram-positive organisms will appear as “clusters” or “bunch of grapes” on a gram stain?

Staphylococci

What family of gram-positive organisms will appear in “chains” and “lancet shape” on a gram stain?

Streptococcus

What test is used to differentiate the different types of Staphylococcus?

Coagulase test

Which Staph organism causes beta hemolysis on BAP?

S. aureus

Name the two tests that are used to differentiate between Micrococcus and Staphylococcus.

• Modified oxidase

• Bacitracin sensitivity

Which staphylococcus species is associated with hospital acquired infections

S. epidermis

What staphylococcus species is associated with UTI in sexually active young women

S. saprophyticus

What test is used to determine the presence of Staph. saprophyticus from a urine culture

Novobiocin susceptibility test

Which Staphylococcus aureus toxins are associated with food poisoning?

Toxins A, B, and D

List the four hemolysins produced by Staphylococcus aureus

alpha, beta, gamma, delta

What is the function of Protein A - Staphylococcus aureus?

• Binds the fragment crystallizable (Fc) portion of antibodies to avoid phagocytosis

  • Masking of its immunogenic proteins with host proteins to look like “self”

  • Assists in blocking phagocytosis

  • Negates the protective effects of IgG

Carbuncle

Boils that have multiple lesions and may progress into deeper tissues

Furuncle

A painful inflammation of the skin and subcutaneous tissue

Folliculitis

Mild inflammation of a hair follicle or oil gland

bullous impetigo

• Large pustules surrounded by small zone of erythema (redness)

• Spread by direct contact and fomites; highly contagious

What is another name for bullous exfoliative dermatitis

Ritter disease, SSSS

What is Toxic Shock Syndrome?

• Rare multisystem disease

• Association with super-absorbent tampons

• Clinical presentation-sudden onset of

  • Fevers, chills, vomiting

  • Diarrhea, muscle aches, rash

• Fatal in 2-5% of cases due to multiorgan system failure

List the possible causes of Toxic Epidermal Necrolysis.

• Antimicrobial drugs

• Anticonvulsive agents

• Hypersensitivity reactions

Which causes the symptoms of food poisoning - the toxin or bacteria

Toxin

What are the symptoms found in patients with food poisoning caused by Staph. aureus?

• Appear rapidly about 2 to 8 hours after ingesting food

• Usually resolve in 24-48 hours, sometimes less

• Nausea, vomiting, abdominal pain, and cramping

• Diarrhea, and headache also possible

Name the coag-negative staph (CNS) that can create a biofilm on implant devices.

S. epidermis

What CNS can mimic Staphylococcus aureus infections and is known to have mecA?

S. lugdunesis

List the common microscopic findings for staphylococcus infections.

• Numerous GPC

• PMNs

What are the colony characteristics after 18-24 hours of incubation for staphylococcus?

round, smooth, white, creamy

Which coagulase test detects extracellular free coagulase?

Tube coagulase

Name other tests that are used to help differentiate staphylococcus species.

• Coagulase

• Catalase

• Novobiocin

• Oxidase

Name some ways to control the spread of MRSA.

• Barrier protection

• Contact isolation

• Handwashing

What is the antibiotic of choice for MRSA infections?

Vancomycin

Which gene is responsible for most oxacillin resistance in Staph. aureus?

mecA gene

What test should be performed on Staphylococcus aureus to check for penicillin resistance?

Beta-lactamase

Which antibiotic has been found to be a better mecA inducer to detect MRSA?

Cefoxitin

What is the gold standard for detecting MRSA?

Nucleic acid probes or PCR amplification

What diffusion test is performed if there is a discrepancy between Clindamycin and Erythromycin results?

D-zone test

What gas do streptococcus species tend to like?

Increased conc of CO2

What do Strep pneumoniae and young strep colonies have in common?

• Have a capsule

• Small, smooth, glistening, and dome shaped

• coin shaped colonies after prolonged incubation

What are the three types of hemolysis that streptococcus organisms create on BAP?

• Alpha

• Beta

• Nonhemolytic/gamma

What is another name for Strep. pyogenes?

Group A Streptococcus (GAS)

What does the capsule on Strep. pyogenes prevents?

Opsonized phagocytosis by neutrophils or macrophages

Name the virulence factors that Strep. pyogenes produces and the possible function of each.

• Streptolysin O— Responsible for hemolysis on BAP, destroys WBCs, platelets, RBCs, and other cells, only active under anaerobic conditions

• Streptolysin S— Responsible for hemolysis seen around colonies incubated aerobically; can lyse RBCs & WBCs; nonimmunogenic

• DNases A-D— All strains of S. pyogenes produce at least one DNase, most common is DNase B

• Hyaluronidase (spreading factor)— Bacteria use this enzyme to separate the tissue and spread the infection

• Streptococcal pyrogenic exotoxins—superantigens, 4 types (Spec A, B, C, F)

• Streptokinase—GAS causes lysis of fibrin clots through streptokinase action on plasminogen

What test can be performed to check for recent infection of Strep. pyogenes and is known to produce hemolysis on BAP?

ASO titer, Streptolysin produces hemolysis on BAP

What is Strep. pyogenes commonly known for?

Causing Strep throat

What is another name for bacterial pharyngitis?

Strep throat/streptococcal pharyngitis

What is necrotizing fasciitis?

Infection characterized by rapidly progressing inflammation & necrosis of the skin, subcutaneous tissue, and fascia. Flesh eating disease

Name the pyodermal infections caused by Strep. pyogenes.

• Impetigo

• Erysipelas

• Cellulitis

• Scarlet fever

What are the two serious complications that are considered “Post-Streptococcal Sequelae”?

• Rheumatic fever

• Acute Glomerulonephritis

What is Streptococcus agalactiae also known as?

Group B Streptococcus

Name the virulence factor that Strep. agalactiae is known to have.

Capsule—prevents phagocytosis but is ineffective after opsonization

Strep agalactiae infections are the leading cause of death in what patient population?

Infant population

What are the two types of onset and the medical condition observed in each?

• Early onset—membrane rupture, develops into pneumonia or meningitis with bacteremia

• Late onset—death occurs if treatment is not started immediately

Pregnant women are tested for Group B Strep at what time during their pregnancy?

35 to 37 weeks gestation

Under CDC recommendations, pregnant women will receive prophylactic antimicrobial therapy for what reasons

• Women with previous history

• An unknown status of GBS at time of delivery

What clinical infections does Strep. pneumoniae cause?

• Pneumonia in older adults and in patients with underlying disease

• Sinusitis

• Otitis media-frequent isolate in children younger than 3 years of age

• Bacteremia

• Meningitis

• Pneumococcal pneumoniae

What type of predisposing conditions play a factor in Strep. pneumoniae infections?

• Alcoholism

• Anesthesia

• Malnutrition

• Viral infections of the upper respiratory tract

• Older adults at increased risk

List the virulence factors produced by Strep. pneumoniae.

• Capsular polysaccharide

  • strains without a capsule are nonpathogenic

• Toxins produced

  • Hemolysins

  • IgA protease

  • Neuraminidase

  • Hyaluronidase

What are the colony characteristics for a young culture of Strep. pneumoniae?

Round, glistening, wet, mucoid, dome-shaped appearance

What are the two common tests used for Strep. pneumoniae identification?

• Optochin susceptibility

• Bile solubility test

What antibiotic is given to treat Strep. pneumoniae?

• Penicillin

What does “viridians” mean?

Green

Viridians strep is normal flora to what body parts/areas?

• Upper Respiratory Tract

• Female genital tract

• GI tract

What is the most common cause of subacute bacterial endocarditis?

Viridians Streptococci

Name the two most common Enterococcus organisms.

• E. faecalis

• E. faecium

What kind of catalase results would Enterococcus give? What is another name?

• Weak bubbling in catalase test

• Group D strep

What type of virulence factors do Enterococcus faecalis have and their role?

• Surface adhesin proteins

• Extracellular protease

• Gelantinase

  • Might play a role in colonization and adherence to heart valves and renal epithelial cells

• Produces a two-subunit toxin termed cytolysin

What type of clinical infections does Enterococcus cause?

• Nosocomial infections

• Endocarditis

• Bacteremia may occur in immunocompromised patients

What antibiotics is Enterococcus resistant to?

• Aminoglycosides

• Beta-lactams

• Glycopeptides

VRE is known to have how many phenotypes? Which ones are the most common phenotypes?

• nine phenotypes

• VanA & VanB are the most common

What is Bacitracin used for?

• Used as presumptive test for S. pyogenes

• Helpful in screening for GAS in throat cultures

What is CAMP test used for?

Detects the production of enhanced hemolysis

Describe the Hippurate Hydrolysis test.

• Differentiates Group B streptococci from other Beta-hemolytic streptococci

• Group B strep possess the enzyme hippuricase which hydrolyzes sodium hippurate forming sodium benzoate and glycine

PYR testing can be used for presumptive identification of what organisms?

• GAS

• nonhemolytic enterococci

What is Optochin test used to detect?

S. pneumoniae

Name the two tests that will be positive for Enterococcus but negative for Group D Strep.

• PYR test

• Salt tolerance test

What organism is the bile solubility tests diagnostic for?

diagnostic for S. pneumoniae

What is the antibiotic of choice for treatment?

• Vancomycin combined with a third-generation cephalosporin

• Ceftriaxone

• Amoxicillin

• Doxycycline

What two antibiotics have shown an increase of resistance?

• Vancomycin

• Penicillin-resistant strains