2 - BACTERIOLOGY: Gram Positive Bacteria 2025

Staphylococcus aureus

Gram positive cocci in clusters, catalase positive, coagulase positive

Staphylococcus aureus

Most common infection in open fractures?

Staphylococcus saprophyticus

Gram positive cocci in clusters, catalase positive, coagulase negative, Novobiocin resistant

Staphylococcus epidermidis

Gram positive cocci in clusters, catalase positive, coagulase negative, Novobiocin sensitive

Staphylococcus aureus

(Affects the tricuspid valve)

An IV drug user who develops endocarditis. What is the causative agent

Staphylococcus epidermidis

A patient with a prosthetic heart valve develops endocarditis. What is the causative agent?

Viridans Streptococci

A patient who underwent dental surgery develops endocarditis. What is the causative agent?

Colonoscopy to determine presence of Colon cancer

A patient with marantic endocarditis. Culture done showing growth of S. bovis. What is the next best step?

Enterococcus faecalis

A patient who underwent GI/GU surgery who develops endocarditis. What is the causative agent?

Streptococcus agalactiae

Gram positive cocci in chains, catalase negative, beta hemolytic, bacitracin resistant, CAMP positive

Streptococcus pyogenes

Gram positive cocci in chains, catalase negative, beta hemolytic, bacitracin sensitive, PYR test positive

Polyarthritis

Carditis

Subcutaneous nodules

Erythema marginatum

Sydenham chorea

Jones criteria for acute rheumatic fever includes:

Streptococcus pneumoniae

Gram positive cocci in chains, catalase negative, alpha hemolytic, optochin sensitive and bile soluble. Positive Quellung reaction

Streptococcus bovis

Gram positive cocci in chains, catalase negative, gamma hemolytic, no growth in 6.5% NaCl

mecA gene

Gene that mediates methicillin resistance in

S. aureus

Brodie abscess

Sequestered focus of osteomyelitis caused by S. aureus arising in the metaphyseal area of a long bone

Stratum granulosum

In Ritter disease, separation of epidermis happens at what layer?

Toxic Shock Syndrome

A case of fever, hypotension, strawberry tongue, desquamating rash and multi -organ involvement (>3) in patients with history of using tampon or nasal packing of epistaxis

S. aureus has no site of pyogenic inflammation and blood CS negative

Difference in Toxic Shock Syndrome caused by S. aureus and S. pyogenes

Erythrogenic toxin

Toxin that causes Scarlet fever

Anti-Streptolysin O

Elevated titers suggest antecedent Streptococcal pharyngitis

Anti-DNAse B

Elevated titers suggest antecedent Streptococcal skin infection

Streptococcus pyogenes

An 8 year old female presented to the ER hypotensive and suddenly went to cardiac arrest. History revealed that she had multiple migrating sites of arthritis, serpiginous rashes on the trunk and fever prior to the onset of hypotension. Pathology report showed presence of Aschoff bodies and Anitschkow cells in the myocardium. What is the most likely causative agent in this patient's condition?

Erysipelas

(Different from Erysipeloid caused by Eryslipelothrix)

Superficial infection extending into dermal lymphatics

Alpha toxin

Toxin of Staphylococcus that causes necrosis of the skin and hemolysis

Exotoxin B

Toxin of Streptococcus that rapidly destroys tissue and causes Necrotizing Fasciitis

Acute Rheumatic Fever

(due to cross-reacting antibodies to M-protein)

A case of fever, migrating joint pains in the knees and
elbows, and has raised erythematous serpentine-like lesions on the back with history of pharyngitis in the past. What is the most likely diagnosis?

Streptococcus agalactiae

Most common cause of neonatal pneumonia, sepsis, and meningitis

35-37 weeks

Pregnant women should be screened for Group B Streptococci colonization at what age of gestation?

Streptococcus pneumoniae

Most common cause of CAP across all ages

Rusty colored sputum

Characteristic sputum of patients infected with S. pneumoniae?

Both are spore-forming, but Bacillus species are aerobic while Clostridium species are anaerobic

Difference between Bacillus and Clostridium species

Bacillus anthracis

A 30-year-old male was noted to have a malignant pustule. Culture showed that the organism present is gram (+) bacilli, spore-forming, aerobic and non-motile.

Cutaneous anthrax

Most common form of anthrax

Inhalational Anthrax

Most severe form of anthrax

Ciprofloxacin

Drug of choice for cutaneous anthrax

Gram (+) spore-forming bacilli, aerobic, motile

A case of food poisoning after eating reheated fried rice. What is the characteristics of this organism?

Metronidazole

A 40-year-old carpenter sustained a punctured wound on his right hand a week ago. He noted to experience muscle rigidity thus came for consult. What is the preferred antibiotic for this case?

Inhibiting the release of GABA by cleaving of synaptobrevin 2

What is the mechanism leading to the patient in the previous case to develop such symptoms?

Blocking the release of acetylcholine

Mode of action of botulinum toxin

Ingestion of spores in household dust or honey

Most common source of infection in Floppy Baby Syndrome

Clostridium perfringes

A 30 year old female suffered major injuries to her left arm after a motorcycle accident. She was brought to the ER due to high grade fever. Her left arm is swollen with dark serous fluid draining from the wound. Crepitus can also be felt. What is the most likely causative agent?

Lecithinase

Toxin responsible for gas gangrene

Egg yolk agar

Agar used for C. perfringens

Clindamycin, 2nd and 3rdCephalosporins and Ampicillin

Antibiotics that can cause pseudomembranous colitis

Stop the antibiotic responsible for the infection

1st step in treating C. difficile infection

Vancomycin

Antibiotic of choice for treatment of C. difficile

Inhibits protein synthesis by adding ADP-ribose to elongation factor 2

What’s the mechanism of the exotoxin of C diphtheria?

Loeffler’s medium or Potassium tellurite

Culture media of C. diphtheria

Erythromycin

Antibiotic choice for C. diphtheria

-Ingestion of unpasteurized milk products

-Across placenta or contact during delivery

A newborn who was diagnosed with neonatal sepsis was admitted in the hospital. Culture shows a facultative intracellular rod that exhibits cold enhancement and a narrow zone of beta hemolysis. This organism can be transmitted by:

Listeriolysin

The organism discussed in the previous case escapes from the phagosome via which toxin?

Actinomyces israelii

A 30yr old man got into a fight and broke his jaw a few days ago which now has developed an abscess with draining pus. Anaerobic culture showed molar tooth colonies. What is the causative agent?

Penicillin

Treatment of choice for the causative agent discussed in the previous case?

Nocardia asteroides

A 40yr old HIV patient came due to chronic cough. PPD showed a negative result. Fite faraco stain demonstrated that organism is weakly acid fast. Culture showed orange colonies. What is the causative agent?

Co-trimoxazole

Drug of choice for Nocardia infection