1st PowerPoint . . . General info on BACTERIA

Question 1

How is Gram (+) differentiated?

Answer 1

It starts with a catalase test ( catalase present?? colag or not!) then if catalase is not present . . . can be further classified by hemolysis capabilities

Question 2

Staphylococci

Answer 2

are common colonizers of the skin and nose which also cause a wide range of infections! Gram+ cocci, clusters (grapes) CATALASE IS PRESENT

Coagulase-positive –> Staphylococcus aureus (MRSA and MSSA)

Coagulase-negative –> Staphylococcus epidermidis

Question 3

Staphylococci can cause . . .

Answer 3

• mild to severe skin infections (ABSSSI / SSTI)
• life threatening pneumonia (PNA)
• Bacteremia/ endocarditis
• Osteomyelitis
• UTI
• Major players in post-surgical infections
• Adhere to foreign material and catheters (biofilms)!!!

Question 4

Streptococci (catalase negative) are grouped based on. . .

Answer 4

(1) hemolytic phenotype on blood agar and (2) β-hemolytic strep are further classified based on the Lancefield system

Gram+, chains or pairs
Zones of clearance on blood agar

Question 5

Streptococci α-hemolytic (partial hemolysis green/brown)

Answer 5

S. pneumoniae & Viridans Streptococci (S. mutans/ salivarius/ mitis)

Question 6

Streptococci gamma-hemolytic (No hemolysis)

Answer 6

(formerly Group D but reclassified as Enterococci)

Question 7

Streptococci Beta-hemolytic (complete, clear)

Answer 7

Lancefield classes based on cell wall carbohydrates

GROUP A –> S. pyogenen (GAS)
GROUP B –> S. agalactiae

Question 8

Group A – S. pyogenes causes . . .

Answer 8

---Cellulitis, necrotizing
fasciitis (SSTI)
– Pharyngitis (“Strep throat”)
– Rheumatic fever
– Scarlet fever
– Glomerulonephritis

Question 9

Group B - S. agalactiae causes . . .

Answer 9

Neonatal meningitis

Question 10

Viridans Streptococci (α - hemolysis) causes . . .

Answer 10

– Dental caries
– Bacteremia/ Endocarditis
(immunocompromised)

Question 11

Streptococcus pneumoniae is one of the most common causes of . . .

Answer 11

upper respiratory tract infections (URTI/URI)!!! MOST LIKELY CAUSE OF CAP

-- Gram +, diplococci
• α-hemolytic
• Polysaccharide capsule (encapsulated)
– >90 serotypes
– Target for vaccine

Question 12

Encapsulated bacteria are especially difficult to clear for asplenic patients

Answer 12

• Lack filtration mechanism of splenic macrophages
• Cannot clear encapsulated organisms
– S. pneumoniae
– H. influenzae
– N. meningitidis
• Patients are at risk for fulminant sepsis syndrome

Question 13

Enterococci (γ-hemolysis=none) can cause . . .

Answer 13

UTIs, intraabdominal infections, bacteremia and endocarditis

 Gram+ cocci, diplococci or short chains
 Enterococcus faecalis ( increase prevalent, decrease AMR)
 Enterococcus faecium (decrease prevalent, increase AMR)
 Opportunistic
 Antibiotic resistance is their best defense (e.g., Vancomycin Resistant Enterococci - VRE)
 Common colonizers of the gastrointestinal tract & the
female genital tract

Question 14

Gram NEGATIVE bacteria can be largely classified based on. . .

Answer 14

shape, lactose fermentation, oxidase and H2S-production

Lactose ferm?? PINK! No? Clear

Oxidase assay: Assay for bacterial cytochrome c oxidases(enzyme) which participate in cellular respiration. If the enzyme is present, it will oxidize
the assay substrate resulting in a visible color change.

Bacterial species capable of producing H₂S use enzymatic action to release sulfide from cysteine or thiosulfate present in the medium

Question 15

Clinically important Gram NEGATIVE bacteria that are NOT rod shaped include –> Haemophilus influenzae and Neisseria sp. . .

Answer 15

• Haemophilus influenza (Coccobacilli)
– No capsule • Colonizes URT • Causes otitis media, sinusitis, CAP
- Encapsulated - more virulent, Not regular colonizer. Causes meningitis/sepsis

Neisseria sp. (diplococci)
• Neisseria meningitidis–> Humans are the only natural host, Colonizes oro/nasopharynx. Encapsulated, Causes meningitis and less, commonly PNA
• Neisseria gonorrhoeae (STD)

Question 16

Pseudomonas spp. are Gram NEGATIVE rods (non-lactose fermenting,
oxidase +) . . .

Answer 16

highly Abx resistant and cause severe opportunistic (often hospital associated/acquired (HA)) infections !!

1. Opportunist (Risk factors: Immunocomp., Broad-spectrum abx, Ventilation)
2. Can colonize upper respiratory tract of immunocomp pt. –> Cystic fibrosis
   (Pseudomonas aeruginosa)
3. CAN FORM BIOFILM
4. Infections: Nosocomial Infections, Hospital-acquired pneumonia (HAP), Febrile neutropenia, SSTI, UTI, HIGHLY ABX RESISTANT !!!

Question 17

Clinically important anaerobic bacteria include

C. difficile (gram +) and B. fragilis (gram neg)

Answer 17

• Clostridium spp. (Gram+ rod)
– C. diff! –> Most serious cause of antibiotic‐associated diarrhea (AAD)
– C. perfringens –> Food poisoning, gas gangrene

• Bacteroides fragilis (Gram (‐) rod, gut)
— CAUSES MOST INTRA ABDOMINAL INFECTION
― Normally comprises only 0.5% fecal flora
― Involved in 90% of anaerobic peritoneal infections