Wk 1 Gram Positive Bacteria

COCCI

What are the three main Gram (+) cocci bacteria?

1. Staphylococci

2. Streptococci

3. Enterococci

What are the main Staphylococci pathogens? How are they further categorized?

Coagulase (+)

• Staph. aureus

Coagulase ( - )

• S. epidermidis

• S. saprophyticus

What does a coagulation test show?

Positive Test — clumps; indicates Staph. aureus

Negative Test — no clumps

Is S. aureus normal flora or a colonizer? What infections can it cause?

Colonizer

Causes skin infections:

• cellulitis w/ abscesses

• bacteremia

• endocarditis

• osteomyelitis

• food poisoning

• toxic shock syndrome

Is S. epidermidis normal flora or a colonizer? What kind of infection(s) can it cause?

Normal Flora of SKIN

Common contaminant of blood cultures

Can Cause:

• Endocarditis

• Infected foreign bodies

• Line infection (e.g. catheter)

What kind of infection(s) can S. saprophyticus cause?

UTIs

What are particular risks with Staphylococcus aureus?

Methicillin susceptibility (MSSA vs MRSA)

Severity of dz can be high, with high mortality

What are the main Streptococci pathogens?

1. Streptococcus pneumoniae

2. S. pyogenes

3. S. agalactiae

4. Viridans Streptococci

What infection(s) can Streptococci pathogens cause?

• Pharyngitis (Strep Throat)

• Skin and soft tissue infections

• Pneumonia

• UTIs

• Intra-abdominal infection

• Endocarditis

What are the three Hemolysis types? How do they appear on an agar plate?

A) Alpha-hemolytic — partial lysis of RBCs; appears as greenish color

B) Beta-hemolytic — complete lysis of RBCs; stark yellow color

C) Gamma hemolysis — NO lysis of RBCs; no change

What are the main pathogens that fall under the Lancefield groups (A-U) based on antigenic differences in carbohydrates located in cell wall?

*Group A: S. pyogenes (‘GAS’)

*Group B: S. agalactiae

Group D: S. bovis

*Is Streptococci considered normal flora or a colonizer?

Both

Normal flora of throat, skin, and intestines

Oropharynx:

• Normal Flora — Viridans Strep.

• Carrier — S. pneumoniae

Skin:

• Carrier — S. pyogenes

Lower Intestinal Tract:

• Normal Flora — Enterococci, Viridans Strep.

How does Streptococci typically appear on a gram stain?

Purple (Gram +)

Chains (S. pneumoniae in pairs)

What hemolytic category does S. pyogenes (Group A) fall under? Is it considered normal flora or a colonizer?

Beta hemolytic

Can colonize throat and skin

What infection(s) can S. pyogenes cause?

Pharyngitis — Strep Throat

Cellulitis (skin infection)

• one of two most common orgs

• e.g. Necrotizing Fasciitis

What hemolytic category does S. agalactiae (Group B) fall under? Is it considered normal flora or a colonizer?

Beta-hemolytic

Normal flora of GI

What infection(s) can S. agalactiae cause?

Neonatal sepsis and meningitis

• infected in utero or during birth

• premature membrane rupture in colonized women

• low-birth-weight

• didn’t receive prenatal care

Screen at 35-37 wks

What hemolytic category does Viridans Streptococci fall under? Is it considered normal flora or a colonizer?

Alpha-hemolytic

Normal flora of GI and oropharynx

Many different species (viridans)

What kind of infection(s) can Viridans Streptococci cause?

Common cause of infective endocarditis — org enters bloodstream from oropharynx as a result of poor oral hygiene or after dental surgery (travels to heart)

GI orgs can cause intra-abdominal abscess

What hemolytic category does Streptococcus pneumoniae fall under? Is it considered normal flora or a colonizer?

Alpha-hemolytic

Colonizer in ~10-50% of population in oropharynx

What kind of infection(s) can Streptococcus pneumoniae cause? What is important about their structure?

Respiratory Tract Infections — otitis media, sinusitis, *pneumonia, *meningitis

Structure has a capsule:

• Binds in respiratory tract to prevent phagocytosis

• Allows for vaccine targeting

What hemolytic category does Group D Streptococci fall under? What infection(s) is it associated with?

Gamma hemolytic

S. bovis (now S. gallolyticus)

Bloodstream infection strongly associated w/ colon cancer

In summary, how are Streptococci pathogens sorted based on hemolytic category?

Alpha-Hemolytic:

• Strep. pneumoniae

• Strep viridans

Beta-Hemolytic:

• Strep. pyogenes

• Strep. agalactiae

Gamma-Hemolytic:

• Strep bovis

What hemolytic category does Enterococci fall under? Is is considered normal flora or a colonizer? What is additionally important about this categorization?

Alpha-hemolytic

Normal flora of GI

Tolerates high salt concentration (6.5% NaCl)

What kind(s) of infections can Enterococci cause?

Common cause of hospital-acquired infections

Causes infections of:

• Urinary tract

• Intra-abdominal

• Blood

• Heart (endocarditis)

How do Enterococcus faecalis and Enterococcus faecium compare?

E. faecalis:

• Is most common of Enterococcus species

• Least likely to have extensive resistance (less likely to be Vanco resistant)

• Common cause of UTIs

E. faecium:

• 2nd most common of Enterococcus species

• Naturally more resistant to antibiotics (vs E. faecalis)

• Commonly Vanco resistant (VRE)

Why might pathogens want to lyse RBCs?

When RBCs are lysed, iron is released

Iron helps further facilitate pathogenic growth

We try to avoid administering iron or TPN to pts with infections

Rods

What are spores?

Structures that form inside the cell in response to adverse conditions to serve as preservation factor

Can lay dormant for years, but once conditions are ideal again they germinate (repopulate)

Why are spores a big concern? How do we kill them?

Spores can withstand alcohol and harsh environments

Can only be killed with sporicides or autoclaving (steam at temps > 122C for > 30 min)

Are present in environment; if contact made can get infected (e.g. Soil = C. tetani, C. perfringens; wound infections)

What are the various Non-Spore Forming versus Spore Forming Gram (+) Rods?

(mainly just know bolded ones)

Non-Spore Forming:

• Listeria monocytogenes

• Corynebacterium spp

Spore Forming:

• Bacillus cereus (food poisoning)

• Bacillus anthracis (anthrax)

• Clostridium botulinum (botulism)

• Clostridium perfringens (gas gangrene, food poisoning)

• Clostridioides (Clostridium) difficile (Ab-associated colitis)

• Clostridium tetani (Tetanus)

How is Listeria monocytogenes transmitted? What is important about how it grows?

“Food-Borne” Infection

• transmitted to humans by contact w/ animals or their feces

• Unpasteurized milk or cheese

• Contaminated vegetables

Grows in low temperatures (4 C); continues to grow in fridge

What kind of infection(s) can Listeria monocytogenes cause?

Newborns:

• Meningitis !!!

• Pneumonia

• If pregnant women are infected, can result in septic abortion, stillbirth, premature birth

Immunocompromised (high-dose steroids, malignancy):

• Meningitis !

What are the two major Gram (+) spore-forming rods?

Bacillus species (cereus, anthracis)

Clostridium species (botulinum, perfringens, difficile, tetani)

What vaccines are available for which Gram (+) pathogens?

1. Streptococcus pneumoniae — pneumococcal vaccines

2. C. tetani — tetanus vaccine