Clinical Reasoning: Intro to Microbiology

Acute infective endocarditis

occurs when bacteria enter the bloodstream and travel to and attach to heart valves. This condition usually begins suddenly with a high fever, fast heart rate, fatigue, and rapid and extensive heart valve damage.

congenital heart disease

degenerative valvular disease

intracardiac device

intravenous drug use

open wounds (e.g. eczema) can allow bacteria to get in

what are some risk factors for IE?

petechiae

splinter hemorrhages

Janeway lesions

Osler nodes

Roth spots

common PE findings for those with IE

Strep viridians and Staph aureus

HACEK (less common, but still possible)

what are the most common pathogens for endocarditis?

gram positive cocci

what is the classification for Strep viridans/Staph aureus

Cells stained with crystal violet dye

Gram's iodine added to form complex

Decolorizer added --> dehydrates/tightens peptidoglycan layer

--> G+ hold onto complex

--> G - outer layer degraded so dye is let go

Counterstain (safranin) added, staining it red

--> Does not disrupt G + cells

--> Decolorized G - cells are stained red

gram staining procedure

Vancomycin

first line tx for IE on a native valve

Gram positive --> THICK cell wall

Gram negative --> thin cell wall with outer lipid membrane

what are the differences between gram positive and gram negative cell walls?

gram positive bacteria (including MRSA)

Vancomycin is active against...

interferes with cell wall synthesis

Vancomycin MOA

they have a thin peptidoglycan cell wall that is surrounded by a lipid bilayer --> vancomycin is too large and cannot penetrate to get to cell wall

why doesn't vancomycin work against gram negative bacteria?

Acute bacterial sinusitis

inflammation (allergies, viral infection, chemical irritation) leads to ostial obstruction and stasis; stasis can then lead to secondary bacterial infection

at least one week

bacterial infection in the sinuses should not be suspected unless symptomatic for...

Streptococcus pneumonia -- gram +

Hemophilus influenza -- gram -

Moraxella catarrhalis -- gram -

what are the most common pathogens that cause acute bacterial sinusitis

Streptococcus pneumonia

what are the gram + organism(s) that cause acute bacterial sinusitis?

Hemophilus influenza

Moraxella catarrhalis

what are the gram - organism(s) that cause acute bacterial sinusitis?

Amoxicillin -- good gram positive coverage and some additional gram-negative coverage like H flu and M cat

what is the drug of choice for acute bacterial sinusitis?

travels across membrane of some gram-negative bacteria -- prevents cross-linking

porin channels in H. flu and M.cat allow Amoxicillin into cell

Amoxicillin MOA

Amoxicillin-Clavulanate (Augmentin)

--> esp if they have had ABX within the last 4 weeks

what is a drug that is used in the context of Amoxicillin resistance

Macrolides such as Zithromax

what is a drug used for acute bacterial sinusitis if one is allergic to PCNs?

targeting protein synthesis

Macrolide MOA

Area of colonic wall thickening and pericolonic fat stranding in the distal sigmoid colon consistent with acute diverticulitis

what findings on CT are consistent with acute diverticulitis?

anaerobes (Bacterioides fragilis)

Gram negatives (E coli)

what are the most common bacterial organisms in the colon?

Anaerobe

any organism that does not require molecular oxygen for growth; can often tolerate SOME oxygen; also exist around other bacteria which create a microenvironment by consuming oxygen

gut and mucocutaneous surfaces (skin, mouth, vagina, etc.)

where are anaerobes commonly found?

Metronidazole (Flagyl)

what is the drug of choice for anaerobic infections?

inhibits protein synthesis by interacting with DNA and causing a loss of helical DNA structure and stand breakage

Metronidazole (Flagyl) MOA

because this infxn tends to be polymicrobial -- includes gram negative rods in gut

why do we use a fluoroquinolone along with Flagyl for diverticulitis

Ciprofloxacin

what is the most common agent used in diverticulitis for coverage of GNRs?

inhibits DNA synthesis and replication

Ciprofloxacin MOA