BIOL 314 Module 2

Lectures 4 and 5

Nosocomial infections

Infections that are associated with healthcare, such as hospitals, nursing homes, or home healthcare like self-injections or catheter use

During what time period is it considered a nosocomial infection

48 hours after admission to 30 days after discharge

Risk factors of nosocomial infections

• Prolonged hospital stay

• Antiobiotic use

• Sugery

• Hemodialysis

• ICU

• Immunodeficiency

MRSA Gram stain

Gram-positive

Pseudomonas aeruginosa microbiological findings

• Gram-negative

• Slightly curved individual rods

• Motile

• Produces capsule

• Beta-hemolytic

Pseudomonas aeruginosa gram stain

Gram-negative

C. difficile gram stain

Gram-positive

C. difficile microbiological findings

• Gram-positive

• Obligate anaerobe

• Forms endospores

• Produces exotoxins A and B

MRSA microbiological findings (catalase and coagulase)

• Gram-positive

• Catalase positive (differentiates Staphylococcus from other morphologies)

• Coagulase positive (used to differentiate Staphylococcus aureus from other staphylococci)

• MecA positive (used to differentiate MRSA from other staphylococcus aureus)

Ventilator-associated pneumonia most common pathogens

• Pseudomonas aeruginosa

• Acinetobacter

• Enterobacterales

• Staphylococcus aureus (including MRSA)

• MOST ARE GRAM NEGATIVE

What is MRSA typically resistant to and through what mechanism

• Resistant to beta-lactams

• Produces PBP2a (through the mecA gene), which has very low affinity for antibiotics

Diagnosis of pneumonia

• Signs and symptoms (cough, dyspnea, fever, sputum, etc.)

• Imaging (CXR, then maybe CT if nothing there but still suspected)

• Microbiological evidence (cultures, such as from bronchoalveolar lavage)

• Biomarkers: CRP

Pseudomonas aeruginosa structures and abilities

• Biofilm formation

• Pili and flagella

• Exotoxin ExoU

• Exotoxin A

• Pyoverdine production

• Mex pumps

ExoU

• Produced by P. aeruginosa

• AKA phospholipase A2

• Causes membrane damage (and therefore lysis) in host cells

• Is injected into host cells by type III secretion system (like a needle)

Exotoxin A

• Produced by P. aeruginosa

• Inhibits eukaryotic elongation factor 2, which is vital for protein synthesis

• Halts cell protein synthesis, resulting in cell death

Mex pumps

• Subset of efflux pumps

• Multidrug export pumps

• Found in P. aeruginosa (and some other bacteria)

Carbapenemases

• Enzymes produced by certain drug resistant bacteria

• Break down carbapenems

• More common in Gram-negative bacteria (it exists in the periplasmic space

• Less common in Gram-positive bacteria (they secrete it into the extracellular environment)

Siderophores

Low molecular weight molecules produced by bacteria that bind and transport iron from environments with relatively low iron

Pyoverdine

• Type of siderophore

• Produced by P. aeruginosa

• Once bound to iron, they are attracted to FpvA on the bacterial cell wall

• _______ = your UberEats courier; iron = the burrito you ordered

FpvA

• Transport protein in cell wall of pseudomonas

• Pyoverdine bound to iron is attracted to this protein, allowing iron from the environment to be delivered to

• ____= your front door (which your burrito (iron) was delivered to by your UberEats courier (pyoverdine))

Diagnosis of VAP

2 out of 3 of the following:

• Clinical and resporatory findings

• Imaging

• Microbiological evidence

Is collecting bacteria to culture done before or after antibiotics are started?

Before

When is broad empirical antibitoic treatment indicated?

When the risk of antimicrobial resistance is high, such as following a long hospital stay (greater than or equal to 5 days)

Antipseudomonal antibiotics

• Pipercillin-tazobactam

• Cefepime

• Ceftazidime

• Imipenem

• Meropenem

• Ciprofloxacin

• Levofloxacin

Carbapenems

• Synthetic class of beta-lactams

• Broad spectrum

• Inhibit cell wall synthesis

Cephalosporins

• Broad class of beta lactams

• Divided into 5 generations

• Some generations only work against Gram-negative bacteria, and some work against both

Fluoroquinolones

• Broad spectrum class of antibiotics

• Blocks bacterial DNA replication and repair

Pipericillin-tazobactam

• A penecillin paired with a beta lactamase inhibitor

• Often used to treat pseudomonas

MRSA infection locations

• Skin and soft tissue

• Bacteremia

• Pneumonia

• Endocarditis

• Osteomyelitis

Pathogens treated by vancomycin

• Gram-positive bacteria

• Staph. aureus and C. difficile (though different deliveries)

P. aeruginosa infection locations

• Basically anywhere wet

• Urinary tract

• Lungs

• Burnt tissue

C. difficile exotoxins

• A and B

• They enter the intestinal epithelial cells and inactivate GTPases by glycosylating them

• This results in cells dying and inflammation

C. difficile diagnosis

• Stool sample PCR to test for DNA that encodes exotoxins A and B

• Possibly immunoassay for exotoxins A and B

• X-ray to check for colonic dilation

• Can use sigmoidoscopy, but this increases risk of perforation, especially if there is already colonic dilation so check for that first

C. difficile treatment

• Oral vancomycin

• If severe colonic dilation is present, also treat with IV metronidazole (since the oral vancomycin may be unable to reach some affected tissue)

C. difficile structures and abilities

• Endospore formation (very resistant)

• Exotoxin A and B, which caused cell lysis and inflammation

Risk factors for infection with antibiotic resistant bacteria

• Antibiotic use in preceding 90 days

• Over 5 days of current hospitalization

• Hospital unit or community microbes that are resistant at a high frequency

• Immunosuppression

Diagnostic biomarkers

Used to:

• Differentiate between different types of pathogens (bacterial, viral, fungal, parasitic)

• Identify the causative pathogen

Prognostic biomarkers

Used to:

• Predict the outcome or possible complications

• Inform decisions about care or additional diagnostic tests

Therapeutic biomarkers

Used to:

• Determine initial treatment

• Tailor antibiotics

• Avoid antibiotic side effects

• Prevent overuse of antibiotics

• Minimize antibiotic resistance

Procalcitonin (PCT) value cut-off for determining whether current bacterial infection is likely

0.5 ug/L

MRSA soft tissue infection treatment

IV vancomycin

FTM (fluid glycolate medium)

Used to determine the oxygen requirements of a bacteria (aerobic, anaerobic, etc.)

Where is procalcitonin produced

• In the thyroid

• Upregulated by bacterial cytokines (such as IL-1a, IL-6, and TNF-a)

• Downregulated by INF-y, produced during viral infections

How is NGAL produced

• By neutrophils in response to bacterial components

• Also by damaged microtubules in the kidneys

WHat does high NGAL indicate?

• Bacterial infection or kidney damage

• #controversial

How is PENK produced?

By neurons primarily in the CNS, but also the PNS

What does high PENK indicate?

• Negatively correlated with glomerular filtration rate ([ ] goes up, filtration rate goes down) → indicates acute kidney damage in septic patients

• Predictive of short-term mortality

How is CRP produced?

• Cells in the liver

• In response to cytokines, indicative of infection or inflammation of some sort

What does high CRP indicate?

• Inflammation or infection

• Has low specificity

When should oral antibiotics be used over intravenous?

• Only for pathogens infecting interlumenal areas

• Pathogens that are not near blood vessels and will be safe from antibiotics circulating in the blood

• E.g., C. diff

When should vancomycin be used? What are the downsides?

• Only when it must be, such as when treating MRSA or C. diff

• It can cause liver and kidney damage

• Overuse of the drug when not absolutely necessary could contribute to resistance to the drug

Cetrimide agar

• Solid media used to culture pseudomonas

• GREEN SRUFD IDK ADD MORE

Is MRSA or C diff more likely to spread to the blood? Why?

• MRSA

• C. diff enters through fecal-oral route, while MRSA is often on medical devices and has a wide range of entry points

• C. difficile just likes the intestines man

Leukocytosis cut-off value

11000 cells/uL

Leukocytopenia cut-off

4000 cells/uL

Populations at risk for MRSA

• IV drug users

• AND MORE

You suspect that a patient is infected with staphylococcus. What would a catalase test indicate?

• Positive: it is staphylococcus

• Negative: it something else, such as streptococcus

You suspect that a patient is infected with staphylococcus aereus. What would a coagulase test indicate?

Positive: it is Staphylococcus aereus

Negative: it is a different type of staphylococcus, such as S. epidermidis

You suspect that a patient is infected with MRSA. What would testing for MecA tell you?

Positive: it is MRSA

Negative: it is another type of Staphylococcus aureus

VRE (vancomycin resistant enterococcus)

• Typically E. fascism

• Rarely causes disease in healthy people

• Rectal/perirectal swab or stool culture

• Treat with ampicillin

ESBL (extended spectrum beta-lactam producers)

• Include E. coli and K. pneumoniae

• Resistant to most beta-lactams, except for carbapenems

• Can cause UTIs, pulmonary infections, bacteremia, etc.

Necrotizing fasciitis

• Rapidly spreading bacterial infection of soft tissue

• Destroys muscle fascia, and subcutaneous fat

• Life threatening

• Often involves multiple types of bacteria (70%) but can also be monomicrobial (30%)

Erysipelas

• Skin infection specifically affecting the upper layers of the dermis (does not enter the hypodermis)

• Has clear margins of infection

• Often caused by Streptococcus pyogenes, but occasionally caused by MRSA or other bacteria

• Enters through small breaks in the skin