Infectious Disease I Final O'Donnell Cumulative Material

Cell wall differences + Lectures 7 (Gm-) and 8 (Gm+)

Main biochemical difference between prokaryotic and eukaryotic plasma membranes

Prokaryotic membranes use hopanoids

• Can target these with antibiotics

Eukaryotic membranes use cholesterol

Bacterial Cell Wall

Rigid structure that surrounds the plasma membrane and protects bacteria in many different environments

Consists of peptidoglycan

• Can target this with antibiotics

Functions of the bacterial cell wall

Provides shape

Protects the cell from ossmotic lysis

May contribute to pathogenicity

May protect the bacteria from toxic substances

Peptidoglycan structure

Polysaccharide formed from peptidoglycan subunits

Backbone of alternating sugars N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)

Muramic residues covalently crosslink with each other

• Crosslinks between peptide side chains provide resistance and rigidity

• Can target these crosslinks with antibiotics

Structural differences in cell wall for gram positive and gram negative bacteria

Gram positive

• Thick peptidoglycan layer

Gram negative

• Thin peptidoglycan layer

• Outer membrane

Composition of gram positive cell wall

Composed primarily of peptidoglycan, contain large amounts of teichoic acids

Some have a layer of proteins on surface of peptidoglycan

Composition of gram negative cell wall

Thin layer of peptidoglycan surrounded by an outer membrane, which includes:

• lipids, lipoproteins, and lipopolysaccharide (LPS)

• No teichoic acids

Contain porins, which allow nutrients and water-soluble antibiotics to pass

Porin

Water-soluble channel

Lipopolysaccharide (LPS)

Bacterial structure embedded in the outer membrane of gram negative bacteria that is involved in resisting the immune response

Three parts:

• Lipid A

• Core polysaccharide

• O side chain (O antigen)

Functions of LPS O Antigen

Protection from host defenses

• Blocks lysozyme activity

  • Only enzyme we have that degrades peptidoglycan

• Inteferes with antibody response

Adheres to host tissues

How does O Antigen interfere with antibody response?

It has lots of variability

• Hard for our immune system to recognize/learn this

Function of LPS Core Polysaccharide

Contributes to negative charge on cell surface

• Harder for immune cells to phagocytose

Functions of LPS Lipid A

Attaches LPS to membrane

Helps stabilize outer membrane structure

Can act as an exotoxin (Toxin that is part of the bacteria’s structure)

Released when bacterial cells die

Source of fram negative infection symptoms

• Flu-like symptoms, sore, fever, etc.

Periplasmic Space

Gap between the plasma membrane and the cell wall in gram positive bacteria or the outer membrane in gram negative bacteria

Filled with periplasm

• Periplasmic enzymes

Functions of periplasmic enzymes

Nutrient acquisition

• Bind sugars and amino acids

Electron transport

Peptidoglycan synthesis

Modification of toxic compounds

Inactivation of antibiotics

How does the periplasmic space help bacteria inactivate antibiotics?

Bacteria release enzymes that degrade antibiotics and collect them in the periplasmic space

What color are gram positive bacteria after a gram stain?

Purple

What color are gram negative bacteria after a gram stain?

Pink

One type of bacteria can often cause multiple diseases based on:

The location in the host and virulence factors

What types of bacteria are associated with STIs?

Chlamydia

Neisseria

• Not N. meningitidis

Chlamydia trachomatis

Pleiomorphic, intracellular, gram negative

Most common bacterial STI in the US

Most cases are asymptomatic (“silent” disease)

In women, initially infects the cervix and urethra

• Can spread to fallopian tubes or uterus → Pelvic Inflammatory Disease (PID) → can lead to infertility

Antibiotic resistance is uncommon

No vaccine

Neisseria gonorrhoeae

Gram negative diplococci

2nd most common STI in the US → non-sexual transmittion is rare

Localised mucosal infection, rarely in blood

Test by PCR along with chlamydia

• Specific test for the DNA of the bacteria

95% of men and 50% of women are symptomatic

Can lead to Epididmitis in men and Pelvic Inflammatory Disease in women

Risk of spread is up to 50% (very high for an STI)

Lots of penicillin resistance

No effective vaccine (due to antigenic variation)

Why are gonorrhea and chlamydia tested for at the same time using a PCR test? 

They have similar symptoms, and it is difficult to gram stain chlamydia

Neisseria meningitidis

Gram negative diplococci

NOT an STI

Causes meningitis

• Infect bloodstream or CNS

• Fever, headache, seizures, inflammation, increased cranial pressure-

• Mostly infants and age 18-20

Person to person spread via respiratory route

Can also cause endotoxic shock (released of LPS)

Protect themselves from immune response by incorporating host sugars in the outer membrane to look like host cells

Has a vaccine

Similarities and differences between strains of Neisseria

Both attach with pili and OMPs (outer membrane proteins)

Both express LPS

N. gonnorrhoeae

• No capsule

• Localized infection

N. meningitidis

• Capsule → more invasive

• Systemic infection

Meningitis

Infection and inflammation of the meninges, or membranes around the brain and spinal cord

Neisseria meningitidis vaccine recommendations

First dose recommended at 11 years old

Recommended as early as 2 months old for high risk infants

Booster at 16 years old

• Protects students entering college or the military

What types of bacteria are associated with respiratory infections?

Haemophilus

Bordetella

Moraxella

Legionella

Haemophilus Bacteria

Gram negative coccobacilli

Only found in people

Part of the normal flora in many people

Haemophilus influenzae

Can cause respiratory and sinus infections, otitis media, and conjunctivitis (NOT what causes seasonal influenza)

Most virulent strains have capsules

• Can invade the CNS (meningitis) and the joints (arthritis)

6 serotypes (A-F)

• Different capsules and surface polysaccharides

Haemophilus influenzae Serotype B (Hib)

Most virulent

Capsule includes a polysaccharide called polyribitol phosphate (PRP)

• Vaccine designed against PRP

  • Recommended at 2 months of age

Bordetella pertussis

Gram negative coccobacilli

Destroys cilia in the respiratory tract

Causes whooping cough

• Infants at highest risk

Pertussis toxin

• A-B exotoxin

Antibodies against pertussis toxin prevent colonization of the bacteria

DTaP Vaccine

• Diphtheria, Tetanus, acellular Pertussis

DTaP Vaccine Schedule

2 months, 4 months, 6 months, 15-18 months, and 4-6 years

Booster at 11-12 years

Complications from whooping cough

Nose bleeds and ear infections

Pneumonia

Brain damage

• Mental impairment

• Seizure disorders

Cerebral hemorrhage

Death

Moraxella catarrhalis

Gram negative diplococci

Mostly associated with localized infections like pneumonia, bronchitis, otitis media

• Commonly causes lower respiratory tract infections in elderly patients with other pulmonary conditions

Frequent β-lactamase producer

• Often found with other bacteria, since β-lactamase release can protect other bacteria in the area

Legionella pneumophila

Intracellular gram negative bacilli

Ubiquitous in fresh water and plumbing

• Lives within amoebas, protozoa

Causes necrotizing multifocal pneumonia

• Infects alveolar macrophages, taking control of the ribosomes and mitochondria

• High mortality (15-50%)

  • Respiratory failure, shock

  • Most often seen in immunocompromised and elderly patients

Person to person transmission has not been shown

Necrotizing Multifocal Pneumonia

Inflammation of the lungs and death of lung tissue in multiple areas of the lung

What types of bacteria are associated with gastrointestinal infections?

Straight gram negative rods

• Enterobacterales

Curved gram negative rods

• Vibrio

• Campylobacter

• Helicobacter

Enterobacterales

Straight gram negative bacilli

Large family of enteric bacteria

• Main pathogens are:

  • Escherichia coli

  • Klebsiella

  • Proteus

  • Shigella

  • Salmonella

Especially problematic if they escape the digestive tract

Facultative anaerobes

Shigella and salmonella are very similar genetically and are spread by _____

Contaminated food and fecal-oral route

Key lab finding for E. coli and Klebsiella

Lactose positive

• Can ferment lactose

Escherichia coli

Over 700 different strains

Most common infections:

• Food poisoning/diarrhea (gastroenteritis)

• Urinary tract infections

Also associated with more invasive infections including:

• Pyelonephritis (UTI that spread to kidney)

• PID

• Pneumonia

• Meningitis

Prevention is key for all strains

Classification of E. coli

Classified by surface antigens - important for tracking the origin of outbreaks

• H antigens: flagella

• O antigens: LPS

• K antigens: capsule

• Ex. O157:H7 - found in cow intestines, common source of outbreaks

Classified according to virulence

1. Enteropathogenic (least invasive)

2. Enterotoxic

3. Enteroinvasive

4. Enterohemorrhagic (most invasive)

Enteropathogenic E. coli

Adheres to gut, but doesn’t enter cells

Destroys surface microvilli

Causes diarrhea and vomiting

Injects proteins into the cell, forcing actin rearrangement into pedestal shape

Enterotoxic E. coli

Produces exotoxins

• Cholera-like toxin - causes release of water and iron from cells

• Heat-stabile toxin - prevents uptake of water and iron from cells

Overall effect: severe diarrhea and vomiting

Enteroinvasive E. coli

Actually invades/enters cells

Causes dysentary

• Damages cells of the digestive tract, often killing them

• Often leads to bloody diarrhea and fever

More likely to be fatal

Mostly seen in kids under 5

Enterohemorrhagic E. coli

Doesn’t stay in intestinal tract

Produces an exotoxin from Shigella

Gets into bloodstream and causes systemic infection

• Attacks kidneys (kidney failure)

• Can cause descending UTIs

• Anemia (exotoxins kill red blood cells)

• Hemorrhagic diarrhea

• Combination of symptoms called Hemolytic-uremic Syndrome (Anemia-kidney failure)

Most common cause of acute kidney failure in children

Ex. O157:H7

Klebsiella pneumoniae

Normal part of gut flora

• Doesn’t usually cause disease in health people

Cause of healthcare associated infections

• Pneumonia, bloodstream infections, surgical site infections, meningitis

Becoming very resistant to antibiotics

Carbapenem-resistant Enterobacterales (CRE)

Group of bacteria that are resistant to carbapenems

Caused by plasmids that carry genes for particular enzymes

• KPC (Klebsiella pneumoniae carbapenemase) - most widespread in US

• NDM (New Delhi Metallo-beta-lactamase)

• Oxa-48 (Oxacillinase-48)

Proteus Bacteria

Gram negative bacilli

Lactose negative

Normal part of gut flora

Becomes a problem if it enters the urinary tract

• Most common cause of hospital-acquired UTIs

• Associated with urinary stones and complicated UTIs

Very good at immune invasion

Proteus mirabilis

Most common Proteus bacteria

They can “swarm”

• Lots of flagella

• Move over viscous and solid surfaces

• Issue for urinary catheters, movement to kidneys

Sulfur/rotten egg smell

Campylobacter jejuni

Gram negative curved/spiral bacilli

Microaerophile

Leading cause of gastrointestinal illness in developed countries

• Contaminated food (raw chicken)

Causes diarrhea and dysentary

Usually self-limiting, but antibiotics are required if it escapes the digestive tract

May lead to Guillain-Barré Syndrome

Guillain-Barré Syndrome

Generally proceeded by an infection

Demyelinating neuropathy

Surface antigen on C. jejuni resembles gangliosides on peripheral myelin

• The immune response mistakenly attacks myelin

  • Cross reactive antibodies → detect more than one thing

Therapy for Guillain-Barré Syndrome

Plasmapheresis

• Filters out antibodies from bloodstream

  • Removes cross-reactive antibodies and quiets immune response

High dose immunoglobulin therapy

Helicobacter pylori

Gram negative curved or spiral bacilli

Microaerophile

Limited to the stomach

• Produces urease

  • Allows the bacteria to persist in low pH

Associated with many gastric ulcers

• Antibiotic treatment is common now

May also be associated with gastric cancer

• Chronic inflammation in the gut may lead to rapid turnover of cells

• Link between inflammation and cancer

Zoonosis

Disease primarily of animals that can be transmitted to humans due to direct or indirect contact with infected animals

Yersinia pestis

Gram negative bacilli, zoonotic

Facultative anaerobe

Cause of the Black Death or Bubonic Plague

Killed 1/3 of Europe’s population in the middle ages

• Less concern today due to better sanitation

• Still occasional cases in the southwestern US through encounters with infected rodents or fleas

Concerns due to possible use for bioterrorism

• Potential for person to person spread in densely populated urban areas

SPACE Organisms

5 gram negative bacteria that are opportunistic, found in healthcare settings, and have antibiotic resistance

Pseudomonas aeruginosa

Aerobic gram negative bacilli

Most common SPACE bacteria

Most often seen in patients with another illness/injury

Produces Toxin A

• Prevents protein translation in host cells

Characterized by the formation of a dark blue pigment, pyocyanin

Forms biofilms in the lung

• Problem for cystic fibrosis patients

• Leads to chronic infection, greater inflammation, and higher antibiotic doses (100-1000x the MIC)

  • Once biofilm is established → difficult to get rid of

Pseudomonas aeruginosa is most often seen in patients with another illness/injury such as:

Burns and wounds

• Destruction of blood vessels

• Phagocyte access is limited

Cancer

• Chemotherapy destroys the immune system

Cystic fibrosis

• Altered respiratory epithelium

• Pneumonia

Acinetobacter baumannii

Gram negative pleiomorphic SPACE bacteria

Induces apoptosis of infected cells

Resistant to complement tagging

Forms biofilms

Multiple invasive disease states

• Meningitis, wound infection, bloodstream infections, pneumonia

Recent emergence of multi-drug resistant (MDR) and pan-drug resistant (resistant to everything we have) strains

Bacteroides fragilis

Opportunistic gram negative bacilli

Obligate anaerobe

Part of gut flora, not invasive on its own

• Can even be helpful, people with this bacteria often have lower levels of inflammation in the gut

• Damage/trauma to intestines can allow it to escape and cause abdominal abscesses

• Most commonly isolated bacteria from anaerobic infections

Positive role

• May prevent colitis or inflammatory bowel disease

  • Produces polysaccharide A, which inhibits inflammation

_____ bacteria are most concerning and highest priority in terms of drug resistance

Gram negative

Streptococcus Bacteria

Gram positive cocci, usually in chains

Facultative anaerobic

Characterized by Lancefield carbohydrates and hemolytic activity

Characterization of Streptococcus bacteria by Lancefield carbohydrates

Surface carbohydrates

• Groups A-W

• Groups A, B, and D are the most important clinically

• A few cannot be classified by their carbohydrates and are considered “ungroupable”

  • Ex. S. pneumoniae

Characterization of Streptococcus bacteria by hemolytic activity

Ability to lyse red blood cells

• Alpha-hemolytic → partial hemolysis (Ex. S. pneumoniae)

• Beta-hemolytic → complete hemolysis (Ex. S. pyogenes)

• Gamma-hemolytic → no hemolysis (Ex. Group D strep)

Group A Streptococcus

Most common bacterial cause of sore throat

Also causes toxic shock syndrome and necrotizing fasciitis (flesh-eating disease)

Necessary to quickly identify

• Bacitracin sensitivity

• Rapid Strep test

  • Tests for Group A Lancefield carbohydrates

Streptococcus pyogenes

Group A Streptococcus

Beta-Hemolytic

F protein (an adhesin)

• Attaches to fibronectin on the surface of epithelial cells

M protein

• Part of pili

• Also important for attachment

• Site of extensive antigenic variation

Infections caused by Group A Streptococcus

Pharyngitis (Strep throat)

• Most common infection

• If left untreated can progress to:

  • Scarlet fever

  • Rheumatic fever

Skin Infections including:

• Impetigo

• Necrotizing fasciitis

Streptococcal Toxic Shock Syndrome

Scarlet Fever

Rash all over body

Caused by a superantigen

High fever

Rare if treated with antibiotics

Rheumatic Fever

Life-threatening inflammatory disease

Occurs weeks to years after sore throat

• Group A Strep infection is no longer active

Characterized by fever, endocarditis (inflammation of the endocardium in the heart), joint pain

Why is there a delay between Group A Strep infection and rheumatic fever?

Cell wall is poorly broken down by our enzymes

• Cell wall fragments persist in the body for years after infection and can retrigger the immune response

Antibodies against M-protein cross-react with cardiac myosin, a protein in our heart muscle

• Immune system mistakenly targets myosin in the heart

Impetigo

Highly contagious skin infection

Mostly infants and school-age kids

Open sores around mouth and face

Easily treatable with antibiotics

Necrotizing fasciitis

Typically after a wound in the skin

Can become invasive

Produces superantigens that atack and kill fascia

Can also be caused by other kinds of bacteria

Streptococcal Toxic Shock Syndrome

Rapid, systemic infection

Follows skin infections, rarely follows strep throat

Superantigens are almost always expressed

Rare, but extremely life threatening

Streptococcus pneumoniae

Gram positive diplococci

Ungroupable, but genetically related to Group A

Alpha-hemolytic

A leading cause of pneumonia in the US

• Usually occurs after a cold or other viral infection in healthy people

Has a capsule → can lead to more invasive infections (meningitis, bacteremia (blood infection), sinus infection)

Over 90 serotypes, vaccine provides protection against 23 of them

Antibiotic resistance is common

Teichoic acid in the cell wall attracts a large number of inflammatory cells in the lung

Group B Streptococcus (GBS)

Streptococcus agalactiae

Causes sepsis, meningitis, and pneumonia in newborns

• GBS is in the lower intestine and vaginal tract of 15-40% of healthy adult women

• Passed to newborn during delivery

  • Symptoms can occur weeks later

  • 1 in 2000 births in the US

• Pregnant women are screened for GBS during weeks 35-37 → if positive, deliver antibiotics during labor

Also causes invastive infections in the elderly

Group D Streptococcus

Enterococci (Gut)

Most common ones are Enterococcus faecalis and Enterococcus faecium

• Causes UTIs and soft tissue infections almost exclusively in hospitalized patients with trauma/surgery or that are immunocompromised 

High levels of antibiotic resistance

Why do Group D Streptococcus bacteria have high levels of antibiotic resistance?

Efficient at acquiring plasmids and transposons from other species of bacteria

Complete resistance to cephalosporins, high resistance to most β-lactams and aminoglycosides

• Ampicillins were the most consistently active antibiotic

• If ampicillin-resistant, vancomycin was used

VRE (Vancomycin Resistant Enterococci) are resistant to both vancomycin and ampicillin

Staphylococcus Bacteria

Gram positive grape-like clusters of cocci

Major component of normal skin flora

• Potent opportunist - can cause disease in many ways

Produces IgG binding protein

MSSA and MRSA

Complications of Staphylococcus aureus

Skin lesions (boils, abscesses)

Osteomyelitis (bone infection)

Arthritis

• Most common cause of joint infection

Toxic Shock Syndrome

• Historically associated with tampon usage

• Caused by a superantigen

Scalded Skin Syndrome (under age 6)

• Exfolatin exotoxin (“exfoliate”)

• Epidermis splits from the other layers of the skin

Clostridia Bacteria

Gram positive bacilli

Spore-forming

• Spores last for years

Produce exotoxins:

• C. perfringens → gas gangrene

• C. tetani → tetanus toxin (lockjaw)

• C. botulinum → botulism toxin (flaccid paralysis)

• C. difficile → antibiotic-associated diarrhea

  • Associated with hospital stays and long-term care facilities

  • More common and severe in the elderly

  • Expresses Toxin A and Toxin B

    • Toxin A increases fluid release from the bowel

    • Toxin B kills cells in mucosa

Clostridium botulinum

Pennsylvania is part of the “Botulism Belt”

• Spores of C. botulinum are found in the soil → most likely source of most US cases

• Spores are also found in raw honey and improperly canned foods

In infants, treatment involves BabyBIG

• Human-derived antibodies against the exotoxin