Gram Negative Rods

Question 1

Klebsiella

part of:

motility? capsule?

Infection seein in:

Often resistant to:

Answer 1

part of Intestinal flora

Non-motile, capsular

Infection with impaired host defenses • Alcoholics***, diabetics, sick people (nosocomial)

Infection with aspiration of GI contents • Aspiration pneumonia, Lung abscesses

Often resistant to many antibiotics

Treatment based on susceptibility testing

Question 2

Klebsiella pneumonia & • Lung abscess

Answer 2

Klebsiella pneumonia

Lobar • Occurs in alcoholics or diabetics, often after aspiration • Classically results in red “currant jelly” sputum

Lung abscess

Usually caused by mouth anaerobes • Peptostreptococcus, Fusobacterium, Prevotella, Bacteroides • Can also be due to Klebsiella

Rare cause of UTIs (3-4%) • Liver abscesses • Usually in patients with underlying liver disease or cholangitis

Question 3

2 Special virulence factors of E. Coli

Answer 3

Fimbriae (pili)

Attach to epithelial surfaces • May be specialized for surfaces (i.e. urinary tract)

K capsule

K1 capsular antigen present in 75% meningitis cases (babies) • Inhibits phagocytosis, complement

Question 4

4 E. Coli Diseases:

Answer 4

Watery diarrhea

Bloody diarrhea (dysentery)

UTI/pyelonephritis - E. Coli bacteremia/sepsis (rare), usually from UTI

Meningitis in newborns

Question 5

4 E. Coli Diarrheal Illnesses & trearment:

Answer 5

EnteroINVASIVE E. Coli (EIEC): Invades intestinal mucosa • Necrosis, inflammation, bloody diarrhea • Clinically similar to Shigella (except no toxins)

EnteroTOXIGENIC E. Coli (ETEC): • Two toxins: heat Labile and Stable • Watery (traveler’s) diarrhea (contaminated food/water) • No inflammation/invasion

EnteroPATHOGENIC (EPEC): • No toxin, no inflammation • Blunt villi, prevent absorption • Diarrhea usually in children (p=pediatrics)

EnteroHEMORRHAGIC (EHEC)

• Most E. Coli diarrheas self-limited • Usual treatment is hydration

Question 6

Enterohemorrhagic E. Coli EHEC

sorbitol:

classic serotype:

invasive?

toxin?

toxin effects?

Answer 6

Does not ferment sorbitol (sorbitol-MacConkey agar)

Classic serotype: E. coli O157:H7

Does not invade host cells (toxin causes disease)

Produces Shiga-like toxin → bloody diarrhea • Bacteriophage-encoded (lysogenic) toxin • Usually from undercooked beef

Toxin Effects • Endothelium swells → vessel lumens narrow • Deposition of fibrin/platelets in microvasculature • Hemolysis, inflammation

Question 7

Hemolytic Uremic Syndrome

Complicates:

Common in:

Triad:

TTP:

Usually occurs_days after diarrhea

Answer 7

Complicates ~10% EHEC cases

Common in children

Triad: Hemolytic anemia • Thrombocytopenia • Acute renal failure (uremia)

TTP Thrombotic thrombocytopenic purpura= HUS + fever, mental status changes

Usually occurs 5-7 days after diarrhea

Question 8

Gram Negative Sepsis driven by:

Answer 8

Endotoxin (LPS; Lipid A)

Common scenario: • Elderly patient • UTI (catheter, BPH) • Gram negative sepsis (+ blood cultures)

Question 9

Infectious Diarrhea

Bloody vs watery:

Answer 9

Question 10

Enterobacter

Rare cause of:

Resistant to:

Often treated with:

Answer 10

Rare cause of nosocomial UTIs

Resistant to many antibiotics • Extended-spectrum beta-lactamases (ESBL) • Resistance to most beta-lactams: penicillins, cephalosporins, and aztreonam

Often treated with Carbapenems • Imipenem, Meropenem

Question 11

2 types of Salmonella :

Answer 11

Salmonella typhi → typhoid fever

Non-typhoid strains → Enterica, enteritidis which cause gastroenteritis Nausea, vomiting, cramps, bloody diarrhea • Ingestion of contaminated meat, eggs, poultry

Question 12

Salmonella

mobility?

capsule?

Disseminate through:

lives in:

Differentiate from Shigella by:

invasive? immune response type?

Answer 12

Flagellated and motile

Encapsulated

Disseminate through blood • Osteomyelitis in sickle cell patients

Live in GI tract of mammals, birds, reptiles

Produce hydrogen sulfide • Triple Sugar Iron (TSI) test → media turns black • Differentiates from Shigella

Invades GI mucosa • Cellular response: Largely monocytes

Question 13

Typhoid Fever

caused by:

symptoms:

travelers to these countries at higher risk:

classic features 1 & 2

carrier state:

Answer 13

Salmonella Typhi

Fever, headache, abdominal pain, diarrhea

Travelers to Asia, Africa, South America

Classic feature #1: Rose spots • Faint salmon-colored macules • Trunk and abdomen

Classic feature #2: Pulse-temperature dissociation • High fever → slow pulse

Can remain in gall bladder (carrier state) • Endemic countries 1-4% people may be carriers • May be risk factor for carcinoma

Question 14

Salmonella

diagnosis:

treatment:

Answer 14

Diagnosis: Culture (stool, blood)

Treatment gastroenteritis: • Fluids/electrolytes • Few data showing antibiotics are helpful (may prolong illness) • Difficult to treat: Lots of antibiotic resistance • Antibiotics used in severely ill patients only • Anti-peristalsis meds (Loperamide) contraindicated

Typhoid fever: Ceftriaxone**, **Fluoroquinolones • Typhoid vaccine available • Inactive variant of bacteria given orally • Used for traveler’s to high risk areas

Question 15

Shigella

motility?

invasive?

Spreads:

toxin?

famous for:

Cellular response:

Answer 15

Nonmotile (no flagella)

Invades mucosal cells (M cells in Peyer’s patches) • Macropinocytosis • Induces apoptosis

Spreads from cell to cell • Does not spread via bloodstream (like Salmonella)

Releases Shiga toxin • Cellular invasion most important mechanisms of disease since non-toxin strains still cause disease

Very few bacteria can cause disease (few as 10!)

Cellular response: Largely PMNs

Question 16

Shigella

GI flora?

transmission?

Common in:

Diagnosis:

Treatment:

Answer 16

Not normal GI flora

Fecal-oral transmission

Common in children

Diagnosis: Stool Culture

Treatment: • Fluids/electrolytes • Antibiotics improve symptoms, reduce shedding in stool • Can limit spread •

Ceftriaxone or Ciprofloxacin

Question 17

Salmonella vs Shigella

differentiate:

immune responce:

spread:

antibiotics:

motility:

Answer 17

Question 18

Proteus

Rare cause of:

“_ phenotype”, __ on agar plates

Produces _

Associated with :

Answer 18

Rare cause of UTIs

“Swarm phenotype” • Long flagella • Facilitates urinary ascent • Bulls-eye on agar plates

Produces urease • Converts urea to ammonia

Associated with struvite kidney stones

Question 19

Pseudomonas aeruginosa Toxins

Answer 19

Endotoxin (LPS) • Can cause fever, shock

Exotoxin A • Inactivates elongation factor (EF-2) • EF-2 necessary for protein synthesis

Question 20

5 Pseudomonas Infections 1 distinctive feature:

Answer 20

Pneumonia in cystic fibrosis

Burn infections

Hot tub folliculitis • Tender, itchy papules after using a hot tub or spa

Otitis externa (Swimmer’s ear) • Inflammation of the outer ear and ear canal • Painful ear with discharge

Osteomyelitis in IV drug users

Ecthyma gangrenosum • Black, necrotic ulcers on skin with bacteremia • Invasion/destruction blood vessels by bacteria • Classic case is neutropenic cancer patient in hospital developes fever, chills (bacteremia) & develops black lesions on chest/back

Question 21

H. Pylori

causes:

urease & breathe test:

Answer 21

Causes gastritis and ulcers (abdominal pain)

Urease positive • Hydrolyzes urea to compounds that damage epithelium • Produces ammonium (alkaline) • Protects bacteria from stomach acid

Urea breath test • Patients swallow urea with isotopes (carbon-14 or carbon-13) • Detection of isotope-labelled carbon dioxide in exhaled breath • Indicates urea was split (i.e. urease present)

Question 22

H. Pylori

common in:

HIGHLY associated with:

diagnosis:

Answer 22

Infection common in patients with ulcers

Majority of patients with duodenal ulcers • Many patients with gastric ulcers

MALT lymphoma

Mucosal associated lymphoid tissue • B-cell cancer, usually in the stomach • HIGHLY associated with H. Pylori infection

Diagnosis: • Biopsy • Urea breath test • Stool antigen

Question 23

H. Pylori treatment:

Answer 23

Treatment: “Triple therapy” for 7-10 days • Proton pump inhibitor • Clarithromycin • Amoxicillin/Metronidazole

Testing often repeated to confirm eradication • Breath test, stool antigen, or biopsy

Treatment failures ~20% • Alternate regimens can be tried

Question 24

Legionella stain & culture

Answer 24

Does not gram stain well • Silver stains used • Special culture requirements • Buffered charcoal yeast extract agar (BCYE) • Iron and cysteine added for growth

Question 25

Legionella

infection from:

symptoms + 2 unique features of legionella pneumonia :

Answer 25

Infection from inhalation of aerosolized bacteria • Not airborne • Outbreaks at hotels with contaminated water • Can cause nosocomial pneumonia in nursing homes

Initially mild pneumonia symptoms • Fever; mild, slightly productive cough • Can progress to severe pneumonia • 1.)GI symptoms • Watery diarrhea, nausea, vomiting, and abdominal pain • 2.)Hyponatremia (Na<130 meq/L) common • Can occur in any pnumonia but more common Legionella

Question 26

Legionella classic case & treatment:

Answer 26

Classic Case • Mild cough • Watery diarrhea • Confusion (low Na) • Negative bacteria on gram stain

Treatment: Fluoroquinolone or Macrolide

Question 27

what is Pontiac Fever?

Answer 27

Mild form of Legionella infection • Fever, malaise, chills, fatigue, and headache • No respiratory complaints • Chest radiograph usually normal

Question 28

Bacteroides fragilis

description:

rarely causes:

covered by:

common GI therapy:

Answer 28

Gram (-) rod • Anaerobic bacteria • Normal GI flora • Cause infection after breach of mucosal barrier

Rarely causes infections alone • Usually part of polymicrobial infections from GI tract • Peritonitis (following perforation) • Intraabdominal abscess • Lung abscess (aspiration) • E. Coli/GNRs and B. Fragilis often components together

Covered by metronidazole

Common GI therapy: Cipro/Flagyl • Quinolone for E. Coli • Metronidazole for B. Fragilis