Gram Negative Rods Flashcards
Klebsiella
part of:
motility? capsule?
Infection seein in:
Often resistant to:
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
Klebsiella pneumonia & • Lung abscess
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
2 Special virulence factors of E. Coli
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
4 E. Coli Diseases:
Watery diarrhea
Bloody diarrhea (dysentery)
UTI/pyelonephritis - E. Coli bacteremia/sepsis (rare), usually from UTI
Meningitis in newborns
4 E. Coli Diarrheal Illnesses & trearment:
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
Enterohemorrhagic E. Coli EHEC
sorbitol:
classic serotype:
invasive?
toxin?
toxin effects?
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
Hemolytic Uremic Syndrome
Complicates:
Common in:
Triad:
TTP:
Usually occurs_days after diarrhea
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
Gram Negative Sepsis driven by:
Endotoxin (LPS; Lipid A)
Common scenario: • Elderly patient • UTI (catheter, BPH) • Gram negative sepsis (+ blood cultures)
Infectious Diarrhea
Bloody vs watery:
Enterobacter
Rare cause of:
Resistant to:
Often treated with:
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
2 types of Salmonella :
Salmonella typhi → typhoid fever
Non-typhoid strains → Enterica, enteritidis which cause gastroenteritis Nausea, vomiting, cramps, bloody diarrhea • Ingestion of contaminated meat, eggs, poultry
Salmonella
mobility?
capsule?
Disseminate through:
lives in:
Differentiate from Shigella by:
invasive? immune response type?
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
Typhoid Fever
caused by:
symptoms:
travelers to these countries at higher risk:
classic features 1 & 2
carrier state:
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
Salmonella
diagnosis:
treatment:
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
Shigella
motility?
invasive?
Spreads:
toxin?
famous for:
Cellular response:
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
Shigella
GI flora?
transmission?
Common in:
Diagnosis:
Treatment:
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
Salmonella vs Shigella
differentiate:
immune responce:
spread:
antibiotics:
motility:
Proteus
Rare cause of:
“_ phenotype”, __ on agar plates
Produces _
Associated with :
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
Pseudomonas aeruginosa Toxins
Endotoxin (LPS) • Can cause fever, shock
Exotoxin A • Inactivates elongation factor (EF-2) • EF-2 necessary for protein synthesis
5 Pseudomonas Infections 1 distinctive feature:
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
H. Pylori
causes:
urease & breathe test:
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)
H. Pylori
common in:
HIGHLY associated with:
diagnosis:
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
H. Pylori treatment:
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
Legionella stain & culture
Does not gram stain well • Silver stains used • Special culture requirements • Buffered charcoal yeast extract agar (BCYE) • Iron and cysteine added for growth
Legionella
infection from:
symptoms + 2 unique features of legionella pneumonia :
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
Legionella classic case & treatment:
Classic Case • Mild cough • Watery diarrhea • Confusion (low Na) • Negative bacteria on gram stain
Treatment: Fluoroquinolone or Macrolide
what is Pontiac Fever?
Mild form of Legionella infection • Fever, malaise, chills, fatigue, and headache • No respiratory complaints • Chest radiograph usually normal
Bacteroides fragilis
description:
rarely causes:
covered by:
common GI therapy:
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
