05 Gram-Negative Rods Flashcards
What are the large family of GNRs primarily in the colon?
Enterobacteriaceae
What are the general characteristics of Enterobacteriaceae?
All facultative anaerobes. Ferment glucose, oxidase-negative
What are the common Enterobacteriaceae?
E. coli, Klebsiella, Proteus, Enterobacter, Serratia, Shigella, Salmonella, Yersinia, Vibrio. Pseudomonas aeruginosa
Which Enterobacteriaceae produce exotoxins –> diarrhea?
E. coli, Vibrio
What are the common causes of E. coli?
Most common cause of UTIs, gram-neg bacteremia. Traveler’s diarrhea
What is the most abundant facultative anaerobe in the colon and feces?
E. coli
What is E.coli’s lactose test?
Positive
What are the Virulence factors for E. coli?
Pili (intestinal mucosa, urinary tract epithelium). Capsule (interferes with phagocytosis). Endotoxin. Exotoxins (enterotoxins)
What are the clinical findings for E. coli?
Intestinal tract infections (Traveler’s diarrhea, “dysentery”, fever, abdominal cramping, bloody diarrhea, c/b HUS). Systemic infections
What are the systemic infections caused by E.coli?
UTIs, bacteremia, intra-abdominal infections, neonatal meningitis
What are the characteristics of Klebsiella, Enterobacter, and Serratia?
Opportunists. Large intestine; soil and water. Respiratory tract in 10% of normal hosts (Klebsiella)
What can Klebsiella, Enterobacter, and Serratia cause?
Pneumonia, UTIs, bacteremia
Which ones are lactose-fermenting and lactose-NON-fermenting (Klebsiella, Enterobacter, and Serratia)?
Klebsiella (+), Enterobacter (+), Serratia (-)
What are the characteristics of Proteus, Providencia, and Morganella?
Produce urease –> cleaves urea to form NH3 and CO2 –> alkaline pH in urine, stone formation. Colon; soil, water. Highly motile, lactose (-)
What are some common causes of Proteus, Providencia, and Morganella?
Community and hospital acquired UTI. Stone formation in bladder
What are the common characteristics of Pseudomonas aeruginosa?
Opportunist. Tap water, withstand disinfectants. Colon in 10% of normal hosts, respiratory tract of hospitalized patients
What can Pseudomonas aeruginosa cause?
Pneumonia, UTIs, wound infections, bacteremia
What are the testing results for Pseudomonas aeruginosa?
“Nonfermenter”, lactose (-), oxidase-positive, blue-green pigments “pyocyanin, pyoverdin”
What is the virulence arsenal of P. aeruginosa?
Flagellum. Alginate/biofilm. Pilus. Non-pilus adhesins. LPS. T3SS. Quorum sensing system. Type 1, II secretion system. Crap load of “-ases”
What Quorum Sensing-Controlled Virulence?
“Cell-density” sensing via small signaling molecules. Coordinated expression of virulence genes by an entire bacterial population once a certain density is reached allowing P. aeruginosa to secrete extracellular factors only when they can be produced at high enough levels to overcome host defenses
Which GNR are found in the Respiratory Tract?
Hemophilus influenzae. Legionella pneumophila. Bordetella pertussis
What are the general characteristics of H. influenzae?
Small coccobacillary GNR with polysaccharide capsule (Type B (invasive disease)). Unencapsulated strains - noninvasive disease. Portal of entry is the respiratory tract. Most infections - age 6 months - 6 years
What are the effects of H. influenzae?
Pneumonia in adults. Otitis media, sinusitis, sepsis
What is the Hib vaccine?
Capsular polysaccharide of H. influenzae type b conjugated to carrier protein (i.e. diphtheria toxoid) –> reduce incidence of meningitis by 90% in immunized children, given b/w age 2 and 15 months
What are the characteristics of Legionella pneumophila?
Environmental water sources - air conditioners, water-cooling towers. Nosocomial outbreaks - organisms in water, taps, sinks, showers
What does Legionella pneumophila usually cause?
“Atypical pneumonia” - elderly, immunocompromised patients
How is Legionella pneumophila diagnosed?
Urinary antigen for serogroup 1; culture
How is Bordetella pertussis diagnosed?
Detects by culture or direct fluorescent antibody stain on nasopharyngeal swab
Which GNRs affect the enteric tract?
Salmonella. Shigella. Vibrio. Campylobaccter. Helicobacter
What are the general characteristics of Salmonella?
Notifiable disease; need to determine source. Transmitted by ingestion of food and water contaminated by human and animal wastes; poultry and eggs, dogs and reptiles. Lactose (-) GNR
What are the 3 types of infections caused by Salmonella?
Enterocolitis, Enteric fever (typhoid fever), septicemia
What are the different cultures done for Salmonella?
Stool culture (enterocolitis), blood culture (enteric fevers, septicemia)
What is Enterocolitis?
Invasion of the epithelial and subepithelial tissue of the small and large intestine –> inflammation, diarrhea
What is the incubation period for Enterocolitis?
6-48 hours –> n/v, abdominal pain, diarrhea (self-limited)
What is the most common cause of Enterocolitis?
S. typhimurium. Infectious dose: at least 100,000 organisms
What is Typhoid Fever?
Infection begins in small intestine –> organisms enter and multiply in the mononuclear phagocytes of Peyer’s patches, then spread to phagocytes of the liver, gallbladder, and spleen –> bacteremia
What is the onset of illness like for Typhoid Fever?
Slow, with fever and constipation –> high fever, tender abdomen, enlarged spleen. 3% of patients become chronic carrier –> excrete bacteria in feces for long periods
What is a common cause of Typhoid Fever?
S. typhi
What is Bacteremia?
Accounts for 5-10% of infections. Patients with underlying chronic disease (sickle cell anemia, cancer, AIDS). Child with enterocolitis. Indolent course: fever and focal symptoms of affected organs (bone, lungs, meninges)
What are the characteristics of Shigella sonnei, S. flexneri?
3rd most common cause of bacterial gastroenteritis; age < 5 yo. Causes Enterocolitis. Lactose (-); S. sonnei. Fecal-oral transmission from person to person
What is the infectious dose of S. sonnei, S. flexneri?
Less than 100 organisms. Infects only humans and non-human primates
What is Enterocolitis (dysentery) like for S. sonnei, S. flexneri?
Incubation period 1-4 days, begins with fever and abdominal cramps, followed by diarrhea (watery then blood and mucus), resolves in 2-3 days. Locally invasive, destroying cells of the intestinal mucosa. Rarely penetrates beyond the lamina propria –> phagocytosis
What is Campylobacter?
Comma or S-shaped GNR. Fecal-oral transmission; improperly cooked poultry or cross-contamination by raw poultry
What are the 2 most frequently recovered bacterial gastroenteritis in USA?
Campylobacter jejuni (along w/ Salmonella). Most frequent cause of bacterial gastroenteritis (food poisoning) in college students in US; Males warm-weather months, peak in July. Infants (< 1 yo), adolescents, young adults (15-29)
What is Campylobacter Enterocolitis?
Watery, foul-smelling diarrhea followed by blood stools, fever, severe abdominal pain. Locally invasive, bacteremia rare in immunocompetent patients (rarely in neonates of HIV+). Resistance in fluoroquinolones increasing. Most commonly caused by C. jejuni
For Diarrhea, what are the different differential diagnosis?
Stool specimens, either looking for presence of PMNs (invasive organisms) or absence of PMNs (toxin mediated)
For Diarrhea with the presence of PMNs, what are some common bacterial causes?
Shigella (local). Campylobacter (local). Salmonella (can disseminate, survives w/in phagocytes)
For Diarrhea with the absence of PMNs (toxin-mediated), what are some common bacterial causes?
Vibrio. E. coli. Clostridium perfringens
Which GNRs are Lactose-Negative?
SPASM: Salmonella, Shigella, Serratia. Pseudomonas, Proteus, Providencia. Acinetobacter. Stenotrophomonas maltophilia. Morganella
Which GNRs are Lactose-Positive?
CEEK: Citrobacter. E.coli. Enterobacter. Klebsiella
What are the Anaerobic GNRs?
Bacteroides. Fusobacterium nucleatum. Prevotella melaninogenica
What are the characteristics of Bacteroides?
Peritonitis, abscesses, bacteremia. B. fragilis group is predominant in colon. Non-spore forming anaerobic GNR
How do Bacteroides (i.e. B. fragilis) work with E. coli in the colon?
Mixed facultative (i.e. E. coli) and anaerobic flora (bacteroides) –> E. coli utilize the O2 thereby reducing it to a level that allows the anaerobic Bacteroides strains to grow
What are some infections caused by Bacteroides?
Intrabdominal infections
What are the characteristics of Fusobacterium nucleatum?
Anaerobic GNR. Mouth, colon, female genital tract. Pulmonary, intra-abdominal and pelvic abscesses
What are the characteristics of Prevotella melaninogenica?
Anaerobic GNR. Mouth flora. Oral, pharyngeal, pulmonary abscesses
