ENTEROBACTERIA
Layla Abdulla
TAXONOMY
GENERAL PROPERTIES
• Opportunistic pathogens:
- E. coli
- K. pneumoniae - Enterobacter - Serratia
- Proteus
• Obligate pathogens:
- Salmonella spp.
- Shigella spp.
- Yersinia spp.
- Some E. coli strains
GENERAL PROPERTIES
• Ubiquitous organisms worldwide
• Facultative anaerobic G-negative rods
• Non-spore forming
• Ferment glucose
• Reduce nitrate
• Catalase positive
• Oxidase negative
• Most are motile
Lactose Fermenters Lactose Non-Fermenters
E. coli Salmonella
Klebsiella Shigella
Serratia Yersinia
Enterobacter Proteus
VIRULENCE FACTORS CLASSIFICATION
• Serologic:
1. O polysaccharide
2. K antigen in capsule 3. H protein in flagella
Antigenic Phase Variation
• Heat-stable LPS:
1. Somatic O polysaccharide 2. Core polysaccharide
- Enterobacterial common antigen 3. Lipid A
- Endotoxin activity
VIRULENCE FACTORS
• Capsule
- Hydrophilic capsular antigens - Resistance to serum killing
• Cytotoxin - EHEC
- Shigatoxin
• Enterotoxin
- Heat stable (ETEC) - Heat labile (ETEC)
• Antigenic phase variation
• Type III secretion system
• Sequestration of growth factors
• Antimicrobial resistance
ESCHERICHIA COLI
• Adhesins and exotoxins
• ETEC, EPEC, EAEC, EHEC, EIEC
• Intestinal infections:
- Gastroenteritis
• Extraintestinal infections:
- UTIs ( 80% of community-acquired UTIs) - Neonatal meningitis
- Septicemia (Most common G(-) rods)
• Treatment:
- Symptomatic
- ATB susceptibility tests
SALMONELLA
• Asymptomatic colonization, gastroenteritis, septicemia, enteric fever
• Salmonella Enteritidis:
- #2 most common bacterial cause of gastroenteritis after C. jejuni - Watery diarrhea, fever, vomiting
- Complications: osteomyelitis, cholecystitis
• Salmonella Typhi:
- Typhoid/enteric fever
- Systemic disease, bacteremia. Fever, abdominal pain, headache, constipation more often than ‘pea soup’ diarrhea. Intestinal
hemorrhage
• Treatment:
- Gastroenteritis: Symptomatic
- S. typhi & S. paratyphi: Fluoroquinolones, TMP-SMX, cephalosporins
SHIGELLA
• S. sonnei, S. flexneri, S. dysenteriae
• Fecal-oral transmission
• Shiga toxin (S. dysenteriae) - disrupts protein synthesis, leads to endothelial damage
• Shigellosis
- Gastroenteritis - Watery diarrhea
- Abdominal cramps - Fever
- Tenesmus (± bloody stools) - bacterial dysentery
• Treatment: Fluoroquinolones, TMP-SMX, macrolides
YERSINIA
• Y. enterocolitica:
- Transmission: raw milk, undercooked pork, fecal-oral route - Heat-stable enterotoxin
- Bloody diarrhea. Self-limiting enterocolitis, terminal ileitis
- Compared to C. jejuni, manifests differently:
< 5 years: bloody diarrhea
> 5 years: bloody diarrhea, appendicitis-like pain adults: bloody diarrhea + arthritis
• Y. pestis:
- Bubonic/Pneumonic plague, meningitis
• Treatment:
- Y. enterocolitica: Symptomatic
- Y. pestis: Streptomycin, Doxycycline
KLEBSIELLA PNEUMONIAE
• Large mucoid capsule, viscous colonies
• Urease producing, lactose fermenting
• Diseases:
- Nosocomial
- Wound, soft tissue infections - UTIs
- Lobar pneumonia - Bacteremia
• Treatment:
- Cephalosporins, fluoroquinolone - MDR: Carbapenems, Clindamycin
SERRATIA & PROTEUS & ENTEROBACTER
• Proteus mirabilis:
- ‘Swarming’ motility, urease producing - Fishy odor, alkaline urine sample
- UTIs, Renal stones (struvite, apatite)
• Serratia:
- Motile, some strains produce red pigment - Nosocomial: UTI, respiratory tract, wounds
• Enterobacter:
- Motile, lactose fermenting
- Nosocomial: ATB treatment, indwelling catheters, invasive procedures
- Infect burns, wounds, respiratory and urinary tracts
DIAGNOSIS
• Specimen collection
- Serum: S. typhi and S. paratyphi
- Sputum, blood: Y. pestis, Klebsiella - Urine: Proteus, E. coli, Serratia
- Stool, anal swabs: Gastroenteritis
• Culture
- MacConkey: Lactose fermenters - Hektoen: Salmonella, Shigella - Cold enrichment: Yersinia - 4°C
• Identification - Phenotypic - Genotypic
- Biochemical
DIAGNOSIS
• Serotyping
- E. coli O157:H7
• Serology
- Widal reaction (O, H, Vi) S. typhi & S. paratyphi
• MALDI-TOF - Faster
- Cheaper
- More accurate
- Potential to predict ATB susceptibility
