The document summarizes the Enterobacteriaceae family of gram-negative bacteria. It describes their characteristics including morphology, metabolism, identification of common genera like E. coli, Klebsiella, and Salmonella based on biochemical tests and colony morphology. It also discusses pathogenic species, virulence factors, and infections caused like UTIs, gastroenteritis, and neonatal meningitis. Treatment involves antibiotics, with increasing drug resistance a concern.

1. Enterobacteriaceae
- Enteric gram negative rods
- Coliforms (enteric)
- Intestinal tract of humans, animals and insects
- Opportunistic or true pathogen
- Large heterogenous group
- 25 to 97 enterics
- MORPHOLOGY:
o Short gram negative rods
o Motile (Peritrichous flagella) or Non motile
o Facultative
o Ferment GLUCOSE
o Nitrate to nitrite
o Catalase +
o Oxidase –
o Produce COLICIN (bacteriocin)
- Colonies (selective//differential)
o BAP
 Smooth
 Mucoid
 Swarming pigment
 Large
 Dull gray
 May or may not be hemolytic
o Selenite F, Alkaline Peptone water in Fecal sample (enrich)
- Lactose fermenter RAPIDLY
o E. coli
 Green metallic sheen on EMB
 Motile
 Flat
 Non viscous colonies
 Smooth
 Pink red on MAC
o E. aerogenes
 No metallic sheen
 Motile
 Raised
 More viscous
 Smooth
 Pink on MAC
o K. pneumoniae
 Mucoid growth
 Viscous and Large
 Non motile
 Pink on MAC

2. - Non Lactose Fermenter
o Shigella
 Non motile
 No gas from dextrose
o Salmonella
 Motile
 Gas from dextrose
 Acid
o Proteus
 Motile
 Swarming
 Urea hydrolyzed rapidly
o Pseudomonas
 Motile
 Soluble blue green pigments
 Fluorescing
 Sweet smell
- Antigenic Structure
o O antigens
 Somatic O LPS
 Heat stable
 Heat & Alcohol RESISTANT
 Detected by BACTERIAL AGGLUTINATION
 Antibodies to O Ag predominantly IgM
o H antigen
 H flagellar antigens
 Heat & Alcohol LABILE
 Antibodies to H Ag mainly IgG
 Undergo phase variation
 Interfere with agglutination by anti-O antibodies
o K antigen
 Envelope/Capsular
 Heat labile
 Polysaccharide or protein
 Interfere agglutination by O antisera (boil 15 mins)
 Virulence K1
 Salmonella typhi capsular antigens (Vi Ag)

3. - Escherichia coli
o Inhabitant of GI tract
o Common from colon flora
o Index organism for fecal contamination of water (FECAL COLIFORMS)
o Motile
o Mannitol fermenter
o IMViC [++--]
o BIOCHEMICAL TESTS
 Positive:
 TSI: A/A gas +
 Decarboxylase +
 Indole +
 Beta glucuronidase +
 Negative:
 Urea –
 Citrate –
o VIRULENCE FACTORS
 Lipid A
 Component of endotoxin cause of death in sepsis
 K1 antigen
 Neonatal meningitis
 Enterotoxin (exotoxin)
 Watery diarrhea [ETEC]
 Shiga type toxin 1 & 2 (verotoxin)
 STEC 0157:H7 or EHEC
 Inhibit protein synthesis
 Enteroaggregative ST like toxin
 EAEC
 Hemolysin
 Type III secretion system to deliver effector molecules
 Induced EIEC
 Effacing EPEC by microvilli and pedestal formation
 Adhesins
 Colonization factor
 Antibodies protect from colonization
 Capsule
 Iron capturing ability (enterochelin)
 Outer membrane protein

4. o INFECTIONS
 UTI to Acute cystitis (bladder infection) and pyelonephritis (kidney infection)
 Neonatal meningitis and Septicemia
o Gastroenteritis
 ETEC: traveler’s diarrhea
 EPEC: diarrhea without blood in mucous and malaise
 EIEC: watery diarrhea and scanty stools with blood, pus and mucous
 EAEC: watery diarrhea and dehydration
 EHEC: watery to bloody diarrhea, hemolytic uremic syndrome, does not ferment
sorbitol, SMAC plate, isolate by sero testing
o TREATMENT:
 Sulfonamides, ampicillin, cephalosporins, aminoglycoside
 Multidrug resistant strains
 Susceptibility testing
- Klebsiella Enterobacter Serratia Hafnia KESH spp
o Characteristics
 Positive
 Citrate +
 Urease +
 VP/acetoin +
 Negative
 H2S –
 Deaminase –
 MR –
- Klebsiella
o K. pneumoniae
 TSI: A/A gas +
 Decarb + K/K
 Citrate +
 Urease +
 Indole –
 H2S –
 Non motile
 MR –
 VP +
 Has K and O antigen
o Klebsiella oxytoca
 Positive
 Indole, citrate, urease, malonate
o Ozena: nasal mucosa in K. pneumoniae
o