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Enterobacteriaceae. Enterobacteriaceae. The most important bacterial family in human medicine Well-defined diseases with typical clinical symptoms: Typhoid fever, dysentery and plague Nosocomial infections: Urinary tract infections, pneumonias, wound infections and sepsis.
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Enterobacteriaceae • The most important bacterial family in human medicine • Well-defined diseases with typical clinical symptoms: • Typhoid fever, dysentery and plague • Nosocomial infections: • Urinary tract infections, pneumonias, wound infections and sepsis
Definition and significance • 41 genera with hundreds of species • Gram-negative, facultatively anaerobic rod • Natural habitat: intestinal tract of humans and animals
The Most Important Genera/Species/Vars of Enterobacteriaceae and the Corresponding Clinical Pictures
Virulence and pathogenicity • The most important pathogenicity factors: • Colonizing factors • Invasins • Endotoxin • Exotoxins • Enterobacteriaceae are the most significant contributors to intestinal infections
Identification of Enterobacteriaceae • Gram-negative rod • Usually motile (with few exceptions) • Facultative anaerobes • Grow on simple nutrient media • Oxidase test negative • Ferment glucose with acid or acid and gas
Sero-typing based on antigenic structure • O antigens: Somatic antigens (polysaccharide) • H antigens: Flagellar antigens (protein) • K antigens: Capsular antigens (carbohydrate) • e.g., serovar O18:K1:H7
Natural habitat • Intestinal tract of humans and animals • indicator organism for fecal contamination of water and foods
Infections • Extraintestinalinfections • Intestinal infections (Diarrhoealdiseases)
Extraintestinal infections • Urinary tract infections • Wound infections • Peritonitis • Cholecystitis • Appendicitis • Sepsis and endotoxin induced shock • Neonatal meningitis
Diarrheagenicpathovars • EnteropathogenicE. coli (EPEC) • EnterotoxigenicE. coli (ETEC) • EnteroinvasiveE. coli (EIEC) • EnterohaemorrhagicE. Coli (EHEC) • EnteroaggressiveE. coli (EaggEC)
EPEC • Frequently cause diarrhea in infants • Vomiting, fever and prolonged diarrhoea • Infants mainly • Many serotypes
ETEC • Enterotoxins that cause watery diarrhoea similar to cholera • Infants and adults • Traveler diarrhea • Many serotypes
EIEC • Cause a dysentery like infection of the large intestine (similar to shigellosis) • Fever and colitis • Many serotypes
EHEC • Produce verocytotoxins and cause a hemorrhagic colitis (damage to vascular endothelia ) • Causes life-threatening haemorrhagicdiarrhoea • All ages
EHEC • No pus cells and no fever • It can progress to Haemolytic Uremic Syndrome → Renal failure • O157:H7 or verocytotoxin-producing E. coli • Contaminated meat products, unpasteurized milk and diary products
EaggEC • Chronic watery diarrhoea • Mainly in children
Klebsiellapneumoniae • Four subspecies: • K.p.pneumoniae • K.p. aerogenes • K.p. ozaenae • K.p. rinhoscleromatis
Infections caused by Klebsiellaspecies • UTI • Wound infections • Chest infections
Medically important Proteus species • P. mirabilis • UTI • Wound infection • Septiceamia • Occasionally meningitis and chest infections • P. vulgaris • UTI and wound infections
Other enterobacteria • Enterobacter • Citrobacter • Serratia • Opportunistic pathogens: • UTI • Wound infections • Septiceamia • Pulmonary infections
Laboratory diagnosis • Specimens: • Urine, pus, faeces, CSF, blood, sputum • Direct examination: • Gram –ve bacilli • Few capsulated • Culture aerobically at 36-37° C: • Blood agar • MacConkey agar • CLED • XLD and DCA
UTI • Midstream urine • Bacterial count • CFU/ml • ≥105/ml indicate an infection • 104/ml doubtful significance • ≤103/ml indicate a contamination
MacConkey agar showing lactose and non-lactose fermenting colonies