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

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

Escherichia coli Klebsiella and Proteus

Escherichia coli

Escherichia coli on ChromID CPS agar

Natural habitat

Intestinal tract of humans and animals

indicator organism for fecal contamination of water and foods

Infections

Extraintestinal infections

Intestinal infections (Diarrhoeal

diseases)

Extraintestinal infections

Urinary tract infections

Wound infections

Peritonitis

Cholecystitis

Appendicitis

Sepsis and endotoxin induced shock

Neonatal meningitis

Diarrheagenic pathovars Enteropathogenic E. coli (EPEC)

Enterotoxigenic E. coli (ETEC)

Enteroinvasive E. coli (EIEC)

Enterohaemorrhagic E. Coli (EHEC)

Enteroaggressive E. 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

haemorrhagic diarrhoea

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

Klebsiella species

Klebsiella species

Klebsiella pneumoniae

Four subspecies:

K.p. pneumoniae

K.p. aerogenes

K.p. ozaenae

K.p. rinhoscleromatis

Infections caused by Klebsiella species

UTI

Wound infections

Chest infections

Proteus species

Proteus species on Blood Agar

Medically important Proteus species

P. mirabilis UTI Wound infection Septiceamia Occasionally meningitis and chest

infections

P. vulgaris UTI and wound infections

Other enterobacteria

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

Escherichia coli (Gram negative)

Oxidase test