Download 5-Lactose Fermenters

Microbiology/Bacteriology-5
Assistant Prof. Dr.Alaa H. Al-Charrakh
Enterobacteriaceae (Lactose-fermeners):
• Large family of gram-negative rods –
• Occur as free-living in nature OR
• As part of normal flora of colon of human
and animals.
Four metabolic characteristics:
1. Facultative anaerobic
2. Ferment glucose
3. Oxidase - negative
4. Nitrate - positive
Grouping on the basis of lactose fermentation:
A. Lactose fermenters
Produce pink-red colonies on MacConkey agar:
n Escherichia
n Klebsiella
Coliforms
n Citrobacter
n Enterobacter
n Serratia
B. Non-lactose fermenters
Pale-colour colonies on MacConkey agar
n Salmonella
n Shigella
n Proteus.
ESCHERICHIA COL
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Gram-negative bacilli
Motile
Some strains capsulated
Normal flora of colon in man and animals
° Excreted in stool
° contamination of water supplies – used as indicator to test faecal
contamination of water
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ANIGENIC STRUCTURE
1. Somatic (O) antigen
2. Capsular (K) antigen
3. Flagellar (H) antigen
4. Pili : help in attachment and virulence
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Bind to D-mannose residues on surface of cells.
Pyelonephritis associated pili (Pap) and
Intestinal colonization factor antigen
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Microbiology/Bacteriology-5
Assistant Prof. Dr.Alaa H. Al-Charrakh
Virulence factors for UTI:
° Adherence to uroepithelial cells by Pap pili
° Capsule (K-antigen)
° Siderophore – help survival of E.coli in iron-poor environment of human
body fluids
DISEASES CAUSED BY E.COLI
1. Urinary Tract Infection (UTI)
• Commonest cause (70-90%)
• More common in females due to shorter urethra
• 105 bacteria / ml of urine is significant
• Common cause of hospital-acquired UTI
due to urinary catheters
Cystitis (infection of bladder)
• Pain (dysuria)
• Frequency of micturation
• More common in females due to shorter urethra
Pyelonephritis (infection of kidney)
• Fever (chills)
• Flank pain
2. INTESTINAL INFECTIONS
a) Enterotoxigenic E.coli (ETEC)
• Virulence due to enterotoxins
• Act on small intestine
• Watery diarrhoea (common cause of traveler’s diarrhoea)
• Transmitted by contaminated food and water
b) Enteropathogenic E.coli (EPEC)
° Adhere to enterocytes, cause destruction of
microvilli of small intestine.
° Infantile and childhood diarrhoea (20% of bottle-fed)
° Stool : watery, non-purulent, no blood
c) Enteroinvasive E.coli (EIEC)
° Cause invasion of enterocytes in large intestine
° Necrosis, ulceration and inflammation.
° Stool : scanty, purulent & blood stained
d) Enterohaemorrhagic E.coli (EHEC)
• Due to verotoxin – causes destruction of microvilli
in large intestine.
• Produced by E.coli O157 : H7
• Haemorrhagic colitis with copious bloody stool
without pus cells.
e) Enteroaggregative E.coli (EAEC)
3.
Meningitis in newborns
From mother’s genital tract (colonized with E.coli)
4. Opportunistic Infections
• Peritonitis due to intestinal trauma
• Wound infections
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Microbiology/Bacteriology-5
Assistant Prof. Dr.Alaa H. Al-Charrakh
• Bacteremia gram-negative septic shock
- Beta-lactam antibiotics are not recommended?
5. Hospital-acquired infections
n Common cause
LAB IDENTIFICATION OF E. COLI
Specimens : urine, stool, pus
Culture on:
• MacConkey agar – lactose fermenter
• EMB agar – green metallic sheen
• Indole +ve
• Citrate –ve
• TSI: Slant acid, Butt-acid
Serotyping for enteric pathogens
Coliform Count and Public Health?
TREATMENT OF E. COLI DISEASES
UTI : use antibiotics after C/S
Trimethoprim-sulphamethoxazole
Diarrhoea
° Oral rehydration + ciprofloxacin
Meningitis
• Ceftriaxone (3rd generation cephalosporin)
Others diseases : C/S
• Increasing Resistance in E.coli ?
KLEBSIELLA PNEUMONIAE
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Gram-negative, bacilli
Have thick capsule
Member of normal flora of colon
Free-living in soil and water
10% carrier rate in upper respiratory tract
Have multiple pili - help in adherence to respiratory and urinary epithelium
DISEASES BY K. PNEUMONIAE
An opportunistic pathogen
1. Lobar pneumonia
• In immunosuppressed host
thick mucoid sputum
2. Urinary tract infections
LAB IDENTIFICATION
Culture on Mackonkey agar
• Lactose fermenter & mucoid colonies
Citrate +ve
Indole –ve
TSI: Butt-acidic, Slant-acidic
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Microbiology/Bacteriology-5
Assistant Prof. Dr.Alaa H. Al-Charrakh
Nonmotile
TREATMENT
• Among the most resistant of all enterobactericiae to antimicrobials
especially for Beta-lactam antibiotics.
ENTEROBACTER
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Gram-negative, motile rods
Lactose fermenter
Mucoid colonies on MacConkey Agar
An opportunistic pathogen
Citrate +ve
Antibiotic sensitivity - similar to Klebsiella
SERRATIA
n Late lactose fermenter
• Distinctive brick red colonies by some strains (red colonies on Nutrient agar
medium)
• Opportunistic pathogen (hospital-acquired infection)
n Resistant to commonly used antibiotics like ampicillin
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