gram negative bacilli

1. Enterobacter, Hafnia & Serratia
By Ekta Gupta

2. Enterobacter
Enterobacter is gram negative bacillus that belongs to the
Enterobacteriaceae family.
Similar to Klebsiella in most biochemical reactions (VP
positive and lactose fermenter) bur differs from the latter in
being motile and ornithine decarboxylase positive.

3. Cont….
• E. aerogenes and E. cloacae are the most
commonly isolated species from the clinical
specimens.
• They are also widely distributed in water, sewage,
soil and feces of healthy persons.
• They are opportunistic pathogens, implicated in
infected wounds and urinary and respiratory tract
infections and occasionally septicemia and
meningitis.

4. Cont…
• E. asburiae differs from other Enterobacter in being non-
motile and VP negative. It has been isolated from blood,
wound and feces.
• E. sakazakii strains are biochemically similar to E.
cloacae except that they produce yellow pigment, do not
ferment sorbitol and may give PPA test positive.
They have been isolated from cases of neonatal meningitis
and septicemia,

5. HAFNIA
H. alvei, the only species under genus Hafnia, which is
rarely isolated from wounds, abscess, sputum, urine and
blood.
• It is lactose non-fermenter and positive for lysine and
ornithine decarboxylase.
• Like Serratia, the biochemical reactions are best reliable
when rested at 30'C.

6. SERRATIA
The characteristic property
of Serratia is production
of a red non-diffusible
pigment called prodigiosin,
which is formed optimally
at 30'C.
• S. marcescens is the medically
most important species.
Human infection with
other species is rare.
Effect of Ph, Temp & Incubation time on prodigiosin

7. Cont…
• It is a saprophyte found in water, soil and food. It may grow in
sputum after collection and makes the sputum red (due 10
pigment production). This condition is known as
'pseudohemoptysis'.
• S marcescens is being increasingly
reported in various nosocomial infections,
such as meningitis, endocarditis, septicemia,
urinary, respiratory and wound infections.

8. Cont..
The hospital strain are often non-pigmented and
multiple drug resistant (produce AmpC Beta-
lactamases)
• The biochemical properties of S. marcescens
include: 1-Production of lipase, gelatinase and
DNase
• Resistant to colistin and cephalothin.

9. Thank You