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Psychrotrophic bacteria
isolated from -20°C freezer
Bashir Ahmad, Imran Javed, Aamer Ali Shah, Abdul Hameed
and Fariha Hasan*
Microbiology Research Laboratory, Department of
Microbiology, Quaid-i-Azam University, Islamabad 45320,
Pakistan.
*Corresponding author. E-mail:
farihahasan@yahoo.com.
Accepted 28
December, 2009 |
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Three psychrotrophic bacteria, morpho-physiologically,
identified as Bacillus subtilis MRLBA7, Bacillus
licheniformis MRLBA8 and Bacillus megaterium
MRLBA9 were isolated from -20°C freezer of the Microbiology
Research Laboratory (MRL), Quaid-i-Azam University,
Islamabad, Pakistan. These strains were able to grow
aerobically at 6°C but not at 40°C except MRLBA8 that could
grow at 48°C. None of the isolates showed inhibition of
growth in the presence of glycerol. Isolate MRLBA7, bearing
central spore, grew in the presence of 30% glycerol at 0°C
after 48 h of incubation and showed maximum growth without
glycerol at 25°C after 24 h. Isolate MRLBA8 showed growth in
the presence of 50% glycerol at 4°C after 72 h of incubation
and maximum growth was observed at 20°C in the absence of
glycerol. Isolate MRLBA9 showed growth at 6°C in the
presence of 40% glycerol after 48 h of incubation and
maximum growth was observed at 25°C in the absence of
glycerol. Isolates were susceptible to antibiotics except
Bacillus subtilis MRLBA7 that exhibited antibiotic
resistance against penicillin and fosphomycin, Bacillus
licheniformis MRLBA8 against aztreonam and fosphomycin,
and Bacillus megaterium MRLBA9 against vancomycin and
penicillin. The growth profile and biochemical
characteristics of all the isolates were rather similar to
that of mesophilic counterparts except adaptation to low
temperature. These strains could be used as model microbial
strains for characterization of food contaminants in
freezers, to understand the mechanism of antibiotic
resistance induced at low temperature and as a source of
psychrotrophic enzymes.
Key
words:
Psychrotrophs, Bacillus, antibiotic resistance, growth
characteristics. |
