FACTORS INFLUENCING BACTERIAL GROWTH

FACTORS INFLUENCING BACTERIAL GROWTH

A) SOLUTE AND WATER ACTIVITY

(i) Osmotolerant

·       Able to grow over wide ranges of water activity or osmotic concentration.

·       Example - Staphylococcus aureus.

(ii) Halophile

·       Requires high levels of sodium chloride, usually above about 0.2 M to grow.

·       Examples - Halobacterium, Dunaliella and Ectothiorhodospira.

B) pH

(i) Acidophiles

·       Grow optimum between pH 0 to 5.5.

·       Examples - Sulfolobus, Picrophilus, Ferroplasma, Acontium and Cyanidium caldarium

(ii) Neutrophiles

·       Grow optimum between pH 5.6 to 8.0.

·       Example – Escherichia coli.

(iii) Alkalophiles

·       Grow optimum between pH 8.1 to 11.5.

·       Examples – Bacillus alcalophilus and Natronobacterium. 

C) TEMPERATURE

(i) Psychrophiles

·       Grows well at 0 °C and has an optimum growth temperature of 15 °C or lower.

·       Examples - Bacillus psychrophilus

(ii) Psychrotrophs

·       Can grow at 0 – 7 °C; has an optimum between 20 °C - 30 °C and a maximum around 35 °C.

·       Examples - Listeria monocytogenes and Pseudomonas fluorescens.

(iii) Thermophile

·       Can grow at 55 °C or higher; optimum often between 55 °C and 65 °C.

·   Examples - Geobacillus stearothermophilus, Thermus aquaticus, Cyanidium caldarium and Chaetomium thermophile.

(iv) Hyperthermophile

·       Has an optimum between 80 °C and about 113 °C.

·       Examples - Sulfolobus, Pyrococcus and Pyrodictium.

D) OXYGEN CONCENTRATION

(i) Obligate Aerobe

·       Completely dependent on atmospheric Oxygen for growth.

·       Examples – Micrococcus luteus, Pseudomonas, Mycobacterium

(ii) Facultative Anaerobe

·       Does not require Oxygen for growth, but grows better in its presence.

·       Examples – Escherichia and Enterococcus.

(iii) Aerotolerant Anaerobe

·       Grows equally well in presence or absence of Oxygen.

·       Example - Streptococcus pyogenes.

(iv) Obligate Anaerobe

·       Does not tolerates Oxygen and dies in its presence.

·       Example - Clostridium, Bacteroides, Methanobacterium and Trepomonas agilis

(v) Microaerophile

·    Requires Oxygen levels below 2 – 10 % for growth and is damaged by atmospheric Oxygen levels (20 %)

·       Example - Campylobacter, Spirillum volutans and Treponema pallidum.

E) PRESSURE

(i) Barophilic

·       Growth more rapid at high hydrostatic pressures.

·  Examples – Photobacterium profundum, Shewanella benthica and Methanocaldococcus jannaschii.