Susceptibility of bacteria to oxygen

Bacteria can be sorted into the following groups depending on their tolerance to oxygen3-7:

1. strictly aerobic bacteria: those absolutely requiring molecular oxygen to develop since oxygen is the final obligatory electron acceptor,

2. microaerophiles: those able to use oxygen but developing best in concentrations of oxygen lower than in air,

3. aero-anaerobes or facultative anaerobes: those developing with or without oxygen since their metabolisms are based either on respiration or fermenting processes (Staphylococci and Enterobacteriaceae),

4. aerotolerant anaerobes: those still able to develop in the presence of molecular oxygen but develop better without oxygen (Streptococci and Enterococci)

5. strictly anaerobic bacteria with anoxybiotic metabolism: those for whom molecular oxygen is lethal. These bacteria use fermenting processes to produce energy (the final electron acceptor is organic or mineral but not oxygen) and most of them do not have any of the usual enzymes of respiratory systems such as superoxide dismutase, catalase or peroxidase. The toxic effects of molecular oxygen vary: some bacteria are Extremely Oxygen Sensitive (EOS) and die after a very short exposure. These can only withstand oxygen concentrations under 0.1 %. EOS bacteria which have been studied on man are commensal bacteria of the digestive tract and of the skin and seem to have no pathogenic effects. Some strictly anaerobic bacteria are unable to develop in concentrations of oxygen above 0.5 % (C. haemolyticum). Most of the anaerobic bacteria involved in infectious pathology are moderately anaerobes with an oxygen tolerance of 0.5 to 5 %. These include B. fragilis, C. novyi, P. melaninogenica, Peptostrepto-coccus4A8. In contrast, other anaerobic bacteria can develop in air but only into very small colonies3,7 (Table 1.6-1).

It is to be noted that within each group aerotolerance varies widely. The metabolisms of micro-organisms are also different with in vitro experimentation than is found in in vivo in natural environments5,8.

Table 1.6 -1. In vitro oxygen susceptibility of strictly anaerobic bacteria (from Loesche8)

Pressure of Oxygen

Bacteria

0

1

2

3.5

5

8

15

20

30

45

60

75 90

Clostridium

++

++

++

++

+

0

0

haemolitycum

Peptostreptococcus

++

++

++

++

++

++

+

0

0

Clostridium novyi

++

++

++

++

++

++

+

0

0

Bacteroides oralis

++

++

++

++

++

++

++

++

+,V

+,V

0

0

Prevotella

++

++

++

++

++

++

++

++,

++,

+,V

+,V

0 0

Melaninogenica

V

V

Fusobacterium

++

++

++

++

++

++

++

++

++

++

+,V

0 0

Nucleatum

Bacteroides fragilis

++

++

++

++

++

++

++

++

++

++

+,V

0 0

++ : normal development + : development is slowed

V : development varies with strain or incubation duration 0 : no development

++ : normal development + : development is slowed

V : development varies with strain or incubation duration 0 : no development

0 0

Post a comment