General information on anaerobes

I – Physiology:

Strictly anaerobic bacteria are bacteria hypersensitive to the action of oxygen (anoxybiontiques). They produce their energy and perform their biosynthetic reactions in the absence of the electron acceptor.

Most (exceptions) do not have the conventional enzyme respiratory systems called: cytochromes, catalase, peroxidase. They produce energy during fermentation processes.

These bacteria do not grow in the presence of 20% oxygen in the presence of so

atmospheric air. The sensitivity to oxygen is very variable, however.

Most strict anaerobic with an interest in infectious diseases are moderate anaerobic (tolerant of 0.1 to 5% O2), others only tolerate lower oxygen pressures to 0.1% (EOS bacteria) (extremely oxygen sensitive bacteria). The EOS bacteria studied in humans so very recently, seem devoid of any pathogenic and commensal bacteria are the gut and skin. They probably play an important role because of their metabolic potential and would in the digestive tract vis-à-vis barrier role of other pathogenic bacteria by promoting the balance of intestinal flora. Their study and taxonomy does not fall within the scope of this book.

II – METHODS OF CULTURE AND IDENTIFICATION:

The study, culture and identification of anaerobic bacteria with medical interest require oxygen deprived environments or where the redox potential is low (rh). The usual bacteriology techniques are applicable to the culture and identification of anaerobes.

Techniques for removing oxygen are varied:

– Liquid media boiled to remove oxygen (regeneration)

– Vacuum action and replacement with an inert gas,

– Solid media prereduced anaerobically 5% CO2, 10% H2, N2 qs).

Culture is enhanced by the presence of reducing substances to the thiol groups: thioglycolate, cysteine ​​…

The medium being deprived of oxygen, culture and identification of anaerobic bacteria continue avoiding contact with oxygen in the air:

– Either in a suitable glass making the smallest possible contact with the atmosphere: deep agar tube Veillon, throttle bottles for blood culture, special media marketed to anaerobic blood culture with an inert atmosphere,

– Either by adsorption of alkaline pyrogallol (old method),

– Or in small sealed enclosures (anaerobic gas mixture), anaerobic jars,

– By modern and more effective ways that grow increasingly in large laboratories anaerobic chambers said chambers to charter.

The anaerobic atmosphere is controlled to: ternary mixture 5% CO2, 10% H2, N2 qs; thermostated at 37 ° C in the presence of catalyst (palladium chloride) to remove traces of O2. All bacteriological operations after collection (kept away from air) conducted there. The atmosphere continues performed in anaerobic anaerobic chamber certainly can handle in the best specimens to search anaerobes.

The system in anaerobic jars is the most common and best suited to the needs of a small laboratory. However you need to open the jars to observe crop transplanting etc … resulting in a high mortality of cultures. Therefore are prepared in transparent plastic bags in which it is made anaerobic and to observation boxes without breaking anaerobiosis.

The identification reactions strict anaerobic bacteria utilize conventional carbohydrate fermentation in the detection of enzyme production, the determination by gas chromatography of the end products of fermentative metabolism (ac. Acetic , propionic, iso-butyric, butyric, iso-valeric, valeric, iso-caproic acid, caproic acid, heptanoic) made from standardized anaerobic liquid culture media …

Experimental pathogenicity on the guinea pig or mouse can reproduce, in the case of toxigenic anaerobic animal disease characteristic of the toxin produced by the seed. Neutralizing the effect of the toxin by a specific immune serum allows diagnosis of the germ and the type of toxin, making it possible in some cases to establish a specific serum therapy.

III – OUTLINE CLASSIFICATION OF ANAEROBIC BACTERIA STRICT (with an interest in Medical Bacteriology) (Table I)

Besides numerous saprophytic species, two groups are responsible for disease in humans (not contagious or epidemic)

– Anaerobic spore-forming,

– Non-spore forming anaerobes.

A – Anaerobic spore. Bacilli telluric:

Genus Clostridium. Bacteria in the soil and can survive thanks to their heat-resistant spore

Pathology encountered them:

– In gas gangrene,

– In poisoning and conditions where a neurotropic toxin in the body determines reactions quite characteristic: tetanus, botulism.

Clostridium perfringens can be the agent of either gas gangrene or septicemia or enterocolitis.

B – non-spore forming anaerobes. Flora Veillon:

Most non-spore forming anaerobes are part of the commensal and saprophytic flora of man. They are the so-called endogenous flora Veillon, as opposed to the previous land-based plants.

These bacteria are abundant in:

– Gastrointestinal tract (most of the intestinal flora)

– Oral cavity, nasopharynx,

– Upper part of the respiratory system.

They can determine, on the occasion of a weakening of the body’s defenses or in combination with other germs or putrid infection or sepsis.

IV – CIRCUMSTANCES IN WHICH MUST SEEK ANAEROBIC (Table II):

Outside intoxinations and food poisoning (botulism food poisoning C. perfringens) and outside of tetanus, we will look for anaerobes:

– In the whole blood (5 to 10% may contain anaerobic)

– In all closed especially when pus exudes a foul odor,

– When we see gas at the site of infection (crepitus, myonecrosis suspicion)

– In any secondary infection to bite, intramuscular injection, in trauma, surgery (general surgery, genital tract, orthopedic), a therapeutic aminoglycoside and / or beta-lactam proving to be ineffective,

– In any infection located near a mucosa (anal, oral, genital)

– Each time in a sample there are Gram (+) or (-) on direct examination, but the aerobic culture is negative.

V – FACTORS TO PROMOTE THE ANAEROBIC INFECTIONS:

The redox potential of a normal tissue is -0.1 to 0.2V, the value above which the growth of an anaerobic is not possible. The growth of an anaerobic organism is exponential only when the redox potential is lower (-0.5 V).

This potential is reduced by:

– The development of facultative anaerobic bacteria,

– Inadequate intake of oxygen: in vascular diseases (arteritis, diabetes), trauma and tissue necrosis, hematoma, foreign body, injection of certain drugs to vasoconstrictor effect.

– A factor decreasing the resistance of the body and modifying the bacterial flora balance (cancer, radiation therapy, immunosuppressive, inappropriate antibiotic treatment).