strict anaerobes

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I- INTRODUCTION :

These are bacteria which are composed of many species and can grow that & rsquo; in the absence of 02.

It exists 2 major categories of & rsquo; obligate anaerobes, plus 1 facultative :

  • Anaerobic bacteria are extremely sensitive to’02(E0S) —> no & rsquo; medical interest
  • anaerobic bacteria & rsquo; medical interest
  • optional aero-anaerobic

All the above bacteria use an anaerobic condition in the fermentation process to produce the & rsquo; energy, while use strict aerobic respiration (et done l & rsquo; o 2) as a source d & rsquo; energy.

Two categories of & rsquo; d & rsquo strictly anaerobic; medical interest :

  • sporulated bacteria : the spore is a form of resistance. When the bacterium is a spore form, it n & rsquo; s no & rsquo; metabolic activity. It is found in the & rsquo; as spores environment (called as soil bacteria).

At the & rsquo; Man, the transmission is in the form of spores, and is found in the & rsquo; organism is a spore form, or vegetative form.

Habitat : digestive tract, vaginal cavity and oropharynx.

Very little diversity : we find them all in the same genre : Clostridium (Gram bacilli (+). Examples : C. tetani, C. botulinum, C. difficult, C. perfringens.

  • non-spore-forming bacteria, say medical : they are very varied, with many genres

(Gram bacilli (+) or (-), Cocci Gram (+) or (-). They are found in the & rsquo; environment.

Habitat : digestive tract flora, the vagina and the & rsquo; oropharynx = c & rsquo; is that & rsquo; called flora Veillon.

Table I. Classification of anaerobic (main bacteria).

A simplified classification based on staining Gram and morphology is reported below:

Anaerobic flora

Examples :

  • bacille Gram (+) : Propionibacterium acnes(on the skin)
  • bacille Gram (-) :Bacteroïdes fragilis
  • Cocci Gram (+) : Peptostreptococcus
  • Cocci Gram (-) : Veülonella

Remarks :

-ALL HAVE ANAEROBIC RESISTANCE TO NATURAL AMINOGLYCOSIDE AND ALMOST ALL ARE SENSITIVE ANAEROBIC Metronidazole (Flagyl®).

II- THE ANAEROBIC spore :

Clostridium tetani :

  • Characteristics :

spore-forming bacillus, Gram (+), responsible for Tetanus.

  • Habitat :

digestive tract of animals (equine ++ H * spores in horse manure). L & rsquo; Man is very sluggish.

  • Pathology :

Contamination occurs as spore, When & rsquo; there is a wound (even minimal, the sting of bramble up & rsquo; to open fracture) at the skin or mucous membranes. The spore passing subcutaneous or submucosal becomes vegetative and secretes tetanus toxin. For the spore becomes vegetative, you need a low p02 (tissues of the & rsquo; ischemic body) and nutrients.

CAT before any wound : seek & rsquo; state of tetanus vaccination ; one makes a penicillin administration (against C. tetani et perfringens). Debridement of the wound to the & rsquo; hydrogen peroxide to increase pO2 in the area and limit the growth of bacteria.

  • pathogenicity :

Via a protein exotoxin which enters through axons and which starts at the synapses of neurons : causes paralysis (death by respiratory paralysis).

  • Vaccine :

Based on a toxoid (toxin denatured by heat and formalin).

  • Diagnostic :

It's clinic +++, no bacteriological.

  • Epidemiology :

Touche especially those aged over 57 years on average.

Vaccination is individual, mandatory, and very early.

Treatment : penicillin G

Sérothérapie d & rsquo; emergency (Ig tetanus antitoxin)=SAT.

Clostridium perfringens :

  • Characteristics :

bacille Gram (+) Spore, very aggressive (toxins + various enzymes)

  • Habitat :

Environment, as spores.

Man : digestive tract and vagina

  • pathogenicity :

Infection at d & rsquo; a major injury with ischemia.

  • Compartment syndrome (ou Crush syndrome) causing ischemia and necrosis of the muscles, edema… making it a breeding ground for anaerobic. Moreover C. perfringens leads to necrosis via enzymes, making it a vicious circle.
  • illegal abortion : can pass C. perfringens into the systemic circulation, causing septicemia. It will lead to the destruction of red blood cells, which will lead to the massive release of & rsquo; Hb and functional tubulopathy.
  • Food poisoning : some strains have a very potent enterotoxin causing diarrhea (no fever).
  • Diagnostic : local levies (necrotic tissue), or in foods.
  • Treatment : penicillins.

Clostridium botulinum :

  • Characteristics :

Botulism Manager ; bacille Gram (+)

Botulinum toxin is the & rsquo; a more powerful.

  • Contamination :

Via vegetables, especially those that & rsquo; we find in the land (asparagus +++)

Via ruminants who carry it in their gut (pâté, ham,…)

  • pathogenicity :

The toxin causes paralysis of the muscles of the & rsquo; eye. The first sign of & rsquo; intoxication is a reactive mydriasis.

  • Use of the toxin :

It is used in very small amounts in ophthalmology for cataract surgery.

C & rsquo; is a weapon of war (Biotox) : mydriasis prevents military target, which is a bit annoying for military.

Use in cosmetic surgery.

Clostridium difficile :

  • Characteristics : bacille Gram (+)
  • Habitat : Portage by individuals in infancy (1 at 5 years).
  • pathogenicity :

Some strains produce toxins that cause smaller epidemics of diarrhea with significant intestinal damage —> pseudomembranous colitis may be fatal.

  • Treatment : P-lactamines.

III- BACTERIA nonsporulated. D & rsquo; MEDICAL INTEREST :

They function as opportunistic pathogens.

They are very present in the digestive tract flora, s & rsquo; oropharynx and vagina.

Infections with these bacteria appear when & rsquo; there have been break-mucosal (accident, surgery…)

  • Terrain :
  • cancer, immunodépression,
  • diabetes, alcoholism (affect the vessels and promote the & rsquo; ischemia)
  • l & rsquo; chronic respiratory failure (causes poor oxygenation)
  • Pathology :

Suppuration and septicemia (have to start an abscess : septicopyoémie)

Example : Vincent's angina which is necrotizing ulcerative pharyngitis. Corresponds to the & rsquo; Fusobacterium Association + Spirochètes.

Bacteroides fraeilis :

Many strains produce P-lactamase : so use of the & rsquo; Augmentin.

IV – MAIN FEATURE CULTURE :

The strict anaerobic bacteria can not grow that & rsquo; in the & rsquo; absence of the & rsquo; ambient air or & rsquo; oxygen which will require unusual bacteriological techniques, in the & rsquo; & rsquo absence; oxygen as well when taking, that its transport then its culture and / or isolation. These technical constraints may explain the low frequency of & rsquo; isolation in many laboratories

Specimens – transport :

  • blood culture: When d & rsquo; blood culture, a vial with and without oxygen is routinely seeded
  • other: Some samples will be rapidly performed on a swab then seeding in d & rsquo; an agar medium for transporting (TGV®) or should be & rsquo; avoid intake of & rsquo; air into the syringe. Then their routing will be the fastest possible to the laboratory.

Culture – Isolation :

The constraints already mentioned s & rsquo; still apply avoiding contact with the & rsquo; oxygen:

  • or by working in special chamber (said chamber of Freiter) gas mixture with various (C02, N2…)
  • or more usually in mini room (plastic jar or pouch) and use d & rsquo; a catalyst

chemical (sachet) by inoculating solid media such as agar fresh blood

L’incubation est normalement effectuée dans une étuve en “ambiant air” à 37°C.

Their culture is, in general, difficult and slow (several days), usually obtained on blood agar media with sometimes features, such black pigmentation (Prevotelia melanogenica) or colonies encrusted (Bacteroides urL & rsquo; direct examination after Gram staining

can point to some etiologies (hull or bacillus Gram + or gram -).
L & rsquo; identification is usually biochemical: Example & rsquo; d & rsquo a gallery; identification (Rapid ID
32A).L & rsquo; susceptibility show a specific sensitivity to imidazole (metronidazole or MTR) and

a natural resistance to aminoglycosides.

Table V. Antibiotic susceptibility of the major anaerobic.

V- Conclusion :

Strict anaerobic bacteria represent a large group of microorganisms often overlooked because of their gas requirements.

If & rsquo; we do not put up cultivation techniques and d & rsquo; identification specific to them, we can only suspect their presence in & rsquo; direct examination. Commensal mostly, these bacteria are involved in many d & rsquo; infections that develop in favor of circulatory disorders or problems & rsquo; immunosuppression and whose therapeutic care is often complex.

Courses of Dr. H.ALLAG – Faculty of Constantine