anaerobic bacteria

what are anaerobic bacteria?

bacteria that live well and flourish in environments without oxygen. they are found in deep tissues, subgingival plaque and necrotic areas

what do anaerobic bacterias include?

• obligate, meaning they cannot survive in oxygen

• facultative anaerobes, they cane survive with or without oxygen

what are examples of gram-negative anaerobes?

Gram-negative anaerobes:

1. Porphyromonas gingivalis

2. Prevotella intermedia

3. Fusobacterium nucleatum

4. Tannerella forsythia

5. Treponema denticola (spirochaete, also anaerobic)

what are examples of gram-positive anaerobes?

1. peptostreptococcus

2. Actinomyces (facultative/anaerobic)

3. Clostridium spp. (rarely oral, but important in wound infections)

what is the clinical relevance of anaerobic bacteria in periodontitis ?

anaerobes are major pathogens in chronic periodontitis and aggressive periodontitis. they thrive in deep periodontal pockets, causing:

1. tissue destruction

2. bone loss

3. persistent inflammation

what is the clinical relevance of anaerobic bacteria in endodontic infections?

they are found in necrotic pulp and periapical abscesses. they are often a part of polymicrobial biofilms that resist treatment

what is the clinical relevance of anaerobic bacteria in orofacial infections?

they can cause abscesses, cellulitis and deep space infections. they can spread to facial planes, requiring urgent intervention

what is the clinical relevance of anaerobic bacteria in dentistry?

peri-implantitis and oral malodor or halitosis (bad breathe) also involves anaerobes

how can anaerobes be diagnosed?

it requires anaerobic culture techniques (special transport and growth conditions)

how are anaerobic dental infections often treated?

• metronidazole, which is effective against many anaerobes

• amoxicillin-clavulanic acid, clindamycin are used

• surgical intervention is often needed, such as the drainage of abscesses by incision and flushing with sterile saltwater

how can infection control and prevention of anaerobic bacterias be done?

an emphasis should be placed on:

• good oral hygiene (consistent flossing and brushing)

• effective scaling and root planing

• sterile techniques in endodontic and surgical procedures

so, in summary, what is the importance of anaerobic bacteria in dentistry?

• they are key pathogens in many oral and maxillofacial infections

• understanding their role helps dental students diagnose infections, plan appropriate treatments, prevent complications and give essential knowledge in periodontology, endodontics and oral surgery

how can anaerobic bacteria be divided based on spores?

1. non spore forming

2. spore forming (ex: Clostridia)

what are non spore forming anaerobes?

they are obligate anaerobes that grow well on the anaerobic cooked meat medium and on blood agar plates in a gas pack system

what do non spore forming anaerobes form a major part of?

the normal microbial flora in the mouth, GIT and female genital tract

most infections that are caused by non spore forming anaerobic bacteria are considered to be what?

of endogenous origin

what is Peptostreptococcus?

an anaerobic gram-positive cocci that is an obligate anaerobe

what is peptostreptococcus associated with?

1. gingivitis

2. periodontitis

what is a species most frequently found in the root canals of teeth with periapical abscess?

Peptostreptococcus

what is parvimonas micra?

previously classified as a member of the peptostreptococcus genus, it is an obligate anaerobic gram positive cocci bacteria

what is parvimonas micra considered to be?

the predominant species of Gram-positive anaerobic cocci in the oral flora

what is parvimonas micra associated with?

periodontal destruction and is also commonly isolated from endodontic lesions and peritonsillar infections

what is the veillonella species?

obligate anaerobic gram negative cocci frequently isolated from oral samples and dental plaque

what type of role does the veillonella species play in caries?

a beneficial role since they utilize lactic acid produced by cariogenic bacteria

what are cariogenic bacteria?

microorganism that contribute to the development of dental caries (tooth decay). these bacteria thrive in the oral cavity, specifically within dental plaque and produce acids that erode tooth enamel

what are the most well known cariogenic bacteria?

• streptococcus mutans

• streptococcus sobrinus

• lactobacilli

what are actinomycetes?

members of this genus grow as branching filaments, similar to fungi. they form a significant percentage of the dental plaque in healthy individuals. they are gram positive anaerobic gram positive bacilli

why are actinomycetes considered to be true bacteria?

1. presence of a cell wall like gram positive bacteria

2. lack of nuclear membrane and mitochondria

3. susceptibility to antibacterial but not antifungal chemotherapeutic agents

what dental and oral infections are actinomycetes associated with?

• cervicofacial actinomycosis

• dental caries

• endodontic infections

• odontogenic abscesses

• dental implant associated infections

what is actinomycosis?

a chronic inflammatory suppurative granulomatous disease commonly caused by Actinomyces israelii. it may affect the cervicofacial, thoracic or abdominopelvic regions

what is A. israelii considered to be?

normal flora, meaning it can normally live harmlessly in the mouth, intestine, and female genital tract.

what is the pathogenesis of cervicofacial actinomycosis?

the infection is endogenous and predisposed by conditions causing the organism to invade the tissues, such as untreated dental caries, dental extractions and local trauma

what does cervicofacial actinomycosis affect?

the face, neck and mandible and it is characterized by tissue swelling with fibrosis and draining sinus tracts that discharge pus. the pus contains yellow (Sulphur) granules

how is actinomycosis diagnosed?

the Sulphur granules are crushed and subjected to direct detection by microscopic examination, which reveals filamentous branching Gram-positive bacilli and culturing, which is done on blood agar under anaerobic conditions for at least two weeks

how is actinomycosis identified?

by the morphology of the colobines on the agar, as they have a molar tooth appearance and by immunofluorescence staining

how is actinomycosis treated?

• surgical drainage of pus

• prolonged administration of antibiotics such as penicillin, clindamycin and erythromycin

what are propionibacterium?

gram-positive bacilli, having the typical morphology of diptheroids

what can Propionibacterium propionicum cause?

oral infections

what is Propionibacterium acidifaciens associated with?

dental carries

what is Propionibacterium acnes associated with?

infections related to implanted prostheses

what are Bacteroides?

obligate anaerobic gram negative bacilli that are occasionally associated with infections of the head and neck

what are Bacteroides resistant to?

most strains are resistant to penicillin but they are still sensitive to metronidazole, clindamycin and

chloramphenicol.

what are prevotella?

a group of obligate anaerobic gram negative bacilli which can be involved with nearly all types of oral infections

what is a common anaerobic organism in saliva?

Prevotella melaninogenica

what does Prevotella melaninogenica produce on blood ager?

black pigmented colonies which are fluorescent red under UV light

what are porhyromonas?

gram negative bacteria, with some examples being P. endodontalis and P. gingivalis, which are significant oral pathogens that produce advanced periodontitis and dental root canal infection

what are fusobacterium?

obligate gram negative large fusiform or cigar shaped bacilli

when fusobacterium is combined with spirochaetes, what do they cause?

fusopirochaetal disease, which in the oral cavity, causes acute necrotizing ulcerative gingivitis

F. nucleatums is frequently isolated where?

from peri-apical implantitis, root canal infection and periodontal pockets

F. nucleatums and fusobacterium grows best where?

areas with higher concentration of CO2 (capnophilic)

what are spore forming anaerobes?

clostridium, which are gram positive bacilli shaped obligate anaerobes that produce spores. many clostridia are members of the normal flora of the GIT of humans and animals

what are clostridium of importance in dentistry?

• clostridium tetani causing tetanus

• clostridium perfringens causing gas gangrene

what is clostridium tetani?

the causative agent of tetanus, which is found in the intestinal tract and feces of various animals, thus, its spores are abundant in the soil, especially heavily manured soils

what is the morphology of C. tetani?

gram positive obligate anaerobes that are rods that form a terminal spore with a characteristic drumstick appearance

what is the virulence factor of C. tetani?

produces tetanospasmin which a neurotoxin encoded on a plasmid

what is the incubation period of tetanus?

varies from a few days (5-10) to several weeks

how does tetanus manifest?

with muscle spasms descending from neck to the trunk and limbs. the first symptom is usually trismus (lockjaw)

what is the prognosis of tetanus like?

successful treatment depends on an early diagnosis, especially before a lethal amount of the toxin becomes fixed to neural tissues as binding of the toxin is irreversible and cannot be neutralized by the antitoxin

how is tetanus diagnosed?

laboratory diagnosis is essentially clinical but may need laboratory confirmation. Specimens from the depth of the wound are examined by direct Gram-stained smear, where Gram-positive spore-forming bacilli showing a drumstick appearance are seen. For culture, specimens are cultured on blood agar and incubated anaerobically. The organism shows β-haemolysis.

what is clostridium perfringens?

the most common species among several species of the same genus that can cause gas gangrene.

what is gas gangrene?

or clostridial myonecrosis is an acute disease with a poor prognosis and often a fatal outcome

what is the pathogenesis of gas gangrene?

Clostridial wound infections occur when Clostridium enters damaged tissue that has little or no oxygen. This anaerobic environment usually develops because the blood supply to the tissue is reduced, which can happen due to trauma, surgery, foreign bodies, or malignancy (a cancerous tumor). Clostridium organisms and their spores are commonly found in soil and in human and animal feces. When a wound is contaminated with soil or feces, the spores can enter the traumatized tissue, where the low-oxygen environment allows them to germinate and cause infection.

a lack of oxygenation in open wounds leads to what?

germination of the spores and growth of clostridia. it first multiplies in the subcutaneous tissues (tissues beneath the skin), where it produces gas and causes anaerobic cellulitis. the bacteria then spread deeper into the muscles, where they produce exotoxins that cause extensive cell death. they also produce enzymes such as hyaluronidase, collagenase, and lipase, which break down tissue components and therefore help the infection spread through the tissues.

how is diagnosis of gas gangrene done?

it is mainly done while laboratory diagnosis is performed only to confirm the diagnosis. However, treatment must be started promptly based on the clinical diagnosis without waiting for laboratory results. For laboratory diagnosis, specimens should be taken from the depth of the wound and transferred to the laboratory as soon as possible, preferably in a closed syringe, to prevent exposure to oxygen. A direct Gram-stained smear shows large Gram-positive bacilli. For culture, the specimens are cultured on blood agar and incubated anaerobically.

what is the treatment for gas gangrene?

• radical surgical debridement combined with high doses of antibiotics, with penicillin being the drug of choice

• hyperbaric oxygen therapy might be effective to force oxygen into the wound