Download Anaerobic bacteria

Nocardia
and
Anaerobic bacteria
İ. Çağatay Acuner
M.D., Clinical Microbiologist, Assistant Professor
Department of Microbiology
Faculty of Medicine, Yeditepe University, Istanbul
[email protected]
Nocardia (Actinomycetes)
Nocardia (Actinomycetes)
• Nocardiae are strict aerobic rods that form branched filamentous form in tissues and
culture.
• These filamentous forms resemble the hyphae formed by filamentous fungi (molds), and at
one time Nocardia was thought to be a fungus.
• However, the organisms have a gram-positive cell wall and other cellular structures that are
characteristic of bacteria.
• Most isolates stain poorly with the Gram stain and appear to be gram-negative with
intracellular gram-positive beads
• The reason for this staining property is that nocardiae have a cell-wall structure similar to
that of mycobacteria; "weakly acid-fast"
Nocardia (Actinomycetes)
• Cord factor is an important virulence factor that facilitates intracellular survival
• Nocardia can grow on nonselective laboratory media ; growth is slow, requiring 3 to 5 days
of incubation. (white to orange colonies with aerial hyphae)
• Most infections are caused by a relatively few species
• Identification at the genus level, with in vitro susceptibility testing, is sufficient for the
management of most patients.
Nocardia (Actinomycetes)
Biology, Virulence, and Disease
• Gram-positive, partially acid-fast, filamentous rods; cell wall with mycolic acid
• Strict aerobe capable of growth on most nonselective bacteria, fungal, and mycobacterial
media; however, prolonged incubation (7 days or more) may be required
• Virulence associated with ability to avoid intracellular killing
• Catalase and superoxide dismutase: inactivate toxic oxygen metabolites (e.g., hydrogen
peroxide, superoxide)
• Cord factor: prevents intracellular killing in phagocytes by interfering with fusion of
phagosomes with lysosomes
• Primary disease most commonly bronchopulmonary (e.g., cavitary disease) or primary
cutaneous infections (e.g., mycetoma, lymphocutaneous infection, cellulitis, subcutaneous
abscesses)
• Dissemination most commonly to central nervous system (e.g., brain abscesses) or skin
Nocardia (Actinomycetes)
Epidemiology
• Worldwide distribution in soil rich with organic matter
• Exogenous infections acquired by inhalation (pulmonary) or traumatic introduction
(cutaneous)
• Opportunistic pathogen, causing disease most commonly in immunocompromised patients
with T-cell deficiencies (transplant recipients, patients with malignancies, patients infected
with the human immunodeficiency virus, patients receiving corticosteroids)
Diagnosis
• Microscopy is sensitive and relatively specific when branching, partially acid-fast organisms
are seen
• Culture is slow, requiring incubation for up to 1 week; selective media (e.g., BCYE agar) may
be required for isolating Nocardia in mixed cultures
• Identification at the genus level can be made by the microscopic and macroscopic
appearances (branching, weakly acid-fast rods forming colonies with aerial hyphae)
• Identification at the species level requires genomic analysis for most isolates
Nocardia (Actinomycetes)
Treatment, Prevention, and Control
• Infections are treated with antibiotics and proper wound care
• Trimethoprim-sulfamethoxazole is used for localized infections; combination of antibiotics
such as amikacin with a carbapenem or broad-spectrum cephalosporin is used for severe,
progressive disease; treatment for 6 weeks or more
• Exposure cannot be avoided, because nocardiae are ubiquitous
Nocardia (Actinomycetes)
Acid-fast stain of Nocardia species in Gram stain of Nocardia species in expectorated
expectorated sputum. In contrast with the sputum. Note the delicate beaded filaments.
mycobacteria, members of the genus Nocardia
do not uniformly retain the stain ("partially
acid-fast").
Nocardia (Actinomycetes)
Aerial hyphae of Nocardia.
Orange colonies of Nocardia
Nocardia (Actinomycetes)
Nocardiosis: Clinical syndromes
Bronchopulmonary disease: pulmonary disease with necrosis and abscess formation;
dissemination to central nervous system or skin is common
Mycetoma: chronic, destructive, progressive disease, generally of extremities,
characterized by suppurative granulomas, progressive fibrosis and necrosis, and sinus
tract formation
Lymphocutaneous disease: primary infection or secondary spread to cutaneous site
characterized by chronic granuloma formation and erythematous subcutaneous nodules,
with eventual ulcer formation
Cellulitis and subcutaneous abscesses: granulomatous ulcer formation with surrounding
erythema but minimal or no involvement of the draining lymph nodes
Brain abscess: chronic infection with fever, headache, and focal deficits related to the
location of the slowly developing abscess(es)
Nocardia (Actinomycetes)
Cutaneous lesion caused by Nocardia
Nocardia (Actinomycetes)
Treatment, Prevention, and Control
Nocardia infections are treated with the combination of antibiotics and appropriate surgical
intervention. Trimethoprim-sulfamethoxazole is used most commonly to treat localized
infections.
In patients with severe, progressive disease, a combination of antibiotics is recommended,
such as amikacin with a carbapenem (e.g., imipenem, meropenem) or broad-spectrum
cephalosporin.
In vitro susceptibility tests can be used to guide the selection of antibiotics. Because nocardiae
can disseminate and produce significant disease, therapy should be extended for 6 weeks or
more.
Whereas the clinical response is favorable in patients with localized infections, the prognosis is
poor for immunocompromised patients with disseminated disease.
Nocardiae are ubiquitous, so it is impossible to avoid exposure to them. However,
bronchopulmonary disease caused by nocardiae is uncommon in immunocompetent persons,
and primary cutaneous infections can be prevented with proper wound care.
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive cocci and rods
• The anaerobic gram-positive cocci and non-spore-forming rods are a heterogeneous group
of bacteria that characteristically colonize the skin and mucosal surfaces.
• These organisms are opportunistic pathogens, typically responsible for endogenous
infections and usually recovered in mixtures of aerobic and anaerobic bacteria.
• Additionally, most of these anaerobes have fastidious nutritional requirements and grow
slowly on laboratory media.
• Thus the isolation and identification of individual strains are difficult and often time
consuming.
• Fortunately, the appropriate management and treatment of most infections with these
organisms can be based on the knowledge that a mixture of aerobic and anaerobic
organisms is present in the clinical specimen and does not require the isolation and
identification of the individual organisms.
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive cocci and rods
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive cocci
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive cocci
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Characteristics:
• At one time, all clinically significant anaerobic cocci were included in the genus Peptostreptococcus.
• More sophisticated methods have since been used to reclassify many of these species into six genera.
• Biochemical separation of the different genera is generally unnecessary, and knowledge that an anaerobic
coccus is associated with an infection is typically sufficient.
• The anaerobic gram-positive cocci normally colonize the oral cavity, gastrointestinal tract, genitourinary tract,
and skin.
Diseases:
• They produce infections when they spread from these sites to normally sterile sites. For example, bacteria
colonizing the upper airways can cause sinusitis and pleuropulmonary infections; bacteria in the intestines can
cause intraabdominal infections; bacteria in the genitourinary tract can cause endometritis, pelvic abscesses,
and salpingitis; bacteria on the skin can cause cellulitis and soft-tissue infections; and bacteria that invade the
blood can produce infections in bones and solid organs .
Laboratory:
• Confirmation of infections with anaerobic cocci is complicated by the following three factors:
• (1) care must be taken to prevent contamination of the clinical specimen with the anaerobic cocci that
normally colonize the skin and mucosal surface;
• (2) the collected specimen must be transported in an oxygen-free container to prevent loss of the
organisms; and
• (3) specimens should be cultured on nutritionally enriched media for a prolonged period (i.e., 5 to 7 days).
Treatment and prevention:
• Anaerobic cocci are usually susceptible to penicillin and carbapenems (e.g., imipenem, meropenem).
• Specific therapy is generally indicated in monomicrobic infections; however, because most infections with these
organisms are polymicrobic, broad-spectrum therapy against aerobic and anaerobic bacteria is usually selected.
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive rods
• The non-spore-forming, gram-positive rods are a diverse collection of facultatively anaerobic
or strictly anaerobic bacteria that colonize the skin and mucosal surfaces.
• Actinomyces, Mobiluncus, Lactobacillus, and Propionibacterium are well recognized
opportunistic pathogens,
• whereas other genera such as Bifidobacterium and Eubacterium can be isolated in
clinical specimens but rarely cause human disease.
Diseases associated with some gram-positive anaerobes
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive rods
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive rods;
Actinomyces
• The actinomycetes are true bacteria, although they have in the past been considered to
resemble fungi because they form branching filaments.
• They are related to the corynebacteria and mycobacteria in the chemical structure of their
cell walls.
• It is important to differentiate them from fungi because infections with actinomycetes
should respond to antibacterial agents whereas similar clinical presentations caused by fungi
are resistant to antibacterials (and extremely refractory to treatment by antifungal agents).
• This genus contains many species, some of which are important to humans as producers of
antimicrobial agents.
• A few are pathogenic to humans and animals; A. israelii is a key cause of actinomycosis.
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive rods;
Actinomyces israelii
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Characteristics:
• Gram-positive anaerobic filamentous branching rods. Non-sporing, non-acid fast.
Laboratory identification:
• Forms 'sulfur granules' composed of a mass of bacterial filaments in pus. These can be identified
by washing pus, squashing granules and observing in stained microscopic preparations. Grampositive branching rods also visible in stained pus. Forms characteristic breadcrumb or 'molar
tooth' colonies on blood agar after 3-7 days anaerobic incubation at 35°C.
Diseases:
• Actinomycosis follows local trauma and invasion from normal flora. Hard non-tender swellings
develop which drain pus through sinus tracts. Cervicofacial lesions are most common, but
abdominal lesions after surgery and infection related to intrauterine contraceptive devices also
occur.
Transmission:
• A. israelii is part of normal flora in mouth, gut and vagina. Infection is endogenous. There is no
person-to-person spread.
Pathogenesis:
• Virulence factors not described.
Treatment and prevention:
• Penicillin is the drug of choice. Prolonged treatment is required, accompanied by surgical drainage
.
Anaerobic, non-spore forming Gram-positive bacteria:
Gram-positive rods;
Actinomyces israelii
Anaerobic, spore-forming, Gram-positive rods
Anaerobic, spore-forming Gram-positive rods
Anaerobic, spore-forming Gram-positive rods:
Clostridium
• This genus contains many species of Gram-positive anaerobic spore-forming rods; a few
are aerotolerant.
• Widely distributed in soil and in the gut of humans and animals.
• The spores are resistant to environmental conditions.
• The major diseases associated with species of the genus are gangrene, tetanus, botulism,
food poisoning and pseudomembranous colitis.
• In each of these, the production of potent protein exotoxins is an important cause of
pathology, and in several species the genes encoding toxins are carried by plasmids or
bacteriophages.
Anaerobic, spore-forming Gram-positive rods:
Clostridium perfringens
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Characteristics:
• Anaerobic Gram-positive rods; spore-forming, but spores rarely seen in infected material. More tolerant of
oxygen than other clostridia.
Laboratory identification:
• Hemolytic colonies on blood agar incubated anaerobically. Germination of heat-resistant spores (with subsequent
toxin production) may be responsible for food poisoning. Five types of C. perfringens (A-E) identified on the basis
of toxins produced; type A strains can be further divided into several serotypes.
Diseases:
• Gas gangrene resulting from infection of dirty ischemic wounds. Food poisoning following ingestion of food
contaminated with enterotoxin-producing strains.
Transmission:
• Spores and vegetative organisms widespread in soil and normal flora of humans and animals. Infection acquired
by contact; may be endogenous (e.g. wound contaminated from patient's own fecal flora) or exogenous (e.g.
contamination of a wound with soil, ingestion of contaminated food).
Pathogenesis:
• In ischemic wounds, production of numerous toxins and tissue-destroying enzymes allows organism to establish
itself and multiply in wound. Local action of toxins produces necrosis thereby further impairing blood supply and
keeping conditions anaerobic, and aiding spread of organism into adjacent tissues. Food poisoning results from
the ingestion of large numbers of vegetative cells, which sporulate in the gut and release enterotoxin.
Treatment and prevention:
• Gangrene requires rapid intervention with extensive debridement of the wound. Penicillin is the antibiotic of
choice (alternatively metronidazole, clindamycin or imipenem). Hyperbaric oxygen may also be helpful. Food
poisoning does not usually require specific treatment.
Anaerobic, spore-forming Gram-positive rods:
Clostridium tetani
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Characteristics:
• Gram-positive spore-forming rod with terminal round spore (drumstick). Strict anaerobe.
Laboratory identification:
• Grows on blood agar in anaerobic conditions as a fine spreading colony; 'ground glass' appearance (hand lens
inspection of cultures important).
Diseases:
• Tetanus (lockjaw). Severe disease characterized by tonic muscle spasms and hyperflexia, trismus, opisthotonos
and convulsions.
Transmission:
• Organism widespread in soil. Acquired by humans by implantation of contaminated soil into wound. Wound
may be major (e.g. in war, in road traffic accident) or minor (e.g. a rose-thorn puncture while gardening). No
person-to-person spread.
Pathogenesis:
• Tetanus results from neurotoxin (tetanospasmin) produced by organisms in wound. Toxin genes are plasmidencoded. The organism is non-invasive, but the toxin spreads from site of infection via bloodstream and acts by
binding to ganglioside receptors and blocking release of inhibitory neurotransmitters. Causes convulsive
contractions of voluntary muscles.
Treatment and prevention:
• Antitoxin is available (hyperimmune human gamma globulin; tetanus immune globulin). Metronidazole (or
penicillin) and spasmolytic drugs indicated. Prevention readily available and effective in form of immunization
with toxoid. Usually given in childhood, but if immunization status of injured patient is unknown, toxoid is given
in addition to antitoxin.
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Anaerobic, spore-forming Gram-positive rods:
Characteristics:
Clostridium botulinum
• Anaerobic Gram-positive rods. Not easily cultivated. Produces most potent toxins known to man. Seven
immunologically distinct toxins (A, B, Cα, Cβ, D, E and F) produced by different strains of C. botulinum. Types A,
B and E (and in some cases F) are most commonly associated with human disease: serotypes A and B linked to a
variety of foods (e.g. meat), serotype E especially associated with fish.
Laboratory identification:
• Requires strictly anaerobic conditions for isolation. Grows on blood agar, but very rarely isolated from human
cases of disease. Detection of the toxin or organisms in the food or detection of the toxin or organisms in the
serum or feces of the patient, respectively, is the way of confirming the diagnosis.
Diseases:
• Major pathogen of birds and mammals, rare in humans. Botulism acquired by ingesting preformed toxin.
Disease entirely due to effects of toxin. Infant botulism results from ingestion of organisms and production of
toxin in infant's gut. Associated with feeding honey contaminated with spores of C. botulinum. Wound
botulism: toxin produced by organisms infecting a wound. Extremely rare.
Transmission:
• Soil is the normal habitat. Intoxication most often by ingestion of toxin in foods that have not been adequately
sterilized (e.g. home-preserved foods) and improperly processed cans of food. Toxin is associated with
germination of spores. There is no person-to-person spread.
Pathogenesis:
• Toxin released from organism as inactive protein and cleaved by proteases to uncover active site. It is acid stable
and survives passage through stomach. Taken up through stomach and intestinal mucosa into bloodstream.
Acts at neuromuscular junctions inhibiting acetylcholine release. Results in muscle paralysis and death from
respiratory failure.
Treatment and prevention:
• Supportive therapy is paramount. Trivalent antitoxin is available. In the rare cases of infant and wound
botulism (i.e. when the organism is growing in vivo), penicillin is effective. Prevention relates to good
manufacturing practice. The toxin is not heat stable, therefore adequate cooking of food before consumption
will destroy it.
Anaerobic, spore-forming Gram-positive rods:
Clostridium difficile
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Characteristics :
• Slender Gram-positive anaerobic rod; spore-former; motile.
Laboratory identification:
• Difficult to isolate in ordinary culture because of overgrowth by other organisms; selective
medium CCFA (cycloserine-cefoxitin-fructose agar) may be helpful; however, mere presence of the
organism is not indicative of infection. Diagnosis by detection of toxin in feces (i.e. immunoassay
or tissue culture cytotoxicity assay).
Diseases:
• Pseudomembranous colitis (antibiotic-associated diarrhea). Can be rapidly fatal especially in the
compromised host.
Transmission:
• Component of normal gut flora; flourishes under selective pressure of antibiotics. May also be
spread from person to person by the fecal-oral route.
Pathogenesis:
• Toxin-mediated damage to gut wall. Produces both an enterotoxin (toxin A) and cytotoxin (toxin
B).
Treatment and prevention:
• Oral vancomycin or metronidazole. Other antibiotics should be withheld if possible. Prevention of
cross-infection in hospitals depends upon scrupulous attention to hygiene.
Anaerobic, non-spore-forming Gram-negative bacteria
Anaerobic, non-spore-forming Gram-negative bacteria;
associated diseases
Infection
Bacteria
Head and neck
Bacteroides ureolyticus
Fusobacterium nucleatum
Fusobacterium necrophorum
Porphyromonas asaccharolytica
Porphyromonas gingivalis
Prevotella intermedia
Prevotella melaninogenica
Veillonella parvula
Intraabdominal
Bacteroides fragilis
Bacteroides thetaiotaomicron
P. melaninogenica
Gynecologic
B. fragilis
Prevotella bivia
Prevotella disiens
Skin and soft tissue
B. fragilis
Bacteremia
B. fragilis
B. thetaiotaomicron
Fusobacterium spp.
Anaerobic, non-spore forming, Gram-negative rods
• Historically, all short Gram-negative anaerobic rods or coccobacilli have been classified in
the genus Bacteroides and longer rods with tapering ends in the genus Fusobacterium.
• Recent applications of new techniques to the Bacteroides have resulted in the definition of
two additional genera: Porphyromonas and Prevotella.
• The genus Bacteroides is now restricted to species found among the normal gut flora.
• Prevotella contains saccharolytic oral and genitourinary species, including P.
melaninogenica (formerly B. melaninogenicus), which produces a characteristic black-brown
pigment.
• The genus Porphyromonas contains asaccharolytic pigmented species, which form part of
the normal mouth flora (P. gingivalis) and may be involved in endogenous infection within
the oral cavity.
• The most important non-sporing anaerobe causing infection is B. fragilis,
• although others are much more common (e.g. in gingivitis and other endogenous oral
infections).
Anaerobic, non-spore forming, Gram-negative rods:
Bacteroides
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Characteristics:
• Small pleomorphic Gram-negative rods or coccobacilli. Capable only of anaerobic respiration. Non-spore forming,
non-motile.
Laboratory identification:
• Grows on blood agar incubated anaerobically and in other media designed for isolation of anaerobes. Plates may
require up to 48 h incubation at 35°C for colonies to become visible. Cultures have a foul odor due to the fatty
acid end-products of metabolism. These can be used as identifying characteristics by analysis of culture
supernates by gas-liquid chromatography (GLC). The major products of Bacteroides are acetate and succinate.
Full identification in the diagnostic laboratory is based on biochemical tests and antibiogram. Commercial kits
are available.
Diseases:
• Intra-abdominal sepsis; liver abscesses; aspiration pneumonia; brain abscesses; wound infections. Infections
often mixed with aerobic and microaerophilic bacteria.
Transmission:
• Endogenous infection arising from contamination by gut contents or feces is most common route of acquisition.
Pathogenesis:
• Little is known about the virulence factors of B. fragilis. A polysaccharide capsule and production of extracellular
enzymes (e.g. enterotoxin) are important features. An anaerobic environment is essential and in mixed infections
growth of aerobic organisms probably helps the growth of Bacteroides by using up available oxygen.
Treatment and prevention:
• Metronidazole, imipenem, or beta-lactam-beta-lactamase inhibitor combinations used in therapy. Many strains
produce beta-lactamases and thus susceptibility to penicillin and ampicillin is unreliable. Prevention of
endogenous infection difficult; good surgical technique and appropriate use of prophylactic antibiotics
important in abdominal surgery.
Dental Plaque
&
Odontogenic Infections
Dental Plaque
&
Odontogenic Infections
A unifying hypothesis demonstrating a
microbial shift from a plaque-free tooth
surface and progression to supragingival
and subgingival plaque organisms.