ADVANCED PATHOGENIC BACTERIOLOGY

 

INTRODUCTION

Actinomycosis is an uncommon, indolent, progressively invasive bacterial infection caused by organisms of the Actinomyces species, which are non-motile, filamentous, branching, gram-positive and predominantly anaerobic bacteria. These organisms belong to the phylum, Actinobacteria, in the order Actinomycetales, and family, Actinomycetaceae. They are related to other genera like Corynebacterium, Propionobacterium, Mycobacteriium and Nocardia.

More than thirty species of Actinomyces have been described.

The most common agents in this disease are A. israelii and A. gerencseriae, but at least four other Actinomyces species (A. naeslundii, A. viscosus, A. odontolyticus, and A. meyeri), Propionibacteriumpropionicum(formerly Arachniapropionica), and Bifidobacteriumdentium (formerly Actinomyceseriksonii) may also be responsible for similar or identical clinical symptoms. Furthermore, eight new Actinobacillus species (A. europaeus, A. funkei, A. graevenitzii, A. neuii, A. radicidentis, A. radingae, A. turicensis, and A.urogenitalis) as well as the related taxonActinobaculumschaaliihave recently been described that were all derived from clinically less specific inflammatory conditions, and two former Actinomyces species (A. bernardiae and A. pyogenes) have been placed in the genus Arcanobacterium.

Actinomycesbovis causes granulomatous infections in cattle; however, this species has never been proven as a human pathogen and earlier reports of human A. bovis infections most probably were due to A. israelii. Ten additional Actinobacillus species have as yet solely been isolated from animal sources.

Members of the genera Actinomyces, Actinobaculum, Propionibacterium, and Bifidobacterium are morphologically similar, anaerobic to less stringently anaerobic (provided by Fortner's method) to capnophilic or aerotolerant (facultatively anaerobic), nonsporulating, gram-positive bacteria that tend to form branching rods and filaments and have a fermentative type of carbohydrate metabolism. Filamentous, microscopic colonies of Actinomyces species can be detected within 2 to 4 days of anaerobic incubation at 36 ± 1 °C. Mature colonies require 7 to 14 days to develop. Characters that differentiate these four genera from each other and from other anaerobically growing nonsporulating gram-positive bacteria are derived from cell wall or whole-cell analysis, acid end-product analysis, and certain physiological tests. These last tests are particularly necessary for differentiating between the various Actinomyces species (80), but rapid and reliable identification to the species level may also be achieved by using serologic techniques such as direct or indirect immunofluorescence.

Actinomycosis-producing actinomycetes may be distinguished from aerobic, filamentous bacteria such as Nocardia species, Rothiadentocariosa, or Corynebacterium (Bacterionema) matruchotii by the type of carbohydrate metabolism (nocardiae are aerobes), by differences in cell wall composition (nocardiae and C. matruchotii contain meso-diaminopimelic acid, arabinose and galactose as well as mycolic acids in their walls), by partial acid-fastness and aerial filaments (nocardiae), and by resistance to penicillin (nocardiae). R. dentocariosa, which is often difficult to distinguish from aerobically growing Actinomyces species, is characterized by its ability to reduce nitrate as well as nitrite.

Characteristic actinomycotic lesions usually do not develop in the absence of concomitant flora that may consist of aerobic and/or anaerobic species.

Actinomyces is a genus of the Actinobacteria class of bacteria. They are all gram-positive. Actinomyces species are facultatively anaerobic (except A. meyeri and A. israelii both obligate anaerobe), and they grow best under anaerobic conditions. Actinomyces species may form endospores, and, while individual bacteria are rod-shaped, Actinomyces colonies form fungus-like branched networks of hyphae.

The aspect of these colonies initially led to the incorrect assumption that the organism was a fungus and to the name Actinomyces, "ray fungus" (from Greekactis, ray, beam and mykes, fungus).

Actinomyces species are ubiquitous, occurring in soil and in the microbiota of animals, including the human microbiota. They are known for the important role they play in soil ecology; they produce a number of enzymes that help degrade organic plant material, lignin, and chitin. Thus their presence is important in the formation of compost. Certain species are commensal in the skin flora, oral flora, gut flora, and vaginal flora of humans and livestock. They are also known for causing diseases in humans and livestock, usually when they get an opportunity to gain access to the body's interior through wounds. As with other opportunistic infections, people with immunodeficiency are at higher risk. In all of the preceding traits and in their branching filament formation, they bear similarities to Nocardia.

Like various other anaerobes, Actinomyces species are fastidious and thus not easy to culture and isolate. Clinical laboratories do culture and isolate them, but a negative result does not rule out infection, because it may be due simply to reluctance to grow in vitro

Causes

Actinomycosis in animals is caused by Actinomycesbovis (whereas human infections are usually due to A. israelii). The Actinomyces bacteria that cause lumpy jaw are always present in a healthy cattle's mouth. In order for infection to occur, there must be tissue damage, which is often caused by unusually rough feed that scratches the mouth of the animal or by contact with sharp objects, such as sticks or brambles. Given the mode of infection, lumpy jaw is not contagious.

 

 

Epidemiology

Actinomyosis is a subacute to chronic bacterial disease that is characterized by slowly progressing suppurativefibrosing inflammation, development of draining sinus tracts that may discharge characteristic "sulfur granules," and direct dissemination via contiguous tissues. It most commonly involves the cervicofacial area, thorax or abdomen, including the pelvis, but rarely also the central nervous system (CNS), skin or bone (85, 87). The disease is worldwide in distribution and more common in males.

The etiology of human actinomycoses is complex in two respects: the principal etiological agents of the disease do not belong to a single species, but to a variety of different members of the genera Actinomyces, Propionibacterium, and Bifidobacterium. Furthermore, essentially all of the typical actinomycotic lesions contain between one and 10 bacterial species in addition to the pathogenic actinomycetes. These concomitant bacteria apparently act as synergistic pathogens that strengthen the comparatively low invasive power of the pathogenic actinomycetes and are in particular responsible for the early symptoms of the disease and for treatment failures. Since the etiologic term "actinomycosis" therefore circumscribes a polyetiologic inflammatory syndrome rather than a disease attributable to a single pathogen, it appears to be more appropriate to refer to this group of closely related conditions as "actinomycoses" in the plural.

Habitat

Actinomycetes are a saprophyte which means it rows well in a moist, moderate to tropical atmosphere. It is commonly found in compost piles and forest floor liters. It is also found in humans and cattle bodies, in the mouth, throat and intestinal tract.

            Actinomyces species are ubiquitous, occurring in soils and in micro biota of animals including human micro biota. Some species are commensally in the skin flora, oval flora, gut flora and vainal flora of humans and animals. (Wikipedia 2017, Murray et al, 1990).

Phylogenetic

            Phylogenetic trees based on 16S ribosomal RNA (16SrRNA) sequences have shown that the genus Actinomyces is quite diverse, exhibiting polyphyletic branching into several clusters. The genera Actinomyces and Mobiluncus form a monophyletic clade in a phylogenetic tree constructed using RpoB, RpoC, and DNA gyrase B protein sequences. This clade is also strongly supported by a conserved signature indel consisting of a three-amino-acid insertion in isoleucine tRNAsynthetase found only in the species of the genera Actinomyces and Mobiluncus.

CLINICAL MANIFESTATIONS

CervicofaciaActinomycosis:

Cervicofacialactinomycosis is the most common form, accounting for about 50 % of all cases.

Characteristic risk factors are poor oral hygiene resulting in periodontal abscesses or dental decay; orofacial trauma; foreign bodies penetrating the mucosal barrier such as bone splinters, fish bones or spicules of grass or grain; and dental procedures. One to several weeks after dental extraction or mouth trauma, or spontaneously, the infection typically causes a painful, indurated cutaneous and soft tissue swelling ("woody" fibrosis) or presents as typical odontogenic abscess. The slowly enlarging inflammatory mass is most frequently located in tissue adjacent to the body of the mandible (53.6%), but may also involve cheek (16.4%), chin (13.3%), ramus and angle of the mandible (10.7%), upper jaw (5.7%) and mandibular joint (0.3%) (33). Over ensuing weeks to months, the overlying skin may develop a bluish discoloration and become adherent, and the mass may become fluctuant and develop draining extra or intra-oral sinuses that may extrude sulfur granules. Trismus may be prominent early in the patient's course; however, cervical lymphadenopathy is uncommon. Direct extension may involve the tongue, sinuses, and meninges and rarely, contribute to periostitis or osteomyelitis of the mandible.

Thoracic Actinomycosis:

Actinomycosis of the lung and pleura comprises 15-20% of cases and is usually secondary to aspiration but rarely may occur secondary to hematogenous dissemination. A low-grade pneumonitis develops that tends to invade the pleura, possibly resulting in empyema necessitatis and a draining chest wall fistula. Prior to pleural invasion, the patient's symptoms may be minimal and nonspecific (malaise, weakness); however, progression of infection may be associated with fever, productive cough (rarely hemoptysis), and weight loss, which may be severe. Pleuropulmonaryactinomycosis may be complicated by direct extension into the mediastinum, pericardium, thoracic vertebrae, or subphrenic spaces, occasionally leading to paravertebral or even psoas abscesses. Pulmonary actinomycosis may disseminate hematogenously, and multiple subcutaneous nodules or neurologic symptoms resulting from a brain abscess may be the presenting manifestation of the disease.

AbdominopelvicActinomyosis:

Actinomycosis of the abdominopelvic region is responsible for about 20% of cases, and can be divided into gastrointestinal and pelvic disease.

Gastrointestinal Actinomycosis:

Actinomycosis of the gastrointestinal tract most commonly develops in the ileocecal region, but it may also primarily involve the esophageal, gastric or anorectal areas. There is often a previous history of appendicitis. Fever, abdominal pain, a palpable mass, and the development of an external sinus may be the presenting features. Alternatively, the diagnosis may be considered only after an indurated draining sinus fails to heal following surgical drainage of a presumed appendiceal abscess. Purulent drainage may contain sulfur granules. In some patients, a primary ileocecal infection may cause secondary pelvic actinomycosis.

Pelvic Actinomycosis:

Pelvic actinomycosis has been recognized with increasing frequency. Predisposing factors include intrauterine devices (IUDs), vaginal pessaries, prolapse of the uterus, and septic abortion. Symptoms may include pelvic pain, leukorrhea, menorrhagia, and amenorrhea, associated with fever, malaise, weakness, and weight loss, in any combination. Actinomycosis should be considered in any woman with a history of IUD use who presents with abdominal pain or a pelvic mass. Recently, Fiorino reviewed 92 cases of actinomycotic abscesses associated with IUD use or intravaginal foreign bodies. The patients had a mean age of 37 years (range 20-77), and had been using an IUD for an average of 8 years. Presenting symptoms included abdominal pain, and weight loss, and these patients frequently demonstrated vaginal discharge, fever, anemia and leukocytosis. Almost 90% of patients were found at surgery to have uni- or bilateral tubo-ovarian abscesses. The inflammatory process commonly involved other organs directly, or indirectly by adhesions or compression, in particular the large and small bowel, bladder, ureters, and liver.

Actinomycosis of the Central Nervous System:

Actinomycoses of the brain and the spinal cord are rare conditions. CNS involvement may follow thoracic or abdominal infections by hematogenous spread or may result from direct dissemination of a cervicofacial lesion. It usually presents as a brain abscess that, depending on its localization, may lead to a headache, increased intracranial pressure, focal seizures, hemiparesis, aphasia, ataxia, or abnormal reflexes. Several cases of brain abscesses due to A. meyeri have been reported. This species has a higher predilection for dissemination than other species.

Actinomycosis of the Bone and Skin:

In contrast to animal actinomycoses, osseous involvement is very uncommon in humans. It usually results from direct extension of an adjacent soft tissue focus leading to periostitis and finally to localized areas of bone destruction surrounded by areas of increased bone density. The mandible, ribs, and spine are the bones most frequently involved.

Cutaneous actinomycotic infections are extremely rare and mostly result from wounds that were contaminated with saliva or dental plaque material, either by human bites or as a consequence of fist-fight trauma. Hematogenous spread to the skin has also been observed. The clinical picture of these cutaneous or wound actinomycoses (punch actinomycoses) is very similar to that of the cervicofacial form.

Other Conditions Caused by Fermentative Actinomycetes:

Some Actinomyces species (e.g. A. naeslundii, A. viscosus, A. odontolyticus) may be involved in the complex etiology of caries and periodontal disease. In addition, these and other species, in particular the recently described ones, may cause non-specific suppurative lesions such as wound infections, abscesses or empyemas, as well as infections of the urogenital tract, infections of root canals of teeth and even endocarditis and septicemia.

Virulence Factors in Actinomyces

            Aggregatibacteractinomycetemcomtant has shown to possessa myriad of virulence factors that enhances its survival in the oral cavity and enable it to circumuent the host protective strategies. Virulence factors that promote the colonization and persistence in the oral cavity are;

1.      Adhesive

2.      Invasins

3.      Bacterion

4.      Antibiotic resistance

 

1.      Adhesins: is a bacterial surface component involved in adhesions to a specific substrate. These are proteinaceos structure found on the surface of the bacterial all which interact and bind to specific receptors in saliva, on the surface of tooth, on extracellular matrix protein and on epithelial cells. Cell surface entities medating adherence include flimbriae, extracellular amorphous material and extracellular vesicle.

2.      invasin:invasinof aggregatibacteractinomycetemcomitansis a rapid mechanism involving the formation of cell surface “craters” or apertures with up-like rims. These inversion as a indentation on the cell surface, as well as in membrane ruffles where they appear to be entering the epithelial cells.

3.      Bacterion: is hyperlink referring to Trojan bacteria to inhibit the growth of related bacterial strain. In aggregatibacteractinomycetemcomitant,they are associated with both the bacterial cells and extracellular vesicles. These toxic agents can confer a colonization advantages for the bacterium by lessenin the ecological pressure associated with competition by other organisms for both nutrients and space. (Malik et al. 2015).

4.      Antibiotics resistant: is a form of hyperlink drug resistance whereby same sub population of microrganismare able to survive after   exposure to one or more antibiotics. Poor permeability of the outer membrane is responsible for the microbial resistance in gram-negative organism. Approximately 30% of oral aggregatibacteractinomycetemcomitans to benzylpenicilin. (Malik et al 2015).

Pathology

Actinobacteria are normally present in the gums and are the most common cause of infection in dental procedures and oral abscesses. Many Actinomyces species are opportunistic pathogens of humans and other mammals, particularly in the oral cavity. In rare cases, these bacteria can cause actinomycosis, a disease characterized by the formation of abscesses in the mouth, lungs, or the gastrointestinal tract. Actinomycosis is most frequently caused by A. israelii, which may also cause endocarditis, though the resulting symptoms may be similar to those resulting from infections by other bacterial species. Aggregatibacteractinomycetemcomitans has been identified as being of note in periodontal disease.

The genus is typically the cause of oral-cervicofacial disease. It is characterized by a painless "lumpy jaw". Lymphadenopathy is uncommon in this form of the disease. Another form of actinomycosis is thoracic disease, which is often misdiagnosed as a neoplasm, as it forms a mass that extends to the chest wall. It arises from aspiration of organisms from the oropharynx. Symptoms include chest pain, fever, and weight loss. Abdominal disease is another manifestation of actinomycosis. This can lead to a sinus tract that drains to the abdominal wall or the perianal area. Symptoms include fever, abdominal pain, and weight loss. Actinomyces species have also been shown to infect the central nervous system in a dog "without history or evidence of previous trauma or other organ involvement.

Pelvic actinomycosis is a rare but proven complication of use of intrauterine devices. In extreme cases, pelvic abscesses might develop. Treatment of pelvic actinomycosis associated with intrauterine devices involves removal of the device and antibiotic treatment.

Pathogenesis

Nearly all of the microbes etiologically involved in the development of human actinomycoses belong to the indigenous microflora of the human mucous membranes, in particular in the oral cavity, but also in the gastrointestinal and female genital tracts. Thus, most members of the actinomycotic flora possess low inherent pathogenicity so that local tissue ischemia resulting from circulatory or vascular diseases, crush injuries, or foreign bodies, or from the reducing and necrotizing capacity of simultaneously present additional microbes is necessary to allow the infection to establish itself in tissues, and to invade surrounding healthy areas. In consequence, apart from "punch actinomycoses" following human bites or fist-fight injuries, the disease is always endogenous in origin and therefore neither liable to cause outbreaks nor to be transmitted from person to person.

Laboratory Diagnosis

Actinomycosis may be considered when a patient has chronic progression of disease across tissue planes that is mass-like at times, sinus tract development that may heal and recur, and refractory infection after a typical course of antibiotics.

A definitive diagnosis cannot be made solely on clinical grounds. The diagnosis of actinomycosis may be difficult and often depends on a heightened level of clinical suspicion and prior notification of the clinical laboratorian and pathologist. Bronchoscopy and bronchoalveolar lavage fluid examination and culture may be useful in thoracic actinomycosis  but may also produce misleading results due to contamination of the specimens with the normal oropharyngealmicroflora. Detection of the causative agents by Gram stain and culture from an appropriately obtained specimen is needed. Exudates and biopsy material are particularly suitable for examination, and should be cultured promptly under anaerobic conditions.

After a sample is obtained, it should be examined by standard histologic methods, anaerobic culture for 2 weeks, and immunofluorescence if available. Culture is the least reliable method of verifying infection (in Fiorino's series only 35% of cultures were positive for fermentative actinomycetes (r21) when standard aerobic and anaerobic culture techniques are used. However, an 86% success rate has been reported for samples cultured in the presence of metronidazole, which inhibits the growth of faster growing anaerobes (92), and, as indicated by the overall number of culture-proven cases (47, 69, 81) and the percentage of culture-positive IUD specimens (17, 18), even better results may be obtained when transparent agar media, Fortner's (22) method for producing a semianaerobic atmosphere, and microscopic examination of the cultures for up to 14 days of incubation at 36 ± 1°C are used (81). The last procedure also facilitates the detection of actinomycete colonies among a usually large amount of various colony types of concomitant microbes.

Because of the polymicrobial nature of the disease, culture and Gram stain of abscess aspirates, sinus discharge, bronchial secretions or biopsy specimens may have important implications for the choice of adjunctive antibiotics. Microorganisms may be scarce in pathologic specimens, so detection may require diligent searching of multiple tissue sections. The presence of sulfur granules is highly suggestive but not diagnostic of disease. These sulfur granules are visible with the unaided eye (diameter up to 1 mm) as yellowish to reddish to brownish particles that consist of spherical segments of filamentous actinomycetemicrocolonies, various concomitant bacteria and surrounding tissue reaction material, in particular polymorphonuclear granulocytes. Serodiagnosis of actinomycosis by detection of precipitating or other antibodies has not been a particularly useful diagnostic test. Demonstration of pathogenic actinomycetes from smears of lesions by immunofluorescence is a more promising technique. More recently, molecular genotypic techniques have been utilized for identification of Actinomycesspecies. 16 S ribosomal RNA (rRNA) gene sequencing is now becoming the standard method of identification in most academic and reference laboratories.

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry is a newer, promising technology that can accurately identify Actinomyces at the genus level, although precise species identification can sometimes be difficult.

Misdiagnosis

As is often the case, there are diseases/conditions with signs and symptoms that are similar to actinomycosis. As such, misdiagnoses can occur. Some examples include abscesses caused by grass seeds, woody tongue, bottle jaw, cancerous growths, and irritation caused by lodged objects.

Treatment

Treatment for actinomycosis consists of antibiotics such as penicillin or amoxicillin for 5 to 12 months, as well as surgery if the disease is extensive.

Prevention

There are no specific measure for preventing actinomycosis, however, maintenance of good oral and dental hygiene particularly removal of dental plague, may reduce risk of oral infection including low-grade periodontal diseases with actinomyces species. Appropriate antibiotic prophylaxis should be used when the mouth or gastrointestinal tract is penetrated (Wint and Solan, 2016).

 

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