Actinomycetes are a group of bacteria that have characteristics of both bacteria and fungi. They form branching filaments called hyphae and can cause a disease called actinomycosis. Actinomycosis typically presents as lumps containing yellow sulfur granules that form draining sinus tracts. It is most commonly found in the face or neck after dental procedures. Diagnosis involves identifying the filaments and sulfur granules in tissues or drainage under the microscope. Treatment involves prolonged high dose penicillin or tetracycline therapy. Good dental hygiene can help prevent actinomycosis.

1. I N T R O D U C T I O N
B Y
P R O M I S H N E U P A N E
M . S C M M
Actinomycetes,

2. Introduction
 Actinomycetes are Gram-positive, catalase-positive,
nonmotile bacilli. They are considered to be
transitional forms between bacteria and fungi.
 Like bacteria they possess cell wall, containing
muramic acid. They also possess prokaryotic nuclei
and are susceptible to antibiotics
 like fungi, they form delicate filaments called hyphae
similar to the hyphae form in fungi.
 These hyphae forms are seen in bacteria isolated by
culture and are also seen in clinical specimens

3. Classification
 Depending on the presence or absence of mycolic acids
in the cell wall, aerobic actinomycetes can be broadly
classified into two groups as follows:
 1. Actinomycetes with mycolic acids: This group
includes members of three families:
Corynebacteriaceae, Mycobacteriaceae, and
Nocardiaceae. Members of all these genera stain
poorly with Gram stain and are partially acid fast
 2. Actinomycetes without mycolic acid: This group
includes many opportunistic pathogens, such as
Actinomadura, Nocardiopsis, Streptomyces,
Dermatophilus, Oerskovia, Rothia, Tropheryma, and
thermophilic actinomycetes— Saccharopolyspora,
Saccharomonospora, and Thermoactinomyces.

6. Actinomyces
 Actinomyces israeli is the most common Actinomyces
causing human infection. Other species are Actinomyces
gerencsonei, Actinomyces turicensis, Actinomyces
radingae, Actinomyces europaeus, Actinomyces
naeslundii, Actinomyces odontolyticus, Actinomyces
viscosus, Actinomyces meyeri, and Propionibacterium
propionicum.

7. Morphology
 Morphology Actinomyces show the following features
Actinomyces organisms are Gram-positive, nonmotile,
nonsporing, and non–acid-fast bacilli.
 They measure 0.5–1 m in diameter.
 They often grow in filaments that separate into bacillary and
coccoid filaments. .

8. Culture
 Culture Actinomyces organisms are facultative
anaerobes.
 They grow better under anaerobic or
microaerophilic conditions at an optimum
temperature of 35–37°C.
 Presence of 5–10% CO2 facilitates the growth.
 Actinomyces species grow slowly; they need a
longer incubation period of 3–4 days. A.
israeli may require even 7–14 days for growth.

9.  Media used
 1. Brain heart infusion agar: Brain heart infusion
(BHI) agar or heart infusion agar supplemented with 5%
defibrinated rabbit, sheep, or horse blood is the enriched
medium used frequently for Actinomyces.
 On these media, in anaerobic to microaerophilic
conditions, the bacteria form colonies with a
characteristic molar-tooth appearance.
 2. Liquid media: Heart infusion blood and
thioglycollate blood supplemented with 0.1–0.2%
sterile rabbit serum are the examples of liquid media
used for culture of Actinomyces species.

14. Pathogenesis and Immunity
 Actinomyces species are present as normal flora of the oral
cavity and also in the lower gastrointestinal tract and
female genital tract of human hosts.
 The actinomyces by themselves are not virulent, but they
require the presence of devitalized or dead tissue and a
break in the continuity of the mucosal membranes to
facilitate their invasion into deeper tissues and cause
infection
 Establishment of human infection by Actinomyces always
requires the presence of companion bacteria
 These companion bacteria help in initiation of infection by
producing a toxin or enzyme or by inhibiting host
immunity.
 These companion bacteria include Bifidobacterium dentium,
Actinobacillus actinomycetemcomitans, Eikenella corrodens,
Haemophilus aphrophilus, Bacteroides, Fusobac terium,
staphylococci, and anaerobic streptococci.

15.  Once the infection is established by Actinomyces, the
immune system of the infected human host stimulates an
intense inflammatory response in the form of a
suppurative granulomatous and fibrotic
reaction.
 Infection by Actinomyces typically spreads contiguously
and invades surrounding tissues and organs.
 Finally, the infection results in the production of
draining sinus tracts, which contain lot of damaged
tissue.
 Bacteria from this site may disseminate through blood
circulation to distant organs.

16. Clinical Syndromes.
 Actinomyces causes actinomycosis
 ◗ Actinomycosis –
 Actinomycosis is a subacute and chronic bacterial
infection characterized by contiguous spread and
suppurative and granulomatous
inflammation.
 The condition is associated with the formation of
multiple abscesses and development of sinus
tracts discharging white to yellowish granules,
known as sulphur granules.
 Actinomycosis may manifest as (a) cervicofacial
actinomycosis, (b) thoracic actinomycosis, and (c)
actinomycosis of the abdomen and pelvis.

18. Cervicofacial actinomycosis:
 It is the most common manifestation in humans
comprising about two-thirds of reported cases.
 The infection occurs in the cervicofacial region, which
typically occurs following oral surgery in patients with
poor oral hygiene.
 Initially, the condition manifests as a swelling of the soft
tissue of the perimandibular area and subsequently, during
the course of the infection, the disease spreads directly into
the adjacent tissues and leads to formation of fistulas.
 These fistulas or sinus tracts discharge purulent
material containing yellow granules, known as sulfur
granules. If left untreated, this condition may spread to
the blood and eventually to the brain and to the orbit.

19. Thoracic actinomycosis:
 This condition is responsible for 15–20% of cases of
actinomycosis.
 It is caused by aspiration of oropharyngeal secretions
containing Actinomyces and occasionally during
perforation of the esophagus.
 The condition also occurs by direct spread from an
actinomycotic lesion of the nape of the neck or the
abdomen, or through blood circulation from other
distant sites.
 The condition commonly presents as a pulmonary
infiltrate or mass involving the lung.
 The condition, if left untreated, can spread outwardly
through the pleura, pericardium, and chest wall,
ultimately leading to the formation of multiple sinuses
that discharge sulfur granules.

20. Actinomycosis of the abdomen and pelvis:
 This condition accounts nearly 10–20% of reported
cases. The ileocecal region is the most common site
involved in the condition.
 The condition typically presents as a slowly growing
tumor. The infection subsequently spreads and
involves abdominal organs including the
abdominal wall, leading to the formation of
draining sinuses.
 . Actinomycosis of pelvis is commonly associated with
prolonged (for many years) use of intrauterine
contraceptive devices. The infection spreads directly
from uterus to pelvis.

21. Epidemiology
 Actinomycosis is distributed worldwide. The condition
is more common in rural areas and in farm
workers. The condition is seen more commonly in
individuals with poor dental hygiene and in the
people with low socioeconomic conditions.
 Men are affected more commonly than women (male
to female ratio is 4:3) with the exception of pelvic
actinomycosis. Majority of the cases are reported in
young and middle-aged patients.

22. Laboratory Diagnosis
 Specimens-
 The specimens include sputum, bronchial
secretions and discharges, and infected tissues.
 All these specimens may contain large number of sulfur
granules. The sulfur granules are also present on the
dressings removed from a draining sinus tract
 It is essential to transport these specimens immediately
to the laboratory for processing, preferably under
anaerobic conditions.

23. Microscopy
 Sulfur granules are white to yellow and vary in size from
minute specs to large granules. These granules are separated
from pus and other specimens and are collected directly from
draining sinuses.
 These are crushed between two slides and are stained by
Gram or Ziehl–Neelsen staining method, using 1% sulfuric
acid for decolorization.
 The stained smears on microscopic examination show Gram-
positive hyphal fragments surrounded by peripheral zone of
swollen, radiating, club-shaped structures presenting a
sunray appearance.
 These club-shaped structures are Gram positive, acid fast,
and are believed to be antigen complexes.

25. Culture
 Sulfur granules or pus-containing Actinomyces are
immediately cultured under anaerobic conditions at 35–
37°C for up to 14 days.
 The specimens are inoculated on blood agar, BHI
agar, and into thioglycollate broth and incubated
anaerobically at 37°C.
 A. israeli produces large (0–5 mm in diameter), white,
smooth, entire or lobulated colonies resembling
molar tooth after 10 days of anaerobic incubation.

27. ◗ Identification of bacteria
 Actinomycetes colonies are identified by microscopy,
biochemical reactions, direct fluorescent antibody test,
and gel immunodiffusion test

28.  Molecular Diagnosis
 DNA probes and PCR (polymerase chain
reaction) have
 been evaluated and used with high sensitivity and
specificity
 for accurate identification of Actinomyces species in
clinical specimens.

29. Treatment and Prevention
 High-dose penicillins or tetracyclines given over a
prolonged period are the mainstay of therapy for
actinomycosis.
 Metronidazole, cotrimoxazole, and
sulfamethoxazole, and penicillinase-resistant penicillins,
such as methicillin, oxacillin, and cloxacillin do not have
activity against Actinomyces species.
 Surgical therapy is included for more extensive and
complicated cases of actinomycosis.
 Prevention- Good dental hygiene and oral
hygiene are important in prevention of the disease.