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SECTION 2
Bacterial Infections Requiring
Gram-Positive Bacilli
Bacillus Species Infections II-2-2
II-2-6
Corynebacterium Species Infections II-2-10
Listeria Species Infection II-2-14
Rhodococcus Species Infection II-2-16
Gram-Positive Cocci
Staphylococcus Species Infections II-2-18
Streptococcus and Enterococcus Species Infections II-2-24
Gram-Negative Bacilli
II-2-28
Gram-Negative Zoonotic Pathogen Infections II-2-36
Primary Gram-Negative Respiratory Pathogen Infections II-2-40
Gram-Negative Cocci
Neisseria and Moraxella Species Infections II-2-46
Spirochete Bacteria
Borrelia Species Infections II-2-50
Leptospira Species Infection II-2-54
II-2-56
Acid-Fast Bacilli
Mycobacterium Tuberculosis Complex Infections II-2-60
II-2-66
Intracellular Bacterial Infections
Chlamydophila and Chlamydia Species Infections II-2-70
Rickettsia Species Infections II-2-74
BACILLUS SPECIES INFECTIONS
A brain from a patient with disseminated Bacillus
anthracis infection demonstrates diffuse hemorrhagic
meningoencephalitis, which is pathognomonic for the
disease. (Courtesy CDC/PHIL.)
TERMINOLOGY
Definitions
Latin: "Bacillum" (walking stick due to rod-shaped
organism)
Manifestations
Bacterial Infections: Bacterial Infections Requiring Culture/Ancillary Confirmation
Anthrax (Bacillus anthracis)
ETIOLOGY/PATHOGENESIS
Environmental Exposure
Bacillus species are widely present in environment
Spores are extremely resistant and have been found in
virtually every habitat
Natural infection by B. anthracis can occur by contact
with infected animals and animal products (hides,
etc.), though purposeful infection can also occur via
an act of bioterrorism
Bacillus cereus is often associated with food-borne
illness, though other vectors such as contaminated
laundry and disinfectant wipes have been described
within hospital environment
Bacillus thuringiensis preparations are used as
biopesticides, which can result in occupational
exposure
Infectious Agents
Clinically relevant species include: B. anthracis,
B. cereus, and B. thuringiensis, known collectively
as the "B. cereus group," along with a few other
nonpathogenic species
B. anthracis
Contains 2 large plasmids (pXO1 and pXO2) that
encode virulence factors (lethal toxin, edema toxin)
and polyglutamate capsule
II
B. cereus
Produces emetic toxin (encoded on a plasmid) and
enterotoxin
2
Bacillus species appears on Gram stain as long chains of
rod-shaped bacilli. Infections with Bacillus warrant careful
clinical investigation. (Courtesy CDC/PHIL.)
There are reports of virulent strains carrying
plasmids similar to B. anthracis
B. thuringiensis
Produces insecticidal toxins (Cry and Cyt) that form
parasporal crystals
CLINICAL ISSUES
Presentation
B. anthracis has 3 clinical types: Cutaneous,
gastrointestinal, and pulmonary
Cutaneous anthrax is most common cause of
naturally acquired anthrax
Characteristic lesion is an ulceration with a
blackened eschar, unaccompanied by fever, pus, or
pain
Eschars may be surrounded by substantial edema
Gastrointestinal anthrax can develop after eating
raw or undercooked meat of infected animals
Ulcerations can be confined to oral cavity or
develop throughout GI tract
Pulmonary anthrax occurs with breathing of spores
Active infection occurs in lymph nodes
Presents with fever, dyspnea, and cyanosis
Can rapidly progress to circulatory collapse and
death
B.cereus is an opportunistic pathogen and a causative
agent of food-borne illness and occasional nosocomial
outbreaks
Food-borne illness can be associated with a wide
variety of foods and be of emetic (commonly
associated with rice) and diarrheal types
Illness in immunocompromised individuals can be
severe and includes bacteremia/sepsis, pneumoniae,
abscess, osteomyelitis, meningitis, ocular infections,
and brain hemorrhage
B. thuringiensis is predominantly an insect pathogen
and uncommon cause of human gastroenteritis and
wound and burn infections
2
BACILLUS SPECIES INFECTIONS
Etiology
Bacillus species are widely present in environment
Natural infection by Bacillus anthracis can occur by
contact with infected animals and animal products
(hides, etc.), though purposeful infection can also
occur via an act of bioterrorism
Clinical Issues
Cutaneous anthrax is most common cause of
naturally acquired anthrax
Ingestion anthrax can develop after eating raw or
undercooked meat of infected animals
Inhalation anthrax occurs with breathing of spores
B. cereus is an opportunistic pathogen and a
causative agent of food-borne illness and occasional
nosocomial outbreaks
Laboratory Tests
Blood
Gram stain: Gram-positive rods, spores may be
apparent
Capsule stains: Great majority of B. cereus and B.
thuringiensis isolates will not produce a capsule
India ink exclusion
McFadyean reaction (polychrome methylene blue)
DFA stains with antibodies specific for
polyglutamate capsule
Treatment
Drugs
B . anthracis
Usually susceptible to penicillin
Other useful drugs include tetracyclines,
fluoroquinolones and chloramphenicol
B. cereus and B. thuringiensis
Produce -lactamases, resistant to all -lactams
except carbapenems
Options include vancomycin, clindamycin,
fluoroquinolones, aminoglycosides, and
carbapenems
Prognosis
B. anthracis mortality
Cutaneous: 10-20% no treatment, 1% with
treatment
Inhalation: 65-89% with treatment
B. cereus mortality varies widely with
immunocompetency of patient
MICROBIOLOGY
Characteristics
Phylum: Firmicutes; class: Bacilli; order: Bacillales;
family: Bacillaceae; genus: Bacillus
Gram-positive (though some may appear gramvariable or even gram-negative), rod-shaped organism
Aerobic (or facultatively anaerobic) growth
Key Facts
Microscopic Pathology
Pulmonary (anthrax): Pleural effusions, pulmonary
edema, and hyaline membrane formation more than
pneumonia; limited neutrophilic reaction
Lymphatics (anthrax): Hemorrhagic mediastinitis
Epidermis: Necrosis, hemorrhage, acantholysis, and
ulceration with polymorphonuclear infiltrates
Dermis: Edema, coagulation necrosis, hemorrhage,
and vasculitis with marked perivascular inflammatory
infiltrate
CNS anthrax: Low- and high-pressure hemorrhages
along with vasculitis composed of fibrinoid necrosis
and neutrophils in meninges and parenchyma
Forms endospores (usually elliptical and subterminal,
not associated with swollen sporangium in B.
anthracis, B. cereus, or B. thuringiensis)
B. thuringiensis also characteristically produces
parasporal crystals
Catalase positive, often motile (except B. anthracis and
Bacillus mycoides)
Culture
All Bacillus species grow on blood agar
Spores can be generated by heat treatment
B. anthracis
B. cereus and B. thuringiensis
MACROSCOPIC FEATURES
Gross Features of Bacillus Infections
Diffuse hemorrhagic meninges is pathognomic of
anthrax
Pleural effusions (most characteristic feature of
anthrax) and pulmonary edema
Lymphatogenous spread from lungs results in
hemorrhagic mediastinitis in anthrax ("shotgun
thorax")
Endophthalmitis (B. cereus)
MICROSCOPIC PATHOLOGY
Histologic Features
Gram and capsule stains as for blood
Bacterial Infections: Bacterial Infections Requiring Culture/Ancillary Confirmation
Forms medium, gray, flat, irregular, nonhemolytic
colonies on blood agar that are susceptible to
gamma phage
PLET agar can be used for selective media
Form a variety of colony morphologies on blood
agar
Often demonstrate some -hemolysis (differentiates
from B. anthracis)
Disseminated B. cereus shows small to large focal
hemorrhages
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BACILLUS SPECIES INFECTIONS
Silver stains and PAS with diastase may better
highlight organisms in tissue
Pulmonary anthrax has hyaline membrane formation
more so than a true pneumonia with a limited
neutrophilic reaction
Anthrax in skin
Epidermis shows necrosis, hemorrhage,
acantholysis, and ulceration with
polymorphonuclear infiltrates
Dermis shows edema, coagulation necrosis,
hemorrhage, and vasculitis with marked perivascular
inflammatory infiltrate
GI
Anthrax has 2 main forms
Hemorrhagic ulcers confined to oropharyngeal
region
Concentrated in terminal ileum and cecum with
mesenteric hemorrhagic lymphadenitis and
peritonitis
B. cereus infection shows liver abscesses, pancolitis,
typhlitis
CNS
Anthrax: Low- and high-pressure hemorrhages along
with vasculitis composed of fibrinoid necrosis and
neutrophils in meninges and parenchyma
B. cereus infection: In immunosuppressed
(usually in setting of malignancy): Meningitis,
meningoencephalitis, subarachnoid hemorrhage,
and brain abscesses
Bacterial Infections: Bacterial Infections Requiring Culture/Ancillary Confirmation
ANCILLARY TESTS
Immunohistochemistry
Important component to diagnosis of anthrax in tissue
sections, remaining positive as many as 10 days after
antibiotic treatment begins
Antibodies are available to B. anthracis cell wall
antigen and capsule (USAMRIID, Frederick, MD)
Both antibodies cross-react with other Bacillus species,
though a double-positive is highly specific for B.
anthracis
Immunofluorescence
DFA assay can be done using IHC antibodies
PCR
Laboratory Response Network (LRN) real-time assay
for B. anthracis (detects plasmid and chromosomal
components)
16S rRNA sequencing has limited ability to
differentiate members of B. cereus group
PCR assays are available for detection of B. cereus
enterotoxin and emetic toxin, though their reliability
has not been established
DIFFERENTIAL DIAGNOSIS
Skin Lesions Mimicking Cutaneous Anthrax
Brown recluse spider bite, ulceroglandular tularemia,
plague, ecthyma gangrenosum, spotted fever rickettsial
infection, scrub typhus (differentiated by culture and
IHC)
Gastrointestinal Infections
Clostridium difficile infection, IBD, ischemia
Respiratory Infections
Pneumonia, transfusion-associated acute lung injury
DIAGNOSTIC CHECKLIST
Pathologic Interpretation Pearls
Finding of gram-positive rods should alert to possible
Bacillus infection
B. anthracis should be suspected if in context of
characteristic skin lesions or pulmonary effusions
B. cereus is likely in context of food poisoning or in
immunocompromised patients
Culture is gold standard for diagnosis, but IHC with
antibodies against cell wall and capsule is extremely
helpful
SELECTED REFERENCES
1. Bottone EJ: Bacillus cereus, a volatile human pathogen.
Clin Microbiol Rev. 23(2):382-98, 2010
2.
Kolst AB et al: What sets Bacillus anthracis apart from
other Bacillus species? Annu Rev Microbiol. 63:451-76,
2009
3. Guarner J et al: Histopathology and
immunohistochemistry in the diagnosis of bioterrorism
agents. J Histochem Cytochem. 54(1):3-11, 2006
4. Hoffmaster AR et al: Characterization of Bacillus cereus
isolates associated with fatal pneumonias: strains are
closely related to Bacillus anthracis and harbor B. anthracis
virulence genes. J Clin Microbiol. 44(9):3352-60, 2006
5. Guarner J et al: Pathology and pathogenesis of
bioterrorism-related inhalational anthrax. Am J Pathol.
163(2):701-9, 2003
6. Shieh WJ et al: The critical role of pathology in the
investigation of bioterrorism-related cutaneous anthrax.
Am J Pathol. 163(5):1901-10, 2003
7. De BK et al: A two-component direct fluorescent-antibody
assay for rapid identification of Bacillus anthracis. Emerg
Infect Dis. 8(10):1060-5, 2002
8. Grinberg LM et al: Quantitative pathology of inhalational
anthrax I: quantitative microscopic findings. Mod Pathol.
14(5):482-95, 2001
9. Dixon TC et al: Anthrax. N Engl J Med. 341(11):815-26,
1999
10. Logan NA et al: Identification of Bacillus strains using the
API system. J Gen Microbiol. 130(7):1871-82, 1984
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Serologic Testing
Antibodies to anthrax toxin proteins, protective
antigen (PA) lethal factor (LF), and edema factor (EF),
are commercially available and have been used for
ELISA testing of patient serum
Microscopic Features
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Bacterial Infections: Bacterial Infections Requiring Culture/Ancillary Confirmation
BACILLUS SPECIES INFECTIONS
(Left) A large cerebral
abscess is present in
this brain tissue from a
atient with disseminated
Bacillus cereus infection.
Note the central necrosis
, rim of inflammation
, and scattered fibrin
, consistent with
hematogenous spread.
(Right) A small cerebral
hemorrhage is seen within
the brain of a patient with
disseminated Bacillus cereus
infection.
(Left) Meningeal vessels
from a case of disseminated
Bacillus cereus infection
show fibrin thrombi .
(Right) A brain abscess
from a patient with acute
myelogenous leukemia
and disseminated Bacillus
cereus infection is shown
with large rods seen on
Gram staining. Note that
the normally gram-positive
bacteria are only partially
icking up the tissue Gram
stain.
(Left) A brain abscess
from a patient with acute
myelogenous leukemia
and disseminated Bacillus
cereus infection is shown
with large rods , seen on
silver staining. (Right) A large
ulcer from a patient with
invasive candidiasis was
overlain by gram-positive
rods consistent with Bacillus
species and confirmed by
molecular testing.
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CLOSTRIDIOSIS AND OTHER ANAEROBIC INFECTIONS
This Gram stain from an autopsy of a patient who died of
myonecrosis shows dense growth of C. septicum grampositive rods.
TERMINOLOGY
Definitions
Greek: "Kloster" (spindle)
ETIOLOGY/PATHOGENESIS
Bacterial Infections: Bacterial Infections Requiring Culture/Ancillary Confirmation
Environmental Exposure
Clostridia are resilient sporulating organisms found in
a wide variety of natural habitats: Soil, sewage, water
Much of normal human intestinal, vaginal, and oral
microbiota is composed of anaerobes
Bacteroides species comprise 30% of total gut bacteria
(most of which are benign commensals)
Fusobacterium nucleatum is a major component of
dental plaque
Infectious Agents
Sporulating, gram-positive anaerobes
Clinically relevant species include: Clostridium
botulinum, Clostridium difficile, Clostridium
perfringens, Clostridium septicum, Clostridium sordellii,
Clostridium tetani
Nonsporulating gram-positive anaerobes
Clinically relevant species
Cocci: Finegoldia (Peptostreptococcus) magna,
Parvimonas (Micromonas, Peptostreptococcus) micros,
Peptoniphilus asaccharolyticus, Peptostreptococcus
anaerobius, etc.
Bacilli: Propionibacterium acnes, Lactobacillus spp.,
Bifidobacterium spp.
Gram-negative anaerobes
Clinically relevant species
Cocci: Veillonella spp.
Bacilli: Bacteroides spp., Fusobacterium spp.,
Prevotella spp., Porphyromonas spp.
II
Pathogenicity of Bacteroides is associated with a
distinctive capsular polysaccharide
2
Fusobacterium is a very long, thin filamentous bacterium
usually found vertically oriented in the amnion. It
is associated with severe chorioamnionitis. (From DP:
Cytopathology.)
Invasive Fusobacterium spp. have been shown to
be rich in adhesions and other surface-associated
proteins as compared to noninvasive strains
CLINICAL ISSUES
Epidemiology
Clostridial disease
C. botulinum
Infant botulism is associated with exposure to soil,
dust, and honey
Food-borne botulism is associated with ingestion
of preformed toxin in food
Wound botulism is associated with production of
toxin by C. botulinum organisms in wound
C. difficile
Part of intestinal flora of 3-5% of healthy adults
Disease is associated with age, hospital or long-
term care facility, bowel surgery, antibiotic use,
IBD, use of proton pump inhibitors
C. perfringens
Skin and soft tissue infections associated
with crush-type injury, artery laceration,
soil-contaminated open long bone fractures,
penetrating injuries involving bowel leakage into
abdominal cavity
Enteric infections associated with improperly
cooked meat or meat products (due to survival of
spores)
C. septicum
Associated with occult colon cancer, diverticulitis,
bowel surgery, hematological malignancy,
diabetes, AIDS, radiation and chemotherapy,
neutropenia
C. sordellii
Associated with induced or spontaneous abortion
as well as childbirth (both vaginal and cesarean
section)
C. tetani
6
CLOSTRIDIOSIS AND OTHER ANAEROBIC INFECTIONS
Clinical Issues
Clostridia can cause a wide array of infections
C. difficile: Antibiotic-associated
pseudomembranous colitis
C. perfringens and C. septicum: Soft tissue infections
(gas gangrene)
Bacteroides spp.
Major component of polymicrobial anaerobic
infections with a propensity for abscess formation
Fusobacterium spp.
F. nucleatum causes periodontal disease and
obstetric infections, as well as multiorgan
disseminated disease
F. necrophorum is causative agent of Lemierre
syndrome, as well as a frequent component of
anaerobic joint infections
Key Facts
Microscopic Pathology
C. difficile colitis
C. perfringens (type C)
Clostridial myonecrosis (C. perfringens, C. septicum, C.
histolyticum, C. novyi)
Bacteroides and Fusobacterium
Bacterial Infections: Bacterial Infections Requiring Culture/Ancillary Confirmation
Mild disease may only demonstrate a mildly
inflamed colonic mucosa with luminal mucus
Enteritis necroticans lesions being in proximal
jejunum and are characterized by mucosal
ulceration, submucosal edema, mixed
inflammatory infiltrate, and necrosis
Necrosis of skin, soft tissue, and muscle
Abscess (intraabdominal, brain, liver)
Often in mixed anaerobic infection
Associated with puncture wounds and injection
drugs (also Clostridium novyi)
Bacteroides and Fusobacterium spp.
Usually cause infection in immunocompromised
patients or those with a compromised
gastrointestinal epithelium
Poor dental hygiene may predispose patients to
invasive infection by Fusobacterium spp.
F. nucleatum has been associated with colorectal
cancer, through relationship remains undefined
Presentation
Clostridial disease
C. botulinum
Food-borne disease can be preceded by general
gastrointestinal upset
Hallmark is acute flaccid paralysis
C. difficile
Presents as diarrhea that can be mild or profuse
and contain blood and mucus
Severe disease can cause pseudomembranous
colitis
C. perfringens soft tissue infections (gas gangrene,
clostridial myonecrosis)
Extremely painful and rapidly progressive
May present as necrotizing fasciitis
C. perfringens enteric infections
Usually mild diarrhea unless in context of a
compromised immune system (usually CPE
producing type A)
Necrotizing enterocolitis (NEC) is also associated
with C. perfringens type A and predominately
affects low-birth-weight infants
Can also cause enteritis necroticans or or
necrotizing enteritis (usually alpha and beta toxinproducing type C)
C. septicum
Agent of "spontaneous gas gangrene"
Acute, extremely painful lesions that
characteristically contain gas
C. sordellii
Causes gas gangrene of uterus
Patients are classically afebrile and demonstrate
abdominal pain, hypotension, peripheral edema,
hemoconcentration, and leukocytosis
C. tetani
Tetanospasmin is transported to CNS where it
prevents inhibitory neurotransmission and results
in paralysis and muscle spasms that can last for
weeks
Bacteroides spp.
Major component of polymicrobial anaerobic
infections
Most common cause of anaerobic bacteremia
Frequently isolated from anaerobic joint infections
and intraabdominal abscess
Fusobacterium spp.
F. nucleatum
Periodontal disease
Obstetric and perinatal infections causing preterm
birth, term stillbirth, and fetal demise
Multiorgan disseminated disease
Fusobacterium necrophorum
Lemierre syndrome: Pharyngitis, high fever,
cervical lymphadenopathy, thrombophlebitis of
internal jugular vein, intensely painful metastatic
abscess (commonly lungs, joints, and long bones)
Anaerobic joint infections
Laboratory Tests
Direct examination (smear and Gram stain)
Gram stain of wound smear (showing gram-positive
rods, spores) is critical for diagnosis of clostridial
gas gangrene
Immunoassays
A variety of assays are available to diagnose C.
difficile by EIA
Targets include GDH (general target for all C.
difficile) along with TcdA and TcdB
Cell culture/animal cytotoxicity assay
Traditional gold standard for detection of toxogenic
C. difficile (sensitivity: 94-100%; specificity: 99%)
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CLOSTRIDIOSIS AND OTHER ANAEROBIC INFECTIONS
MICROBIOLOGY
Morphology
Clostridia are gram-positive (though may appear gramvariable or even gram-negative), rod-shaped organisms
with round or pointed ends
May be arranged in short chains or pairs
If endospores are present, they are often wider than
cell, conferring a swollen end or spindle-shaped
appearance
Bacteroides are gram-negative, non-spore-forming rods
(though can be pleomorphic)
When grown in liquid medium, cells develop
bipolar vacuoles and have been compared to safety
pins
Fusobacteium are gram-negative, non-spore-forming
rods
F. nucleatum are filamentous with slender, pointed
ends
F. necrophorum are coccoid
Culture and Identification
Most species are obligate anaerobes, though some
species can grow (though not sporulate) in low-oxygen
environments
CCFA (cycloserine, cefoxitin, fructose agar) is used to
selectively grow C. difficile
Chromogenic agar is available for selective and
differential culture of C. difficile
Bacterial Infections: Bacterial Infections Requiring Culture/Ancillary Confirmation
Bacteroides bile esculin agar can be used to selectively
grow Bacteroides
RapID ANA assay strips (Remel) are commonly used in
clinical labs to identify dozens of medically important
anaerobes
MICROSCOPIC PATHOLOGY
Histologic Features
Clostridium
No histopathological findings present in botulism or
tetanus
C. difficile colitis
Mild disease may only demonstrate a mildly
inflamed colonic mucosa with luminal mucus
With more advanced disease, there is
inflammatory erosion of lamina propria and
development of a fibrinopurulent cap, which
can extend to form a pseudomembrane in severe
disease
C. perfringens (type C)
Enteritis necroticans lesions occur in proximal
jejunum and are characterized by mucosal
ulceration, submucosal edema, mixed
inflammatory infiltrate, and necrosis
Involved vasculature may show congestion,
thrombi, fibrinoid necrosis, and arteritis
Pneumatosis intestinalis and pseudomembranes
II
may be observed
Tissue Gram stain may reveal clostridia (large,
club-shaped, gram-positive rods)
2
Clostridial myonecrosis (C. perfringens, C. septicum,
C. histolyticum, C. novyi)
Necrosis of skin, soft tissue and muscle
Tissue Gram stain may reveal clostridia
Characteristic pauci-inflammatory response
Bacteroides and Fusobacterium
Abscess (intraabdominal, brain, liver)
Septic arthritis
Osteomyelitis
Often in mixed anaerobic infection
In addition, Fusobacterium are associated with
Lemierre syndrome: Suppurative thrombophlebitis
of internal jugular vein, metastatic abscesses of
lungs, joints, and long bones (F. necrophorum)
Chorioamnionitis (F. nucleatum)
ANCILLARY TESTS
PCR
DNA-based assays are available for GDH, and TcdA and
TcdB of C. difficile
PCR assays are available for other clostridial toxins
(e.g., food-borne C. perfringens), though generally only
done in public health laboratories
Caution must be used with these assays, as they would
be expected to detect colonizing organisms that may
contain unexpressed genes for toxins
DIFFERENTIAL DIAGNOSIS
Colitis
Inflammatory bowel disease, diverticulitis, other
infectious colitis
Differentiated by positive stool toxin assay for C.
difficile
Necrotizing Enterocolitis
Bowel ischemia, Crohn disease
Differentiated by presence of bacteria
Necrotizing Fasciitis
Differentiated by lack of gas in tissue, gram-positive
cocci or other organisms present on tissue Gram stain
SELECTED REFERENCES
1. Kuppalli K et al: Lemierre’s syndrome due to Fusobacterium
necrophorum. Lancet Infect Dis. 12(10):808-15, 2012
2. Stevens DL et al: Clostridium. Manual of Clinical
Microbiology (10th Edition). Versalovic et al. ASM press.
834-857. 2011
3. Lauwers G et al: Infections of the gastrointestinal tract.
In Kradin RL: Diagnostic Pathology of Infectious Disease.
Philadelphia: Saunders Elsevier. 215, 2010
4. Huggan PJ et al: Fusobacterial infections: clinical spectrum
and incidence of invasive disease. J Infect. 57(4):283-9,
2008
5. Aldape MJ et al: Clostridium sordellii infection:
epidemiology, clinical findings, and current perspectives
on diagnosis and treatment. Clin Infect Dis.
43(11):1436-46, 2006
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CLOSTRIDIOSIS AND OTHER ANAEROBIC INFECTIONS
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Microscopic Features
Bacterial Infections: Bacterial Infections Requiring Culture/Ancillary Confirmation
(Left) This section
demonstrates colon with
necrosis of the epithelium
and pseudomembrane
formation in fulminant C.
difficile colitis. (Right) This
acute clostridial myonecrosis
is characterized by abundant
necrotic debris including
skeletal muscle fibers
with coagulative necrosis
and large spaces within
the tissue, the histologic
correlate of gas gangrene.
(Left) This Gram
stain shows dense
colonies of Parvimonas
(Peptostreptococcus) micros
in a patient who developed
anaerobic osteomyelitis.
(Right) Acute osteomyelitis
is a diagnosis that is strictly
defined by the presence
of neutrophils in close
association with pits in the
bone, often giving the bone
a "moth-eaten" appearance.
Cultures from this
specimen grew Parvimonas
(Peptostreptococcus)
micros and Fusobacterium
nucleatum.
(Left) Clostridial myonecrosis
is characterized by abundant
coagulative necrosis of
the soft tissues, often
tracking along fascial
lanes. Inflammation may
be sparse in neutropenia.
(Right) This section shows
monochorionic, diamniotic
dividing membranes with
Fusobacterium infection
in twin A , but not in
twin B . Because twin
is usually located closer
to the cervix, its amniotic
sac is more susceptible to
ascending infection than
that of twin B. (From DP:
Cytopathology.)
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