chapter28.pptx

CHAPTER 28 (A)
SKIN, SOFT TISSUE
AND
MUSCULOSKELETAL
INFECTIONS
Part III
Microbiology as Applied to Infectious
Diseases
Universities Press
3-6-747/1/A & 3-6-754/1, Himayatnagar
Hyderabad 500 029 (A.P.), India
Email: info@universitiespress.com
marketing@universitiespress.com
Phone: 040-2766 5446/5447

Dr Sonal Saxena, MD
Director Professor and Head of the Department of Microbiology
Maulana Azad Medical College,
New Delhi
and
Dr Amala A Andrews, MD
Maulana Azad Medical College,
New Delhi
UNIVERSITIES PRESS PVT LTD

INFECTIONS OF THE SKIN
AND SOFT TISSUES
Infection of intact skin: Certain pathogens and toxins cause severe
infections or reactions when they come in contact with skin (ecthyma
gangrenosum)
Through a breach in the continuity: Certain microorganisms breach
the skin’s natural defences through cuts, wounds, burns or bites
Disruption of normal microbial population of the skin: Infection
occurs by new organisms in the surrounding skin and tissue (e.g.,
staphylococcal and streptococcal infections)
Pathogens colonising the skin via different routes: Some
microorganisms cause reactions that manifest as skin rashes or lesions
(intracellular infection—herpes type I, dermal capillary plexus—
varicella, cutaneous nerve route—herpes-zoster)
This Photo by Unknown Author is licensed under CC BY

INFECTIONS OF THE SKIN AND SOFT TISSUES
Primary infections: Organisms invade the body from the external environment through breaks
in skin caused by burns, injury, bites or surgery
Secondary infections: Organisms reach the site through the blood as a part of a systemic
disease

INFECTIONS OF THE DERMIS AND EPIDERMIS
Cutaneous infections
Impetigo: Involve epidermis and occurs often on the face and most often in children
Erysipelas: Involves the dermis as an erythematous painful lesion
Cellulitis: Affects the deep dermis; diffuse erythematous lesion without a clear margin
Folliculitis: Involves hair follicle; it is a localised papule containing pus
Papular and nodular lesions: Dracunculiasis, creeping eruptions and larva migrans
Crusted lesions: Impetigo and ringworm
Abscess: Involves deep dermis; furuncle/carbuncle/boil. An inflamed nodule with a central region
that is purulent with a raised point skin infections can be:
Vesicles—viral infections, zoster, shingles and hand, foot and mouth disease
Bullae—necrotising fasciitis and gas gangrene

SUBCUTANEOUS
TISSUE
INFECTIONS
Necrotising fasciitis—soft tissue infections involving the
fascia and muscles overlying soft tissues; caused by group
A streptococci, S. aureus, Bacteroides and Clostridium
species
Progressive bacterial synergistic gangrene—usually a
post-operative complication following a thoracic or
abdominal surgery, caused by S. aureus, Proteus and
anaerobic streptococci
Myositis—may vary from necrosis of muscle to
necrotising cutaneous myositis or anaerobic myonecrosis

APPROACH TO
THE DIAGNOSIS
OF SKIN AND
SOFT TISSUE
INFECTIONS

BONE AND JOINT
INFECTIONS
 OSTEOMYELITIS
 INFECTIOUS ARTHRITIS (SEPTIC ARTHRITIS)
This Photo by Unknown Author is licensed under CC BY-ND

OSTEOMYELITIS
ACUTE OSTEOMYELITIS
Etiology: Bacterial (mostly Staphylococcus) ,
Common involves the ends of the long bones
in children
Clinical: Abrupt-onset bone pain and
localised tenderness at the site of infection
Route of entry: Hematogenous or following
trauma caused by a penetrating injury
CHRONIC OSTEOMYELITIS
Etiology: Fungal or tubercular (Pott’s disease)
Insidious onset—the bone is necrosed, and
sequestrum (avascular necrotic bone) is
formed
Prosthetic-associated osteomyelitis: S. epidermidis
Osteomyelitis in sickle cell anemia: Salmonella
species

SEPTIC
ARTHRITIS
Bacteria may invade the joint space and cause infectious
arthritis
Large, weight-bearing joints like the knee or hip are often
involved
The source of infection is often the skin, from where the
bacteria reach the bones through the bloodstream
Clinical: Acute onset with fever, joint pain, redness and
swelling are the cardinal features
Etiology: Staphylococcus aureus (most common), N.
gonorrhoeae in sexually active individuals (the knee, wrist,
ankle or elbow may be involved), S. epidermidis and other
coagulase-negative staphylococci in prosthetic joints

MANAGEMENT
Laboratory Diagnosis
Samples: Bone sequestrum (in osteomyelitis) and joint aspirates (in arthritis), blood for culture
Gram stain: Bacteria and polymorphs seen
Culture: On blood agar to yield the organism. Blood culture may yield the organism in around
30% of acute cases of osteomyelitis and septic arthritis
Treatment
Empiric treatment with vancomycin and cefazolin must be started early to prevent damage to
the bone
Intravenous antibiotic treatment may be necessary in acute osteomyelitis and septic arthritis
Removal of joint fluid by arthrocentesis may be required, in addition to antibiotic therapy

BURN WOUNDS
Etiology
Gram-positive bacteria: Staphylococcus aureus (including MRSA), Staphylococcus spp.,
Enterococcus spp. and the beta-hemolytic Streptococcus group
Gram-negative bacteria: Pseudomonas species, Acinetobacter baumanii, Stenotrophomonas,
Proteus species, Escherichia coli and Enterobacter species.
Fungi: Fusarium, Zygomycetes and Aspergillus

STREPTOCOCCI
Impetigo and pyoderma
Erysipelas: Rapidly progressing infection with brawny edema
and a rapidly advancing margin
Cellulitis: Acute, rapidly spreading infection of the skin and
subcutaneous tissue with pain, tenderness and edema and
diffuse margins
Necrotising fasciitis: Mixed aerobic and anaerobic bacterial
infection, S. pyogenes (particularly M types 1 and 3, which
form pyrogenic exotoxin A) cause extensive necrosis of the
subcutaneous and muscular tissues and adjacent fascia

STAPHYLOCOCCI
Corynebacterium minutissimum (erythrasma)
Common among dark-skinned individuals who sweat profusely, diabetes, obese and with poor hygiene
Most common: Glabrous areas of the body, skin folds, the groin, axilla, inner thighs and the skin between the
toes
Clinical: Red, scaly patch initially, with a well- defined margin—turns into a brown patch
Fig. 28.5
Erythematous
lesions with
superficial
ulceration due to
Staphylococcus
aureus (Source:
CDC, PHIL, Image
ID 7826)

BACILLUS ANTHRACIS
Aerobic, gram-positive, non-motile, sporulating bacillus 3–10 µm long in
chains (end to end) and has the appearance of a bamboo stick or boxcar
Capsule: Polysaccharide made up of polymer of d–glutamic acid. Loss of the
plasmid leads to the loss of virulence hence attenuation, used in the making of
the anthrax spore vaccine (Sterne vaccine)
Anthrax toxin:
Protective antigen factor (PA or factor II): binding fraction on the target cell
surface
Edema factor (EF or factor I): Activated only inside the target cells, leading
to intracellular accumulation of cyclic AMP; causes edema and the other
biological effects of the toxin
Lethal factor (LF or factor III): Causes cell death, but the mechanism of this
action is not known
This Photo by Unknown Author is licensed under CC BY-SA

CLINICAL FEATURES
Cutaneous anthrax
Lesion is malignant pustule seen on exposed parts of body (face, neck, hands, arms and
back)
Starts as a papule 1–3 days after infection and becomes vesicular, containing fluid,
which may be clear or bloodstained with several satellite lesions
The whole area is congested and edematous and covered with a black eschar
Hide porter’s disease in dock workers who would carry loads of hides and skins on their
bare backs
Cutaneous anthrax generally resolves spontaneously, but 10–20 per cent of untreated
patients develop fatal septicemia or meningitis
Pulmonary anthrax (wool-sorter’s disease)
Workers of wool factories
Spores inhalation from infected wool
Can progress to hemorrhagic pneumonia and dissemination into the meninges
Fig. 28.7 Cutaneous lesion (malignant pustule)
with black central eschar and edematous raised
margin; satellite lesions are seen (Source: CDC,
PHIL, Image ID 20334)

CLINICAL
FEATURES
Intestinal anthrax
Seen in communities consuming undercooked or uncooked
meat
Severe enteritis with bloody diarrhea occurs
Ending fatally if left untreated
Anthrax meningitis or meningoencephalitis
Infection disseminates to the CNS via the bloodstream
CSF: Hemorrhagic and the condition may be mistaken for
cerebrovascular accident, often fatal

LABORATORY DIAGNOSIS
Specimen
Pus from the cutaneous lesions
Blood and CSF
Sputum in cases of pulmonary anthrax
Feces in the case of gastroenteritis
Microscopy
Gram-positive bacilli with the morphology of anthrax bacilli with
spores.
Immunofluorescent microscopy: A specific immunoglobulin tagged
with a fluorescent stain
Fig. 28.8 Bacillus anthracis in blood: gram-
positive rods, showing bamboo stick
appearance in a smear from a automated
blood culture bottle (Source: CDC, PHIL,
Image ID 17099)

Spores stained by
M’Fadyean reaction with polychrome methylene blue: Blood
film stained with polychrome methylene blue for a few
seconds shows, an amorphous purplish material around the
bacilli (capsular material)
Sudan black B stain: Fat globules may be made out within the
bacilli

Culture
Temperature: 12–45°C (optimum 35–37°C)
Blood agar: Non-hemolytic, 2–3 mm in diameter, raised, dull, opaque and
greyish-white with a frosted glass appearance
Under low-power microscope: edge of the colony is seen to be composed
of long, interlacing chains of bacilli, resembling locks of matted hair
(Medusa head appearance)
Solid medium containing 0.05–0.50 units of penicillin/mL: Cells become
large and spherical within 3–6 hours and arrange themselves in chains on
the surface of the agar (string of pearls reaction); specific to B. anthracis
Gelatin stab culture
Inverted fir tree appearance
Selective medium
PLET medium (polymyxin, lysozyme, ethylene diamine tetraacetic acid
(EDTA) and thallous acetate) added to heart infusion agar
Fig. 28.9 Non-hemolytic, dry colonies
of B. anthracis bearing the
characteristic Medusa head
appearance on blood agar (Source:
CDC, PHIL, Image ID 17099)

Animal inoculation
◦ Guinea pigs, rabbits and mice
Serological demonstration
◦ Ascoli’s thermoprecipitin test for anthrax antigen in tissue extracts
◦ A direct fluorescent antibody test (DFA) for capsule- specific staining and polysaccharide cell
wall antigen detection
Serology for antibodies
◦ Acute and convalescent phase sera detected by gel diffusion, complement fixation, antigen-
coated tanned red cell agglutination and ELISA
Molecular typing
◦ MLVA (multiple-locus variable number tandem repeat analysis) or AFLP (amplified fragment
length polymorphism)

BIOSAFETY AND PREVENTION
General methods
◦ Improvement of factory hygiene
◦ Proper sterilisation of animal products like hides and wool.
◦ Carcasses buried deep in quicklime or cremated to prevent soil contamination.
Vaccine
oPre-exposure: Only high-risk individuals, five doses followed by booster
oPost-exposure: The vaccine is given after exposure to anthrax along with antibiotics
Types
◦ Pasteur’s anthrax vaccine
◦ Sterne vaccine: Spores of attenuated strains of a non-capsulated, avirulent, mutant bacillus, used for
animals
◦ Mazzucchi vaccine: Spores of a stable, attenuated Carbazoo strain in 2% saponin

TREATMENT
Uncomplicated cutaneous anthrax: Single oral agent (fluoroquinolone or doxycycline) for 7–14
days
Systemic anthrax: Antitoxin with antibiotic.
Antitoxin
Human anthrax immunoglobulin (anthrasil)
Monoclonal antibodies to the protective antigen (obiltoxaximab or roxibacumab)
Pre-exposure prophylaxis for inhalation anthrax in adults is with ciprofloxacin and doxycycline
for 60 days along with the vaccine (AVA BioThrax)


CHAPTER 28 (B)
SKIN, SOFT TISSUE
AND
MUSCULOSKELETAL
INFECTIONS
Part III
Diseases
Universities Press
3-6-747/1/A & 3-6-754/1, Himayatnagar
Phone: 040-2766 5446/5447

CLOSTRIDIA
Gram-positive anaerobic bacteria which form heat-resistant
spores
Commensal flora in gut of humans and animal
Cause gas gangrene, tetanus, botulism, food poisoning and
pseudomembranous colitis
Pathogenicity
Exotoxin: Pathogenic clostridia produce powerful exotoxins
which are responsible for the pathogenesis and disease, e.g.,
tetanus, botulism and gas gangrene
Invasive toxin: C. perfringens, besides being toxigenic, is also
invasive and can spread along the tissues and even cause
septicemia
This Photo by Unknown Author is licensed under CC BY-NC-ND

Gram-positive, rods, highly
pleomorphic, 3–8 micron,
spore-forming, shape and
position vary
Spherical or oval; terminal,
subterminal, central
Motile, stately motility
MORPHOLOGY

CULTURE
Anaerobic
Aerotolerant
Low redox potential by adding reducing
substances – unsaturated fatty acids, ascorbic
acid, glutathione, cysteine

GROWTH
REQUIREMENTS
pH 7–7.4
Temperature 37°C
Some are thermophillic, psychrophilic
BA hemolytic
Robertson’s cooked meat – turbidity, gas
Saccharolytic and proteolytic
Litmus milk medium, production of acid, gas, clot detected

SPORE
Central – spindle – C. bifermentans
Subterminal – club – C. perfringens
Oval terminal – tennis racquet – C. tertium
Spherical terminal – drumstick – C. tetani
Exhibit variable resistance to heat, drying and disinfectants

SPORE
ARRANGEMENTs

Clinical case 1
A 50-year-old man met with a road traffic accident in which he
sustained multiple fractures with open wounds and a crush injury
of the leg. He was taken to the nearest hospital two days later, at
which time, he was found to be in shock.
He was started on supportive therapy and antibiotics. There was
edema and pain at the site of injury with increased
discolouration and a serous discharge. The area around the
wound had crepitus on palpation.
Microscopic examination of the wound discharge showed the
presence of thick, brick-shaped, gram-positive bacilli along with
gram-positive cocci. Based on a provisional diagnosis of gas
gangrene, immediate surgical treatment with extensive excision
of the local area (to prevent further spread) and intravenous
penicillin with clindamycin were given.
The exudate was also inoculated into Robertson’s cooked meat
medium. Clostridium perfringens and peptostreptococci grew in
the culture.

CLOSTRIDIUM
PERFRINGENS
Large rectangular, stout, gram-positive,
capulated, non-motile bacillus, 4–6 x l µm.
Pleomorphic, single, chains
Spores: Subterminal, Not produced in artificial
media

CULTURE
Microphilic – aerophilic anaerobes
pH – 5–8, temperature 20–50°C (45°C)
RCM (pink) – 4–6 hrs
Media: NA, BA, thioglycolate broth, RCM
BA: Polymyxin, neomycin, iron, citrate (black colonies)
BA: Rabbit, sheep, human colonies show target hemolysis
Litmus milk – fermentation of lactose, change of litmus – blue to red
Acid coagulates casein – clotted milk disrupted – stormy fermentation

VIRULENCE
FACTORS
Strains – five types A–E
Toxins – most prolific of toxin producing bacteria
Four major toxins – alpha, beta, epsilon and iota
Alpha toxin – most important biologically, lethal,
dermonecrotic and hemolytic
Table 28.6 Toxins produced by C. perfringens types

CLOSTRIDIUM
PERFRINGENS
Enzymes
Neuraminidase destroys myxovirus
receptors
Hemagglutinin – active against RBCs
Fibrinolysin
Bursting factor – muscle lesions in
gas gangrene
Circulating factor – increase in
adrenal sensitivity

GAS GANGRENE
Type A
Commonly seen in association
with other clostridia
Wound contamination
Anaerobic cellulitis
Muscle tissues are invaded –
anaerobic myositis
Fig. 28.10 Gas gangrene of the lower limb showing
edema and discoloured skin

PATHOGENESIS OF GAS GANGRENE
Exogenous: Clostridia usually enter a wound along with implanted foreign particles such as
soil, road dust, bits of clothing or shrapnel. They may also be present on skin, especially that
of the perineum and thighs
Endogenous: Infection may also develop after surgical procedures (especially amputations
for vascular disease) and even injections (especially adrenaline)

CLOSTRIDIUM SEPTICUM
Pleomorphic bacillus
Oval, central/subterminal spores
Anaerobic. saccharolytic, abundant gas
Four distinct toxins
Alpha toxin is hemolytic, demonecrotic and lethal
Gas gangrene in humans

CLOSTRIDIUM
NOVYI
Large, pleomorphic bacillus
Oval, subterminal spores
Strict anaerobe
Type A – causes gas gangrene
Large amounts of edema fluid, little or no
observable gas, high mortality

CLOSTRIDIUM HISTOLYTICUM
Oval, subterminal, bulging spores
Proteolytic
Gas gangrene in humans
Infection – exogenous/endogenous
Exogenous – implanted foreign particles
Endogenous – clean surgical procedures

ANAEROBIC WOUND
INFECTIONS
Simple wound contamination – no invasion of
tissue
Anaerobic cellulitis – invasion of fascial planes,
minimal toxin production, no invasion of muscle
tissue
Anaerobic myositis – gas gangrene, invasion of
muscle tissue, abundant formation of exotoxins

CLINICAL PRESENTATION
Incubation period – 7 hours to 6 weeks
C. perfringens – 10–48 hours
C. septicum – 2–3 days
C. novyi – 5–6 days
Increasing pain, tenderness and edema over the affected part
Accumulation of gas – crepitus
Untreated – profound toxemia and prostration

Specimen
Films – edge of affected area, tissue from necrotic area, exudate from deeper part of
wound
Exudate collected from depth of wound – collected by capillary pipette or swab
Necrotic tissue/muscle fragments
Blood cultures in C. perfringens and C. septicum infections
However, C. perfringens bacteremia may occur without gas gangrene

MICROSCOPY
C. perfringens – Gram-positive bacilli without
spores
C. septicum – boat- or leaf-shaped
pleomorphic bacilli
C. novyi – large bacilli with oval or subterminal
spores
Fig. 28.13 Methylene blue-stained culture
specimen revealing the presence of numerous
Clostridium septicum bacteria (note the
absence of spores) (Source: CDC, PHIL, Image
ID 217)

CULTURE
Robertson’s cooked meat medium:
Fresh and heated blood agar
Target hemolysis resulting from a narrow zone of complete hemolysis due to theta toxin
and a much wider zone of incomplete hemolysis due to the alpha toxin
This double zone pattern of hemolysis may fade on longer incubation

NAEGLER’S REACTION
C. perfringens grown on media containing
Fildes peptic digest of sheep blood and human
serum with antitoxin on one half of the plate
Colonies on the half without antitoxin will be
surrounded by a zone of opacity
No opacity around the colonies on the half of
the plate with antitoxin
Fig. 28.14 Nagler’s reaction—on the right, the
presence of toxin produces opacity in the serum
due to the breakdown of lecithin

CULTURE
FIG. 28.15 REVERSE CAMP TEST

TREATMENT AND PROPHYLAXIS
Surgery: Most important therapeutic and prophylactic
Damaged tissue removed extensively and promptly
Hyperbaric oxygen
Antibiotics: Metronidazole I/V – before surgery and every 8 hours
Mixed aerobic and anaerobic infection: combination of metronidazole with
amoxicillin and gentamicin.
Passive prophylaxis – anti-gas gangrene serum given I/M
10,000 IU – C. perfringens
10,000 IU – C. novyi
5000 IU – C. septicum

Clinical Case 2
A 20-year-old woman presented to the surgery outpatient
department with a soft, painless swelling on her left jaw, which
was covered with exudate from a discharging sinus. She gave a
history of trauma to the jaw.
On macroscopic examination of the pus, a light-coloured granule
was found in the exudate. Gram stain of the granule showed the
presence of filamentous, branching, gram-positive bacilli.
The condition was diagnosed as cervicofacial actinomycosis and
the woman was treated with intravenous penicillin G (8 million
units per day) for two weeks followed by oral penicillin.

ACTINOMYCETES
Actinomycetes are bacteria that possess a cell wall containing muramic acid
They have prokaryotic nuclei and are susceptible to antibiotics
Superficially resemble fungi due to branching filaments
Gram-positive filaments may break into bacillary or coccoid elements, non-motile, non-
sporing, non-capsulated
Most are free-living in soil

ACTINOMYCES
Anaerobic actinomyces: Non-acid fast, anaerobic or
microaerophilic; Arachnia, Bifidobacterium and Rothia
Aerobic: Aerobic, may be acid fast; Nocardia, Actinomadura,
Dermatophilus and Streptomyces
Streptomyces may cause diseases but they are a major source
of antibiotics

ACTINOMYCES

ACTINOMYCOSIS
Actinomyces israelii is the most common causative agent of actinomycosis
Four main clinical types are seen
◦ Cervicofacial: Indurated lesion on the cheek and submaxillary region
◦ Thoracic: Lesions in the lung, may involve the pleura and pericardium, spreading
outwards through the chest wall
◦ Abdominal: Lesion is usually around the cecum, involving neighbouring tissues
and abdominal wall

ACTINOMYCOSIS
 Pelvic: Associated with the use of intrauterine device (IUD), abscess
in bone and soft tissues with chronic draining sinuses to the
exterior
 Causes disease of gums, gingivitis, periodontitis and sublingual
plaques leading to root surface caries
 May present as mycetoma, treated with penicillin for several weeks

LABORATORY
DIAGNOSIS OF
ACTINOMYCOSI
S
Specimens collected are pus or tissues; in pulmonary
disease, sputum
Sulphur granules are demonstrated in pus
Direct microscopy: Dense network of thin Gram-positive
filaments surrounded by peripheral zone of swollen,
radiating, club-shaped structures presenting a sun ray
appearance; the clubs are antigen–antibody complexes

LABORATORY
DIAGNOSIS OF
ACTINOMYCOSIS
Fig. 28.17 (a) Sulphur granules in
section with H and E stain and (b)
gram-positive filamentous bacilli in
pus

LABORATORY DIAGNOSIS OF
ACTINOMYCOSIS
Isolation in culture: Sulphur granules or pus inoculated into thioglycolate
liquid medium or streaked on brain–heart infusion agar incubated
anaerobically at 37°C
Liquid medium, A. israelii produces fluffy ball colonies at the bottom
Solid medium, Actinomyces israelii produces spidery colonies in 48–72
hours, becomes heaped up, white, irregular smooth large colonies in 10 days
Treatment: Penicillin, tetracycline for months supplemented with surgery

NOCARDIA
Resembles Actinomycetes morphologically but it is aerobic
Nocardia are Gram-positive and some species like N. asteroides and N.
brasiliensis are acid-fast
Found in soil and infection is exogenous
Causes cutaneous, subcutaneous and systemic lesions
Common species are N. asteroides, N. brasiliensis and N. caviae

NOCARDIA
Morphology
Filaments, rod-shaped bacteria that do not
produce spores, non-motile, catalase positive
and weakly acid fast by Kinyoun’s acid fast
staining method
N. asteroides is most commonly involved in
human disease
Transmission is through contaminated soil and
not from humans or animals

NOCARDIA
Clinical forms
Cutaneous: Local abscess, cellulitis or lymphocutaneous lesions, subcutaneous
actinomycotic mycetoma
Systemic: Manifests as pulmonary disease, pneumonia, lung abscess or resembles
tuberculosis
Metastatic manifestation: May involve the brain, kidneys and other organs
Systemic nocardiosis occurs more often in immunodeficient persons

LABORATORY DIAGNOSIS OF NOCARDIOSIS
Direct microscopy: Weakly acid fast; branching, beaded filaments in smears
from tissues
Isolation in culture: Grows on ordinary media forming dry, granular
wrinkled colonies, producing pigment ranging from yellow to red
Treatment: Resistant to penicillin; cotimoxazole and minocycline are used
Surgery is performed to remove mycetomas
In immunocompromised, amikacin and cefotaxime are used

MYCETOMA FROM BACTERIAL CAUSES
Usually caused by
Actinomyces israelii, A. bovis
N. asteroides, N. brasiliensis, N. caviae
Actinomadura madurae, A. pelletierii
Streptomyces somaliensis
Botryomycosis: Mycetoma-like lesion produced by Staphylococcus aureus
and other pyogenic bacteria

ACTINOMYCOTIC MYCETOMA
Mycetoma is a localised chronic granulomatous involvement of
subcutaneous and deeper tissues affecting the foot and hand and
presenting as swelling with multiple discharging sinuses
First described by Gill 1842—maduramycosis
Actinomycotic—granules are yellow or white, filaments are thin (1 µm)
May be due to fungus, filaments are thicker (4–5 µm), granules are black

CHAPTER 28 (C)
SKIN, SOFT TISSUE
AND
MUSCULOSKELETAL
INFECTIONS
Part III
Diseases
Universities Press
3-6-747/1/A & 3-6-754/1, Himayatnagar
Phone: 040-2766 5446/5447

BURKHOLDERIA
PSEUDOMALLEI
Melioidosis
Glanders-like disease, epizootic in rodents in Southeast
Asia, India and North Australia
Also called the Vietnam time-bomb disease
In India, western and southern belts, spike following the
rainy season
Treatment: Carbapenems, imipenem, meropenem and
ceftazidime

Microscopy: Small, irregularly staining, gram-negative bacilli, bipolar ‘safety- pin appearance’
with methylene blue stain
Culture
Dry, wrinkled colonies on blood and MacConkey agars.
Selective medium: Ashdown’s selective agar (ASA) medium (gentamicin and crystal) violet
Biochemical tests: Non-fermentative, oxidase positivity, esculin hydrolysis and reduction of
nitrate, intrinsic resistance to polymixin B
PCR test or an automated VITEK system
Serology: Not much useful

BURKHOLDERIA MALLEI
Glanders: Primarily of equine animals (horses, mules and asses
Slender, non-motile, gram- negative bacillus, 2–5 × 0.5 mm stains irregularly with beaded
appearance
Aerobe and facultative anaerobe, growing on ordinary media under a wide temperature range
Colonies, which are small and translucent initially, become yellowish and opaque
Biochemically inert
Human infection: Occupational, acute or chronic and is protean in character
Respiratory tract, skin or subcutaneous tissues involved
In acute glanders: Fever, mucopurulent nasal discharge and severe prostration, high fatality
B. mallei is one of the most dangerous bacteria to work with

PATHOGENESIS
Two thermolabile exotoxins, one lethal and the other
necrotising,
Human infection is usually acquired by the contamination
of wounds, skin abrasions or by inhalation
Acute: Generalised infection as acute septicemia, or
subacute typhoid-like disease or pneumonia with hemoptysis
resembling tuberculosis. High case fatality rate
Chronic: Multiple caseous or suppurative foci, with abscess
formation in the skin and subcutaneous tissues, bones and
internal organs
Long latency and reactivation may occur as the bacillus can
survive intracellularly in the reticuloendothelial system

NON-TUBERCULOUS MYCOBACTERIA
Mycobacteria other than mammalian tubercle bacilli – human disease resembling tuberculosis
Non-tuberculous Mycobacterium – NTM
Earlier called ‘atypical’, MOTT (Mycobacterium other than tubercule bacilli)
Opportunistic infections in human beings

RUNYOUN
CLASSIFICATION
Four groups
Group I – photochromogens
Group II – scotochromogens
Group III – non-photochromogens
Group IV – rapid growers

RUNYOUN
CLASSIFICATION

GROUP I – PHOTOCHROMOGENS
Important species
◦ M. kansasii
◦ M. marinum
◦ M. simiae
No pigment in dark – exposed to light one hour – reincubated – yellow orange
pigment

M. KANSASII Chronic pulmonary disease – resembling
tuberculosis
Affects upper lobes with cavity formation
Isolated from tap water samples around the
world
Second most common NTM – lung disease after
M. avium complex

M. MARINUM
Warty skin lesion
Swimming pool/fish tank granuloma
Poor growth at 37°C
Negative nitrate test

GROUP II – SCOTOCHROMOGENS
Form pigmented colonies even in the dark
M. scrofulaceum – cervical adenitis
M. gordonae – rare cause of pulmonary disease
M. szulgai – scotochromogen at 37°C and photochromogen at 25°C

GROUP III – NON-PHOTOCHROMOGENS
Do not form pigment even when exposed to light.
Important pathogens
M. avium
M. intracellulare
M. xenopi

M. INTRACELLULARE
Battey bacillus
Lymphadenopathy, pulmonary lesions or disseminated disease – AIDS

GROUP IV –
RAPID
GROWERS
Colonies appear within seven days of
incubation
Medically important
M. fortuitum
M. chelonei
Chronic abscess following injection of vacine.

SKIN PATHOGENS
M. ulcerans – Buruli ulcer
Ulcers on legs or arms – minor injuries
Indurated nodules – indolent ulcers
Smears – large clumps of bacilli

SKIN PATHOGENS
Tests used for identification

TREATMENT
Resistant to the usual anti-tuberculous drugs
M. avium, M. kansasii – respond to prolonged treatment with – rifampicin,
isoniazid and ethambutol
Other combinations – clofazimine, quinolones, newer macrolides

MYCOBACTERIUM
LEPRAE
Disease of antiquity
India – since Vedic times
Biblical times – Middle East
Hansen – 1868 – lepra
bacillus
Not possible to grow – in
culture media

MYCOBACTERIUM LEPRAE
Morphology
Straight or slightly curved rod – 1.8 × 0.2–0.5 µm
Acid fast – 5% H2SO4
Morphological index – uniformly stained bacilli
Bacilli – singly and groups
‘Globi’, ‘cigar bundles’

M. LEPRAE

CULTIVATION
Not possible to cultivate – media, tissue culture
Generation time – 12–13 days
Cultivation
Foot pad of mice
Nine-banded armadillo (Dasypus novemcinctus)
Adaptation in artificial media – ICRC bacillus

LEPROSY
Chronic granulomatous disease
Four types
Lepromatous
Tuberculoid
Dimorphus
Indeterminate

LEPROMATOUS LEPROSY
In large numbers, resistance – low
Bacilli are seen in large numbers
Multibacillary
Bacilli invade mucosa of nose, mouth and upper respiratory tract
Shed in large numbers in nasal and respiratory secretions
Cell-mediated immunity is deficient
Lepromin test – negative

LEPROMATOUS
LEPROSY

TUBERCULOID LEPROSY
High degree of resistance
Skin lesions few
Neural involvement early
Bacilli scanty
Paucibacillary
Cell-mediated immunity adequate
Lepromin test positive

TUBERCULOID
LEPROSY

BORDERLINE LEPROSY
Dimorphous
Characteristics of both lepromatous and tuberculoid

INDETERMINATE
LEPROSY
Not characteristic of either tuberculoid or
lepromatous
In many persons – spontaneous healing

IMMUNOLOGY
Exclusive human disease
Bacilli shed in nasal secretions
Mode of entry – respiratory tract – skin
Highly communicable
Incubation period 2–5 years

CLASSIFICATION
Ridley and Jopling – 1966
Five groups
Tuberculoid (TT)
Borderline tuberculoid (BT)
Borderline (BB)
Borderline lepromatous (BL)
Lepromatous (LL)

IMMUNITY
•Cell-mediated immunity
•Lepra reaction
•Type I – ‘reversal reaction’ – lepra reaction
•Type II – ‘erythema nodosum leprosum’
•Lepromin test
•Early reaction – Fernandez
•Late reaction – Mitsuda

•Specimen
◦ nasal smear
◦ skin smear – slit skin smear
◦ nerve biopsy

MICROSCOPY
Ziehl–Neelsen – 5% sulphuric acid
Grading of smears
1–10 bacilli in 100 fields: 1+
1–10 bacilli in 10 fields: 2+
1–10 bacilli per field: 3+
More than 1000 bacilli, clumps: 6+

MICROSCOPY
Bacteriological index (BI) – totalling the number
of pluses scored and divided by the number of
smears
Morphological index (MI) – expressed as
percentage of solid fragmented granular
bacilli/uniformly stained bacilli out of the total
number counted

TREATMENT
Dapsone – first effective agent
Drug resistance
• Paucibacillary – rifampicin 600 mg once a month and dapsone 100 mg daily for 6
months
• Multibacillary – rifampicin 600 mg once a month, dapsone 100 mg daily and
clofazimine 50 mg daily for 2 years
Multi drug therapy

PROPHYLAXIS
Long-term chemoprophylaxis
BCG vaccine

CHAPTER 28 (D)
SKIN, SOFT TISSUE
AND
MUSCULOSKELETAL
INFECTIONS
Part III
Diseases
Universities Press
3-6-747/1/A & 3-6-754/1, Himayatnagar
Phone: 040-2766 5446/5447

VIRAL INFECTIONS OF
THE SKIN

Lesions in the skin are manifestations of viral
pathogenesis affecting other systems
Etiology
The virus remains restricted to the skin at the
site of infection, e.g., molluscum contagiosum
Intracellular infections of the squamous
epithelium (HSV1), dermal capillary plexus
(varicella), cutaneous nerve roots (hepres-
zoster) or viruses associated with viremia
Most cutaneous manifestations of systemic
viral infections are in the form of vesicles or
rashes due to microhemorrhages

Table 28.9
Mucocutaneous lesions
caused by viruses

VARICELLA-
ZOSTER VIRUS
(VZV)
 Morphology is similar to that of herpes simplex virus
 Causative agent of varicella & herpes zoster
 During primary infection: Varicella
 Reactivation: Herpes zoster
 Only one antigenic type is known

VARICELLA (CHICKEN POX)
 Common in childhood but may occur at any age
 Route of entry: Respiratory tract or conjunctiva
 Incubation period: 2 weeks
 Source of infection: Varicella/herpes zoster cases
 No animal reservoir

VARICELLA IN
CHILDREN
 Presence of skin & mucosal lesions
 Centripetal in distribution (appears
first on trunk)
 The stages of rash: Macule, papule,
vesicle, pustule and scab
 Rapid evolution of lesions

VARICELLA IN ADULTS
 Severe form
Complications
• Pneumonia (more common)
• Myocarditis
• Nephritis
• Acute cerebellar ataxia
• Meningitis & encephalitis
• Secondary bacterial infections
• Reye’s syndrome (h/o intake of salicylates)
 Postherpetic neuritis may occur
Fig 43.5: Generalised herpes zoster
outbreak due to the varicella-zoster virus
(VZV)

CHICKENPOX IN PREGNANCY &
NEONATAL VARICELLA
 More severe in pregnant women
 First half of pregnancy
• Asymptomatic
• Fetal varicella syndrome: Cicatrising skin lesions, hypoplasia of the limbs, chorioretinitis &
CNS defects
 Near delivery
• Neonatal varicella

 Microscopy
• Tzanck smears
 Multinucleated giant cells
 Type A intranuclear inclusion bodies
• Electron microscopy
 Virus isolation
• Human amnion, human fibroblast, HeLa
or Vero cells
 Viral antigen detection:
• Immunofluorescence
• ELISA
 PCR

PROPHYLAXIS AND TREATMENT
 Live-attenuated vaccine: Oka strain of VZV
 Varicella-zoster immunoglobulin (VZIG)
 Infection control measures
 Acyclovir and famciclovir: Indicated in immunodeficient, elderly

Universities Press
© Universities Press (India) Private Limited
Clinical Case 1
A 50-year-old, HIV-positive man developed painful vesicular
eruptions on the right side of his spine in the lumbar region.
Scrapings from the base of the lesions were positive for the
VZV antigen by the direct fluorescent antibody test.
A culture from the fluid was inoculated on cell lines and the
PCR test was positive for varicella-zoster virus. The patient
was treated with acyclovir. On further enquiry, the patient
revealed to the doctor that he had had chickenpox in
childhood.

HERPES ZOSTER
(SHINGLES,
ZONA)
 Reactivation after primary varicella
infection
 Unilateral rash
 Limited to area supplied by a single
sensory ganglion
 Lesions similar to varicella lesions
 Pain at the affected area
Other complications
• Herpes zoster ophthalmicus
• The Ramsay Hunt syndrome

HERPES ZOSTER (SHINGLES, ZONA)
Herpes-zoster represents a mode of evolutionary adaptation by the VZ virus which is an
obligate human parasite
The ability of the virus to remain latent and reappear as zoster years later confers on it a great
survival advantage
HHV-7: Exanthema subitum
HHV-8/Kaposi’s sarcoma-associated herpes virus (KSHV)
Herpes virus simiae: B virus
Molluscum contagiosum virus
Papilloma virus

CYTOMEGALOVIRUSES
 Largest viruses in the herpesvirus family
 Size ranges from 150 to 200 nm
 Infect humans & animals
 Infected cells are enlarged
 Presence of intranuclear inclusions in infected cells

MODE OF
TRANSMISSION
Salivary or other secretions
Sexual contact
Blood transfusion
Organ transplants

CLINICAL FEATURES
Congenital infections
 Fetal death
 The cytomegalic inclusion disease: Microcephaly, chorioretinitis, cerebral calcification &
mental retardation
Infection in infants
Primary CMV infection in mother during pregnancy:
 Cytomegalic inclusion disease in infants
Reactivation in mother during pregnancy:
 Chronic subclinical infection in infants

CLINICAL FEATURES
Infection in children
 Asymptomatic primary infection
 Heterophile, antibody-negative, infectious
mononucleosis
Immunocompromised host
 Severe & fatal infections

PREVENTION AND TREATMENT
 Screening of blood and organ donors
 Acyclovir is useful in prophylaxis
 Ganciclovir and foscarnet are effective for treatment
 No vaccine is available

LABORATORY
DIAGNOSIS
Specimens
 Urine, saliva, semen and cervical
secretions
 Demonstration of cytomegalic
cells (owl’s eye): Less reliable
Isolation
 Human fibroblast cultures & shell
vial cultures
Serology
 Demonstration of IgM antibody
for primary infection
 IgG avidity test
Fig 43.7: H and E stained lung tissue showing ‘owl’s eye’-like inclusion
bodies of cytomegalovirus × 1,000

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