Transcript infectivity

Group B strep. Listeria and
Mycobacterium leprae. Clostridium
tetani and botulism
Dr.Mohammad Shakeeb, MD
Specialist in clinical
pathology/Microbiology and
immunology
Streptococcus agalactiae
• Str. agalactiae is equivalent to Lancefield group B streptococci.
• Its primary human habitat is the colon.
• 10–40% of women intermittently carry Str. agalactiae in the
vagina.
• Since 1960 it has become the leading cause of neonatal
infections in industrialized countries.
• Important cause of morbidity among peri-partum women and
non-pregnant adults with chronic medical conditions.
• Among β-hemolytic streptococci, Str. agalactiae is the most
frequent isolate from blood cultures.
Pathogenesis
•





Str. agalactiae produces several virulence factors, including:
Hemolysins.
Capsule polysaccharide.
C5a peptidase.
Hyaluronidase (not all strains).
Various surface proteins that bind human IgA and serve as
adhesins.
• Among the hemolysins produced by Str. agalactiae, one,
known as the CAMP factor.
• so-called because it was originally described by Christie,
Atkins and Munch-Petersen.
• plays an important role in the recognition of this species in
the laboratory.
• The CAMP factor lyses sheep or bovine red blood cells
pretreated with the β-toxin of Staph. aureus.
CAMP (Christie Atkins MunchPetersen) Test
• Results:
1- Positive : arrowhead
(wedge)-shaped
zone
of
enhanced
hemolysis
at
junction of 2 organisms (Strep
agalactiae & Listeria).
2- Negative : NO enhancement
of hemolysis (Strep pyogenes).
Clinical features
 Infection in the neonate
• Two different entities are recognized:
1. Early-onset disease, most cases of which present at or within
12 h of birth.
2. Late-onset disease, presenting more than 7 days and up to 3
months after birth.
• Early-onset disease
• This results from ascending spread of Str. agalactiae from the
vagina into the amniotic fluid.
• Then aspirated by the infant and results in septicemia in the
infant or the mother, or both.
• Infants borne by mothers carrying Str. agalactiae may also
become colonized during passage through the vagina.
• Depending on the site of initial contamination, neonates may
be ill at birth or develop acute and fulminating illness a few
hours, or a day or two, later.
•






•
clinical symptoms include :
lethargy
cyanosis and apnea
shock
Meningitis
pulmonary infection
death will occur if treatment is not instituted quickly.
As a result of improved recognition and prompt treatment of
babies with symptoms, the fatality rate has been reduced to
less than 10%.
• Considerable morbidity persists among some survivors,
especially those with meningitis.
• Risk factors for neonatal colonization and infection are:
 premature rupture of membranes.
 prolonged labor.
 premature delivery.
 low birth-weight.
 intrapartum fever.
• Late-onset disease
• Purulent meningitis is the most common manifestation.
• septic arthritis, osteomyelitis, conjunctivitis, sinusitis, otitis media,
endocarditis and peritonitis also occur.
• The incidence of invasive infection is higher among pre-term infants
than among those born at term.
• Many cases are acquired in hospital.
• Ward staff can be carriers of Str. agalactiae.
• contamination of the baby may occur during nursing procedures,
with subsequent baby-to-baby spread.
• Mastitis in the mother has also been described as a source of
infection.
 Infections in the adult
• Ascending spread of Str. agalactiae leading to amniotic
infection may result in :
 Abortion.
 Chorioamnionitis.
 Post-partum sepsis (endometritis) and other infections (e.g.
pneumonia) in the postpartum period.
• Str. agalactiae is also a frequent cause of infection in certain
risk groups of non-pregnant adults.
• Disease may manifest as sepsis, pneumonia, soft tissue
infections such as cellulitis and arthritis, and urinary tract
infections complicated by bacteremia.
• The risk factors in these patients are diabetes mellitus, liver
cirrhosis, renal failure, stroke and cancer
• Older age, independent of underlying medical conditions,
increases the risk of invasive Str. agalactiae infection.
Laboratory diagnosis
• Streptococci grow well on blood or chocolate agar.
• Blood agar is preferred because the hemolytic properties of
the organism can be assessed.
• When culturing vaginal/rectal swabs from pregnant women
specifically for group B streptococci, specimens should first be
inoculated to a selective broth, such as Lim or carrot broth.
• Treatment
• Most strains of Str. agalactiae are susceptible to penicillin,
macrolides and glycopeptides.
• A screening-based approach in which all pregnant women at
35–37 weeks’ gestation are screened for Str. agalactiae
colonization in vaginal and rectal specimens.
• All
identified
carriers
are
offered
intrapartum
chemoprophylaxis.
Listeria
• Organisms of the genus Listeria are non-sporing, Grampositive bacilli.
• Almost all cases of human listeriosis are caused by L.
monocytogenes.
• The disease chiefly affects:
 The immunosuppressed and elderly.
 Pregnant women.
 Unborn or newly delivered infants.
• Listeriosis is transmitted predominantly by the consumption
of contaminated food.
Listeria monocytogenes
Description
• Most cases of human listeriosis are caused by serovars 4b,
1/2a and 1/2b.
• Large food-borne outbreaks have been caused predominantly
by serovar 4b strains.
• The properties of the organism favour food as an agent in
transmission of listeriosis.
• Growth at refrigeration temperatures is relatively slow, with a
maximum doubling time of about 1–2 days at 4°C.
Pathogenesis
• Intracellular bacteria.
• The organism attaches to and enters a variety of mammalian
cells, apparently by normal phagocytosis.
• Once internalized, it escapes from the phagocytic vacuole by
elaborating a membrane-damaging toxin called listeriolysin O.
• L. monocytogenes grows in the cytosol and stimulates
changes in cell function that facilitate its direct passage from
cell to cell.
• The organisms induce a reorganization of cellular actin such
that short filaments and actin-binding proteins adhere to the
bacteria.
• This complex appears to propel the organisms through the cell
to pseudopods in contact with adjacent cells.
• Bacterium-produced membrane-degrading phospholipases
then mediate the passage of the organism directly to a
neighboring cell.
• This allowing avoidance of the extracellular milieu, including
cells of the immune system.
Clinical aspects of infection
• L. monocytogenes principally causes intra-uterine infection,
meningitis and septicemia.
• The incubation period varies widely between individuals from
1 to 90 days.
• with an average for intra-uterine infection of around 30 days.
 Infection in pregnancy and the neonate.
• Maternal listeriosis occurs throughout gestation, but is rare
before 20 weeks of pregnancy.
• Pregnant women often have very mild symptoms.
• Chills, fever, back pain, sore throat and headache, sometimes
with conjunctivitis, diarrhea or drowsiness.
• May be asymptomatic until the delivery of an infected infant.
• Symptomatic women may have positive blood cultures.
• With the onset of fever, fetal movements are reduced, and
premature labor occurs within about 1 week.
• Outcome for the infant is more variable.
• Abortion, stillbirth and early-onset neonatal disease are
common, depending on the gestation at infection.
• Neonatal infection is divided into disease of early (<2 days
old), intermediate (3–5 days old) and late (>5 days old) onset.
 Adult and juvenile infection
• In adults and juveniles the main syndromes are septicaemia
and central nervous system infection.
• Most cases occur in immunosuppressed patients receiving
steroid or cytotoxic therapy or with malignant neoplasms.
 Gastroenteritis
 Rarer manifestations of listeriosis include arthritis, hepatitis,
endophthalmitis, pneumonia, endocarditis.
Transmission
• Microbiological and epidemiological evidence supports an
association with many food types (dairy, meat, vegetable, fish
and shellfish) in both sporadic and epidemic listeriosis.
• Hospital cross-infection between newborn infants occurs.
Diagnosis and treatment
• Conventional culture of blood and or CSF remain the
mainstays of treatment .
• PCR based procedures for amplification of L. monocytogenesspecific DNA sequences from serum and CSF have been
reported.
• Many patients have been treated successfully with ampicillin
or penicillin with or without an aminoglycoside.
• The mortality rate in late neonatal disease is about 10%.
• the mortality rate in early disease is 30–60%, and about 20–
40% of survivors develop sequelae such as lung disease,
hydrocephalus or other neurological defects.
• Early use of appropriate antibiotics during pregnancy may
improve neonatal survival.
• The mortality rate in both adult meningitis and bacteremia is
about 20–50%.
Mycobacterium leprae
• M. leprae has never been cultivated in vitro.
• Leprosy bacilli resemble tubercle bacilli in their general
morphology.
• But they are not so strongly acid-fast.
• The bacilli are typically found within macrophages in dense
clumps.
• A characteristic surface lipid, peptidoglycolipid-1 (PGL-1), has
been extracted from M. leprae.
Pathogenesis
• Mycobacterium leprae is transmitted from human to human
through prolonged contact.
• between exudates of a leprosy patient’s skin lesions and the
abraded skin of another individual.
• The infectivity of M. leprae is low, and the incubation period
protracted.
• clinical disease may develop years or even decades after initial
contact with the organism.
Clinical significance
• Leprosy is a chronic granulomatous condition of peripheral
nerves and mucocutaneous tissues, particularly the nasal
mucosa.
• It occurs as a continuum between two clinical extremes:
 Tuberculoid leprosy.
 Lepromatous leprosy .
• In tuberculoid leprosy, the lesions occur as large maculae
(spots) in cooler body tissues, such as skin (especially the
nose, outer ears, and testicles), and in superficial nerve
endings.
• Neuritis leads to patches of anesthesia in the skin.
• The lesions are heavily infiltrated by lymphocytes and giant
and epithelioid cells, but caseation does not occur.
• The patient mounts a strong cell-mediated immune response
and develops delayed hypersensitivity.
• There are few bacteria in the lesions (paucibacillary).
• The course of lepromatous leprosy is slow but progressive.
• Large numbers of organisms are present in the lesions and
reticuloendothelial system (multi-bacillary).
• The results of a severely depressed immune system.
• No well-formed granulomas emerge.
Laboratory identification
• M. leprae is an acid-fast bacillus.
• It has not been successfully maintained in artificial culture .
• Laboratory diagnosis of lepromatous leprosy, in which
organisms are numerous, involves acid-fast stains of
specimens from nasal mucosa or other infected areas.
• In tuberculoid leprosy, organisms are extremely rare, and
diagnosis depends on clinical findings and the histology of
biopsy material.
Treatment and prevention:
• Several drugs are effective in the treatment of leprosy,
including sulfones such as dapsone, rifampin, and
clofazamine.
• Treatment is prolonged, and combined therapy is necessary to
ensure the suppression of resistant mutants.
Clostridium botulinum
• It is a strictly anaerobic Gram-positive bacillus.
• It is motile and has spores that are oval and sub-terminal.
• It is a widely distributed saprophyte found in soil, vegetables,
fruits, leaves, manure, the mud of lakes and sea mud.
• Its optimal growth temperature is about 35°C, but some
strains can grow and produce toxin at temperatures as low as
1–5°C.
• Spores of some strains withstand boiling in water (100°C) for
several hours.
• They are usually destroyed by moist heat at 120°C within 5
min.
• Insufficient heating in the process of preserving foods is an
important factor in the causation of botulism.
• Carefully controlled injections of toxin are used to treat
involuntary muscle disorders, and as an ‘anti-aging’ remedy.
Pathogenesis
• There are several types of botulinum toxin, designated A
through G.
• human disease is almost always caused by types A, B, or E.
• botulinum toxins affect peripheral cholinergic synapses by
blocking the neuromuscular junction and inhibiting release of
the neuro-transmitter acetylcholine, preventing contraction
and causing flaccid paralysis .
• Both botulinum and tetanus toxins are AB-type toxins
comprised of an activity domain (A) and a binding domain (B).
• The disease has been linked to a wide range of foods, including
preserved hams)‫(الخنزير‬, large sausages of the salami type, homepreserved meats and vegetables, canned products such as fish, and
even hazelnut purée )‫(هريس البندق‬and honey.
• Foods responsible for botulism may not exhibit signs of spoilage.
• The pre-formed toxin in the food is absorbed from the intestinal
tract.
• Intestinal proteolytic enzymes do not inactivate it.
• After absorption, botulinum toxin binds irreversibly to the
presynaptic nerve endings of the peripheral nervous system and
cranial nerves.
• Inhibits acetylcholine release.
Clinical features
• The period between ingestion of the toxin and the
appearance of signs and symptoms is usually 1–2 days.
• The oculomotor muscles are affected, and the patient may
have diplopia and drooping eyelids with a squint.
• There may be vertigo and blurred vision.
• There is progressive descending motor loss with flaccid
paralysis.
• No loss of consciousness or sensation.
• There are difficulties in speech and swallowing.
• Death is due to respiratory or cardiac failure.
• Rare cases of wound infection with C. botulinum resulting in
the characteristic signs and symptoms of botulism have been
recorded.
• Infant botulism
• The ‘floppy child syndrome’ describes a young child, usually
less than 6 months old.
• Flaccid paralysis that is ascribed to the growth of C. botulinum
in the intestine.
• At a stage in development when the colonization resistance of
the gut is poor.
• Some cases have been attributed to the presence of C.
botulinum spores in honey.
• When the honey was given as an encouragement to feed, the
ingested spores were able to germinate and produce toxin in
the infant gut.
Laboratory diagnosis
• The organism or its toxin may be detected in the suspected
food.
• Samples of feces or vomit may also yield such evidence.
Treatment
• The priorities are:
 To remove unabsorbed toxin from the stomach and intestinal
tract
 To neutralize unfixed toxin by giving polyvalent antitoxin .
 To give relevant intensive care and support.
Control
 Great care must be taken in canning factories to ensure that
adequate heating is achieved in all parts of the can contents.
 Home canning of foodstuffs should be avoided.
 A prophylactic dose of polyvalent antitoxin should be given
intramuscularly to all persons who have eaten food
suspected of causing botulism.
Clostridium tetani
• The tetanus bacillus is a motile, straight, slender, Grampositive rod.
• A fully developed terminal spore gives the organism the
appearance of a drumstick with a large round end.
• It is an obligate anaerobe.
• Spores of some strains resist boiling in water for up to 3 h.
• They may resist dry heat at 160°C for 1 h, and 5% phenol for 2
weeks or more.
• Glutaraldehyde is one of the few chemical disinfectants that is
assuredly sporicidal.
Pathogenesis
• Germination of spores and their outgrowth depend upon
reduced oxygen tension in devitalized tissue and non-viable
material in a wound.
• Tetanus bacillus remains strictly localized.
• But tetanus toxin is elaborated and diffuses.
• organism’s neurotoxin (tetanospasmin) is the essential
pathogenic product.
• Toxin diffuses to affect the relevant level of the spinal cord
(local tetanus) and then to affect the entire system
(generalized tetanus).
• It is transported from an infected locus by retrograde
neuronal flow or blood.
• Once the entire toxin molecule has been internalized into
presynaptic cells, the light chain is released and affects the
membrane of synaptic vesicles.
• This prevents the release of the neurotransmitter γaminobutyric acid.
• Motor neurons are left under no inhibitory control and
undergo sustained excitatory discharge.
• motor spasms of tetanus.
• The toxin exerts its effects on the spinal cord, brainstem,
peripheral nerves, at neuromuscular junctions and directly on
muscles.
Clinical features of tetanus
• The onset of signs and symptoms is gradual.
• starting with some stiffness and perhaps pain in or near a
recent wound.
• In some cases the initial complaint may be of stiffness of the
jaw (lockjaw).
• Pain and stiffness in the neck and back may follow.
• The stiffness spreads to involve all muscle groups.
• ‘sardonic grin’: facial spasms
• (opisthotonos):spasm of the back muscles produces extreme
arching of the back.
• The period between injury and the first signs is usually about
10–14 days.
• A severe case with a relatively poor prognosis shows rapid
progression from the first signs to the development of
generalized spasms.
• Sweating, tachycardia and arrhythmia, and swings in blood
pressure, reflect sympathetic stimulation.
Treatment
• The patient is given 10 000 units of human tetanus
immunoglobulin (HTIG) in saline by slow intravenous infusion.
• Full wound exploration and debridement is arranged, and the
wound is cleansed and left open with a loose pack.
• Penicillin or metronidazole is given for as long as considered
necessary to ensure that bacterial growth and toxin
production are stopped.
Laboratory diagnosis
• Gram smears of the wound exudate and any necrotic material
may show the typical ‘drumstick’ bacilli.
• Direct culture of unheated material on blood agar incubated
anaerobically is often the best method of detecting C. tetani.
Epidemiology
• Tetanus bacilli may be found in the human intestine.
• infection seems to be derived primarily from animal feces and
soil.
• The organism is especially prevalent in manured soil.
Prevention:
• Active immunization with tetanus toxoid (formalin-inactivated
toxin) prevents tetanus.
• It is usually administered to children as a triple vaccine with
diphtheria toxoid and pertussis antigens (DTaP).
• Circulating antibody levels gradually decline and that many
older individuals lose protection.
• booster immunizations with a preparation of diphtheria and
tetanus toxoids given every 10 years throughout life are
recommended.
• Tetanus immunoglobulin can be used to give immediate
passive immunity to injury victims with no history of
immunization.
• Active immunization should also be started.
• Antitoxin and toxoid, administered in different areas of the
body, can be given simultaneously.