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.