Download Slide 1

Gram-Negative Rods
General Classification
• Based on source or site of infection
1. Enteric tract
2. Respiratory tract
3. Animal sources
Source or site of infection
• Enteric tract
Both within and outside:
Escherichia, Salmonella
Primarily within:
Shigella, vibrio, Campylobacter
Outside only: Klebsiella-Enterobacter-Serratia
group, Proteus-Providencia-Morganella group,
Pseudomonas, Bacteroides
Source or site of infection (continued)
• Respiratory tract:
Haemophilus, Legionella, Bordetella
• Animal sources:
Brucella, Francisella, Pasteurella, Yersinia
Classification
Based on morphology, biochemical traits and
genetic (phylogenetic) relationship
•
•
•
•
Enterobacteriaceae
Pseudomonaseae
Vibrionaceae
Cocobacilli
Enterobacteriaceae
• A heterogenous family
• Mostly found in colon of human and other
animals
• Different pathogenetic mechanisms
• Facultative anaerobic
• Glucose fermentation
• None have cytochrome oxidase
• Reduce nitrates to nitrites
Most important genuses
in Enterobacteriaceae family
•
•
•
•
•
•
•
•
Escherichia
Shigella
Salmonella
Klebsiella
Enterobacter
Serratia
Proteus
Yersinia
In contrast to
Enterobacteriaceae
• Pseudomonas
Gram negative rods:
• Non-fermenting (Strict aerobic)
• Not reduce nitrate
• Oxidase-positive
General structure of cells in
Enterobacteriaceae
• All have Endotoxin
• Some have Exotoxins, mostly called enterotoxins
• Three surface antigens:
O antigen: outer polysaccharide portion of the lipopolysaccharide
(repeating 3-4 oligosaccharide sugars 15-20 times). A basis for the
serologic typing (about 2000 types of Salmonella and 150 types of E.
coli).
H antigen: on the flagellar protein (in E.coli and Salmonella and not in
Klebsiella and shigella). Unusual H antigens in Salmonella called
phase 1 and phase 2. The organism can reversibly change in
antigenicity to evade the immune response.
K polysaccharide antigen: In encapsulated organisms such as Klebsiella.
Identified by quellung (capsular swelling) reaction in the presence of
specific antisera used for epidemiologic purposes. In S. typhi, it is
called Vi (or virulence) antigen.
quellung (capsular swelling)
reaction
Laboratory diagnosis
• Culture for isolation
Suspected specimens are inoculated onto 2 media:
1. Blood Agar 2. A selective differential medium
(MacConkey’s agar or eosin-methylene blue, EMB
agar. The differential ability is based on lactose
fermentation as the most important criterion in
identification of these organism. Non lactose
fermenters form colorless colonies. Selective
effect is exerted by bile salts or bacteriostatic
dyes
Laboratory diagnosis (continued)
• Culture for identification
• Screening biochemical tests for a final
definitive identification:
Triple sugar Iron Agar (TSI)
Almost enough to identify the genus but array of
20 or more biochemical tests to identify the
species.
Triple Sugar Iron Agar and Urea Agar
Triple Sugar Iron Agar
• Indicator : Phenol red.
• Components:
- Iron or Ferrous sulfate
- 3 sugars: glucose, lactose, and sucrose
• Black FeS indicates the production of SH2
(Ferrous
sulfate + Solfate reductase  ferro sulphide (Sfe)
Different observations for TSI
Reactions
Slant
Button
Gas
H2S Representative genera
Acid
Acid
+
-
Escherichia, Enterobacter, Klebsiella
Alkaline
Acid
-
-
Shigella, Serratia
Alkalin
Acid
+
+
Salmonella, Proteus
Alkalin
Alkalin
-
-
Pseudomonas
Urea Agar
Indicator: Phenol red.
Component : Urea
If the bacterium Produces
urease:
Urea is hydrolyzed to NH3 and
CO2 ---> light orange changes
to reddish purple (in Proteus
and K pneumoniae
Amonium citrate (Simmons Citrate)
Indicator: Bromothymol blue
If the bacterium can utilizes
ammonium dihydrogen phosphate
(a salt of ammonium) and sodium
citrate as sole source of nitrogen
and carbon, the indicator turns to
blue at alkalin pH due to releasing
ammonia.
Motility
• SIM medium: SH2, Indole, Motility
• Proteus: Swarms
• Differentiation between Enterobacter cloacae
(motile) from Klebsiella pneumoniae (Non motile)
Indole
• Tryptophan  Tryptophanase 
Deamination  Intermediate products: Indole
+ ….
• Detection: 5 drops Kovac’s reagent (contains
paradimethlaminobenzaldehyde = PDAB) is
added  Red ring
Serology
Usually in Salmonella, Shigella and E.coli final
detection (serotyping) by agglutination Ag+Ab test.
Coliforms
• That part of this family which are normal inhabitants of the colon:
E. coli
Enterobacter
Klebsiella
Citrobacter
So, E.coli is the indicator for fecal contamination of water supply:
Lactose fermentation, Acid and gas production, growth at
44.5 C and typical colony on EMB.
4 colony count per dL in drinking water is indicative of
unacceptable fecal contamination.
Antibiotic therapy
• Must be individually tailored to the antibiotic
sensitivity test (Antibiogram).
• Penicillin and cephalosporin families.
Aminoglycosides (Gentamicin, amikacin,
kanamycin, streptomycin …),
Chloramphenicol, tetracyclines, quinolones
and sulfonamides.
Escherichia coli
• Diseases
1. Diarrhea or dysentery
2. UTI
2. The most common cause of sepsis among
negative rods
3. One of the 2 important causes of neonatal
meningititis (the other is the group B
streptococci) due to colonization of vagina by
these organisms in about 25% of pregnant
women.
Virolence factors:
•
•
•
•
Pili
Capsule
Endotoxin
Two exotoxins (enterotoxins).
E. coli pili (fimbriae)
mannose
galactose
– glycolipids
– glycoproteins
25
Pathogenesis
• E. coli attaches to the surface of jejunum and
ileum by Pili  Bacteria synthesize
enterotoxins (exotoxins determined by
plasmids)  Diarrhea
• The toxins are strikingly cell-specific: Cells of
colon are not susceptible due to lack of
receptors for the toxins.
•
•
•
•
Enteropathogenic E. coli (EPEC)
Enterotoxigenic E. coli (ETEC)
Enteroinvasive E. coli (EIEC)
Enterohemorrhagic E. coli (EHEC)
Enteropathogenic E. coli (EPEC)
destruction of surface microvilli
• fever
• diarrhea
• vomiting
• nausea
• non-bloody stools
Gut lumen
• Diarrhea is self-limited and short duration (1-3 days)
28
Enterotoxigenic E. coli
• Travellers diarrhea
• Diarrhea like cholera but milder
Diarrhea is self-limited and short
duration (1-3 days)
29
Enterotoxigenic E. coli (ETEC)
• Heat labile toxin (LT)
–like choleragen
–Adenylate cyclase activated
–cyclic AMP concentration
–secretion water/ions (potassium and
chloride)
• Heat stable toxin (ST)
– Guanylate cyclase activated
– cyclic GMP concentration
– uptake water/ions (Sodium and Chloride)
30
Enterohemorrhagic E. coli (EHEC)
• Produce verotoxin which works like Shiga
toxin
• Hemorrhagic
– bloody, copious diarrhea
– few leukocytes
• hemolytic-uremic syndrome
– hemolytic anemia
– thrombocytopenia (low platelets)
– kidney failure
Enterohemorrhagic E. coli
• Usually O157:H7
Flagella
Transmission electron
micrograph
32
Enteroinvasive E. coli (EIEC)
Very similar to Shigella species (in biochemical
and morphological traits)
• Non lactose fermantative
• Non motile
• Invades to epithelial mucosal cells
• Cause enteric inflammation
E. coli Transmission
Meat products or sewagecontaminated vegetables
34
UTI
• The most common agent for UTI (Cystitis,
pyelonephritis): fever, chills, flank pain
• Occurs primarily in women
Attributed to 3 features which facilitate ascending
infection into bladder:
1. A short urethra
2. Proximity of the urethra to the anus
3. Colonization of vagina by members of fecal flora.
• The most frequent cause of nosocomial UTI.
(equally in both men and women and associated
with using catheters)
Systemic infection
• Capsule and endotoxin play a prominent role
• Capsular polysaccharide interferes with
phagocytosis (Serotype having K1 causes
neonatal meningitis).
• LPS during sepsis causes fever, hypotension
and disseminated intravascular coagulation.
Treatment
• Antibiogram for most infections
• A combination of ampicillin and gentamicin in
neonatal meningitis
• Rehydration for diarrhea
Prevention
• No passive or active immunisation
• Prompt withdraw of catheters and
intravenous lines
• Caution regarding uncooked food and
unpurified water while traveling.
Shigella
• Important properties
- Non lactose fermenting
- Distiguishable from Salmonella by: no gas, no
H2S, nonmotile.
- Divided into 4 groups based on O antigen: A,
B, C and D.
- Having an enterotoxin called Shiga toxin
Disease: Shigellosis
• Only a human disease
• Transmitted from person to person by
asymptomatic carriers (oral fecal transmission)
• 4 F’s – fingers, flies, food, feces
• Food-born outbreaks outnumber water-born
outbreaks by 2 to 1.
• In mental hospitals and day-care nurseries
• Children <7 accounts for half of shigella
positive stool culture
Pathogenesis
• Exclusively in gastrointestinal tract
• Bloody diarrhea (dysentery): Invading the
mucosa of the distal ileum and colon.
• Local inflammation accompanied by
ulceration occurs, but the organisms rarely
penetrate the wall or enter the bloodstream
unlike salmonellae.
• Although some have an enterotoxin, invasion
is not only due to enterotoxin.
Most invasive species
• S. dysenteriae causes the most severe disease
but S. sonnei causes mild disease but more
frequent
Clinical findings
• Incubation period: 1-4 days
• Symptoms: Fever, abdominal cramps,
followed by diarrhea (watery at first but later
contains blood and mucus).
• It can be mild or severe depending 2 major
factor: The species of Shigella and the age of
the patient.
Clinical findings
• Resolves in 2-3 days but antibiotic can
shorten the course.
• Serum agglutinins appear after recovery but
are not protective because the organism does
not enter the blood.
Lab diagnosis
• Non-lactose fermenting……
• Slide agglutination to detect its group
• Methylene blue stain of a fecal sample to
determine whether PMNs are present: An
invasive one: Shigella, Salmonella or
Campylobacter rather than a toxin-producing
organism such as V. cholerae, E. coli or
Clostridium perfringens or certain viruses or
Entamoeba histolytica.
Treatment
• The main treatment: Fluid and electrolyte
replacement.
• No antibiotic in mild cases
• Antibiogram test: Trimethoprim sulfamethoxazole or ampiciln.
• Antiperistaltic drugs are contraindicated as
they prolong the fever, diarrhea an excretion.
Prevention
• Interruption of fecal-oral transmission by
proper sewage disposal, chlorination of water
and personal hygiene.
• No vaccine
• Antibiotic prophylactic is not recommended.
Salmonella
Important properties
• Not ferment lactose
• Produce H2S, Gas, motile
Naming the salmonella
1.
2.
3.
4.
5.
S. typhi
S. paratyphi (A, B, C…)
S. typhimurium
S. choleraesuis
S. enteritidis (1500 serotypes)
Diseases
- Enterocolitis (S. typhimurium)
- Enteric fever (typhoid fever) (S. typhi and S.
paratyphi)
- Septicemia with metastatic abscesses (S.
choleraesuis)
Diseases
• Enterocolitis
An invasion of the epithelial and subepithelial
tissue of the small and large intestines.
Penetration both through and between the
mucosal cells: Inflammation and diarrhea.
PMN response limits the infection to the gut
and the adjacent mesenteric lymph nodes.
The dose of Salmonella required: at least
100,000 while for Shigella: 100 organisms.
• Typhoid (Enteric fevers)
Infection begins in the small intestine but few
gastrointestinal symptoms occur.
• The organisms multiply in the mononuclear
phagocytes of peyer’s patches, then spread to
the phagocytes of the liver, gallbladder and
spleen leading to bacteremia and then fever.
• Septicemia
Accounts for only about 5-10% of Salmonella
infections and occurs in:
More common in patients with chronic disease
or children with enterocolitis.
It leads to seeding of many organs, with
osteomyelitis, pneumonia, and meningitis as
most common sequelac.
Clinical findings of Enterocolitis
• Incubation period: 6-48 hours
Symptoms:
Nausea, Vomiting, Abdominal pain and diarrhea
with or without blood
The disease is self-limited. Treatment only in the
very young and very old.
S. typhimurium: the most common cause of
enterocolitis.
Typhoid or Enteric fever
• Typhoid or Enteric fever caused by S. typhi
and S. paratyphi (A, B and C).
- The illness is slow, with fever and constipation
rather than vomiting and diarrhea.
- After the first week, bacteremia becomes
sustained. High fever, tender abdomen, and
enlarged spleen occur.
Typhoid (continued)
• Rose spot (rose-coloured papules) on the
abdomen are associated with typhoid fever
but occur only rarely.
• The disease begins to resolve by the third
week but intestinal hemorrage or perforation
can occur.
• 3% of typhoid fever patients become chronic
carriers. The carrier rate is higher among
women.
Septicemia
• S. choleraesuis: most often cause septicemia.
• Symptoms:
- Fever
- Little or no enterocolitis
- Focal symptoms: bone, lung, or meninges.
Transmission of salmonella
• The epidemiology of Salmonella infections:
ingestion of food and water contaminated by
human and animal wastes.
• S. typhi, transmitted only by humans, but
other species have a significant animal
reservoir.
• Human sources are either persons who
temporarily excrete the organism during or
shortly after enterocolitis or chronic carriers
who excrete the organism for years.
Transmission
• The most frequent animal source is poultry
and eggs, but meat products that are
inadequately cooked have been implicated as
well.
• Dogs and other pets including turtles are
additional sources.
Lab. diagnosis
• Enterocolitis: isolated from stool
• Enteric fever: blood culture during first 2
weeks of illness.
• Septicemia: Blood culture
• Lactose -, Gallery, MacConkey
• Gas and H2S (S. type: no gas)
• Serological tests by their O, H and Vi antigens
• Selological detection for Ab if culture is
negative.
Treatment
• Enterocolitis: Self-limited.
• Fluid and electrolyte replacement.
• Antibiotic can select mutants resistant and
increase the frequency of the carrier state.
• Antimicrobial agents are indicated only for
neonates or persons with chronic disease
who are at risk of septicemia and
disseminated abscesses.
Treatment
• Enteric fever and Septicemia: Ampicillin or
chloramphenicol.
• Ampicillin: in patients who are chronic
carriers of S. typhi.
• Cholecystectomy may be necessary to abolish
the chronic carrier state.
• Focal absesses should be drained.
Prevention
•
•
•
•
•
•
•
•
Public health and personal hygiene measures.
Proper sewage treatment
A chlorinated water supply
Cultures of stool samples from food handlers
Hand washing
Pasteurization of milk
Proper cooking of poultry and meat
Two vaccine confer protection against S. typhi
but no common
Genus: Yersinia
Species: Yersinia pestis
and Yersinia enterocolitica
• Small gram negative bacillus, bipolar staining
(like a safety pin),capsule in freshly isolated
organism but lost with passage. Non motile.
• Disease
Plague or black death
Pathogenesis
• Urban cycle
Transmission of the bacteria among urban rats
with the rat flea as vector.
This cycle predominates during times of poor
sanitation, eg. Wartime, when rats proliferate
and come in contact with the fleas in the
sylvatic cycle.
Epidemiology
• Endemic in the wild rodents of Europe and
Asia for thousands of years.
• 99% of cases of plague occur in Southeast
Asia.
• Enzootic (sylvatic) cycle consists of
transmission among wild rodent by fleas.
• Rodents are relatively resistant to disease.
• Humans are accidental hosts and cases of
plague occur as a result of being bitten by a
flea that is a part of the sylvatic cycle.
Event within the flea
• The flea ingests the bacteria while taking a
blood meal from a bacteremic rodent.  The
blood clots in the flea’s stomach owing to the
action of the enzyme coagulase made by the
bacteria.  The bacteria are trapped in the
fibrin and proliferate to large numbers.  The
mass of organisms and fibrin block the
proventriculus of the flea’s intestinal tract.
During its next blood meal the flea
regurgitates the organisms into the next
animal. Because the proventriculus is
blocked, the flea gets no nutrition. 
becomes hungrier  loses its natural host
selectivity for rodents  more readily bites a
human.  The bacteria inoculated by bite
spread to the regional lymph nodes 
become swollen and tender called buboes and
this plague is called bubonic plague. 
The organisms can reach high concentrations
in the blood and disseminate to form
abscesses in many organs.  The endotoxinrelated symptoms, including disseminated
intravascular coagulation and cutaneous
hemorrhages, probably were the genesis of
the term ‘black death’.
Respiratory droplet transmission
• Respiratory droplet transmission of the
organism from patients with pneumonic
plague can occur.
Virulence factors
• Capsule antigen (F-1) which protects against
phagocytosis.
• Endotoxin
• Exotoxins (block beta adrenergic receptors)
• V antigen protein
• W antigen protein
Clinical findings
• Bubonic plague, is the most frequent form,
begins with pain and swelling of the lymph
nodes draining the site of the flea bite and
systemic symptoms such as high fever,
myalgias, and prostration.
• The buboes are an early characteristic finding.
• Septic shock and pneumonia are the main lifethreatening subsequent events.
• Pneumonic plague can arise either from
inhalation of an aerosol or from septic emboli
that reach the lung.
• Untreated bubonic plague is fatal in
approximately half of the cases.
• Untreated pneumonic plague is invariably
fatal.
Lab. diagnosis
• The best procedure: Smear and culture of
blood or pus from the bubo.
• Giemsa’s or Wayson’s stain reveals the typical
safety-pin appearance of the organism better
than does Gram’s stain.
• Fluorescent-antibody staining can be used to
identify the organism in tissues.
• A rise in antibody titer to the capsule antigen
can be useful.
Treatment
• The treatment of choice is a combination of
streptomycin and tetracycline.
• Due to the rapid progression of the disease,
treatment should not wait for the results of
the bacteriologic culture.
• Incision and drainage of the buboes are not
usually necessary.
Prevention
Prevention
• Controlling the spread of rats in urban areas.
• Preventing rats from entering the country by
ship or airplane.
• Aviding flea bites.
• Avoiding contact with dead wild rodents.
• A patient with plague must be placed in strict
isolation (quarantine) for 72 hours after
antibiotic therapy is started.
• Only close contacts need receive prophylactic
tetracycline.
• There is no vaccine for citizens normally. But a
killed organism vaccine protecting bubonic but
not pneumonic plague was used by USA forces
during Vietnam wars.
Vibrionaceae
• Curved or “comma-shaped” gram-negative
rods.
- 2-4 u
- Against Enterobacteriaceae, they have monotricus
not peritricus flagellum.
- All members live in aqueous material.
- Genus Vibrio lives in rivers, salt waters like beaches.
Vibrio cholerae
-
Facultative anaerobic
Can tolerate pH=9
Fermenting sucrose
Oxidase positive
Monotricus flagellum
Vibrio cholerae
• Two groups according to the nature of its O
cell wall antigen:
- O1 organisms (cause epidemic cholera
disease)
- Non-O1 organisms (either cause sporadic
disease or are non- pathogenes).
• O1 organisms:
have two biotypes (El Tor and cholerae) and 3
serotypes (Ogawa, Inaba and Hikojima)
Epidemiology
• Infects only humans
• Transmitted by fecal contamination of water
and food.
• Asymptomatic carriers: individuals in the
incubation or convalescing period
• Recent pandemic: 1960s-1970s, over 3
continents (Africa, Europe and Asia): El Tor
biotype/ usually Ogawa serotype.
• Factors predisposing to epidemics:
Poor sanitation, malnutrition, overcrowding
and inadequate medical services.
Quarantine measures failed to prevent the
spread of the disease due to many
asymptomatic carriers.
Pathogenesis
• Colonization (approximately 1 billion
organism must be ingested, because the
organism is particularly sensitive to stomach
acid.):
Adherence to the cells of brush border of the
gut is related to secretion of mucinase:
dissolves the glycoprotein coating over the
intestinal cells.
• Multiplication and secretion of enterotoxin.
• Enterotoxin (Choleragen) first binds to a sialic
acid-containing ganglioside receptor on the
surface of the enterocyte.
• Then enterotoxin catalyzes the addition of ADPribose to the coupling protein, resulting in the
activation of adenylate cyclase  increase in
cAMP  Secretion of the secretion of H20, Na+,
K+, Cl-, and HCO3- into the lumen of the small
intestine.
• Massive watery diarrhea without
inflammatory cells.
• Morbidity and death are due to
dehydration and electrolyte imbalance.
• If treatment is instituted promptly, the
disease runs a self-limited course in up to
7 days.
Clinical findings
• Watery diarrhea in large volumes (the
hallmark of cholera) without cells.
• Non-bloody rice-water stool
• No fever
• Symptoms are referable to the dehydration:
the loss of fluid and electrolytes leads to
cardiac and renal failure. Acidosis and
hypokalemia occur as a result of loss of
bicarbonate and potassium in the stool.
• Mortality rate without treatment is 40%
Lab diagnosis
• Rice-watery diarrhea with no inflammatory
cells.
• During an epidemic a clinical judgment is
made (little need for the laboratory.)
• Colorless colonies on MacConkey’s agar
(lactose is fermented slowly).
• Culture in selective medium: TCBS
(yellow colonies with average size and thin edge)
• Oxidase positive (distinguishes it from
members of Enterobacteriaceae)
• On TSI, Acid/Acid without gas or H2S.
• Serologic test (agglutination)
• Retrospective diagnosis serologically by
detecting a rise in antibody titer in acute and
convalescent-phase sera.
Treatment
• Prompt, adequate replacement of water and
electrolytes (orally or intravenously).
• Tetracycline is not necessary but do shorten
the duration of symptoms and reduce the
time of excretion of organisms.
Prevention
• Providing clean water and food supply.
• Vaccine has limited usefulness (50% effective
for 3-6 months)
• Tetracycline for prevention is effective in
close contacts but cannot prevent the spread
of a major epidemic.
• Prompt detection of carriers is important in
limiting outbreaks.
Psuedomonaceae
•
•
•
•
Gran Negative rods
Nonfermentative (Strict aerobic)
Oxidation of sugars
Cytochrome C oxidase
Pseudomonas aeroginosa
(Piocianic bacillus)
• Growth in soil and water containing only
traces of nutrients.
• A remarkable ability to withstand
disinfectants (found in soap solutions, in
antiseptics and in detergents).
• Persistent in the hospital environment
• An important role in hospital-acquired
infections
P.a. Producing 2 pigments:
Pyocyanin (colors the pus in a wound bluegreen)
Pyoverdin /Fluorescein (a yellow-green
pigment that fluoresces under ultraviolet light
In the lab, these pigments diffuse into the agar,
imparting a blue-green color that is useful in
identification of the species.
• In cystic fibrosis patients, P. aeroginosa has a
slime layer (glycocalyx):
• very mucoidal colonies. The slime layer
mediates adherence of the organism to
mucous membranes of the respiratory tract
and prevents antibody from binding to the
organism.
Epidemiology
• 10% of people carry it in the normal flora of
the colon and on the skin in moist areas.
• It can colonize the upper respiratory tract of
hospitalized patients.
• Its ability to grow in simple aqueous solutions
has resulted in contamination of respiratory
therapy and anesthesia equipments, and
even distilled water.
• An opportunistic pathogen. e.g. in those with
extensive burns (skin host defenses are
destroyed), those with chronic respiratory
disease (such as cystic fibrosis),
immunosuppressed, those with catheters.
• 10-20% of hospital-acquired infections.
Pathogenesis
• Virulance factors:
- Endotoxin
- Exotoxin A (inhibits eukaryotic protein
synthesis by the same mechanism as diphteria
exotoxin)
Clinical finding
• Can cause infections virtually anywhere in the
body, but more frequent in:
- Urinary tract infections (UTIs)
- Pneumonia
- External otitis
- Wound infections (especially burns).
From these sites, the organism can enter the
blood, causing sepsis with mortality rate of
over 50%.
Lab diagnosis
• Gram negative rods
• Non-lactose-fermenting (colorless) colonies
on MacConkey or EMB agar.
• In TSI: Alkalin/Alkalin
• Oxidase-positive
• Blue-green pigment on nutrient agar
• Fruity aroma
• Catalaze and gelatinase positive
Oxidase Test
Detecting cytochrome C oxidase enzyme
Indicator: 1% tetra methyl-para-phenylene diamine
dihydrochloride
Treatment
• Resistant to many antibiotics
• Antibiogram test is essential
• Usually is chosen from penicillins or
cephalosporins along with an aminoglycoside.
Prevention
• Keeping neutrophil counts above 500/uL
• Removing indwelling catheters promptly
• Taking special care of burned skin
Spirochetes
•
•
•
•
•
Thin-walled
Spiral rods
Flexible
Motile
Having an axial filament under the outer
sheath
• Treponema
- Seen only by darkfield microscopy, silver impregnation, or
immunofluorescence.
- No growth in bacteriologic media.
• Leptospira
- Seen only by darkfield microscopy, silver impregnation, or
immunofluorescence.
- Growth in bacteriologic media
• Borreliae
-
Larger than two others
Seen by Giemsa’s and other blood stains
Seen in the standard light microscope
Growth in bacteriologic media
Treponema pallidum pallidum
(The bacterial agent of syphilis)
• Subspecies pallidum (not bejel, pinta, yaws).
• Trasnsmission and Epidemiology
- Transmission from spirochete-containing
lesions of the skin or mucous membranes
- From pregnant women to their fetuses.
- Blood transfusion during early syphilis.
- A worldwide STD
- The incidence is increasing
Pathogenesis & Clinical finding
• No important toxins or enzymes.
• Primary stage  Chancre in 2 – 10 weeks
(average 21 days).
The ulcer heals spontaneously, but spirochetes
spread widely in tissues.
• Secondary stage: Lesions as maculopapular
rash or moist papules on skin and mucous
membranes. Or organ involvement
(meningitis, nephritis, hepatitis….).
• Secondary lesions are rich in spirochetes and
highly infectious but heal spontaneously.
• Tertiary stage: One-third of early syphilis
cases progress to cure without treatment.
Another third remain latent; i.e. no lesions
appear, but positive serologic tests indicating
continuing infections (Asymptomatic).
• In the remainder, the disease progresses to
the late, tertiary stage.
- Granulomas (gummas), especially of skin and
bones, central nervous system involvement
(e.g. tabes, paresis), or cardiovascular lesions
(eg, aortitis, aneurysm).
- In tertiary stage, the treponemes are very
rare.
•
-
Tertiary stage:
Gumma
Paralysis
Blindness
Insanity
Death
Congenital syphilis
• Fetus infection through her/his mother by
transplacental passage after the third month
of pregnancy.
• Unless treated promptly, multiple fetal
abnormalities.
• Early congenital syphilis occurs in children
between 0 and 2 years old. After, they can
develop late congenital syphilis.
• Symptomatic newborns, if not stillborn, are
born premature, with enlargement of the
liver, spleen, skeletal abnormalities,
pneumonia
• malformations of teeth or bones and by active
mucocutaneous syphilis at birth or shortly
thereafter, and by ocular or neurologic
changes.
• Babies with congenital syphilis can have
symptoms at birth, but symptoms can develop
two weeks to three months later, including:
• anemia
• fever
• rashes
• skin sores*
• swollen liver and spleen
• various deformities
• weak/hoarse crying sounds
• yellowish skin (jaundice)
When infected infants become older
children and teenagers, late-stage
syphilis symptoms may occur, including
damage to:
bones
brain
eyes
ears
Teeth
Immunity
• Immunity to syphilis is incomplete: Antibodies
are produced but not stop the progression of
the disease.
• Patients with early syphilis who have been
treated can contract syphilis again.
• Patients with late syphilis are relatively
resistant to reinfection.
Lab diagnosis
• Microscopy
Demonstrating spirochetes by darkfield or
immunofluorescence microscopy.
• Nonspecific serologic tests
- Nontreponemal antigens (extracts of normal
mammalian tissues. eg. Cardiolipin from beef
heart) react with “reagin” antibodies in serum
samples from patients with syphilis.
- VDRL (Venereal Disease Research Laboratory)
- RPR (Rapid plasma reagin)
• Antibodies are detectable in the majority of
patients at the time the primary lesion
appears.
• Always present in secondary syphilis.
• False-positive reactions occur in infections,
such as hepatitis and infectious
mononucleosis and in various autoimmune
disease.
Specific serologic tests
• Involving the use of treponemal antigens.
• T. pallidum extracted from experimentally
infected rabbits reacts in immunfluorescence
(FTA-ABS) or hemaglutination (TPHA) tests
with specific antitreponemal antibodies,
which arise within 2-3 weeks of syphilitic
infection.
Treatment
• Penicillin G (A single injection of benzathin
penicillin G)
• Tetracycline or erythromycin if given for
prolonged periods.
Prevention
• Administration of antibiotic after suspected
exposure.
• The presence of any sexually transmitted
disease makes testing for syphilis mandatory.
• No vaccine is available.
Borrelia recurrentis
• Causing relapsing fever
• During infection, the antigens of these
organisms undergo variation. As antibodies
develop against one antigen, variants emerge
and produce relapses of the illness.
• Relapses can be repeated 3-10 times.
• Transmission from person to person by
human body louse
• Humans are the only hosts
• Diagnosis
- Seeing the large spirochetes in stained smears
of peripheral blood.
- Culture in special media
- Serological tests are rarely useful
- Treatment: Tetracycline
• Borrelia burgdorferi  Transmitted by tick
bite  Lyme disease
• Reservoirs: Mice and deer
Rickettsiae
• Very short rods and barely visible in the light
microscope
• Structurally gram-negative but poorly stain
with gram stain.
• Obligate intracellular parasites, so must be
grown in cell culture (The exception is R.
quintana).
• Against chlamydiae divide by binary division
within the host cell not by a distinctive
intracellular cycle.
Lab diagnosis
• The Weil-Felix test detects antirickettsial
antibodies in a patient’s serum by
agglutination of the proteus organism is
based on a cross-reaction, because: Several
rickettsiae (R. prowazekii, R. tsutsugamushi, R.
ricketsii, …) possess antigens that cross-react
with antigenes of OX strains of proteus
vulgaris.
Transmission
• They maintained in nature in certain
arthropods, such as ticks, lice, fleas and mites
and with one exception are transmitted to
humans by the bite of the arthropod.
• The exception to arthropod transmission is C.
burnetii, the cause of Q fever, which is
transmitted by aerosol and inhaled into the
lungs.
• Virtually all rickettsial diseases are zoonoses
with the exception of epidemic typhus which
occurs only in humans.
• R. prowazekii  Epidemic Typhus (by lice)
• R. typhi  Typhus (by lice)
• R. tsutsugamushi  Typhus (by lice)
• Rickettsia rickettsii  Rocky mountain
spotted fever (by ticks)
• Coxiella burnetii  Q fever (inhalation,
contact with the milk, urine, feces, vaginal
mucus, or semen of infected animals.