Medical Microbiology
• Detection of disease:
– Signs & Symptoms
– Traditional Microbiological Identification
• Physiological Characteristics
• Microscopy Techniques
– Biotechnology (e.g. PCR)
– Immunological
•
•
•
•
Serological testing by agglutination
Fluorescent Antibodies
Enzyme Linked Immuno-Absorbance (ELISA) Assay
Western Blots for ELISA confirmation
• Selected “Nasties”:
Agglutination Serological Test
Figure 18.6
Fluorescence Microscopy
direct
ELISA
indirect
Yersinia pestis
Black Death
Taxonomy
• Member of the Enterobacteriaceae family
Yersinia is a Gram-negative coccobacilli
Target Tissues
• This disease direct effects the lymph nodes which can
be found in the groin, neck, and armpits and cause
them to enlarge and suppurate.
Ecology and Infection Process
Flea draws viable Y. pestis organisms
into its intestinal tract, and they multiply.
•
Biological vectors
Fleas
Rodents
Some Y. pestis in the flea regurgitated
when the flea gets its next blood meal thus
transferring the infection to a new host.
A few bacilli are taken up by tissue macrophages
after they lose their capsular layer. Macrophages
can’t kill Y. pestis and provide protected
environment for bacilli so they can re-synthesize
their capsular layer.
The re-encapsulated organisms then kill the
macrophage and are released into the
extracellular environment where they travel to
draining lymph nodes.
Symptoms
Bubonic Plague
bacteria infect lymph nodes
• Bubos
Fever
Headache
Vomiting Blood
Diagnostic Tests
•
Take smear from blood or feces
for bubonic plague
> bacteria has “safety pin”
appearance
Can also use FA (fluorescent-antibody) test
All plague bacilli have unique diagnostic envelope glycoprotein called
the Fraction 1 (F1) antigen
Treatments and Preventive
Measures
7- to 10-day course of antimicrobic therapy
• streptomycin
• chloramphenicol
• tetracycline
Vaccine:
Y. pestis organisms grown in artificial media, inactivated with
formaldehyde, and preserved in 0.5% phenol. The vaccine contains
trace amounts of beef-heart extract, yeast extract, agar, and
peptones and peptides of soya and casein.
Control of rat populations concurrent with elimination of their flea
prevent spread of the plague to humans.
Epidemiology: Transmission
Bubonic
Infected Rodent  Fleas  Humans
Can also enter through breaks in skin when handling infected animal
Prevalence and Distribution in Global
Human and Animal Populations
1000- 3000 cases reported
annually across the world
•Africa (most cases)
•Asia
•Northeastern Brazil
•Andes Mountain Regions
•US (19-40 cases a year mostly
in Western areas such as
New Mexico and Arizona)
Mortality
Bubonic Plague
Untreated 50- 60% mortality rate
Treated 5 – 20% mortality rate
Killed one third of the world’s population during the 14th century
Latest reports
As of 15 March 2001, World Health Organization has
reported a total of 436 suspected cases, including 11 deaths
in Nyanje area in Zambia.
As of 27 May 2002, the Malawian Ministry of Health has
reported a total of 71 cases of bubonic plague in Malawi.
Latest research
EVOLUTION: A single gene change in a relatively
benign recent ancestor of the bacterium that causes
bubonic plague played a key role in the evolution of the
deadly disease from a germ that causes a mild human
stomach illness acquired via contaminated food or water
to the flea-borne agent of the "Black Death.”
GENETICS: Research on three genes, hemin storage
(hms) genes, in Y. pestis that change it from a harmless,
long-term inhabitant in the flea midgut to one that
amasses in its foregut.
PREVENTION: Current prevention measures include
dusting family pets with insecticides to prevent the
spread of the Yersinia pestis organism from the native
prairie dog populations