Microbial diseases of
the Nervous system
MMI 342
Objectives
• Overview of the Nervous system
• Understand the characteristics of H. influenzae
• Know the mode of transmission of H. influenzae
• Explain the virulence factors of H. influenzae
• Explain the pathogenesis of H. influenzae
• Know the laboratory diagnosis of H. influenzae
• Understand the epidemiology, prevention and treatment of H.
influenzae infections
• Differentiate H. influenzae from other species of same genus
Introduction
Anatomy of the NS
• The human nervous system is organized into two divisions:
• central nervous system: brain & spinal cord
• peripheral nervous system: nerves that branch off from the brain
(cranial nerves) & spinal cord (spinal nerves)
• Both the brain and the spinal cord are covered and protected
by three continuous membranes called meninges, i.e
• the outermost dura mater,
• the middle arachnoid mater, &
• the innermost pia mater.
• Between the pia mater and arachnoid membranes is a space
called the subarachnoid space filled with cerebrospinal fluid ~
100-160ml (for an adult).
Introduction
Anatomy of the NS
• Infections of the Nervous System are mostly devastating
• Damage to the brain and spinal cord can lead to deafness,
blindness, learning disabilities, paralysis, and death.
• Protecting the nervous system from accident and infection
by bone and other structures is crucial.
Introduction
Anatomy of the NS
• The blood–brain barrier prevents pathogens that circulate in
the bloodstream from entering the brain and spinal cord.
• Cerebrospinal fluid (CSF) of the CNS is vulnerable due to
lack of many of the defenses found in the blood like
complement, antibodies etc.
• Pathogens capable of causing diseases of the nervous
system often have special virulence characteristics that
enable them to penetrate available defenses.
Introduction
Anatomy of the NS
• Inflammations of the brain tend to alter the blood–brain
barrier thereby affecting its selective permeability.
• An inflammation of the meninges is called meningitis.
• An inflammation of the brain is called encephalitis.
• An inflammation of both the brain and the meninges is called
meningoencephalitis.
Bacterial Diseases of the Nervous System
• Microbial infections of the CNS are infrequent but often
have serious consequences.
• Some bacterial pathogens for the nervous system include
1. Neisseria meningitides,
2. Hemophilus influenzae,
3. Mycobacterium tuberculosis,
4. Clostridium tetani
5. Streptococcus pneumoniae, and
6. Listeria monocytogenes.
Haemophilus Influenzae
Haemophilus
SPECIES
• Haemophilus Influenzae
SCIENTIFIC CLASSIFICATION
• Haemophilus Influenzae biotype aegyptius
• Kingdom : Bacteria
• Haemophilus haemolyticus
• Phylum:
• Haemophilus ducreyi
• Class:
• Family:
Proteobacteria
Gamma Proteobacteria
Pasteurellaceae
• Haemophilus aprophilus
• Haemophilus parainfluenzae
• Haemophilus parahaemolyticus
• Genus :
Haemophilus
• Haemophilus paraphrophilus
Haemophilus
Blood loving
Gram negative coccobacilli
Pleomorphism & Fastidious
Require 1 or 2 growth factors present in
blood
X factor – heme, hematin
V factor - nicotinamide adenine
dinucleotide (NAD)
Important species
H influenzae, H aegypticus, H ducreyi
Haemophilus spp & growth factor
Species
Factor X
Factor V
H influenzae
+
+
H parainfluenzae
-
+
H aegyptius
+
+
H ducreyi
+
-
H aphrophilus
+/-
-
Haemophilus influenzae
• small, facultative anaerobe & Gram-negative
rods - coccobacillary shape.
• non-motile, often encapsulated, non-spore
forming
• complex nutritional growth requirements for
blood-containing media (X & V factors).
• exclusively found in humans
• cause respiratory infections - major cause of
purulent meningitis
Haemophilus influenzae
• encapsulated strains are subclassified in serovars a-f based on the
fine structure of their capsule polysaccharides.
• Serovar b (Hib) causes most Haemophilus infections in humans
• Other Haemophilus species either infect only animals or are found in
the normal human mucosal flora.
• H. parainfluenzae, H. hemolyticus, H. segnis, H. aphrophilus, and H.
paraphrophilus.
• occasionally cause infections.
Haemophilus influenzae
• is a facultative anaerobe requiring growth factors X and V in
culture medium.
• The X factor is hemin, required by the bacteria to synthesize
enzymes containing heme (cytochromes, catalase, oxidases).
• its cultivation need exogenous hematin and/or nicotinamide
adenine dinucleotide (NAD) growth factors.
Haemophilus influenzae
• These growth factors, X factor (hematin) and V factor (NAD),
are both present in erythrocytes
• Staphylococcus aureus, produce excess NAD and secrete it into
the medium.
• This allows H. influenzae to proliferate in the immediate vicinity
of S. aureus colonies.
• This is called satellite phenomenon
• The medium normally used to culture H. influenzae is chocolate
agar containing sufficient amounts of the X and V factors.
c
(a) Gram-stained cerebrospinal fluid sediment preparation. Fine, Gram-negative rods surrounded by a capsule
(serovar b). (b, c) Satellite colonies of Haemophilus influenzae surrounding the Staphylococcus aureus
streak. S. aureus provides small amounts of V factor. The blood agar contains free X factor.
H. influenzae - Satellitism
S aureus
,
,
,
,
,
,
,
,
H influenzae
colonies
,
,
,
,
,
,
,
,
Blood agar
Haemophilus influenzae
• may or may not have a capsule.
• capsulated species are divided into six serotypes, designated a-f, based on
the capsular polysaccharide antigen.
• The type b capsule is made up of a polymer of ribose, ribitol, and phosphate,
called polyribitol phosphate (PRP).
• These surface polysaccharides are strongly associated with virulence,
particularly H. influenzae type b (Hib).
• The non-encapsulated (non-typable), H. influenzae can be classified by a
number of typing schemes based on outer membrane proteins and other
factors.
• These protein systems can also be applied to capsulated H. influenzae but
have no particular association with virulence.
Haemophilus influenza
MODE OF
TRANSMISSION
• Airborne
• aerosol
VIRULENCE FACTORS: H. influenzae
• Outer membrane protein - Helps in adherence to epithelial
cells
• Pili - Helps in adherence to epithelial cells.
• Immunoglobulin A1 Protease - Causes breakdown of IgA,
facilitate colonization on the mucosal surface
• Lipopolysaccharides - Causes meningococcal inflammation
• Capsular polysaccharides - PRP of the capsule is
antiphagocytic- resists phagocytosis of the bacteria
Pathogenesis: H. influenzae
1. H. Influenzae enters the human host by respiratory
route
2. Pilus and non pilus adhesions of the bacteria mediate
colonization in the nasopharynx and oropharynx
mucosa
3. escape the 1st line of defense such as the adhesive
mucus matrix, inactivate the mucociliary escalator
and deactivate the IgA, how?
4. Lipid A lipopolysaccharides impairs ciliary function
(ciliostasis) and IgA1 protease breakdown IgA1
• Paralysis of cilia (ciliostasis)
• Sloughing of ciliated cells
• Penetrate the mucus layer and deactivate IgA1
5. Disrupts the tight junctions of the epithelial cells and
cause damage of the respiratory mucosa. Access to the sub
mucosa and eventually the bloodstream.
6. A large bacterial load or the viral infection potentiate the
bacterial infection that invade mucosa, via the sub mucosa
and enter the blood stream
7. The presence of antibodies, complement components and
phagocytes cause clearance of bacteremia. The serum
bacteriocidal effects should avoided
8. The absence of anti PRP antibodies contributes to bacterial
infection
9. High grade bacteremia leads to spread to various sites
including meninges, subcutaneous tissue, joints, pleura and
pericardium
10. Responsible for causing Meningitis, Arthritis, pneumonia and
endocarditis
11. Colonization of noncapsulated strains will directly extend to
sinuses, eustachian tube etc cause sinusitis and otitis media
http://dx.doi.org/10.1016/B978-0-12-397169-2.00097-4
In the nervous system
12. Portal of entry into the subarachnoid space is the choroid
plexus (region with excess blood flow)
13. Enters the endothelial cells via the transcytosis (endocytosis)
process. Also, the inflammatory response in BS causes
damage to endothelial tight juctions  disrupting the
selective permeability of the blood-brain barrier
14. Negligible immune defence are present in CSF but fragments
of peptidoglycan layer stimulate the production of TNFα &
IL-1β by glial and endothelial cells
15. TNFα & IL-1β triggers an inflammatory cascade  an
influx of leukocytes into the subarachnoid space  causing
cerebral oedema, raised intracranial pressure and neuronal
damage.
16. Oxygen radicals and excitatory amino acids have also been
shown to contribute to neuronal cell damage
Clinical Syndrome
Symptoms and Signs
• Haemophilus influenzae causes many different types
of infections.
• Respiratory infections
• Blood infections
• Meningitis
• Symptoms depend on the part of the body that is
infected.
https://www.cdc.gov/hi-disease/about/symptoms.html
1. Bloodstream Infection
• Fever and chills
• Excessive tiredness
• Pain in the belly
• Nausea with or without vomiting
• Diarrhea
• Anxiety
• Shortness of breath or difficulty breathing
• Altered mental status (confusion)
• Bloodstream infection from H. influenzae can occur with or
without pneumonia.
2. Meningitis
• Fever
• Headache
• Stiff neck
• Nausea with or without vomiting
• Photophobia (eyes being more
sensitive to light)
• Altered mental status (confusion)
Newborns and infants with meningitis may be irritable, vomit, feed
poorly, or appear to be slow or inactive and presence of a bulging
fontanelle.
3. Pneumonia
• Fever and chills
• Cough
• Shortness of breath or difficulty breathing
• Sweating
• Chest pain
• Headache
• Muscle pain or aches
• Excessive tiredness
Cellulitis cause by H. influenzae in foot
Cellulitis caused by H. influenzae in cheek
H. influenzae causing Otitis Media
Laboratory Diagnosis
Specimens
CSF, sputum, blood
Microscopy
Gram negative coccobacilli
Antigen
detection
Latex agglutination (a- e)
Culture
Chocolate agar – translucent
colony
Blood agar- satellitism
Identification
Antibiotic
Microscopy & slide agglutination
Cefotaxime /ceftriaxone (meningitis)
ampicillin/co-trimoxazole (respiratory infections)
Identification of
the pathogen in
cerebrospinal
fluid, blood, pus,
or purulent
sputum using
microscopy and
culture assays.
H. influenzae - Satellitism
S aureus
,
,
,
,
,
,
,
,
H influenzae
colonies
,
,
,
,
,
,
,
,
Blood agar
Flowchart for isolation of H. influenzae
Treatment
• penicillinase-stable beta lactam antibiotics
• Alternatively, 4-quinolones (not for children)
• Ceftriaxone – drug of choice in meningitis
Epidemiology and Prevention
• H. influenzae is found only in humans
• H. influenzae is a normal nasopharyngeal flora of 20 to
80% of healthy persons.
• causes severe invasive infections (meningitis, sepsis,
epiglottitis) in children
• Meningitis develops in children under 2 years of age
• Immunization with the conjugate vaccine Hib - capsule
polysaccharide epitope “b” conferring immunity is conjugated to
protein
• The immune system does not respond to pure polysaccharide
vaccines until about the age of two, since polysaccharides are
T-independent antigens against which hardly any antibodies are
produced in the first two years of life
• Person-to person spread is blocked by vaccine or prophylaxis
with rifampicin
Haemophilus aegyptius
Gram negative coccobacillus
Purulent conjunctivitis (pink eye)
Brazilian purpuric fever
• High fever & death within 48hrs
Occur in epidemic forms
Common in infants & children
Responds to local sulphonamides & gentamicin
Haemophilus ducreyi
Chancroid or soft sore (STD)
Tender nonindurated irregular ulcers on
gentals with enlarged regional lymph nodes
Gram negative coccobacillus
Grows on chocolate agar with vancomycin
(selective medium)
Identified by agglutination with antiserum
Erythromycin, Sulfonamides,
Streptomycin and Tetracyclines
Haemophilus spp
Abbreviations: X factor, hematin; V factor, nicotinamide adenine dinucleotide (NAD); HMW, high-molecularweight proteins (HMW1, HMW2); a H. parainfluenzae, H. aphrophilus, H. hemolyticus.
Reference
• Sherris Medical Microbiology_ An Introduction to Infectious Diseases
[Kenneth R & George R, 4th ed 2004]
• Microbiology with Diseases by Body System [Robert W.B, Todd P.P]
• Microbiology an introduction [Gerard J.T, Berdell R.F, Christine L.]
• Medical Microbiology [F.H.Kayser et al., Thieme 2005]
• http://dx.doi.org/10.1016/B978-0-12-397169-2.00097-4
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