2. LEARNING OBJECTIVES
Enlist the bacterial causes of meningitis
Describe the morphological features,virulence
factors and diagnosis of following bacteria
Neisseria meningitides
Listeria monocytogenes
Haemophilus influenzae
Streptococcus agalactae
streptococcus pneumonia
3. Meningitis
Meningitis means inflammation but usually
implies serious infection of the meninges
Microorganism reach the meninges either by
direct extension from the ears, nasopharynx,
cranial injury or congenital meningeal defect,
or by bloodstream spread.
Non infectious causes of inflammation
include malignant cells, drugs and blood
following subarachnoid hemorrhage
4. Meningococcal Meningitis
Is inflammation of the meninges-
meningitis, caused by the bacteria
Nesseria meningitidis.
Neisseria meningitidis,Streptococcus
pneumoniae and Haemophilus
influenzae are the most common
agents of bacterial meningitis.
5. Meningococcal Meningitis
Less common bacterial causes of Meningitis, such as
Staphylococci, enteric bacteria, group B streptococci
and Listeria, occur in sub-populations like the
immunocompromised, neonates, or head trauma
patients.
Patients with Meningococcal Meningitis present with
sudden onset of fever, intense headache, nausea,
vomiting, stiff neck and, frequently, a petechial rash
with pink macules or, very rarely, vesicles. Delirium
and coma often appear.
Case fatality rate is between 5% and 15%.
6. Pathology
In acute bacterial meningitis, the pia arachnoid
is congested with polymorphs. A layer of pus
forms. This may organize to form adhesions,
causing cranial nerve palsies and hydrocephalus.
In chronic infection (e.g. TB), the brain is
covered in a viscous grey green exudates with
numerous meningeal tubercles. Adhesions are
invariable. Cerebral edema occurs in any
bacterial meningitis.
In viral meningitis there is a predominantly
lymphocytic inflammatory CSF reaction without
pus formation, polymorphs or adhesions, there is
little or no cerebral edema unless encephalitis
develops.
8. General Characteristics of
Neisseria spp. Aerobic
Gram-negative cocci often arranged in pairs
(diplococci) with adjacent sides flattened (like
coffe beans)
Oxidase positive
Most catalase positive
Nonmotile
Acid from oxidation of carbohydrates, not
from fermentation
11. Encapsulated small, gram-negative
diplococci
Second most common cause (behind S.
pneumoniae) of community-acquired
meningitis in previously healthy adults;
swift progression from good health to
life-threatening disease
Introductionof Neisseria meningitidis
13. Humans only natural hosts
Person-to-person transmission by
aerosolization of respiratory tract
secretions in crowded conditions
Close contact with infectious person
(e.g., family members, day care
centers, military barracks, prisons, and
other institutional settings)
Epidemiology of Meningococcal
Disease
14. Highest incidence in children
younger than 5 years and
particularly those younger than 1
year of age as passive maternal
antibody declines and as infants
immune system matures
Commonly colonize nasopharynx
of healthy individuals; highest oral
and nasopharyngeal carriage rates
in school-age children, young
adults and lower socioeconomic
groups
15. Occurrence
Infections can occur through the year, but are more
common in late winter to early spring.
Mode of Transmission
By direct contact- respiratory droplets from nose and throat
of infected people.
Infection usually causes subclinical infection, severe
systemic infection is rare.
Carrier prevalence can be as high as 25%.
16. Pathogenicity:
Pili-mediated, receptor-specific
colonization of nonciliated cells of
nasopharynx
Antiphagocytic polysaccharide capsule
allows systemic spread in absence of
specific immunity
Toxic effects mediated by
hyperproduction of lipooligosaccharide
Serogroups A, B, C, Y, W135 account for
about 90% of all infections
17. Specific receptors (GD1 ganglioside) for bacterial
fimbriae on nonciliated columnar epithelial cells in
nasopharynx of host
Organisms are internalized into phagocytic
vacuoles, avoid intracellular killing in absence of
humoral immunity and complement system (patients
with late complement deficiencies are particularly at
risk)
Replicate intracellularly and migrate to subepithelial
space where excess membrane fragments are
released
athogenesis of Meningococcal
Disease
18. Hyperproduction of endotoxin (lipid A of
LOS) and blebbing into surrounding
environment (e.g., subepithelial spaces,
bloodstream) mediates most clinical
manifestations including diffuse vascular
damage (e.g., endothelial damage, vasculitis
(inflammation of vessel walls), thrombosis
(clotting), disseminated intravascular
coagulation (DIC)
19. Following dissemination of virulent
organisms from the nasopharynx:
Meningitis
Septicemia (meningococcemia) with or
without meningitis
Meningoencephalitis
Pneumonia
Arthritis
Urethritis
Diseases Associated with
Neisseria meningitidis
25. Large numbers (e.g., >107cells/ml) of
encapsulated, small, gram-negative
diplococci (flattened along adjoining
side) and polymorphonuclear
leukocytes (PMN’s) can be seen
microscopically in cerebrospinal fluid
(CSF)
Laboratory Characterization of
Neisseria meningitidis
30. The quellung reaction
(swelling reaction) forms the
basis of serotyping and relies
On the swelling of the
capsule upon binding of
homologous antibody.
The test consists of mixing a
loopful of colony with equal
quantity of specific antiserum
and then examining
microscopically
for capsular swelling
31. Contd…
Pneumoccus grow only in enriched media. (blood agar, glucose
broth)
aerobes, facultative anaerobes
optimal temperature – 37C (25-42C)
optimal pH – 7.8 (6.5-8.3)
increased growth in 5-10% CO2
39. 3. Haemophilus influenzae
Aerobic , Small, pleomorphic gram-negative coccobacilli
Polysaccharide capsule
Six different serotypes (a-f) of polysaccharide capsule(based on
the antigenicity of capsular polysacchrides)
40. Contd…
95% of invasive disease caused
by type b
The type b capsule is composed of polyribitol phosphates
Unencapsulated and untypeable strains can cause sinusitis and otitis media
but are usually noninvasive
Growth in culture requires heme (X factor) and/or nicotinamide adenine
dinucleotide (NAD) (V factor) for adequate energy production
41. H.INFLUENZAE IS THE LEADING
CAUSE OF MENINGITIS IN YOUNG
CHILDREN
Important cause of URTI(otitis
media,sinusitis and epiglottitis) and
sepsis in children
It causes pneumonia in adults particularly
in those having COPD (chronic
obstructive pulmonary disease)
42. LABORATORY DIAGNOSIS
Specimens:
Oral swab: avoid contamination with oral secretions
Sputum from LRT
Direct needle aspiration
Cerebrospinal fluid (CSF) and blood (>107 bacteria/ml)
Microscopy: both sensitive & specific; G(-)
bacilli in CSF in >80% cases before antibiotics
treatment
43. LABORATORY DIAGNOSIS
Heated blood (chocolate) agar for isolation(to inactivate nonspecific inhibitors of
H.influenzae growth)
Growth require heme (x factor) and nicotinamide adenine dinucleotide, NAD (v factor)
44. Contd..
Definitive identification can be
made by biochemical tests or the
capsular swelling “QUELLUNG
“reaction
Fluorescent-antibody staining of
the organism and
counterimmunoelectrophoresis or
latex agglutination tests detect
the capsular polysacchride.
46. Streptococcus agalactiae
Gram +ive cocci in small chains
Beta haemolytic colonies on blood agar
Lance-field gouping ---group B (specific antiserum)
Hippurate Hydrolysis test +ive
CAMP – TEST +ive (Chtist,Atkin,Mouch,Peterson)
Bacitracin Disk ----Negative
47.
48. FIG. 6. CAMP-
positive Streptococcus
agalactiae (group B) inoculated
at right angles to the test
organism Staphylococcus aureus.
Note the arrow-shaped zones of
enhanced hemolysis.
FIG. 7. CAMP-negative Streptococcus
pyogenes (group A) inoculated at
right angles to the test organism
Staphylococcus aureus. Note the
absence of arrow-shaped zones of
enhanced hemolysis.)
49. Listeria Monocytogenes
Gram +ive , motile rod. Coccobacillus , Non –
capsulated
Motile at 18 – 20 C°, non motile at 37 C°
Tumbling/ Rotating motility
Grows at Refrigerating temp 2-8 C°also
Can cross placenta
Causes meningitis in new born and pregnant women
51. Laboratory Diagnosis
Gram staining----G+ive rods
Small grey coloured colonies
with narrow zone of beta
hemolysis on blood agar
Motile nature differentiate it
from corynaebacteria