2. Bacterial Diseases of the Upper Respiratory
System
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Streptococcal Respiratory Diseases
Properties
Gram positive in reaction
Cocci arranged in pairs or chains during growth
Contain normal flora & pathogenic Spp.
Facultatively anaerobic
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Classification of Streptococci
Based on:
1. Hemolytic rxns on blood agar
Beta haemolytic streptococci; Complete disruption of erythrocytes with clearing of
the blood around the bacterial colonies on BA is called β hemolysis. e.g. S. pyogenes, S.
agalactiae
Alpha haemolytic streptococci: partial/Incomplete lysis of erythrocytes s called α
hemolysis.
e.g. S. pneumoniae
Non-haemolytic or gamma streptococci: Other streptococci are non-hemolytic
(sometimes called gamma hemolysis). e.g. Enterococci
2. Serologic specificity (Lancefield groups A–H)
3. Battery of Biochemical Tests:
4. Group A beta -Hemolytic Streptococci (Streptococcus
pyogens)
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Is the major cause of bacterial pharyngitis and scarlet and rheumatic fevers.
The bacterium shows beta hemolysis after 24 hours on blood agar.
have a number of structures, enzymes, and toxins that enable them to
survive as pathogens in the body. These include the following:
M protein: causes inhibition of complement component C3b, thereby
interfering with opsonization
The hyaluronic acid capsule may “camouflage” the bacterium from
phagocytes.
Streptokinase's are enzymes that break down blood clots, presumably
enabling group A streptococci to spread rapidly through damaged tissues.
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C5a peptidase is an enzyme that breaks down complement protein C5a. With this
enzyme, S. pyogenes decreases the movement of leukocytes into the site of infection.
Pyrogenic (also called erythrogenic) toxins : stimulate leukocytes to release
cytokines that in turn stimulate fever, rash, and shock.
Streptolysins: lyse erythrocytes, leukocytes, and platelets
Pathogenesis
People spread S. pyogenes via respiratory droplets.
Streptococci cause a variety of illnesses depending on the virulence factors.
S. pyogenes frequently infects the pharynx, but the resulting disease is usually temporary, lasting
only until adaptive immune responses against bacterial antigens (particularly M protein and
streptolysins) clear the pathogen, usually within a week.
Typically, strep throat and streptococcal bronchitis occur only when:-
o Normal competing microbiota are missing
6. Signs and Symptoms
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Streptococcal pharyngitis
Laryngitis and bronchitis
Scarlet fever
Complications of some cases of untreated streptococcal pharyngitis
are acute glomerulonephritis and rheumatic fever
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Epidemiology
Most cases of streptococcal pharyngitis occur during the winter and spring
among elementary and middle school children, probably because of
crowded conditions.
One person can spread sufficient bacteria to cause disease by coughing
or sneezing.
Laboratory identification
Specimens for laboratory analysis can be obtained from throat swabs,
sputum, and blood.
S. pyogenes forms characteristic small colonies surrounded by a
large zone of beta hemolysis on sheep blood agar.
This organism is highly sensitive to bacitracin.
Immunological tests
9. Corynebacterium diphtheriae
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Pathogen and Virulence Factors
Is non-endospore-forming, Gram-positive bacteria.
C. diphtheriae is non-capsulate, non-motile, "club-shaped“
bacteria.
Facultative anaerobe
Arranged in angular fashion like Chinese lettering arrangement
Colonizing the skin and the respiratory, gastrointestinal, urinary and
genital tracts.
Virulent C. diphtheriae contains a diphtheria toxin.
The toxin gene is directly responsible for the signs and symptoms of
diphtheria.
10. Pathogenesis and Epidemiology
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C. diphtheriae is transmitted from person to person via respiratory droplets or
skin contact.
Infections with C. diphtheriae have different effects depending on a host’s
immune status and the site of infection.
Infections in immune individuals are asymptomatic
In immunocompromised individuals most severe, resulting in the sudden and
rapid signs and symptoms of diphtheria and cause of childhood death.
12. Diagnosis, Treatment, and Prevention
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Lab. Diagnosis:
Specimens:
Include throat, and, or nasopharyngeal swabs to confirm a
diagnosis of throat diphtheria, and a skin swab if cutaneous
diphtheria is suspected
Microscopy:
C. diphtheriae is gram positive bacteria appear in cluster like
Chinese letters
Culture
C. diphtheriae is facultative anaerobe at optimum temperature of
35–37 ºC.
13. Treatment
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o Early administration of antitoxin formed by the organisms at their site of entry and
multiplication
o The most important aspect of treatment is the administration of antitoxin
(immunoglobulins against the toxin) to neutralize diphtheria toxin.
o Antimicrobial drugs (Penicillin or Erythromycin)
o Penicillin or erythromycin kills Corynebacterium, preventing the synthesis of more
toxin
14. Bacterial Diseases of the Lower Respiratory
System
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Pneumococcal Pneumonia: caused by Streptococcus also called
pneumococcal pneumonia—is the most common type of bacterial pneumonia,
accounting for most cases of community-acquired pneumonia (CAP).
Pathogen and Virulence Factors
Streptococcus Pneumoniae (Pneumococcus)
S. pneumoniae are gram-positive, nonmotile, encapsulated cocci.
In sputum pneumococci are typically arranged in pairs (diplococci); each
coccus is somewhat elongated and pointed at one end but rounded at the
other (lancet-shaped).
S. pneumoniae is the most common cause of pneumonia and otitis
media and an important cause of meningitis and bacteremia
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Pathogenesis and Epidemiology
Pathogenic pneumococci secrete an attachment molecule
Protein that mediates binding of the bacterium to epithelial cells of the
pharynx.
Pneumococci are inhaled occasionally from the pharynx into the lung and
damaged either by a previous viral disease, such as influenza or measles,
or by other conditions, such as alcoholism, congestive heart failure, or
diabetes mellitus.
Virulent serotypes also have polysaccharide capsules that protect them
from lysis by phagocytes and pneumococci that live in and eventually kill
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As the bacteria multiply in the alveoli, they damage the lining of the alveoli,
allowing erythrocytes, leukocytes, and blood plasma to enter the lung.
This fluid fills the alveoli, reducing the lung’s ability to transfer oxygen to the
blood and causing the pneumonia.
It occurs most frequently in fall and winter in children or groups whose immune
responses are not fully active
17. Signs and Symptoms Pneumococcal pneumonia
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Fever
Chills
Congestion
Cough
Chest pain,
Short, rapid breathing, and possibly nausea and vomiting.
18. Laboratory diagnosis
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Specimens for laboratory evaluation can be obtained from a
nasopharyngeal swab, blood, pus, sputum, or spinal fluid.
α-Hemolytic colonies appear on blood agar
Lancet-shaped, gram-positive diplococci are observed on a Gram stain of
the sample.
Growth of these bacteria is inhibited by low concentrations of the
optochin, and the cells are lysed by bile acids (bile solubility positive).
19. Treatment
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Penicillin has long been the drug of choice against S. pneumoniae,
though about a third of pneumococcal isolates are now penicillin
resistant.
Cephalosporin, erythromycin, clindamycin, vancomycin, or
fluoroquinolones are effective alternative treatments.
20. Mycoplasmal Pneumonia
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Mycoplasmal pneumonia is the leading type of pneumonia in children and
young adults, caused by Mycoplasma pneumoniae.
Pathogen and Virulence Factors
Mycoplasma pneumoniae is strictly aerobic and encapsulated.
Lack of cell walls, allowing them to have a variety of shapes.
Further, mycoplasmas have lipids in their cytoplasmic membranes called
sterols, a feature lacking in other prokaryotes.
Microbes that can grow and reproduce independently of other cells.
Their diameters range from 0.1 μm to 0.8 μm.
Originally, scientists thought mycoplasmas were viruses because their
small size and flexibility enable them to squeeze through the pores of
filters that were then commonly used to remove bacteria from solutions;
however, mycoplasmas contain both RNA and DNA, and they divide by
binary fission—traits that viruses lack.
21. Pathogenesis
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Attachment of M. pneumoniae to the base of cilia (p1,p30,p116)
Causes the cilia to stop action, and colonization eventually kills the
epithelial cells.
This interrupts the normal removal of mucus from the respiratory tract by
the ciliary escalator, allowing colonization by other bacteria and causing a
buildup of mucus that irritates the respiratory tract.
22. Signs and Symptoms
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Fever, malaise, headache, sore throat, and excessive sweating, are not typical
of other types of pneumonia; thus is called primary atypical pneumonia.
Primary atypical pneumonia may last for several weeks, but it is usually not
severe enough to require hospitalization or to cause death.
Because symptoms can be mild, the disease is also sometimes called walking
pneumonia
23. Epidemiology
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Nasal secretions spread M. pneumoniae among people in close contacts,
such as classmates, family members, and dormitory residents.
It is the most common form of pneumonia seen in high school and college
students.
Primary atypical pneumonia occurs throughout the year.
.
24. Laboratory diagnosis
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Diagnosis of primary atypical pneumonia is difficult because mycoplasmas
are small and difficult to detect in clinical specimens or tissue samples.
Further, mycoplasmas grow slowly in culture, requiring two to six weeks
before colonies are visible.
Colonies of M. pneumoniae have a grainy appearance when the bacteria
grow on solid surfaces.
Complement fixation, hemagglutination, and immunofluorescent tests
confirm a diagnosis, but such tests are nonspecific.
25. Treatment and prevention
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Treatment
Erythromycin
Prevention
Prevention is difficult because patients are often infected for long periods without signs or
symptoms.
Nevertheless, frequent handwashing and avoidance of contact with contaminated fomites can
limit the spread of the pathogen.
No vaccine against M. pneumonia is available.
26. Klebsiella pneumoniae
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Is an opportunistic pathogen that infects the respiratory systems of
humans and animals following inhalation.
It is a nonmotile, Gram-negative rod that produces a prominent capsule
giving Klebsiella colonies a mucoid appearance and protecting the
bacterium from phagocytosis.
K. pneumoniae may also be involved in meningitis, wound infections,
and urinary tract infections.
Pathogenesis
K. pneumoniae kills alveolar cells and often invades the blood, resulting in
bacteremia.
They release endotoxin, which can trigger shock and disseminated
intravascular coagulation, leading to death.
27. Signs and Symptoms
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Besides the common signs and symptoms of bacterial pneumonia—
coughing, fever, and chest pain
Often involves destruction of alveoli, resulting in the production of
thick, bloody sputum.
Mortality rates are higher than with pneumococcal or Mycoplasmal
pneumonias
29. Laboratory diagnosis
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Specimen: Sputum
Smear: Gram-negative rods
Culture: Large, mucoid, lactose-fermenting colonies on
MacConkey agar.
Treatment
Cephalosporin, and quinolones
Prevention
No vaccine is available.
Prevention involves good aseptic technique by health care workers.
30. Genus Bordetella
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Strictly aerobic, non-spore forming, non motile ,gram negative coccobacilli
that appears singly or in pairs ,Catalase +ve
Fastidious organism (require blood supplemented medium)
Bordetella species include
o B. pertussis, B. parapertussis, B. bronchoseptica,
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Bordetella pertussis is medically importance species
Bordetella pertussis, a highly communicable and important pathogen of
humans, causes whooping cough (pertussis).
Bordetella parapertussis :can cause a similar disease.
Bordetella bronchiseptica: causes diseases in animals, and only
occasionally causes respiratory disease and bacteremia in humans,
primarily in immunocompromised hosts.
32. Bordetella pertussis
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Virulence Factors
Various adhesins and toxins mediate the disease.
Two adhesins are filamentous hemagglutinin and pertussis toxin.
Four toxins are:
Pertussis toxin: interferes with ciliated epithelial cells’ metabolism,
resulting in increased mucus production. (Note that pertussis toxin is both
an adhesin and a toxin.)
Adenylate cyclase toxin: which triggers increased mucus production and
inhibits leukocyte movement, phagocytosis, and killing
Dermonecrotic toxin: which causes localized constriction and
hemorrhage of blood vessels, resulting in cell death and tissue destruction
Tracheal cytotoxin: which at low concentrations inhibits the movement of
cilia on respiratory cells.
33. Pathogenesis
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Via its adhesins, B. pertussis binds to cilia in the trachea and interferes with
their action
Filamentous hemagglutinin also binds to the cytoplasmic membranes of
neutrophils, initiating endocytosis of the bacterium.
B. pertussis survives within the phagocytes, evading the immune system.
Pertussis toxin causes infected cells to produce more receptors for
filamentous hemagglutinin, leading to further bacterial attachment.
Pertussis progresses through three phases
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After an incubation period of about 2 weeks, the "catarrhal stage"
develops, with mild coughing and sneezing.
During this stage, large numbers of organisms are sprayed in droplets, and
the patient is highly infectious but not very ill.
During the "paroxysmal" stage, the cough develops its explosive
character
This leads to rapid exhaustion and may be associated with vomiting
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The "whoop" and major complications occur predominantly in infants.
Major complications like encephalitis.
The white blood count is high (16–30 x103/µL), with an absolute lymphocytosis.
After 3-4 weeks the disease enters
Convalescent stage
Frequency and severity of the coughing gradually decrease
But secondary complications can occur
36. Lab diagnosis
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Specimens:
A saline nasal wash is the preferred specimen.
Culture
For the isolation of B. pertussis must be cultured as soon as possible
after collecting the sample.
A selective and enriched medium such as charcoal cephalexin
blood agar is recommended for the primary isolation of B. pertussis.
Small, smooth, and convex colonies
38. Mycobacterium tuberculosis
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General characteristics
Long, slender rods that are non motile
Strictly aerobic & non – sporulated
Cell walls contain unique class of very long-chain fatty acids (mycolic
acids).
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Cell walls contain mycolic acid, which is responsible for the unique
characteristics of this pathogen, including:
Slow growth
Protection from lysis when cells are phagocytized
Resistance to Gram staining, detergents, and many common
antimicrobial drugs, but not to heat or ultraviolet irradiation
40. Virulence Factors
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M.TB does not possess the classic bacterial virulence factors such as
toxins, capsules, and fimbriae.
However, a number of structural and physiological properties of the
bacterium are contributed to bacterial virulence and the pathology of
tuberculosis
The cell wall of M.TB is thick consisting of
Mycolic fatty acid 60% (long chain fatty acids) impermissive
to different substances
41. Epidemiology
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• The principal mode of transmission is person-to-person transmission by
inhalation of the aerosol or air-borne droplet that contains M.tb bacilli
A total of 1.6 million people died from TB in 2021 (including 187 000 people
with HIV). Worldwide.
TB is the 13th leading cause of death and the second leading infectious killer
after COVID-19 (above HIV and AIDS).
42. Progression of active tuberculosis infection
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A. Primary tuberculosis: occurs in a person who had no previous contact
with the organism.
1. Mycobacterium typically infects the respiratory tract via inhalation of respiratory
droplets from infected individuals.
2. Macrophages in alveoli phagocytize mycobacteria but are unable to digest them, in
part because the bacterium inhibits the fusion of lysosomes to endocytic vesicles.
3. Bacteria replicate freely within macrophages, gradually killing the phagocytes.
Bacteria released from dead macrophages are phagocytized by other macrophages
and beginning the new cycle
43. B. Disseminated tuberculosis
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Results when macrophages carry the pathogen via blood and lymph
nodes to other sites, including bone marrow, spleen, kidneys, spinal
cord, and brain, leading to the destruction of tissue and clinical illness; for
example,
tuberculous osteomyelitis, or
tuberculous meningitis
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C. Reactivation(secondary) of tuberculosis:
Reactivation is apparently caused by an impairment in immune status,
often associated with malnutrition, alcoholism, advanced age, or severe
stress.
Immunosuppressive medication or diseases such as diabetes and,
particularly, AIDS, are common preconditions.
45. Clinical Presentation
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• Weight loss
• Productive cough (For more than 15 days)
• Chest pain
• High fever
• Night sweating
• Blood stained sputum
• M.tuberclosis primarily cause pulmonary disease but it can affect any
organ of the body.
46. Laboratory identification:
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Specimens: Sputum, CSF, Biopsy
1. Microscopic examination
Ziehl Neelson staining / AFS
Specific
Rapid
Cheap
Once the Mycobacteria is stained with primary stain it can
not be decolorized with acid, so-named as acid-fast
bacteria.
47. Procedure
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1. Specked, purulent sputum for smear preparation (do not use
saliva)
2. Heat fix the dried smear,
Since M. tuberculosis can infect almost any organ in the body, the
laboratory could receive a variety of extrapulmonary specimens.
E.g. body fluid, tissue, pus, CSF, urine, etc.
3. Cover the smear with carbon-fuchsin stain
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4. Wash off the stain with clean water
5. Cover the smear with 3% acid alcohol for 5 minutes or until the
smear is sufficiently decolorized. i.e. pale pink.
6. Wash well with clean water
7. Cover the smear with methylene blue for 1 – 2 minutes.
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8. Wash off the stain with clean water.
9. Wipe the back of the slide clean, and place it in a draining
rack for the smear to air dry.
10. Examine the smear microscopically, using the 100x oil
immersion object.
50. Results
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• AFB............. Red, straight or slightly curved rods,
occurring single or in a small groups
• Cells......................................... Blue
• Background Material ……….. Blue
51. REPORTING OF SPUTUM SMEAR
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• When any definite red bacilli are seen report the smear as AFB positive
and give an indication of the number of bacteria present as follows:
1- 9 AFB /100 fields -------------- Report the exact number
10 – 100 AFB/100 fields ------------------ report +
1 – 10 AFB/field --------------------------- report ++
More than 10 AFB/field ------------------ report +++
When no AFB are seen after examining 300 fields report the smear as ‘
No AFB are seen’ do not report as “Negative” because organisms may
be present but not seen in those fields examined.
52. 2. Mycobacterial culture
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There are three formulations
a. Broth media: E.g. Middlebrook 7 H9 & 7H12
• Support growth of small inocula/enrichment media
• Growth is more rapid than solid media
53. B. Semi - solid agar media
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Include Middle brook 7H10 & 7H11 media
The media are used for:
Observing colony morphology (3-8 weeks)
Susceptibility testing
Selective media
54. C. Lowenstein - Jensen egg based media
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Contain defined glycerol, and complex organic substances (eg, fresh eggs or
egg yolks, potato flour, and other ingredients in various combinations).
Malachite green is included to inhibit other bacteria.
Is a solid media used as a selective media with added antibiotics.
Requires about 3 - 8 weeks for growth to occur
