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1. GRAM POSITIVE BACTERIA OF
MEDICAL IMPORTANCE
MEBO JOSEPH
-COTC MTWARA

2. Objectives
• Define gram positive bacteria
• List gram positive bacteria of medical
importance
• Describe basic structure of Gram positive
bacteria
• Describe characteristics of gram positive
bacteria of medical importance.
• Mention diseases they cause, diagnostic
techniques and drug of choice

3. Definition
Gram positive bacteria are bacteria which
appears blue when stained by gram staining
technique; reflecting the colour of primary
stain (either gentian violet, crystal violet or
methyl violet)

4. Examples of Gram positive bacteria of
medical importance
Examples of gram positive bacteria of medical
importance include:
 Staphylococci aureus
Staphylococcus epidemidis
Staphylococcus saprophyticus
Streptococci pyogenes
Streptococcus agalactiae
Streptococcal pneumoniae
Clostridium and Bacillus species

5. Basic structure of Gram positive
bacteria
Gram positive bacterial cell wall
• Thick peptidoglycan layer
• pentaglycin cross linkage.
• Teichoic acid: ribitol TA & glycerol TA
• All species have lipoteichoic acid.

6. Cont….
• The thick peptidoglycan retains the first dye
(crystal violet)
• Cells appear BLUE

7. GRAM POSITIVE CELL WALL
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8. Mohammed Laqqan
Theory behind Gram stain

9. Chapter 4
Gram positive cellwall

10. Gram-positive and gram-negative bacteria. A gram-positive bacterium has a thick layer of peptidoglycan
(filling the purple space) (left). A gram-negative bacterium has a thin peptidoglycan layer (single black
line) and an outer membrane (right). Structures in listed in parentheses are not found in all bacteria. Upon
cell division the membrane and peptidoglycan grow toward each other to form a division septum to
separate the daughter cells. ()
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11. Staphylococcus Bacteria of Medical
Importance
 General Characteristics:
• They are Gram positive cocci bacteria in clusters
• They are round shaped
• All are catalase positive (produce enzyme, catalase that
resists the effect of hydrogen peroxide.)
• They produce beta lactamase enzyme making it
resistant to penicillin
• Staphylococcus aureus is coagulase positive (they cause
clotting of plasma, hence they are resistant to
phagocytosis)

12. Grouping for Clinical Purposes
• 1. Coagulase positive Staphylococci
– Staphylococcus aureus
• 2. Coagulase negative Staphylococci
– Staphylococcus epidermidis
– Staphylococcus saprophyticus
12

13. Gram positive cocci
Catalase Test
Positive
Staphylococci
Negative
Streptococci
Coaggulase Test
Positive Negative
S.aureus Other Staphylococci
Novobiocin test
Positive Negative
S.haemolyticus
S.epidermidis
S.saprophytic
-us 13

14. Streptococcus
Staphylococcus
14

15. Staphylococci Bacteria: Disease they
Cause, Diagnosis and Drugs of Choice
Species Diseases they cause Lab diagnosis Drug of Choice
S. aureus •Abscesses
•Food poisoning
•Toxic shock
syndrome
•Surgical wound
infections
•Septicaemia
•Cellulitis
•Osteomyelitis
Specimens:
•Pus
•Blood
•Other body fluids
Techniques :
•Gram stain (pus
smear and other
body fluids )
•Culture
•Cloxacillin
•Penicillin
•Erythromycin
•Azithromycin
•Ceftriaxone
NB Depending on
sensitivity

16. Cont…
Species Diseases they
Cause
Lab diagnosis Drug of Choice
S. epidemidis •Neonatal sepsis
•Endocarditis on
prosthetic
(artificial) heart
valves
Specimens:
•Pus
•Blood
•Other body fluids
•Techniques :
•Gram stain (pus
smear and other
body fluids )
•Culture
•Vancomycin +
Rifampicin
NB Depending on
sensitivity

17. Cont….
Species Diseases they
Cause
Lab diagnosis Drug of Choice
S. Saprophyticus •Urinary tract
infection (UTI)
Specimens :
•Urine
•Blood
•High Vaginal Swab
(HVS)
Techniques :
•Culture
•Gram stain
•Penicillin G +
Gentamycin
Note: Depending
on sensitivity

18. 18

19. Staphylococcal osteomyelitis in a long bone
19

20. Toxic Shock Syndrome Toxin
• Superantigen
• Non-specific
binding of toxin to
receptors triggers
excessive immune
response
20

21. 21
Effects of
staphylococcal
toxins on skin

22. Staphylococcal scalded skin syndrome.
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23. •Toxic shock syndrome. A case of fatal infection
with cutaneous and soft-tissue involvement is
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24. Pustular impetigo. Note the vesicles at different stages of development,
including pus-filled vesicles on an erythematous base and dry, crusted lesions.
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25. Streptococci Bacteria of Medical
Importance
General Characteristics
• Gram positive cocci in short and long chains
• All are catalase negative

26. Classification of Streptococci
According to their level of haemolysis in blood
agar :
 Alpha haemolytic streptococci (partial hemolysis)
for example S. pneumoniae,
Beta haemolytic streptococci (complete
haemolysis)
for examples S. pyogenes

27. Cont….
According to lancefield grouping (based on
antigenic differences in their cell walls)
• Streptococci are arranged into lancefield
groups A to U denoting the antigenic mark.
Example of lancefield group A is S. pyogenes
and lancefield group B S. agalactiae
NB: Lancefield grouping does not apply to S.
pneumoniae

28. Streptococci Bacteria: Disease They
Cause, Diagnosis and Drugs of Choice
Species Diseases they
Cause
Lab diagnosis Drug of Choice
S. pyogenes •Pharyngitis (URTI)
•Cellulitis
•Immunological
diseases for
example:
Rheumatic fever
Glumerulonephri
tis
Specimens include:
•Throat swabs
•Urine
•Blood
Techniques:
•Culture
•Gram stain
•Serology of blood
sample (Antibody
antigen reaction)
•Penicillin G
•Erythromycin
•Azithromycin

29. Cont…
Species Diseases they
Cause
Lab diagnosis Drug of Choice
S. pneumoniae •Pneumonia
•Mengitis
•Otitis Media
•Sinusitis
Specimens include:
•Cerebral spinal
fluid (CSF)
•Pus
•Blood
Techniques :
•Gram stain
•Culture of CSF and
blood
•Penicillin G
•Chloramphenical
•Benzylpenicillin
•Cloxacillin
•Ceftriaxone

30. cont…
Species Diseases they
Cause
Lab diagnosis Drug of Choice
S. agactiae •Neonatal
Meningitis
•Sepsis
Specimens include:
•Cerebral spinal
fluid (CSF)
•Blood
Techniques :
•Gram stain
•Culture of CSF and
blood
•Penicillin G
•Chloramphenical
•Benzylpenicillin
•Cloxacillin
•Ceftriaxone

31. Hemolytic Patterns on Blood Agar

32. Hemolytic Patterns on Blood Agar
β-Hemolytic
Non-Hemolytic,
α-Hemolytic or
Rarely
β-Hemolytic
β-Hemolytic
Or
Non-Hemolytic

33. Figure 23-6 CAMP (Christie, Atkins, Munch-Petersen) reaction with group B streptococci. Group B streptococci produce a diffusible, heat-stable
protein (CAMP factor) that enhances β-hemolysis of Staphylococcus aureus. S. aureus (streaked from the top to the bottom of the agar plate)
produces sphingomyelinase C, which can bind to erythrocyte membranes. When exposed to the group B CAMP factor, the cells undergo hemolysis
(compare the two positive reactions of enhanced hemolysis, to the left of the S. aureus streak, with the two negative reactions to the right). (From
Howard BJ: Clinical and pathogenic microbiology, St Louis, 1987, Mosby.)
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34. Clinical Diseases - Streptococcus pyogenes

35. Clinical Diseases - Streptococcus pyogenes

40. Streptococcus agalactiae (Group B)
Early (< 1 Week) & Late (> 1 Week) Onset Neonatal Disease)

41. Clostridium Bacteria of Medical
Importance
 General Characteristics of Clostridium Bacteria
• Contain species of Gram positive anaerobic spore forming rods
• Few are aero tolerant (Aerobic)
• They are widely distributed in soil and in the gut of man and
animals
• They are saprophytic bacteria
• The spores are resistant to environmental conditions
• The major diseases associated with these species are tetanus,
gangrene, botulism food poisoning, and pseudo membranous colitis
• In each of these, the production of potent protein exotoxins is an
important course of pathology. Example clostridium tetani,
clostridium perfringens, clostridium botulinum, clostridium difficile

42. Morphological Feature (Bacilli, Drum Stick
Appearance) of Clostridium Species After Gram Stain

43. Characteristics of Clostridium Bacteria, Disease
they Cause, Diagnosis and Drugs of Choice
Species and
Characteristics
Diseases they
Cause
Lab diagnosis Drug of Choice
C. Tetani
•Round terminal
spores
•Strictly anaerobic
•Non-branching
rods
 Tetanus Specimens include:
•Pus
•Infected tissue
Techniques :
•Gram stain
•Culture
•Metronidazole
•Penicillin G
C. perfringens
•Facultative
anaerobes
•Spore forming, but
spores rarely seen
in infected
materials
•Gas gangrene from
infected ischemic
wound
•Food poisoning
Specimens include:
•Pus
•Infected tissue
Techniques :
•Gram stain
•Culture
•Penicillin
•Metronidazole
•Clindamycin

44. Cont…
Species and
Characteristics
Diseases they
Cause
Lab diagnosis Drug of Choice
C. botulinum
•Facultative
anaerobes
•Botulism Specimens include:
•Food sample
Techniques :
•Culture
•Penicillin
C. difficile
•Facultative
anaerobes
•Spore forming
Motile
•Gastroenteritis
•Pseudomembrano
us colitis
Specimens include:
•Stool
Techniques:
•Culture
•Vancomycin
•Metronidazole

45. Bacillus Species of Medical
Importance
General Characteristic of Bacillus Group
• Widely distributed in nature
• Most of them live as saprophytes in the soil, dust,
water and vegetation
• They are able to form resistant spores
• Their spores are centrally located
• Spores are formed only after the organism is shed
from the body

46. Cont….
• They are strictly aerobes
• Bacillus anthracis is a major pathogen of cattle,
sheep, goats, and pigs
• The bacilli are excreted in the feaces, urine, and
saliva of infected animals
• Bacilli can also be found in pastures which have
been contaminated by anthrax spores form
bodies of dead animals, and can remain the
source of infection for many years
• The size of the spore is the same as the size of the
width of the bacteria

47. Morphological features of Bacillus
Species after Gram Stain

48. Bacillus Bacteria, Disease they Cause,
Diagnosis and Drugs of Choice
Species and
Characteristics
Diseases they
Cause
Lab diagnosis Drug of Choice
B. anthracis •Cutaneous anthrax
•Enteric (intestinal)
anthrax
•Pulmonary anthrax
•Meningitis (Occurs
following
bacteraemia)
Specimens include:
•Pus
•Body fluid
•Blood
•Sputum
Techniques :
•Gram stain
•Culture
•Penicillin
•Streptomycin
•Cotrimoxazole

49. Key Points
• Gram positive bacteria are determined by Gram
staining when they retain the colour of primary
stain.
• There is a large group of Gram positive bacteria
but only some causes diseases to man. These
including staphylococcus species, streptococcus
species, clostridium species and bacillus species.
• Most of these bacteria are detected or diagnosed
by Gram staining of the direct sample however,
most of clostridium species requires culture of
the tissue or sample before staining.

50. Evaluation quiz
• What are Gram positive bacteria?
• What are the examples of Gram positive
organisms of medical importance?
• What are the morphological differences of
staphylococci and streptococci groups?
• What are the diseases caused by staphylococci
aureus?

51. medicines for health
51