Microbiology, Parasitology & Entomology – GRAM POSITIVE BACTERIA
Read the complete lesson in an organized slide-by-slide format. This topic contains 53 learning sections from the source presentation.
LESSON CONTENTS — 53 SECTIONS
GRAM POSITIVE BACTERIA OF MEDICAL IMPORTANCE
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
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)
Examples of Gram-positive bacteria of medical importance
Examples of gram-positive bacteria of medical importance include
Staphylococci spp
Streptococci spp
Corynebacterium spp
Listeria spp
Pneumococcus spp
Bacillus species
Clostridium spp
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.
Cytoplasmic membrane (composed of phospholipid bilayer )
Polysaccharides and proteins on cell wall
Structure of peptidoglycan
Cont….
The thick peptidoglycan retains the first dye (crystal violet)
Cells appear BLUE
GRAM POSITIVE CELL WALL
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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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Staphylococcus Bacteria of Medical Importance
General Characteristics
They are Gram positive cocci and appear in clusters
They are round shaped
All are catalase positive (produce catalase enzyme and resist the effect of hydrogen peroxide by producing catalase enzymes that breaks down H202.)
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)
Grouping for Clinical Purposes
Coagulase positive Staphylococci
Staphylococcus aureus
Coagulase negative Staphylococci
Staphylococcus epidermidis
Staphylococcus saprophyticus
Staphylococcus hemolyticus
This categorizes based on the presence and absence of Coagulase enzyme
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Gram positive cocci
Catalase Test
Positive
Staphylococci
Negative
Streptococci
Coagulase Test
Positive
Negative
S.aureus
Other Staphylococci
Novobiocin test
Positive
Negative
S.haemolyticus
S.epidermidis
S.saprophytic-us
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Staphylococci Bacteria: Disease they Cause, Diagnosis and Drugs of Choice
Species
Diseases they cause
Lab diagnosis
Drug of Choice
aureus
Abscesses
Food poisoning
Toxic shock syndrome
Surgical wound infections
Septicaemia
Cellulitis
Osteomyelitis
Specimens
Pus
Blood
Other body fluids
Techniques
Gram stain
Culture method
Cloxacillin
Penicillin
Erythromycin
Azithromycin
Ceftriaxone
NB Depending on sensitivity
Staphylococci Bacteria: Disease they Cause, Diagnosis and Drugs of Choice Cont…
Species
Diseases they Cause
Lab diagnosis
Drug of Choice
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
Staphylococci Bacteria: Disease they Cause, Diagnosis and Drugs of Choice.
Species
Diseases they Cause
Lab diagnosis
Drug of Choice
Saprophyticus
Urinary tract infection (UTI)
Specimens
Urine
Blood
High Vaginal Swab (HVS)
Techniques
Culture
Gram stain
Penicillin G + Gentamycin
Toxic Shock Syndrome Toxin
Superantigen
Non-specific binding of toxin to receptors triggers excessive immune response
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Effects of staphylococcal toxins on skin
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Effects of staphylococcal toxins on skin
Staphylococcal scalded skin syndrome.
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Toxic shock syndrome. A case of fatal infection with cutaneous and soft-tissue involvement is shown.
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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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Streptococci Bacteria of Medical Importance
General Characteristics
Gram positive cocci that appear in short or long chains
All are catalase negative
Classification of Streptococci
According to their level of haemolysis in blood agar
Alpha haemolytic streptococci (partial haemolysis)
for example, S. pneumoniae,
Beta haemolytic streptococci (complete haemolysis)
for examples S. pyogenes
Gamma haemoritic streptococcus (no hemolysis on blood agar)
Hemolytic Patterns on Blood Agar
Hemolytic Patterns on Blood Agar
Classification basing on Lancefield grouping
Is a classification system of streptococcal based on the type of carbohydrate antigen ( c-substance) present on the bacterial cell wall
Streptococci are arranged into Lancefield groups A to V denoting the antigenic mark.
Example
lancefield group A is S. pyogenes an
lancefield group B S. agalactiae
Lancefield grouping does not apply to S. pneumoniae because lancified grouping deals with beta hemolysis streptococci and S.pneumoniae has different antigenic structure on its cell
Streptococci Bacteria: Disease They Cause, Diagnosis and Drugs of Choice
Species
Diseases they Cause
Lab diagnosis
Drug of Choice
pyogenes
Pharyngitis (URTI)
Cellulitis
Immunological diseases for example
Rheumatic fever
Glumerulonephritis
Specimens include
Throat swabs
Urine
Blood
Techniques
Culture
Gram stain
Serology of blood sample (Antibody antigen reaction)
Penicillin G
Erythromycin
Azithromycin
Cont…
Species
Diseases they Cause
Lab diagnosis
Drug of Choice
pneumoniae
Pneumonia
Mengitis
Otitis Media
Sinusitis
Specimens include
Cerebral spinal fluid (CSF)
Pus
Blood
Sputum
Techniques
Gram stain
Culture
Penicillin G
Chloramphenical
Benzylpenicillin
Cloxacillin
Ceftriaxone
cont…
Species
Diseases they Cause
Lab diagnosis
Drug of Choice
agalactiae
Neonatal meningitis
Sepsis
Specimens include
Cerebral spinal fluid (CSF)
Blood
Techniques
Gram stain
Culture of CSF and blood
Penicillin G
Chloramphenicol
Benzylpenicillin
Cloxacillin
Ceftriaxone
Clinical Diseases – Streptococcus pyogenes
Clinical Diseases – Streptococcus pyogenes
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Slide 37
Slide 38
Slide 39
Streptococcus agalactiae (Group B)Early (< 1 Week) & Late (> 1 Week) Onset Neonatal Disease)
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,gas 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
Morphological Feature (Bacilli, Drum Stick Appearance) of Clostridium Species After Gram Stain
Clostridium spp under gram reaction
Characteristics of Clostridium Bacteria, Disease they Cause, Diagnosis and Drugs of Choice
Species and Characteristics
Diseases they Cause
Lab diagnosis
Drug of Choice
Tetani
Round terminal spores
Strictly anaerobic
Non-branching rods
Tetanus
Specimens include
Pus
Infected tissue
Techniques
Gram stain
Culture
Metronidazole
Penicillin G
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
Cont…
Species and Characteristics
Diseases they Cause
Lab diagnosis
Drug of Choice
botulinum
Facultative anaerobes
Botulism
Specimens include
Food sample
Stool sample
Techniques
Culture
Gram stain
Penicillin
difficile
Facultative anaerobes
Spore forming
Motile
Gastroenteritis
Pseudomembranous colitis
Specimens include
Stool
Techniques
Culture
Gram stain
Vancomycin
Metronidazole
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
Cont….
They are strictly aerobes
Bacillus anthracis is a major pathogen of cattle, sheep, goats, and pigs
The bacilli are excreted in the faeces, 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
Morphological features of Bacillus Species after Gram Stain
Bacillus morphology under gram stain
Bacillus Bacteria, Disease they Cause, Diagnosis and Drugs of Choice
Species and Characteristics
Diseases they Cause
Lab diagnosis
Drug of Choice
anthracis
Cutaneous anthrax
Enteric (intestinal) anthrax
Pulmonary anthrax
Meningitis (Occurs following bacteraemia)
Injection anthrax (rare)
Specimens include
Pus
Blood
Sputum
CSF
Other body fluids
Techniques
Gram stain
Culture
Penicillin
Streptomycin
Cotrimoxazole
BACTERIA
SPECIES
STAPHYLOCOCCUS
STAPHYLOCOCCUS AUREUS
STAPHYLOCOCCUS SAPROPHYITCUS
STAPHYLOCOCCUS EPIDERMIDIS
STAPHYLOCOCCUS HEMOLYTCUS
STREPTOCOCCUS
STREPTOCOCCUS PYOGENUS
STREPTOOCOCCUS AGALACTICIAE
STREPTOCOCCUS PNEOUMONIAE
STREPTOCOCCUS VIRIDANS GROUP
CLOSTRIDIUM
CLOSTRIDIAM TETANI
CLOSTRIDIAM BOTULINUM
CLOSTRIDIAM PERFRINGENS
CLOSTRIDIAM DIFFICILE
BACILLUS
BACILLUS ANTHRAX
BACILLUS CEREUS
BACILLUS SUBTILIS
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.
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