Gram Positive Bacteria

GRAM POSITIVE BACTERIA OF MEDICAL IMPORTANCE

Objectives

• Define gram positive bacteria
• List gram positive bacteria of medical importance
• Identify characteristic appearance of gram positive bacteria of ocular
• Describe basic structure of Gram-positive bacteria
• Explain diseases caused by gram positive bacteria of ocular importance.

Outline drugs of choice of treating disaeses caused by gram positive of ocular importance

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 aureus
• Streptococci pneumoniae
• Staphylococci epidermidis
• Streptococcus pyogenes
• Corynebacteria spp

Clostridium tetani

Note: Most gram positive bacterial appear cocci(sphere) in shape and bacilli or coccobacilli

General chracterastic of gram positive

• Thick peptidoglycan cell wall: provides rigidity and retains stain
• No outer membrane : Unlike gram negative bacteria
• Teichoic and lipoteichoic acids: contribute to adhesion and inflammation

Staining property: retain crystal violet stain appear purple/blue under microscopy Virulence factors (ocular relevance) : exotoxin can damage ocular tissues, enzymes eg (coagulase,hyaluronidase): Aid tissue invasion Antibiotic sensitivity. Generally more susceptible to antibiotics than gram negative organisms, but increasing resistance eg MRSA)is a concern. Some require specific agent eg vancomycin for resistant strains

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

The thick peptidoglycan retains the first dye (crystal violet)

Cells appear BLUE

GRAM POSITIVE CELL WALL

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Mohammed Laqqan

Theory behind Gram stain

Chapter 4

Gram positive cellwall

Gram Positive Bacteria

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. () Downloaded from: StudentConsult (on 8 April 2008 11:45 AM)

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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

• 1. Coagulase positive Staphylococci
• Staphylococcus aureus
• 2. 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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Streptococcus

• Staphylococcus

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EYE DISEASES CAUSED BY GRM POSITIVE BACTERIA OF OCULAR IMPORTAMNCE

• Species
• Diseases they cause
• Drug of Choice

Staphlococcus Aureus

• Streptococcus pneumoniae

Staphlococcus Aureus

• Streptococcus pneumoniae
• Conjuctivitis (bacteria)
• Blepharitis
• Keratitis(corneal ulcer)
• Chloramphenicol eyes drop
• Gentamicin drops
• Erythromycin ointment
• Bacitracin ointment
• Erythromycin ointment
• Vancomycin for severe gram positive, cefazolin eye drop

Fluoroquinolone eye drops(ciproflloxacin

EYE DISEASES CAUSED BY GRM POSITIVE BACTERIA OF OCULAR IMPORTAMNCE CONT

• Species
• Diseases they Cause
• Drug of Choice

Staphlococcus. Epidemidis

Staphlococcus. Aureus

• Streptococcus pyogene
• Staphylococcus aureus
• Endophthalmitis (serous intraocular infection)
• Orbital cellure

Intravitreal Vancomycin

• IV vancomycin

Ceftriaxore

EYE DISEASES CAUSED BY GRM POSITIVE BACTERIA OF OCULAR IMPORTAMNCE CONT

• Species
• Diseases they Cause
• Lab diagnosis
• Drug of Choice
• Staphlococcus aureus.
• Staphylococcus aureus
• Streptococcus pneumoniae
• Hordeolum (stye)
• Dacryocystitis
• Specimens :
• Urine
• Blood
• High Vaginal Swab (HVS)
• Techniques :
• Culture
• Gram stain
• Erythromycin ointment
• Bacitracin
• Systemic antibiotics like :Amoxicillin

cloxacillin

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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

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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Gram Positive Bacteria

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

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
• Some 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

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

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

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.

medicines for health

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