Overview of the major bacterial pathogens The major bacterial pathogens are presented in this table:

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1 Practical Microbiology 30/11/2018 University of Sulaimani college of Pharmacy Year2 Lab. 5: Overview of the major bacterial pathogens The major bacterial pathogens are presented in this table: Major Bacterial Pathogens. Type of Organism Genus Readily Gram-stained Gram-positive cocci Gram-negative cocci Gram-positive rods Staphylococcus, Streptococcus, Enterococcus Neisseria Corynebacterium, Listeria, Bacillus, Clostridium, Actinomyces, Nocardia Gram-negative rods Enteric tract organisms Pathogenic inside and outside tract Pathogenic primarily inside tract Pathogenic outside tract Respiratory tract organisms Organisms from animal sources Escherichia, Salmonella Shigella, Vibrio, Campylobacter, Helicobacter Klebsiella-Enterobacter-Serratia group, Pseudomonas, Proteus- Providencia-Morganella group, Bacteroides Haemophilus, Legionella, Bordetella Brucella, Francisella, Pasteurella, Yersinia Not readily Gram-stained Not obligate intracellular parasites Obligate intracellular parasites Mycobacterium, Mycoplasma, Treponema, Leptospira Chlamydia, Rickettsia 1

2 Gram Positive Cocci: There are two medically important genera of gram-positive cocci: Staphylococcus and Streptococcus. Both of them are gram-positive cocci, but they are distinguished by two main criteria. 1. Microscopically: staphylococci appear in grapelike clusters, whereas streptococci are in chains. 2. Biochemically: staphylococci produce catalase (i.e., they degrade hydrogen peroxide), whereas streptococci do not. (Staphylococci) Staphylococci arranged in grape-like clusters,some single cells, pairs, and short chains are also seen.staphylococci grow best aerobically but are facultatively anaerobic, staphylococci produce catalase. Coagulase positive staphylococci: S. aureus, Coagulase negative staphylococci: S. epidermidis, and S. saprophyticus. Medically important Staphyllococci species: Species Coagulase Production Typical Hemolysis Important Features1 Typical Disease S. aureus S. epidermidis S. saprophyticus Beta Protein A on surface None Sensitive to novobiocin None Resistant to novobiocin Abscess, food poisoning, toxic shock syndrome Infection of prosthetic heart valves and hips; common member of skin flora Urinary tract infection Isolation and identification of staphylococci 1. Gram stain: All staphylococci appear as gram-positive cocci, usually in irregular, often grape-like clusters. 2

3 2. Colonial Morphology: Colonies of Staphylococcus on sheep blood agar present themselves as smooth, yellow, white or off-white colonies somewhere in the area of 1 to 2 mm in diameter. S. aureus: On blood agar plates, colonies of Staphylococcus aureus are frequently surrounded by zones of clear beta hemolysis and produce yellow to golden color. S. epidermidis, and S. saprophyticus: non-pigmented, non-hemolytic colonies on blood agar. 3. Novobiocin test : The novobiocin test is used to differentiate coagulase negative staphylococci.most frequently it is used to identify the novobiocin -resistant Staphylococcus saprophyticus. novobiocin Disk Test :A novobiocin-resistant (R) organism is on the left; a susceptible (S) organism is on the right. 3

4 4. Catalase Test: The catalase test is important in distinguishing streptococci (catalase-negative), staphylococci which are catalase positive. The test is performed by flooding an agar slant or broth culture with several drops of 3% hydrogen peroxide. Catalase-positive cultures bubble at once. The test should not be done on blood agar because blood itself will produce bubbles. H2O2 H2O O2 (gas bubbles) This test can be performed on a micro scope slide or by adding hydrogen peroxide directly to the medium containing bacterial growth Catalase Slide Test: Visible bubble production indicates a positive result in the catalase slide test. A catalase-positive organism is on the left. A catalase- negative organism is on the right Catalase Tube Test: The catalase test also may be performed on an agar slant. A catalase-positive organism is on the left. A catalase-negative organism is on the right. 5. Production of coagulase: Production of coagulase is the most important test used to distinguish S. aureus from other staphylococci.the coagulase converts soluble fibrinogen in the plasma into insoluble fibrin Coagulase works in conjunction with normal plasma components to form protective fibrin barriers around individual bacterial cells or groups of cells, shielding them from phagocytosis and other types of attack. 4

5 Main characteristics of Staphylococcus spp. : Test Hemolysis Pigment Staphylococcus aureus Usually beta Often golden-yellow Staphylococcus epidermidis Usually none Usually white Staphylococcus saprophyticus Usually none Usually white Novobiocin test Sensitive Sensitive Resistant Catalase Coagulase Mannitol salt agar or MSA: Mannitol salt agar or MSA is a commonly used selective and differential growth medium in microbiology. It is used for the selective isolation of pathogenic staphylococcus species.if an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red (alkaline) in the agar to turn yellow (acid). *Mannitol fermentors such as S. aureus appear as yellow colonies with yellow zones in the media. *Non-mannitol fermentors such as S. epidermidis, if present, will have clear pink to red colonies with no yellow color change in the medium. Thanks Chiman H. Fattah MSc.Medical Microbiology/Mycology 5