Lec (9) Medical Microbiology Dr. Marwa Kadhim
Streptococcus Bacteria
1- Characters of Streptococci – Gram positive cocci , 1µm diameter, Chains or pairs ,usually capsulated, non motile, non spore forming , facultative anaerobes , fastidious and Catalase negative (Staphylococci are catalase positive )
2- Classification of Streptococci Streptococci can be classified according to: A- Oxygen requirements Anaerobic (Peptostreptococcus) Aerobic or facultative anaerobic (Streptococcus) B- Serology (Lanciefield Classification)
Streptococci
Lanciefield classification
Group A Group B Group C Group D Other groups
S. pyogenes S. agalactiae S. equisimitis Enterococcus (E-U) 1
Lec (9) Medical Microbiology Dr. Marwa Kadhim
C- Hemolysis on Blood Agar (BA)
– -hemolysis Partial hemolysis Green discoloration around the colonies e.g. non-groupable streptococci (S. pneumoniae & S. viridans) – -hemolysis Complete hemolysis Clear zone of hemolysis around the colonies e.g. Group A & B (S. pyogenes & S. agalactiae) – -hemolysis Streptococci No lysis -hemolysis -hemolysis -hemolysis e.g. Group D (Enterococcus spp)
1. Group A Streptococcus pyogenes: have some virulence factors like:
• Lipoteichoic acid (which allows adherence to target host cells).
• M-protein (which resists phagocytic engulfment).
• Tissue damaging toxins such as leukocidin (kills leukocytes) and erythrogenic toxin (damages endothelium).
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Lec (9) Medical Microbiology Dr. Marwa Kadhim
• Tissue damaging enzymes such as proteinase, hyaluronidase, and Dnase (thought to be especially important in infections of the skin and soft tissues as well as the rapid spread of the organism through the lymphatics).
2.Group B Streptococcus agalactiae
Streptococcus agalactiae belongs to Lancefield group B and is the only species that carries the group B antigen. Human pathogenic group B strains possess a polysaccharide capsule which appears to confer virulence. Nine capsular serotypes have been identified, antibodies to which confer type specific protection.
3. Distinctive Features of Enterococci
The Enterococci possess several distinctive features separating them from streptocooci: The enterococci grow in the presence of 6.5 percent NaCl, 40 percent bile, at pH 9.6, at 45°C and in 0.1 percent methylene blue. It survives heating at 60°C for 30 min, a feature distinguishing it from streptococci, and also grows within a wider range of temperatures (10-45°C). On MacConkey medium they produce deep pink colonies. Enterococci are PYRase test positive.
Treatment of streptococcus
If you’re diagnosed with strep throat, your doctor will prescribe an antibiotic to treat the infection. These medications inhibit the spread of bacteria and infections. Several types of antibiotics are available. However, penicillin and amoxicillin are the most common medications given for a strep infection.
Differentiation between -hemolytic streptococci
Hemolysis Bacitracin sensitivity CAMP test
S. pyogenes Susceptible Negative S. agalactiae Resistant Positive
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Lec (9) Medical Microbiology Dr. Marwa Kadhim
Differentiation between a-hemolytic streptococci
Hemolysis Optochin sensitivity Bile solubility Inulin Fermentation
S. pneumoniae Sensitive (≥ 14 mm) Soluble Not ferment
Viridans strep Resistant (≤13 mm) Insoluble Ferment
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Lec (9) Medical Microbiology Dr. Marwa Kadhim
Bacillus bacteria :
Introduction:
The family Bacillaceae consists of different types of bacteria. All of these are able to form endospores. The two clinically important genera are Bacillus (the aerobic and facultative anaerobic spore-formers) and Clostridium (the strict anaerobic spore-formers).
General characteristics of Bacillus
1. The genus Bacillus consists of aerobic bacilli forming heat resistant spores.
2. They are gram-positive.
3. They are generally motile with peritrichous flagella, (bacillus anthracis in non- motile).
4. Most form catalase and most produce acid but not gas from glucose.
5. The genus includes psychrophilic, mesophilic and thermophilic species.
6. Their salt tolerance varies from less than 2 to 25 percent NaCl.
Morphology
B. anthracis is one of the largest of pathogenic bacteria (3 to 8 by 1 to 1.3 μm) and is gram-positive, spore forming bacillus. In cultures, the bacilli are arranged end to end forming long chains. The ends of the bacilli are concave and somewhat swollen so that the chain of bacilli presents is ‘bamboo stick’ appearance.
The cell or even the entire chain is surrounded by a capsule which is polypeptide in nature, being composed of a polymer of D– glutamic acid.
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Lec (9) Medical Microbiology Dr. Marwa Kadhim
Cultural Characteristics
It is aerobe and facultative anaerobe. Temperature range for growth is 12-45°C (optimum 37°C). Optimum pH for growth is 7.4.
1. Nutrient agar: On nutrient agar, colonies are irregularly round, 2-3 mm in diameter, raised, opaque, grayish white, with a frosted glass appearance. The edge of the colony is composed of long, interlacing chains of bacilli; resembling ‘Medusa head appearance’ as in figure below.
Medusa head appearance colonies
2. Blood agar: Colonies on horse or sheep blood agar are non-hemolytic, but some strains produce a narrow zone of hemolysis
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Lec (9) Medical Microbiology Dr. Marwa Kadhim
Anthrax: anthrax is a zoonotic disease (it is transmitted between animals and human). It is mainly of animal disease and transmits from animals to human by different ways causing three types of anthrax disease depending on the site of entry; either cutaneous anthrax (the common and treatable type), pulmonary anthrax ( wool's sorter disease, fatal) or gastrointestinal anthrax (see the diagram below, please).
Ascoli test: it is serological, ring precipitin test using an extract of infected tissue and anthrax antiserum.
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Lec (9) Medical Microbiology Dr. Marwa Kadhim
Treatment of Bacillus anthracis
The standard treatment for anthrax is a 60-day course of an antibiotic, such as ciprofloxacin (Cipro) or doxycycline (Monodox, Vibramycin, others). Which single antibiotic or combination of antibiotics will be most effective for you depends on how you were infected with anthrax, your age, your overall health and other factors. Treatment is most effective when started as soon as possible.
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