Lecture 6Dr. Ismail I. Daood

Medical Microbiology

GENUS : Streptococcus :

The Streptococcus are gram-positive spherical bacteria that general characteristically arranged form pairs or chains of varying length, during growth . The genus Streptococcus includes a large number of species some of them are pathogens, and others are normal flora of the Oropharynx and Gastrointestinal, Urinal tract , skin ,etc.

Diseases associated with Streptococci range from dental plaque and trivial skin infections to life threatening complications such as :

Necrotizingfasciitis, Toxic shock, Rheumatic fever, and Glomerulonephritis.

Streptococcus are gram positive cocci form linear chains of varying length, non motile, non sporing. They require enriched media with blood, serum or chocolate agar. The most pathogenic type for human :

1 -Streptococcus pyogenes.

2 -Streptococcus pneumoniae

3 - Streptococcusviridansor viridans streptococcus include ( S

mitis , S mutans , sanguis ,and others ).

4 – Streptococcusbovis .

5 – Streptococcusagalactiae

Classification :

1. Depend on oxygen (O2) requirement :

a. aerobes

b. obligate anaerobe c. facultative anaerobes.

2. Depend on colony morphology and the hemolytic reactions on

blood agar :

a. Alpha () hemolytic Streptococci incomplete haemolysis which

green appearance a zone of greenish around the colony e.g. Strep.

viridans .

b. Beta () hemolytic Streptococci complete haemolysis which

produces a clear colures zone of haemolysis in blood agar, e.g.,

Streptococcus pyogenes (group A & B).

c. Gamma hemolytic Streptococci. Non-hemolytic.

3. Serological specificity of the cell wall or capsular antigens such as

classify S pneumoniae into over 90 types .

4. Biological reaction and resistance to physical and chemical factors Biochemical reaction :

Biochemical tests include sugar fermentation , tests for the presence of enzymes . Streptococcus are non-fermented lactose, but fermented glucose, maltose producing acid but no gas. Manitol fermented by Strep. pyogenes but Strep. viridans not ferment .Catalase negative, don’t liquefy gelatin, capsule (+ve ).

Pathogenicity :

Most streptococci that contain the group A antigen Streptococcus pyogenes , It is prototypical human pathogen, produces large (1 cm in diameter ) zones of beta haemolysis around colonies It is more invasion and immunologic disorders and produce septicemia , respiratory infections, scarlet fever, toxic shock syndrome ,skin infection, abses, acute rheumatic fever, endocarditis, glomerulonephritis, arthritis, meningitides.

Virulence factors of Streptococcus :

  1. Protein M (antiphagocytic and anticomplement)
  2. Protein F (for adhesion to bind to pharyngeal epithelial cells causes disease.
  3. Protein G (bind IgG preventing phagocytosis)
  4. Substance C (became to development diseases ).
  5. Exotoxins ( Exotoxin A & B and cardiohepatic toxin) causes heart and liver failure.
  6. Hemolysins as (Striptolysin O & S).

7. Capsule (mucopolysuccharids ) most group A to impede

phagocytosis

Laboratory diagnosis :

a. Rapid diagnostic test. ( specimens, smears and swab ).

b.Culture and isolation by bacteriological investigation

c. haemolysis pattern and bacitracin and optochin sensitivity.

Strep. pyogenes( +ve ) to bacitracin

Strep. pneumoniae (+ve) to optochin.

d. Total andDifferential leucocytes count.

e. ESR test

f. Serological and Antigen detection test.( antistreptolysin ) ASOtiter.

Treatment :

Penicillin G but resistant strain as culture sensitivity. Third generation cephalosporin's, vancomycin, riphampin, new generation as azithromycin or clarithromysin.

Gram-Negative Cocci : Neisseriaceae :

General characteristic :

The family Neisseriaceae includes Neisseria and other genus and several species . Neisseria are Gram-negative cocci,that usually occur in pairs . N gonorrhoeae (gonococci ) and N meningitidis

(meningococcoi ) are pathogenic for human , some Neisseriae are normal inhabitants of the human respiratory tract . ranging from 0.6-1.0 m in diameter, kidney-shaped seen as Diplococci, nonmotile, capsulated (+ve), aerobic, oxidase ( +ve ), catalase ( +ve ), individual cocci are kidney-shaped , complex growth requirement ; grow best on chocolate agar as heated blood , hemin , under increased carbon dioxide CO25% optimum temperature at 37oC. Fermented carbohydrate .

Classification :

The Neisseria genus contains two important pathogenic species :

1.Neisseria meningitidis (Meningococcoi) causes cerebrospinal

meningitis in human.

  1. Neisseria gonorrhoeae (gonococcus) causes gonorrhoeae in human.
  2. Other Commensal species non-pathogenic for human as N. pharynges, N sicca, N mucosa

1. Neisseria meningitides :

Neisseria meningitidesis determinants as pathogenicity because it

hasvirulencefactors :

  1. Adhesion factors : Fimbriae and pili.
  2. Capsule.
  3. Endotoxin ,Lipopolysaccharide (LPS).
  4. IgA proteases, which cleave IgA protect bacteria against the effects of secretary IgA.

Pathogenesis :

N. meningitidis is causes meningitis in children, older children, adolescents and adults by inhalation of contaminated droplets, clinical disease and symptoms include, severe headache, fever, stiff neck, vomiting, neurologic signs, myalgias and athralgias, mental status and coma, hypotension, multiple organ failure and septic shock. Also causes pharynitis, pneumonia.

2. Neisseria gonorrhoeae :

Neisseria gonorrhoeaeisdeterminants as pathogenicity because it has Virulencefactors :

  1. pili and fimbriae for adherence to host cells.
  2. Outer membrane proteins (1 and 11)
  3. Endotoxin less toxic than N. meningitides
  4. Capsule
  5. Peptidoglycan
  6. Enzymes, IgA protease and Beta-lactamase.

Pathogenesis :

N. gonorrhoeae is adhere to the surface of epithelial cells by adhesion and invasion those of urethra, genital tract, rectum and throat clout disease and causes arthritis, cevicitis, pelvic inflammatory disease, anorectal gonorrhea.

Lab. Diagnosis :

a- Identification local disease by swab examine the bacteria

microscopy directly.

b- Culture and isolation

c- Serology test

d- Direct immunofluorescence (using fluorescent ant-N.

gonorrhoeae Antibodies).

Treatment :

Combination of drugs common STD,Ceftriaxone, Cefixim as oral

dose, Cefotaxime, Amoxicillin, Ciprofloxacin.

Moraxella :

Moraxella catarrhalis was named Branhamella catarrhalis and before that Neisseriacatarrhalisthisorganism causative agent is ranked third behind H. influenzae and S. pneumonia causes otitis media, sinusitis, pneumonia , conjunctivitis , bronchitis, tonsillitis bacteremia and septicemia. It is cocci, diplococci gram ( -ve ), oxidase-positive, DNase ( +ve), catalase (+ve) aerobic, colonize in oral and nose. Most strains of Mcatarrhalis from clinically significant infections produce Beta lactamase .

Gram-Positive Rods Bacteria / (Bacilli) :

The gram-positive rods can be classified as either non-spore forming or spore forming. Clostridium and bacillus are both spore-forming. Clostridium are anaerobic and bacillus are aerobic.

Anaerobic Clostridium :

The genus clostridium include over 50 species gram-positive ,spore forming bacilli . most common pathogens :

  1. Clostridium perfringens (welchii)
  2. Clostridium tetani
  3. Clostridium botulinum
  4. Clostridium difficile.

1. Clostridium perfringens :

Clostridium perfringens causes ( most associated) with gas gangrene. There are at least 12 different soluble antigens which there are five types from A to E distinguished by the various of toxins produce. All types produce the alpha toxin have varying activities , including tissue necrosis and haemolysis . Also associated with food poisoning. It is gram positive, bacillus, about 4-6 m by 1 m, capsulate when seen in tissue, anaerobe, grows rapidly at 37oC in cooked meat broth and even more at up to 45oC. spore resist forming, grow on blood agar colonies are large, round, smooth regular with complete haemolysis, non motile.

Pathogenicity :

Cl. perfringens produces 12 exotoxins and enterotoxin .Gas gangrene occurs when a soft tissue wound is contaminated by Cl. Perfringens ,as occurs in trauma , septic abortion , and war wounds .Bacteremia associated with Cl. Perfringens can be rapidly fatal.

a- Exotoxins (-toxin, -toxin, E toxin and T-toxin). All of toxin are

lethal.

c- Enterotoxin (inhibit glucose transport, causes protein loss, and

damages the epithelium).

b- Causes skin and soft tissue infections, wounds infection as exogenous contamination occur (e.g., from soil, water or sewage) and endogenous contamination cause infections most are secondary to abdominal surgery or trauma which allow contamination of tissues with fecal or genital tract secretions. Localized cellulites, enteritis necrotic, gas gangrene (myonecrosis) .Food poisoning (type A spores ).

Clostridium tetani :

1