number Done by Corrected by Doctor Hamed Al-Zoubi

Transcription

1 m number 10 Done by Mohammad Sinnokrot Corrected by Doctor Hamed Al-Zoubi

2 Gram Positive Cocci (Staphylococcus, Streptococcus and Enterococcus) Last lecture we talked about Staphylococcus, today we will talk about Streptococcus and Enterococcus. Streptococcus General features: *Facultative anaerobics. *Catalase-negative. *Grow in: A) Chains (Str. pyogenes) B) Pairs (Diplococci) like Str. pneumonia. Classification: according to: 1-patterns of haemolysis. 2-lancfield grouping. Pattern of haemolysis(according to the destruction of red blood cells on blood agar): 1- Alpha-haemolysis: Partial haemolysis turning blood to green, caused by hydrogen peroxide secreted from some bacteria. 2- Beta-haemolysis: Gives clear zone in the blood around the bacterium. 3- Gamma-haemolysis. (not required). One of the bases when classifying streptococci is determining the type of haemolysis. So, for diagnosis, we have to grow the bacteria sample on a blood agar to see the type of haemolysis. Another way to classify streptococci is Lancefield grouping, and it s based on the antigen that exist in the carbohydrates of the cell wall. These types of carbohydrates are symbolized as letters (A, B, C ). Why? For example, when we give bacteria for an animal his immunity system will produce antibodies according to the polysaccharides on the cell wall (according to the Antigens).

3 So, when we give bacteria from group A (antigen A), antibodies A will be produced, and when we give antigen B, antibodies B will be produced. Notes about the table: Only Pyogenic group is Beta-haemolytic, others are either alpha or none (Str.anginosus is sometimes an exception). Mitis group bacteria present in the mouth. That s why dentists years ago used to give their patients antibiotics against Mitis bacteria if they got bleeding in their mouth. Group A streptococcus (Streptococcus pyogenes) Virulence factors: 1. F-protein: a protein expressed on the surface of Str. Pyogenes, Interacts with host fibronectin (a matrix protein on eukaryotic cells), mediates attachment and internalization to host cells. 2. M proteins : these proteins can bind various plasma proteins of the host masking the bacterial surface with host proteins, giving the ability to

4 resist phagocytosis (anti-phagocytic, more than 100 serotypes of M protein). 3. Hyaluronic capsule: consist of hyaluronic acid which is also found in the host, that s why it has anti-phagocytic effect. 4. Hyaluronidase: Hyaluronidase degrades hyaluronic acid of the connective tissue that helps the bacteria to spread through our tissues. 5. Streptokinase: Fibrinolysis; the enzymatic breakdown of the fibrin in blood clots. It helps in spreading the infection. 6. DNAse enzymes: hydrolyse nucleic acids and allows the bacteria to escape from the DNA net released from phagocytes ( neutrophil extracellular traps ). * Dr. Hamed pointed out a difference between streptococcus and staphylococcus, which is some kinds of staphylococcus has an enzyme called coagulase, this enzyme makes clots in the blood of humans, the opposite of what streptokinase does. As a result, staphylococcus hide behind the clots so usually there is abscesses (for more details review the last lecture), but in case of fibrinolysis we re more likely to notice cellulitis (inflammation and redness of the skin) and swelling. 7. Streptolysin O and S: Lyse erythrocytes, polymorphonuclear leucocytes and platelets by forming pores in their cell membrane. a) Streptolysin S: is responsible for the β-haemolysis b) Streptolysin O: Intravenous injection into experimental animals causes death within seconds, as the result of an acute toxic action on the heart. 8. Pyrogenic toxins A, B, C: Super antigens, leads to tissue destruction, toxic shock-like syndrome (similar to toxic shock syndrome in staph). Clinical features: Noninvasive infections, Invasive infections & Immune sequalae. 1. Noninvasive infections: Noninvasive means that the bacteria do not get into the blood so it doesn t attack other organs and it remains at the same tissue.

5 Examples: a) Pharyngitis (sore throat), you can notice it as pustular (abscesses) and white dots. b) Skin impetigo. c) Scarlet fever, patient suffers from rash (picture B), fever, lymph nodes enlargement and the tongue might be affected (picture A). 2. Invasive infections: Involvement of the infection below the skin and the bacteria goes to blood, and these infections are worse than noninvasive infections. Examples: 1. Necrotizing fasciitis: Severe infection of fat and fascia. We should remove the damaged tissue (Debridement) to make sure the bacteria don t go to the blood because it spread out so fast. 2. Toxic shock syndrome. 3. Meningitis.

6 3. Immune sequalae: It s not caused by the bacteria itself, but by our immune system. Bacteria has antigenic structure against which our body will develop antibodies, sometimes these antigenic structures have some similarity with our tissues, so immune system attack the bacteria and develop antibodies against its antigen, since there is some similarity to some antigens on the tissues the antibodies will attack them and this is called autoimmune. Examples: 1. Rheumatic fever: Common between children and it usually follows pharyngitis and usually it affects the heart valves, joints and the brain. 2. Glomerulonephritis: Follows skin infections. Group B streptococcus (Streptococcus agalactiae) Characteristics: Facultative anaerobic, encapsulated gram-positive Produces a narrow zone of Beta-haemolysis on blood agar (Not as clear as group A). Part of normal flora of throat, colon, urethra and, importantly, in 10-40% of women vagina. (Group A rarely present as normal flora, B is common). Positive CAMP test. Enhanced Beta-haemolysis in the area of connection between the Group B streptococcus and the staphylococcus aureus in blood agar. Major virulence factors: 1. Haemolysin (including CAMP factor). 2. Polysaccharide capsule. 3. Peptidase and hyaluronidase enzymes. Clinical features: 1. Non-pregnancy associated infections (infects adults): *Pneumonia, UTIs, meningitis, infective endocarditis and soft tissue infection (multisystem involvement). *Sepsis and septic shock.

7 Usually in unhealthy people e.g. chronic illnesses, immunocompromised and elderly. 2. Pregnancy associated infections (infects neonate): Mode of transmission: Vertical (Ascending from vagina to placenta), during delivery and birth canal passage of the baby (intrapartum fever) or after birth We mentioned that group B streptococcus often present in vagina, so in case of a pregnant woman these bacteria can transport to the baby through the placenta and cause Chorioamnionitis (inflammation of the fetal membranes) or abortion, or it will transport to the baby during childbirth causing sepsis. If a diagnosis for a pregnant woman showed that she has Group B we give her and the child (after birth) antibiotics, usually penicillin, if patient is allergic use erythromycin or clindamycin. Slide were cancelled by the doctor but he talked a little about it as an extra information, you can go to the slide or the record to check it. Streptococcus pneumonia Member of the oropharyngeal flora of 5-70% of the population (according to age and time of year; common in winter months), with the highest isolation rate in children during. Diplococci, catalase negative. It mainly affects upper and lower respiratory tract, and may affect other sites such as the joints, peritoneum, endocardium, biliary tract and, in particular, the meninges. Virulence factors: 1. Capsule:

8 a) The capsular polysaccharide is a crucial virulence factor, and it s antigenic (make a special antigen for every type of capsule; more than 100 capsular serotype). b) Antiphagocytic and anticomplement. c) About 90% of cases of bacteraemic pneumococcal pneumonia and meningitis are caused by some 23 serotypes. 2. Lipoteichoic acid and choline binding proteins For adhesion. 3. IgA1 protease. IgA1 is an antibody produced by human immune system, and IgA1 protease cleaves IgA1 in the hinge region to stop it from working. 4. Pneumolysin (pore forming toxin). Pneumococci produce an intracellular membrane-damaging toxin known as pneumolysin, which is released by autolysis. Pneumolysin also suppresses organism-targeted immunity (Neutrophils, lymphocyte proliferation and immunoglobulin synthesis). Pneumolysin is immunogenic and might be suitable for a new pneumococcal vaccine. 5. Autolysin When this enzyme activated, the pneumococcal autolysin breaks the peptide cross-linking of the cell wall peptidoglycan, leading to lysis of the bacteria and increasing of septic and toxic outcome. When the bacteria suicide (Autolysis) because of lacking nutrients, it will enable the release of pneumolysin and release of peptidoglycans from cell wall leading to massive inflammatory response and sepsis to these peptidoglycan fragments. Source: normal flora of humans is the source of streptococcus pneumonia which are commonly found in the upper respiratory tract of healthy persons throughout the world. Occurrence: Pneumococcal infections are among the leading causes worldwide of illness and death for young children, persons who have underlying debilitating medical conditions and the elderly. 1 million deaths yearly worldwide. 6 million cases of otitis media in USA. The estimated global annual incidence is 1-3 per 1000 of the population, with a > 5% case fatality rate. Mode of Transmission:

9 Pneumococci are transmitted by aspiration or from person-to-person by droplet spread and indirectly through articles freshly soiled with respiratory discharges. Cultivation and identification: Using blood agar. Colonies of pneumococci are α-haemolytic and smooth dome shaped. During prolonged incubation, autolysis of bacteria within the flat pneumococcal colonies results in a typical subsidence of the center ('draughtsman colonies'). How Streptococcus pneumonia appears in blood agar. Optochin sensitive and bile (10% sodium sodium deoxycholate) soluble. You can detect the capsule using antibodies by mixing a suspension of pneumococci with type-specific antisera increases the visibility of the capsule in the microscope, and is the basis of the quellung reaction or capsular swelling test. And you can detect the capsule by the addition of India ink to a suspension of pneumococci shows the presence of the capsule as a clear halo around the organisms. Treatment:

10 You can use Penicillin (I.V benzylpenicillin (penicillin G) or oral phenoxymethylpenicillin (penicillin V)). But try to use other options since the resistance increase against penicillin and mediated by PBP alteration you can use ceftriaxone, vancomycin/clindamycin. Also consider other option in case of hypersensitivity to penicillin, you can use erythromycin or clindamycin, but resistance to erythromycin occurs and is common in some countries. Vaccines: They are ways of protection not treatment. There are 2 types: 1- Non-conjugated: Taken from the 23 serotypes to capsule (we talked about above) and made a vaccine from them because they are common, but you can t give these vaccines to children under 2 years; because their immune system is not matured enough to memorize these antigens. 2- Protein conjugated: They are made for children under 2 years because we can t give them the previous type, so another type of vaccines has been made which the polysaccharide of the capsule in attached with a protein, this vaccine is administered and the immune system will produce memory cells for the proteins attached and these cells last longer than if proteins are not attached (more than 10 years). Only 13 types of protein conjugated vaccines has been made (7-11 according to the slides) Enterococcus Is part of the normal flora of the colon (that s why it s called entero). The species most commonly associated with human disease are E. faecalis and E. faecium. The diseases with which they are associated are: urinary tract infection, infective endocarditis, biliary tract infections, suppurative abdominal lesions, peritonitis. Bacteraemia carries a poor prognosis as it often occurs in patients with major underlying pathology and in those who are immunocompromised.