number Done by Corrected by Doctor Hamed Al-Zoubi

Transcription

1 number 9 Done by Mohammed Al askar & Muhammed Alajmi Corrected by مها أبو عجمية Doctor Hamed Al-Zoubi 1

2 Gram positive cocci There are 3 types of gram positive cocci :- 1- Staphylococcus ( what we are going to discuss ) 2- Streptococcus 3- Enterococcus. **coccus = spherical Staphylococcus o basic characteristics and distinctive features: 1. Facultative anaerobic ( as we mentioned in sheet 4 ) 2. Catalase-Positive ما ي ميزها عن غيرها meaning that being catalasepositive is a unique feature of Staphylococcus, because Streptococci and Enterococci are both Catalase Negative. 3. Resistant to dry conditions and high salt concentrations 4. It is part of normal flora on skin and upper respiratory tract of human. And also found in animals ( animals can transfer it ) 5. Staphylococcus aureus ( type of staphylococcus ) is present in the nose of 30% of healthy people as a normal flora but can cause infections where there is lowered host resistance o Sources of infection :- 1- Healthy carriers 2- Animals ( Mastitis from the milk ), 3- Infected lesions ( e.g. wounds, suppurations l) can be transferred by food - NOTE: Suppuration is the process of pus formation/discharging- o -You should know that Staphylococcus: o Spread from colonized sites ( e.g. Skin ) occurs by hand, clothing, dust and desquamation ( the dead layers of skin). o The major pathogen within the genus, Staphylococcus aureus : which is coagulase positive ( coagulase = enzyme that is produced by Bacteria and cause clotting in human plasma. 2

3 o There are at least 30 species of staphylococci, all of which lack this enzyme (coagulase). These coagulase-negative staphylococci (CNS): o Skin commensal, part of the normal flora of the skin. o Staphylococcus Coagulase-Negative are opportunistic pathogens that cause infections by forming biofilms, colonizing prostheses (biomedical devices e.g. urinary catheters and pacemaker ) or foreign bodies that grow on these devices. Here are two types of CNS :- 1- Staph. epidermidis : related to the upper part of the skin 2- Staph. saprophyticus : it causes urinary tract infections. (Mainly in pregnant women) **Both are catalase-positive and coagulase-negative Staphylococcus aureus infections 3

4 Examples on Staphylococcus aureus Infections: *Bloodstream infections:- - Septicemia causes sepsis or septic shock - Bacteremia ** Sinusitis, Conjuctivitis, meningitis **دقيقه كنتاكي عند الباب نشوفكم الصفحه اللي بعدها** **عافيه على قلبي...نكمل** *first picture: carbuncle (hair follicles infection) A boil (furuncle) is an infection of a hair follicle. (Furunculosis) A carbuncle is an infection of a group of hair follicles *second picture: Impetigo Impetigo: an infection in skin, blistering, causing vesicles/ follicles with inflammatory fluid and when it breaks open, it develops a dry yellow-brown (golden) crust. Staphylococcus aureus Description: 4

5 *Gram positive coccus usually arranged in grape-like clusters *When grown on many types of agar for 24h at 37 C, individual colonies are circular, 2 3 mm in diameter, with a smooth, shiny surface; colonies appear opaque and are often pigmented (golden yellow, aureus ). * First picture: gram positive - Cluster *Second picture: colonies on agar notice the (golden yellow) color. (Blood media) -The main distinctive diagnostic features of Staphylococcus aureus are: - o Production of an extracellular enzyme (coagulase) which converts plasma fibrinogen into fibrin. o Production of thermostable nucleases that break down DNA (DNAase) o Production of a surface-associated protein known as clumping factor or bound coagulase that reacts with fibrinogen (same as collagen but on the surface). - Staphylococcus aureus Virulence factors :- Virulence Factors are responsible for the establishment of infection Cell wall polymers such as Peptidoglycans in the cell wall and teichoic acid, Cell surface proteins such as protein A 5

6 All of them help the bacteria to escape the immune system and give the bacteria the ability to perform its endotoxin like activity Toxins such as Enterotoxins, TSST-1, Epidermolytic toxins, Panton-Valentine Leukocidin o Enterotoxins ( toxins produced by the bacteria ): Enterotoxins, types A E, G, H, I and J, produced by up to 65% of strains of Staph. Aureus, sometimes singly and sometimes in combination. Some produce only one toxin and others more than one. they can withstand exposure to 100 C for several minutes. These toxins are superantigens, as a result cytokines such as tumour necrosis factor TNF will be released, which play an important role in the elevation of the body temperature, causing vasodilation, and decreasing blood pressure. Voila These enterotoxins when ingested as preformed toxins in contaminated food, can within a few hours induce the symptoms of staphylococcal food poisoning ( nausea, vomiting and diarrhoea). o Toxic shock syndrome toxin (TSST-1) * Causes toxic shock syndrome, a multi-system disease. * a link was established with the use of highly absorbent tampons (in menstruating women) *it is a superantigen, which activates T cells resulting in the liberation of cytokines such as TNF NOTE: Enterotoxins & TSST-1 are superantigens, that is, they are potent activators of T cells (T lymphocytes), so they can activate directly the T cells without activating the antigen-presenting cells (specialized cells take the antigen and present it to the immune system to make an action), resulting in cytokines release. o Epidermolytic toxin (types A and B) (epidermo- in the skin // lytic - destroy) 6

7 These toxins are commonly produced by strains that cause blistering diseases and they induce intraepidermal blisters range in severity from: )فقاعات بسيطه( o Trivial o Distended blisters of pemphigus neonatorum Scalded skin syndrome is one of the manifestations of epidermolytic toxins in small children: where the toxin spreads systemically and Extensive areas of skin are affected, which, after the development of a painful rash, slough off; the skin surface resembles scalding (fig) o Panton-Valentine leukocidin (PVL) - it is a toxin secreted by Staph. Aureus. It can adversely affect cells. It kills the leukocytes resulting in leucopenia. - there is an association between necrotizing pneumonia and some cssti= complicated Skin and Soft Tissue Infections, caused by PVLpositive strains of CA-MRSA (community acquired MRSA) #Methicillin-resistant Staph. aureus ( MRSA ) -meca gene: a bacterial gene by which resistance to certain antibiotics is encoded. -SCCmec: Staphyloccal Casette Chromosome mec, is region of the bacterial chromosome, there are at least 6 different types recognised - Why Staphylococcus aureus is resistant (MRSA)? Because these meca genes that are carried on SCCmec encode a penicillin binding protein 2a, and thus this bacteria becomes resistant to all beta lactam antibiotics 7

8 - MRSA causes the same range of infections as MSSA (methicillin sensitive Staph. Aureus), but it is more difficult to treat than infections caused by MSSA. - Community and Hospital acquired MRSA :- * HA-MRSA: Hospital Acquired MRSA, which occurs in people with recent hospitalisation or surgery, and immunocompromised patients *CA-MRSA: Community Acquired MRSA, which occurs in healthy people with no recent healthcare contact (no recent hospitalisation) Risk factors:- (who is affected) 1- Healthcare workers 2- Debilitated patients (immunocompromised) 3- Recurrent hospital admission 4- Abuse of Antibiotic Control MRSA:- (Prevention) 1- Education and antibiotic stewardships (promoting the appropriate and careful use of antibiotics by prescribers) 2- Fast detection, search and destroy 3- Surveillance 4- Isolation 5- Hand hygiene (washing your hands) Staphylococcus aureus diagnosis: Specimens: - Pus from abscesses, wounds, burns, etc. is much preferred to swabs. - Sputum from patients with pneumonia (e.g. postinfluenzal or ventilator-associated pneumonia); - bronchoscopicspecimens, e.g. bronchoscopic lavage, are increasingly used in critically ill patients. - Faeces or vomit from patients with suspected food poisoning, or the remains of implicated foods. 8

9 - Blood from patients with suspected BSI (bloodstream infection) such as septic shock, osteomyelitis or endocarditis. - Mid-stream urine from patients with suspected cystitis or pyelonephritis. NOTE: :midstream urine: a urine specimen collected after some urine has been voided but before bladder is fully emptied (middle of a flow of urine) - Anterior nasal and perineal swabs from suspected carriers; nasal swabs should be rubbed in turn over the anterior walls of both nostrils. Diagnosis : -first we use the microscope to demonstrate the characteristic clusters of Gram-positive cocci ( can be staph, Strepto, or Entero ) -after that the organisms cultured readily on blood agar and most other media within 24 h or less. -if Catalase positive staph - coagulase test is performed to distinguish Staph. aureus from coagulase-negative species and - antimicrobial susceptibility testing with cefoxitin to confirm MRSA using standard methods. (If Staph. Was resistant to cefotixin, it is most likely MRSA) - Typing: phage and genetic typing for MSSA and MRSA respectively. -Staphylococcus aureus - treatment - MSSA: Follow local antibiotic guide lines and lab. Results - MRSA and CNS strains : resistant to all β-lactam agents, and often to other agents such as the aminoglycosides and fluoroquinolones. - Choice: Glycopeptides (vancomycin or teicoplanin) Linezolids ( ففز بعلم تعش حيا به أبدا *** الناس موتى وأهل العلم أحياء ) 9