Path 3100 Medical Microbiology PDF

Path 3100. Medical Microbiology Staphylococcus Gram positive cocci Dr. Elena Y Enioutina, M.D., Ph.D.  Objectives Describe the classification of Staphylococcus and the major Describe characteristics of S. aureus, S. epidermidis, S. saprophyticus. Associa...

Path 3100. Medical Microbiology Staphylococcus Gram positive cocci Dr. Elena Y Enioutina, M.D., Ph.D.  Objectives Describe the classification of Staphylococcus and the major Describe characteristics of S. aureus, S. epidermidis, S. saprophyticus. Associate Staphylococcus species with the major diseases Associate they cause. Identify areas of the human body where Staphylococcus may Identify reside. Discuss the significance of methicillin-resistant Discuss Staphylococcus aureus (MRSA). Staphylococcus: Biology - Gram-positive cocci - “grape-like” clusters, but can appear as a single cell (0.5 to 1.5 μm) - facultative anaerobes (capable of anaerobic and aerobic growth) - non-motile - non-spore-forming - catalase positive - genus -> 80 species and subspecies - part of normal microbiome of skin, mucous membranes and feces https://www.ncbi.nlm.nih.gov/books/NBK470553/ Clinically Important Species S. aureus - the most virulent S. epidermidis S. saprophyticus Methicillin-Resistant S. aureus (MRSA) is causative agent of serious infections in hospitalized patients and outside the hospital in previously healthy children and adults  Common Staphylococcus Species and Their Diseases Organism Diseases Staphylococcus aureus Toxin mediated (food poisoning, scalded skin syndrome, and toxic shock syndrome), Cutaneous infections (carbuncles, folliculitis, furuncles, impetigo, and wound infections), other (bacteremia, endocarditis, pneumonia, empyema, osteomyelitis, and septic arthritis) S. epidermidis Bacteremia; endocarditis; surgical wounds; opportunistic infections of catheters, shunts, and prosthetic devices S. lugdunensis Endocarditis S. saprophyticus Urinary tract infections Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20 Staphylococcus aureus  S. aureus, Virulence Factors Virulence Factors Biological Effects Structural Components Capsule Inhibits chemotaxis and phagocytosis; inhibits proliferation of mononuclear cells Slime layer Facilitates adherence to foreign bodies Protein A Inhibits antibody-mediated clearance by binding IgG1, IgG2, and IgG4 Fc receptors; leukocyte chemoattractant; anticomplementary Toxins Cytotoxins Toxic for many cells, including erythrocytes, fibroblasts, leukocytes, macrophages, and platelets Exfoliative toxins (ETA, Serine proteases affecting the stratum granulosum epidermis ETB) Enterotoxins Stimulate release of inflammatory mediators, increasing intestinal peristalsis and fluid loss, as well as nausea and vomiting Toxic shock syndrome Superantigen (stimulates T cells and release of cytokines); produces cellular toxin-1 destruction of endothelial cells Enzymes Coagulase Converts fibrinogen to fibrin Hyaluronidase Hydrolyzes hyaluronic acids in connective tissue, promoting spread of staphylococci in tissue Lipases Hydrolyze lipids Nucleases Hydrolyze DNA Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20 S. aureus : Laboratory Testing Specimen:  Successful detection of organisms in a clinical specimen depends on the type of infection (e.g., abscess, bacteremia) and the quality of the material submitted for analysis.  Specimen depends on site of infection Methods:  Culture, Gram Stain and other methods of identification  Carrier screening using molecular detection (such as PCR) for S. aureus and MRSA from certain specimen types  S. aureus: Culture http://www.bacteriainphotos.com/Sta phylococcus%20aureus.html Clinical specimens should be inoculated onto nutritionally enriched agar media supplemented with sheep blood Incubation at 37°C in usually aerobic environment S. aureus grows producing large smooth colonies seen within 24 hours With time, S. aureus colonies will gradually turn yellow (aureus or gold) All isolates of S. aureus produce hemolysis on sheep blood agar  Staphylococcus Identification Gram stain Gram+ cocci Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20  Staphylococcus Identification Catalase Test The catalase test is important test used to determine whether a gram-positive cocci is a staphylococci or a streptococci Staphylococci are positive Streptococci are negative http://www.bacteriainphotos.com/catalase_test.html  Staphylococcus Identification (cont.) Coagulase Test Coagulase test is used to differentiate Staphylococcus aureus from coagulase-negative staphylococci Staph. aureus is positive  Other Staph. species are coagulase negative https://www.asmscience.org/content/education/imagegallery/i https://en.wikipedia.org/wiki/Coagulase mage.3207 Rapid Latex Agglutination test for Staphylococcus aureus Latex agglutination test helps to identify Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) Detects coagulase and/or protein A Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20 Staphylococcus aureus diseases: Staphylococcus aureus causes most severe infections Skin and soft tissue infections Osteomyelitis Pneumonia Food poisoning Gastroenteritis Toxic shock syndrome Toxin factors of Staphylococcus aureus for intracellular survival S. aureus: Diseases Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20  S. aureus: Diseases (cont.) Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20 Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20  Diseases caused by S. aureus Fig. 18.3 Staphylococcal scalded skin syndrome. Fig. 18.6 Pustular impetigo. Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20 Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20 Fig. 18.7 Staphylococcus aureus carbuncle https://www.wikihow.com/Recognize-Staph- Infection-Symptoms Case Study A critically ill 14-year-old boy comes to the ER with a 5 mm diameter pustule at the upper right corner of his mouth. He squeezed this between two fingernails despite an admonition by his grandmother not to do so. Approximately 24 hrs. later he had a headache, shaking chills, and a fever to 105°F. He then developed progressive redness and swelling of his eyes. Four blood cultures were drawn and all 4 had bacterial growth. Methicillin-Resistant S. aureus (MRSA)  MRSA was first discovered in 1961 in England  First case in the US in 1980s  It is NOW resistant to methicillin, amoxicillin, penicillin, oxacillin, and other common antibiotics  Bacterial resistance to methicillin and related penicillins and cephalosporins is mediated by acquisition of a gene (mec A and mec C) that codes for a penicillin-binding protein with low affinity to penicillin https://en.ssi.dk/surveillance-and-preparedness/surveillance-in-denmark/annual-reports-on-disease- incidence/mrsa-2019 Who is susceptible to MRSA infection? Staphylococcus aureus is one of the most common pathogens in health care facilities and in the community Hospital-acquired Community-associated MRSA is now the most common cause of community-acquired skin and soft-tissue infections Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20  MRSA skin infections MRSA skin infections often appear as wounds that are: red, swollen, painful, have pus or other drainage https://www.everydayhealth.com/infectious-diseases/staph- mrsa/truth-about-mrsa-infection/ MRSA may cause: Bacteremia Pneumonia Surgical site infections Endocarditis Bone and joint infections  MRSA in Hospitals According to CDC, ~5% of patients in U.S. hospitals carry MRSA in their nose or on their skin. > 126,000 nosocomial infections/year and 5,000 deaths/year > $2.5 billion in U.S. spent on these infections (ASCLS Today, June 2008)  Treatment of MRSA MRSA strains are resistant to all β-lactam antibiotics: penicillins, cephalosporins, carbapenems; aminoglycosides and macrolides Penicillin Methicillin group (MRSA) Vancomycin or daptomycin (potential development of VISA or VRSA strains) Synercid, Linezolid, Daptomycin Vancomycin is still the drug of choice for intravenous therapy, with daptomycin, tigecycline, or linezolid acceptable alternatives. Oral therapy of non-life-threatening infections: trimethoprim- sulfamethoxazole (Bactrim), doxycycline or minocycline, clindamycin or linezolid. Coagulase-negative Staphs Common inhabitants of human skin and mucous membranes S. epidermidis is the most common species in CoNS infections, followed by S. hominis, S. haemolyticus, and S. capitis Staphylococcus epidermidis is part of our normal flora of the nasal mucosa and the umbilicus of the newborn  Coagulase-Negative Staphylococcal Diseases Murray, et al. Medical Microbiology, 9th ed. Accessed 6/20/20 Staphylococcus epidermidis- the “accidental” pathogen Biology: Normal microbiome of skin Catalase-positive Coagulase-negative staphylococci Low virulence An opportunistic pathogen Disease: Endocarditis, prosthetic infections, IV site infections In nosocomial drain-associated cases of meningitis/ventriculitis, the S. epidermidis group were responsible for 73% of documented infections Staphylococcus saprophyticus Biology: Gram-positive Catalase-positive Coagulase negative non-hemolytic Disease: S. saprophyticus subsp. saprophyticus is the second most frequent causative microorganism of uncomplicated lower UTI in young, sexually active women Resistant to Novobiocin The antibiotic of choice in uncomplicated S. saprophyticus UTIs is nitrofurantoin (Macrobid) or Trimethoprim-sulfamethoxazole  Thank you! Any questions, email me