Microbiology Lecture 2 PDF

12/19/2024 Microbiology Lecture 2 S. Aureus Growing on SBA Micrococcus ◆ An environmenta...

12/19/2024 Microbiology Lecture 2 S. Aureus Growing on SBA Micrococcus ◆ An environmental isolate ◆ Gram Positive Cocci ◆ often confused with Staphylococcus ◆ Not normally considered pathogenic ◆ can cause opportunistic infections – catalase positive group – immunocompromised patients ◆ Intracranial abscesses ◆ Pneumonia ◆ Micrococcus ◆ Septic arthritis ◆ Meningitis ◆ Staphylococcus ◆ Infections of indwelling medical devices ◆ Rothia Copyright © 2019 by Elsevier Inc. All rights reserved. 1 2 3 Ways to distinguish Micrococcus Microdase (Modified Oxidase) Test from Staphylococcus Micrococcus ◆ rapid test ◆ – produce a bright yellow pigmented colony – modified oxidase positive ◆ detects the cytochrome enzyme ◆ All Micrococcus species possess ◆ Staphylococcus – produce acid from glucose cytochrome C enzyme anaerobically – susceptible to lysis by – most staphylococci lack it. lysostaphin – produce acid from glycerol in the presence of erythromycin 4 5 6 1  12/19/2024 Isolation of Staphylococci Identification Tests: Catalase Rapid Methods of ID ◆ Grow easily on blood agar plates and ◆ BBL staphyloslide thioglycolate ◆ Principle: tests for enzyme catalase ◆ Staphaurex® ◆ If heavily contaminated, they can be 2 H2O2 2 H2O + O2 ◆ BactiStaph® selected with the following: ◆ Drop H2O2 onto smear – Figure 14.9 – Mannitol salt agar ◆ Bubbling = POS (Most bacteria, O2 ◆ Plasma-coated carrier particles (e.g., – Columbia colistin-nalidixic acid agar (CNA) generated) latex) detect both clumping factor – Phenylethyl alcohol agar ◆ No bubbling = NEG (streptococci and and protein A. ◆ Selective media other lactic acid bacteria, no O2 – Particularly useful for ID of methicillin- – CHROMagar Staph aureus generated) resistant S. aureus (MRSA), which are ◆ Selective media weakly positive or negative in slide Copyright © 2019 by Elsevier Inc. All rights reserved. coagulase test 7 8 9 Mode of Transmission and Rapid Methods of ID Staphylococcus aureus Predisposing Conditions of S. aureus ◆ Real-time polymerase chain reaction (PCR) ◆ Mode of transmission: traumatic introduction – For MRSA and methicillin-sensitive S. aureus (MSSA) ◆ #1 pathogen of human – Needle stick ◆ Qualitative nucleic acid hybridization assays interest – Destruction of skin layers (burns, road targeting rRNA sequences for staphylococcal ID ◆ #1 cause of HAI rash) from blood cultures ◆ Found as normal flora – Medical procedures ◆ Matrix-assisted laser desorption/ionization time- – human skin ◆ Predisposing conditions of-flight (MALDI-TOF) mass spectrometry – mucosal membranes – Continues to be integrated as U.S. Food and – Chronic infections ◆ Usually beta-hemolytic Drug Administration (FDA) approval occurs – Indwelling devices on BAP – Skin injuries Copyright © 2019 by Elsevier Inc. All rights reserved. – Immune response defects Copyright © 2019 by Elsevier Inc. All rights reserved. 10 11 12 2  12/19/2024 Staphylococcus Staphylococcus aureus - Staphylococcus aureus General Characteristics Characteristics Characteristics cont. ◆ Definitive characteristic Gram positive cocci ◆ – Occur in pairs and clusters – Coagulase production ◆ Serological ◆ Catalase positive ◆ Two types of coagulase agglutination test – Used to distinguish from Streptococcus – Bound ◆ Reduce nitrates to nitrites – Free – Uses latex particles ◆ Can grow in high salt concentrations ◆ Bound coagulase ◆ coated with fibrinogen – 7.8% and above – clumping factor in the cell wall. and IgG ◆ Non-motile ◆ non-spore forming – Test by putting rabbit plasma on slide and mixing in colonies. – Tests for two ◆ Most are facultative anaerobes – Clumping = S. aureus characteristics ◆ 3 main species ◆ Free coagulase ◆ clumping factor (bound – Staphylococcus aureus – an extracellular enzyme coagulase) – Staphylococcus epidermidis – Staphylococcus saprophyticus – Test by placing colonies in a tube ◆ protein A (found in S. with rabbit plasma, incubate 4 hours and observe for aureus cell wall) solidification – 20 second rapid test – Solidification = S. aureus – Prevent autolysis and false- negative result 13 14 15 Staphylococcus aureus Staphylococcus aureus Virulence Factors of S. aureus: Characteristics cont. Pathogenicity Cellular components ◆ Ferments mannitol ◆ Pathogenicity/Virulence ◆ Enzymes – appears yellow on MSA – Coagulase – Cellular components – Hyaluronidase ◆ Produces Dnase – a heat stable – Lipase nuclease – Enterotoxins ◆ Produces phosphatase – Exfoliative toxin ◆ Protein A ◆ Odor – gym socks – Cytolytic toxins – dirty feet Copyright © 2019 by Elsevier Inc. All rights reserved. 16 17 18 3  12/19/2024 Virulence Factors of S. aureus Virulence Factors of S. aureus S. aureus: Toxic Shock Syndrome Enterotoxins Exotoxins Exotoxin Association with super-absorbent tampons ◆ Heat-stable exotoxins that cause  ◆  Clinical presentation diarrhea and vomiting – Toxic shock syndrome toxin-1 – High fever (TSST-1) aka toxin F – Rash of trunk spreading to extremities ◆ Toxins A through E and G through J – pyrogenic exotoxin – Watery diarrhea (nine total) – Chromosomal-mediated toxin – Vomiting ◆ Dehydration – Resistant to gastric acid and associated – TSST-1 and B, C, G, and I are  Extreme cases lead to hypotension and shock. with food poisoning superantigens.  Disseminated intravascular coagulation (DIC) – Produced by phage group I  Increase in blood urea nitrogen (BUN) and creatinine – causes toxic shock syndrome  Fatal in 2% to 5% of cases due to multiorgan ◆ high fever, vomiting, diarrhea, and system failure severe shock Copyright © 2019 by Elsevier Inc. All rights reserved. Copyright © 2019 by Elsevier Inc. All rights reserved. 19 20 21 Staphylococcus aureus S. aureus: SSSS S. aureus: Toxic Epidermal Necrolysis Exfoliative toxin ◆ Exfoliative toxin ◆ Bullous exfoliative dermatitis  Abbreviated as TEN – aka epidermolytic – Staphylococcal scalded skin syndrome  Multiple causes toxin – Drug induced (SSSS) – causes the – Infections epidermal layer – Occurs primarily in newborns and previously healthy young children – Vaccines of the skin to ◆ Cause officially not known slough off – May occur in adults – Scalded skin  Similar to SSSS ◆ More likely to occur in renal failure patients syndrome – Treatment with steroids helpful ◆ Immunocompromised ◆ Unlike SSSS – Ritter’s disease  High mortality rate Copyright © 2019 by Elsevier Inc. All rights reserved. Copyright © 2019 by Elsevier Inc. All rights reserved. 22 23 24 4  12/19/2024 Staphylococcus aureus Staphylococcus aureus S. aureus: Food Poisoning Cytolytic toxins Cytolytic toxins ◆ Toxin, not bacterial growth, causes disease. ◆ Extracellular proteins that affect red blood cells ◆ Extracellular proteins that affect red blood cells (RBCs) and leukocytes (RBCs) and leukocytes ◆ Enterotoxin A, B, D (A and D most common) – Hemolysins and leukocidins – Hemolysins and leukocidins – From enterotoxin-producing strains contaminating the rich foods (mayonnaise) ◆ Αlpha toxin ◆ Leukocidins – Inadequate refrigeration – Hemolyzes red blood cells – Delta toxin – Also called Panton-Valentine leukocidin (PVL) ◆ Symptoms – can destroy platelets – cause severe tissue damage – Exotoxin kills polymorphonuclear leukocytes. – Appear rapidly about 2 to 8 hours after ingesting ◆ Beta toxin – Helps prevent phagocytosis food – Often associated with community-acquired infections – Hemolyzes red blood cells – Usually resolve in 24 to 48 hours, sometimes less ◆ Gamma toxin – Nausea, vomiting, abdominal pain, and cramping – Less toxic than alpha or beta Copyright © 2019 by Elsevier Inc. All rights reserved. 25 26 27 Staphylococcus aureus Methicillin-Resistant Staphylococci Treatment Infections ◆ Methicillin-resistant S. aureus - MRSA Septicemia Antibiotics ◆ Methicillin-resistant S. epidermidis ◆ ◆ ◆ Endocarditis – most resistant to Penicillin ◆ Pneumonia ◆ β-Lactamase testing should be done – MRSE ◆ Osteomyelitis – Methicillin, nafcillin, or oxacillin ◆ Abscess of organs and muscle ◆ ◆ first choice 40-55% now resistant ◆ Community-acquired MRSA (CA-MRSA) ◆ UTI’s ◆ Some of the most common – Vancomycin 2nd choice – Can be greater than 50% of isolates in some infections involve the skin – Wound infections ◆ First cases of resistance have been reported areas – Boils – Cellulitis – Newer drugs ◆ Health care–associated/community onset – Impetigo ◆ ◆ Linezolid Synercid MRSA (HACO-MRSA) ◆ Hospital-associated MRSA (HA-MRSA) ◆ Teicoplanin – Pose serious threats to health institutions Copyright © 2019 by Elsevier Inc. All rights reserved. 28 29 30 5  12/19/2024 Methicillin-Resistant Staphylococci Methicillin-Resistant Staphylococci Vancomycin-Resistant Staphylococci ◆ BioMérieux ◆ Infection control ◆ VRSA and VISA – Recommends PBP2a to be used to – Barrier protection determine methicillin resistance for – Vancomycin-resistant S. aureus (VRSA) and – Contact isolation MIC=1or2 vancomycin-intermediate S. aureus (VISA) – Handwashing ◆ mecA gene – Isolated in United States 2002 ◆ Treat with vancomycin – Encodes penicillin-binding proteins (PBPs) – Often in patients with underlying conditions – Test for susceptibility with cefoxitin disk – Only a small fraction of the population – Important to adhere to infection control expresses the phenotype despite having the practices and guidelines to hopefully limit ◆ Borderline oxacillin-resistant S. aureus the emergence of this highly resistant genetic potential. (BORSA) organism ◆ Gold standard - mecA gene detected by – Can separate from MRSA on oxacillin salt agar plate PCR Copyright © 2019 by Elsevier Inc. All rights reserved. Copyright © 2019 by Elsevier Inc. All rights reserved. 31 32 33 Coagulase Negative Macrolide Resistance D-Test Positive Isolate Staphylococcus ◆ Resistance to clindamycin may not ◆ Most identified are be obvious Staphylococcus epidermidis – Erythromycin and clindamycin should have same resistance patterns ◆ Found as normal skin ◆ If not, perform D test flora and on the mucous membranes ◆D test – Use erythromycin and clindamycin disks ◆ Frequently seen as contaminants of ◆ Growthbetween disks but not on side of specimens collected clindamycin disk from or through the skin – Inducible resistance – Most common contaminant of blood cultures 34 35 36 6  12/19/2024 Coagulase Negative StCoagn (C=S) Identification Staphylococcus epidermidis Staphylococcus Pathogenicity ◆ Not normally ◆ Coagulase negative ◆ Predominantly nosocomial infections pathogenic but can be opportunistic ◆ Does not ferment mannitol – Skin flora gets introduced in catheters, – Endocarditis heart valves, CSF shunts – SBE – subacute ◆ Not usually beta-hemolytic bacterial endocarditis – Produces a slime layer (biofilm) that ◆ IV drug users ◆ Novobiocin used to helps adherence to prosthetics and ◆ Immunocompromised differentiate other patients Coagulase negative avoidance of phagocytosis Patients with defective Staphylococcus from – UTIs ◆ heart valves Staphylococcus – Indwelling medical saprophyticus devices – Staphylococcus ◆ Artificial joints saprophyticus ◆ Novobiocin resistant ◆ seen in UTI’s of women in childbearing years 37 38 39 Staphylococcus saprophyticus Novobiocin Susceptibility Test Staphylococcus lugdunensis ◆ Can cause both community- ◆ UTIs in young sexually active women associated and hospital-acquired – Due in part to increased adherence to infections epithelial cells lining the urogenital tract ◆ Can be more virulent than S. aureus ◆ Rarely present in other skin areas or and can clinically mimic S. aureus mucous membranes infections ◆ Urine cultures ◆ Known to carry mecA (that encodes –If present in low amounts oxacillin resistance) (