Micro 3

organisms in this solo revolve around being

catalase positive or negative

catalase is the enzyme that releases water and oxygen from

hydrogen peroxide

Staphylococcus species are primarily (not all) catalase

positive

Streptococcus species are primarily catalase

negative

Staphylococcus (genus) is

facultative anaerobic

the primary serological test used to differentiate within Staphylococcus

coagulase

Staphylococcus is known to produce

gram positive cocci in clusters

Normal microbiota (habitat) of Staphylococcus Aureus

Anterior nares - nasal colonization (carriers harbor strains)

Staphylococcus aureus virulence factors

catalase - enzyme that converts hydrogen peroxide into oxygen and water, penicillinase, beta lactamase - cleans the beta-lactam ring of the penicillin molecule, rendering it ineffective, coagulase - binds plasma fibrinogen and activates a cascade of reactions causing plasma to clot, polysaccharide capsule - inhibits phagocytosis

Staphylococcus aureus virulence factors proteins and toxins

protein A - allows the organism to bind directly to the immunoglobulins, decreasing the immune-mediated response Alpha toxin - disrupts smooth muscle in blood vessels and is toxic erythrocytes, leukocytes, hepatocytes, and platelets, heat stable enterotoxins A-E resistant to hydrolysis by the gastric and intestinal enzymes, Toxic shock syndrome toxin I, DNase - hydrolyzes DNA and uses it as a carbon source for energy and growth

Staphylococcus aureus spectrum of disease, toxin mediated

Scaled skin syndrome, toxic shock syndrome, food poisoning

Staphylococcus aureus spectrum of disease, localized skin infections

Follicullitis, Furuncles, Carbuncles

Staphylococcus aureus scaled skin syndrome is caused by

toxins A and B, effectiveness of these toxins decreases after the age of five

Staphylococcus aureus toxin mediated diseases

Toxic shock syndrome is caused by toxic shock syndrome toxin (TSST-1) which bypasses normal pathway of T cells and causes an over-activation of cytokines and inflammatory cells, Food poisoning causes rapid response from food containing enterotoxins from Staph aureus usually within 30m to 8hrs.

Staphylococcus aureus methods of identification

mostly pigmented a creamy yellow, most colonies are beta-hemolytic, gram stain will show a gram-positive cocci in clusters, catalase positive, coagulase positive - if positive can presumptively call staph aureus - positive for both free and bound coagulase

two different kinds of coagulase

bound (clumping factor) - detected using a rapid slide test (slide coagulase test), extracellular (free) - detected using a tube coagulase test and performed by inoculating a tube containing plasma and incubating at 35C (Staph aureus contains both types of coagulase)

Staphylococcus aureus susceptibility testing

Penicillinase-resistant penicillins (ex: methicillin, nafcillin, oxacillin) are mainstay for therapy but resistance is common - resistance leads to MRSA, MRSA is caused by certain strains carrying a gene called mecA which encodes a protein called PBP-2a, if oxacillin or cefoxitin is resistant, all beta-lactam antibiotics are considered resistant, Vancomycin is the most used cell wall-active agent as an alternative for treatment for resistant strains

Inducible Clindamycin resistance (for MRSA)

Macrolides and lincosamides have been used for MRSA but inducible resistance needs to be tested, Macrolide resistance shows a similar resistance pattern to erythromycin, resistance is mediated by a gene msrA or the activity of a methylase enzyme that alters the ribosomal binding site erm causing macrolide resistance, a manual method called “the D test” can be used to test for inducible clindamycin resistance with Clindamycin and Erythromycin antibiotic disks are used on a Mueller Hinton agar - if resistant then “D-zone” will show

Coagulase negative Staphylococcus epidemiology

Normal microbiota - skin, mucous membrane, mode of transmission - endogenous strain implantation of medical devices into a sterile stie

Staphylococcus Saprophyticus (coagulase negative) epidemiology

normal microbiota - genitourinary tract, mode of transmission - notably in young sexually active females

Coagulase negative Staphylococcus epidermidis virulence factors

Staphylococcus epidermidis: Biofilm production (on prosthetics)

Coagulase negative Staphylococcus spectrum of disease

Staphylococcus epidermidis: Nosocomial infections, bacteremia associated with indwelling vascular catheters, endocarditis associated with prosthetic cardiac values Staphylococcus saprophyticus: UTIs in sexually active young women, second most common cause of urinary tract infections in young females

Staphylococcus epidermidis: methods of identification

catalase positive, anaerobic glucose fermentation positive, coagulase negative

Staphylococcus Haemolyticus: methods of identification

Beta-hemolytic, catalase positive, coagulase negative, anaerobic glucose fermentation positive

Staphylococcus saprophyticus: methods of identification

appearance: very glossy and bright white in color, yellows as it ages, novobiocin: resistant, anaerobic glucose fermentation positive

Coagulase-variable staphylococcus epidemiology

Normal microbiota: variety of animals (dogs)

Coagulase-variable Staphylococcus spectrum of disease

Staphylococcus lugdunesis Spectrum of disease: septic arthritis, Staphylococcus intermedius and pseudintermedius: skin infections

Staphylococcus lugdunensis: methods of identification

catalase: positive, coagulase variable: clumping factor - positive, tube coagulase - negative, anaerobic glucose fermentation positive

Staphylococcus intermedius methods of identification

appearance: smooth, glossy, and usually nonpigmented, coagulase variable: clumping factor - variable, tube coagulase - negative, PYR positive, Polymyxin B susceptible

Staphylococcus pseudintermedius methods of identification

appearance: similar to staph aureus, catalase: positive, coagulase variable: clumping factor - negative, tube coagulase - positive Polymyxin B resistant

Coagulase negative and variable Staphylococcus antimicrobial susceptibility testing

check for inducible clindamycin resistance, if an organism is cefoxitin or oxacillin resistant, it is considered resistant to all beta lactam agents, Staphylococcus saprophyticus show intrinsic resistance to novobiocin

Micrococcus species and Rothia mucilaginosa epidemiology

normal microbiota: skin, Oropharynx, mode of transmission: typically results from endogenous strains in immunocompromised hosts

Micrococcus species and Rothia mucilaginosa virulence factors and spectrum of disease

virulence factors: probably of extremely low virulence, spectrum of disease: usually considered contaminants clinical specimens

Micrococcus species methods of identification

appearance: dry, yellow, catalase: positive, anaerobic glucose fermentation: negative, modified oxidase: positive

Rothia muscilaginose: methods of identification

Appearance: sticky, catalase: variable, lysostaphin: resistant

Micrococcus species and Rothia mucilaginosa antimicrobial susceptibility testing

A specialized CLSI guidelines handbook called the M45 gives guidelines for organisms that are not routinely given AST

Catalase negative, gram-positive cocci general characteristics

produces gram positive cocci in pairs or chains, facultative anaerobic, Beta-hemolytic Streptococcus has different antigens that are distinguished by the Lancefield classification system (A - pyogenes, B - agalactiae, C - dysgalactiae, D - enterococcus and bovis, F and G - viridans, anginosus or constellatus)

Streptococcus pyogenes epidemiology

habitat: not considered normal microbiota, almost always considered clinically significant

Streptococcus pyogenes virulence factors

M protein - Antiphagocytic, produces several enzymes and hemolysins that contribute to tissue invasion and destruction, Streptolysin O - immunogenic, capable of lysing cells, broken down by oxygen, will be beta hemolytic in only anaerobic conditions, Streptolysin S - nonimmunogenic capable of lysing erythrocytes, leukocytes, and platelets in the presence of room air, oxygen stable, will be beta hemolytic in both aerobic and anaerobic conditions

Streptococcus pyogenes virulence factors proteins

cross reaction of antibodies produced against streptococcal antigens and human heart tissue (cause of Rheumatic fever), deposition of antibody-streptococcal antigen complexes in kidney results in damage to gomeruli (causes acute poststreptococcal glomerulonephritis)

Streptococcus pyogenes spectrum of disease

Acute pharyngitis, Necrotizing fasciitis, Post streptococcal infections - Rheumatic fever, acute postreptococcal glomerulonephritis

Streptococcus pyogenes post-streptococcal infections

Glomerulonephritis: approx 10 days following group A strep pharyngitis and up to 3 weeks following group A skin infections, Acute rheumatic fever: streptococcal pharyngitis typically precedes the onset of ARF by 1 to 5 weeks

Streptococcus pyogenes methods of identification

Appearance: small beta hemolytic colonies with a large zone of hemolysis, gram stain shows GPC in pairs or chains, catalase negative, Bacitracin susceptible (any zone size), PYR positive, Lancefield group A

Streptococcus Agalactiae: epidemiology

Normal microbiota: female genital tract and lower GI tract, mode of transmission: mother in utero or during delivery

Streptococcus agalactiae: spectrum of disease

most infections involve neonates and infants, often preceded by premature rupture of mother’s membranes

Streptococcus agalactiae: methods of identification

medium size beta-hemolytic colonies have a small zone of hemolysis, catalase negative, Bacitracin resistant, CAMP test positive, Hippurate hydrolysis positive, Lancefield group B

Streptococcus agalactiae camp test

a positive reaction is denoted by the appearance of an arrowhead shape

Beta-hemolytic Streptococci C virulence factors

infections occasionally have been associated with acute pharyngitis

Beta-hemolytic streptococcus groups C, F, and G: method of identification

appearance: small beta-hemolytic, C and G have a wide zone of beta-hemolysis, F narrow zone, catalase negative, bacitracin resistant, CAMP test negative, Hippurate hydrolysis negative, must be identified by serological methods like the PathoDxtra kit

Beta-hemolytic Streptococcus antimicrobial susceptibility testing (test question)

Penicillin with or without an aminoglycoside is the drug of choice, when Streptococcus aglactiae is found in a patient who is pregnant inducible clindamycin resistance must be tested if mother is penicillin allergic (D test)

Streptococcus pneumoniae epidemiology

habitat: colonizer of the nasopharynx

Streptococcus pneumoniae virulence factors

Polysaccharide capsule that inhibits phagocytosis, Streptococcus pneumoniae Type III will show an overexpression in capsular material and cause a mucoid appearance

Streptococcus pneumoniae spectrum of disease

leading cause of meningitis and pneumonia with or without bacteremia

Streptococcus pneumoniae methods of identification

Appearance: small gray colonies that show alpha hemolysis, as the colonies age, the center of the colony dip down to form a “donut” appearance, Type III will be mucoid due to overproduction of the capsular material, gram stain will show GPC in pairs, another term is lancet shaped GPC, catalase negative, bile solubility positive, optochin susceptible (> 14mm diameter)

Streptococcus pneumoniae: antimicrobial susceptibility testing

no resistance has been found for vancomyin

Enterococcus species epidemiology

mode of transmission: contaminated medical equipment, immunocompromised patients are at risk of developing infections with antibiotic resistant strains (VRE)

Enterococcus species spectrum of disease

health care-associated, urinary tract infections

Enterococcus species methods of identification

appearance: can show either alpha, beta, or gamma hemolysis, catalase: negative, growth in 6.5% NaCl, PYR positive, Esculin positive

Enterococcus species: antimicrobial susceptibility testing

Enterococcus faecalis is ampicillin susceptible, Enterococcus faecium is ampicillin resistant, this species is also more likely to become vancomycin resistant, Enterococus gallinarum and casseliflaus are intrinsically vancomycin resistant

Streptococcus viridians epidemiology

normal microbiota: oral cavity, mode of transmission: endogenous strain most notable infections result from dental manipulations

Streptococcus viridian groups: spectrum of disease

slowly evolving endocarditis

Streptococcus viridians methods of identification

appearance: pinpoint to small colonies that show alpha or gamma hemolysis. as the colony ages, some colonies can mimic Streptococcus pneumoniae with the “donut” appearance, catalase negative, optochin resistant, PYR negative, Esculin negative

Group D Streptococcus (not Enterococcus)

apart of the Streptococcus viridans group, usually gamma hemolytic Streptococcus, Esculin positive, PYR negative, This has been labeled as the Bovis group (bovis, infantarius, equinis, gallolytius)

Aerococcus species spectrum of disease

urinary tract infections: Aerococcus urinae