MICR 300 Med Micro Exam 2

Nonselective primary plating medium, differential for hemolysis

blood agar

Nonselective enriched medium made with lysed red blood cells (releasing X and V factor), used to cultivate fastidious respiratory pathogens

chocolate agar

enriched nonselective medium used primarily to isolate and cultivate fungi

sabouraud dextrose agar

Selective media for gram-negative (bile salts and crystal violet inhibit gram positives), differential for lactose fermentation

MacConkey agar

Selective media for staphylococci (high NaCl concentrations inhibit most others), differential for mannitol fermentation (changes phenol red indicator to yellow)

mannitol salt agar

Selective media for gram-negative enterics, differential for lactose fermentation (color of colonies)

eosin methylene blue

selective media for gram-negative enteric pathogens (inhibits most normal gut flora), differential for lactose fermentation and hydrogen sulfide. Differentiates Salmonella from Shigella

hektoen enteric agar

Salmonella grows ____ centered colonies on HE agar

black

Shigella grows ____ colonies on HE agar

green

Selective, chocolate-based culture medium containing antibiotics (vancomycin, colistin, nystatin, trimethoprim) to suppress normal mucosal flora while isolating fastidious Neisseria gonorrhoeae

modified thayer martin agar

selective media for gram positives, can isolate Staphylococcus and Streptococcus from clinical specimens containing heavy gram-negative flora

phenylethyl alcohol agar (pea)

selective media for gram-positives (gram-negatives inhibited by colistin and nalidixic acid). Differential for hemolysis patterns

Columbia CNA agar

Selective medium for mycobacteria; egg-based solid slant using malachite green and penicillin/nalidixic acid to suppress other bacteria. Highly stable for long incubations

lowenstein jensen agar

selective media for cultivating mycobacteria; clear and transparent (can inspect for “fried egg” colonies), uses specific antibiotics to inhibit contaminents

Middlebrook 7H11

specialized selective medium for Legionella pneumophila, which requires L-cysteine and iron salts for growth. Has component that detoxifies metabolic byproducts in the medium

buffered charcoal yeast extract agar

differentiates staphylococcus (+) vs streptococcus (-) for ability to detoxify hydrogen peroxide

catalase test

tests for the enzyme that converts fibrinogen to fibrin, causing plasma to clot. differentiates Staphylococcus aureus (+) from other staphylococci

coagulase test

biochemical test that differentiates Pseudomonas (+) from Enterobacterales (-)

oxidase test

Measures growth inhibition around filter disk on blood agar. Differentiates sensitive Streptococcus pneuomoniae from other alpha-hemolytic viridans

optochin sensitivity test

Tests bacterial lysis in the presence of ____; differentiates Streptococcus pneumoniae (clear/lyses) from other alpha-hemolytic streptococci (which remain turbid)

Bile solubility test

Growth inhibition test using a low-concentration disk on blood agar. Differentiates Group A streptococcus (susceptible) from other beta-hemolytic streptococci (resistant)

bacitracin sensitivity test

multi-well systems that perform multiple biochemical reactions simultaneously, creating a metabolic profile that is matched against a database to identify the species

commercial biochemical panels

sample collected directly from a normally sterile body site (e.g. blood, cerebrospinal fluid, etc)

direct specimen

sample originating from a sterile site that must pass through a non-sterile site during collection (e.g. sputum, clean-catch urine)

indirect specimen

diagnostic yield and accuracy of laboratory testing depends directly on proper collection technique, site selection, appropriate containers, and rapid transport under correct conditions

specimen quality rule

isolated colony or population of microbes containing only a single species; required for accurate biochemical identification and susceptibility tests

pure culture

in vitro testing performed on a cultured pathogen isolate to determine its susceptibility to resistance to specific antibiotics

antimicrobial susceptibility testing

A rapid diagnostic tool that identifies cultured bacteria or fungi within minutes by analyzing their protein spectrum mass-to-charge ratios

MALDI-TOF

A molecular diagnostic assay that amplifies and detects specific microbial DNA or RNA sequences directly from clinical samples without requiring viable bacterial culture (PCR)

nucleic acid amplification test

Immunoassay using manufactured antibodies to bind and detect specific pathogen components, surface proteins, or toxins directly in patient samples

antigen detection test

Diagnostic testing that measures patient serum for host-produced antibodies (IgM/IgG) against a pathogen, indicating recent or past infection

serology

Test type for when a viable bacterial isolate is required for susceptibility testing

culture

Test type for when the pathogen is slow or difficult to culture or is an obligate intracellular

molecular NAT PCR

Test type for when a rapid point-of-care result is needed within minutes (strep throat/flu)

antigen test

Test type for figuring out a patient’s past exposure, latent infection, or stage of disease

serology antibody detection

Test type for when immediate visualization of cell morphology or parasite structures is needed

microscopy

complete destruction and removal of all microbial life including endospores

sterilization

application of chemical agents to living skin or tissue to reduce microbial load

antisepsis

microorganisms from within the patient’s own microbiota

endogenous

microorganisms from outside the patient

exogenous

Spaulding classification: devices that enter sterile tissue or the vascular system are _____ that must be _____

critical items, sterilized

Spaulding classification: devices that contact mucous membranes or non-intact skin are _____ that must be _____

semi critical items, high level disinfection

Spaulding classification: items that only touch intact skin are _____ that must be _____

non critical items, low level disinfection

disinfection that kills all microorganisms except when high numbers of endospores are present

high level disinfection

disinfection that kills all vegetative bacteria, mycobacteria, most fungi and viruses (not endospores)

intermediate level disinfection

disinfection that kills most vegetative bacteria and some fungi and viruses; not mycobacteria or endospores

low level disinfection

test vials containing standardized bacterial endospores (such as Geobacillus stearothermophilus spores) used to validate that a sterilization cycle in the autoclave was successful

biological indicator

endospore-forming bacterium used as the biological indicator to monitor dry heat and ethylene oxide gas sterilization

bacillus atrophaeus

liquid chemical agent used for high-level disinfection; can achieve chemical sterilization with long exposure time

glutaraldehyde

gaseous chemical sterilant used for heat sensitive or moisture sensitive instruments; requires long aeration times to purge toxic gas residues

ethylene oxide

Waxy, long-chain fatty acids present in the Mycobacterium cell envelope. Creates a hydrophobic barrier responsible for acid-fast staining, environmental stability, and resistance to disinfectants and antibiotics

mycolic acid

Specialized staining technique for bacteria with lipid-rich walls (Mycobacterium). Target organisms resist acid-alcohol decolorization and stain bright pink/red against a blue/green background

acid fast/kinyoun stain

An organized nodular focus of immune cells (activated macrophages, epithelioid cells, giant cells, and lymphocytes) formed to wall off intracellular mycobacteria that the host immune system cannot immediately eradicate

granuloma

in vivo diagnostic test in which a purified protein derivative is injected intradermally; induration (swelling) measured 48–72 hours later indicates a Type IV delayed-type hypersensitivity reaction. False-negatives can occur in immunocompromised patients

tuberculin skin test

Diagnostic blood test for M. tuberculosis. Measures IFN-gamma released by sensitized host T cells exposed to specific M. tuberculosis antigens

interferon gamma release assay

Environmental mycobacteria found in soil and water. Opportunist pathogens that cause pulmonary disease in susceptible hosts

nontuberculous mycobacteria

genus: gram-negative diplococci with a “coffee bean” shape

neisseria

pathogen: non-encapsulated, gram-negative diplococcus. Transmitted sexually and has no vaccine

Neisseria gonorrhoeae

Systemic complication occurring when N. gonorrhoeae spreads through the bloodstream from a mucosal site, presenting with fever, pustular skin lesions, tenosynovitis, and septic arthritis

Disseminated gonococcal infection

pathogen: encapsulated gram-negative diplococcus. Colonizes human nasopharynx, transmitted via respiratory droplets. Has vaccine.

neisseria meningitidis

Individuals that lack terminal complement proteins required for the membrane attack complex (MAC), aka terminal complement deficiency, are at a dramatically higher risk for _____ infections

neisseria

pathogen: fastidious, small, gram-negative coccobacillus requiring X factor (heme) and V factor (NAD) for growth

Haemophilus influenzae

heme

X factor

NAD/NADP

V factor

major encapsulated serotype of H. influenzae historically responsible for severe invasive disease in young children. Vaccine preventable

H. influenzae type b

Medical emergency caused by invasive H. influenzae type b, characterized by rapid inflammation and swelling of the epiglottis, leading to life-threatening upper airway obstruction in young children

acute epiglottitis

Non-encapsulated strains of H. influenzae that form part of the normal upper respiratory flora but cause localized mucosal respiratory infections: otitis media, sinusitis, and bronchitis/pneumonia

nontypeable NTHi

pathogen anchors: Acid fast bacilli, cavitary lung lesions, recent travel/immigration, bloody cough, weight loss

Mycobacterium tuberculosis

pathogen anchors: acid fast bacilli, AIDS, diarrhea, no lung lesions, fever, weight loss, lady windermere syndrome

MAC

acid fast bacilli, cannot be cultured, numb skin patches, hypopigmented skin lesions, thickened peripheral nerves, facial lesions

mycobacterium leprae

pathogen anchors: gram negative “coffee bean” diplococci, sexually active, purulent discharge, septic arthritis (joint aches), needs enriched media to grow

neisseria gonorrhoea

pathogen anchors: encapsulated gram-negative “coffee bean” diplococci, petechial rash, dorms/barracks, stiff neck, vomiting, light sensitivity, termical complement deficiency

neisseria meningitidis

small gram-negative coccobacilli, unvaccinated child, epiglottitis or “cherry red” swolen airway, seizures

haemophilus influenzae type b

small gram negative coccobacilli, no capsule, localized mucosal respiratory infections, child with ear infection or adult with chronic bronchitis

nontypeable haemophilus influenzae

strawberry tongue and “sandpaper” rash

scarlet fever by streptococcus pyogenes

Sikolsky sign positive (skin sloughing with light touch)

staphylococcal scalded skin syndrome by s. aureus

new heart murmur after dental world

bacterial endocardiis by s. mutans or s. mitis

Gram positive bacilli, Broad-spectrum antibiotics (clindamycin/fluoroquinolones) kill gut flora, pathogen overgrows, Toxin A & B cause watery diarrhea & pseudomembranous colitis. Clean surfaces with bleach/sporicides.

Clostridioides difficile

Gram positive bacilli, Spores enter puncture wound and releases tetanospasmin neurotoxin, blocks inhibitory neurotransmitters (GABA & glycine) causing spastic paralysis, lockjaw (trismus), and arched back. Prevented by DTaP vaccine.

Clostridium tetani

Gram positive bacilli, Preformed toxin in canned food (adults) or spores in raw honey (infants: "floppy baby syndrome"), blocks acetylcholine (ACh) release, descending flaccid paralysis (double vision, drooping eyelids, muscle weakness).

Clostridium botulinum

Gram positive bacilli, rauma/war wounds, gas gangrene (alpha toxin/lecithinase) with crepitus (crackling gas under skin); double zone of hemolysis on blood agar.

Clostridium perfrigens

Gram positive bacilli, spore-forming, encapsulated, soil reservoir; non-hemolytic "Medusa-head" colonies. Causes cutaneous anthrax (painless black eschar) or inhalation anthrax (woolsorter's disease: widened mediastinum on X-ray)

bacillus anthracis

Gram positive bacilli, Tumbling motility at room temp, grows in fridge (4°C); transmitted via unpasteurized dairy, soft cheeses, and deli meats. Causes spontaneous abortion in pregnant women and meningitis in newborns and elderly.

listeria monocytogenes

Gram positive bacili, Club-shaped rods in palisades ("Chinese characters"); produces diphtheria toxin (inhibits EF-2), grey pseudomembrane in back of throat + "bull-neck" lymphadenopathy.

corynebacterium diptheriae

Gram negative enteric, lactose fermenter, large mucoid polysaccharide capsule; classic cause of pneumonia in alcoholics and diabetics with "currant-jelly" (bloody/mucous) sputum.

klebsiella pneumoniae

Gram negative enteric, lactose fermenter, undercooked ground beef, Shiga-like toxin, bloody diarrhea WITHOUT fever, can cause kidney failure

EHEC

Gram negative enteric, lactose fermenter, #1 cause of UTIs

UPEC

Gram negative enteric, non lactose fermenter, motile, produces H2S (black colonies on HE agar), high infectious dose (poultry, eggs, reptiles). Causes gastroenteritis or typhoid fever.

salmonella

Gram negative enteric, non lactose fermenter, non-motile, NO H2S (green colonies on HE agar), extremely low infectious dose (10–100 bacteria), human-only. Produces Shiga toxin, severe bacillary dysentery (bloody stool with PMNs).

shigella

Gram negative enteric, non lactose fermenter, displays swarming motility on agar; produces urease (splits urea to raise urine pH >7), causes struvite / staghorn kidney stones.

proteus mirabilis

gram negative, obligate aerobe, Oxidase positive, non-lactose fermenter. Produces blue-green pyocyanin pigment and a fruity/grape-like odor. Exotoxin A inhibits EF-2. Classic cause of infections in burn patients, Cystic Fibrosis lung disease, swimmer's ear, and hot tub folliculitis.

pseudomonas aeruginosa

gram negative, grows on Regan-Lowe / Bordet-Gengou agar. Produces tracheal cytotoxin (kills ciliated respiratory cells), causes Whooping Cough

bordetella pertussis

Gram negative, strict aerobe, Oxidase negative. Major cause of ventilator-associated pneumonia (VAP) and bloodstream infections in ICUs; notorious for extreme multidrug resistance.

acinetobacter baumannii

Curved Gram-negative rod + "Rice-water" watery stools + Severe dehydration + Cholera toxin (activates cAMP)

vibrio cholerae

Pathogen anchors: Curved Gram-negative rod ("gull-wing" shape) + Poultry exposure + Bloody diarrhea + Associated with Guillain-Barré syndrome

campylobacter jejuni

Curved gram negative rod + Strongly Urease positive + Causes peptic ulcers and gastric carcinoma

helicobacter pylori

Small Gram-negative coccobacillus + Unpasteurized goat milk/cheese or livestock contact + Undulant (waving) fever + Survives inside macrophages

brucella spp

Gram negative, environmental water systems / A/C units + Grows on BCYE agar + Severe pneumonia accompanied by hyponatremia (low sodium) and GI symptoms

legionella pneumophila

Gram negative, fastidious rod + Cat scratches/bites + Regional lymphadenopathy (Cat-Scratch Disease

bartonella henselae

Gram negative, Rabbit/tick exposure + Ulceroglandular tularemia + Low infectious dose

francisella tularensis