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pathogens Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

strict pathogens

A

organisms that are always associated with human disease
Mycobacterium
tuberculosis (tuberculosis),
Neisseria gonorrhoeae (gonorrhea),
Francisella tularensis (tularemia),
Plasmodium spp (malaria),
rabies virus (rabies)

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2
Q

opportunistic pathogens

A

organisms hat are part of the normal microbial flora, but establish disease under certain conditions
Staphylococcus aureus (repiratory/skin),
Escherichia coli (GI tract),
Candida albicans (GI tract)

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3
Q

normal microbiotia of the skin

A

colonizers
- aerobic and anaerobic diptheroid bacilli (Corynebacterium,
Propionibacterium)
- non-hemolytic aerobic and anaerobic staphylococci (Staphylococcus epidermis, other coagulase-­‐negaAve staphylococci)
- gram positive, aerobic, spore-forming bacilli
- fungi and yeast in skin folds
- acid-fast, nonpathogen mycobacteria (external ear, genitalia)

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4
Q

ear pathogens

A

Colonizers:
coagulase-­‐negaAve
Staphylococcus

Pathogens:
S. pneuomoniae,
Pseudomonas aeruginosa, and
Enterobacteriaceae

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5
Q

mouth, oropharynx, and nasopharynx (upper respiratory tract) pathogens

A

colonizers:
Corynebacteria, staphylococci (S. epidermidis,
S. aureus), streptococci, pneumococci, haemophili

pathogens:
Streptococcus pyogenes, Streptococcus pneumoniae,
Staphylococcus aureus, Neisseria meningi*dis, Haemophilus influenzae, Moraxella catarrhalis, and Enterobacteriaceae

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6
Q

lower respiratory tract pathogens

A

colonizers: generally sterile, but can be colonized with secretions from the upper respiratory tract

pathogens:
S. pneumoniae,
S. aureus, Enterobacteriaceae
such as Klebsiella, Peptostreptococcus
and other anaerobic cocci, and gram-negative rods
rare: Candida

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7
Q

eye pathogens

A

colonizers: coagulase-negative staphyloccoci, Haemophilus, Neisseria, viridans streptococci

pathogens: S. pneumoniae, S. aureus, H/ influenzae, N. gonorrhoeae, Chlamydia trachomatis, P. aeruginosa, Bacillus cereus

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8
Q

esophagus pathogens

A

colonizers:
microorganisms arriving with saliva and food

Pathogens: Candida and viruses (herpes simplex virus, cytomegalovirus)

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9
Q

stomach pathogens

A

Colonizers: acid-­‐tolerant and lactic acid­‐producing bacteria
(Lactobacillus,
Streptococcus), Helicobacter pylori

Pathogens:
H. pylori, enteric bacteria

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10
Q

small and large intestine pathogens

A

colonizers: mostly anaerobic bacteria, fungi, viruses

pathogens: common causal agents of gastroenteritis such as Salmonella and Campylobacter

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11
Q

anterior urethra pathogens

A

colonizers: lactobacilli, streptococci, coagulase-negative staphylococci

pathogens: Enterococcus, Enterobacteriaceae, Candida, N. gonorrhoeae, C. trichomatis

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12
Q

vagina pathogens

A

colonziers: lactobacilli, staphylococci, streptococci, enterobacteriaceae

pathogens: N. gonorrhoeae, Tricoomonas vaginalis, C. albicans, herpes simplex virus, papillomavirus

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13
Q

cervix pathogens

A

colonziers: not typically colonized

pathogens: N. gonorrhoeae, C.trachomatis, Actinomyces

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14
Q

beta-lactams antibiotics

A

target bacterial cells wall synthesis; not typcially effective against beta-lactamase producing bacteria

ex. penicllins, cephalosporins, monobactams, carbapenems

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15
Q

cell wall/peptidoglycan synthesis inhibitors antibiotics

A

glycopeptides/lipopptides: for use against bacteria with beta-lactam resistance

ex. vancomycin, daptomycin
bacitracin = only used for topical applications against gram positive bavteria

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16
Q

protein synthesis inhibitors antibiotics

A

tetracyclin/doxycycline/minocycline - not effective against fungi, readily absorbed into the intestine; penetrates poorly into CSF
chloramphenicol - rapidly absorbed into GI tract and can be distributed to CNS and CSF
macrolides
clindamycin/lincomycin
aminoglycosides

17
Q

quinolines antibiotics

A

inhibitors of bacterial DNA synthesis
4 generations

18
Q

bacillus

A

bacillus anthracis
bacillis cereus

spore-forming gram-positive bacteria
aerobic
rod-shaped
most species don’t cause disease

saprophytic organisms prevalent in soil, water, air, and vegetation

Typical organisms
– cell size: 1 x 3-4 μM
– Square ends, arranged in long chains
– Spores located in center of non-motile bacteria
* Culturing
– Round colonies
– Hemolysis
* Not common with B. anthracis
* Common with B. cereus and saphrophytic bacilli
– Growth in gelatin resembles an inverted fir tree
* Growth characteristics – Saphrophytic bacilli
* Simple sources of nitrogen and carbon for energy and growth
– Spores
* Resistant to environmental changes
– Withstand dry heat and certain chemical disinfectants for moderate periods
– Can persist in dry earth for years
* Animal products can be sterilized by autoclaving

19
Q

bacillus anthracis

A

spore-forming gram-positive bacteria

Spores found in contaminated
soil

causes anthrax - primarily a diseases of herbivores; occasionally a disease of humans
types of infection - cutaneous anthrax (rarely fatal), GI anthrax (20-60% fatal), inhalation anthrax (usually fatal)

capsule - made of poly-D-glutamic acid, anti-phagocytic, capsule gene is encoded on a plasmid

anthrax toxins - exotoxins, encoded on plasmid pXO1, 3 proteins (protective antigen, edema factor, lethal factor)

susceptible hosts - proliferate at site of entry, capsules remain intact, surround by large amount of proteinaceous fluid, very few leukocytes, rapid dissemination to the bloodstream
resistant hosts - proliferation of only a few hours, large accumulation of leukocytes, capsules disintegrate, bacteria remain localized

**see lecture 3 slides 40-44 for clinical findings and laboratory tests

treatment - cirpofloxacin (quinolone antibiotic) or penicillin G + gentamycin/streptomycin

20
Q

bacillis cereus

A

spore-forming gram-positive bacteria

produces toxins - illness is more an intoxication rather than an infection

causes food poisoning
- emtic or diarrheal
difficult to diagnose from stool samples becasue some is already present in normal stool specimens

associated with localized infection: skin, eye infections, systemic infections (endocarditis, meningitis, osteomyelitis, pneumonia)

resistant to antimicrobial agents - penicillins (B. cereus produce beta-lactamases, cephalosporins - class of beta-lactam antibiotics

severe non-foodborne infections are treated with vancomycin or clindamycin with or without amino-glycosides

21
Q

clostridium

A

spore-forming gram-positive bacteria

Clostridium botulinum, Clostridium tetani, and invasive Clostridia

anaerobic

large, gram positive rods
motile
decomposes proteins or form toxins
natural habitat is soil or intestinal tract
includes bacteria that cause botulism, tetanus, gas gangrene, and pseudomembrane colitis

Typical organisms
– Spores have larger diameter than rods
– Mobile via peritrichous flagella

Culturing
– Anaerobic, with some species being aerotolerant
– Use of blood-enriched plates

Colony forms
– Produce large, raised colonies
– Zone of β-hemolysis on blood agar

Growth characteristics
– Saccharolytic or proteolytic classification based on sugar fermentation or protein digestion

Antigenic characteristics
– Have some anAtigens, but have specific soluble antigens that allow for grouping

22
Q

Clostridium botulinum

A

spore-forming gram-positive bacteria

causal agent of botulism - more intoxication rather than disease and occurs after ingestion of contaminated food
- resulting paralysis leads to death

found in soils and occasionally animal feces - vegetative cells and endospores

distinguished by antigenic type of toxin produced

spores are highly resistant

toxin produced during growth and liberated during autolysis of bacteria
- absorbed from gut and binds to receptors of presynaptic membrane of motor neurons of the PNS and cranial nerves

pathogenesis
- sources of botulism
1. ingestion - non-cooked foods
2. infant botulism - honey or jarred baby food

clinical findings - symptoms begin 18-24 hours after ingestion, signs of paralysis are progressive, death occurs from respiratory paralysis or cardiac arrest, no fever, those that recover do not produce anti-toxin

lab tests - mouse bio-assay is gold standard

treatment - antitoxins available for types A, B, and E; adequate respiration must be provided, mortality rate has been reduced from 65% to 25%; in infant botulism, most infants recover from supportive care alone, but antitoxin therapy is recommended

what’s at risk is home-canned foods

23
Q

Clostridium tetani

A

spore-forming gram-positive bacteria

casual agent of tetanus

found in soil and feces of animals - horses
can be distinguished by their specific flagellar antigens
all share a common O antigen
all produce the neurotoxin tetanospasmin

toxin can be small amount for lethal, neuronal effects, physiological effects causing hyperreflexia

pathogenesis
- not an invasive organism, toxin released from vegetative cells reaches CNS

clinical findings - incubation period is 4-5 days, characterized by tonic contraction of voluntary muscles, death results from interference with respiration process, mortality rate is high

diagnosis - anaerobic culture of tissue may yield the organism, detection of toxin via neutralization using specific antitoxin

prevention with immunization

treatment - penicillin, antitoxin intramuscular administration

24
Q

invasive Clostridia

A

spore-forming gram-positive bacteria

large variety of toxins produced
- results in spreading infection
- effects include lethal, necrotizing, and hemolytic properties

C.perfringens
- alpha toxin = lecithinase (lecithin = important component of cell membrane)
- enterotoxin also produced
- symptoms include nausea, vomiting, and fever
- illness is similar to that produced by B. cereus
- illness is self-limiting

pathogenesis
- spores reach tissue via soil or fecal contamination; spore germinate –> vegetative cells multiply –> carbohydrate fermentation –> gas production
- aids in the spread of infection
- tissue necrosis occurs –> hemolytic anemia –> severe toxemia and death
- clostridial myoecrosis - mixed infection

clinical findings = from a contaminated wound, infection spreads in 1-3 days, food poisoning

lab tests - spores not usually present because of large gram positive rods, look for hemolysis, colony morphology, if gas produced, C.perfringens is suspected

treatment - surgery, antimicrobial drugs penicillin, hyperbaric oxygen used, anti-toxins

25
Q

corynebacterium

A

aerobic, non-spore forming gram positive bacteria

irregularly shaped
high G-C content

corynebacterium diphtheriae

26
Q

corynebacterium diphtheriae

A

aerobic, non-spore forming gram positive bacteria

major pathogen of corynebacteria
granules stain deeply with aniline dyes
stains lie parallel or acute angles

culturing - blood agar, tellurite agar

pathogenesis - casual agent of diphtheria (2 types = respiratory or cutaneous), toxin producing (exotoxin)

clinical findings - respiratory = sore throat and low grade fever, prostration, dyspnea

lab tests - smears, agar, toxin testing

resistance - resistance to disease depends on neutralizing anti-toxin in the bloodstream and tissues

treatment - successful treatment needs rapid suppression of toxin-producing bacteria; antimicrobial drugs, administration of specific anti-toxin at the site of infection or entry

prevention - immunization in childhood

27
Q

listeria

A

aerobic, non-spore forming gram positive bacteria

everywhere, hardy (large temp range for growth, can grow in pH range 4.4 to 9.4, can grow under aerobic and anaerobic conditions, halotolerant)

10 species

short gram positive rod
facultative anaerobe
motile
temperature range for growth optimal 30-37C
catalase positive
+/- hemolytic activity

lab tests - beta hemolysis, CAMP test, beta-lysin disk

culture and growth characteristics - growth on bile and esculin
- ferric ammonium citrate allows for detection of esculin hydrolysis
- esculin hydrolysis causes blackening of the agar
- produces beta-glucosidases
- has phospho-inositol phospholipase C activity
- ferments xylose
- used in combination with PI-PLC in agars
(positive PI-PLC colonies = blue, negative PI-PLC colonies = white, positive xylose fermentation = yellow agar, negative xylose fermentation forms no halo)

13 serotypes

Disease manifestations
– Healthy individuals: self-limiting gastroenteritis
– Immunocompromised individuals: possible systemic infections leading to meningitis, encephalitis
– Pregnant women: infection of developing fetus, leading to abortion, stillbirth, or neonatal infections

lab tests - forms umbrella shape in motility tubes, catalase positive, gram positive, hemolysis, verification by PCR, serology, or biochemical tests

treatment - antimicrobial drugs are effective against listeria spp

28
Q

erysipelotthrix

A

aerobic, non-spore forming gram positive bacteria

29
Q

corynebacterium diphtheriae

A
30
Q

erysipelotthrix rhusiopathiae

A

aerobic, non-spore forming gram positive bacteria

produces small, transparent glistening colonies
alpha-hemolytic on blood agar
catalase negative
oxidase negative
indole negative
growth on triple sugar iron agar results in H2S production
can appear as singles, short chains, long non-branching filaments, random
distributed in land and sea animals ,bot vertebrates and invertebrates
causes disease in pigs, turkeys, ducks and sheep
highly susceptible to penicillin G; resistant to vancomycin

Medical Microbiology (2 decks)

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