pathogens Flashcards
strict pathogens
organisms that are always associated with human disease
Mycobacterium
tuberculosis (tuberculosis),
Neisseria gonorrhoeae (gonorrhea),
Francisella tularensis (tularemia),
Plasmodium spp (malaria),
rabies virus (rabies)
opportunistic pathogens
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)
normal microbiotia of the skin
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)
ear pathogens
Colonizers:
coagulase-‐negaAve
Staphylococcus
Pathogens:
S. pneuomoniae,
Pseudomonas aeruginosa, and
Enterobacteriaceae
mouth, oropharynx, and nasopharynx (upper respiratory tract) pathogens
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
lower respiratory tract pathogens
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
eye pathogens
colonizers: coagulase-negative staphyloccoci, Haemophilus, Neisseria, viridans streptococci
pathogens: S. pneumoniae, S. aureus, H/ influenzae, N. gonorrhoeae, Chlamydia trachomatis, P. aeruginosa, Bacillus cereus
esophagus pathogens
colonizers:
microorganisms arriving with saliva and food
Pathogens: Candida and viruses (herpes simplex virus, cytomegalovirus)
stomach pathogens
Colonizers: acid-‐tolerant and lactic acid‐producing bacteria
(Lactobacillus,
Streptococcus), Helicobacter pylori
Pathogens:
H. pylori, enteric bacteria
small and large intestine pathogens
colonizers: mostly anaerobic bacteria, fungi, viruses
pathogens: common causal agents of gastroenteritis such as Salmonella and Campylobacter
anterior urethra pathogens
colonizers: lactobacilli, streptococci, coagulase-negative staphylococci
pathogens: Enterococcus, Enterobacteriaceae, Candida, N. gonorrhoeae, C. trichomatis
vagina pathogens
colonziers: lactobacilli, staphylococci, streptococci, enterobacteriaceae
pathogens: N. gonorrhoeae, Tricoomonas vaginalis, C. albicans, herpes simplex virus, papillomavirus
cervix pathogens
colonziers: not typically colonized
pathogens: N. gonorrhoeae, C.trachomatis, Actinomyces
beta-lactams antibiotics
target bacterial cells wall synthesis; not typcially effective against beta-lactamase producing bacteria
ex. penicllins, cephalosporins, monobactams, carbapenems
cell wall/peptidoglycan synthesis inhibitors antibiotics
glycopeptides/lipopptides: for use against bacteria with beta-lactam resistance
ex. vancomycin, daptomycin
bacitracin = only used for topical applications against gram positive bavteria
protein synthesis inhibitors antibiotics
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
quinolines antibiotics
inhibitors of bacterial DNA synthesis
4 generations
bacillus
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
bacillus anthracis
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
bacillis cereus
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
clostridium
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
Clostridium botulinum
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
Clostridium tetani
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
invasive Clostridia
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
corynebacterium
aerobic, non-spore forming gram positive bacteria
irregularly shaped
high G-C content
corynebacterium diphtheriae
corynebacterium diphtheriae
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
listeria
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
erysipelotthrix
aerobic, non-spore forming gram positive bacteria
corynebacterium diphtheriae
erysipelotthrix rhusiopathiae
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
