Bacteria

Question 1

Staphylococcus aureus

Answer 1

GRAM+ cocci in clusters; produces the enzyme coagulase; alpha hemolytic (completely hemolyze the blood cells present on agar plates); anterior nares colonization is common, handwashing stops transmission, produces enterotoxins in rich foods

Question 2

What are the manifestations of Staphylococcus aureus and how is it treated?

Answer 2

skin infections like a furuncle (boil), carbuncle (multiple boils combined), bullous impetigo (superficial blisters), deep lesions (acute osteomyelitis), scalded skin syndrome (desquamation), toxic shock syndrome, staphylococcal food poisoning (intoxication by enterotoxin) wound infections
Treatment: antimicrobials (MRSA is treated with vancomycin)

Question 3

Streptococcus agalactiae

Answer 3

group B, beta-hemolytic (complete lysis of RBCs); can cause neonatal sepsis from mother’s vaginal flora

Question 4

What are the manifestations of Streptococcus agalactiae and how is it treated?

Answer 4

pneumonia and meningitis, serious infections in adults
Treatment: penicillin

Question 5

Streptococcus pneumoniae

Answer 5

GRAM+ cocci usually arranged in pairs, alpha hemolytic (ability to partially lyse RBCs) can cause pneumonia (dangerous for the young and old), respiratory colonization is common, transmission via aerosol droplets

Question 6

What are the manifestations of Streptococcus pneumoniae and how is it treated?

Answer 6

pneumococcal pneumonia (usually lobar) and pneumococcal meningitis (cause of bacterial meningitis) can also cause sinusitis and ear infections
Treatment: Penicillin (although some are penicillin-resistant)

Question 7

Viridans group streptococcus

Answer 7

alpha-hemolytic streptococci (but are not S. pneumonia) GRAM+ in chains

Question 8

What are the manifestations of Viridans and how is it treated?

Answer 8

normal flora of the mouth and nasopharynx, with low to no virulence (not typically causing disease) however can cause bacterial endocarditis (when it reaches damaged heart valves)
Treatment: penicillin

Question 9

Streptococcus pyogenes

Answer 9

GRAM+ cocci; in chains/pairs; classified based on cell wall carbohydrates; beta-hemolytic (can completely lyse RBCs) due to streptolysin S and/or O; most common cause of pharyngitis, droplets spread over short distances; skin colonization and skin trauma can lead to impetigo; hospital outbreaks due to carriers (with no symptoms)

Question 10

What are the manifestations of Streptococcus pyogenes and how is it treated?

Answer 10

streptococcal pharyngitis (strep throat), impetigo, erysipelas, scarlet fever (produces superantigens), streptococcal toxic shock syndrome (can lead to nec fasc!), acute rheumatic fever (autoimmune state)
Treatment: penicillin

Question 11

Bacillus anthracis

Answer 11

GRAM+, spore forming rods, spores survive boiling; endospores survive in nature (soil); primarily a disease of herbivores (horses, sheep, cattle); human infection is through spores derived from these herbivores being inoculated through the skin; contaminated materials can be imported, aerosolized anthrax spores are a biological warfare threat; weapons-grade spores are specially treated

Question 12

What are the manifestations of Bacillus anthracis and how is it treated?

Answer 12

papule lesion (can look like an insect bite) then progresses to a black scab surrounded by edema; lesion heals slowly/very little systemic symptoms; pulmonary anthrax acquired by inhaling spores; fever and cough progress to cyanosis, hemorrhagic mediastinitis, meningitis and death
Treatment: cipro and doxycycline

Question 13

Clostridium tetani

Answer 13

anaerobe; respires via fermentation; GRAM+ rods; spore forming, tetanospasmin (neurotoxic exotoxin)- degrades protein required for NT release and causes unopposed firing of the active motor neurons, causing spastic paralysis; deactivated toxin is used as vaccine against toxin; spores found in the environment (soil) and germinate in wounds; tetanospasmin production at the local site ascends through nerves to the CNS producing contractions of both protagonist and antagonist muscles

Question 14

What are the manifestations of Clostridium tetani and how is it treated?

Answer 14

masseter muscles often first affected (lock-jaw), respiratory muscle spasms, etc.
Treatment: human tetanus immune globulin (HTIG) given to neutralize toxin, DTaP vaccine in childhood

Question 15

Clostridium botulinum

Answer 15

anaerobe; respires via fermentation; GRAM+ rods, spore-forming; botulinum toxin cleaves attachment protein receptors at NMJ, blocking ACh (causes flaccid paralysis), one of the most potent toxins in nature; widely distributed in nature, alkaline foods favor toxin production (veggies), toxin is readily absorbed in the bloodstream, paralysis of diaphragm, cardiac arrhythmias and bp instability

Question 16

What are the manifestations of Clostridium botulinum and how is it treated?

Answer 16

12-36 hours after ingestion: nausea, dry mouth, diarrhea, can then cause blurred vision, pupillary dilation, involuntary eye movements; finally paralysis which first occurs with ocular, laryngeal, and respiratory muscles, mortality rate 10-20%
Treatment: antitoxin, supportive measures (ventilation)

Question 17

Haemophilus influenzae

Answer 17

tiny, GRAM- coccobacilli; require hematin and NAD; unable to lyse RBCs (only grows on chocolate agar in lab); nasopharyngeal colonization common, most commonly causes meningitis in children under 2; immunization has dramatically reduced disease

Question 18

What are the manifestations of Haemophilus influenzae and how is it treated?

Answer 18

meningitis, acute epiglottitis (infection that can block the airway), can cause cellulitis, conjunctivitis, otitis media, and sinusitis
Treatment: amoxicillin or azithromycin is usually given (vaccine available for prevention)

Question 19

Bordetella pertussis

Answer 19

fastidious (requires special nutrients in order to grow), and growth is slow; contagious, spread through airborne droplets; immunization reduces disease but outbreaks continue due to vaccine compliance; high mortality in infants, adults experience milder disease and pertussis is not diagnosed; immunity wanes with age, boosters needed

Question 20

What are the stages/manifestations of Bordetella pertussis?

Answer 20

prolonged course of 3 overlapping stages
- catarrhal phase (1-2 weeks) with a severe runny nose, fever, fatigue, sneezing, etc.; most communicable phase
- paroxysmal phase (2-4 weeks) with coughing episodes, inspiratory whoop following cough, vomiting, high WBC count
- convalescent phase (3-4 weeks) where symptoms slowly fade away; pneumonia is a common complication

Question 21

How is Bordetella pertussis treated?

Answer 21

antimicrobials during catarrhal phase
most sensitive test for this: PCR testing

Question 22

Legionella pneumophila

Answer 22

GRAM- rod; associated with aerosols distributed by humidifying and cooling systems; person to person transmission is unknown

Question 23

What are the manifestations of Legionella pneumophila and how is it treated?

Answer 23

severe toxic pneumonia occurring in 5% of those exposed; high mortality in immunocompromised patients
- difficult to culture, PCR is most reliable
Treatment: levofloxacin which is a fluoroquinolone

Question 24

Neisseria Gonorrhoeae

Answer 24

GRAM- diplococci; fastidious (special medium for growth); contain a variant of LPS (shorter and lacks the O-antigen portion) called LOS; rates among adolescents are high and increasing; sexually transmitted; inability to detect (asymptomatic) hampers control (mostly in women); lack of appreciation in this disease’s importance

Question 25

What are the manifestations of Neisseria Gonorrhoeae and how is it treated?

Answer 25

urethritis and endocervicitis are primary infections
- in men (purulent urethral discharge and dysuria)
- in women (vaginal discharge, urinary frequency, dysuria, abdominal pain) symptoms can be mild or absent in either sex; other local infections can occur (rectal and pharyngeal); PID can develop in women with fever, lower abdominal pain, adnexal tenderness, high WBC count; caused by spread of organism into fallopian tubes producing salpingitis and into the pelvic cavity; PID can lead to infertility and ectopic pregnancy
Treatment: 3rd generation cephalosporins used due to extensive resistance

Question 26

Escherichia coli

Answer 26

GRAM- rods that are large; present in nature and the intestinal tract, UTIs and acute diarrhea are the most common manifestations; accounts for 90% of cystitis and pyelonephritis (UTIs) in healthy people in the US, reservoir for these infections is the patient’s own intestinal E. coli microbiota which contaminates the perineal and urethral area; one of the most common causes of neonatal meningitis (infection from vaginal flora); extraintestinal, non UTI infections are uncommon unless there is significant breach in host defense

Question 27

Escherichia coli pathotypes:

Answer 27

ETEC: enterotoxigenic; responsible for repeated diarrhea in infants in developing countries from contaminated food and/or water; caused by LT and/or ST enterotoxin

EPEC: enteropathogenic; linked to diarrhea outbreaks in nurseries in the late 1950s (healthcare associated); organisms attach to small intestine enterocytes using bundle-forming pili to form clustered microcolonies; lesions then progress with localized loss of microvilli and changes in the cell morphology

EHEC: enterohemorrhagic; linked to consumption of contaminated animal products, but human-human transmission is possible; causes bloody diarrhea and hemolytic uremic syndrome; low infectious dose (strain O157:H7)

Question 28

What are the manifestations of Escherichia coli and how is it treated?

Answer 28

UTIs (dysuria and frequency), ETEC and EPEC diarrhea is watery, EHEC diarrhea is bloody, HUS (low urine output) can progress to renal failure
usually tested in a direct gram stain of the urine or detections of toxin in stool
Treatment: amoxicillin, trimethoprim-sulfa, cipro

Question 29

Yersinia Pestis

Answer 29

nonmotile, GRAM- rod; cause of the “Black death” plague in Europe in the 14th century; sylvatic transmission among rodents is primary reservoir; rat migration to cities increased human risk; fleas become infected and the bacteria multiply in the gut of the flea, blocking digestive tract; when flea bites a new host- it regurgitates the organism because flea’s gut is blocked; bubo is the initial lesion; secondary pneumonia can occur

Question 30

What are the manifestations of Yersinia Pestis and how is it treated?

Answer 30

bubonic plague mortality is 50-75% in untreated cases (fever and painful bubo) death from LPS shock within hours to days; pneumonic plague is fatal if untreated (fever, fatigue, tightness of chest) need antibiotic therapy
Treatment: streptomycin, tetracycline, etc.

Question 31

Pseudomonas aeruginosa

Answer 31

GRAM-, motile rod (flagella); resistant to many antimicrobials, green when grown on agar plates; present in the environment (water/soil); nosocomial, occasionally colonizes humans; multiplies in humidifiers, solutions and medications; highest risk in immunocompromised patients; respiratory colonization of cystic fibrosis becomes chronic

Question 32

What are the manifestations of Pseudomonas aeruginosa and how is it treated?

Answer 32

infected burn wounds and environmentally contaminated wounds; common cause of swimmer’s ear; contamination of contact lenses leads to keratitis (can destroy cornea); bacteremia can lead to ecthyma gangrenosum (papules progress to necrotic ulcers)
Treatment: ?? resistant to many antimicrobials

Question 33

Burkholderia cepacia

Answer 33

causes similar infections to pseudomonas (burns, wounds, lungs) but not usually as common or severe; nosocomial, present in the environment, especially water

Question 34

Capnocytophaga

Answer 34

GRAM- rods; normal flora in the mammal oropharyngeal tract (mouth and throat); opportunistic pathogen, transmitted via animal bites (dogs and cats)

Question 35

What are the manifestations of Capnocytophaga and how is it treated?

Answer 35

inflammation at the site of the bite wound; can progress to septicemia and endocarditis; also can cause gum disease
Treatment: penicillin or clindamycin

Question 36

What are Mycobacteria?

Answer 36

have a strange cell wall; known as acid-fast (contains a large amount of long chain fatty acids called mycolic acids that form a waxy coat); once stained–they are difficult to decolorize so a special staining procedure is used called acid-fast staining; most species grow very slowly

Question 37

Mycobacterium tuberculosis (and types)

Answer 37

growth takes weeks; spread by respiratory droplets and AIDS enhances this spread
- Primary TB is where bacteria invade and multiply inside alveolar macrophages; killing ability of phagosome is blocked, immune response is triggered, bacteria can disseminate, cytokines attract T cells and other immune cells to the alveoli;
- Latent TB where primary lesions heal once immunity develops, some TB bacteria enter the latent state rather than dying; not fully understood
- Reactivation TB where the latent bacteria reactivate; immune-mediated destruction forms pulmonary cavities

Question 38

What are the manifestations of Mycobacterium tuberculosis and how is it treated?

Answer 38

Primary TB: causes formation of granuloma in the alveoli, granuloma grows and leads to necrosis in the center of the lesion; either asymptomatic or only have fever/fatigue
Reactivation TB: most common in older men (malnutrition, alcoholism, diabetes, stress, smoking); cough, fever, fatigue, sweating, weight loss) cavities form in lungs
Testing: TB skin test, chest X-ray, other blood tests, acid-fast staining
Treatment: drugs must penetrate lipid-rich wall; multidrug therapy decreases probability of resistance; treatment lasts 6-9 months and patient compliance is a problem

Question 39

Mycobacterium leprae

Answer 39

obligate intracellular parasite, target is Schwann cells of the PNS, peripheral nerves are demyelinated

Question 40

What are the manifestations of Mycobacterium leprae and how is it treated?

Answer 40

tuberculoid leprosy: primarily results in skin and nerve involvement with flattened plaques on the face, trunk, and limbs with raised red edges and dry pale hairless centers
lepromatous leprosy: large, more severe, and more infiltrative
Treatment: multi-drug therapy, long-term

Question 41

Treponema pallidum

Answer 41

spirochete, spiral structure involved in motility; does not grow in culture; GRAM- but does NOT contain LPS (lipopolysaccharide); transmitted by contact with mucosal surfaces or blood, congenital infection is transplacental; sexually transmitted disease (syphilis)

Question 42

What are the manifestations of Treponema pallidum and how is it treated?

Answer 42

• Primary syphilis: painless, hardened ulcer starts the disease, heals after weeks
• Secondary syphilis: 2-8 weeks after chancre (hardened ulcer), can cause rash, nontender lymph node enlargement, fever, fatigue; lesions of the rash contain large amounts of organism and is highly infectious, resolves in days-weeks, but ⅔ of patients enter latent stage (mothers can transmit infection to fetus throughout latency)
• Tertiary syphilis: 15-20 years after primary infections; neurosyphilis, cardiovascular syphilis, and gummas
  Testing: darkfield microscope to view organisms, rapid plasma regain (RPR) tests used to detect infections; confirmatory tests use actual T. pallidum organism as antigen to test patient’s blood for antibodies
  Treatment: penicillin

Question 43

Chlamydia trachomatis

Answer 43

obligate intracellular bacteria; GRAM- but lack peptidoglycan between membranes; has a unique replication cycle (has to be inside a host cell in order to replicate)

Elementary body (EB)- small, hardy, infectious
Reticulate body (RB)- larger, fragile intracellular replicative form

EBs infect cells and convert to RBs; RBs multiply then revert back to EBs to leave the cell and infect others
Infects conjunctiva and genital tract; neonatal conjunctivitis is contracted from mother infection; prevalence is 5% in general US population

Question 44

What are the manifestations of Chlamydia trachomatis and how is it treated?

Answer 44

Trachoma: chronic inflammation of the eyelid and increased vascularization of the corneal conjunctiva
Genital infections: UTIs, PID which can cause permanent fertility problems; swollen lymph nodes in groin
- PCR testing is most reliable
Treatment: Azithromycin

Question 45

Rickettsia rickettsii

Answer 45

obligate intracellular bacteria (has to be present inside a host cell in order to replicate); small, GRAM- coccobacilli; spread by ticks, mortality is 25% if left untreated, most dangerous among children under 10

Question 46

What are the manifestations of Rickettsia rickettsii and how is it treated?

Answer 46

Rocky Mountain spotted fever: caused by this; incubation time of 2-14 days after tick bite; can include fever, headache, rash, mental confusion, and muscle pain; rash is most characteristic but might not occur (spreads from extremities to trunk and involves palms/soles) complications can occur
Treatment: Doxycycline