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Bacteriology Flashcards

1
Q

What are bacterial pili composed of and what is their function?

A

composed of glycoprotein and mediate adherence, including formation of the sex plus during conjugation

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2
Q

Describe the composition and purpose of a bacterial capsule.

A
  • most are an organized, discreet layer of polysaccharides

- they function to protect the cell from phagocytosis

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3
Q

What is a bacterial glycocalyx?

A
  • a loose network of polysaccharides

- which mediates adherence to surfaces, especially foreign substances like catheters

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4
Q

Describe a bacterial outer membrane.

A
  • found only in gram-negatives, they are composed of an outer leaflet containing endotoxin with embedded proteins like porins and an inner leaflet of phospholipids
  • endotoxin is responsible for inducing an immune response and porins regulate transport
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5
Q

What is the bacterial periplasm?

A
  • found only in gram-negatives, it is the space between the cytoplasmic membrane and outer membrane
  • it includes many hydrolytic enzymes like beta-lactamases
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6
Q

What is the function of the bacterial cell wall?

A

it gives the cell rigid support and protects it against osmotic pressure damage

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7
Q

What are lipoteichoic acids?

A

a unique component of gram-positives which extends form the cytoplasmic membrane out through the cell wall and is responsible for inducing TNF and IL-1

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8
Q

What is the purpose of the cytoplasmic membrane of bacteria?

A

it is the inner, phospholipid bilayer which contains many embedded proteins such as PBP and serves as the site for oxidative and transport enzymes

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9
Q

Describe the outer structure of gram-positive bacteria.

A
  • an inner cytoplasmic membrane with lipoteichoic acids that extend outward
  • a thick peptidoglycan cell wall
  • an organized, discrete polysaccharide capsule
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10
Q

Describe the outer surface of gram-negative bacteria.

A
  • an inner cytoplasmic membrane
  • the periplasmic space containing a thin, peptidoglycan cell wall
  • and outer membrane containing endotoxin in the outer leaflet and embedded porins
  • an organized, discrete polysaccharide capsule
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11
Q

What are the end results of a Gram stain?

A
  • gram positives with thick peptidoglycan layers retain the initial crystal violet dye
  • gram negatives with thin peptidoglycan layers turn red or pink with the counterstain
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12
Q

Giemsa stain is used for which 5 organisms?

A
  • Chlamydia
  • Borrelia
  • Rickettsia
  • Trypanosomes
  • Plasmodium
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13
Q

PAS can be used to stain for which bacterial organism?

A

Tropheryma whipplei of Whipple disease

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14
Q

What is Ziehl-Neelsen stain?

A

also known as carbo fuchsin, it stains mycolic acids in the cell wall of acid-fast bacteria

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15
Q

Which 3 organisms require a silver stain?

A

fungi, Legionella, and H. pylori

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16
Q

What is an indicator media?

A

one that yields a color change in response to the metabolism of certain organisms, e.g. MacConkey agar

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17
Q

What makes anaerobes intolerant of oxygen?

A

they lack catalase and/or superoxide dismutase and are therefore very susceptible to oxidative damage

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18
Q

Which bacteria are obligate intracellular and why are they?

A
  • Rickettsia, CHlamydia, and COxiella (“stay inside when it’s Really CHilly and COld”)
  • all rely on the host for ATP production
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19
Q

Which bacterial species are facultative intracellular?

A

Some Nasty Bugs May Live FacultativeLY

  • salmonella
  • neisseria
  • brucella
  • mycobacterium
  • listeria
  • francisella
  • legionella
  • yersinia pestis
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20
Q

Which bacteria species are encapsulated?

A

Please SHINE My SKiS

  • Pseudomonas
  • Salmonella
  • H. influenza
  • Neisseria
  • E. coli
  • Strep pneumo
  • Klebsiella
  • Strep, Group B
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21
Q

Which bacterial species are catalase-positive?

A

Cats Need PLACESS to Belch their Hairballs

  • Nocardia
  • Pseudomonas
  • Listeria
  • Aspergillus
  • Candida
  • E. coli
  • Staph
  • Serratia
  • B. cepacia
  • H. pylori
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22
Q

Which bacteria utilize the IgA protease virulence factor?

A

S. pneumo, H. influenzae type B, and Neisseria, which all colonize respiratory mucosa

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23
Q

What is the function fo the Protein A virulence factor and which bacteria utilizes it?

A

a protein, expressed by S. aureus, that binds the Fc region of IgG and prevents opsonification

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24
Q

Describe the process of bacterial transformation.

A

bacteria are known as “component” if they have the ability to take up naked DNA from the environment

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25
Q

Describe the process of F+/F- bacterial conjugation.

A
  • the F+ plasmid contains genes required for sex plus formation and conjugation
  • the bridge forms and a single strand of plasmid DNA (no chromosomal DNA) is transferred
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26
Q

What is the difference between F+ conjugation and Hfr conjugation?

A
  • F+ conjugation involves only transfer of plasmid DNA
  • Hfr occurs in bacteria that have incorporated the F+ plasmid into their chromosomal DNA, thus transfer may include the plasmid and some chromosomal genes
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27
Q

Describe the process of generalized transduction.

A
  • a lytic phage infects the bacterium, leading to cleavage of bacterial DNA
  • parts of this fragmented chromosomal DNA may get packaged into phage capsids
  • when these phages infect another bacterium, there can be a transfer of genes
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28
Q

Describe the process of specialized transduction.

A
  • a lysogenic phage infects a bacterium and incorporates it’s DNA into bacterial DNA at a specific location
  • when the phage DNA is excised, flanking genes may be excised as well
  • this DNA is packaged and may infect another bacterium
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29
Q

Name five bacterial toxins that are encoded in a lysogenic phage?

A

ABCD’S

  • group A strep erythrogenic toxin
  • Botulinum toxin
  • Cholera toxin
  • Diphtheria toxin
  • Shiga toxin
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30
Q

What must you do to kill spore-forming bacteria?

A

autoclave them

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31
Q

How does endotoxin compare to exotoxin?

A
  • source: exotoxins found in a variety of gram positives and negatives while endotoxin is found on only negatives
  • secretion: exotoxins are secreted, endotoxins are not
  • dose: exotoxins require much lower doses to cause significant problems and be fatal
  • genetics: exotoxins are encoded on plasmids or by bacteriophages, endotoxin is part of the bacterial chromosome
  • antigenicity: exotoxins induce high-titer antibodies called antitoxins but endotoxin is poorly antigenic
  • heat stability: exotoxins destroyed quickly at 60 degrees Celsius but endotoxins are stable at 100 degrees Celsius for an hour
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32
Q

Through what mechanism does diphtheria toxin act?

A

it ADP-ribosylates and inactivates EF-2

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33
Q

List the bacteria (other than S. pyogenes), mechanism, and effects associated with exotoxin A.

A
  • Pseudomonas
  • an AB toxin that ADP-ribosylates and inactivates EF-2
  • causes host cell death
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34
Q

List the bacteria, mechanism, and effects associated with Shiga toxin

A
  • shigella
  • an AB toxin that inactivates the 60S ribosome by removing adenine from rRNA
  • causes GI mucosal damage, leading to dysentery, and enhances cytokine release, causing HUS
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35
Q

List the bacteria, mechanism, and effects associated with shiga-like toxin.

A
  • EHEC
  • an AB toxin that inactivates the 60S ribosome by removing adenine from rRNA
  • enhances cytokine release, causing HUS
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36
Q

List the bacteria, mechanism, and effects associated with heat-liable toxin.

A
  • ETEC
  • an AB toxin that overactivates AC, increases cAMP, increases Cl- secretion into gut lumen, causes an efflux of water
  • watery diarrhea
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37
Q

List the bacteria, mechanism, and effects associated with heat-stable toxin.

A
  • ETEC
  • overactivates GC, increases cGMP, reduces NaCl reabsorption, and causes an efflux of water into gut lumen
  • watery diarrhea
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38
Q

List the bacteria, mechanism, and effects associated with edema toxin.

A
  • B. anthracis
  • an AB toxin that mimics AC to raise cAMP levels
  • responsible for edema surrounding black eschar
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39
Q

List the bacteria, mechanism, and effects associated with cholera toxin.

A
  • V. cholerae
  • an AB toxin that inactivates Gs, activating AC, raising cAMP, increasing Cl- secretion into the gut, and causing an efflux of water
  • watery diarrhea
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40
Q

List the bacteria and mechanism associated with pertussis toxin.

A
  • Bordatella pertussis

- an AB toxin that disables Gi, over activating AC, raising cAMP, and impairing phagocytosis

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41
Q

List the bacteria, mechanism, and effects associated with tetanospasmin.

A
  • C. tetani
  • an AB toxin protease that cleaves SNARE, a set of proteins required for vesicular fusion and NT release, and inhibits release of inhibitor neurotransmitters from Renshaw cells
  • causes spastic paralysis, risks sardonicus, and lock jaw
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42
Q

List the bacteria, mechanism, and effects associated with botulinum toxin.

A
  • C. botulinum
  • an AB toxin protease that cleaves SNARE, a set of proteins required for vesicular fusion and NT release, and inhibits release of ACh at the neuromuscular junction
  • causes a flaccid paralysis
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43
Q

What is the difference between tetanospasmin and botulinum toxin?

A
  • both are proteases that cleave SNARE and inhibit vesicular fusion and thus NT release
  • tetanospasmin inhibits release of inhibitory neurons, causing a spastic paralysis, whereas botulinum toxin inhibits release of ACh, causing a flaccid paralysis
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44
Q

List the bacteria, mechanism, and effects associated with alpha toxin.

A
  • C. perfringens
  • a phospholipase/lecithinase that degrades tissue and cell membranes
  • responsible for myonecrosis and hemolysis (the double zone of hemolysis)
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45
Q

List the bacteria, mechanism, and effects associated with streptolysin O.

A
  • Strep pyogenes
  • a protein that degrades cell membranes
  • lyses RBCs and contributes to B-hemolysis
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46
Q

List the bacteria, mechanism, and effects associated with toxic shock syndrome toxin.

A
  • S. aureus
  • links MHC-II and TCR and causes a cytokine storm
  • causes fever, rash, and shock
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47
Q

List the bacteria (other than Pseudomonas), mechanism, and effects associated with exotoxin A.

A
  • S. pyogenes
  • links MHC-II and TCR and causes a cytokine storm
  • causes fever, rash, and shock
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48
Q

What are the components of endotoxin and which is toxic?

A

composed of O antigen, a core polysaccharide, and lipid A, the toxic component

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49
Q

Describe the downstream effects of endotoxin.

A
  • binds TLR4 (CD14) on macrophages and induces release of IL-1 and IL-6, leading to fever; TNF, leading to fever and hypotension; and NO, leading to hypotension
  • activates complement with C3a and C5a leading to histamine release, contributing to hypotension and edema, and C5a serving as a neutrophil chemotactic factor
  • activates tissue factor, inducing the coagulation cascade and causing DIC
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50
Q

Staph aureus

A
  • a gram-positive cocci that grows in clusters with a yellow pigment and colonizes the nasopharynx
  • it is catalase positive, coagulase positive, mannitol-fermenting, and beta-hemolytic
  • it’s primary virulence factor is protein A, which binds the Fc portion of IgG and prevents opsonification
  • clinically, it is known for causing a secondary pneumonia with patchy infiltrates, septic arthritis (#1 cause), a variety of skin infections (including impetigo and abscesses), acute endocarditis (usually of the tricuspid valve in IV drug users), and osteomyelitis (#1 cause)
  • it produces exfoliative toxin, a tissue protease responsible for the desquamative rash known as scalded skin syndrome; toxic shock syndrome toxin, a superantigen causing fever, rash, and sepsis; and preformed heat-stable enterotoxin, causing rapid-onset vomiting/food poisoning after eating unrefrigerated meats
  • it is best treated with nafcillin
  • MRSA is defined by altered PBPs and requires treatment with vancomycin
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51
Q

Describe staphylococcal toxic shock syndrome.

A
  • it is mediated by TSST, a super antigen that causes non-specific binding of MHC-II and TCRs
  • characterized by fever, vomiting, rash, desquamation, shock, and end-organ failure
  • commonly cause elevation of AST, ALT, and bilirubin
  • associated with prolonged use of vaginal tampons or nasal packing
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52
Q

Staph epidermidis

A
  • a gram positive cocci that grows in clusters
  • catalase and urease positive but coagulase negative
  • can be distinguished from S. saprophyticus because S. epidermidis is novobiocin sensitive
  • it produces biofilms and frequently infects prosthetic joints, catheters, and artificial heart valves, causing an endocarditis
  • because it colonizes the skin, it is a frequent contaminant of blood cultures
  • best treated with vancomycin and joint replacement
53
Q

Staph saprophyticus

A
  • a gram positive cocci that grows in clusters
  • catalase and urease positive but coagulase negative
  • can be distinguished from S. epidermidis because S. saphrophyticus is novobiocin resistant
  • commonly causes uncomplicated urinary tract infections in young, sexually active females and is the #2 cause of UTI overall
54
Q

Streptococcus pyogenes (Group A)

A
  • a gram positive cocci that grows in chains
  • beta-hemolytic and bacitracin-sensitive with a hyaluronic acid capsule
  • it causes impetigo, pharyngitis, and cellulitis/erysipelas (#1 cause)
  • it also causes three toxigenic diseases mediated by the Spe toxins: scarlet fever with strawberry tongue, pharyngitis, and a desquamative “sandpaper” rash that spares the perioral region or face; toxic shock-like syndrome mediated by SpeA/C, two superantigens; and necrotizing fasciitis, mediated by SpeB
  • it causes two immunologic conditions: rheumatic fever (type II HSN) and post-strep glomerulonephritis (type III HSN)
  • there are three major virulence factors: streptolysin, which causes hemolysis; streptokinase, which activates plasmin, and a DNase
  • diagnosis of rheumatic fever and PSGN can be made using antistreptolysin O (ASO) titers, but skin infections are associated with a poor ASO response and anti-DNase tiers should be checked to improve sensitivity
55
Q

What kind of capsule surrounds S. pyogenes? Why is this clinically important?

A
  • a hyaluronic acid capsule

- HA is also found in our connective tissue so it isn’t antigenic

56
Q

What is erysipelas?

A

an infection of the superficial dermis with well-defined, indurated, raised borders, often caused by S. pyogenes

57
Q

How does the pathogenesis of rheumatic fever fever differ from that of post-strep glomerulonephritis.

A
  • rheumatic fever is a type II hypersensitivity and only arises after pharyngitis; it can be prevented with treatment of the pharyngitis using penicillin
  • post-strep glomerulonephritis is a type III hypersensitivity and can arise following pharyngitis or a skin infection; it can occur even following treatment with penicillin
58
Q

Streptococcus agalactiae (Group B)

A
  • a gram positive cocci that grows in chains
  • beta-hemolytic, bacitracin-resistant, CAMP test positive, and hippurate hydrolysis positive
  • utilizes a polysaccharide capsule
  • the #1 cause of meningitis in neonates, it also causes sepsis and pneumonia in this population
  • pregnant women should be swabbed at 35 weeks to assess whether they are colonized; to prevent infection of a neonate, the mother should receive penicillin if positive
59
Q

What is the CAMP test? Which organism can it help identify?

A
  • it is a test whereby bacteria are plated with S. aureus

- this can help ID group B strep, which have an expanded zone of hemolysis in this setting

60
Q

Which organism is most often described as hippurate hydrolysis positive?

A

S. agalactiae (group B)

61
Q

Strep pneumo is the number one bacterial cause of what diseases?

A

MOPS

  • meningitis
  • otitis media
  • pneumonia (lobar)
  • sinusitis
62
Q

Streptococcus pneumoniae

A
  • a gram positive, lancet shaped diplococcus
  • it is bile-soluble, alpha-hemolytic, and optochin-sensitive
  • it’s primary virulence factors are a polysaccharide capsule and an IgA protease
  • it is the number one cause of MOPS: meningitis, otitis media, pneumonia, and sinusitis
  • the pneumonia is typically a lobar pneumonia and associated with a “rusty” sputum
  • it should be treated with macrolides or ceftriaxone
  • there is a 7 valent protein-conjugated vaccine available for children under two and a 23 valent polysaccharide vaccine available for adults
63
Q

Describe the available vaccines for Strep pneumo.

A
  • there is a 7 valent conjugated vaccine available for infants under two years old (prevnar)
  • there is a 23 valent polysaccharide vaccine available for adults (pneumovax)
64
Q

Streptococcus Viridans Group

A
  • a gram positive coccus
  • unencapsulated, optochin-resistant, and bile-resistant
  • colonizes the oropharynx and causes dental carries
  • when it enters the blood, it makes dextrans from glucose, which allow it to bind fibrin-platelet aggregates on damaged heart valves; for this reason it is a common cause of subacute endocarditis of previously damaged valves, typically the mitral valve
65
Q

What virulence factor is critical for Streptococcus Viridans to cause endocarditis?

A

its ability to convert dextrans to glucose, which allow it to bind fibrin-platelet aggregates on previously damaged heart valves

66
Q

Enterococcus

A
  • a group of gram positive cocci, including E. faecium, which is less common but more potent, and E. faecalis
  • bile resistant and grow in up to 6.5% NaCl
  • cause UTI, endocarditis, and biliary tree infections
  • VRE is a important nosocomial infection and should be treated with linezolid or tigecycline
67
Q

Bile-resistant bacteria share what ability?

A

the ability to hydrolyze esculin

68
Q

What is lethal factor?

A

a Bacillus anthracis exotoxin that serves as a protease, cleaves MAPK, and causes the tissue necrosis of an eschar

69
Q

Bacillus anthracis

A
  • gram positive, obligate aerobes with a poly-D protein capsule that take the shape of rods in chains
  • capable of forming spores, which can be found in the soil and often accumulate in the wool of animals
  • produce two exotoxins: edema factor, which acts like AC to increase cAMP levels, and lethal factor, which is a protease and cleaves MAPK to cause tissue necrosis
  • cutaneous anthrax causes a painless, black eschar; pulmonary anthrax arises from inhalation of spores which germinate and rapidly spread to the mediastinum, causing mediastinal widening and pulmonary hemorrhage
  • best treated with fluoroquinolones and doxycycline
70
Q

Which bacteria has a poly-D protein capsule?

A

B. anthracis

71
Q

Bacillus cereus

A
  • a gram positive rod capable of forming spores
  • emetic-type is caused by the preformed toxin, cereulide, and is characterized by nausea and vomitting within 1-5 hours of eating reheated rice or pasta
  • diarrheal type is characterized by watery, non-bloody diarrhea and GI pain within 8-18 hours
72
Q

Clostridium tetani

A
  • an obligate anaerobe, spore-forming, gram positive rod
  • spores are found in the soil, infect puncture wounds, germinate, and produce a toxin known as tetanospasmin
  • this toxin travels retrogradely through motor neurons to inhibitory interneurons, known as Renshaw cells, in the spinal cord; it cleaves SNARE proteins and inhibits release of GABA and glycine, leading to a spastic paralysis
  • presents with lockjaw, risus sardonicus (evil smile), and opisthotonos (backward arching of the back)
  • prevent with a toxoid vaccine
  • treat with antitoxin, vaccine booster, diazepam, and wound debridement
73
Q

Describe the pathogenesis of tetanus.

A
  • spores germinate at a puncture site and bacteria produce tetanospasmin
  • tetanospasmin travels retrogradely through motor neurons to inhibitory interneurons in the spinal cord called Renshaw cells
  • in these cells, the toxin cleaves SNARE proteins and inhibits vesicle fusion and release of GABA/glycine
  • motor neurons become overactive and this results in a spastic paralysis with lock jaw, risus sardonicus, and opisthotonos
74
Q

How does transmission of C. botulinum differ between adults and children?

A
  • C. botulinum is a relatively weak anaerobe, so ingestion of spores in adults isn’t problematic as C. botulinum is outcompeted by enteric flora
  • this isn’t the case in neonates and infants who have less established flora
  • as such, adults get botulism from ingestion of pre-formed toxin produced by spores that germinate in the anaerobic environment of canned foods
  • babies, though, get botulism from ingestion of spores, usually found in honey, which then produce toxin
75
Q

Clostridium botulinum

A
  • an obligate anaerobe, spore-forming, gram positive rod
  • produces a heat-liable toxin that cleaves SNARE, inhibits vesicular fusion, and impairs ACh release at the NMJ
  • it presents as a descending flaccid paralysis or floppy baby syndrome
  • adults are affected after consuming preformed toxin produced by germinating spores in canned foods
  • babies are affected after consuming spores found in honey which later germinate and produce toxin
  • best treated with antitoxin
76
Q

How is botulinum toxin used clinically?

A

to treat focal dystonia, achalasia, and muscle spasms

77
Q

Clostridium difficile

A
  • an obligate anaerobe, spore-forming, gram positive rod
  • often seen as a nosocomial infection in those who have been taking clindamycin or ampicillin
  • spread by healthcare workers who don’t wash their hands well
  • exotoxin A, aka enterotoxin, targets the brush border, damages the mucosal lining of the colon, and causes watery diarrhea
  • exotoxin B, aka cytotoxin, causes actin depolymerization, necrosis of colonic mucosal surfaces, and the formation of pseudomembranes
  • diagnosis is made using a PCR TOXIN ASSAY of the stool
  • treat with oral vancomycin or metronidazole
78
Q

Clostridium perfringens

A
  • obligate anaerobe, spore-forming, gram positive rods, which produce a double zone of hemolysis on blood agar
  • spores are found in the soil and commonly infect combat wounds or those who suffer motorcycle accidents
  • after germinating, spores form alpha toxin, a lecithinase, which damages cell membranes
  • this toxin mediates hemolysis, myonecrosis with gas gangrene, and a delayed watery diarrhea
  • preferred surgical debridement and penicillin
79
Q

Corynebacterium diphtheriae

A
  • gram positive rods which are club-shaped, contain metachromatic granules, and form V or Y shapes
  • spread via respiratory droplets, colonize the oropharynx, and may spread in the blood
  • they produce an extoxin encoded by beta-prophage, which ADP-ribosylates and inactivates EF-2, inhibiting protein production by host cells
  • the bacteria cause “bull neck” lymphadenopathy, pseudomembrane formation in the oropharynx, a potentially fatal myocarditis with heart block and arrhythmia, and nerve deficits beginning in the posterior pharyngeal wall
  • diagnosis is made by culture on cystine-tellurite or Loeffler’s medium in combination with the Elek’s test to distinguish toxigenic species from nontoxigenic ones
  • toxoid vaccine is available (DTaP)
80
Q

What is the preferred empiric treatment for meningitis for adults? How does this change for elderly patients?

A
  • use vancomycin and ceftriaxone to cover gram positives and negatives
  • add ampicillin to cover listeria in the elderly
81
Q

Listeria

A
  • a beta-hemolytic, catalase-positive, facultative intracellular, gram positive rod
  • has extracellular tumbling motility but uses actin rockets to travel intracellularly
  • grows at low temperatures and frequently contaminates dairy products like soft cheeses
  • infection is common in pregnancy, newborns, and the elderly causing abortion and meningitis
  • preferred treatment is ampicillin
82
Q

Actinomyces

A
  • a filamentous, branching, gram-positive rod
  • distinguished from Nocardia because actinomyces is an obligate anaerobe
  • constitutes normal oral flora and infections are often associated with jaw trauma
  • disease course is slow, beginning with a non-tender lump on the jaw that later forms an abscess with sulfur granules draining from a sinus tract
  • treated with penicillin
83
Q

Nocardia

A
  • a filamentous, branching, gram-positive rod
  • urease positive, catalase positive, and weakly acid-fast
  • distinguable from actinomyces because it is an obligate aerobe
  • causes a pneumonia with lung abscesses that may resemble TB, brain abscesses, or a cutaneous infection
  • best treated with sulfonamides
84
Q

Mycobacterium tuberculosis

A
  • an obligate aerobe, acid-fast bacterium
  • grown on Lowenstein-Jensen agar
  • infects and replicates within macrophages, using sulfates to prevent phagolysosome fusion
  • cord factor is a glycolipid that causes the bacteria to clump into a “serpentine cord”, inhibits macrophage maturation, and induces release of TNF-a
85
Q

What is cord factor?

A

a tuberculosis virulence factor that causes the bacteria to clump into a “serpentine cord”, inhibits macrophage maturation, and induces release of TNF-a

86
Q

Mycobacterium leprae

A
  • an acid-fast bacterium which can’t be grown in vitro
  • armadillos serve as the primary reservoir and there is human-to-human spread of the lepromatous form
  • if there is a strong Th1 response to infection, it will be contained within macrophages and the tuberculoid form predominates, presenting with well-demarcated, hairless skin lesions
  • if there is a predominant Th2 response, it isn’t well contained and the lepromatous form predominates, presenting with leonine facial deformity, a rash covering extensor surfaces, and a symmetric stocking-glove pattern of neuropathy
  • the tuberculoid form should be treated with dapsone and rifampin with clofazimine added if lepromatous
87
Q

Describe lepromatous leprosy.

A
  • occurs in those for whom the Th2 response predominates and the infection can’t be controlled
  • presentation includes leonine facial deformity, a rash on the extensor surfaces, and a symmetrical stocking-glove pattern of neuropathy
  • this form can be spread via a human-to-human route
  • should be treated with rifampin, dapsone, and clofazimine
88
Q

Neisseria spp.

A
  • a group of oxidase-positive, gram-negative diplococci
  • grown on chocolate agar or VPN, also known as Thayer-Martin agar, with vancomycin, polymyxin, and nystatin
  • two main virulence factors are fibrae that undergo frequent antigenic variation and IgA protease
89
Q

Neisseria meningitidis

A
  • a maltose-fermenting, oxidase-positive, gram-negative diplococci with a polysaccharide capsule
  • grown on chocolate agar or VPN, also known as Thayer-Martin agar, with vancomycin, polymyxin, and nystatin
  • spread via respiratory secretions and common in dorms
  • pathogenesis begins with blebbing off of the membrane containing the endotoxin lipooligosaccharide (LOS), which generates a severe inflammatory response
  • the inflammatory response leads to capillary permeability and platelet consumption, causing shock, a petechial rash, and potentially Waterhouse Friderichsen syndrome
  • vaccination against the polysaccharide capsule is available except for the B subtype
  • treat with ceftriaxone; use rifampin as prophylaxis for close contacts
90
Q

Neisseria gonorrhea

A
  • oxidase-positive, gram-negative diplococci
  • it is facultative intracellular with a tropism for PMNs
  • grown on chocolate agar or VPN, also known as Thayer-Martin agar, with vancomycin, polymyxin, and nystatin
  • causes a urethritis, prostatitis, or orchitis in men
  • causes PID in women with a thick, white, purulent discharge as well as Fitz-Hugh Curtis syndrome with peritoneal inflammation and “violin string” adhesions
  • may cause an asymmetric septic arthritis, most commonly of the knee, which won’t gram stain as it is intracellular
  • vertical tranmission is possible during birth and will cause a purulent conjunctivitis within 5 days of birth leading to blindness if untreated
  • treat with ceftriaxone and add macrolides or doxycycline to treat the presumed co-infection with chlamydia
91
Q

What is Fitz-Hugh Curtis syndrome?

A
  • a rare complication of N. gonorrhea PID
  • the peritoneum, diaphragm, and/or liver become inflamed
  • as a result, thin “violin string” adhesions form between these structures
92
Q

What lab features can help distinguish N. meningitidis from N. gonorrhea.

A
  • meningitidis is encapsulate, ferments maltose, and is spread via respiratory secretions
  • gonorrhea is unencapsulated, facultative intracellular, and spread via sexual contact
93
Q

How should gonorrhea infection be treated?

A

with ceftriaxone plus doxycycline or macrolides for the presumed chlamydia co-infection

94
Q

Bordatella pertussis

A
  • a gram negative coccobacillus
  • spreads via respiratory droplets and utilizes filamentous hemagglutinin, an adhesin, to bind the respiratory tract
  • produces three toxins: pertussis toxin, which ADP-ribosylates and inactivates Gi to increase cAMP; adenylate cyclase toxin, which mimics AC and directly increases cAMP; and tracheal toxin, which destroys ciliary respiratory epithelial cells
  • causes an extreme leukocytosis because pertussis toxin inhibits Gi and thus signaling of chemokine receptors
  • known for causing whooping cough with a catarrhal phase, paroxysmal phase, and convalescent stage
  • prevent with an acellular vaccine
  • treat using macrolides
95
Q

Haemophilus influenzae

A
  • a gram negative coccobacillus
  • requires chocolate agar with factors V (NAD+) and X (hematin) or can be co-plated with S. aureus, which can provide factor V through hemolysis of RBCs
  • transmitted via respiratory droplets to cause epiglottis with a “cherry red” epiglottis, inspiratory stridor, and drooling; otitis media; and pneumonia
  • only strains with the type B capsule can cause meningitis
  • a vaccine with type b capsular polysaccharide conjugated to diphtheria toxoid should be given 2-18 months after birth
  • treat with amoxillin of mucosal infections and ceftriaxone for meningitis; rifampin as prophylaxis for close contacts
96
Q

Legionella pneumophila

A
  • an oxidase-positive, gram-negative rod that requires silver stain to visualize
  • grown on BCYE with cysteine and iron
  • causes pontiac fever, a self-limiting illness characterized by fever and malaise
  • or an atypical pneumonia with patchy infiltrate and consolidation of one lobe, more commonly seen in smokers and presenting with high fever, headache or confusion, hyponatremia, and diarrhea
  • diagnose with a rapid urine antigen test
  • fluoroquinolones and macrolides are treatment options
97
Q

Describe Legonnaire’s disease.

A
  • an atypical pneumonia with patchy infiltrate and consolidation of one lobe
  • most commonly seen in smokers
  • presenting with diarrhea, hyponatremia, high fever, and headache or confusion
98
Q

Chlamydiae trichomatis

A
  • a weakly gram-negative, obligate intracellular microbe that is best visualized with Giemsa stain
  • cell wall lacks muramic acid, a classic peptidoglycan component, and thus beta-lactamases are ineffective
  • has a two part life cycle involving infective elementary bodies (elementary enter) and reticular bodies, which are capable of replication through binary fission
  • microscopy can be used to visualize inclusion bodies, which are dense areas of replicating reticular bodies
  • serotypes A-C are transmitted via hand-to-eye contact or via fomites and cause trachoma, a chronic infection leading to blindness (#1 cause of blindness worldwide)
  • serotypes D-K are sexually transmitted and cause urethritis/PID with a watery discharge, ectopic pregnancy, neonatal pneumonia with a staccato cough, and neonatal conjunctivitis (which presents in 1-2 weeks in contrast to gonorrhea which has a more rapid onset)
  • serotypes L1-L3 cause lymphogranuloma venereum, which manifests as a painless genital ulcer followed weeks later by painful inguinal lymphadenopathy
  • all serotypes can be complicated by Reiter’s syndrome of uveitis, urethritis, and arthritis
  • diagnosed using nucleic acid amplification test (NAAT)
  • treat using macrolides or tetracyclines and add ceftriaxone to treat presumed co-infection with gonorrhea
99
Q

Chlamydiae pneumoniae and Chlamydophila pisttaci

A
  • weakly gram-negative, obligate intracellular microbes that are best visualized with Giemsa stain
  • cell wall lacks muramic acid, a classic peptidoglycan component, and thus beta-lactamases are ineffective
  • two part life cycle involving infective elementary bodies (elementary enter) and reticular bodies, which are capable of replication through binary fission
  • microscopy can be used to visualize inclusion bodies, which are dense areas of replicating reticular bodies
  • classically spread via contact with bird droppings
  • both organisms cause an atypical pneumonia in elderly patients
  • diagnosed using nucleic acid amplification test (NAAT)
  • treat using macrolides or tetracyclines
100
Q

Gardnerella vaginalis

A
  • a gram-variable rod
  • associated with sexual activity but not sexually transmitted
  • infection occurs when the normal vaginal flora becomes imbalanced with less lactobacillus, which allows the pH to rise above 4.5, a suitable environment for Gardnerella
  • causes bacterial vaginosis with a thin, grayish-white discharge that has a “fishy smell”
  • adding 10% KOH to this discharge will enhance the fishy odor and is considered diagnostic
  • diagnosis can be aided by finding clue cells (epithelial cells covered by bacteria) on wet mount
  • treat with metronidazole
101
Q

Rickettsia spp.

A
  • a gram-negative coccobacilli that doesn’t gram stain
  • obligate intracellular because they require CoA and NAD+ from host cells
  • most cause a small-vessel vasculitis that contributes to a petechial or maculopapular rash
  • diagnosed using the Weil-Felix test, an agglutination test that makes use of the cross-reactivity of antibodies to Rickettsia for Proteus
  • treated using doxycycline
102
Q

What is the difference between anaplasmosis and ehrlichiosis?

A
  • caused by Anaplasma and Ehrlichia, both are transmitted via ticks and cause rickettsial diseases without rash
  • ehrlichiosis will have morulae (mulberry-like inclusions) within monocytes where as anaplasmosis has morale in the cytoplasm of granulocytes
103
Q

Rickettsia prowazeki

A
  • a gram-negative coccobacillus that doesn’t gram stain
  • obligate intracellular because it requires NAD+ and CoA from host cells
  • transmitted via louse, which defecate on skin and cause itching, which drives the feces in and causes infection
  • common amongst military recruits and prisoners of war
  • causes epidemic typhus, which classically presents with a petechial rash that begins centrally and expands outward, sparing the hands, feet, and head
  • additional symptoms include MSK pain, pneumonia, and encephalitis with dizziness, fever, and confusion
  • preferred treatment is doxycycline
104
Q

Ricketssia rickettsii

A
  • a gram-negative coccobacillus that doesn’t gram stain
  • obligate intracellular because it requires NAD+ and CoA from host cells
  • spread by the dermacenter tick via direct biting
  • causes Rocky Mountain Spotted Fever, which presents with a classic rash that begins 2-14 days after infection on the ankles and wrists before spreading centrally, not sparing any skin
  • additional symptoms include headache, MSK pain, and fever
  • treat with doxycycline
105
Q

Rickettsia ricketsii

A
  • a gram-negative coccobacillus that doesn’t gram stain
  • obligate intracellular because it requires NAD+ and CoA from host cells
  • transmitted directly via dermacenter tick bites
  • causes rocky mountain spotted fever with a characteristic rash beginning on the hands and feet 2-14 days after infection and then spreading centrally, not sparing any skin
  • additional symptoms include headache, myalgia, fever
  • treat with doxycycline
106
Q

Borrelia burgdorferi

A
  • a spirochete that can be visualized with Wright or Giemsa stain
  • transmitted via the ixodes tick, which uses the white-footed mouse as a reservoir for larvae and white-tailed deer as the obligatory host of adults, found in the NE US
  • causes lyme disease characterized by a flu-like illness and bull’s eye rash in the first stage, bilateral Bell’s palsy and heart block secondary to myocarditis in the second stage, and migratory polyarthritis with encephalopathy in the third stage
  • should be treated in the early stages with tetracyclines and in the later stages with ceftriaxone
107
Q

Leptospira interrogans

A
  • a spirochete said to have a “question mark-shape”
  • found in the water of tropical areas that has been contaminated by dog urine, often in those who participate in water sports
  • can initially cause a mild illness with fever and non-suppurative conjunctivitis
  • spreads hematogenously to cause renal dysfunction and jaundice
108
Q

Treponema Pallidum

A
  • a spirochete that requires dark field microscopy for direct visualization
  • primary syphillus arises as the bacteria damage blood vessels leading to an area of ischemic necrosis seen as a a painless chancre
  • secondary syphillus is a systemic disease characterized by a rash that affects the hands and feet and condyloma late, which are flat-topped cutaneous lesion
  • tertiary syphillus presents with soft growths with firm necrotic centers known as gummas, aortitis leading to “tree-barking” and possibly a thoracic aortic aneurysm, damage to the posterior columns known as tabes dorsalis, and Argyll Robertson pupils, which accommodate but do not react to light
  • congenital syphillus presents with Saber shins, an anterior bowing of the tibia; a saddle-shaped nose; Hutchinson’s teeth (notched incisors) and Mulberry molars (enamel outgrowths); and congenital deafness
  • VDRL is a screening test and looks for antibodies against treponema but false-positives can be seen in those with SLE, leprosy, mono, rheumatoid factor, or IV drug use
  • the confirmatory test is the more specific FTA-Abs
  • best treated with penicillin; if they are allergic, desensitize them and still treat with penicillin
  • treatment can lead to Jarisch-Herxheimer reaction: dying spirochetes release lots of LPS with a cytokine storm hours after treatment
109
Q

Enterobacter

A
  • a motile, gram-negative bacillus, which ferments lactose
  • a common cause of nosocomial UTI and pneumonia
  • often displays multi-drug resistance
110
Q

Serratia

A
  • a motile, gram-negative bacillus, which ferments lactose and forms a red pigment
  • a common cause of nosocomial UTI and pneumonia
  • often displays multi-drug resistance
111
Q

Klebsiella

A
  • an immotile, polysaccharide-encapsulated, gram-negative bacillus that ferments lactose
  • a common cause of nosocomial UTI and pneumonia
  • the pneumonia is most often seen in alcoholics and others at risk for aspiration
  • clinically, it is often associated with a red-currant jelly sputum and complicated by abscesses, resembling TB
112
Q

Salmonella typhi

A
  • a motile, encapsulated, acid-labile gram-negative bacillus
  • forms black colonies on Hektoen enteric agar because it is H2S-positive
  • facultative intracellular with macrophages and resides in the gall bladder of chronically infected carriers
  • presents with a “rose spot” rash and “pea-soup” diarrhea
  • the #1 cause of osteomyelitis in those with sickle cell disease
  • can be prevented with a live-attenuated vaccine, but is best treated with fluoroquinolones
113
Q

Salmonella enteritidis

A
  • a motile, encapsulated, acid-labile gram-negative bacillus
  • forms black colonies on Hektoen enteric agar because it is H2S-positive
  • facultative intracellular within macrophages
  • its primary virulence factor is a T3SS
  • chickens are the primary reservoir and it is contracted via consumption of contaminated, uncooked meat
  • causes a self-limiting inflammatory diarrhea
114
Q

Shigella

A
  • an immotile, acid-stable, facultative intracellular, gram-negative bacillus, which forms green colonies on Hektoen enteric agar, differentiating it from salmonella
  • taken up by M cells and spread via actin-rockets, using a T3SS and shiga toxin to inhibit the 60S ribosomal subunit of host cells
  • causes an inflammatory, bloody diarrhea in most cases and can induce HUS, usually in children under 10 years old
115
Q

Yersenia enterocolitica

A
  • an encapsulated, gram-negative bacillus that survives cold temperatures well
  • known for its bipolar, “safety pin” staining
  • found in puppy feces and contaminated dairy products
  • causes a bloody diarrhea and may present with right lower quadrant pain, mimicking appendicitis
116
Q

Yersenia pestis

A
  • an encapsulated, gram-negative bacillus
  • uses a T3SS to inject yersenia outer proteins (Yops), which are the primary virulence factors
  • the primary reservoir is prairie dogs and it is spread to humans via a flea vector
  • causes buboes (very painful, swollen, erythematous lymph nodes) to form and can precipitate DIC with tissue necrosis, which is why it is known as the black plague
  • best treated with aminoglycosides or doxycycline
  • a killed vaccine is available but not widely used
117
Q

E. coli

A
  • a group of lactose-fermenting, encapsulated, catalase-positive, gram-negative bacilli
  • form metallic green colonies on eosin methylene blue (EMB) agar
  • they rely on fibrae to cause UTI and are the #1 cause
  • they rely on the K capsular antigen to cause neonatal meningitis
118
Q

EHEC

A
  • a lactose-fermenting, encapsulated, catalase positive gram-negative, which forms green colonies on EMB agar
  • unique in that they do not ferment sorbitol like most other species of E. coli
  • commonly contaminates undercooked meats and O157:H7 is the most important serotype
  • utilize a shiga-like toxin which inhibits the 60S ribosomal subunit and thus cause bloody diarrhea as well as HUS
119
Q

ETEC

A
  • a lactose-fermenting, encapsulated, catalase-positive, gram-negative, which forms green colonies on EMB agar
  • commonly referred to as traveler’s diarrhea and found in contaminated water sources, usually in developing nations
  • utilizes a heat-labile enterotoxin, which increases cAMP, and a heat-stable enterotoxin, which increases cGMP, to cause a watery diarrhea
120
Q

Campylobacter

A
  • an oxidase positive, curved, gram-negative rod
  • thermophilic and prefers to grow at 42 degrees Celsius
  • contaminates poultry and causes a bloody diarrhea
  • may also be complicated by either reactive arthritis or Guillain-Barre syndrome with an ascending paralysis
121
Q

Vibrio cholerae

A
  • an acid-labile, oxidase-positive, “comma-shaped” gram-negative bacillus
  • spread via the fecal-oral route and is endemic to South American countries with poor sanitation
  • it uses fibrae to attach the the wall of the intestine but does not invade; instead, it secretes cholera toxin, which constitutively activates AC and increases cAMP levels
  • causes a watery diarrhea described as “rice water stool”
122
Q

H. pylori

A
  • a motile, oxidase-positive, urease-positive, curved, gram-negative rod
  • strongly associated with duodenal and gastric ulcers, increasing the risk for adenocarcinoma and MALToma
  • treated with amoxicillin/metronidazole, clarithromycin, and a proton-pump inhibitor
123
Q

P. aeruginosa

A
  • an encapsulated oxidase-positive, catalase-positive, obligate-aerobe gram-negative rod
  • it forms greenish-blue colonies in culture and produces a grape-like, fruity smell
  • it relies on exotoxin A, which ADP-ribosylates and inactivates EF-2, inhibiting protein synthesis much like diphtheria toxin
  • it thrives in aquatic environments and causes “hot tube folliculitis”, which is a pruritic, papular rash
  • it commonly infects burn wounds and is a major cause of respiratory failure in patients with cystic fibrosis
  • it is a leading cause of osteomyelitis in diabetics and IV drug users
  • it also causes otitis externa, nosocomial pneumonia, catheter-associated UTIs
  • it is best treated with piperacillin, fluoroquinolones, and aminoglycosides
124
Q

P. aeruginosa

A
  • an encapsulated, obligate aerobe, oxidase-positive, catalase-positive, gram-negative rod
  • it forms greenish-blue colonies in culture and produces a fruity, grape-like smell
  • it relies on exotoxin A, which ADP-ribosylates EF-2, inhibiting protein synthesis, much like diphtheria toxin
  • commonly infects burn wounds and is a major cause of respiratory failure in patients with cystic fibrosis
  • it causes “hot tub” folliculitis, which is a pruritic, papular rash as well as otitis externa known as “swimmer’s ear”
  • is a significant cause of osteomyelitis in IV drug users and diabetics as well as a primary cause of nosocomial pneumonia, and catheter-associated UTI
  • sepsis and dissemination can lead to cutaneous ecthyma gangrenosum, characterized by black, necrotic lesions
  • should be treated with piperacillin, aminoglycosides, and fluoroquinolones
125
Q

Proteus

A
  • a gram-negative rod said to have swarming motility and a fishy odor, which commonly causes UTI
  • because of its urease-positive nature, it produces an alkaline environment suitable for the formation of stag-horn magnesium ammonium phosphate calculi
  • it should be treated with sulfonamides
126
Q

Bartonella henselae

A
  • a gram-negative rod transmitted via cat scratches
  • visualization requires use of Warthin-Starry silver stain
  • in immunocompotent hosts, it presents as cat scratch fever with fever and regional lymphadenopathy
  • in immunocompotent hosts, it presents as bacillary angiomatosis with lesions ranging from reddish papules to high vascularized nodules
  • should be treated with doxycycline or aminoglycosides
127
Q

Brucella

A
  • a facultative intracellular, gram-negative rod
  • transmitted via exposure to farm animals or consumption of unpasteurized dairy products
  • brucellosis presents with an undulating fever, anorexia, hepatosplenomegaly, and swollen lymph nodes
  • it can also cause osteomyelitis
  • treat with doxycycline plus rifampin
128
Q

Francisella tularensis

A
  • a facultative intracellular, gram-negative coccobacillus
  • rabbits are the reservoir and it is transmitted via ticks
  • it causes an ulcer at the site of infection and spreads into the reticuloendothelial system where it causes lymphadenopathy and caseating granulomas
  • treat using aminoglycosides
129
Q

Pasteurella multocida

A
  • an encapsulated, oxidase-positive, catalase-positive, gram-negative rod
  • grown on sheeps blood agar and demonstrates bipolar, “safety pin” staining
  • transmitted via cat and dog bites, it causes cellulitis and osteomyelitis
  • should be treated with penicillins

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