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Flashcards in Gram negative Deck (23)
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0
Q

Nosocomial infections

A
Hospital acquired infections
Factors:
- surgery, procedures
- indwelling devices - ex UTI
- chronically ill, immunosuppression
- use of antibiotics - disrupt normal microbiome
Sources:
- vectors (neckties, hands)
- patient's own skin
1
Q

“Opportunistic” infection

A

Causes disease only in “compromised” patients

  • immune fx (AIDS, chronic disease, suppression)
  • innate protective mechanisms (ex CF -> mucociliary clearance)
  • physical barriers (cut, hot tub)

Widespread in env’t
- less specialized to human host
Should be preventable!
Virulence factors: LPS (-> inflammatory response), adhesins, nutrient acquisition, toxins

2
Q

Opportunistic antibiotic resistance

A

Frequently carry antibiotic resistance

Intrinsic
- natural competition with antibiotic producers in soil environment
- Pseudomonas aeruginosa, Acinetobacter baumanii, Burkholderia
Acquired - increased resistance in ICU
Biofilms - significantly enhances resistance

Can’t develop resistance to soap!

3
Q

Biofilms

A

Surface-associated cells + extracellular matrix
May be single or multi-organism
Can occur quickly in the right environment
- ex lung, heart valves -> endocarditis, catheters
- high availability of nutrients (ex parenteral nutrition)
Active dispersal from biofilm -> blood-stream infection

Resistance to antibiotics - both diffusion and specific induction of genes (ex protective polysaccharide coating)
Quorum sensing - detect high density of similar organisms -> induce virulence factors

4
Q

E coli as opportunistic pathogen

A

Most common opportunistic infection!

E coli strains that are normally commensal ->
UTI
Meningitis
Bacteremia

Common virulence = toxins, capsule, pili

vs specialized strains -> gastroenteritis

5
Q

Uropathogenic E coli (UPEC)

A

95% of all non-nosocomial UTIs
Women (anatomy, intercourse), catheters
Few serogroups
- different strains -> different adhesins and pili allow colonization

Ascending route: ureter -> cystitis (dysuria, urgency) -> pyelonephritis (flank pain, fever)
“Bacteruria” > 10’5/mL (lower levels don’t count because part of normal microflora)
Self limiting, antibiotics for pyelonephritis
Recurrent infection due to re-entry or biofilm in urothelium -> re-emergence with stress

6
Q

UPEC virulence factors

A

Adhesion is necessary for colonizing -> invasion of urothelium

  • > biofilm on catheter, “pods” replicating in epithelium
  • measure with hemagglutination assay (+ mannose)

P pili -> Gal-Gal glycolipids on RBC’s, urothelium

  • Gal-Gal is P1 blood group -> more UTI’s
  • > pyelonephritis

Mannosides/mannoproteins - on urothelium, bound by many E coli structures

  • if binding is blocked by additional mannose -> mannose sensitive (MS)
  • ex MS - Type 1 pili -> cystitis
  • not blocked by mannose -> resistant (MR)
  • ex MR - Prs pili, S pili, Dr adhesin -> cystitis; F adhesin -> pyelo

Other factors: LPS, capsule, motility, exotoxins

7
Q

E coli bacteremia

A

Leading nosocomial bacteremia
UTI, catheter -> invades urothelium
- common if UTI + urinary obstruction

Similar strains to UTI
K1 capsule -> serum resistance (blocks complement -> escapes phagocytosis)
- polysialic acid (sim to Neisseria meningititis)
- similar to host glycoproteins -> no immune response
- 20-40% prevalence of E coli K1

Severe inflammatory response due to LPS

8
Q

E coli meningitis

A

Newborns!
Colonized -> bacteremia -> CSF (mechanisms unclear)
K1 capsule - escapes phagocytosis
- 20-40% prevalence (vertical transmission from mother)
Siderophores - chelation may be useful therapy
Hemolysin

9
Q

Overview of Gram (-) opportunistic

A
E coli (UTI, bacteremia, meningitis)
Pseudomonas aeruginosa
Klebsiella pneumoniae
Enterobacter cloacae
Serratia marcesens
Proteus vulgaris, Proteus mirabilis
Acinetobacter
10
Q

Pseudomonas aeruginosa

A

Wide range of sites: burns, eye, catheters, devices, urinary
Pneumonia (esp ventilator aka VAP)
Bacteremia if compromised

Virulence:
LPS
T3SS-secreted exotoxins:
 - ExoA - inhibits protein synthesis
 - ExoS, ExoT - enzyme, modifies cell regulation
 - ExoU - phospholipase -> surfactant
Elastase -> lung connective tissue
Pyocyanin toxin -> cell produces ROS
 - also blue-green -> "aeruginosa"
 - only produced by colonies after quorum sensing
Capsule
Pili

Obligate aerobe - grows only in aerobic culture
- technically can use nitrate ETC, ferment Arg
Lots of antibiotic resistance

11
Q

Chronic Pseudomonas

A

Cystic fibrosis -> biofilm, chronic infection (80% prevalence)

  • mutates -> produces alginate slime -> resists phagocytosis
  • decline due to immune response (bacterial load constant)
  • never eliminated, manage with antibiotics

Pseudomonas also chronic in COPD
CF - also susceptible to Burkholderia cepacia complex = deadly

12
Q

Klebiella pneumoniae

A
Pneumonia - esp chronic medical (ex alcoholism -> aspiration)
 -> red currant jelly
UTI
Wounds
Bacteremia, meningitis possible
Diarrhea (enterotoxic strains)

Virulence from capsule
- resists complement, phagocytosis
- identification via mucoid colony morphology
Toxins (specific strains)

13
Q

Enterobacter cloacae

A

Normal gut flora -> burns, wounds, repiratory, UTI, catheters
Unknown virulence factors (makes biofilms)
- O, H, K antigens
- some strains make toxins
Similar to Klebsiella but motile, less heavily encapsulated

Often nosocomial, after antibiotic therapy (resistance!)
ex - epidemic from infected catheter insertions (E. cloacae and E. agglomerans)

14
Q

Serratia maracens

A

Common in env’t
- prodigiosin = red pigment (competition with fungi)
Less GI colonization but reservoir in infants
Respiratory (ex respiratory -> pneumonia)
Urinary
Septic arthritis

Often after broad-spectrum antibiotics
Instrumentation - ex heroin addicts

Virulence:
Swarming motility
MS-fimbrae (mannose sensitive), proteases (vs IgG), siderophores

15
Q

Proteus

A

P vulgaris, P mirabilis

UTI’s

Virulence:
Swarming motility - produce mucous + flagella -> swim
(also P aeruginosa, E coli, S marcesens)
Urease -> NH3 -> alkaline -> salt crytals -> stones -> colonize -> chronic infection
- also detect via pH phenol red

16
Q

Acinetobacter baumanii

A

Non-fermenter, oxidase negative (similar to Pseudomonas)
Nosocomial - devices, wounds, lung, urinary
Frequent multi-drug resistance (BAD)

Virulence: capsule polysacc, adhesins, protease, lipase, LPS
- colonization factors

17
Q

Morganella

A

Opportunistic Gram (-) pathogen
similar to Proteus
Urinary

18
Q

Providencia

A
Nosocomial
Urinary*
Blood
Wounds
Respiratory
19
Q

Citrobacter

A

C diversus -> neonatal meningitis, brain abcesses

C freundii -> enterotoxigenic

Urinary
Makes toxins

20
Q

Edwardsiella

A

Gram negative
Causes gastroenteritis, wounds, sepsis
Rare

21
Q

Gram negative diagnostics

A

Colony - size, shape, color, smell
Selective media - ex Pseudomonas is resistant to most antibiotics

Assays - fermentation, gas production, oxidase, urease
Lactose fermenters - E coli, Klebsiella, Enterobacter cloacae
Most facultative anaerobes
- Acinetobacter - non-fermenter
- Pseudomonas - “constitutive aerobe”, non-fermenter

22
Q

Treatment of Gram (-)

A

Antibiotics based on strain, site

CRE = carbapenem resistant Enterobacteriaciae
- Klebsiella, E coli
Acinetobacter often multi-drug resistant