Gram Negative Bacteria Flashcards
Gram Negatives
thinner peptidoglycan layer much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane.
The alcohol degrades the outer membrane; incapable of retaining the violet stain
Outer membrane contains lipopolysaccharide (LPS) endotoxin
Neisseria
Gram-negative “coffee bean” diplococci
N. gonorrhoeae
Gram-negative “coffee bean” diplococci
fimbriae (pili)
LPS endotoxin
and transmission is via sexual contact or vaginal delivery
–>Gonorrhea
associated with pelvic inflammatory disease (PID) –> sterility
Causes conjunctivitis in neonates (opthalmia neonatorum)
Dx- urethral exudate containing gram (-) negative intracellular diplococci,
Thayer-Martin VCN lysed RBC media
Historically used penicillin and quinolones but now have resistance to both.
Can cause sepsis with C5-C9 deficiencies
N. meningitidis
(meningococcus)
antiphagocytic capsule
Meningococcal endotoxin LPS is toxic (hemorrhage/petichiae and sepsis)
High rates of infection in complement deficiencies C5-C9
Meningitis
DX- CSF on Thayer-Martin VCN media and PCR
Moraxella & Kingella
Gram-negative diplococcus
Moraxella catarrhalis
common cold, otitis media and sinusitis
resistant to beta-lactams
Moraxella lacunata conjunctivitis
Kingella kingae
Coliforms
Gram-negative bacilli that resemble Escherichia coli
Oxidase negative
Ferment lactose (except proteus and serratia)
Many can produce H2S
E. coli, proteus, serratia, klebsiella and enterobacter may produce urinary tract infections
E. coli - 85% of urethrocystitis cases, 80% of chronic bacterial prostatitis cases and 90% of acute pyelonephritis
E. coli - diarrheas
Proteus responsible for renal infection with staghorn calculi (urease and subsequent alkalization and supersaturation of urine)
K. pneumoniae responsible for 3% of bacterial pneumonia cases
also often Nosocomial or hospital-acquired infections
Escherichia
Gram negative bacilli
Ferment lactose
E. coli with K1 antigen (provides the organism with an increased resistance to phagocytosis and the action of complement) - propensity for producing neonatal meningitis
Urinary tract infections via fecal material contamination
Pathogenic diarrheal E. coli
Pathogenic diarrheal E. coli (4 types)
Enterotoxigenic
= traveler’s diarrhea. ST heat stable and LT heat labile
Enteroinvasive = shigella-like diarrhea. Bloody stool, shiga-like toxin destruction of cells
Enteropathogenic –> infantile diarrhea, salmonella-like
Enterohemorrhagic = hemorrhagic colitis, grossly bloody stool. 0157:H7, shiga-like cytotoxins (“verotoxins”)
Klebsiella
Gram-negative bacilli
Ferment lactose (reddish on McConkey’s agar)
Encapsulated
K. pneumoniae
Most common cause of nosocomial respiratory tract infections
Bacterial pneumonia
Urinary tract infections
(exams like to say looks like red jelly sputum)
K oxytoca
can cause colitis
Klebsiella granulomatis
–> granuloma inguinale (donovanosis) = painless genital ulcers –> scarring with lymphatic blockage
Enterobacter
Gram-negative rods
Ferment lactose
Possess inducible beta-lactamases
Enterobacter cloacae
Normal gut flora
Sometimes causes lower respiratory tract, urinary tract and intra-abdominal infections
nosocomial outbreaks (surgical equipment, etc.)
Enterobacter aerogenes
Nosocomial opportunistic infections
Serratia
Gram-negative rod
Non-lactose fermenter, but red on MacConkey agar
Prodigiosin - characteristic red pigment
S. marcascens- hospital-acquired infections (common respiratory and urinary tracts; associated with catheters)