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)
Proteus
Gram-negative bacilli
Non-lactose fermenting**
cause urinary tract infections,
wound infections
Proteus mirabilis
Swarming motility (very motile)
Urease alkalinizes urine –>struvite stones
Proteus vulgaris & Proteus penneri
Shigella
Shigella is negative everything:
Gram-negative rod
Non-lactose fermenting
Do not produce H2S
Non-motile
Shiga toxin (A subunit inhibits 60s ribosome and protein synthesis)
Shigella dysenteriae
bacillary dysentery
cramps and a watery, bloody diarrhea
Other species of Shigella produce milder diarrheal disease
Rx - fluid with electrolytes as most infections are self limited
Salmonella
Gram-negative bacilli
Non- lactose fermenting
Produce H2S (from ferrous sulfate in media) –> black colonies. Distinguishes it from shigella.
Facultative intracellular parasite
2 species [S. bongori and S. enterica (which has 6 subspecies)]
“Vi” or capsular antigen
by oral ingestion of the bacteria via contaminated food (poultry), water
Activation of adenylate cyclase –> diarrhea
Septicemia - may be caused by any species but S. enterica enterica serovar Choleraesuis common
rx– no antibiotic needed for enteritis, but 3rd gen cephalosporins or quinolones for salmonella
Salmonella enterica enterica, serovar Enteritidis
Enteroinvasive gastroenteriti
after 1-3 day incubation, usually self-limited
S. enterica enterica, serovar Typhi
Enteric (typhoid) fever – after 10-14 days incubation, bacteria leave the intestine and multiply within lymphoid tissues and later get intestinal symptoms, may mimic appendicitis
Pseudomonas
Gram negative RODS
Oxidase-positive
Nonfermentative
green colonies
Antiphagocytic exopolysaccharide (alginate) slime biofilm
produce pigments (fluorescent pyoverdin and pyocyanin)
Exotoxin A is most toxic, mechanism identical to diphtheria toxin)
an opportunistic pathogen
bacterial vasculitis
produces skin lesions known as ecthyma gangrenosum
commonly present in lungs of patients with cystic fibrosis
hot tub folliculitis
Burkholderia
Gram-negative rods
Oxidase-positive
Burkholderia cepacia- in cystic fibrosis
Burkholderia pseudomallei (melioidosis)
Stenotrophomonas maltophilia
Gram-negative rod
Most non-fermentative
Oxidase +/-
immunocompromised patients
Legionella
Gram-negative bacilli
ubiquitous aquatic
Several species produce hemolysins and there are some reports of exotoxins
multiply within macrophages (intracellular pathogen)
L. pneumophila
- Legionnaires’ disease
- Pontiac fever
dx- charcoal yeast extract agar
prevention: - regular maintenance of air conditioning
Fusobacterium
Gram-negative fusiform BACILLI
Anaerobic
F. necrophorum
- peritonsillar abscesses
Produces hemagglutinin which leads to septic thrombophlebitis of internal jugular vein (Lemierre syndrome)
Dx – anaerobic cultures, PCR
Main Vibrio types
V. parahaemolyticus
V. vulnificus
V. cholerae, toxigenic 01 (travel)
Vibrio cholerae
Gram negative “curved” rods with single polar flagellum; “vibrate”
Oxidase +
a disease of poor sanitation (water with human fecal contamination)
Potent enterotoxin choleragen
–> overproduction of cyclic AMP
“rice water stool”
dx– fluid and electrolyte replacement
Campylobacter jejuni
Gram-negative curved rods (Greek “campylo“ = curved)
Non-lactose fermenter
LPS endotoxin
Ingestion of contaminated water, milk or undercooked foods (raw clams)
Helicobacter pylori
Gram-negative helically shaped
Non-lactose fermenter
Lives in the mucus layer above the gastric epithelium and produce urease
Associated with chronic gastritis, gastric and duodenal ulcers, gastric adenocarcinoma and gastric MALT lymphoma
Feco-oral or oral-oral transmission
rx- clarithromycin-based triple therapy or bismuth quadruple therapy
Bacteroides
Gram-negative bacilli or cocco-bacilli
Anaerobic (obligate)
B. fragilis has an anti-phagocytic capsule
Opportunistic with immunosuppression
dx- Opportunistic with immunosuppression
Prevotella
Prevotella sp. are similar to, and previously classified as, bacteroides
Part of the normal oral and vaginal flora
Can cause obstetric and gynecologic infections, aspiration pneumonia, chronic otitis media and sinusitis, and abscesses in lung, oral cavity, brain abscesses, and human bite wounds
Acinetobacter baumannii
Gram-negative coccobacillus
Nosocomial infections
Haemophilus
Gram-negative coccobacilli
Capsule is major virulence determinant
H. influenzae type b - most common cause of bacterial meningitis in children 6 months-2 years
H. ducreyi –chancroid (soft chancre)
H. parainfluenzae - pneumonia, endocarditis
H. aegypticus -conjunctivitis
prevention: Hib vaccine
Bordetella
Gram negative coccobacilli
Encapsulated
several exotoxins: filamentous hemagglutinin, pertussis toin, invasive adenylate cyclase toxin, tracheal cyotosxin, lethal (dermonecrotic) toxin
B. pertussis - whooping cough: catarrhal stage, paroxysmal phase, convalescent phase
prevention: DTaP vaccine x 5 followed by Tdap in adulthood
Yersinia
Gram negative, bipolar staining coccobacilli
Non-lactose fermenter
Glucose fermenter
Y. enterocolitica and Y. pseudotuberculosis
intestinal parasite of animals causing disease via ingestion of contaminated food or water
self-limited ileitis, gastroenteritis
Y. pestis Bubonic plague (black death) maintained among rodent populations (ground squirrels, prairie dogs, great gerbils/black rats
Two antiphagocytic components
F1 antigen and the V & W antigens (both required for virulence
Bubonic plague
Septicemic plague
Pneumonic plage
Prevention: - Vector control and inactivated Y. pestis vaccine for lab personnel handling organism
Francisella tularensis
Gram-negative pleomorphic coccobacillus
Intracellular pathogen
Tularemia
Ulceroglandular via handling rabbits
Pneumonic
Brucella
Gram negative coccobacilli
Intracellular parasites
Generally zoonosis via occupational exposure to infected animal
Outbreaks via ingestion of unpasteurized milk products and undercooked meat
B. melitensis – goat, sheep, camels
Unpasteurized milk caused Malta/undulant/Mediterranean fever
B. suis - pigs
Brucellosis
Undulant fever
B. melitensis and B. suis are more transmissible to humans
Pasteurella multicida
Gram-negative coccobacilli
from lots of animals, but in the class example the cat!
