Gram Negative Bacteria

Question 1

Gram Negatives

Answer 1

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

Question 2

Neisseria

Answer 2

Gram-negative “coffee bean” diplococci

Question 3

N. gonorrhoeae

Answer 3

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

Question 4

N. meningitidis

Answer 4

(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

Question 5

Moraxella & Kingella

Answer 5

Gram-negative diplococcus

Moraxella catarrhalis
common cold, otitis media and sinusitis
resistant to beta-lactams

Moraxella lacunata conjunctivitis

Kingella kingae

Question 6

Coliforms

Answer 6

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

Question 7

Escherichia

Answer 7

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

Question 8

Pathogenic diarrheal E. coli (4 types)

Answer 8

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”)

Question 9

Klebsiella

Answer 9

Gram-negative bacilli
Ferment lactose (reddish on McConkey’s agar)
Encapsulated

Question 10

K. pneumoniae

Answer 10

Most common cause of nosocomial respiratory tract infections
Bacterial pneumonia
Urinary tract infections

(exams like to say looks like red jelly sputum)

Question 11

K oxytoca

Answer 11

can cause colitis

Question 12

Klebsiella granulomatis

Answer 12

–> granuloma inguinale (donovanosis) = painless genital ulcers –> scarring with lymphatic blockage

Question 13

Enterobacter

Answer 13

Gram-negative rods
Ferment lactose
Possess inducible beta-lactamases

Question 14

Enterobacter cloacae

Answer 14

Normal gut flora
Sometimes causes lower respiratory tract, urinary tract and intra-abdominal infections

nosocomial outbreaks (surgical equipment, etc.)

Question 15

Enterobacter aerogenes

Answer 15

Nosocomial opportunistic infections

Question 16

Serratia

Answer 16

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)

Question 17

Proteus

Answer 17

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

Question 18

Shigella

Answer 18

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)

Question 19

Shigella dysenteriae

Answer 19

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

Question 20

Salmonella

Answer 20

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

Question 21

Salmonella enterica enterica, serovar Enteritidis

Answer 21

Enteroinvasive gastroenteriti

after 1-3 day incubation, usually self-limited

Question 22

S. enterica enterica, serovar Typhi

Answer 22

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

Question 23

Pseudomonas

Answer 23

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

Question 24

Burkholderia

Answer 24

Gram-negative rods
Oxidase-positive

Burkholderia cepacia- in cystic fibrosis

Burkholderia pseudomallei (melioidosis)

Question 25

Stenotrophomonas maltophilia

Answer 25

Gram-negative rod Most non-fermentative Oxidase +/- immunocompromised patients

Question 26

Legionella

Answer 26

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

Question 27

Fusobacterium

Answer 27

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

Question 28

Main Vibrio types

Answer 28

V. parahaemolyticus V. vulnificus V. cholerae, toxigenic 01 (travel)

Question 29

Vibrio cholerae

Answer 29

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

Question 30

Campylobacter jejuni

Answer 30

Gram-negative curved rods (Greek "campylo“ = curved) Non-lactose fermenter LPS endotoxin Ingestion of contaminated water, milk or undercooked foods (raw clams)

Question 31

Helicobacter pylori

Answer 31

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

Question 32

Bacteroides

Answer 32

Gram-negative bacilli or cocco-bacilli Anaerobic (obligate) B. fragilis has an anti-phagocytic capsule Opportunistic with immunosuppression dx- Opportunistic with immunosuppression

Question 33

Prevotella

Answer 33

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

Question 34

Acinetobacter baumannii

Answer 34

Gram-negative coccobacillus Nosocomial infections

Question 35

Haemophilus

Answer 35

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

Question 36

Bordetella

Answer 36

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

Question 37

Yersinia

Answer 37

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

Question 38

Francisella tularensis

Answer 38

Gram-negative pleomorphic coccobacillus Intracellular pathogen Tularemia Ulceroglandular via handling rabbits Pneumonic

Question 39

Brucella

Answer 39

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

Question 40

Pasteurella multicida

Answer 40

Gram-negative coccobacilli | from lots of animals, but in the class example the cat!