Chapter 20: Gram Negative Pathogenic Bacteria

Question 1

What are some general characteristics about gram negative pathogens?

Answer 1

Constitute largest group of human bacterial pathogens

Due in part to Lipid A in bacterial cell wall (triggers fever, vasodilation, inflammation, shock, disseminated intravascular coagulation (DIC))

Most Gram-negative bactera that breach skin or mucous membranes grow at 37 degrees Celsius

Question 2

What is the only Gram negative cocci genus?

Answer 2

Neisseria

Nonmotile, aerobic bacteria, arranged as diplococci

Oxidase positive- distinguishes from many Gram-negative pathogens

Have fimbriae (adhesion), capsules (protect against phagocytosis), and vairable cell wall antigens composed of lipooligosaccharide

Fastidious in nature- grows on chocolate agar or Thayer-Martin agar

Two pathogenic species to humans- N. gonnorhoeae, N. meningitidis

Question 3

What are the characteristics of Neisseria gonorrhoeae?

Answer 3

Causes gonorrhea

Gonococci adhere to the genital, urinary, and digestive tract via fimbriae and capsules, protected by secreting protease enzyme that cleaves IgA

Can survive inside phagocytic cells

Men- painful urination, pus-filled discharge

Women- asymptomation, PID, proctitis, gingivitis, and pharyngitis

In children- opthalmia neonatorum (during childbirth infection passed)

Question 4

How is a Neisseria gonorrhoeae infection diagnosed, treated, and prevented?

Answer 4

Diagnosis- asymptomatic cases diagnosed with genetic probes, Gram-negative diplococci in pus, grow on Thayer-Martin media, ferments only glucose

Treatment- complicated due to resistant strains, broad-spectrum antibiotics like cephalosporins, long term immunity does not develop due to variable surface antigens

Prevention- abstinence, monogamy, proper use of condoms

Question 5

What are some characteristics of Neisseria meningitidis?

Answer 5

13 antigenic strains cause disease; A,B,C, and W135 most common

Can survive in neutrophils and macrophages

Polysaccharide capsule resists lytic enzymes of phagocytosis

Causes blebbing- a process of shedding outer membrane

Can be normal microbiota of upper respiratory tract, transmitted by respiratory droplets

Question 6

How is N. meningitidis pathogenic and what diseases does it cause?

Answer 6

Life-threatening when bacteria invade blood or CSF

Most common cause of meningitis in individuals under 20yrs

Bacteria transmitted among people living in close contact

Meningococca meningitis- death within 6 hours, abrupt sore throat, fever, headache, stiff neck, vomiting, and convulsions

Meningococcal septicemia (blood poisoning)- life threatening, petechiae- minute hemorrhagic skin lesions on trunk and lower extremities which can combine together to form black lesions

Question 7

How is N. meningitidis infection diagnosed, treated, and prevented?

Answer 7

Diagnosis- gram negative diplococci in phagocytes of CNS, presence on antibodies against bacteria, ferments both glucose and maltose

Treatment- intravenous antibiotics like ceftiaxone, a cephalosporin

Prevention- asymptomatic carriers make eradication unlikely, vaccination against capsular strains of A,C,Y & W-135, NOT B STRAIN

Question 8

What are the two families of pathogenic, Gram-negative bacteria that are facultatively anaerobic?

Answer 8

Two families contain most human pathogens

Enterobacteriaceae

Pasteurellaceae

Oxidase test distinguishes between these two families

Includes important nosocomial pathogens

Question 9

What is the result of an oxidase test for the family Enterobacteriaeceae?

Answer 9

Negative- no purple color

Question 10

What is the oxidase test result for the family Pasteurellaceae?

Answer 10

Positive- Purple

Question 11

Give a brief overview of the Family Enterobacteriaceae?

Answer 11

Intestinal microbiota of most animals and humans

Ubiquitous in water, soil, and decaying vegetation

Enteric bacteria are the most common Gram-negative pathogens of humans

Some have capsules, others only have loose slime layer

Question 12

What are the antigens and virulence factors typical of an enteric cell?

Answer 12

Antigens- K, H, and O

O- outer membrane, Lipid A

K- capsular antigens

H- flagellar antigens

Type III secretion system

Virulence factors: fimbria, exotoxin, adhesin, plasmid, iron-binding protein, hemolysin

Question 13

How is an Enterobacteriaceae infection diagnosed, treated, and prevented?

Answer 13

Diagnosed- enteric bacteria in urine, blood, or CSF, use of selective and differential media, biochemical tests rapidly identify enteric bacteria

Treatment- Diarrhea is typically self-limited

Prevnetion- good personal hygiene and proper sewage control

Question 14

What are the three groups that the Enterobacteriaceae family is broken into?

Answer 14

Colioforms- ferment lactose, normal microbiota but may be opportunistic pathogens

Noncoliforms- do not ferment lactose

True pathogens

Question 15

What are some characteristics about Coliform Opportunists?

Answer 15

Aerorbic or faculatatively anaerobic, Gram-negative, rod shaped bacteria that ferment lactose

Can be diagnosed by growth on MacConkey’s agar of Eosin-Methylene blue agar

Commonly found in soil, on plants, and on decaying vegetation

Colonize the intestinal tract of animals and humans

Coliforms in water indictative of impure water and poor sewage treatment

Question 16

What are some characteristics of Escherichia coli?

Answer 16

Most common and important of coliforms

Numerous O, H, and K strains

Virulent strains have genes for fimbriae, adhesins, and exotoxins located on virulence plasmids

Can cause septicemia, UTIs, meningitis, gastroenteritis most common disease (mediated by exotoxins)

Common cause of non-nosocomail UTIs

Question 17

What is the most common strain of E. coli?

Answer 17

E. coli O157:H7

Most prevalent pathogenic E. coli in developed countries

Causes diarrhea, UTIs, neonatal meningitis, sepsis, pneumonia, hemorrhagic colitis, hemolytic uremic syndrome

Associated with consumption of uncooked ground beef

Produces Shiga-like toxin

Question 18

How can E. coli strains by clasified by Serotyping?

Answer 18

Based on reactivity of highly variable bacterial surface molecules with different antibodies

Two types of structures- O and H antigens

Over 700 antigenic types, or serotypes

Serotyping is still important in distinguishing the small number of strains that actually cause disease

Question 19

How can E. coli be classified by virotype?

Answer 19

At least four virotypes

All cause some form of diarrhea

Question 20

Define Enterotoxigenic E. coli (ETEC)

Answer 20

Causes Traveller’s Diarrhea (LT and ST) toxin

Question 21

Enteropathogenic E. coli (EPEC)

Answer 21

Causes Traveller’s diarrhea (no toxin)

Question 22

Enterohemorrhagic E. coli (EHEC)

Answer 22

Causes bloody diarrhea (Shiga-like toxin)

Question 23

Enteroinvasive E.coli (EIEC)

Answer 23

Like shigella, bloody diarrhea with fever

Question 24

What are important characteristics of Klebsiella?

Answer 24

Are non-motile (No H antigen)

Digestive and respiratory tracts, opportunists

Capsule protects the bacteria from phagocytosis

K.pneumonie- most commonly isolated pathogenic species

May be involved in bacteremia, meningitis, wound infections, UTIs

Question 25

What are important charactertistics of Serratia?

Answer 25

Produce a red pigment when grown at room temperature

Can grow on catheters, saline solutions, and on other hospital supplies

Can cause life-threatenign opportunistic infection in immunocomprimised patients

Difficult to treat due to resistance to antimicrobial drugs

Question 26

What are important characteristics of Enterobacter, Hafnia, and Citrobacter?

Answer 26

Found in soil, water, decaying vegetation, and sewage

Reside in digestive tracts of animals and humans, opportunists

Frequently involved in nosocominal infections of immunocompromised patients

Difficult to treat due to resistance ot antimicrobial drugs

Only differentiate using biochemical tests

Question 27

What is the clinically relevant noncoliform opportunist?

Answer 27

Proteus

Very motile (swarming movement)

Proteus mirabilis is most commonly associated with human disease

UTIs in patients with long term catheters

Infection-induced kidney stones, bacterium breaks down urea to produce ammonia which raises pH, ions precipitate out of solution

Resistant to many antimicrobial drugs

Question 28

What are the three bacterial species that are considered truly pathogenic enterobacteriaeceae?

Answer 28

Non-lactose fermeting Salmonella, Shigella, and Yersinia

Almost always pathogenic due to numerous virluence factors

Type III secretion system

Introduce proteins that inhibit phagocytosis, rearrange the cytoskeletons of eukaryotic cells, induce apoptosis

Question 29

What are the important characteristics of Salmonella?

Answer 29

Urease and oxidase negative, nonmotile

In the intestines and feces of birds, reptiles, and mammals

Most human infections due to consuming food contamined with animal feces

Poultry and eggs are common sources of Salmonella

Can cause salmonellosis and typhoid fever

Reproduce within food vesicles

Question 30

What are the characteristics of typhoid fever?

Answer 30

Caused by Salmonella enterica serotype typhi

Humans are the only host

Ingest bacteria in contaminated food or water

Bacteria can pass through intestines into the bloodstream, peritonitis can result

Treat with fluid and electrolyte replacement, ampicillin, or ciprofloxacin

Vaccines provide temporary protection to travelers

Question 31

What are important characteristics of Shigella?

Answer 31

Oxidase and urease negative

Primarily a parasite of the digestive tract of humans

Produce diarrhea-inducing enterotoxin

Cause shigellosis- abdominal cramps, diarrhea, and bloody stools

Multiplies in cytosol

4 defined species:

S. dysenteriae- produces Shiga toxin (acts on 60S ribosome and stops protein synthesis)

S. flexneri

S. boydii

S. sonnei

Question 32

What are important characteristics of Yersinia?

Answer 32

Normal pathogen of animals

Three important species-

Y. enterocolitica- causes of inflammation of the intestinal tract, transmitted by fecal-oral route

Y. pseudotuberculosis- similar to Y. enterocolitica but less servere

Y. pestis- extremely virulent, causes bubonic plague and pneumoinc plague

Question 33

How is Yersinia pestis transmitted?

Answer 33

Rats, moles, and voles are natural hosts of Y. pestis

If natural hosts comes in direct contact with person or flea (vecor) comes in contact, form a bubo (swollen lymph node)

Also transmitted airborne

Question 34

How is Y. pestis diagnosed, treated, and prevented?

Answer 34

Diagnosis and treatment must be rapid- fast progression and deadliness of plague

Diagnosis- characteristic symptoms usually sufficient for diagnosis

Treatment- many antibacterial drugs are effective against Yersinia