Chapter 20: Gram Negative Pathogenic Bacteria Flashcards
What are some general characteristics about gram negative pathogens?
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
What is the only Gram negative cocci genus?
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
What are the characteristics of Neisseria gonorrhoeae?
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)
How is a Neisseria gonorrhoeae infection diagnosed, treated, and prevented?
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
What are some characteristics of Neisseria meningitidis?
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
How is N. meningitidis pathogenic and what diseases does it cause?
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
How is N. meningitidis infection diagnosed, treated, and prevented?
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
What are the two families of pathogenic, Gram-negative bacteria that are facultatively anaerobic?
Two families contain most human pathogens
Enterobacteriaceae
Pasteurellaceae
Oxidase test distinguishes between these two families
Includes important nosocomial pathogens
What is the result of an oxidase test for the family Enterobacteriaeceae?
Negative- no purple color
What is the oxidase test result for the family Pasteurellaceae?
Positive- Purple
Give a brief overview of the Family Enterobacteriaceae?
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
What are the antigens and virulence factors typical of an enteric cell?
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
How is an Enterobacteriaceae infection diagnosed, treated, and prevented?
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
What are the three groups that the Enterobacteriaceae family is broken into?
Colioforms- ferment lactose, normal microbiota but may be opportunistic pathogens
Noncoliforms- do not ferment lactose
True pathogens
What are some characteristics about Coliform Opportunists?
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
What are some characteristics of Escherichia coli?
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
What is the most common strain of E. coli?
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
How can E. coli strains by clasified by Serotyping?
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
How can E. coli be classified by virotype?
At least four virotypes
All cause some form of diarrhea
Define Enterotoxigenic E. coli (ETEC)
Causes Traveller’s Diarrhea (LT and ST) toxin
Enteropathogenic E. coli (EPEC)
Causes Traveller’s diarrhea (no toxin)
Enterohemorrhagic E. coli (EHEC)
Causes bloody diarrhea (Shiga-like toxin)
Enteroinvasive E.coli (EIEC)
Like shigella, bloody diarrhea with fever
What are important characteristics of Klebsiella?
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
What are important charactertistics of Serratia?
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
What are important characteristics of Enterobacter, Hafnia, and Citrobacter?
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
What is the clinically relevant noncoliform opportunist?
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
What are the three bacterial species that are considered truly pathogenic enterobacteriaeceae?
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
What are the important characteristics of Salmonella?
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
What are the characteristics of typhoid fever?
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
What are important characteristics of Shigella?
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
What are important characteristics of Yersinia?
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
How is Yersinia pestis transmitted?
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
How is Y. pestis diagnosed, treated, and prevented?
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
