Gram-Negative Bacilli Flashcards
General characteristics of Enterobacteriaceae
- Gram (-) Bacilli
- NSF (Non-spore forming)
- Some are motile and nonmotile
- FA (Facultative anaerobes)
- (-) Oxidase
- Ferment glucose but otherwise vary in carbohydrate utilization
- Most reduce Nitrate to Nitrites
Name the motile Enterobacteriaceae
peritrichous
Name the nonmotile Enterobacteriaceae
Klebsiella, Shigella, Yersinia
Which surface antigen is known as the somatic antigen or cell wall antigen
O antigen
Characteristics of O antigen
Heat and alcohol stable
Usually detected by bacterial agglutination
Which surface antigen is known as the capsular antigen or fimbrial antigen
K antigen
True or False: The K antigen is external to the O antigens on some but not all Enterobacteriaceae
True
Characteristics of K antigen
Heat labile and may be associated with virulence
Which surface antigen is known as the flagellar antigen
H antigen
Characteristics of H antigen
Heat- and alcohol-labile antigen
Found on the surface of flagella
How can H antigens be presented within a single serotype ?
Either or Both of two forms: Phase 1 (lower case letters) Phase 2 (arabic numerals)
Phase variation occurs with which surface antigen
H antigen
General characteristics of Enterobacteriaceae coliforms
- Aerobic and FA
- NSF
- Gram (-) rods
- Cytochrome oxidase (-)
- Capable of growth in the presence of bile salts
- Lactose fermenters
What are the normal enteric flora do Coliforms include ?
Escherichia, Klebsiella, Enterobacter, and Citrobacter
Differentiate fecal coliforms from non fecal coliforms
Fecal coliforms:
- Ferment lactose at 44.5°C
- the indicator organism of choice for fecal contamination
Nonfecal coliforms:
- Does not ferment lactose
- their detection in water supply or other materials may mean false positive for fecal contamination
Which noncoliforms are included in the opportunistic, normal gut flora ?
Proteus, Morganella, Providencia, Edwardsiella, Serratia, Hafnia
Which noncoliforms are included in the pathogenic enterics ?
Salmonella, Shigella, Yersinia enterocolitica and Y. pseudotuberculosis
Which noncoliforms are included in the pathogenic, non-enteric ?
Yersinia pestis
Habitat of enterobacteriaceae
ubiquitous in nature
most are found in intestinal tract (colon)
This coliform is also referred to as colon bacillus
Escherichia coli
Where do E. coli strains that cause UTI originate from ?
Large intestine as resident biota
Why is UTI of E. coli more common in women ?
Due to their relatively short urethras that promote ascending infection to the bladder (cystitis) and occasionally, the kidneys
What are uropathogenic E. coli ?
Strains that cause lower urinary tract and acute pyelonephritis in otherwise healthy hosts
How does P fimbrae assist uropathogenic E. coli ?
Allow the bacteria to attach to the urinary epithelial mucosa and not be washed out with urine flow
How do hemolysins assist uropathogenic E. coli ?
Kill immune effector cells and inhibit phagocytosis and chemotaxis of certain white blood cells
How do aerobactins affect uropathogenic E. coli ?
Allows the bacterial cell to chelate iron, as free iron is not available in the body for the bacteria to use
This is also known as enterovirulent E. coli
Diarrheagenic E. coli
What are the 5 categories of diarrheagenic E. coli ?
Enteropathogenic E. Coli Enterotoxigenic E. coli Enterohemorrhagic E. coli Enteroinvasive E. coli Enteroaggregative E. coli
Characteristics of EPEC
low-grade fever, malaise, vomiting, and profuse, watery diarrhea
Stool typically contains large amounts of mucus
Adhere to intestinal epithelial cells in localized microcolonies producing characteristic histopathologic lesions known as “attaching and effacing lesions”
Enteropathogenic E. coli
What facilitates the “attachment” or promotes the tight adherence characteristic of EPEC ?
EPEC adherence factor (EAF)
and the chromosomal locus of enterocyte effacement (LEE) pathogenicity island
What is the “effacement” of EPEC ?
loss of microvilli
formation of filamentous actin pedestals or cup-like structures
occasionally, entry of the EPEC into the mucosal cells
What are the two clinical syndromes associated with ETEC ?
“weanling diarrhea” among children in tropical and subtropical
climates, especially in developing countries
“Traveler’s diarrhea” (also referred to as “Montezuma’s revenge”; “Delhi belly”)
Characteristics of ETEC
Produces a typically mild, self-limiting disease which is abrupt in onset with short incubation period
profuse watery diarrhea (similar with V. cholerae), usually without blood, mucus, or pus; accompanied by mild abdominal cramps; usually without vomiting or fever
How is the pathology of ETEC mediated by fimbrae ?
Facilitates colonization of ETEC on the proximal small intestine by binding to specific receptors on the intestinal microvilli
Which fragment of the heat labile toxin of ETEC activates cellular adenylate cyclase, and what does it do ?
A moiety (fragment)
increase in the conversion of adenosine triphosphate to cyclic adenosine monophosphate (cAMP)
What does the accumulation of cAMP means in ETEC ?
hypersecretion of both electrolytes and fluids into the intestinal lumen, resulting in watery diarrhea similar to cholera
Which fragment of the heat labile toxin of ETEC is known as the binding portion ?
B moiety (fragment)
Which exotoxin of ETEC stimulates guanylate cyclase ? and what does this lead to ?
Heat stable toxin
Increased production of cyclic guanosine monophosphate, accumulation of which also causes hypersecretion
How is ETEC commonly spread ?
- consumption of contaminated food or water
- poor hygiene, reduced availability of sources of potable water
- inadequate sanitation
How is EHEC commonly spread ?
Food and food products such as processed meats, unpasteurized dairy products, apple cider, bean sprouts, and spinach
This type of diarrheagenic E. coli is associated with colitis, and hemolytic uremic syndrome (HUS)
EHEC
Which of the EHEC’s verotoxin is a phage-encoded cytotoxin ?
Verotoxin I
Of the E. coli serotypes that produce Shiga toxin which is the most common and is the one that can be identified most readily in clinical specimens ?
O157:H7
How is EIEC transmitted from one person to another ?
Direct transmission from person to person via the fecal-oral route has been reported
Characteristics of EIEC
fever, colitis, severe abdominal cramps (tenesmus), malaise, and watery diarrhea with blood, mucus and leukocytes in stool
Characteristics of EHEC
Produces a watery diarrhea that progresses to bloody
diarrhea with abdominal cramps and low-grade fever or an absence of fever but the stool does not contain
leukocytes
This diarrheagenic E. coli adheres to epithelial cells in a pattern resembling a pile of stacked bricks
EAEC
Characteristics of EAEC
watery, mucoid diarrhea with low grade fever and little or no vomiting, white blood cells and red blood cells are typically absent from the stool
EAEC pathology has been associated with what factors ?
St-like toxin, LT toxin, and fibril colonization factors called “AAFs” (aggregative adherence fimbriae)
How can newborns be infected with E. coli ?
- infection in the birth canal just before or during delivery
- when the mother’s vagina is heavily colonized
- infection may also result if contamination of the amniotic fluid occurs
How are newborns highly susceptible to E. coli ?
They lack in IgM antibodies
What coliform is also known as Friedlander’s bacillus
Klebsiella
What is the most commonly isolated klebsiella species ?
Klebsiella pneumoniae
Describe the sputum produced by klebsiella pnuemoniae
thick, mucoid, and brick red, or thin and “currant jelly-like” in appearance
Characteristics of Klebsiella pneumoniae
Also produces urinary tract infection, wound infections, meningitis, bacteremia with focal lesions (e.g., lives abscesses) in debilitated patients
Which klebsiella specie has their pathology associated with a large polysaccharide capsule that confers protection against phagocytosis and antimicrobial absorption ?
Klebsiella pneumoniae
Isolates of this Klebsiella specie have also been linked to antibiotic/antimicrobial-associated hemorrhagic colitis (AAHC)
Klebsiella oxytoca
What is AAHC ?
a distinct form of antibiotic-associated diarrhea, in which C. difficile is absent and where patients experience a sudden onset of bloody diarrhea often in combination with severe abdominal cramps
Klebsiella specie that has been isolated from cerebral abscesses and nasal mucosa in ozena
Klebsiella pneumoniae subspecies ozaenae
Klebsiella specie that has been isolated from patients with rhinoscleroma
Klebsiella pneumoniae subspecies rhinoscleromatis
Klebsiella specie that causes granulomatis inguinale
Klebsiella granulomatis
Difference between klebsiella and enterobacter species ?
Eneterobacter is motile
What are the two most common isolates from the Enterobacter species ?
Enterobacter cloacae and Enterobacter (now Klebsiella) aerogenes
Clinical relations to Enterobacter cloacae and Enterobacter (now Klebsiella) aerogenes
Causes a broad range of hospital-acquired infections
Enterobacter isolate that come from diverse geographic and ecologic sources
Enterobacter (now Pantoea) agglomerans
Which enterobacter specie was responsible for an outbreak of septicemia caused by contaminated
intravenous fluids ?
Enterobacter (now Pantoea) agglomerans
This Enterobacter specie typically produces a yellow pigment and is sometimes referred to as yellow-pigmented E. cloacae
Enterobacter (now Cronobacter) sakazakii
This Enterobacter specie is associated with contaminated powdered infant formula and has also been isolated from cultures taken from brain
abscesses and respiratory and wound infections
Enterobacter (now Cronobacter) sakazakii
Where is Enterobacter gergoviae usually isolated from ?
Has been found in respiratory samples and is rarely isolated from blood cultures.
Where is Enterobacter hormaechei usually isolated from ?
human sources such as blood, wounds, and sputum
Which coliform Enterobacteriaceae has been earlier classified within the tribe Salmonelleae ?
Citrobacter species
What medium can Citrobacter species grow on ?
Simmons citrate medium
Where is Citrobacter freundii isolated from ?
known as an extra intestinal pathogen, it can also be
isolated in stool cultures
Other than UTI what other infections can arise from Citrobacter freundii ?
nosocomial infectious diseases including pneumonias, and intraabdominal abscesses as well as endocarditis in intravenous drug abusers
What is clinically significant with Citrobacter koseri ?
pathogen documented as the cause of nursery outbreaks of neonatal meningitis and brain abscesses
What are the prevention and control of coliforms ?
Enteropathogenic E. coli serotypes should be controlled like salmonellae
How are proteus species normally transmitted ?
Within hospitals or other institutions, these bacteria commonly are transmitted by personnel, instruments, or parenteral medications.
How is transmission of the proteus species controlled ?
handwashing, rigorous asepsis, sterilization of equipment, disinfection, restraint in intravenous therapy, and strict precautions in keeping the urinary tract sterile (ie, closed drainage).
Of the proteus genus, which species are widely recognized human pathogens ?
P. mirabilis and P. vulgaris
What is the correlation with Proteus species and promoting struvite kidney stone (also called calculi) formation ?
They produce urease resulting in rapid hydrolysis of urea with liberation of ammonia
Rapid hydrolysis of urea causes the urine to become alkaline, making acidification virtually impossible
Name the importance of the Dienes Phenomenon ?
It is used to differentiate the two strains of Proteus for epidemiological purposes
What clinical manifestations are correlated to Morganella morganii ?
UTI, wound infections, neonatal sepsis
Compare Morganella morganii and the Proteus species
Both produce urease and are motile, but Morganella morganii does not swarm
What clinical manifestations are correlated to P. rettgeri ?
pathogen of urinary tract
caused occasional outbreaks in health care settings
implicated in diarrheal disease among travelers
What clinical manifestations are correlated to P. stuartii ?
outbreaks in burnt units
Why is it difficult to treat immunocompromised patients infected with P. rettgeri and P. stuartii ?
Due to their resistance to antimicrobials
What is the chief reservoir for E. tarda ?
reptiles and freshwater fish
What are the clinical manifestations for E. tarda ?
may cause a variety of extraintestinal infections; wound infections resulting from trauma, often related to aquatic accidents
implicated in abscesses that may lead to bacteremia or myonecroses
Name the key characteristic of E. tarda
production of abundant amounts of hydrogen sulfide
What are the three hydrolytic enzymes produced by the Serratia species ?
Gelatinase
Lipase
DNase
Differentiate the documented pigments produced by the Serratia species
Prodigiosin - the non-water-soluble, and non-diffusible pigment
Pyrimine - the water-soluble and diffusible pigment
Which species of the genus Serratia is mostly associated with a variety of human infections ? and what are those infections ?
non-pigmented S. marcescens
pneumonia, bacteremia, and endocarditis, especially in narcotics addicts and hospitalized patients.
What are the six subspecies of S. enterica ?
S. enterica subsp. enterica (also called subspecies I)
S. enterica subsp. salamae (subspecies II)
S. enterica subsp. arizonae (subspecies IIIa)
S. enterica subsp. diarizonae (subspecies IIIb)
S. enterica subsp. houtenae (subspecies IV)
S. enterica subsp. indica (subspecies VI)
Which strain of S. enterica is the cause of most human illnesses ?
S. enterica subspecies enterica
What are two species that comprise the genus Salmonella ?
S. enterica and S. bongori
Which salmonella strains are primarily infective for humans ?
Salmonella Typhi
S. Choleraesuis
perhaps S. Paratyphi A and S. Paratyphi B
How are the salmonella strains normally transmitted ?
oral route, usually with contaminated food or drink
What is the mean infective dose to produce clinical or subclinical infection in humans for Salmonella ?
10^5 – 10^8 salmonellae
What population is usually affected by Typhoid fever and why ?
occurs more often in tropical and subtropical areas
outbreaks has been associated with:
improper disposal of sewage
poor sanitation
lack of a modern potable water system
What is the major cause of bacterial enteric illness in both humans and animals ?
Salmonellosis
What are the factors responsible for the virulence of salmonellae ?
Fimbriae - used in adherence and in initiating
intestinal infection
The ability of salmonellae to traverse intestinal
mucosa
Enterotoxin - produced by certain Salmonella
strains that cause gastroenteritis
Vi antigen (virulence or capsular antigens) - found in some strains.
Which Salmonella strain is most correlated to Typhoid fever ?
S. typhi
What is the onset of Typhoid fever ?
approximately 9 to 14 days after ingestion of the organisms
depends on the number of organisms ingested — the
larger the inoculum, the shorter the incubation period.
What symptoms do the patient develop once the S. typhi invades and penetrates the intestinal mucosa
?
fever, accompanied by: malaise lethargy myalgia anorexia a continuous dull frontal headache constipation instead of diarrhea
How does S. typhi multiply once it has invaded the body ?
lymphatic system -> bacteria eventually reach the
bloodstream -> spread to the liver, spleen, and bone marrow
engulfed by mononuclear phagocytes — where they multiple intracellularly
What is the significance of the second release of S. typhi into the body after intracellular multiplication ?
febrile episodes are more evident
organisms may be easily isolated from the blood
When do “rose spots” appear during Typhoid fever and where ?
2nd week around the umbilical region
Which organ becomes the foci of long-term carriage of S. typhi during typhoid fever ?
gallbladder
What are the complications of Typhoid fever ?
necrosis in the gallbladder leading to necrotizing cholecystitis
necrosis of the Peyer’s patches leading to hemorrhage
perforation of the bowel
What is Salmonella bacteremia collectively referred to as ?
nontyphoidal Salmonella
Which salmonella strains is commonly associated with Salmonella bacteremia ?
S. choleraesuis
but may be caused by any salmonella serotype such as Typhimurium, and Paratyphi
What are the characteristics of Salmonella bacteremia ?
may occur with and without extraintestinal foci of infection
prolonged fever and intermittent bacteremia
What is the most common manifestation of salmonella infection ?
Enterocolitis
Which salmonella strain is the common cause for enterocolitis ?
S. Typhimurium and S. Enteritidis
but can be caused by any of the more than 1400 group I serotypes of salmonellae.
What are the characteristics of salmonella enterocolitis ?
Nausea, headache, vomiting, and profuse diarrhea, low grade fever
inflammatory lesions are present in the small and large intestinal mucosa and stools have few leukocytes
What are the phases of Typhoid fever ?
(a) Ingested bacteria invade the intestinal lining
(b) From this site, they enter the blood stream, causing septicemia and endotoxemia
(c) Infection in the lymphatic tissue of the small intestine can produce varying degrees of ulceration and perforation of the intestinal wall
How can the carrier state of salmonella strains be resolved ?
antimicrobial therapy if gallbladder infection is not evident
cholecystectomy has been the only solution to the chronic state of enteric carriers
What are the two available typhoid vaccines in the US ?
oral live, attenuated vaccine and a Vi capsular polysaccharide vaccine for intramuscular use
What is the prevention and control for typhoid ?
prevent contamination of food and water by rodents or other animals that excrete salmonellae
Infected poultry, meats, and eggs must be thoroughly cooked
Carriers must not be allowed to work as food handlers, strict hygiene
Vaccination is recommended for travelers to endemic regions
What is the group, type, and other name for Shigella dysenteriae, under Ewing’s classification ?
A, Shiga’s bacillus / Japanese dysentery bacillus
What is the group, type, and other name for Shigella flexneri, under Ewing’s classification ?
B, Flexner’s bacillus or Strong’s bacillus /Philippine dysentery bacillus
What is the group, type, and other name for Shigella boydii, under Ewing’s classification ?
C, Boyd’s bacillus / British dysentery bacillus
What is the group, type, and other name for Shigella sonnei, under Ewing’s classification ?
D, Sonne-Duval’s bacillus / US dysentery bacillus
What is the reservoir for Shigella spp ?
Humans and large primates
How is shigella transmitted ?
4F: food fingers feces and flies
direct person-to-person contact
fecal-oral route
transmitted by flies, fingers, and food or water contaminated by infected persons
What makes shigellosis highly communicable ?
low infective dose (approximately less than 100 bacilli) required to produce the disease
What is the possible cause of irritation of the bowel wall in shigellosis ?
Endotoxins
What are the characteristics of Shigella dysenteriae toxin ?
Antigenic protein
Enterotoxin
Neurotoxin
How does shigella dysenteriae toxin produce diarrhea ?
inhibits sugar and amino acid absorption in the small intestine
What is the time of onset for symptoms of shigella species ?
24 - 48 hours
What symptoms mark the onset of shigella species ?
high fever, chills
abdominal cramps
pain accompanied by tenesmus (rectal spasms)
watery diarrhea progresses to bloody stools containing mucus and numerous leukocytes
What complications may arise with shigellosis ?
Rectal prolapse
Ileus, with marked abdominal dilation, possibly leading to toxic megacolon
How is transmission of shigella controlled ?
sanitary control of water, food, and milk; sewage disposal and fly control
isolation of patients and disinfection of excreta
detection of subclinical cases and carriers, particularly food handlers
antibiotic treatment of infected individuals.
What are the Yersinia species that can cause zoonoses in man, yersinioses ?
Y. pestis
Y. enterocolitica
Y. pseudotuberculosis
How can Y. enterocolitica be transmitted ?
animals, including domestic swine, cats, and dogs
ingestion of contaminated food, often pork, and vacuum-packed deli meat, beef, lamb, chicken, and possibly chocolate milk and water
What is the mean infective dose to produce clinical or subclinical infection in humans for Y. enterocolitica ?
10^8 – 10^9 yersiniae must enter the alimentary tract
What is the onset process of Y. enterocolitica in relation to acute gastroenteritis ?
the yersiniae multiply in the gut mucosa during the incubation period of 4-7 days
This leads to inflammation and ulceration, and leukocytes appear in feces
What clinical manifestations can arise from Y. enterocolitica ?
acute gastroenteritis
appendicitis-like syndrome
less frequently: septicemia, arthritis, and erythema nodosum
What is the chief reservoir for Y. pseudotuberculosis ?
Rodents, particularly guinea pigs
What is a significant characteristic of Y. pseudotuberculosis ?
caseous swellings called pseudotubercles
When ingested, the organisms spread to the mesenteric lymph nodes, producing a generalized infection that is usually self-limiting
What clinical manifestations can arise from Y. pseudotuberculosis ?
septicemia accompanied by mesenteric lymphadenitis
This noncoliform is also referred to as the plague bacillus
Y. pestis
What is the chief reservoir of Y. pestis ?
rodents
How is Y. pestis transmitted ?
From rodents, by bites of fleas
contact with:
wild animals (sylvatic plague)
domestic or semi domestic animals (urban plague)
infected humans
What is the most common form of plague ?
Bubonic form or glandular form
What is the onset of bubonic form of plague ?
2 - 5 days
What clinical manifestations can arise from bubonic form of plague ?
high fever
painful, swollen, and necrotic regional lymph nodes (typically in the groin, less often in the axilla) known as buboes (s. bubo; G. boubon, the groin)
What form of plague occurs when the bacteria spread to the bloodstream ?
Septicemic form
What are the early and late manifestations of septicemic form of plague ?
Early manifestations:
vomiting and diarrhea
disseminated intravascular coagulation leads to hypotension
altered mental status
Later manifestations:
renal and cardiac failure
Terminally:
pneumonia and meningitis
Scientific name of the flea used to transmit Yersina pestis ?
Xenopsylla cheopsis
When does the pneumonic form of Y. pestis occur as bubonic or septicimic ?
When organisms proliferate in the bloodstream and respiratory tract
Symptoms of pneumonic form of Y. pestis ?
fulminant course with chest pain, cough, hemoptysis, and severe respiratory distress
True or false: Some of the yersiniae possess lipopolysaccharides that have endotoxic activity when released
False; all yersiniae possess…
This factor yield the requirement for calcium for growth of the yersiniae at 37°C
V and W antigens
This factor is involved in dissemination of the organism from the flea bite injection site
pPCP1
In relation to the plasmid pPCP1 describe the temperature-dependent coagulase activity
20°–28°C, the temperature of the flea
In relation to the plasmid pPCP1 describe the temperature-dependent fibrinolytic activity
35°–37°C, the temperature of the host
How does pFra/pMT help cause diseases by Y. pestis ?
encodes the capsular protein (fraction F1) that is produced mainly at 37°C and confers anti-phagocytic properties
this plasmid contains genes that encodes
phospholipase D, which is required for organism survival in the flea midgut
What is yersinibactin ?
A factor that allows Y. pestis to cause diseases which is encoded by a pathogenecity island (PAI), is an
iron-scavenging siderophore
What is the prevention and control of Y. pestis related diseases ?
surveys of infected population
immediate notification to health authorities once infection has been diagnosed
patients with suspected plague must be isolated
Characteristics of Plesiomonas shigelloides
oxidase + catalase + glucose fermenting polar flagella gram - rod
What is the chief reservoir of Plesiomonas shigelloides
aquatic environments that are limited geographically by its minimum growth temperature of 8° C
fresh and estuarine water, usually in tropical countries
What are the three major clinical types of gastroenteritis caused by Plesiomonas shigelloides ?
common watery or secretory diarrhea
subacute or chronic disease that lasts from 14 days to 2 to 3 months
invasive, dysenteric form that resembles colitis
