A brief description about important members of Enterobacteriaceae

1. Enterobacteriaceae
Aman Ullah
B.Sc. MLT
M. Phil Microbiology
Master in Health Research
Certificate in Health Professional Education

2. Common characteristics
• Gram-negative
• Short rods
• Facultative anaerobe
• Ferments glucose and a wide range of
carbohydrates
• Oxidase negative

3. Escherichia coli

4. Pathogenesis/Clinical Significance
• E. coli is part of the normal flora in the colon of humans and
other animals,
• Pathogenic both within and outside the gastrointestinal tract.
• E.coli species possess three types of antigens: O, K, and H.
• Pili facilitate the attachment of the bacterium to human
epithelial surfaces
• Pathogenic E. coli “virotypes” differ from the normal flora E.
coli by the acquisition of genes that encode new virulence
factors allowing for toxin production and attachment to or
invasion of host cells.

5. Pathogenesis/Clinical Significance
Urinary tract infections (UTI)
• E. coli is the most common cause of UTIs, especially in women
• Symptoms include dysuria, urinary frequency, hematuria, and
pyuria
Meningitis in infants
• E. coli and group B streptococci are the leading causes of
neonatal meningitis
• E. coli strains that cause meningitis express the K1
capsule, which is chemically identical to the capsule
produced by serogroup B meningococci

6. Pathogenesis/Clinical Significance
Diarrhea
• Several categories of
diarrhea are caused
by different strains of
E. coli
Lab diagnosis
• Specimens: depend
on the site of
infection
• Diagnose on the base
of culture and
sensitivity

7. Salmonella
• Salmonella enterica serovar Typhi
• Salmonella enterica serovar Typhimurium

8. Salmonella enterica serovar Typhi
Pathogenesis/Clinical Significance
• S. enterica serovar Typhi is transmitted between humans, without
animal or fowl reservoirs
• Infection is via the oral–fecal route, generally through food or water
contaminated by human feces
• Young children and older adults are particularly susceptible to
Salmonella infections, as are individuals in crowded institutions or
living conditions
• S. enterica serovar Typhi causes disease by attaching to and
invading macrophages of the intestinal lymphoid tissue (Peyer's
patches)
• The bacteria replicate rapidly within these cells, and eventually
spread to the reticuloendothelial system (including both liver and
spleen, which become enlarged) and potentially to the gallbladder.

9. Pathogenesis/Clinical Significance
• Enteric (typhoid) fever
• This is a severe, life-threatening systemic illness, characterized
by fever and, frequently, by abdominal symptoms
• About 30 percent of patients have a faint, maculopapular rash
on the trunk (termed "rose spots")
• After 1 to 3 weeks of incubation, S. serovar Typhi can enter
the blood, with the resulting bacteremia causing fever,
headache, malaise, and bloody diarrhea
• Perforations of the intestine can lead to hemorrhage
• Some infected individuals may become chronic carriers for
periods as long as years due to persistent residual infection of
the gallbladder

10. Salmonella enterica serovar Typhimurium
Pathogenesis/Clinical Significance
• S. enterica serovar Typhimurium (and other Salmonella species that
cause enterocolitis) reside in the gastrointestinal tracts of humans,
other animals, and fowl
• They are transmitted through contaminated food products, or via
the oral/fecal route
Enterocolitis (gastroenteritis, foodborne infection)
• Contaminated poultry products including eggs are the primary
vehicles for infection of humans by serovar Typhimurium, although
raw milk and pets such as turtles also transmit the disease
• Salmonella adhere to and invade enterocytes of both the small and
large intestine, causing a profound inflammatory response. Within
10 to 48 hours after ingestion, nausea, vomiting, abdominal
cramps, and diarrhea ensue
• Diarrhea usually ends spontaneously within a week.

11. Lab diagnosis
• Blood, urine and blood for culture and
sensitivity
• Serologic tests for antibodies against O
antigen in patient's serum also aid in the
diagnosis

12. Shigella
• Med. Imp. Species: Shigella sonnei and dysenteriae
Pathogenesis/Clinical Significance
• Shigella species are spread from person to person, with
contaminated stools serving as a major source of organisms
• Flies and contaminated food and water can also transmit
the disease
• S. sonnei invades and destroys the mucosa of the large
intestine but rarely penetrates to the deeper intestinal
layers
• S. dysenteriae also invades the colonic mucosa but, in
addition, produces an exotoxin (Shiga toxin) with
enterotoxic and cytotoxic properties

13. Shigella
Bacillary dysentery (shigellosis)
• This disease is characterized by diarrhea with
blood, mucus, and painful abdominal cramping
• The disease is generally most severe in the young
and in older adults, and among malnourished
individuals, in whom shigellosis may lead to severe
dehydration and even death
Lab diagnosis
• Stool for C/S

14. Yersinia pestis
Pathogenesis/Clinical Significance
• Y. pestis is endemic in a variety of mammals, both urban and sylvatic, and is
distributed worldwide.
• Infection is transmitted by fleas, which serve to maintain the infection within
the animal reservoir
• The organism can also be transmitted by ingestion of contaminated animal
tissues and via the respiratory route.
• Organisms are carried by the lymphatic system from the site of inoculation to
regional lymph nodes, where they are ingested by phagocytes
• Y. pestis multiplies in these cells. Hematogenous spread of bacteria to other
organs and tissues may occur, resulting in hemorrhagic lesions at these sites
Bubonic (septicemic) plague
• The incubation period (from flea bite to development of symptoms) is generally
2 to 8 days. Onset of nonspecific symptoms, such as high fever, chills, headache,
myalgia, and weakness that proceeds to prostration, is characteristically
sudden. Within a short time, the characteristic, painful buboes develop,
typically in the groin, but they may also occur in axillae or on the neck
• Blood pressure drops, potentially leading to septic shock and death.
Pneumonic plague
• If plague bacilli reach the lungs, they cause a purulent pneumonia that is highly
contagious, and, if untreated, is rapidly fatal.

15. Lab diagnosis
• Laboratory identification can be made by a
gram stained smear, and culture of an aspirate
from a bubo (or sputum in the case of
pneumonic plague)

16. OTHER ENTEROBACTERIACEAE
• Other genera of Enterobacteriaceae, such as
Klebsiella, Enterobacter, Proteus, and Serratia,
which can be found as normal inhabitants of the
large intestine, include organisms that are
primarily opportunistic and often nosocomial
pathogens
• Widespread antibiotic resistance among these
organisms necessitates sensitivity testing to
determine the appropriate antibiotic treatment

17. Enterobacter
• They rarely cause primary disease in humans
but frequently colonize hospitalized patients,
especially in association with antibiotic
treatment, indwelling catheters, and invasive
procedures
• These organisms may infect burns, wounds,
and the respiratory (causing pneumonia) and
urinary tracts

18. Klebsiella
• Klebsiellae are large, nonmotile bacilli that
possess a luxurious capsule
• Klebsiella pneumoniae and Klebsiella oxytoca
cause necrotizing lobar pneumonia in individuals
compromised by alcoholism, diabetes, or chronic
obstructive pulmonary disease.
• K. pneumoniae also causes UTI and bacteremia,
particularly in hospitalized patients

19. Serratia
• The species of Serratia that most frequently
causes human infection is Serratia marcescens
• Serratia can cause extraintestinal infections
such as those of the lower respiratory and
urinary tracts, especially among hospitalized
patients

20. Proteus, Providencia, and Morganella
• Members of these genera are agents of urinary tract
and other extraintestinal infections
• Proteus species are relatively common causes of
uncomplicated as well as nosocomial UTI
• Other extraintestinal infections, such as wound
infections, pneumonias, and septicemias, are
associated with compromised patients
• Proteus organisms produce urease, which catalyzes the
hydrolysis of urea to ammonia. The resulting alkaline
environment promotes the precipitation of struvite
stones containing insoluble phosphates of magnesium
and phosphate.

21. Questions/Suggestions
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