Members of the group
1. Family
Enterobacteriacae
2. Family
Vibrionacae
FAMILY
ENTEROBACTERIACAE
General characteristics
1. They
are small, facultatively anaerobic, non–sporeforming rods.
2. All
members ferment glucose, reduces nitrites and oxidase negative. They don’t
liquefy alginate.
3. Most
of them are motile because of peritrichous flagella that aids in
differentiating them from Pseudomonas and Vibrios. Others are non–motile like
Klebsiella and Shigella
4. All
ferment glucose with the production of acid and gaseous formation in the form
of CO2 and H2 varies with species
5. On
BAP, they cannot be differentiated; they appear as grayish, moist, smooth
colonies. Some of them produces hemolysis
6. They
can tolerate the presence of bile salts and bacteriostatic dyes
7. Capsules
are formed by a few like Klebsiella, E. coli strains, Enterobacter and Serratia
8. A
number of enterics harbor an extrachromosomal element that code for the
production of bactericidal substances known as colicin. They attack only
susceptible strains and this selectivity in action has been used with certain
species of bacteria as an epidemiologic tool and known as colicin typing.
Members of the Family
Enterobacteriacae
1. Escherichia
2. Edwardsiella
3. Citrobacter
4. Salmonella
(formerly Arizona)
5. Shigella
6. Klebsiella
7. Enterobacter
8. Hafnia
9. Serratia
10. Proteus
11. Providencia
12. Morganella
13. Erwinia
14. Yersinia
Antigenic structure
Antigenic characteristics play an
important role in epidemiology and classification
1. O
or somatic antigen – made up of lipopolysaccharide, responsible for
endotoxic activity. It is found on external cell membrane
2. H
or flagellar antigen – made up of protein found only in motile
strains. Letter H is derived from Hanch, meaning, a thin film displayed by
motile strains when grown on moist agar
3. K
or capsular antigen – made of polysaccharide. In some Klebsiella, this
exists as true capsules and can be type by Quellung test. The
best known K antigen is the Vi antigen of Salmonella typhosa. This is heat
labile and has the capacity to mask the somatic antigen of the cell.
****** GENUS ESCHERICHIA *******
Escherichia coli (The Colon
Bacillus)
These organisms predominate in the
large intestine. They are useful in maintaining the normal balance of the
intestinal flora. They are also used as an indicator organism in the
bacteriological analysis of water supply. If present, it can be assumed that the
water has been contaminated from a fecal source. They are short and plump
motile rods.
Such name is given to this organism
because it is predominant facultative bacteria in a large bowel. (Bacteroides
fragilis – predominant bacteria in stool which is strict anaerobic).
Strains of E.coli:
1. E.
coli variety communior – ferments sucrose
2. E.
coli varieity communis – does not ferment sucrose
3. E.
aurescences – yellow orange pigment production
Toxins produced by E. coli
1. Enterotoxins – a bacterial
substance found in plasmids that exerts its effects in the intestinal tract.
2. Verotoxin – VTEC (verotoxin–producing
E. coli) which is associated with diarrhea, hemorrhagic colitis and hemolytic–uremic
syndrome)
3. SLT – Shiga–like
toxin
Four distinct groups of E. coli
involved in gastroenteritis
1. EPEC
(Enteropathogenic E. coli) – causes relapsing watery diarrhea;
non– invasive, does not produce toxins and is involved in the outbreak of
hospital acquired infantile diarrhea in children.
2. EIEC
(Enteroinvasive E. coli) – produces Shigella like disease
(dysentery like diarrhea). It invades the intestinal epithelium. It is mixed
with bacillary dysentery with blood streak in stool
3. ETEC
(Enterotoxigenic E. coli) – causes intestinal infections like
Traveler’s diarrhea or Turista Belly Delhi diarrhea. Infections other than
diarrhea are hemorrhagic colitis and dysentery also. They produce enterotoxin.
4. EHEC
(Enterohemorrhagic E. coli) – causes grossly bloody diarrhea with
little or no fever. It is associated with the consumption of the undercooked
infected hamburger from a fast food chain.
EAEC (Enteroadherent
E. coli)
or agglutinating E. coli – still understudy
Infectious diseases associated
with E. coli
1. Intestinal
infection
2. Urinary
tract infection (asymptomatic bacteriuria, cystitis, pyelonephritis, prostitis)
3. Bacteremia
4. Neonatal
meningitis
5. Pneumonia
6. Septicemia
Laboratory diagnosis
1. Stained
smear
2. Culture
a. EMB
(Eosin Methylene Blue) – greenish metallic sheen
b. MacConkey
– dry pink colonies due to lactose fermentation, colorless if non–lactose
fermenter
c. XLD
(Xylose Lysine Decarboxylase) – yellow colonies
d. SSA
– pink colonies
3. Biochemical
reaction
a. TSI:
A/Ag
b. IMViC:
++ – –
c. Lysine
decarboxylase (–)
d. Acetate
(+)
4. Serologic
typing
Other species of Escherichia
1. E.
adenocarboxylata – base of DNA homology studies
2. E.
hermanii – isolated from blood and spinal fluid, would infections and feces
3. E.
vulneris – wound infections
4. E.
biattae – isolated from the intestine of cockroach
5. E.
fergusonii – from the scientist William Ferguson
****** GENUS EDWARDSIELLA ******
Edwardsiella tarda
·
The only specie implicated in
human disease
·
Motile, non–lactose fermenters
·
TSI: K/Ag with H2S;
IMViC: ++ – – ; LD (+)
****** GENUS CITROBACTER ******
This was formerly classified as the
Bathesda–Ballerup group.
Citrobacter freundii – morphologically
similar to E. coli and biochemically resembles Salmonella. It causes UTI and
sepsis
a. TSI:
A/Ag with H2S
b. LD
(+)
I
M Vi C H2S Urease production Growth on KCN
E. coli +
+ –
– (–) negative negative
Salmonella – + – + (+) negative
negative
Citrobacter – + – + (+) positive
positive
****** GENUS SALMONELLA ******
Characteristics
1. All
Salmonella are motile (peritrichous) except Salmonella typhosa and Salmonella
gallinarum
2. They
never ferment lactose or sucrose or sucrose. They form acid and sometimes gas
from glucose and mannose. They usually produce H2S.
3. They
survive freezing in water for long periods.
4. They
are resistant to certain chemicals, e.g., brilliant green, sodium deoxycholate
and sodium tetrathionate.
5. They
are non–encapsulated, gram negative rods.
According to Kauffman–White antigenic
scheme, there are 2,000 species of Salmonella because of its antigenic type but
Ewing proposed three species which are Salmonella typhosa or typhi (Eberth’s
Bacillus), Salmonella cholerasuis, Salmonella enteritidis. So, for example,
Salmonella typhimirum became Salmonella enteritidis serotype typhimirum.
Antigenic structure
1. O
antigen
– somatic antigen, heat stable, antibodies are IgM class, lipopolysaccharide in
content.
2. H
antigen –
flagellar, heat labile, antibodies are IgG class, protein antigen
3. Vi
antigen
– virulence antigen, a type antigen increased in carriers; found in Salmonella
typhi, prevents phagocytosis and their intracellular destructions.
Types of diseases produced by
Salmonella
1.
Enteric fever
or typhoid fever
This is
produced mainly by S. typhi, S. paratyphi A and S. schottmuelleri. It is
characterized by a long incubation period (10–14 days) and there is general
invasion of the body. There is leukopenia, rose spots are seen in pre–
antibiotic area, the chief complaints are intestinal hemorrhage and
perforation.
2.
Septicemia
This is
associated most commonly with S. cholerasuis. There is early invasion of the
bloodstream but intestinal manifestations are often absent. Blood cultures are
positive.
3.
Enterocolitis
This is the
most common manifestations of Salmonella infection. Most prominent organism is
S. typhimurium. It is characterized by profuse diarrhea with few leukocytes in
the stool. Blood cultures usually negative.
Salmonellosis – a type of
disease / infection where a carrier plays a very important role.
Indication
of Salmonellosis:
a. Severe
headache
b. Continuous
fever for 3 days, no lowering of temperature
c. Diarrhea
is not experienced for the first week of infection
Mode of transmission
The organism almost always enters via
the oral route, usually with contaminated food or drink. The main effective
dose 105–108 Salmonella.
Laboratory diagnosis
1. Stained
smear
2. Culture
a. Blood
culture – 1st week – most reliable
b. Stool
and urine culture – 2nd and subsequent weeks
Media used
a. SSA
(Salmonella–Shigella Agar) – colorless to black center
b. XLD
(Xylose Lysine Deoxycholate) – pink to red colonies with black center
c. BSA
(Bismuth Sulfite Agar) – green black colonies
d. BGA
(Brilliant Green Agar) – pink white, opaque surrounded by brilliant red medium
e. Selenite
F broth – enrichment medium for Salmonella
3. Biochemical
reaction
a. TSI:
Salmonella typhi = K/A + small amount of H2S (described as mustache
sulfide on TSI)
Other Salmonella
= K/Ag + H2S (large amount)
b. IMViC:
– + – +
c. LD
(+)
4. ELISA
5. Fluorescent
antibody test
6. Widal
test – agglutination test for typhoid fever. At least two specimens (serum),
obtained at intervals of 7–10 days. Serial dilutions of unknown serum are tested
against antigens from representative Salmonella. The results are interpreted:
a. High
or rising titer of O suggests that active infection is present
b. High
or rising titer of H suggests past immunization or past infection
c. High
titer or antibody to Vi seen in some carriers
7. Limulus
test – is used to detect endotoxin. Production of endotoxin is indicated by the
presence of a visible gel in a very low concentration in lysates of washed
amebocytes of horse crab.
8. Ileal
loop test – is used to detect enterotoxin. Enterotoxin production is indicated
by the ballooning of the intestinal tract or ileap loop due to the accumulation
of fluid in the intestinal tract.
Arizona hinshawii
a. Normally
present in the intestinal content of reptiles
b. They
are motile and imitate Salmonella sp., distinguished from Salmonella by their
last lactose fermentation and their growth in sodium malonate medium (green
color)
Positive
result: blue color
c. Present
classification system place this organism in the genus Salmonella
d. TSI:
A/Ag + H2S; IMViC: – + – +; LD(+)
****** GENUS SHIGELLA ******
Characteristics
1. The
natural habitat of Shigella is limited to the intestinal tract of humans and
other primates.
2. They
are slender, non–encapsulated and non–motile
3. They
do not ferment lactose except Shigella sonnei
4. They
form acid from carbohydrates
5. They
are aerobic and anaerogenic (organisms that do not produce gas during
fermentation)
Classification of Shigella
based on Mannitol Fermentation
A.
Non–mannitol
fermenters
1. Shigella
dysenteriae
– Dysentery Bacillus or Shigella’s Bacillus
2 types of
toxins
a. Exotoxin
– neurotoxin
b. Enterotoxin
– similar to cholera toxin
B.
Mannitol
fermenters
1. Non–lactose
fermenters
a. Shigella
flexneri
– Strong’s Bacillus
b. Shigella
boydii
– Boyd’s Bacillus or Newcastle–Manchester Bacillus
2. Late
lactose fermenters
a. Shigella
sonnei
– Sonne Duval Bacillus or Sonne’s Bacillus
Ewing’s classification of
Shigella
Serogroup
A – Shigella dysenteriae
Serogroup
B – Shigella flexneri
Serogroup
C – Shigella boydii
Serogroup
D – Shigella sonnei
Pathogenicity
The infective dose is less than 103
organisms. The essential pathologic process is invasion of the mucosal
epithelium. All Shigella sp. causes Bacillary Dysentery, a painful diarrhea
characterized by watery feces with mucus flex, blood streaks, fishy odor and
plenty of pus cells (in amoebic dysentery, small amount of pus cells are seen).
Laboratory diagnosis
1. Stained
smear
2. Culture
a. EMB,
MacConkey, SSA, XLD, Deoxycholate citrate – colorless colonies
b. Hektoen
Enteric Agar (HEA) – green or blue–green colonies
c. GN
broth – best enrichment medium
3. Biochemical
reaction
a. TSI:
K/A; IMViC: + + – –; LD +
4. Salmonella
typing
****** GENUS KLEBSIELLA ******
Characteristic
1. They
exhibit mucoid growth, large polysaccharide capsules and non–motile
2. They
usually give positive results for lysine decarboxylase and citrate
Klebsiella pneumonia
a. Common
name: Friedlander’s Bacillus, Bacillus mucosus capsulatus
b. It
causes severe enteritis, pneumonia, septicemia, bacteremia, meningitis, UTI. It
can also produce extensive hemorrhagic necrotizing consolidation of the lung.
Laboratory
diagnosis
a. Culture:
(1) EMB
– purple colonies
(2) MacConkey,
SSA – pink colines
(3) XLD
– yellow colonies
On these
media, they produce a large, mucoid colony that have a tendency to coalesce
(gathering of colonies)
(4) String
test (+)
b. Neufeld–Quellung
reaction: due to the presence of capsule
c. Biochemical
test: TSI: A/Ag; IMViC: – – + +; Growth in KCN; Urease(+)
The KES group
(Klebsiella, Enterobacter, Serratia) are all VP (+) which use butanediol
pathway
Other members of this genus:
1. Klebsiella
oxytoca
– only indole (+) member of Klebsiella; disease is similar to Klebsiella
pneumonia
2. Klebsiella
ozanae
– Ozena – atropic, odiferous, disease of the nasal mucosa, biochemically
inactive strain of Klebsiella pneumonia.
3. Klebsiella
rhinoscleromatis
– Rhinoscleroma – a destructive granuloma of the nose and the pharynx
4. Klebsiella
planticola
– environmental organisms which also cause UTI and wound infection.
****** GENUS ENTEROBACTER ******
1. Formerly
called Aerobacter
2. Oftentimes
confused with Klebsiella which is non–motile and ornithine decarboxylase
negative while this genus is motile and positive for ornithine decarboxylase
and urease
3. Members
of the genus are:
a. Enterobacter
aerogenes – maybe found free–living as well as in the living intestinal tract
and causes UTI and sepsis
b. Enterobacter
cloacae
c. Enterobacter
agglomerans
d. Enterobacter
gergoviae
e. Enterobacter
sakazakii
f.
Enterobacter taylorae
****** GENUS HAFNIA
******
·
Formerly classified as
Enterobacter hafniae but is now given its own genus and known as Hafnia alvei.
·
Biochemical reaction:
a. MacConkey
– colorless after 24 hours or slightly pink in 24 to 48 hours.
b. EMB
– lavender or colorless
c. XLD
– red, yellow or colorless with or without black centers
d. HEA,
SSA, DC – colorless
******* GENUS SERRATIA ******
a. They
are motile, non–lactose fermenters but with sucrose fermenter
b. Some
strain produces a red, non–water soluble pigment known as prodigiosin.
The production of this pigment is enhanced by incubation at room temperature
c. They
also produce Dnase, lipase and gelatinase
d. Members
are:
(1) Serratia
marcescens or Bacillus prodigiosus – a common opportunistic pathogen in
hospitalized patient. Non–pigmented strains causes pneumonia, bacteremia and
endocarditis especially narcotics addict and hospitalized patients.
(2) Serratia
odoriferi
– characterized by musty, punget odor
(3)
Serratia
rubidae
(4)
Serratia
liquifaciens
****** GENUS PROTEUS
******
Characteristics
1. They
are actively motile at 37oC, pleomorphic, all are non–lactose
fermenters, all urease & phenylalanine positive
2. They
rapidly hydrolyze urease in 2 – 4 hours
3. There
are two species
a.
Proteus
vulgaris
b.
Proteus
mirabilis
– tend to swarm on moist agar, producing a bluish gray confluent surface growth
that gives off burnt powder odor
4. Dienes
phenomenon
– different strains of Proteus when inoculated in a culture medium swarm
towards each other but they do not mingle thus leaving a demarcation line
between them.
Proteus species produces the enzyme urease,
a nephrotoxin causing intrainvasion of the renal tubular epithelium resulting
in the precipitation of magnesium phosphate and formation of renal stones.
Motile strains of Proteus contain H
antigen in addition to the somatic O antigen. Certain strains of Proteus (OX
strains) are agglutinated by the serum of patients with rickettsial infections
because they share a common antigen. These strains (OXK, OX2 and OX19) are used
as antigens in the Weil–Felix test.
****** GENUS PROVIDENCIA ******
There are four species on this genus,
all of which causes urinary tract infections:
a. Providencia
alcalifaciens
b. Providencia
stuarii
c. Providencia
rettgeri (formerly Proteus rettgeri)
d. Providencia
rustiganii
****** GENUS MORGANELLA ******
Morganella morganii – formerly
known as Proteus morgana
****** GENUS YERSINIA ******
Yersinia pestis (Plague
Bacillus)
Characteristics
a. It
is plump, gram negative rod that exhibits striking bipolar staining with
special stains. It is non–motile.
b. It
grows as facultative anaerobe on many bacteriologic media. Growth is more rapid
in media containing blood or tissue fluid and fastest at 30oC.
c. In
Wayson stain, it will exhibit safety pin appearance
Antigenic
structure
a. Lipopolysaccharide
– has an endotoxic activity when released
b. Virulence
factors: coagulase, bacteriocin (pesticin), isocitrate lyase
Pathogenicity
This organism
is a pathogen of rodents and transmitted to man thru the bit of oriental rat
flea (Xenopsylla cheopis)
Three types of
Human plague
a. Bubonic
plague – buboes (lymph nodes) – swollen, particularly in the axilla and infects
inguinal region.
b. Pneumonic
plague – airborne transmission, results from inhalation in droplet nuclei
c. Septicemic
plague – “Black Death” in history due to Schwartzmann phenomenon, black
purpuric lesion in the body (area of hemorrhages)
Yersinia enterocolitica and
Yersinia pseudotuberculosis
Characteristics
a. They
are non–lactose fermenters, gram negative rods that are urease positive and
oxidase negative
b. They
are motile at 25oC but non–motile at 37oC
c. Yersiniosis
is the disease produced.
Pathogenicity
Yersinia
enterocolitica has been isolated from rodents and domestic animals (e.g. sheep,
cattle, dogs, swine and cats) and water contaminated by them. They are motile
with peritrichous or paripolar flagella. Human transmission is through
contamination of food, drink and fomites. Cultivation using Cofsulodin–Irgasan–Novobiocin
(CIN) is more preferred because the microorganism is overgrown by other
intestinal flora and other enteric group.
Yersinia
pseudotuberculosis occurs in domestic animals, which excrete the organism in
feces. Human infection is through ingestion of materials contaminated with
animal feces. Person to person transmission is very rare.
Early symptoms
include fever, abdominal pain and diarrhea. At times, abdominal pain is severe
and located in the right lower quadrant, suggesting appendicitis.
Other Yersinia species which
are opportunistic pathogen:
1. Yersinia
intermedia
2. Yersinia
kristensenii
3. Yersinia
freduikaenii
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