Microbiology Lab 3

1
Microbiology Lab 3 4

• Enteric Bacteriology

2
What are the Enteric Bacteria?
Enterobacteriaceae? What do they ferment and
produce? When motile, what type of flagella do
they have?

• The Enteric bacteria are bacteria that colonize
  or infect the Gi tract.
• Enterobacteriaceae are enteric Gram-negative rods
  that ferment glucose and other sugars, reduce
  nitrate to nitrite or nitrogen gas.
• They have peritrichous flagella when motile.
• Most genera in this family are either normal
  microflora, environmental bacteria, or enteric
  pathogens.

3
Why are enterobacteriaceae called facultative
organisms? Do they have an electron transport
system? What other bacteria are commonly found in
the colon? Is Pseudomonas considered
Enterobacteriaceae?

• Although their environement in the bowel is
  anaerobic, Enterobacteriaceae are called
  facultative organisms because they grow both in
  the prescence and absence of oxygen.
• Enterobacteriaceae possess an electron transport
  system that enables them to oxidize a wide
  variety of organic compounds.
• Other bacteria commonly found in the colon, such
  as the enterococci (streptococcus species),
  lactobacilli, certain obligate anaerobes, and
  Pseudomonas aeruginosa may also appropriately be
  referred to as enteric bacteria.
• However, Pseudomonas species are not
  enterobacteriaceae because they use oxidative
  metabolism exclusively and have polar flagella.

4
What is the most abundant bacteria in the GI
tract, and what are some of their features? What
are some other anaerobic organisms that live in
the GI, and which are most important?

• The most abundant bacteria in the GI tract are
  the obligately anaerobic Bacteroides species.
• Non-spore forming.
• Gram-negative rods.
• Outnumber all facultative anaerobes by more than
  1001 in the colon.
• Fusobacteria are another genus of anaerobic
  Gram-negative rods that live in the lower GI
  tract.
• Among the anaerobic gram-positive organisms,
  anaerobic streptococci, clostridia and
  Actinomyces are the most important.

5
What are some important functions of our normal
colonic flora? How does treatment with
antibiotics affect this?

• Synthesis of vitamin K by E.coli and other
  enteric rods.
• Deconjugation of bile salts by Bacteroides.
• Protection by the normal flora against infection
  of the GI tract by pathogens such as Salmonella
  and Shigella.
• Treatment with antibiotics can greatly modify the
  normal flora of the GI tract and thereby increase
  the susceptibility to gastrointestinal infection
  by pathogenic microorganisms. This example of
  bacterial antagonism is probably related to
  competition for anatomical sites and nutrients,
  and also the production of bacteriocins by
  resident bacteria.

6
Which enteric bacteria cause disease in the GI
tract? Which species are unable ferment lactose?

• Except for Salmonella, Shigella, Yersinia and
  certain strains of E.coli, enteric bacteria
  seldom cause disease in the GI tract.
• Salmonella, Shigella, and Yersinia differ from
  all other Enterobacteriaceae except Proteus in
  being unable to ferment lactose.
• Consequently, bacteriology laboratories often
  issue preliminary reports indicating the presence
  or absence of non-lactose fermenting organisms in
  stool cultures before definitive identification
  is achieved.
• Some E.coli possess specific virulence genes that
  make them capable of causing diarrhea.
• There is no simple, practical way to
  differentiate these enteropathogenic E.coli from
  saprophytic E. coli.

7
How can normal flora go bad?

• Within the intestinal lumen, enteric bacteria
  play an important role in the normal physiology
  of the gastrointestinal tract.
• In contrast, if they escape the intestinal lumen,
  they are capable of causing severe infections,
  even life-threatening septicemia, in tissues and
  other organs.
• Such situations may occur as the result of
  perforation of the GI tract, infection of the
  obstructed urinary tract, infection of the
  biliary tree, and colonization of the skin or
  mucous membranes of immunologically or
  anatomically compromised people.

8
What is most responsible for the adverse systemic
effects of Gram-negative bacterial infections?
How do obligate anaerobes cause the same kinds of
disease as other enteric bacteria?

• All Gram-negative rods contain endotoxin, which
  is the moiety responsible for many of the adverse
  systemic effects of Gram-negative bacterial
  infections.
• The obligate anaerobes are capable of causing
  some of the same kinds of diseases as the other
  enteric bacteria, but they can only establish
  infection in tissue when oxidation-reducation
  potential is lowered.
• Pathogenic clostridia can cause disease by
  producing exotoxins, either in the intestine, in
  foods that are ingested, or in wounds.

9
How are facultative enteric organisms identified?
What is selective media? What are some
examples of selective media?

• Facultative enteric organisms are identified by a
  combination of criteria, including cell and
  colony morphology, motility, and a variety of
  biochemical reactions.
• Both selective and differential media are
  used to isolate and identify enteric
  Gram-negative organisms, particularly the
  Enterobacteriaceae.
• Selective media is formulated with antibiotics or
  other substances that inhibit the growth of
  unwanted bacteria, but allow growth of the
  desired organisms.
• Examples of selective media for the
  Enterobacteriaceae are Eosin-Methylene Blue (EMB)
  and MacConkey agar
• both suppress the growth of Gram-positive
  organisms and thus aid in the isolation of
  Enterobacteriaceae from mixed cultures.

10
Why do we need differential media? What are
some examples of differential media? What is the
pH indicator in EMB? MacConkey?

• Because most enterobacteriaceae cannot be
  differentiated from one another on blood agar
  plates, differential media are used to
  distinguish the different colony morphologies or
  to detect substrate utilization.
• In addition to selecting for Enterobacteriaceae,
  EMB and MacConkey agar are also differential
  media because they allow the microbiologist to
  identify bacteria that are able to ferment
  lactose, which is the only fermentable
  carbohydrate in these media.
• The colonies of lactose fermenters are colored
  because the acid they produce from lactose
  fermentation converts a pH indicator in the
  medium to its colored acidic state.
• The pH indicator in EMB is methylene blue, which
  turns blue at acidic pH.
• The pH indicator in MacConkey agar is neutral
  red, which turns red at acid pH.
• The colonies of lactose non-fermenters are
  colorless because the bacteria metabolize
  proteins in the media without producing acid.

11
Comment on the motility of the enteric bacilli.
What is required for motility? What type of this
appendage do different enteric bacteria have?
How can we observe motility?

• Most enteric bacilli are motile, but some are
  not.
• Motility is dependent upon flagella, hair-like
  appendages that propel the bacterium towards
  nutrients and away from some chemical stimuli.
• The flagella of motile enterobacteriaceae are
  peritrichous (distributed around the entire
  circumference of the bacterium), while those of
  Pseudomonas species are limited to a polar
  location.
• Flagella are not visible under the light
  microscope unless they are swollen by mordants
  used in certain specialized flagellar stains.
• The motility can be assessed by observing
  bacteria suspended in a drop of broth culture
  (wet mount) under the microscope or by visual
  examination of bacterial growth in a semi-solid
  medium with low agar content.
• Motile bacteria move away from the original
  inoculation site (e.g. when stabbed in the
  center of a tube of semi-solid media) and make
  most of the medium tubid.
• Since non-motile bacteria grow only where they
  are inoculated, turbidity in cultures of
  non-motile bacteria is limited to the inoculated
  (stabbed) area of the tube.

12
Give a quick summary of what tests are used to
differentiate between which organisms.

• Use the oxidase test to differentiate between
  members of Family Enterobacteriaceae and Genus
  Pseudomonas.
• Use a flagella stain to differentiate between
  nonmotile (Klebsiella and Shigella) and motile
  members of Family Enterobacteriaceae.
• Use EMB agar to differentiate between lactose
  fermenters such as E.coli and Klebsiella, and
  organisms incapable of fermenting lactose.
  Remember this includes the enteric pathogens
  Shigella and Salmonella. Using EMB selective
  agar, a selective and differential media, allows
  one to find a needle in the haystack (i.e. the
  lactose negative pathogen among a lot of lactose
  fermenting normal flora in stool.)

13
Give some more details about the oxidase test.

• Cytochrome c oxidase is an enzyme found in many
  electron transport chains (ETC), including the
  ETC of Genus Pseudomonas.
• Members of the Family Enterobacteriaceae have
  electron transport chains, but these ETCs lack
  cytochrome c oxidase.
• A very quick and easy way to start classifying a
  Gram negative rod is to do the oxidase test. The
  presence of cytochrome c oxidase can be detected
  when colonies are exposed to methylphenylenediamin
  e that acts as an electron donor to the
  cytochrome oxidase.
• If the bacteria have cytochrome c oxidase, they
  can oxidize the compound (remove electrons),
  converting it into indolphenol oxide which is
  blackish purple in color.
• No color change indicates a negative test.

14
Explain a little about the Flagella stain.

• Another rapid way to start classifying a Gram
  negative rod is to do a special stain which
  allows the type of flagella to be visualized
  under a light microscope.
• If motile, members of family Enterobacteriaceae
  possess peritrichous flagella.
• Pseudomonas aeruginosa has polar flagella.

15
Explain a little about motility tubes

• Motility tubes can be hard to read.
• Motility tubes are made of semisoft agar. The
  organism in question is inoculated into the tube
  by stabbing it into the center of the agar.
• Motile bacteria will be able to swim away from
  the point of inoculation, and cause the entire
  tube of agar to look turbid.
• Nonmotile organisms can only grow at the point of
  inoculation.
• Of the tests you have seen demonstrated, this one
  and the flagella stain, would allow you to
  determine if you were looking at Shigella or
  Salmonella.

16
What components of the EMB and MacConkey agar
function in what ways?

• Eosin Methylene Blue (EMB) agar
• The presence of eosin in the media inhibits
  growth by Gram Positive organisms.
• The only sugar is lactose. If an organism has
  the enzymes that allow lactose fermentation, acid
  is produced and the change in pH will cause the
  colony to be colored.
• Peptone is the energy source if the organism is
  unable to ferment lactose.
• Colonies will be a shade of white if they are
  lactose negative.
• MacConkey agar
• A high bile content in the agar inhibits the
  growth of gram-positive organisms.
• If lactose can be fermented, acid is produced and
  the pH change will cause the colony to be
  colored.
• If lactose cannot be fermented, peptone will be
  used as an energy source, and no color change
  will be seen.

17
What are some facts about E.coli you should know?

• Grows with a green sheen on EMB agar.
• Can be a primary pathogen (like 0157H7) or an
  opportunistic pathogen.
• Is part of the normal GI flora, and has a
  commensal relationship with its host.
• Synthesizes vitamin K
• Deconjugates bile salts and sex hormones
• Protects against colonization by enteropathogens
  by occupying receptors and producing colicins.

18
What are some important facts about Klebsiella?

• Produces a large, goopy capsule in high glucose.
• Nonmotile (lacks H antigen)
• Does not cause enteric infections, but is often a
  cause of extraintestinal infections in hospital
  patients.
• Can be a primary or opportunistic pathogen.

19
What are some important facts about Shigella?

• Nonmotile (lacks H antigen)
• Does not make gas from formic acid.
• Primary pathogen, but is usually not invasive
  beyond the colon.
• All species are obligate human pathogens
• Most virulence factors are plasmid encoded.
• Cause Dysentery

20
What are some important facts about Salmonella?

• All make H2S except S.typhi
• Primary pathogen
• S.typhi and S.paratyphi are obligate human
  pathogens.
• Cause diseases such as
• Typhoid fever
• Gastroenteritis
• Septicemia

21
What are some important facts about Proteus?

• Swarms on agar plates. On a BAP, this looks like
  someone pressed an orange skin on the plate. On
  EMB, which inhibits swarming, it looks like
  ripples when a rock is thrown in the water.
• Has a urease that helps it cause UTIs. In fact,
  if the urine has an alkaline pH on a dipstick
  test, think about Proteus as a cause of the UTI.
• This raises the pH to levels greater than pH 8,
  which promote the production of struvite,
  ammoniomagnesium phostphate stones.
• These stones obstruct urinary flow and are hiding
  places for the organisms.
• Is an opportunistic pathogen.
• The ability to swarm is due to hundreds of
  flagella per cell. Swarming on the surface of
  the blood agar plate is uninhibited.

22
What are some facts about Pseudomonas aeruginosa?

• Gram negative rod.
• Polar flagella
• Oxidase positive (cytochrome c oxidase)
• Although Pseudomonas aeruginosa is a faculatative
  organism, it can only oxidize sugars because it
  lacks the glycolytic enzymes.
• In anaerobic conditions, it uses nitrate as the
  terminal electron receptor.
• Produces pgiments like pyocyanin and fluorescin.
• Strains in the lungs of CF pateints produce a
  large amount of alginate, a slimy capsule.
• Most strains produce Exotoxin A which blocks
  protein synthesis by ADP-ribosylating EF2.
• Makes a large number of enzymes such as
  lecithinase, gelatinase, collagenase, etc. The
  most important of these is elastase, which allows
  invvasion of blood vessels (causes ecthyma
  gangrenosa in neutropenics).
• Can be normal bowel flora.
• Opportunistic pathogen that attacks neutropenics,
  burn victims and those who have had their normal
  flora disrupted by antibiotics.
• Often acquired nosocomially.
• Hard to kill since it often carries antibiotic
  resistance genes and the cross-linking of the LPS
  side chains makes the outer membrane very
  impermeable.

23
What are some facts about Obligate Anaerobes?

• Obligate anaerobes cannot survive in oxygen
  because they lack enzymes that allow them to
  detoxify the super oxide ion (i.e. peroxidases,
  catalase, and most importantly, superoxide
  dismutase). They thrive in a reducing
  environment.
• Obligate anaerobes are opportunistic pathogens
• They are normal inhabitants of the oral cavity,
  vagina, and gut.
• Disease is associated with tissue injury
  compromise of vasculature (diabetes, etc.)
• Host defense against the obligate anaerobes
• In healthy tissues, the increased redox potential
  usually kills them.
• Phagocytes also eat and dispose of the anaerobes
  mainly through the myeloperoxidase pathway.
• Clinical Presentation
• Obligate anaerobes usually presents as a mixed
  infection. The facultative organisms present use
  up the O2, which allows the anaerobes to
  proliferate. Facultative organism may also
  provide essential nutrients. As the tissue
  breaks down, there is invasion by polys.
  Eventually, a purulent abscess is formed and
  walled off.
• Tule of thumb Anaerobes cause infections in
  injuries adjacent to their normal habitat.

24
What are some important facts about Bacterioides
fragilis?

• As a class, they are the most common bacteria in
  feces.
• Their LPS is much less toxic than that of Family
  Enterobacteriaceae.
• Can deconjugate bile salts.
• Polysaccharide capsule can produce an abscess by
  itself.
• Can make Vitamin K.
• Resistant to Penicillin because it produces
  beta-lactamase. Needs to be treated with
  metronidazole.
• Has a primitive ETC which uses fumurate as a
  terminal electron receptor.

25
What are some facts about Prevotella
melaninogenica?

• Forms black colonies on certain types of agar.
• Bile sensitive.
• Virulence factors include a collagenase,
  leukocyte inhibitory factor and a capsule.
• 10-25 are PCN resistant.

26
Give some facts about Fusobacterium nucleatum and
necrophorum.

• Pale staining, slender, gram negative rods with
  tapered ends.
• No capsule.
• LPS is more potent than that of the
  Enterobacteriaceae.
• Necrophorum
• On Gram stain, have broader, rounded ends and a
  central aneurism.
• Virulence factors include luekocidin and
  hemolysin.
• Nucleatum
• On Gram stain look like slivers of glass with
  thin pointed ends.

27
Give some facts about Clostridium as a species,
and about C. perfringens, and C. tetani.

• Species
• Cause soft tissue infections.
• Soil and indigenous flora.
• Form spores under adverse conditions.
• Gram positive rods that are large and
  pleiomorphic.
• If motile, peritrichous flagella.
• C. Perfringes
• Non-motile
• 90 of the cases of gas gangrene and food
  poisoning.
• Will not form spores on artificial media.
• Double zone of hemolysis on blood agar.
• Makes alpha-toxin which is a calcium dependent
  phospholipase, also known as lecithinase. This
  causes lysis of RBCs and other cells.
• C. Tetani
• Motile
• Produces terminal spores in adverse conditions
• Tetanus toxin is plasmid encoded
• Disease tetanus can be acquired when terminal
  spores are inoculated into a site of injury.
  Redox potential drops, and then C. tetani can
  grow.
• 50 of the time, there is no history of a wound.
• Block the normal inhibition of spinal motor
  neurons by preventing release of inhibitory
  transmitters (glycine and gamma-amino butyric
  acid).

28
Give some facts about peptostreptococci
(anaerobic streptococci)

• Inhabit the mouth and intestine.
• Can cause brain, liver, breast, and lung
  abscesses.

29
Give some facts about Actinomyces israelii.

• Molar-tooth colonies observed under the
  dissecting scope.
• Gram positive, branching, beaded rods.
• Causes actinomycosis, a chronic destructive
  abscess in connective tissue. The abscess
  expands by burrowing through sinuses tracts to
  the surface with no regard for tissue planes.
• sulfur granules are seen in pus. They are
  composed of bacteria in a matrix of calcium
  phosphate.
• NOT acid-fast. This can be used to distinguish
  it from its look-alike, Nocardia.
• Nocardia, a soil organism, is also Gram positive,
  branching rod, it is partially acid fast and
  penicillin resistant.
• Actinomyces israelii is sensitive to PCN.

30
The next group of slides is simply photos and
brief explanations of Facultative Organisms
and Obligate Anaerobescolony characteristics
and gram-stains.
31
Pseudomonas Aeruginosa Facultative organism
Gram-negative rods, not bipolar, oxidase
positive, mucoid green/grey colonies, nonspecific
hemolysis, lactose negative.
32
P. aeruginosa on TSA
33
Bacterioides fragilis
Bacterioides fragilis Obligate anaerobe
White/cloudy pigment, no hemolysis, Gram-negative
rods.
34
E. coli
Facultative organism Med grey colonies on blood
agar (left) , odor, motile, B-hemolytic (middle),
green-sheen on EMB since it ferments lactose
(lactase positive, upper right), Gram negative
rod (upper left)
35
Klebsiella pneumoniae
Facultative organism Gram negative rod
surrounded by a clear capsule, bipolar staining.
No hemolysis, medium sized grey colonies.
36
Klebsiella (lactose-fermenting)
vs.
Proteus (non-lactose) on EMB
37
Salmonella Enteriditis
BAP
MacConkey agar
Facultative organism Med grey, semi-mucoid, no
hemolysis (on BAP), lactose negative (on
MacConkey), Gram-negative, bipolar staining rods.
38
Shigella sonnei
Facultative organism Medium whitish mucoidish
colonies, lactose negative (not shown),
Gram-negative rod, bipolar staining.
39
Proteus mirabilis
Swarm on BAP - stone ripples
Swarm on EMB - orange peel
Long swarm cells many peritricious flagella
Facultative organism gram negative rod,
peritrichous flagella, lactase negative, small,
clear colonies on EMB, and swarm on BAP.
40
Salmonella BAP
EMB
Salmonella enteritidis facultative organism
gram negative, bipolar staining, lactase negative.
Anaerobic BAP
41
Enterococcus
Anaerobic BAP
BAP
Facultative organism no growth on EMB (tells you
it is gram positive), gram positive cocci in
chains.
EMB
42
C. difficile
Anaerobic, white/cloudy colonies, Hemolysis
(double zone!), gram positive rods, no spores,
associated with gas gangrene and dirt.
43
C. perfringens
C. tetani
C. tetani anaerobic as well, Rough colonies,
gram positive rods with spores.
44
C. perfringens
Double B-hemolysis
45
C. perfringens anaerobic BAP -- double ß-hemolysis
46
Fusobacterium nucleatum
Actinomyces israelii showing white molar tooth
colonies (classic). Gram-positive rods,
branching.
Both nucleatum and necrophorum have the fused
look. Both have white colonies and Nucleatum has
mucoid and necrophorum has volcano colony
characteristics.
47
Viridans Streptococci
Gram-positive cocci in chains. No growth on EMB,
extra-small greenish colonies exhibiting
alpha-hemolysis.
48
Prevotella Melaninogenica

• No real pixonly one I could find
• Black/gray pigment
• Hemolysis
• Gram negative cocci
• TINY!
• Characteristic fluorescence of Prevotella
  melaninogenica under long wave-length UV light.
• Young colonies are best, in older colonies, the
  production of black pigment obscures the
  fluorescence.

49
Case descriptions and identification of unknowns
50
MacConkey
EMB plate

• Unknown A A previously healthy 25 year old
  student developed fever (to 38.5), chills,
  abdominal cramping, nausea and diarrhea 48 hours
  after ingesting a wide variety of food and drink
  at an international food fair in Balboa Park.
  His stool was moderate in volume, loose but not
  watery, did not contain visible blood or mucous.
  Gram stain showed polymorphonuclear leukocytes
  but was otherwise unreavealing.
• Microorganism A, the cause of this patients
  illness, was isolated on culture (Above
  MacConkey on the left, and EMB on the right), is
  identified as Gram-negative on Gram stain, and a
  flagella stain revealed peritrichous flagella.
• What is the organism?
• Answer We are supposed to observe that the
  organism grew aerobically, was non-lactose
  fermenting, colonies are small and clear, of
  course has peritrichous flagella, and is gram
  negative.
• Salmonella Enteritidis is the organism.

51
EMB
Blood Agar Plate (BAP)
Anaerobic BAP

• Unknown B A 70-year old man with a history of
  prostatic hypertrophy and recurrent E.coli
  urinary tract infections underwent a
  transurethral prostatectomy. He received
  perioperative antibiotic prophylaxis with Ancef
  (a cephalosporin) and gentamicin (an
  aminoglycoside) and had an indwelling Foley
  catheter postoperatively. Three days after
  surgery, he developed fever and chills, and
  microorganism B was isolated from his urine and
  from a blood culture. Gram stain showed
  Gram-positive cocci in chains.
• What organism is he infected with?
• Answer From the gram stain alone, we are
  thinking Streptococcus speciesand because of the
  history, this makes us think of the anaerobic
  streptococcus Enterococcus Faecalis. We confirm
  this by seeing that there is no growth on EMB
  (since EMB restricts growth of gram-positiveswhic
  h is one of the reasons it is useful). We also
  note that colonies are small and grey on blood
  agar, and growth is seen anaerobically as well.
  All of which confirm the organism is Enterococcus
  Faecalis.

52
EMB plate
Blood Agar
Gram Stain

• Unknown C An 82 year old woman residing in a
  nursing home developed a flu-like illness with
  fever, headache, malaise, myalgia and cough. She
  had refused influenza immunization. Her fever
  declined, and she felt somewhat better on the
  third day after onset. On the fourth day,
  however, her fever increased to 40C, and she
  developed a right lower lobe pneumonia.
  Microorganism C was isolated from her sputum.
• What is the organism causing this womans
  illness?
• Answer From the gram stain, we can see that the
  organism is a rod with a clear capsuleit is
  supposedly a gram-negative rod. From the EMB
  plate, we see that there are purple, mucoid,
  large coloniesletting us know that the organism
  ferments lactose. On blood agar, we see mucoid
  colonies again. The organism is
• Klebsiella Pneumoniae

53
BAP
BAP to light

• Unknown D A 24 year old woman suffered a crush
  injury to her left leg with a compound fracture
  of her tibia and fibula when her off-road vehicle
  overturned. She underwent open reduction, and
  her soil-contaminated wounds were debrided and
  dressed. Two days later, she developed severe
  pain in the involved leg. A thin serosanguineous
  discharge was noted from her wounds, her leg
  became edematous with bronze discoloration, and
  an x-ray revealed gas in the soft tissues. A
  gram stain of the serosanguinous discharge was
  notable for the absence of white blood cells the
  culture yielded microorganism D.
• What bacteria is causing this presentation?
• Answer We see white/cloudy pigment, double-beta
  hemolysis, and note that it is a gram-positive
  rod with no spores. All of this, plus the
  presentation (especially the gas gangrene and
  soil contaminant) leads us to the conclusion that
  the organism is Clostridium Perfringes.

54
Can the facultative Gram-negative enteric rods be
readily distinguished from one another by Gram
Stain? Can they be distinguished from the
obligate anaerobes?

• They can not be distinguished from one another by
  Gram stain.
• They can be distinguished from obligate anaerobes
  because of the fusiform morphology.

55
Can Bacterioides be distinguished from
fusobacteria by Gram stain?

• Yes.

56
Which organisms have a putrid or fecal odor?

• Anaerobes (as a class)

57
Can you distinguish C. perfringens from C. tetani
by Gram Stain?

• YES.
• C. tetani has spores (looks like a ball on a
  stick)

58
Name two characteristics of C. perfringens that
distinguish it from all other Clostridia.

• Double-zone hemolysis.
• Non-motile.

59
Which facultative anaerobes can you presumptively
identify by their appearance on EMB? By their
odor?

• E.coli green sheen
• Klebsiella mucoid

60
Does E.coli grow anaerobically?

• YES. It is facultative.

61
How does the colonial morphology and Gram stain
appearance of Actinomyces israelii differ from
the characteristics of the other obligate
anaerobes you have examined?

• Branching rods
• molar-tooth colonies

62
What is the difference between Actinomyces
israelii and Nocardia asteroides, another beaded,
branching, gram-positive bacillus?

• Both are branching rodshowever
• Their Acid-fast properties differ.