·
An understanding of normal, or indigenous, microflora is essential in order to appreciate
the abnormal. Usually, anatomic sites contiguous to mucous membranes are not
sterile and have a characteristic normal flora.
The skin flora differs as a function of location.
Skin adjacent to mucous membranes may share some of the normal flora of the
gastrointestinal system. Overall, the predominant bacteria on the skin surface
are S. epidermidis and Propionibacterium,
an anaerobic diphtheroid.
The gastrointestinal tract is sterile at birth
and soon develops a characteristic flora as a function of diet. In the adult,
anaerobes such as B. fragilis and Bifidobacterium
may outnumber coliforms and enterococci
by a ratio of 1000:1. The colon contains 1011 to 1012 bacteria per gram of
feces.
The mouth is part of the gastrointestinal tract,
but its indigenous flora shows some distinct differences. While anaerobes are
present in large numbers, particularly in the gingival crevice, the eruption of
teeth at 6 to 9 months of age leads to colonization by organisms such as
Streptococcus mutans and S. sanguis,
both alpha-hemolytic streptococci. An edentulous person loses alpha-hemolytic
streptococci as normal flora.
Soon after birth, the vagina becomes colonized by
lactobacilli. As the female matures, lactobacilli may still be predominant, but
anaerobic cocci, diphtheroids,
and anaerobic Gram-negative rods also are found as part of the indigenous
flora. Changes in the chemical or microbiologic ecology of the vagina can have
marked effects on normal flora and may promote infection such as vaginitis or vaginosis.
·
Two human forms of ehrlichiosis
can occur:
human monocytic ehrlichiosis (HME),
caused by E. chaffeensis; and
human granulocytic ehrlichiosis
(HGE), caused by an Anaplasma phagocytophilum.
Ehrlichiosis
was previously recognized only as a veterinary pathogen. HME infection is
transmitted by the brown dog tick and A. americanum.
HGE infection is transmitted by I. scapularis, the
same tick that transmits Lyme disease. Both infections cause fever and leukopenia. A rash rarely occurs. E. chaffeensis
infects monocytes, and HGE infects granulocytes; both
organisms produce inclusion bodies called morulae.
·
Listeria is a common
inhabitant of farm animals and can be readily isolated from silage, hay, and
barnyard soil. Humans at the extremes of age are most susceptible to Listeria infection but only recently has food been
implicated as a vehicle. In the outbreak in Nova Scotia, it is likely that the
cabbage used for the coleslaw was fertilized with animal droppings and not
properly washed prior to consumption. Major Listeria
outbreaks associated with cheese have been seen in the United States and most
likely have originated from contaminated milk.
·
Adenosine triphosphate
(ATP) is believed to be generated at three reaction points in the electron
transport chain: the reductions of flavoprotein, cytochrome b, and cytochrome c.
This phenomenon, demonstrated in experiments with mammalian mitochondria, can
be expressed in terms of the relationship between the moles of ATP generated
for each atom of oxygen consumed—the P/O ratio. In mammalian cells, the P/O
ratio is 3; that is, there are three segments in the electron transfer chain in
which there is a relatively large free energy drop. In bacteria, however, there
appears to be only one or two of these segments. Loss of these phosphorylation sites as well as reactions that bypass
these sites of ATP synthesis account for the lower P/O ratio in bacteria. Some
bacteria, such as Mycobacterium phlei, have P/O
ratios of 3.
·
Penicillin-resistant, non--lactamase-producing,
vancomycin-resistant, Gram-positive cocci are most likely Enterococcus
faecium. There are a variety of mechanisms for vancomycin resistance in E. faecium
and they have been termed Van A, B, or C. These isolates have become one of the
most feared nosocomial pathogens in the hospital
environment. Unfortunately, no approved antibiotics can successfully treat vancomycin-resistant enterococci
(VRE), only some experimental antibiotics such as Synercid.
·
Wound exudates smell bad owing to production of
organic acids by such anaerobes as B. fragilis. Black
exudates or a black pigment (heme) in the isolated
colony is usually a characteristic of Bacteroides (Porphyromonas) melaninogenicus,
not B. fragilis.
·
The structural integrity of the beta-lactam ring in penicillins is
essential for their antimicrobial activity. Many resistant strains of
staphylococci produce an enzyme, penicillinase, that cleaves the beta-lactam
ring at the carbon-nitrogen bond. Other organisms, including certain coliform bacteria, produce an amidase
enzyme that inactivates penicillin by disrupting the bond between the radical
and nitrogen in the free amino group.
·
6-Phosphogluconic acid is a characteristic
metabolic intermediate in the pentose-phosphate metabolic pathway. This pathway
is used by heterolactic fermenters
such as Leuconostoc, the organism responsible for the
fermentation of cabbage in the production of sauerkraut. Leuconostoc
is a Gram-positive bacterium with a dextran capsule.
·
Dipicolinic acid, formed in the synthesis of diaminopimelate
(DAP), is a prominent component of bacterial spores but is not
found in vegetative cells or eukaryotic appendages or fimbrial
structures. The calcium salt of dipicolinic acid
apparently plays an important role in stabilizing spore proteins, but its
mechanism of action is unknown. Dipicolinic acid synthetase is an enzyme unique to bacterial spores.
·
ADP-ribosylates Gs =
Turn the On, On
Vibrio
ETEC
Bordetella pertussis
Pseudomonas
Diptheria
·
Enterococcus is the only
nitrite negative UTI.
·
Cultures of Actinomyces
grow as white masses with a domed surface, which is called a “molar tooth”
appearance.
·
Nocardiae are aerobic and acid-fast, in contrast to Actinomyces species, which are strict anaerobes and not
acid-fast.
Actinomyces israelli is treated with penicillin and Nocardia
asteroides is sensitive to trimethoprim-sulfamethoxazole.
·
L. monocytogenes is a
short, gram-positive, non-spore-forming bacillus that can produce neonatal
disease or can result in stillbirth. Characteristics that are unique to Listeria include a tumbling motility on hanging drop and an umbrella-shaped
motility pattern when a specimen is stabbed into a test tube agar slant.
Listeria may
be mistaken for diphtheroids on Gram stain;
both are gram-positive bacilli. Listerial infection
often occurs in immunocompromised patients. Risk
factors include cirrhosis, neoplastic disease, renal
failure, pregnancy, chronic steroid therapy, and extremes of age (i.e., very
young and elderly).
·
Bartonella infections
are also characterized by proliferations of blood vessels. Examples of Bartonella include B. quintana,
B. henselae, and B. bacilliformis,
B.bacilliformis, the causative agent of Oroya fever.
B. quintana is spread by the human body louse and
is the causative agent of trench fever (seen in the trenches of World War I)
and bacillary angiomatosis. This latter term refers
to a lesion seen in patients with AIDS consisting of a lobular proliferation of
capillaries with abundant leukocytoclastic debris.
B. henselae is the
causative agent of cat-scratch fever. Histologically,
this disease is characterized by the formation of stellate
microabscesses with necrotizing granulomas.
·
Persons with acute and chronic alcoholism
become infected with Klebsiella pneumoniae,
most often by aspiration. K. pneumoniae pneumonia
often localizes in the upper lobe, sometimes the minor fissures bows downward,
reflecting the bogginess of the upper lobe involved with this infection.
·
The process of transduction involves the transfer
of a portion of DNA from one bacterium to the chromosome of another bacterium
by means of a viral infection.
Conjugation
is the transfer of a so-called male chromosomal DNA to the DNA of an acceptor,
or female, bacterial cell.
Colinearity
defines the relationship between genes and proteins in that the sequence of
amino acids in proteins is a result of the sequence of base triplets in
template genes.
Recombination is simply the exchange of sequences
between two molecules of DNA.
Transformation results when exogenous DNA
fragments are incorporated into the chromosome of another organism, as in the
transformation of pneumococcal bacteria that led Avery and McLeod to recognize
the genetic significance of DNA.
·
ENTEROBACTERIACEAE ANTIGENIC MARKERS:
1. O-Antigen: Carbohydrate in the cell wall.
2. K-Antigen: Capsular antigen, when present.
3. H-Antigen: Flagellar
antigen, when present: Campylobacter, Helicobacter, Escherichia.
4. F-Antigen: Pili
antigen.
·
ENTEROTOXINS A, B, C1, C2, D: Affects the
GI-tract in S. AURES food poisoning.
·
Virulence of S.saprophyticus:
Urease: Enable survival in urinary tract.
Tropic for urinary transitional epithelium.
Lysostaphin
is lethal to S. AURES and other bugs.
·
B. anthracis species
is identified by a String of Pearls formation in penicillin. The
colonies are susceptible to penicillin, whereas other Bacillus species are not.
B. Cereus
is penicillin-resistant. They will form chains of rods rather than string of pearls in
penicillin suspension.
·
FRANCISELLA
TULARENSIS: CYSTEINE-AGAR must be
used.
·
In Legionella, Dieterle Silver Stain
shows rod shaped bacteria within macrophages. NO STAIN with Gram Stain,
Acid-Fact Stain, or H&E. CYSTEINE is absolutely required for growth.
·
Y. pestis, Bacteria reproduce
in flea to the point where they clog the proventriculus.
Human bite ------> inoculation of bacteria into host.
·
Pyoderma of
Streptococci:
IMPETIGO:
Cutaneous lesions in kids, usually on face. Very
similar to the Staph bullous lesions, except that
these are vesicular lesions because these are actually full of bugs.
ERYSIPELAS:
Cutaneous lesions in adults. Painful.
Again contains organisms.
·
Todd-Hewitt Broth: Done when few organisms
were recovered.
Strep: Granular precipitates on sides and
bottom of tube.
Staph: Diffuse turbidity.
·
CAMP TEST: Mix normally non-hemolytic Staph Aureus with specimen, and
hemolytic zone is augmented. Staph Aureus is normally
only hemolytic at 4C.
·
ENTEROCOCCUS FAECALIS (GROUP D)
Virulence:
LIPOTECHOIC acid, very lipid rich, leads
to gram-variable appearance.
Treatment:
Penicillin resistant, strongly, due to altered Penicillin-binding proteins.
Also have acquired vancomycin and gentamycin resistance.
·
Vincent's Disease can be confused with diphtheria.
Vincent's Disease is pseudomembranous
pharyngitis, and is caused by poor oral hygiene.
Vincent's
will show halitosis and signs of gingivitis (swelling, bleeding).Stain with
Vincent's disease will show a whole mess of bacteria -- both Gram (+) and Gram
(-), while Diphtheria will show only slender Gram (+) rods.
·
P. Vulgaris:
Positive for metabolizing tryptophan ------> indole
Ampicillin-resistant.
Use aminoglycoside and then wait for sensitivity
tests.
P. Mirabilis: Negative
for metabolizing tryptophan ------> indole
Treated
with Ampicillin
·
NEISSERIA MENINGIDITIS (MENINGEOCOCCUS)
Type-B is the most virulent because it is
not immunogenic -- we cannot make protective antibodies against it.It is made out of alpha-2,8-n-acetylneuraminic
acid. It is rapidly degraded and thus not immunogenic.
LPS:
Induces the Schwartzman
Reaction. Causes the rash and can lead to necrosis.
·
BRUCELLOSIS:
Brucella Agar = Selective Agar containing Erythritol, which the
bugs subsist on.
Erythritol is found in reproductive tract of cattle, hence these bugs cause abortion in cattle. Humans
don't have erythritol so no abortion happens.
·
BORRELIA BURGDORFERI:
Enriched
Selected Kelly's Medium. Enriched
with fatty acids, but it's still difficult to grow.
·
The 16S rRNA of each species of
bacteria has stable (conserved)
portions of the sequence. Many copies are present in each organism. Labeled
probes specific for the 16S rRNA of a species are
added, and the amount of label on the double-stranded hybrid is measured. This
technique is widely used for the rapid
identification of many organisms. Examples include the most common and
important Mycobacterium species, Coccidioides immitis, Histoplasma capsulatum, and
others.
Portions of the 16S
rRNA are conserved across many species of
microorganisms. Amplifying the 16S rRNA using primers
to these conserved regions allows isolation and sequencing of the variable
regions of the molecules. These variable sequences are genus- or
species-specific markers that allow identification of microorganisms. Pathogens
that are difficult or impossible to culture in the laboratory have been
identified using this technique. One example is Tropheryma whipplei, the cause of Whipple's disease.
·
CHOLERA:
HOLDING MEDIA: VR Medium, Cary-Blair Medium, Autoclaved sea
water
ENRICHMENT MEDIA: Allkaline
Peptone water at pH 8.2, Monsur's Taurocholate
tellurite peptone water at pH 9.2,
PLATING MEDIA: Alkaline Bile salt agar, Monsur's Gelatin taurocholate trypicase tellurite agar(GTTA) Medium, TCBS Medium.
V. cholerae O139 Bengal is in fact virtually identical to V. cholerae O1 El Tor except for two important differences: production of the novel O139 LPS and of an immunologically related O-antigen polysaccharide capsule. Encapsulation is not a
feature of O1 strains and may explain the resistance of O139
strains to human serum in vitro as well as the occasional development of O139 bacteremia.
No comments:
Post a Comment