bacteriology lec. copy ppt
TRANSCRIPT
Specimen Collection
Basic Principles of Specimen Collection
To ensure appropriate specimen management:
If possible, collect the specimen in the acute phase of the infection and before antibiotics are administered.
Select the correct anatomic site for collection of the specimen.
Collect the specimen using the proper technique and supplies with minimal
contamination from normal flora. Collect the appropriate quantity of
specimen. Package the specimen in a container
designed to maintain the viability of the organisms and avoid hazards that result from leakage.
Label the specimen accurately with the specific anatomic site and the patient information.
Transport the specimen to the laboratory promptly or make provisions to store the specimen in an environment that will not degrade the suspected organisms.
Consideration in Specimen Collection: Specimen should be collected in sterile
containers. Swabs are not recommended for
collection because:
a. they do not provide sufficient quantity
b. they can easily be contaminated
c. can become dried out, leading to a loss of organisms.
Swabs are appropriate if specimens are from:
a. external ear c. upper respiratory tract
b. eye d. genital tract
Patients-Collected SpecimensThe specimens commonly obtained by the patient are:a. urine c. stoolb. sputum
Things to Consider in Collecting Urine Sample:a. It must be a clean-catch midstream urine
specimen.
b. First morning specimen is preferred
c. The patient collects this specimen following cleansing of the external genitalia.
Things to Consider in Collecting Sputum Sample:
a. The first early morning specimen is preferred.
b. The patient should rinse the mouth with water and expectorate with the aid of
a deep cough directly into a sterile container.
c. Patients with dentures should remove the dentures first.
2 Methods of Collecting Stool Specimen:
a. rectal swab b. stool excreted
Rectal Swab: 3 specimens should be collected, once a day for 3 days.
Stool Excreted: stool should never be taken from the toilet and should not be contaminated with urine.
SPECIMENPATIENT
PREPARATIONCONTAINER/MINIMUM QUANTITY
Blood Culture Disinfect skin w/ alcohol
Blood culture media set (aerobic & anaerobic bottles) or vacutainer tube w/ SPS(adults: 20 ml. per set; children: 5-10 ml. per set).
Ear: Outer Ear Remove debris or crust from ear canal with saline moistened swab; rotate swab in outer canal.
Swab transport system
Eye: Conjunctiva Sample both eyes; use separate swabs moistened with sterile saline
Swab transport system
SPECIMEN COLLECTION GUIDELINES
Feces Collect directly into container, avoid contamination w/ urine
Clean, leak-proof container or enteric transport system
Fungal Scrapings Wipe nails or skin w/ alcohol;Hair: 10-12 hairs w/ shaft intactNails: clip affected areaSkin: scrape skin at outer edge of lesion
Clean, screw-cap container
Genitalia: Vagina Remove mucus before collection; do not use lubricant on speculum, swab endocervical canal or vaginal mucosa
Swab transport system or JEMBEC transport system
Lesion/ Wound/Abscess (Superficial)
Wipe area w/ sterile saline or alcohol, swab along outer edge.
Swab transport system
Respiratory tract: Lower sputum
Rinse mouth or gargle w/ water, instruct to cough deeply into container
Sterile, screw-cap container
Throat Swab posterior pharynx, tonsils and inflamed areas
Swab transport sytem
Urine: Clean-catch midstream
Clean external genitalia, begin voiding and after several ml. have passed, collect midstream w/o stopping flow of urine
Sterile, screw-cap container or Urine transport kit
Labelling & Requisitions:
Proper identification of each specimen
includes a label firmly attached to the
container with the following information:
Name / age Date of collection
Room number Time of collection
Physician’s name Laboratory number
Culture site
Labelling and requisitions will determine exactly what needs to be done.
Laboratory Safety
Laboratory personnel must adhere to
strict safety guidelines as they begin to work
w/ the patient’s specimen and must wear
protective clothing and specimens should be
opened only in a biological safety cabinet.
Preservation, Storage and Transport of Specimen
Specimen Storage:
Some specimens such as urine, stool,
sputum, swabs (not for anaerobes) can be
maintained at refrigerator temperature (40C)
Pathogens that are cold sensitive
maybe found in other specimens that should
be kept at room temperature.
Transport Media
Transport media contain substances that do not promote multiplication of microorganisms but ensure the preservation especially specimens collected by swab.
Ex: Stuart or Amie’s transport media
Cary-Blair transport media
Blood: Broth culture medium
Bacterial Cultivation
Cultivation – is the process of taking the
bacteria from the infection site and letting it
grow in an artificial environment called the
culture media.
3 Main Purposes of Bacterial Cultivation:
a. To grow and isolate all bacteria present in a clinical specimen.
b. To determine w/c of the bacteria that
grow are most likely to cause infection and
w/c are likely contaminants or colonizers.
c. To obtain sufficient growth of clinically
relevant bacteria to allow identification and
characterization
Nutritional Requirement - this include:
gases nitrogen
water sources for carbon
various ions energy
2 Phases of Culture Media:
a. liquid (broth) b. solid (agar)
In broth media, bacterial growth is
indicated by a change in the broth’s appearance from clear to turbid.
Solid media are made by adding agarose.
With appropriate incubation, bacterial cell inoculated onto the agar medium will proliferate to sufficient number (bacterial population – “colony”) that can be seen by the naked eye.
Classification of Media According to
Function / Use:
a. Enrichment Media – contain specific
nutrients required for the growth of
particular bacterial pathogens (fastidious
organisms) that may be present alone or w/
other bacteria in the specimen.
b. Selective Media – support the growth of
one type or group of microbes but not
another. This medium may contain
inhibitory substances such as antimicrobials,
dyes or alcohol.
Ex: Mac-Conkey agar for enteric gm (-)
bacilli.
c. Differential Media – employ some factors
that allow colonies of one bacterial species
or type to exhibit certain metabolic or culture characteristics that can be used to distinguish them from other bacteria growing on the same agar plate.
Ex: Mac-Conkey agar – inhibits gm(+) and differentiates gm(-) bacilli on the basis of lactose fermentation.d. Supportive Media – contain nutrients that
support growth of most non-fastidious
organisms w/o giving any particular
organism a growth advantage.
CULTURE MEDIA & ITS USEMEDIUM 10 PURPOSE
Blood Agar Cultivation of fastidious microorganisms, determination of hemolytic reactions
Chocolate Agar Cultivation of Haemophilus spp. and pathogenic Neisseria spp.
Eosin Methylene Blue (EMB)
Isolation and differentiation of lactose-fermenting and non lactose-fermenting enteric bacilli
MEDIUM 10 PURPOSE
Mac-Conkey Agar Isolation and differentiation of lactose-fermenting and non lactose-fermenting enteric bacilli
Salmonella-Shigella (SS) Agar
Selective for Salmonella and Shigella spp.
Selenite broth Enrichment of isolation of Salmonella spp.
Thayer-Martin Agar Selective for N. gonorrhea & N. meningitidis
Thioglycollate broth Supports growth of anaerobes, aerobes, microaerophillic, and fastidious organisms
MEDIUM 10 PURPOSE
Thiosulfate Citrate Bile Salts (TCBS) agar
Selective and differential for vibrios
Trypticase Soy Broth (TSB)
Enrichment broth used for subculturing various bacteria from primary agar plates.
Xylose Lysine Desoxycholate (XLD) agar
Isolation and differentiation of Salmonella and Shigella spp. from other gm(-)enteric bacilli
Brain-Heart Infusion (BHI) – is a
nutritionally rich medium used to grow
various microorganisms, either as a broth or
as an agar, with or w/o added blood.
Chocolate agar – is essentially the same as
blood agar except that during preparation
the red blood cells are lysed when added to
molten agar base. This lysis releases intra-
Cellular nutrients such as hemoglobin, hemin
and the coenzyme nicotinamide adenine
dinucleotide into the agar for utilization by
fastidious bacteria.
The most common bacterial pathogens
that require this enriched medium for growth
include Neisseria gonorrhea, the causative
agent of gonorrhea, and Haemophilus spp.
Mac-Conkey agar – is the most frequently
used primary selective and differential agar.
This medium contains crystal violet dye to
inhibit the growth of gm(+) bacteria and
fungi, and allows many types of gm(-)
bacilli to grow.
With Neutral red indicator – resulting to
pink to red colonies.
Sheep Blood agar – this medium supports all but the most fastidious clinically significant bacteria.
Certain bacteria produce extracellular enzymes that lyse red blood cells in the agar known as hemolysis.
Types of Hemolysis produced by bacteria:a. alpha hemolysis c. gamma or no b. beta hemolysis hemolysis
Thayer-Martin agar – is an enrichment and
selective medium for the isolation of
Neisseria gonorrhea and Neisseria
Meningitidis. The enrichment portion of the
medium is the basal components and the
chocolatized blood, while the addition of
antibiotics provides a selective capacity.
The antibiotics include colistin to inhibit
other gm(-) bacteria, vancomycin to inhibit
gm(+) bacteria, and nystatin to inhibit yeast.
The antimicrobial trimethoprim is also
added to inhibit Proteus spp., w/c tend to
swarm over the agar surface and mask the
detection of individual colonies of the two
pathogenic Neisseria spp.
Thioglycollate broth – contains many nutrient factors, including casein, yeast and beef extracts, and vitamins to enhance the growth of most medically important bacteria. This agar supplement and the presence of thioglycolic acid, w/c acts as a reducing agent to create an anaerobic environment deeper in the tube, allows anaerobic bacteria to grow.
Xylose-Lysine-Desoxycholate (XLD) agar –a phenol red indicator in the medium detects increased acidity from carbohydrate fermentation. Because of decarboxylation of lysine, the pH (culture environment) increases thus causing the pH indicator to turn red. These colonies often exhibit a black center that results from Salmonella
spp. Producing H2S.
Preparation of Artificial Media:Generally, media are reconstituted by
dissolving a specified amount of media powder, w/c usually contains all necessary components in water. Boiling is often required to dissolve the powder, but specific manufacturer’s instructions printed in media package inserts should be followed exactly. Most media require sterilization so that only
bacteria from patient specimens will grow
and not those that are contaminants from
water or the powdered media.
Media Sterilization
The timing of autoclave sterilization
should start from the moment the
temperature reaches 1210C and usually
requires a minimum of 15 mins.
Streaking an Agar Plate for Isolation: The 3 Sector Method
1. Lift the lid of the petri plate just enough
to insert the inoculating loop. Keeping the
loop parallel w/ the agar surface and starting
at 12:00 position, zigzag the loop back &
forth across the agar surface until you have
covered approximately 1/3 of the plate.
2. Sterilize the inoculating loop in your
gas burner and stick the loop into the agar at
the edge of the agar to cool.
3. Now rotate the plate 450 counterclock –
wise so that the area you just streaked at the
12:00 position is now at the 9:00 position.
4. Take the sterile inoculating loop and
drag it through “area 1” two-three times
to pick up some of the bacteria already on
the plate and spread them over half the
remaining plate. Do not touch “area 1” after
the first 2 or three drags.
5. Sterilize the inoculating loop in your
gas burner and stick the loop into the agar at
the edge of the agar to cool.
6. Now rotate the plate 450 counterclock-wise
so that the area 2 that you just streaked at the
12:00 position is now at the 9:00 position.
7. Take the sterile inoculating loop and
drag it through “area 2” two-three times to
pick up some of the bacteria already on the
plate and spread them over most of the
remainder of the plate. Do not touch “area
2” after the first two or three drags and be
careful not to drag the loop into “area 1.”
8. Close the lid of the plate and sterilize
the inoculating loop.
Incubation:Incubation conditions must be
considered when a medium is inoculated. Most bacteria cultures are incubated at 350C to 370C.
Classification of Bacteria as to Oxygen Requirement:
a. Aerobes – bacteria that grow in ambient air or in the presence of an oxygen.
b. Anaerobes – bacteria that grow in the absence of an oxygen.
c. Microaerophiles – bacteria that grow w/ reduced oxygen and increased carbon dioxide.
d. Capnophiles – bacteria that require an increased concentration of carbon dioxide (ex. by a candle jar, carbon dioxide incubator).
MICROORGANISM CULTURAL APPEARANCE
Staphylococci Small to medium, opaque, smooth, slightly raised, translucent, creamy yellow
Streptococci Grayish white, small or minute, matte or glossy, flat.
B. Anthracis Medium-large, gray, flat, irregular w/ swirling projections (“Medusa head”).