Stoke Method Of Antimicrobial Sensitivity Testing

Figure 57-3 Method for inserting a calibrated loop into urine to ensure that the proper amount of specimen adheres to the loop.

Loop Gram Ileal Conduit
Figure 57-4 Method for streaking with calibrated urine loop to produce isolated colonies and countable colony-forming units.

ileal conduits, and suprapubic aspirates should be plated with the larger calibrated loop. The communication of pertinent clinical history to the laboratory is essential so that appropriate processing can be performed.

The choice of which media to inoculate depends on the patient population served and the microbiologist's preference. The use of a 5% sheep blood agar plate and a MacConkey agar plate allows detection of most gram-negative bacilli, staphylococci, streptococci, and enterococci. To save cost and somewhat streamline

Bullseye Urine Culture
Table 57-1 Overview of Bactériologie Culture Systems for Urine

Cultiire System

Principle

Comments)

Bactercult (Wampole Laboratories, Princeton, NJ.)

Sterile, disposable tube coated with culture medium; contains phenol red indicatorfor presumptive ID of common uropathogens

Colonies counted

Bullseye Urine Plate (HealthLink Diagnostics, Southeast VetLab Supply, Miami, Ra.)

Five-chambered plate containing mediator isolation and ID of common uropathogens and their AST patterns

Colonies counted; direct AST

Dlasllde (Dlatech Diagnostics, Inc., Boston, Mass.)

TTansparerrt-hinged plastic casing contains CLED and MacConkey agais for detection and presumptive ID of common im pathogens

Growth Is compared with reference photographs for quantitation, morphology, and color

DIP N COUNT (Starplex Scientific, Etobiocoke, Ontario, Canada)

Paddle contains CLED and MacConkey or EMB agar

Colonies are compared with a color density chart; color chart is used for ID

onSlte Urine Culture Device (TREK Diagnostic Systems, Westiake, Ohio)

Transparent hinged casing with 5% blood, Columbia CNA and CLED agars. Kit contains a plastic sampler for Inoculation.

Colonies counted.

. Rainbow (Biolog, Inc., Hayward, Calif.)

Rainbow agar CP-8 used with eight confirmation spot tests for ID of eight microorganisms causing UTIfmedium contains chromogenic substrates that color microorganisms

Interpretation may occur within 3 to 6 hr for rapidly growing organisms

URI-CHECK (Troy Biologlcals, Inc., Troy, Mich.)

Dipsllde culture forthe enumeration and ID of uropathogens; dipsllde contains CLED and MacConkey or EMB agar; similar to DIP N COUNT

Growth density is compared with chart

Uri-Kit/Uri-Three (Culture Kits, Inc., Norwich, NY.)

Agar plate systems used to detect common uropathogens; Url-KIt is plastic-hinged case containing CLED medium; Uri-Three triplata contains 5% blood and MacConkey and CLED agars

Growth density is compared with a colony density chart

UricultTrio (Orion Diagnostica, Espoo, Finland)

Three-medium dipsllde containing CLED, MacConkey, and a ^-glucuronidase substrate for enumeration of microorganisms and presumptive identification of Escherichia coll

£ co//appears as brown colonies i

From Ctaridge JE, Johnson JR, Pezzto MT: Laboratory diagnosis of urinary tract infections. In Weissfeld AS, coortTmaling editor: Cumitech 2B, Washington, DC, 1998, American Society tor Microbiology.

AST, Antimicrobial susceptibility testing; ID, Identification; U7I, urinary tract Infection.

culture processing, many laboratories use an agar plate split in half (biplate); one side contains 5% sheep blood agar and the other half contains MacConkey agar.

In some circumstances, enterococci and other streptococci may be obscured by heavy growth of Entero-bacteriaceae. Because of this possibility, some laboratories add a selective plate for gram-positive organisms, such as Columbia colistin-nalidixic acid agar (CNA) or phenylethyl alcohol agar. Although some discriminatory capability may be added, cost is also added to the procedure. In addition to increased cost, inclusion of plated media selective for gram-positive organisms generally provides no or limited additional information. Many European laboratories use cystine-lactose electrolyte-deficient (CLED) agar. In recent years, chromogenic media has been introduced and become commercially available from a number of manufacturers that allows for more specific direct detection and differentiation of urinary tract pathogens on primary plates. This media uses enzymatic reactions to identify E. coli and jEntero-coccus without additional confirmatory testing from urine specimens as well as providing presumptive identification of S. saprophytics, Streptococcus agalactiae, Klebsiella-EnterobaOer-Serratia and the Proteus-Morganella-Providentia groups.

Before inoculation, urine is mixed thoroughly and the top of the container is then removed. The calibrated loop is inserted vertically into the urine in a cup. Otherwise, more than the desired volume of urine will be taken up, potentially affecting the quantitative culture result (Figure 57-3). A widely used method is described in Procedure 57-1. If the urine is in a small-diameter tube, the surface tension will alter the amount of specimen picked up by the loop. A quantitative

Table 57-2 Criteria for Classification of Urinary Tract Infections by Clinical Syndrome

Criteria

Category

Clinical

Laboratory

Acute, uncomplicated UTI in women

Dysuria, urgency, frequency, suprapubic pain No urinary symptoms in last 4 wk before current episode No fever or flank pain

0 WBC/mm3 5:103 CFU/mL uropathogens* in CCMS urine

Acute, uncomplicated pyelonephritis

Fever, chills

Rank pain on examination Other diagnoses excluded

No history or clinical evidence of urologic abnormalities

alt) WBC/mm3

a1 o* CFU/mL uropathogens in CCMS urine

Complicated UTI and UTI In men

Any combination of symptoms listed above

One or more factors associated with complicated UTIi

k10 WBC/mm3

a105 CFU/mL uropathogens in CCMS urine

Asymptomatic bacteriuria

No urinary symptoms

  • gt;10 WBC/mm3
  • 10s CFU/mL in two CCMS cultures >24 hrs apart

From Stamm WE: fo/Mon 20(suppl 3):S151,1992. Uropathogens; Organisms that commonly cause UT1s.

^Factors associated with complicated UTI include any UTI In a male, Indwelling or intermittent urinary catheter, >100 mL of postvoid residual urine, obstructive uropathy, urologic abnormalities, azotemia (excess urea In ttie blood, even without structural abnormalities), end renal transplantation. UTI, Urinary tract Infection; W8C, white blood ceSs; CPU, colony-forming unit; CCMS, clean-catch midstream urine.

pipette should be considered if the urine cannot be transferred to a larger container. Once inoculated, the plates are streaked to obtain isolated colonies (Figure 57-4).

Once plated, urine cultures are incubated overnight at 35° C. For the most part, incubation for a minimum of 24 hours is necessary to detect uropathogens.12 Thus, some specimens inoculated late in the day cannot be read accurately the next morning. These cultures should either be reincubated until the next day or possibly interpreted later in the day when a full 24-hour incubation has been completed.

During the past several years, a number of self-contained bacteriologic culture systems for urine have been introduced. For larger diagnostic laboratories, these systems increase efficiency while decreasing costs and turn-around time. Although the review of each of these systems is beyond the scope of this chapter. Table 57-1 provides an overview of the more commonly used systems; the reader is referred to the list of additional reading at the end of this chapter for more information.

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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Responses

  • ulrike
    What streaking method is best for urine?
    3 years ago
  • Mary
    What is the minimum number of hours colonies should be for sensitivity testing ?
    11 months ago

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