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Testing
Microbiology
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VITA-TECH provides comprehensive microbiology services which strictly follow NCCLS protocols and guidelines and feature fully automated identification and sensitivity testing. MIC (Minimum Inhibitory Concentration) data are currently available by request.
Culture and Identification
Culture and identification of aerobic bacteria isolates is routinely performed for each specimen; anaerobic culture is done on appropriate samples and as requested. The laboratory can provide a preliminary report on aerobic growth or no growth at 24 hours.
Identification and antimicrobial susceptibility testing results of fast-growing aerobes is usually completed in 48 to 72 hours. Culture and identification of fastidious organisms and anaerobes requires additional time. Positive Salmonella or Campylobacter jejuni culture results take four to five days. Fungal cultures are held for two weeks if the KOH preparation is negative and for three weeks if the KOH preparation is positive before being discarded as negative.
Antimicrobial Susceptibility Testing
The purpose of susceptibility testing is to determine the likelihood of successfully treating a patient's infection with a particular antimicrobial agent. Antimicrobial susceptibility (sensitivity) testing is performed for aerobic isolates considered as significant pathogens. Antimicrobial susceptibility testing of anaerobes is not performed.
The microbiology laboratory performs antimicrobial susceptibility testing by the microdilution method (automated Microscan panels) and the disc diffusion procedure (Kirby-Bauer), following NCCLS protocols and guidelines. Separate panels of antimicrobial agents are tested for Gram-positive and Gram-negative bacterial pathogens relevant to veterinary practice. Susceptibility testing of fungal isolates is not performed.
General Collection Guidelines
Aerobic Culture Swabs
After the sample is collected with a sterile rayon swab, the inoculated swab must be
immersed completely in the Amies transport medium found in the transport tube. Charcoal
transport medium swabs are needed only for Taylorella equigenitalis, the agent for contagious equine metritis.
Anaerobic Culture
Anaerobic culture is performed routinely on aspirates or exudate from:
Since urinary tract infections are rarely caused by anaerobes, urine collected by cystocentesis is cultured for anaerobes only if requested. For pustules, ulcers, and fistulas, intact lesions should be selected as the sample site since surface swabbing of these sites will result in the recovery of superficial contaminants. The surface of the site must be aseptically prepared, and fluid or exudate collected by aspiration by lancing or with a sterile needle. For abscess, exudate from the edge of the abscess should be submitted with scrapings of the abscess wall since the centre of an abscess is often sterile. Anaerobes survive well in purulent exudate and blocks of moist tissue and are preferred over swabs. Tissue blocks (4 cm2) or fluid (3 ml) should be submitted in an anaerobic transport medium unit or in a plain red top. Tissues and fluids should be refrigerated to prevent decomposition. Anaerobic bacteria must be protected from oxygen and will not survive in aerobic transport medium. For the survival of anaerobes, please ensure the inoculated swab is submerged in anaerobic transport medium. Anaerobic swab specimens should be held and shipped at room temperature (25oC) unless transport is delayed. Anaerobes comprise a major component of the normal flora of mucosal surfaces. Consequently, specimens collected from these body sites are generally unacceptable for anaerobic culture.
Blood Culture
Blood culture bottles should be used for the collection of specimens. Please call VITATECH for detailed instructions on inoculation of vials and transportation of samples
before sample collection. Serum, swabs of blood, or blood mixed with an anticoagulant or EDTA are not suitable for culture.
Ideally, two blood samples, drawn approximately one hour apart from different venous sites, should be submitted. This helps determine if bacteremia is transient or continuous and also minimizes false-positive diagnosis due to skin contamination. Blood samples may also be collected within 24 hours of each other. Samples should be drawn before systemic antimicrobial therapy is initiated. The venipuncture site must be aseptically prepared to reduce skin contamination. For small animals, 1-5 ml of blood should be drawn for each sample; for large animals, up to 10 ml blood should be drawn. Blood culture samples should be stored at room temperature.
Fastidious Organisms (Mycoplasma, Chlamydia, Mycobacteria)
Mycoplasma & Chlamydia
VITA-TECH performs DNA testing for Chlamydia and Mycoplasma as well as rapid immunoassay for Chlamydia. VITA-TECH does not culture for these organisms. DNA testing is advantageous over culture for fastidious organisms, as it is highly specific and sensitive and will detect both viable and non-viable organisms. Organisms that frequently die in transport and storage will still be detected.
Fluid, exudate, feces, tissue or plain rayon swab specimens are suitable for testing. Transport media is not required. Feces, fluid and tissue should be refrigerated to prevent decomposition. Refrigeration of swabs is necessary only if transportation is delayed.
Mycobacteria
The lab prepares and examines Ziehl-Neelsen-stained smears for the presence of acid-fast bacilli, (e.g. for Mycobacterium paratuberculosis), but cannot culture mycobacteria.
Fecal Culture
1-5 g of feces submitted in an enteric transport medium unit is preferred. Affected stool (e.g. diarrheic, bloody or mucousy) should be collected for culture. Rectal swabs are less suitable specimens.
Samples should be held at room temperature at all times. Refrigeration is detrimental to specimens, especially for the detection of Campylobacter jejuni. Repeat samples are worthwhile for intermittently shed bacteria such as Salmonella. DNA-PCR testing for enteric pathogens is also available by the DNA laboratory.
Fungal Culture
For dermatophytes, submit skin scrapings and scurf, plucked hairs with roots, and claw nails in a sealed paper fungal envelope. Plastic or glass containers are not recommended
for storing sample material as specimen will not stay as dry compared to storage in fungal envelopes. Skin lesions should be cleaned of contaminating bacteria with 70% alcohol and allowed to dry before sampling. Specimens should be held at room temperature.
For the diagnosis of infection by various invasive fungi such as Candida albicans and Cryptococcus neoformans, dimorphic fungi (Blastomyces dermatitidis, Histoplasma capsulatum, Coccidioides immitis, and Sporothrix schenckii), Aspergillus spp. and the Zygomycetes, it is important to demonstrate tissue invasion. Specimens should be submitted for cytology or histopathology as well as fungal culture. Samples for invasive fungi (aspirated fluids, swabs, tissue) should be refrigerated. For the safety of laboratory personnel, please indicate if fungi infection is suspected on the requisition form.
Milk Specimens
Good collection technique is important to ensure that milk samples are not contaminated by flora from the udder skin, feces, or dust. Samples should be submitted in a sterile milk vial or a red top tube. Swabs are not suitable. Milk specimens should be kept refrigerated immediately after collection. Anaerobic culture of milk is performed only upon request.
Necropsy Specimens
It is important to collect tissues as soon as possible after death to minimize postmortem invasion by bacteria. Submit tissues in individual sterile Whirlpack bags or sterile widemouthed containers. Transport specimens in a clean plastic bag to prevent spillage and cross contamination. Tissues must be refrigerated during transport to prevent decomposition.
Urine Specimens
Fresh urine should be submitted in a sterile urine jar or red top tube. Swabs are not suitable. Samples must be refrigerated immediately after collection but should not be allowed to freeze. False positive results may occur if samples are left at room temperature. False negative results may occur if the urine is refrigerated for an extended period, depending on the bacterial species present. Samples should be transported to the lab as soon as possible after collection.
Urine collection method used should be indicated on the requisition form. Sample collected by cystocentesis is preferred to obtain an uncontaminated specimen. The needle insertion site should be aseptically prepared in the same manner as for venipuncture. Catheterized and midstream clean-catch urine samples may become contaminated with lower urogenital tract bacteria and WBCs in both male and female animals. If three or more different types of bacteria are recovered from a clean-catch sample, it is usually due to contamination and a repeat culture is recommended. A urine specimen can be taken near the end of antimicrobial treatment to assess the effectiveness of the therapy and also after the completion of therapy to check whether infection has recurred. It is recommended to wait 4-7 days after therapy has been discontinued to resample. |
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