|This Month: Focus on Microbiology
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ANTECH Advances in Blood Fluid Culturing: Adoption of the BD BacTec™ 9050 System
|BacTec™ 9050 Incubator/Reader
ANTECH has adopted an improved blood and body fluid culture system over the past two years, providing a leap forward in microorganism recovery for our clients. The BD BacTec™ 9050 system was selected over competing systems for four significant benefits:
1. Antibiotic neutralization. A high percentage of pets have received antibiotics by the time they have their blood cultured. The BacTec culture bottles supplied by ANTECH (aerobic & anaerobic) incorporate antibiotic neutralizing resin beads to enhance organism recovery in this scenario.
2. Higher sensitivity. The sensitivity of the BD BacTec™ system is much higher than previous-generation systems; thus, very small numbers of organisms can be detected. For example, the sensitivity of anaerobic cultures is 10 – 50 CFU/ml. The sensitivity gains are attributed to:
- Highly nutritious growth media. Both the Peds Plus™ (aerobic) and BacTec™ Plus (anaerobic) bottles contain an enriched soybean-digest broth. The fungal bottle contains supplemented Middlebrook and Brain Heart infusion broth formulations in addition to other active ingredients that support the growth of yeasts and filamentous fungi.
- Continuous agitation. The BacTec™ system’s continuously agitating incubator enhances the recovery and growth rate of the microorganisms.
3. Faster detection; quicker TAT. The BacTec™ 9050 features a continuously monitoring fluorescent technology sensor that checks samples for growth every 20 minutes, compared to daily checks in the past. The result: positives are discovered in as little as 4 hours, and negatives are confirmed in 5 days, cutting the previous time to confirmed negatives in half!
4. Low volume draws. A volume as small as 0.5 ml is acceptable with the Peds Plus™ aerobic culture bottle, an important advantage when dealing with your smallest patients.
The table below details the appropriate culture bottles to use for different organism types and includes guidelines on optimal fill rates. We encourage you to download the complete table, titled “ANTECH Blood/Fluid Culture Ordering Guide for Optimal Organism Recovery” via the link provided below, and display it in your hospital for your staff’s reference.
Click Here to download the complete ANTECH Blood/Fluid Culture Ordering Guide guide.
BD, BacTec™ and Peds Plus™ are trademarks owned by Beckton Dickinson and Company.
MIC Sensitivity Testing at ANTECH: Continuing innovation
Minimum Inhibitory Concentration (MIC) sensitivity testing using the microdilutional technique is the gold standard method for antimicrobial susceptibility testing. To determine an MIC, standardized suspensions of the bacterium being evaluated are incubated with serial concentrations (usually 3 to 6 doubling dilutions) of each antibiotic being evaluated. The lowest concentration of antibiotic that inhibits bacteria from replicating is, by definition, the MIC for that antibiotic. In addition to indicating whether a bacterium is likely to be resistant or susceptible to a particular antibiotic, MIC testing also indicates the relative effectiveness of different antibiotics to which a bacterium is sensitive and guides the recommended dose of each appropriate antibiotic (the higher the MIC relative to its breakpoint, the higher the dose needed and vice versa).
Dosing guidelines. ANTECH’s proprietary dosing guidelines, developed for ANTECH by David Aucoin, DVM, Dipl. ACVCP and author of Target, The Antimicrobial Reference Guide to Effective Treatment, are integrated as a value-added feature within the MIC report -- increasing your chance of treatment success. ANTECH’s Internal Medicine consultants are well versed in MIC result interpretation and can provide further guidance as needed.
New sensitivity panels. ANTECH is expanding its MIC offerings over the next several months to include MIC reporting and dosing guidelines for Staphyloccoci (both methicillin sensitive and methicillin-resistant strains), Enterococci, and Ear pathogens – with better antibiotic choices for these agents. With the rapid increase in methicillin-resistant Staphylococcus pseudintermedius (MRSP) recently seen in companion animal medicine (see article below), the new ANTECH sensitivity panels promise to help practitioners start patients on the best antibiotic sooner and avoid the frustration of needing to call in for additional antibiotic testing.
MRSP + MRSS: Staph species on the move
The emergence of methicillin-resistant Staphylococcus infections continues to grow across the country in both general and specialty small animal practices. Since 2005, when the first methicillin-resistant Staphylococcus aureus (MRSA) was recorded at ANTECH Diagnostics, a number of trends have emerged:
- The culture frequency of Staphylococcus spp. has remained constant at 25% of all organisms.
- Only 3-4% of all Staphylococci cultured from dogs and cats are S. aureus and methicillin-resistant S. aureus (MRSA) makes up less than 1% of all cultured Staphylococci, so MRSA is not the issue!
- Methicillin resistance has spread to the species of Staphylococcus most common in pets; namely, Staphylococcus pseudintermedius (60% of all Staph cultured) and Staphylococcus schelferi subsp. coagulans(15% of all Staph cultured). The frequency of methicillin resistance seen by ANTECH in these two species -– MRSP and MRSS -- has grown 70-80% since 2009 (see graph).
- MRSP and MRSS, unlike MRSA, are commonly multidrug-resistant (MDR) and difficult to treat, with only chloramphenicol and amikacin having dependable sensitivities.
MRSP and MRSS have not been found to carry different toxins or to be more pathogenic than methicillin-sensitive Staphylococci spp; however, this could change if either organism adapts in a manner similar to the so-called “community acquired” form of MRSA found in humans. If certain toxins (superantigens) become more common or are expressed in greater amounts, the pathogenicity of these very common bacteria could become highly problematic in companion animal practice.
How can you curb MRSP and MRSS? Currently, the best approach to stop the spread of these bacteria is by stopping their physical transfer through these easy steps:
- Wash hands (or alcohol wash) frequently.
- Wear gloves when examining patients with obvious skin disease.
- Teach your clients that simple hygiene, not isolation or panic, is all that is needed to stop the spread of methicillin-resistant Staph infections.
Managing Hyperthyroid Cats with Hill’s Prescription Diet y/d Feline Thyroid Health
Recent studies indicate that use of Hill’s® Prescription Diet® y/d™ Feline Thyroid Health -- a newly launched low iodine diet from Hill’s Pet Nutrition -- can result in normalization of T4 levels in hyperthyroid cats, providing a nutritional therapy option for management of this disease1-3. Iodine is an essential component of both T4 and T3; without iodine the thyroid cannot produce thyroid hormones. The low-iodine y/d diet reduces thyroid hormones in cats; it does not cure hyperthyroidism but offers control of the disorder. By 4 weeks, about 75% of hyperthyroid cats exclusively eating y/d will be euthyroid and by 8 to 12 weeks, approximately 90% of cats will be euthyroid. Additional study is needed to determine if the magnitude of T4 concentration affects the time required to become euthyroid.
The main indication for use of the y/d diet would be in cats that are not candidates for definitive treatment of the thyroid tumor(s) with radioiodine or surgery. In addition, nutritional management with y/d food can be considered for cats whose owners are not able to give oral medication and cats that develop side effects with methimazole or carbimazole. The y/d diet represents a new alternative medical treatment for hyperthyroidism that will certainly have advantages over other medical alternatives such as ipodate, herbal extracts, or homeopathic drugs.
Managing Hyperthyroidism in Newly Diagnosed Cats without Renal Disease.
Initial evaluation including CBC, serum chemistries, urinalysis, and total T4 concentration is indicated to confirm the diagnosis and identify concurrent diseases. Most cats transition to the y/d food over 7 days, however some may need longer (several weeks). Initial recheck visits are recommended 4 and 8 weeks after transition to y/d is complete. These visits should include a physical exam, T4 determination, BUN, serum creatinine, and a urine specific gravity. If the T4 level is not in the normal reference range by 8 weeks, another recheck visit should be scheduled 4 weeks later. Long-term rechecks are suggested every 6 months; these should include a physical exam, T4, CBC, serum chemistries, and urinalysis.
Managing Hyperthyroidism in Newly Diagnosed Cats with Concurrent Renal Disease.
If y/d is used to manage cats with concurrent hyperthyroidism and kidney disease, initial rechecks should occur 2, 4, and 8 weeks after transition to y/d is complete. Long-term rechecks should be performed every 3-4 months indefinitely. As with the newly diagnosed cats without renal disease, the initial rechecks should include a physical exam, T4 determination, BUN, serum creatinine, and a urine specific gravity. These are general guidelines only and clinical judgment may be needed to make decisions for individual patients.
Transitioning from Anti-Thyroid Medications to y/d Diet.
Cats already being treated with anti-thyroid medication (most commonly methimazole or carbimazole) can also be transitioned to the y/d diet. However, it is important that the anti-thyroid medication has not been compounded with any substance that contains iodine; extra iodine may interfere with the diet’s ability to lower thyroid hormones. The following transition protocol is recommended:
- A physical exam, CBC, serum chemistries, urinalysis, and T4 determination should be performed at the time of the initial transition to y/d.
- In addition, after starting the diet, immediately decrease the daily medication dose by 50% and discontinue the medication when the cat is eating y/d exclusively for 1-2 weeks.
- Recheck visits should occur at 4 and 8 weeks after transition to y/d is complete, and should include a physical exam, T4 determination, BUN, serum creatinine, and urine specific gravity. If the cat has concurrent kidney disease the initial rechecks should be at 2, 4, and 8 week . The serum T4 is expected to be lower by the first recheck and within the reference range in most cats within 8 weeks.
- Long-term rechecks should be scheduled every 6 months for cats without kidney disease and every 3-4 month for cats with kidney disease.
Again, these are general guidelines and clinical judgment may be needed to make decisions for individual patients. If you need assistance with complicated cases (eg, hyperthyroid cats with concurrent kidney disease), you are encouraged to call the Hill's Veterinary Consultation Service (1-800-548-8387).
- Melendez LM, Yamka RM, Burris PA. Titration of dietary iodine for maintaining normal serum thyroxine concentrations in hyperthyroid cats. ACVIM Forum 2011 (abstract). J Vet Intern Med. 2011;25:683.
- Melendez LM, Yamka RM, ForesterSD et al Titration of dietary iodine for reducing serum thyroxine concentrations in newly diagnosed hyperthyroid cats [abstract]. J Vet Intern Med 2011;25:683
- Yu S, Wedekind KJ, Burris PA et al. Controlled level of dietary iodine normalizes serum total thyroxine in cats with naturally occurring hyperthyroidism [abstract]. J Vet Intern Med 2011;25:283
Hill’s®, Prescription Diet®, and y/d™ are trademarks owned by Hill’s Pet Nutrition, Inc.
© 2011 ANTECH Diagnostics®. All rights reserved.