References 1. Raj, P. 1994. Classification of the medi-

cally important viruses: DNA viruses. Clin. Microbiol. Newslett. 16:121-124.

2. Bradley, D. W. et al. 1988. Etiological agent of enterically transmitted non-A, non-B hepatitis. J. Gen. Virol. 69:731- 738.

3. Center for Disease Control and Preven- tion. 1994. Emerging infectious dis- eases: Hantavirus Pulmonary Syndrome, United States, 1993. MMWR 43:45--47.

4. Kingsbury, D. W. 1988. Biological con- cepts in virus classification. Intervirol-

ogy 29:242-253.

5. Koonin, E. V. et al. 1992. Computer-as- sisted assignment of functional domains in the non-structural polyprotein of hepatitis E virus: delineation of a new group of animal and plant positive- strand RNA viruses. Proc. Natl. Acad. Sci. USA 89:8259-8263.

6. Mattern, CFT: Structure and classifica- tion of viruses, p. 559-570. In S. Baron (ed.), Medical microbiology, 3rd ed., Churchill Livingstone, New York, 1991.

7. Matthews, R. E. F. 1982. Classification and nomenclature of viruses. Fourth Re- port of the International Committee on

Taxonomy of Viruses. lntervirology 17:1-200.

8. Melnick, J. L. 1991. Structure and clas- sification of viruses, p. 1-23. In R.B. Belshe (ed.), Human virology, 2nd ed. Mosby-Year Book, Inc., St. Louis, MO.

9. Murphy, F. A. and D. W. Kingsbury. 1990. Virus taxonomy, p. 9-35. In BaN. Fields and D.M. Knipe (eds.), Virology, 2rid ed. Raven Press, Ltd., New York.

10. Tam, A. W. et al. 1991. Hepatitis E vi- rus (HEV): molecular cloning and se- quencing of the full-length viral genome. Virology 185:120-131.

Editor ia l

Veterinary Antimicrobial Susceptibility Testing Coming of Age

Joel E. Mortensen, Ph.D. Director of Microbiology St. Christopher's Hospital for Children Philade~Thia, PA 19134

Thomas R. Shryock, Ph.D. Senior Microbiologist Animal Science Discovery and Development Lilly Research Laboratories Eli Lilly and Company Greenfield, IN 46140

Clinical microbiology laboratories in hospitals, clinics, or private settings are accustomed to handling bacterial patho- gens from humans, conducting stand- ardized antimierobial susceptibility testing (AST), and reporting results to physicians. On the other hand, veteri- nary AST (VAST) is conducted by a va- riety of laboratories ranging from the large state-of-the-art (university, state, or private) to a practitioner's back of- flee; all without accepted guidelines or standards. It has been the custom for the more proficient laboratories to follow the existing National Committee for Lalxr- rat t~ Standards (NCCL~) standards, but each may use different modifications of these ~ocedmes to accommodate the fas- tidious pathogens associated with veteri- nary bacteriology. In addition to the discrepancies of media and methods,

the only source of interpretive criteria for determining the susceptibility of vet- exinary pathogens has been developed using human pathogens, pharmacokinet- ics, and clinical trials. These extrapo- lated criteria have led to some confusion when veterinary laboratory re- sults are applied in actual clinical veteri-

nary practice. To address this situation the NCCLS

Area Committee on Microbiology has

recently formed a subcommittee (NCCLS Subcommittee on Veterinary Antimicrobial Susceptibility Testing) to address the unique needs of labora- tories and clinicians dealing with an- timicrobial susceptibility testing of bacteria from cattle, swine, poultry, horses, dogs, and lactating dairy cattle.

The subcommittee was formed in 1993 and comprises representatives from the animal health industry, univer- sity laboratory diagnosticians, test equipment manufactm'ers, government regulatory officials, veterinarY.% and members of the human use AST com- mittee. The VAST subcommittee is charged with the task of developing standards for the performance of AST and rational interpretive criteria for spe- cific antibiotics and animal species, and

assisting government and animal health industry regulatory groups in develop- ing the testing criteria for new as well as for existing antimicrobial agents.

The fast step taken by the subcom- mittee was to develop methodological standards for VAST. It was decided to use the current NCCLS documents for easily grown aerobic Imlhogens such as gram-negative organisms (e.g., pas- teurellae, entcrics) and gnun-positive or- ganisms (e.g., staphylococci and streptococci) as a starting point in devel- oping a tentative document of specific veterinary standards (1, 2). In addition, current working groups are addressing standardization of media and conditions for the growth of fastidious pathogens such as Actinobacillus pleuropneumo- niae (swine respiratory pathogen) and Haemophilus somnus (cattle pathogen). Anaerobic microorganisms, mycobacte- ria, mycoplasma, spirochetes, and agents of minor disease concern have been intentionally excluded at this time. Quality control organisms and antimi- erobial agents used in both human and veterinary medicine are accepted by the subcommittee (e.g., penicillins, erythro- mycin, tetracycline, tested with Ameri- can Type Culture Collection strains);

134 0196-4399/94/$0.00 + 07.00 © 1994 Elsevier Science Inc. Clinical Microbiology Newsletter 16:16,1994

however, animal-use-only antibiotics will need to have specific guidelines supplied by the manufactm'er.

The next major area of concern for the subcommittee has been the develop- ment of appropriate inteqxetive criteria. The VAST has again started with era'- rent NCCLS documents to develop therapeutically useful interpretive crite- ria (3, 4). Three types of data form the basis for these criteria. The first is epidemiologieal. The MIC breakpoint and zone size scattergrams should de- fine boundaries that separate specified populations of relevant isolates into clusters with comparable susceptibili- ties (SJ,R). Second, the pharmacokinet- ics of the antibiotic should demonstrate that achieved levels in body fluids or tis- sue exceed the MIC for the indicated pathogen. Third, the clinical outcome of treatment of the animal should correlate with the MIC breakpoint and zone di- ameter interpretation (i.e., cure and sus- ceptible; failure and resistant). The concepts of epidemiological, pharma- cokinetic, and clinical studies are the ba- sis for interpretive criteria for human medicine as well as veterinary medi- cine. Unlike the situation in human medicine, in veterinary medicine these concepts must be adapted to each indi- vidual animal species. For example, for lactating dairy cow mastitis products, efficacy is based upon the isolation of the pathogen and determining its sus- ceptibility prior to treatment, then sam-

piing milk at various limes post-treat- ment to detect a bacteriologic cm'e. De- termining the exact pharmacokinetics of the compound in mammary gland tis- sue is difficult; however, residue infor- mation based upon the milk concentration at 12 h post-treatment may be sufficient for establishing MIC breakpoints. The correlation of the MIC of the isolate, clinical (animal) out- come, and antimicrobial pharmacokinet- ics serves to establish the validity of the interpretive standards, especially when a statistically valid population of ani- mals is evalua_ted. Establishing in vivo efficacy for bovine respiratory disease could be more difficult as the flora from the easily cultured bovine nasal pas- sages may not be truly representative of the lower respiratory tract pathogen population (5). Obtaining isolates from the lower respiratory tract would re- quire an invasive procedure that could affect disease outcome. In this case, an indirect correlation between the sample population of pathogens that cause bo- vine respiratory disease (although not necessarily from the treated cattle them- selves), pharmacokinetics, and clinical response of treated cattle in a herd are used to set the interpretive criteria.

It is the expectation of the NCCLS VAST subcommittee that these forth- coming standards will provide the vet- erinary practitioner and clinical laboratories a more reliable, stand- ardized basis on which to perform and

interpret AST. By applying the rigorous standards used in human clinical micro- biology settings to the veterinary labora- tory, the end result should be a more rational basis for drag use to improve animal health, and increase safety (food and animal).

References 1. National Committee for Clinical [alxa'a-

tory Standards. 1994. Methods for dilu- tion anfmicrobi~ susceptlq~ility tests for bacteria that grow aembically----thkd edi- tion. Aplroved standard. NCCLS Docu- meat M7-A3. Villanova, PA.

2. National Committee for Clinical Labo- ratory Standards. 1994. Performance standards for antimicrobial disk suscep- tibility tests--fifth edition. Approved standard. NCCLS Doounent M1-AS. Villanova, PA.

3. Watts, J. L. and R. J. Yancey. 1994. An- timicrobial susceptibility testing of vet- erinary pathogens: current methods and future directions. Large Animal Prac- tice, In press.

4. National Committee for Clinical Labo- ratory Standards. 1993. Development of in vitro susceptibility testing criteria and quality control parameters. Ap- proved standard. NCCLS Docmnent M23-A. Villanova, PA.

5. Mechor, G. D., G. K. Jim, and E. D. Janzen. 1988. Comparison of penicillin, oxytetracycline, and trinaethoprim-sul- fadoxine in the treatment of acute undff- fereatiated bovine respiratory disease. Can. Vet. J. 19:438 ~3.

Case Report

Non-Beta-Hemolytic Group A Streptococci Isolated from Abscess

Jasmeet Mangat, B.S. (ASCP)MT Smita Triverdi, B.S. (ASCP)MT Hiroshi Takahashi, B.S. (ASCP)MT Microbiology Department The Permanente Medical Group, Inc. Re- gional Laboratory Berkeley, CA 94710

David Enfield, M.D. Pathology Department Kaiser Foundation Hospital San Francisco, CA 94119

Roger Baxter, M.D. Department of Medicine Kaiser Foundation Hospital Oakland, CA 94611

Although the existence of non-beta- hemolytic group A streptococci has been reported, it is difficult to deter- mine whether the failure of an isolate to demonstrate beta hemolysis is due to cultural factors such as incubation at- mosphere or constituents in the media

(1, 2, 3). We describe here a case in which group A streptococci that failed to demonstrate beta hemolysis was iso- lated from an abscess.

In October 1993, a previously well 15- yr-old Hispanic female with a medical history significant for scoliosis and mild acne vulgaris presented to the Kaiser Foundation Hospital Pe01a~c Clinic in Oakland, California, with an abscess on the proximal phalange of the right in-

Clinical Microbiology Newsletter 16:16,1994 © 1994 Elsevier Science Inc. 0196-4399/94/$0.00 + 07.00 135