This study demonstrates the feasibility of using a pooling strategy to increase capacity and conserve resources during surge testing and periods of enhanced influenza surveillance when the prevalence is low.

We report the isolation and identification of two natural pathogens of Arabidopsis thaliana, Pseudomonas viridiflava and Pseudomonas syringae, in the midwestern United States. P. viridiflava was found in six of seven surveyed Arabidopsis thaliana populations. We confirmed the presence in the isolates of the critical pathogenicity genes hrpS and hrpL. The pathogenicity of these isolates was verified by estimating in planta bacterial growth rates and by testing for disease symptoms and hypersensitive responses to A. thaliana. Infection of 21 A. thaliana ecotypes with six locally collected P. viridiflava isolates and with one P. syringae isolate showed both compatible (disease) and incompatible (resistance) responses. Significant variation in response to infection was evident among Arabidopsis ecotypes, both in terms of symptom development and in planta bacterial growth. The ability to grow and cause disease symptoms on particular ecotypes also varied for some P. viridiflava isolates. We believe that these pathogens will provide a powerful system for exploring coevolution in natural plant-pathogen interactions.

The recommended breakpoints for the cefoxitin disk diffusion test for Staphylococcus aureus were recently modified. In this large-sample study, cefoxitin sensitivity and specificity compared to those of oxacillin were 97.3% and 100%, respectively. This study validated the new cefoxitin breakpoints for the detection of mecAmediated resistance in S. aureus.Staphylococcus aureus is a serious current health care concern. Both community-associated methicillin-resistant S. aureus (MRSA) and health care-associated MRSA are growing threats to the immunocompromised, as well as to the general public. Accurate detection of methicillin resistance in S. aureus is of the utmost importance to ensure effective treatment for the affected patient and to prevent further transmission.The mecA gene confers resistance to methicillin in S. aureus. The gene is located on the staphylococcal chromosome cassette mec and encodes penicillin binding protein 2a (PBP2a). PBP2a is located in the bacterial cell wall and has a low binding affinity for ␤-lactams (1, 2). This study evaluated the new Clinical Laboratory Standards Institute (CLSI) breakpoints for the cefoxitin disk test for determining mecA-mediated resistance in S. aureus (4).CLSI recommends usage of cefoxitin instead of oxacillin when using the disk diffusion method to determine resistance against methicillin for S. aureus (4). Cefoxitin results are easier to interpret and are thus more sensitive for the detection of mecA-mediated resistance than oxacillin results (5, 6, 7, 9-11). The recommended resistance and susceptibility breakpoints for the 30-g cefoxitin disk test used to detect mecA-mediated resistance in S. aureus were changed in January 2007 by CLSI from Յ19 mm and Ն20 mm to Յ21 mm and Ն22 mm, respectively. This study sampled a large number of recent S. aureus isolates to compare the performance of the cefoxitin disk test at the new breakpoints to that of the 1-g oxacillin disk test.Between August and September 2007, a total of 1,611 nonduplicate S. aureus isolates were collected by 53 Wisconsin clinical laboratories (up to 20 consecutive MRSA and methicillin-susceptible S. aureus isolates per laboratory) and submitted to the Wisconsin State Laboratory of Hygiene. Species identification was confirmed by colony morphology, coagulase slide test, subsequent tube test, and biochemicals. The isolation sites of the S. aureus isolates collected were as follows: skin and soft tissue (1,159 isolates; 71.9%), urine (136 isolates; 8.4%), respiratory tract (130 isolates; 8.1%), bloodstream (65 isolates; 4.0%), and other (121 isolates; 7.5%).Susceptibility to antimicrobial agents for confirmed S. aureus isolates was evaluated by the CLSI disk diffusion method on Mueller-Hinton agar (3). All agar plates and antibiotic disks were obtained from Remel (Lenexa, KS). A direct colony suspension of each S. aureus isolate was prepared to a 0.5 McFarland standard and plated on Mueller-Hinton agar. The zones of inhibition were measured using the Biomic V 3 system

Antimicrobial susceptibility testing (AST) of clinical isolates of Nocardia is recommended to detect resistance to commonly used antimicrobial agents; such testing is complicated by difficulties in inoculum preparation and test interpretation. In this study, six laboratories performed repetitive broth microdilution testing on single strains of Nocardia brasiliensis, Nocardia cyriacigeorgica, Nocardia farcinica, Nocardia nova, and Nocardia wallacei. For each isolate, a total of 30 microdilution panels from three different lots were tested at most sites. The goal of the study was to determine the inter-and intralaboratory reproducibility of susceptibility testing of this group of isolates. Acceptable agreement (>90% agreement at ؎1 dilution of the MIC mode) was found for amikacin, ciprofloxacin, clarithromycin, and moxifloxacin. After eliminating MIC values from single laboratories whose results showed the greatest deviation from those of the remaining laboratories, acceptable agreement was also found for amoxicillin-clavulanic acid, linezolid, minocycline, and tobramycin. Results showed unsatisfactory reproducibility of broth microdilution testing of ceftriaxone with N. cyriacigeorgica and N. wallacei, tigecycline with N. brasiliensis and N. cyriacigeorgica, and sulfonamides with N. farcinica and N. wallacei. N. nova ATCC BAA-2227 is proposed as a quality control organism for AST of Nocardia sp., and the use of a disk diffusion test for sulfisoxazole is proposed as a check of the adequacy of the inoculum and to confirm sulfonamide MIC results. N ocardia species are ubiquitous in the environment and have been implicated in a variety of human infections, especially in immunocompromised patients. In these patients, infection most frequently begins in the lungs, but can quickly disseminate to nearly every organ of the body. Nocardia can also cause disease in the immunocompetent host, in whom it is usually introduced through traumatic injury (2).Nocardia species are known to vary in their susceptibilities to various antimicrobial agents, and some species, especially Nocardia farcinica and members of the Nocardia transvalensis complex, have been shown to be particularly resistant to commonly used antimicrobial agents. Therefore, susceptibility testing should be performed on any Nocardia isolate considered to be of possible clinical significance.In 2003, the Clinical and Laboratory Standards Institute (CLSI) published an approved standard (M24A) for susceptibility testing of mycobacteria, nocardiae, and other aerobic actinomycetes, which specifies the broth microdilution method as the recommended procedure for susceptibility testing of aerobic actinomycetes (6). This document has recently been updated (5). Several years of experience in testing Nocardia isolates at the University of Texas Health Science Center and at the National Institutes of Health have demonstrated difficulties that may occur in inoculum preparation due to the propensity for clumping demonstrated by these organisms. In addition, determination of susc...

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