Clinical isolates of Staphylococcus intermedius masquerading as methicillin-resistant Staphylococcus aureus.

Staphylococcus intermedius is a zoonotic organism that can be associated with human disease. We report two separate cases of S. intermedius infection in which a false-positive rapid penicillin binding protein 2a latex test in conjunction with the phenotypic properties of beta-hemolysis and coagulase positivity allowed the clinical isolates to masquerade as methicillin-resistant Staphylococcus aureus. 16S rRNA gene sequencing and the absence of mecA revealed the strains to be methicillin-susceptible S. intermedius.

Convenient selective differential broth for isolation of vancomycin-resistant enterococcus from fecal material.

Studies have shown that vancomycin broth enrichment is superior to direct plating for the detection of vancomycin-resistant enterococcus (VRE), but vancomycin selective broth is not generally commercially available. We developed an easy-to-prepare VRE selective differential broth and compared it to direct plating on bile esculin azide (BEA) agar for the isolation of VRE from fecal samples. A total of 528 consecutive rectal swabs and stools were inoculated onto BEA agar and into BEA broth with vancomycin at a concentration of 15 microg/ml (BEA VAN15 microg/ml broth). After 1 to 2 days of incubation, broths were subcultured to BEA VAN6 microg/ml agar. Bile esculin-positive colonies from the direct and broth subculture plates were evaluated for the presence of VRE by standard microbiological techniques. Addition of the broth enrichment step led to the detection of significantly more VRE isolates than did direct plating alone (28 versus 18 VRE isolates, respectively). In all, 30 VRE strains were isolated from 29 cultures, all of which were Enterococcus faecium. MICs of vancomycin ranged from 32 microg/ml (n = 2) to > 256 microg/ml (n = 28). Twenty-two VRE isolates were available for further testing: sixteen exhibited a VanA phenotype and six were of the VanB phenotype. van genotypes were in agreement with phenotypes for all VRE isolates except one, which could not be genotyped. The broth method also resulted in significantly fewer bile esculin-positive, non-VRE isolates requiring further workup. We have thus developed an easily prepared vancomycin selective differential broth that is significantly more sensitive and specific in the detection of VRE than is direct fecal plating to BEA agar.

NmcA carbapenem-hydrolyzing enzyme in Enterobacter cloacae in North America.

An imipenem-resistant Enterobacter cloacae isolate was recovered from the blood of a patient with a hematologic malignancy. Analytical isoelectric focusing, inhibitor studies, hydrolysis, induction assays, and molecular sequencing methods confirmed the presence of a NmcA carbapenem-hydrolyzing enzyme. This first report of NmcA detected in North America warrants further investigation into its distribution and clinical impact.

Nocardia veterana, a new emerging pathogen.

Nocardia veterana is a newly described species named after the veteran's hospital where it was first isolated. This initial type strain was not thought to be clinically significant. We describe three cases of pulmonary disease attributable to N. veterana: two cases in patients presenting with multiple pulmonary nodules in a setting of immunocompromise and one case of exacerbation of chronic pulmonary disease. The isolates were susceptible to ampicillin, imipenem, gentamicin, amikacin, and trimethoprim-sulfamethoxazole and had reduced susceptibilities to ceftriaxone, cefotaxime, minocycline, and ciprofloxacin. The MICs of amoxicillin-clavulanate were higher than that of ampicillin alone, and the bacteria produced a beta-lactamase detectable only after induction with clavulanic acid. Phenotypically, the isolates could not be characterized beyond the Nocardia genus level. All three isolates were definitively identified as N. veterana by PCR and sequencing of the 16S rRNA gene. On the basis of their susceptibility and restriction enzyme analysis profiles, our findings indicate that they could potentially be misidentified as N. nova. These cases illustrate the pathogenic potential of this newly described species and emphasize the importance of accurate identification of Nocardia isolates to the species level by integrated use of phenotypic and genotypic methods.