Testing of the susceptibility to 12 antimicrobial agents, including P-lactams, aminoglycosides, ciprofloxacin, and erythromycin, was performed by broth microdilution on 78 consecutive clinical isolates of Nocardia asteroides. Surprisingly, a limited number of patterns of susceptibility were identified that included all drug classes, with 95% of isolates exhibiting one of five patterns. One group (17%) exhibited resistance to the broad-spectrum cephalosporins, one group (18%) was susceptible to both ampicillin and erythromycin, one group (17%) was susceptible to ampicillin and carbenicillin but intermediate in susceptibility to imipenem, and the most common group (35%) was resistant to ampicillin but susceptible to the broad-spectrum cephalosporins and imipenem. The most active parenteral agents were amikacin (95%), imipenem (88%), ceftriaxone (82%), and cefotaxime (82%), while the most active oral agents were the sulfonamides (100%), minocycline (100%), and ampicillin (40%). Additional studies are needed to determine whether differences in ,l-lactamases relate to varying Il-lactam resistance and whether taxonomic differences that correlate with the different susceptibility groups can be identified.There have been a number of recent reports of testing of the susceptibility of Nocardia asteroides to newer antimicrobial agents, including the fluorinated quinolones, the carbapenems, broad-spectrum cephalosporins, and various clavulanic acid combinations (1, 3-8, 10, 12, 21). In general, these studies have shown variable degrees of susceptibility to each of these groups of agents. The reason for this variability is unknown, since drug resistance in nocardiae presumably reflects primary (intrinsic) resistance as most infections are acquired from the environment outside the hospital. Whether there are unlimited patterns of resistance or just a few patterns has never been addressed.While performing susceptibility testing of clinical isolates of nocardia, we noted that most isolates of N. asteroides fell into one of four patterns of susceptibility that involved all classes of drugs. Details of these drug patterns and their taxonomic implications are presented. MATERIALS AND METHODSOrganisms. Seventy-eight consecutive isolates of N. asteroides submitted for susceptibility testing to our laboratory were studied. Isolates were identified to species by standard methods (11); the majority of strains were identified by the Mycology Section of the Texas Department of Health, Austin.Susceptibility testing. Susceptibility testing was performed by broth microdilution, using cation-supplemented MuellerHinton broth and 96-well plates that contained 0.1 ml of drug per well. Ampicillin, carbenicillin, cefotaxime, ceftriaxone, imipenem, minocycline, erythromycin, ciprofloxacin, sulfamethoxazole, amikacin, kanamycin, and gentamicin were prepared in twofold dilutions from diagnostic powders and added to the microdilution wells by using the Mini Quick Spense II System (Bellco Glass, Inc., Vineland, N.J.). The plates were stored at -70°C u...

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Bacitracin resistance (bacitracin MIC, >256 g ml ؊1 ) has been reported in Enterococcus faecalis, and in the present study we report on the genetic basis for this resistance. Mutagenesis was carried out with transposon Tn917 to select for E. faecalis mutants with decreased resistance to bacitracin. Two bacitracin-sensitive mutants (MICs, 32 g ml ؊1 ) were obtained and Tn917 insertions were mapped to genes designated bcrA and bcrB. The amino acid sequences of BcrA (ATP-binding domain) and BrcB (membrane-spanning domain) are predicted to constitute a homodimeric ATP-binding cassette (ABC) transporter, the function of which is essential for bacitracin resistance in E. faecalis. The bcrA and bcrB genes were organized in an operon with a third gene, bcrD, that had homology to undecaprenol kinases. Northern analysis demonstrated that bcrA, bcrB, and bcrD were transcribed as a polycistronic message that was induced by increasing concentrations of bacitracin but not by other cell wall-active antimicrobials (e.g., vancomycin). Upstream of the bcrABD operon was a putative regulatory gene, bcrR. The bcrR gene was expressed constitutively, and deletion of bcrR resulted in a bacitracin-sensitive phenotype. No bcrABD expression was observed in a bcrR mutant, suggesting that BcrR is an activator of genes essential for bacitracin resistance (i.e., bcrABD). The bacitracin resistance genes were found to be located on a plasmid that transferred at a high frequency to E. faecalis strain JH2-2. This report represents the first description of genes that are essential for acquired bacitracin resistance in E. faecalis.

Previous studies of Mycobacterium fortuitum identified isolates that did not fit its two recognized biovariants. Eighty-five clinical isolates of this group, the "third biovariant complex", were evaluated. They represented 16% of 410 isolates of M. fortuitum submitted to a Texas laboratory and 22% of 45 isolates in Queensland, Australia. Most infections (76%) involved skin, soft tissue, or bone and occurred after metal puncture wounds or open fractures. Isolates differed from biovar fortuitum in resistance to pipemidic acid and use of mannitol and inositol as carbon sources. Two subgroups were present, and examples were deposited in the American Type Culture Collection. Isolates were resistant to doxycycline and one-third were resistant to cefoxitin. All were susceptible to amikacin, ciprofloxacin, sulfamethoxazole, and imipenem. Surgical debridement combined with drug therapy based on in vitro susceptibilities resulted in cures of cutaneous disease or osteomyelitis. DNA homology studies are needed to determine the taxonomic status of these organisms.

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We examined the effect of introducing type I or IV staphylococcal cassette chromosome mec (SCCmec) elements on the growth yield of Staphylococcus aureus in glucose-limited continuous culture. Type I showed increased glucose consumption and ATP demand per gram of cells synthesized and decreased cell yield compared to those of the parent strain. In contrast, type IV SCCmec elements had no adverse energetic effect.

Avoparcin was used as a feed additive in New Zealand broiler production from 1977 until June 2000. We report here on the effects of the usage and discontinuation of avoparcin on the prevalence of vancomycinresistant enterococci (VRE) in broilers. Eighty-two VRE isolates were recovered from poultry fecal samples between 2000 and mid-2001. VRE isolates were only obtained from broiler farms that were using, or had previously used, avoparcin as a dietary supplement. Of these VRE isolates, 73 (89%) were VanA-type Enterococcus faecalis and nine (11%) were VanA-type Enterococcus faecium. All E. faecalis isolates were found to have an identical or closely related pulsed-field gel electrophoresis (PFGE) pattern of SmaI-digested DNA and were susceptible to both ampicillin and gentamicin. The PFGE patterns of the nine E. faecium isolates were heterogeneous. All VRE contained both the vanA and ermB genes, which, regardless of species or PFGE pattern, resided on the same plasmid. Eighty-seven percent of the VRE isolates also harbored the tet(M) gene, while for 63 and 100%, respectively, of these isolates, the avilamycin and bacitracin MICs were high (>256 g/ml). Five of eight vancomycin-resistant E. faecalis isolates recovered from humans in New Zealand revealed a PFGE pattern identical or closely related to that of the E. faecalis poultry VRE isolates. Molecular characterization of Tn1546-like elements from the VRE showed that identical transposons were present in isolates from poultry and humans. Based on the findings presented here, a clonal lineage of VanA-type E. faecalis dominates in VRE isolated from poultry and humans in New Zealand.

The susceptibility to ciprofloxacin of 548 clinical isolates of rapidly growing mycobacteria belonging to eight subgroups or species was determined. The 170 isolates of Mycobacteriumfortuitum biovar. fortuitum were most susceptible; the MIC for 90% of the organisms was 0.125 ,Ig/ml. The other biovariants of M. fortuitum, M. smegmatis, and the M. chelonae-like organ'isms were less susceptible; the modal MIC was 0.5 ,ig/ml, and the MIC for 90% of organisms was 1.0 ,ug/ml. The two subspecies of M. chelonae were generally resistant, with only 8% of 206 isolates falling in the moderately susceptible category (MIC, 2 gig/ml) and only 2% falling in the susceptible category (MIC, sl ,ug/ml). MICs of ofloxacin averaged 1 to 2 dilutions higher than those of ciprofloxacin for all subgroups tested. Three patients with M. fortuitum cutaneous disease relapsed after an initial response to therapy with ciprofloxacin, and their isolate was shown to have acquired drug resistance.Mutational frequencies for M. fortuitum with ciprofloxacin were relatively high (10-5 to l0-7), and MICs for single-step mutants were similar to those for the clinically resistant strains. Thus, despite the excellent activity of ciprofloxacin against rapidly growing mycobacterial groups other than M. chelonae, single-drug therapy should be used with caution because of the risk of development of mutational resistance.The rapidly growing mycobacteria produce a wide spectrum of clinical diseases. The most common is a localized cutaneous infection that follows open trauma or a puncture wound (18). Optimal therapy for these infections appears to be surgical debridement and antimicrobial therapy based on susceptibility testing (3,17). Drugs that have proven effective in this setting include amikacin, doxycycline, sulfonamides, erythromycin, and cefoxitin (3,15,17).Recent studies have suggested that the newest class of antibiotics-the fluorinated quinolones-has good activity against the rapidly growing mycobacteria, especially Mycobacterium fortuitum and Mycobacterium smegmatis (2,5,12,13,16,21). However, none of these studies included large numbers of isolates, and there have been only three case reports of the clinical use of the newer quinolones as single agents (6, 19; L. W. Rumans and P. G. Anikerholz, Abstr. Annu. Meet. Am. Soc. Microbiol. 1989, U56, p. 164) and one study in which the drug was used in combination (20). We tested the susceptibilities to the quinolones of a large number of isolates of rapidly growing mycobacteria that had been identified to species and subspecies. We report the results of these studies, case studies of four patients with cutaneous infections due to M. fortuitum whose isolates were resistant to ciprofloxacin after drug therapy, and the mutational frequency of isolates of M. fortuitum to ciprofloxacin resistance.( Isolates of M. fortuitum biovar. peregrinum and the unnamed third biovariant complex were separated from isolates of M. fortuitum biovar. fortuitum on the basis of the resistance of M. fortuitum biovar. peregrinum ...