(25,27). This resistance has been attributed to slow hydrolysis mediated by 1-lactamase (33) or diminished penetration of these agents across the bacterial outer membrane (3, 21, 26) or both.Plasmid-mediated P-lactamases conferring resistance to the newer cephalosporins were first detected in gram-negative bacilli in Europe in 1983 (15). Resistant organisms harboring a variety of these enzymes carried on transferable plasmids have been isolated with increasing frequency in Europe over the past several years (5,7,11,13,14,23,29,31,34). Two well-described 3-lactamases in this class from France include a cefotaxime-hydrolyzing enzyme denoted CTX-1, or TEM-3, and a ceftazidime-hydrolyzing enzyme designated CAZ-1, or 23,30). Another ceftazidime-hydrolyzing enzyme, RHH-1, was identified in England in 1987 (31). The occurrence of a similar enzyme in the United States has only recently been reported in a preliminary communication from

The broad host range antibiotic resistance plasmid pAM,B1 was transferred from Streptococcus faecalis to 9 of 15 Listeria monocytogenes strains by conjugation. L. monocytogenes transconjugates could transfer the plasmid either among L. monocytogenes strains or back to S. faecalis. Transfer between the various strains occurred without any detectable plasmid DNA rearrangements. The pAMP1 replicon was stable in L. monocytogenes-it was retained without antibiotic selection when the bacteria were grown in culture media or passed in mice-and the presence of pAMP1 had no major effect on L. monocytogenes virulence. These data suggest that pAM,B1 or its derivatives might serve as useful L. monocytogenes cloning vehicles. The data presented also demonstrate that pAMP1 is compatible with two different native L. monocytogenes plasmids and that Listeria species harbor native plasmids in addition to the 38.5-megadalton plasmid pRYC16 previously reported by Perez-Diaz et al. (J. C. Perez-Diaz, M. F. Vicente, and F. Banquero, Plasmid 8:112-118, 1982). Of 29 L. monocytogenes strains screened, 7 contained plasmid DNA. Four strains had similar if not identical plasmids that were 34 megadaltons in size, whereas three other strains contained either a 53-, 44-, or 32-megadalton plasmid; none of these plasmids has the same restriction pattern as pRYC16. DNA homology experiments indicate that the various plasmids are related and suggest that there may be a common set of sequences present in all of the plasmids examined.

An epidemic of nosocomial ceftazidime-resistant Klebsiella pneumoniae was correlated with production of a ceftazidime-hydrolyzing enzyme with an isoelectric point of 5.6 (BMH-1). BMH-1 was encoded on a large transferable plasmid conferring multiple antibiotic resistance. The gene that encodes BMH-1 was identical to the gene that encodes the TEM-26 extended-spectrum beta-lactamase.

The in vitro activities of a new catechol-containing monobactam, BMS-180680 (SQ 84,100), were compared to those of aztreonam, ceftazidime, imipenem, piperacillin-tazobactam, ciprofloxacin, amikacin, and trimethoprim-sulfamethoxazole. BMS-180680 was often the most active compound against many species of the family Enterobacteriaceae, with MICs at which 90% of the isolates were inhibited (MIC90s) of < or = 0.5 microg/ml for Escherichia coli, Klebsiella spp., Citrobacter diversus, Enterobacter aerogenes, Serratia marcescens, Proteus spp., and Providencia spp. BMS-180680 had moderate activities (MIC90s of 2 to 8 microg/ml) against Citrobacter freundii, Morganella morganii, Shigella spp., and non-E. aerogenes Enterobacter spp. BMS-180680 was the only antibiotic evaluated that was active against >90% of the Pseudomonas aeruginosa (MIC90, 0.25 microg/ml), Burkholderia cepacia, and Stenotrophomonas maltophilia (MIC90s, 1 microg/ml) strains tested. BMS-180680 was inactive against most strains of Pseudomonas fluorescens, Pseudomonas stutzeri, Pseudomonas diminuta, and Burkholderia pickettii. BMS-180680 was moderately active (MIC90s of 4 to 8 microg/ml) against Alcaligenes spp. and Acinetobacter lwoffii and less active (MIC90, 16 microg/ml) against Acinetobacter calcoaceticus-Acinetobacter baumanii complex. BMS-180680 lacked activity against gram-positive bacteria and anaerobic bacteria. Both tonB and cir fiu double mutants of E. coli had greatly decreased susceptibility to BMS-180680. Of the TEM, PSE, and chromosomal-encoded beta-lactamases tested, only the K1 enzyme hydrolyzed BMS-180680 to any measurable extent. Like aztreonam, BMS-180680 bound preferentially to penicillin-binding protein 3. The MICs of BMS-180680 were not influenced by the presence of hematin or 5% sheep blood in the test medium or with incubation in an atmosphere containing 5% CO2. BMS-180680 MICs obtained under strict anaerobic conditions were significantly higher than those obtained in ambient air.

A gene, designated msp, that encodes a major secreted polypeptide with a molecular mass of approximately 60 kilodaltons (kDa) was cloned from Listeria monocytogenes 10403. DNA hybridization analysis indicated that the msp gene was highly conserved among 15 independent L. monocytogenes isolates and that each of 5 isolates tested secreted a 60-kDa polypeptide that was immunologically related to the msp gene product. DNA sequences related to msp were not detected in any other Listeria species or in strains of Bacillus cereus, Bacillus thuringiensis, Streptococcus pyogenes, or Streptococcus pneumoniae when standard stringent DNA hybridization conditions were used. Under nonstringent conditions, related sequences were detected in Listeria ivanovii, Listeria seeligeri, and Listeria innocua, and immunoblot analysis indicated that these strains secreted polypeptides of about 60 kDa that were immunologically related to the msp gene product. The possibility of using the msp gene as a probe for the detection of L. monocytogenes and the potential functions of the msp gene product are discussed.