, 24 patients in intensive care units at Tisch Hospital, New York, N.Y., were infected or colonized by carbapenem-resistant Klebsiella pneumoniae. Pulsed-field gel electrophoresis identified a predominant outbreak strain, but other resistant strains were also recovered. Three representatives of the outbreak strain from separate patients were studied in detail. All were resistant or had reduced susceptibility to imipenem, meropenem, ceftazidime, piperacillin-tazobactam, and gentamicin but remained fully susceptible to tetracycline. PCR amplified a bla KPC allele encoding a novel variant, KPC-3, with a His(272)3Tyr substitution not found in KPC-2; other carbapenemase genes were absent. In the outbreak strain, KPC-3 was encoded by a 75-kb plasmid, which was transferred in vitro by electroporation and conjugation. The isolates lacked the OmpK35 porin but expressed OmpK36, implying reduced permeability as a cofactor in resistance. This is the third KPC carbapenem-hydrolyzing ␤-lactamase variant to have been reported in members of the Enterobacteriaceae, with others reported from the East Coast of the United States. Although producers of these enzymes remain rare, the progress of this enzyme group merits monitoring.

Ertapenem (MK-0826, L-749,345) is a 1-␤-methyl carbapenem with a long serum half-life. Its in vitro activitywas determined by broth microdilution against 3,478 bacteria from 12 centers in Europe and Australia, with imipenem, cefepime, ceftriaxone, and piperacillin-tazobactam used as comparators. Ertapenem was the most active agent tested against members of the family Enterobacteriaceae, with MICs at which 90% of isolates are inhibited (MIC 90 s) of <1 g/ml for all species. Ertapenem also was more active than imipenem against fastidious gram-negative bacteria and Moraxella spp.; on the other hand, ertapenem was slightly less active than imipenem against streptococci, methicillin-susceptible staphylococci, and anaerobes, but its MIC 90 s for these groups remained <0.5 g/ml. Acinetobacter spp. and Pseudomonas aeruginosa were also much less susceptible to ertapenem than imipenem, and most Enterococcus faecalis strains were resistant. Ertapenem resistance, based on a provisional NCCLS MIC breakpoint of >16 g/ml, was seen in only 3 of 1,611 strains of the family Enterobacteriaceae tested, all of them Enterobacter aerogenes. Resistance was also seen in 2 of 135 anaerobes, comprising 1 Bacteroides fragilis strain and 1 Clostridium difficile strain. Ertapenem breakpoints for streptococci have not been established, but an unofficial susceptibility breakpoint of <2 g/ml was adopted for clinical trials to generate corresponding clinical response data for isolates for which MICs were as high as 2 g/ml. Of 234 Streptococcus pneumoniae strains tested, 2 required ertapenem MICs of 2 g/ml and one required an MIC of 4 g/ml, among 67 non-Streptococcus pyogenes, non-Streptococcus pneumoniae streptococci, single isolates required ertapenem MICs of 2 and 16 g/ml. These streptococci also had diminished susceptibilities to other ␤-lactams, including imipenem as well as ertapenem. The Etest and disk diffusion gave susceptibility test results in good agreement with those of the broth microdilution method for ertapenem.

Three autolytic-defective mutants of Streptococcus faecium (S. faecalis ATCC 9790) were isolated. All three autolytic-defective mutants exhibited the following properties relative to the parental strain: (i) slower growth rates, especially in chemically defined medium; (ii) decreased rates of cellular autolysis and increased survival after exposure to antibiotics which block cell wall biosynthesis; (iii) decreased rates of cellular autolysis when treated with detergents, suspended in autolysis buffers, or grown in medium lacking essential cell wall precursors; (iv) a reduction in the total level of cellular autolytic enzyme (active plus latent forms of the enzyme); (v) an increased ratio of latent to active forms of autolysin; and (vi) increased levels of both cellular lipoteichoic acid and lipids.

GELRITE gellan gum (formerly known as PS-60 and S-60) is a new naturally derived, highly purified polysaccharide which displays several interesting properties, including selfgelling. The suitability of GELRITE as an agar substitute was tested by evaluating the performance of several media selected from among those most commonly used in the isolation, identification, and enumeration of microorganisms in clinical laboratories. Fifty different bacterial species previously implicated in human infections served as test strains. On the basis of the various parameters considered, namely, colony characteristics, biochemical reactions, hemolytic patterns, and plating efficiency, media gelled by agar and by GELRITE compared quite favorably.

Norfloxacin is a new orally absorbed quinoline derivative structurally related to nalidixic acid but showing an expanded antibacterial spectrum which includes Enterobacteriaceae, Pseudomonas aeruginosa, Streptococcus faecalis, and staphylococci, among other susceptible bacterial species. The application of the regression line and error rate-bounded methods of analysis to the minimal inhibitory concentration and zone size data collected on 413 clinical isolates favored the selection of a 10-Ig disk content and the adoption of the following interpretive zone size breakpoints for antimicrobial susceptibility testing with norfloxacin: -17 mm for susceptible, 13 to 16 mm for intermediate, and c12 mm for resistant categories. It is proposed that isolates with minimal inhibitory concentrations of <16 and -32 ,ug/ml be considered susceptible and resistant to norfloxacin, respectively. Differences in the antibiotic disk contents and in vitro antibacterial spectra and pharmacokinetic properties, together with the much lower rates of cross-resistance reported between norfloxacin and related drugs, strongly argue against the use of the "class disk" concept in this instance and suggest that the 10-pg norfloxacin susceptibility disk should be tested separately.Norfloxacin (MK-0366, AM-715) is a new orally absorbed quinoline compound structurally related to nalidixic acid (4, 8). Earlier reports (3-7) have shown the antibacterial spectrum of norfloxacin to include Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter calcoaceticus, Neisseria gonorrhoeae, Ureaplasma urealyticum, Streptococcus faecalis, and staphylococci. Norfloxacin is less active against other streptococci and is practically inactive against anaerobes (7). The broader antibacterial spectrum and increased potency of this compound compared with those of existing analogs and its favorable pharmacological properties (1) have stimulated an interest in the further development of this organic acid as a potentially suitable addition to the current list of antimicrobial agents used in the treatment of urinary tract infections. We report herein a summary of a study intended to define the tentative interpretive guidelines for disk diffusion susceptibility testing with norfloxacin. MATERIALS AND METHODSBacterial spedes. A total of 413 clinically significant isolates comprising 20 different bacterial species were used in the present investigation. These were acquired within the past year as fresh isolates from several medical institutions geographically distributed across the United States. Upon receipt, the identity of each isolate was verified, the antibiogram to common agents was determined, and the organisms were stored at -70°C. The 41 nalidixic acid-resistant cultures used in a later experiment were identified from a collection of approximately 2,000 clinical isolates similarly acquired and handled. Before testing, each frozen culture was regrown in a blood-based agar medium.Antibacterial agents. Test compounds of known potencies were provided as follows: norflox...