Against Aerobic Gram-Negative Bacilli

ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Dec. 1979, p. 6-6 0066-0/79/1-06/05$0.00/0 Vol., No. 6 In Vitro Activity of LY17935, a New 1-Oxa Cephalosporin, Against Aerobic Gram-Negative Bacilli DENNIS G. DELGADO, CARMEN J. BRAU, C. GLENN COBBS, AND WILLIAM E. DISMUKES* Division of Infectious Diseases, Department ofmedicine, The University ofalabama School ofmedicine, Birmingham, Alabama 359 Received for publication 10 September 1979 A total of 3 clinical aerobic gram-negative bacillary isolates were tested against LY17935, a new 1-oxa cephalosporin, and compared with other cephalosporins, penicillins, and aminoglycosides by a broth microdilution technique. (HR756), a new semisynthetic cephalosporin, and LY17935 were more active, and showed lower minimun inhibitory concentrations (rantes, -O.1 to.0,ug/ml), than cefamandole, cefoxitin, and cefazolin against Escherichia coli, Klebsiella spp., Enterobacter spp., Proteus mirabilis, indole-positive Proteus spp., Serratia marcescens, Providencia spp., and Citrobacter spp. Against P. aeruginosa, piperacillin, azlocillin, and mezlocillin were the most active betalactam agents; 6,ug/ml inhibited 99, 93, and 7%, of the isolates, respectively. LY17935 and cefotaxime at,ug/ml inhibited 71% of Pseudomonas isolates, whereas the aminoglycosides gentamicin, tobramycin, and amikacin at a concentration of,ug/ml inhibited,, and 93%, respectively. Minimum bactericidal concentrations were determined for all isolates and were generally the same as the minimum inhibitory concentrations. LY17935 is a new parenteral semisynthetic facturers: LY17935, cefamandole, and tobramycin by Eli Lilly and Co.; carbenicillin and 1-oxa cephalosporin antibiotic which has been shown in preliminary in vitro testing to be highly ticarcillin by Beecham Laboratories; azlocillin active against gram-negative microorganisms including Pseudomonas aeruginosa and Enterotion; piperacillin by Lederle Laboratories; ami- and mezlocillin by Delbay Research Corporabacteriaceae resistant to other cephalosporins kacin by Bristol Laboratories; cefazolin by and cephamycins (). The purpose of this study Smith, Kline, and French Laboratories; cefoxitin was to determine the comparative in vitro susceptibility of 3 clinical gram-negative bacillary ratories; and cefotaxime (HR756) by Hoechst- by Merck, Sharp, and Dohme Research Laboisolates to LY17935 and nine other antimicrobial agents. Determination of MICs. Minimum inhibi- Roussel Pharmaceuticals, Inc. Microorganisms. A total of 3 clinical tory concentrations (MICs) were determined by gram-negative bacillary isolates were tested. All a microdilution technique as described by Barry isolates were obtained from patients at University Hospital, the Birmingham Veterans Adminler-Hinton broth. With calibrated pipettes, 50 (1). Antibiotic dilutions were prepared in Muelistration Hospital, and Baptist Montclair Hospital, Birmingham (kindly supplied by Kather- each well of a U-shaped microtiter plate (Dy-,ul of each antibiotic dilution was transferred to ine Hunter). Isolates of all species except three natech, Inc., Alexandria, Va.), with resulting final antibiotic concentrations ranging from 0.1 represented recent consecutive clinical isolates from different patients. Some strains of Pseudomonas aeruginosa, Serratia marcescens, and Organisms to be tested were picked from nu- to 6 ug/ml. Acinetobacter calcoaceticus had been stored trient agar slants and suspended in 1 ml of frozen and were included to provide an evaluation of LY17935 against known multiresistant tion at 37 C, the cultures were adjusted to 10' Mueller-Hinton broth. After overnight incuba- strains. The isolates were maintained on nutrient agar slants (BBL Microbiology Systems, Farland standard and then diluted 1:1,000 with colony-forming units per ml with a Mc- Cockeysville, Md.) at room temperature during Mueller-Hinton broth. A 0.05-ml amount of the testing, and stock cultures were frozen in skim culture dilution was added to each well of the milk at -600C. microtiter plate, resulting in a final inoculum of Antibiotics. Sterile standardized powders 5 x 10 colony-forming units per ml. were kindly provided by their respective manu- The microtiter plates were incubated for 1 h 6 Downloaded from http://aac.asm.org/ on August 6, 01 by guest

VOL., 1979 at 370C. The MIC was defined as the lowest concentration of antibiotic that inhibited visible growth. Determination of MBCs. The minimum bactericidal concentrations (MBCs) of the antibiotics were determined by subculturing pl of the broth from each well exhibiting no visible growth onto a culture plate of Mueller-Hinton agar with a replicator-type inoculator similar to that described by Zinner (5). After overnight incubation at 370C, the MBCs were defined as the lowest concentration of antibiotic yielding less than five colonies, i.e., the concentration at which at least 99.9% of the bacteria were rendered nonculturable. The MBCs were either equal to or no more than twofold greater than the MICs for all of the isolates tested; accordingly, the detailed MBC data are not included. Microdilution studies. The activity of LY17935 against 3 gram-negative bacillary isolates was compared with that of cefotaxime, cefamandole, cefoxitin, cefazolin, carbenicillin, ticarcillin, gentamicin, tobramycin, and amikacin. The 75 P. aeruginosa isolates were also tested against piperacillin, azlocillin, and mezlocillin. The results of these studies are shown in Table 1. LY17935 and cefotaxime inhibited strains of Escherichia coli at lower concentrations than did any of the other cephalosporins or cephamycins tested. For example, 6 and 9% of the E. coli isolates were inhibited by 50.1 ug of LY17935 and cefotaxime per ml, respectively. Similarly, these two agents were the most active of the beta-lactam antibiotics against Kiebsiella pneumoniae, Kiebsiella oxytoca, Enterobacter aerogenes, Enterobacter cloacae, Proteus mirabilis, and indole-positive Proteus spp. Against P. aeruginosa, piperacillin, azlocillin, and mezlocillin were the most active beta-lactam agents; at a concentration of 6,ug/ml, these agents inhibited 99, 93, and 7% of the isolates, respectively. LY17935 and cefotaxime showed activity comparable to that of carbenicillin and ticarcillin, inhibiting 71% of the isolates at a concentration of,ug/ml. None of the other cephalosporins or cephamycins inhibited these organisms at concentrations below 6,g/ml. was the most active aminoglycoside against these isolates. Twenty-two isolates of P. aeruginosa were resistant to LY17935 (MIC >,ug/ml). Of these, five may have been progeny of the same strain as determined by susceptibility patterns. LY17935 and cefotaxime were several-fold more active against S. marcescens than any of the other antibiotics tested; ug of LY17935 or cefotaxime per ml inhibited 90% of the strains. and cefamandole were the next most NOTES 65 active beta-lactams; a concentration of,ug/ml inhibited and 70% of the isolates, respectively. and carbenicillin were the most active beta-lactam antibiotics against A. calcoaceticus: a concentration of 3 pug/ml inhibited 9 and % of the isolates, respectively. and LY17935 were the next most active; pg/ml of either drug inhibited 5 and %, and 3,ug/ ml inhibited 9 and 9% of the strains, respectively. Against Providencia spp., cefotaxime and LY17935 showed the greatest antibacterial activity among the beta-lactam drugs; 1 pug of cefotaxime and ug of LY17935 per ml inhibited 100% of the isolates, respectively. was more active than either cefamandole or cefazolin. had the greatest activity against Citrobacter spp.; a concentration of,ug/ml inhibited 69% of the strains, and,ug/ml inhibited 1%. LY17935, cefamandole, and cefoxitin showed comparable activity; a concentration of ug of each of these antibiotics per ml inhibited 1, 75, and 69% of the strains, respectively. In summary LY17935 is highly active against aerobic gram-negative microorganisms, including P. aerugnosa and Enterobacteriaceae resistant to other cephalosporins and cephamycins., another new cephalosporin, has been shown to inhibit aerobic gram-negative bacteria at concentrations much lower than those required by other cephalosporins (, 3). Neu et al. () compared the activity of LY17935 with other beta-lactam compounds and noted that it had equal or slightly less activity than cefotaxime against members of the Enterobacteriaceae, but - to 3-fold more activity than the other cephalosporins against these same organisms. LY17935 was twofold more active than cefotaxime and fourfold more active than carbenicillin and ticarcillin against P. aeruginosa. LY17935 and cefotaxime were equally active against S. marcescens. Neu et al. also showed that LY17935 had significant activity against other gram-negative bacteria, including Bacteroides spp., Haemophilus influenzae, and Neisseria gonorrhoeae and against gram-positive cocci including staphylococcal and streptococcal organisms (). In the present study, LY17935 and cefotaxime were more active than cefazolin, cefamandole, and cefoxitin against all the aerobic gramnegative isolates tested. In the lower MIC ranges, i.e., so.5 pg/ml, cefotaxime was slightly more active than LY17935 against K. pneumoniae and E. aerogenes, and these two new cephalosporins had equal activity against E. coli, K. oxytoca, E. cloacae, P. mirabilis, indole-positive Proteus spp., and Providencia spp. In contrast Downloaded from http://aac.asm.org/ on August 6, 01 by guest

66 NOTES ANTimICROB. AGENTS CHEMOTHER. TABLE 1. In vitro activity of LY17935 againt aerobic gram-negative bacili compared with other cephalosporum penicillins, and aminoglycosides Organism (no. of strains) Antibiotic Range of MIC (jag/mi) 50% MIC (ug/ml) 90% MIC (jg/mi) E. coli (50) LY17935 50.1-1 so.1 so.1- so.1 s0.1-6 1- - - 1- -3-1-3 K. pneumoniae (5) LY17935 c0.1-1 s0.1- c0.1-1 6-3 - 6 - - - - 1 - K. oxytoca (5) LY17935 c0.1- so.1 so.1- -O.1-6 1- - 6- Ticarchllin 3- - - 1-1 E. aerogenes (5) LY17935 50.1-6 SO.1-1 50.1 1-3 - 3-3 - TiccilHin - 1- - 1-3 E. cloacae () LY17935 s0.1-50.1- - 3 - - - 3-3 - 1-1 -6 P. mirabilis (50) LY17935 50.1-50.1 0.1 50.1-50.1 50.1-1 - 1-6 3 Downloaded from http://aac.asm.org/ on August 6, 01 by guest

VOL., 1979 NOTE3S 6B7 TABLE-continued Organism (no. of straim) Antibiotic Range of MIC (pg/ml) 50% MIC (jg/ml) 90% MIC (pg/ml) s0.1-1 1 S0.1-1 1 - - -3 Proteus spp. (30) (indole-positive) 50.1-1 C0.1 C0.1 LY17935 0O.1-1 C0.1 1-1-3 - - 11-6 -6-1 -6 P. aeruginosa (75) LY17935 - - 6 6- - 6-3 Piperacillin - 3 Azlocillin - 3 Mezlocilhin - - 0.1- -6 S. marcescens (50) LY17935 - C0.1- _0.1 - - 6- CarbeniciUin - 1- - 1 3 - -6 A. calcoaceticus (50) LY17935 1-6 3 3-6 3 3-6 - 6 - CarbeniciUin - 6-3 -6 1-6 1-6 Providencia spp. () LY17935 50.1- -1 1-3 - 6- CarbeniciUlin - 11 - -3-6 3 - Downloaded from http://aac.asm.org/ on August 6, 01 by guest

6 NOTES TABLE 1. Continued Organism (no. of strains) Antibiotic Range of MIC (,ug/ml) 50% MIC (pg/ml) 90% MIC (ug/ml) Citrobacter spp. () LY17935-1 - - 1 3-6- 6 6 - - - 1-1 Amilcacin 1- to the data reported by Neu et al. (), our results showed that cefotaxime in the lower MIC ranges had greater activity than LY17935 against S. marcescens, and at a concentration of,ug/ml LY17935 and cefotaxime had equivalent activity against P. aeruginosa (71% of Pseudomonas isolates were inhibited by both agents). Our in vitro results indicate that (i) LY17935 has significant antibacterial activity against the clinically important Enterobacteriaceae and the nosocomial nonfermentative gram-negative pathogens, P. aeruginosa and A. calcoaceticus; (ii) the activity of LY17935 and cefotaxime against aerobic gram-negative bacilli is similar, and (iii) the activity of both LY17935 and cefotaxime against aerobic gram-negative bacilli exceeds that of three of the more recently introduced cephalosporins, namely, cefazolin, cefoxitin, and cefamandole. This work was supported in part by Eli Lilly Research Laboratories grant 0D. ANTIMICROB. AGENTS CHEMOTHER. James A. Hafner of I:li Lilly was of continuous help to us. Thanks are also due to Rebecca Cooper and Deborah Duke for secretarial assistance. LITERATURE CITED 1. Barry, A. L. 1976. Broth dilution techniques, p. 9-10. In The antimicrobic susceptibility test: principles and practice. Lea and Febiger, Philadelphia.. Hamilton-Miller, J. M. T., W. Brumfitt, and A. V. Reynolds. 197. (HR756), a new cephalosporin with exceptional broad spectrum activity in vitro. J. Antimicrob. Chemother. :37-. 3. Neu, H. C., N. Awapokee, P. Aswapokee, and K. P. Fu. 1979. HR756, a new cephalosporin active against gram-positive and gram-negative aerobic and anaerobic bacteria. Antimicrob. Agents Chemother. 15:73-1.. Neu, H. C., N. Aswapokee, K. P. Fu, and P. Aswapokee. 1979. Antibacterial activity of a new 1-oxa cephalosporin compared with that of other,-lactam compounds. Antimicrob. Agents Chemother. :11-19. 5. Zinner, S. H. 1975. New aminoglycoside antibiotics for use against pseudomonas and klebsieila, p. 109-1. In J. Klastersky (ed.), Clinical use of combinations of antibiotics. John Wiley and Sons, New York. Downloaded from http://aac.asm.org/ on August 6, 01 by guest