In vitro activity of meropenem (SM-7338), imipenem, and five other antibiotics against anaerobic clinical isolates

DIAGN MICROBIOLINFECTDIS 1990;13:57-61

57

In vitro Activity of Meropenem (SM-7338), Imipenem, and Five Other Antibiotics Against Anaerobic Clinical Isolates Patrick R. Murray and Ann C. Niles

The in vitro susceptibility of 513 recent anaerobic clinical isolates was evaluated against meropenem (SM-7338), a new carbapenem, and six other antibiotics. Virtually all Gram-positive and Gram-negative anaerobic bacteria tested were susceptible to meropenem (defined as MICs ~ 8 IJ,g/ml) with 99.8% of the isolates inhibited by. <~ 4 txg/ml. The activity of meropehem was comparable to imipenem for most clinical isolates.

Minor differences were observed for Ciostridium and Veillonella (meropenem more active) and other Gram-positive bacilli (imipenem more active). Meropenem inhibited all anaerobes resistant to clindamycm and metronidazole. Bactericidal tests performed with meropenem demonstrated killing activity against all isolates except Clostridium and Lactobacillus.

INTRODUCTION

openem (formerly SM-7338). Substitution of a 5dimethyl carbamoylpyrrolidin moiety in the carbapenem nucleus rendered meropenem resistant to dihydropeptidase hydrolysis (Moellering et al., 1989). Preliminary studies have demonstrated that the antimicrobial activity of meropenem was not abrogated by the biochemical modification of the carbapenem nucleus. Meropenem has a broad spectrum of in vitro activity against Enterobacteriaceae spp., Pseudomonas spp., Haemophilus spp., Neisseria spp., oxacillin-susceptible staphylococci, Streptococcus spp., and selected anaerobes (Bauernfeind et al., 1989; Clarke and Zemcov, 1989; Edwards et al., 1989; Jones et al., 1989a,b; King et al., 1989; Neu et al., 1989; Schito et al., 1989; Sentochnik et al., 1989). In the study reported here, we compared the activity of meropenem with imipenem and five other antibiotics against a diverse collection of anaerobic clinical isolates.

Carbapenem antibiotics, such as imipenem, have a broad spectrum of activity against most bacterial pathogens, in part due to their resistance to beta-lactamase hydrolysis (Barry et al., 1985; Barza, 1985). Unfortunately, many of these antibiotics are hydrolyzed in vivo by renal dihydropeptidase-1, so metabolism can potentially reduce their activity to nontherapeutic levels. This problem can be circumvented by combining the carbapenem with an inhibitor of dihydropeptidase activity such as cilastatin (Kahan et al., 1983). Another approach is the biochemical modification of the carbapenem molecule, the strategy that was used successfully in the development of the new carbapenem, mer-

From the Washington UniversitySchool of Medicine (P.R.M.), and Barnes Hospital ClinicalMicrobiologyLaboratory (P.R.M., A.C.N.), Saint Louis, Missouri. Address reprint requests to: Dr. P. R. Murray, Barnes Hospital Clinical MicrobiologyLaboratory,St. Louis, MO 63110. Received October 10, 1989; revised and accepted November 16, 1989. © 1990 ElsevierScience PublishingCo., Inc. 655 Avenue of the Americas, New York, NJ 10010 0732-8893/90/$3.50

MATERIALS A N D METHODS Organisms A total of 513 anaerobic bacteria isolated within 12 months from clinical specimens submitted to the Barnes Hospital Clinical Microbiology Laboratory were evaluated. Organisms were selected to include

58

P.R. M u r r a y a n d A.C. Niles

a b r o a d r e p r e s e n t a t i o n of all c o m m o n clinical species and w e r e identified by s t a n d a r d laboratory proced u r e s (Allen et al., 1985). All o r g a n i s m s w e r e subcultured a minimal n u m b e r of times before the susceptibility tests w e r e p e r f o r m e d . Selected isolates resistant to clindamycin or m e t r o n i d a z o l e were used to determine the activity of m e r o p e n e m against these p r o b l e m organisms. TABLE 1.

Antibiotics M e r o p e n e m was supplied by ICI Pharmaceuticals G r o u p (Wilmington, Delaware). All other antibiotics used in these studies ( i m i p e n e m , clindamycin, chloramphenicol, piperacillin, cefoxitin, a n d metronidazole) w e r e furnished by their respective m a n ufacturers.

In Vitro Activity of M e r o p e n e m Against Anaerobic Clinical Isolates MIC (p.g/ml)

Organism (No. Tested)

Bacteroides fragilis group (148)

Bacteroides spp. (80)

Fusobacterium spp. (23)

Clostridium perfrin,gens (57)

Clostridium spp. (65)

Peptostreptococcus spp. (72)

Veillonella spp. (15)

Antibiotic Meropenem [mipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem Imipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem Imipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem Imipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem lmipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem Imipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem Imipenem Piperacillin

Range .008-2 .008-1 .06- > 128 <~.004-> 128 .015-8 .06-128 .06-> 128 <~.004-16 <~.004-4 .016->128 ~<.004-> 128 .008->128 .06->128 .06-> 128 <~.004-2 .008-1 ~.004-128 .015->128 .03-16 .015-32 .008->128 ~<.004-. 008 .008-.06 <~.004-4 .008-4 .5-2 .06-1 .06-4 <~.004-4 ~<.0044 <~.004->128 .008->128 .0154 .015->128 .015->128 <~.004-1 ~<.004-.5 <~.004-32 .008-64 .034 .008-8 .03-> 128 <~.004-. 12 .015-.5 .06-64

MICso

MIC~<)

.12 .06

.25 .25

8 .25 2 8 .5 .03 .03 2 .03 1 2 .5 .008 .03 .03 .03 .12 .06 .06 <~.004 .03 .015 .25 1 .25 .5 .25 .5 1 .05 .25 8 .25 .008 .008 .03 .06 .25 .12 .25 .03 .12 16

64 64 4 32 1 .12 .25 32 128 4 64 4 .5 .5 .5 128 4 4 1 <~.004 .06 .06 2 2 .5 1 1 2 4 64 2 64 2 .25 .06 .06 4 2 1 >128 .06 .25 32

Percent Susceptible ~ 100 100 96 84 100 88 97 99 100 95 86 94 89 91 100 100 100 78 100 96 91 100 100 100 93 100 100 100 100 100 98 72 100 71 95 100 100 100 88 100 100 78 100 100 100

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In vitro Activity of M e r o p e n e m

TABLE 1.

Continued MIC (p.g/ml)

Organism (No. Tested)

Lactobacillus spp. (4)

Bifidobacterium spp. (11)

Eubacterium spp. (15)

Actinobacillus spp. (23)

Antibiotic Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem lmipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem lmipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem Imipenem Piperacillin Clindamycin Chloramphenicol Cefoxitin Metronidazole Meropenem Imipenem Piperacillin Clindamycin Chloramphenicol Ce foxi tin Me tron idazole

Range .015--~128 .015-2 .25-4 .12-1 .25-4 .06-1 .12-4 .015-128 4-16 128- ~ 128 > 128 .03-2 .015-.5 <~.004-2 ~.004-.06 .25-2 1-16 .5-4 .008-.25 4.004-.25 .008-16 <.004-.25 .12-2 .015-4 .03->128 ~.004-2 .008-1 .015-32 ~.004-16 .06--4 .008-16 .5- > 128

MIC~ .03 .5 1 .5 4 1 2 .12 4 > 128 > 128 .5 .12 .12 .015 .5 8 2 .12 .015 1 .015 2 1 .5 .06 .03 .5 .06 .25 .12 64

MICg0 .06 1 4 1 -------1 .25 2 .06 2 16 2 .12 .12 8 .25 2 4 32 .25 .06 2 1 2 1 > 128

Percent Susceptible" 93 100 100 100 100 100 100 75 75 0 0 100 100 100 100 100 100 100 100 100 100 100 100 100 87 100 100 100 96 100 100 43

dSusceptibility was defined by current NCCLS standards (M11-T2, 1989): imipenem, 48 ~g/ml; piperacillin ~ 128 ~.g/ml;clindamycin 42 ~g/ml; chloramphenicol ~ 16 tag/ml; cefoxitin <~16 ~g/ml; metronidazole 416 ~.g/ml. lmipenem standards were used for meropenem tests. This is consistent with the pharmacokinetic properties of meropenem (Bax et al., 1989).

Susceptibility Test Methods

RESULTS

MICs a n d MBCs of the s e v e n antibiotics for the test o r g a n i s m s were d e t e r m i n e d by the broth dilution p r o c e d u r e s r e c o m m e n d e d by the National C o m m i t tee for Clinical Laboratory S t a n d a r d s (NCCLS, 1989) and American Society for Microbiology (Sutter, 1985). MIC tests w e r e p e r f o r m e d in broth microdilution trays using Wilkins-Chalgren broth prepared in-house a n d incubation in an anaerobic c h a m b e r for 48 hr. MBC tests w e r e d e t e r m i n e d by the m a c r o b r o t h dilution procedure. Jones a n d G a r d i n e r (1989c) rep o r t e d that m e r o p e n e m , unlike i m i p e n e m ( S h u n g u et al., 1985), is m o r e stable in broths c o m m o n l y used for anaerobic susceptibility testing. Thus, special testing m e t h o d s were u n n e c e s s a r y .

M e r o p e n e m had excellent activity against the anaerobic isolates tested in this study, with 512 (99.8%) of the 513 isolates inhibited by ~ 4 ~g/ml. This activity is c o m p a r a b l e to that seen with i m i p e n e m a n d superior to the other antibiotics tested (Table 1). The MIC values for m e r o p e n e m a n d i m i p e n e m w e r e essentially identical for all m a j o r o r g a n i s m g r o u p s with the exception of Clostridium perfringens a n d other clostridial species a n d Veillonella spp. ( m e r o p e n e m m o r e active) a n d the n o n s p o r e - f o r m i n g G r a m - p o s itive bacilli ( i m i p e n e m m o r e active). Both m e r o p e n e m a n d i m i p e n e m inhibited all 69 clindamycin resistant isolates, including 25 f r o m the Bacteroides fragilis g r o u p (Table 2). Likewise, these

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P.R. Murray and A.C. Niles

TABLE 2.

Activity of Meropenem Against 69 Clindamycin-Resistant Anaerobic Bacteria Range of MIC Values (ixg/ml)

Organism (No. Tested) Bacteroides fragilis group (25) Bacteroides spp. (7) Fusobacterium spp. (5) Clostridium spp. (20) Peptostreptococcus spp. (9) Other anaerobes (3)

Meropenem

lmipenem

0.015-0.5 0.06-2 0.12-2 <~0.004-1 ~0.004-1 0.06-4

0.03-0.5 0.03-4 0.5-1 0.008-4 0.008-0.5 0.03-1

two carbapenem antibiotics were very active against metronidazole-resistant anaerobes (Table 3). The bactericidal activity of meropenem against 34 anaerobic bacteria was measured. MBC:MIC ratio was ~<4 for 13 of 15 B. fragilis group isolates, four of five fusobacteria, zero of five clostridia, two of five peptostreptococci, and three of four lactobacilli. With the exceptions of the Clostridium spp. and Lactobacillus spp., all anaerobic bacteria were killed by <~4 ixg/ml of meropenem (Table 4). However, despite MICs of 0.5-1 lag/ml for five isolates of Clostridium, the meropenem MBCs were t>64 txg/ml. Similarly, the MBCs for three of the four lactobacilli were /> 16 txg/ml.

DISCUSSION Previous studies demonstrated meropenem had excellent activity against most major groups of bacteria. Meropenem inhibited 90% of Enterobacteriaceae at ~0.25 ~,g/ml as well at H. influenzae, Branhamella catarrhalis, and Neisseria gonorrhoeae. Inhibition of methicillin-resistant staphylocci generally required

TABLE 3.

higher concentration of meropenem compared with methicillin-susceptible staphylococci, and meropenem had modest activity against Pseudomonas spp. and Enterococcus spp. Preliminary studies indicated that meropenem had excellent activity against all common groups of anaerobic bacteria (Edwards et al., 1989; Jones et al., 1989b; Neu et al., 1989; Sentochnik et al. 1989), as has also been reported for imipenem (Nasu et al., 1981; Tally and Jacobus, 1983). This is consistent with the data observed herein. Particularly noteworthy was the impressive activity of both carbapenems against clinical isolates resistant to clindamycin (Table 2) or metronidazole (Table 3). A total of 16% of the Bacteroides fragilis group isolates in this study were resistant to clindamycin (MIC />4 }xg/ml), and 3% were resistant to metronidazole (MIC/>32 ixg/ml). All of these isolates were inhibited by <~0.5 txg/ml of meropenem. In view of the excellent in vitro activity of meropenem against both aerobic and anaerobic bacteria, as well as its chemical stability in vivo and in vitro (Jones et al., 1989b), we believe the clinical efficacy of this carbapenem should be examined.

Activity of Meropenem Against 50 Metronidazole-Resistant Anaerobic Bacteria Range of MIC Values (txg/ml)

Organism (No. Tested) Bacteroides fragilis group (5) Bacteroides, other spp. (6) Fusobacterium spp. (2) Clostridium spp. (3) Peptostreptococcus spp. (16) Other anaerobes (18)

Meropenem

Imipenem

0.03-0.5 0.06-4 1-2 0.03-4 <~0.004-1 0.015-4

0.03-0.5 0.015-4 0.5 0.008-2 <~0.004-0.5 0.008-1

In vitro Activity of M e r o p e n e m

TABLE 4.

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Bacteriostatic and Bactericidal Activity of M e r o p e n e m

Organisms (No. Tested) Bacteriodes fragilis group ( 1 5 ) Fusobacterium spp. (5) Clostridium spp. (5) Peptostreptococcus spp. (5) Lactobacillus spp. (4)

MIC (~g/ml)

MBC (~g/ml)

0.03(1)%0.06(3), 0.12(7), 0.25(2), 0.5(2) 0.008(4), 0.06(1) 0.5(4), 1(1) 0.008(3), 0.03(1), 0.06(1) 0.25(1), 4(2), 8(1)

0.06(1), 0.12(1), 0.25(6), 0.5(2), 1(3), 2(1), 4(1) 0.03(3), 0.06(2) 64(4), 128(1) 0.008(2), 0.5(2), 1(1) 1(1), 16(2), 32(1)

aNumber with indicated MIC or MBC in parentheses.

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