In vitro susceptibility of Campylobacter fetus subsp. jejuni to N-formimidoyl thienamycin, rosaramicin, cefoperazone, and other antimicrobial agents.

The activities of 11 antimicrobial agents against 36 strains of Campylobacter fetus subsp. jejuni were studied by a broth microdilution method. All strains were susceptible to 7 of the 11 antimicrobial agents. Of the newer agents tested N-formimidoyl thienamycin (MK0787) and rosaramicin had very good activity, whereas cefotaxime, moxalactam, and cefoperazone had poorer activity.

The activities of 11 antimicrobial agents against 36 strains of Campylobacter fetus subsp. jejuni were studied by a broth microdilution method. All strains were susceptible to 7 of the 11 antimicrobial agents. Of the newer agents tested Nformimidoyl thienamycin (MK0787) and rosaramicin had very good activity, whereas cefotaxime, moxalactam, and cefoperazone had poorer activity.
Enteric and disseminated diseases caused by Campylobacter fetus subsp. jejuni are being reported in increasing numbers, and the spectrum of pathology due to this bacterium is expanding (3,6,8,9,13). The current drug of choice, based only on in vitro data, is erythromycin, although tetracycline, gentamicin, and chloramphenicol have also been used successfully (6). This study was done to determine whether there has been any change in the pattern of susceptibility of C. fetus subsp. jejuni to certain established antibiotics and to evaluate the activity of some newer antimicrobial agents, namely, N-formimidoyl thienamycin (MK0787), rosaramicin, and cefoperazone, against this bacterium.
A total of 36 strains of C. fetus subsp. jejuni were studied, and they consisted of 20 obtained from patients with diarrhea and 16 from the rectal contents of chickens. All strains were isolated by filtration technique (4) or by direct plating of stool specimens onto selective media (BBL Microbiology Systems, Cockeysville, Md; Oxoid Ltd., Columbia, Md; Scott Laboratories, Inc., Fiskeville, R.I.). Typical colonies were picked off and identified to subspecies level as described by Grant et al. (4).
The antimicrobial agents tested were N-formimidoyl thienamycin (Merck & Co., Inc.   the MICgo was 0.5 jtg/ml for both drugs. All but two strains were inhibited by 0.5,ig of erythromycin per ml, and all strains were susceptible to 0.5 Ag of gentamicin per ml. Cefotaxime, ampicillin, and chloramphenicol had lower activity, with MIC5o's of 2 ,ug/ml and MICOgo's of 4.0 ,ug/ml. With 4 j,g/ml inhibiting all strains, cefotaxime was the most active in this group. Moxalactam had an MIlso of 16 ,ug/ml, showing only slight activity against most strains. Rifampin, cefoperazone, and vancomycin did not inhibit any strains at a concentration of 128 ,ig/ ml. N-Formimidoyl thienamycin demonstrated the highest activity against C. fetus subsp. jejuni in this study, confirming earlier reports of overall superior activity of the thienamycin antibiotics in comparison with established antimicrobial agents and the newer cephalosporin or cephamycin antibiotics with an expanded gram-negative antibacterial spectrum (7; H. C. Neu and P. Labthavikul, Program Abstr. Intersci. Conf. Antimicrob. Agents Chemother. 20th, New Orleans, La., abstr. no. 260, 1980). The clinical significance of this in vitro finding awaits further investigation. Rosaramicin also showed very good activity and appeared better than erythromycin, an observation that has been made of the activity of the two drugs against several species (12). Thus rosaramicin is potentially an alternative NOTES 851 drug (with superior activity) to erythromycin, which is currently the recommended drug for C. fetus subsp. jejuni enteritis (6).
The activities of gentamicin and cefotaxime were judged good from our results and compared favorably with the results of other investigators (10). In this study ampicillin and chloramphenicol inhibited over 90% of the strains tested at concentrations that are easily achievable in the blood. Previous studies have shown the activity of ampicillin to range from good (1) to poor (5) in vitro and similarly variable in vivo (2,11).
The high MIC9o's of moxalactam would appear to preclude its use for C. fetus subsp. jejuni infections in spite of the good serum concentrations achievable by parenteral administration of this drug. All of the newer antibiotics had good activity against C. fetus subsp. jejuni in this study, with the exception of cefoperazone. Their clinical usefulness remains to be confiumed.