ANTMCROBAL AGENT AND CHEMOTHERAPY, Feb., p. 8-8 Copyright American ociety for Microbiology Vol., No. Printed in U..A. n Vitro Antimicrobial usceptibility of Anaerobic Bacteria solated from Clinical pecimens WLLAM J. MARTN, MLDRED GARDNER, AND JOHN A. WAHNGTON Mayo Clinic and Mayo Foundation, Rochester, Minnesota 90 The minimal inhibitory concentrations of clinical isolates of anaerobic bacteria to 0 different antimicrobial agents were determined by an agar-dilution technique. Nearly all strains were resistant to kanamycin and gentamicin, although moderate activity to both drugs was noted with Fusobacterium sp., anaerobic cocci, some strains of Bacteroides melaninogenicus, and nonsporeforming gram-positive bacilli. Chloramphenicol at.,ug/ml inhibited all but three of the strains tested. Tetracycline at 6.,ug/ml had high activity against all groups tested, with the exception that only 9% of strains of Bacteroidesfragilis were inhibited at this concentration. Excluding certain species of Bacteroides, the majority of anaerobes were inhibited by penicillin at.,ug/ml or less and by cephalothin at.,ug/ml or less. Lincomycin at 6.,ug/ml or less was active against nearly all strains. Erythromycin at a concentration of.,ug/ml was active against B. fragilis; however, erythromycin was less active against the other groups. Most of the minimal inhibitory concentrations of lincomycin exceeded those of clindamycin by fourfold; Rifampin inhibited virtually all strains at. /Ag/ml. The increasing recognition of the role of anaerobic bacteria in infections has made it necessary for the clinician to become familiar with the classification and nomenclature of this large group of organisms. n contrast to the clinically significant aerobic and facultatively anaerobic bacteria, the fastidious nature of the anaerobic bacteria precludes the prompt performance of antimicrobial susceptibility tests. Therefore, appropriate antimicrobial therapy is contingent on awareness of the possibility of infection by anaerobic bacteria and familiarity with susceptibility patterns of these bacteria. This report presents the minimal inhibitory concentrations (MC) of clinical isolates of anaerobic bacteria to 0 different antimicrobial agents. n addition, the minimal bactericidal concentrations (MBC) of several antibiotics against isolates of Bacteroides fragilis from blood will be presented. MATERAL AND METHOD All anaerobic bacteria tested represented isolates from clinical material submitted to the ection of Clinical Microbiology during portions of an 8-month period beginning in November 0 [for the total experience during this period, with classification by specimen source and species isolated, see report by Martin (6)]. ubcultures of anaerobic bacteria were made at the time of initial isolation and stored at Presented at the Eleventh nterscience Conference on Antimicrobial Agents and Chemotherapy. Atlantic City, N.J., 9 to October. - C according to the methods described by Dowell and Hawkins (). The strains examined in this study were selected primarily on the basis of source and frequency of isolation. n this laboratory, all specimens, other than those from the throat, sputum, vagina, stomach, urine, and stool, are examined routinely for the presence of anaerobes; anaerobic cultures are performed on other specimens only by special request. Antimicrobial susceptibility testing was performed, with certain modifications, by the method of Finegold et al. (), by using the agar-dilution technique and the inocula-replicator device of teers et al. (8). solates were incubated anaerobically for 8 hr in thioglycolate medium (-C, BBL) enriched with sterile rabbit serum and, when necessary, with menadione. The broth culture was diluted to provide an inoculum of 0 to 06 colony-forming units on the surface of the agar. erial twofold dilutions of antibiotics were incorporated in brain-heart infusion (BH) agar (BBL) with % sheep blood so as to yield final concentrations ranging from 0. to,ug/ml. These plates were prepared on the day before the test and stored overnight at room temperature, rather than at C, to prevent the increased oxygen absorption which occurs at refrigerator temperatures. After inoculation, all plates were incubated, including controls with known MC values, in an anaerobic incubator (National Appliance Co., Portland, Ore.) at 7 C using the GasPak (BBL) modification described by Gardner and Martin (8). The MC, which was determined after 8 hr of incubation, was defined as the lowest concentration permitting no growth, a barely visible fine haze, or not more than one discrete colony (). The MBC of six antibiotics against strains of B. 8 Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest
VOL., N VTRO ANTMCROBAL UCEPTBLTY 9 fragilis isolated from blood were determined in the following manner. Twofold dilutions of penicillin G, tetracycline, chloramphenicol, lincomycin, clindamycin, and erythromycin were prepared in.0-ml amounts of BH broth (BBL) containing % sheep blood. Forty-eight-hour broth cultures were diluted : in BH broth containing % sheep blood;.0 ml of this suspension was added to each tube containing antibiotic so as to yield final concentrations ranging from 0. to,ug/ml. This inoculum provided adequate growth in the control tube (without antibiotic) within 8 hr. All tubes were incubated anaerobically (GasPak) at 7 C and examined at 8 hr. The MC was defined as the lowest concentration of antibiotic that completely inhibited visible growth. MBC was determined by transferring 0.0 ml from each tube without visible or with barely visible growth to quarter sections of BH agar plates (BBL) with % sheep blood and incubating anaerobically at 7 C for 8 hr. The lowest antibiotic concentration from which subcultures showed no growth represented the MBC. solation, subculture, and most biochemical tests were carried out according to the procedures outlined by Dowell and Hawkins () using the GasPak (BBL) system. Prereduced media (cott Laboratories, nc., Chapel Hill, N.C.) were used for the differential carbohydrate fermentations. dentification and speciation of the anaerobic isolates was according to the criteria of Dowell and Hawkins (). REULT With the exception of certain species of Bacteroides, penicillin G was highly active, against most anaerobes tested, at 6.,ug/ml or less (Table Bacteroides fragilis... B. incommunis... B. variabilis... B. oralis... B. terebrans... B. melaninogenicus... Bacteroides Fl, F, F........ Fusobacterium fusiforme... Fusobacterium sp... Clostridium perfringens... Clostridium sp... Peptococcus sp... Peptostreptococcus sp... Veillonella sp... Propionibacterium acnes... Eubacterium lentum... E. alactolyticum... Eubacterium sp... Bifidobacterium sp... Catenabacterium filamentosum... Catenabacterium sp... ). Bacteroides incommunis, B. variabilis, and B. terebrans were less susceptible; penicillin G exhibited little or no activity against B. fragilis at 6.,ug/ml. Cephalothin (Table ) generally exhibited a similar degree of activity against the same species but at concentrations of.,g/ml or less. t is noteworthy that only 6% of strains of Eubacterium lentum were inhibited at this concentration, compared to % of the strains of E. alactolyticum and Eubacterium sp. Tetracycline at 6.,g/ml was active against the majority of strains in most of the groups tested; some strains were resistant (Table ). t is significant that only 9% of strains of B. fragilis and 0% of strains of B. terebrans were inhibited by this concentration. Although relatively few in number, % of the strains of E. alactolyticum and 0% of the Eubacterium sp. were inhibited by this concentration, whereas 8% of the strains of E. lentum were susceptible. The data for chloramphenicol are shown in Table. At a concentration of. jig/ml, all but three of the strains tested were inhibited. Erythromycin was active against many strains at a concentration of.,ug/ml or less (Table ). Less activity was exhibited against strains of B. incommunis, B. variabilis, B. terebrans, E. alactolyticum, Eubacterium sp., and Veillonella. Although both strains of Catenabacterium sp. were inhibited at 0.,ug/ml, the three strains of TABLE. usceptibility of anaerobic bacteria to penicillint G tested 9 0 9 8 7 7 6 0. Cumulative percentages at various concentrations (ug/ml) 0 6 6 8 8 8 9 8 0. 9 89 88 9 9 77 0 0 6 9 9 6 7 98 6.6 8 8 9. 9 99 6. 7 86. 7 70 89 Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest
MARTN, GARDNER, AND WAHNGTON ANTMCROB. AG. CHEMOTHER. TABLE. usceptibility of anaerobic bacteria to cephalothinl Cumulative percentages at various concentrations (Ag/ml) 0. 0..6. 6.. Bacteroides fragilis... 9 9 B. incommunis... 0 0 B. variabilis... B. oralis... B. terebrans... 0 B. melaninogenicus... 9 6 6 69 79 9 Bacteroides Fl, F, F 8 7 6 8 Fusobacterium 8 6 7 78 fusijormė... Fusobacteriumn sp.... Clostridium perfringens... 8 7 70 Clostridium sp... 7 88 Peptococcus sp... 8 6 78 88 89 98 99 Peptostreptococcus sp... 7 7 70 78 99 Veillonella sp... 69 8 Propionibacterium acnes... 6 69 88 9 Eubacterium lentum... 7 8 6 8 E. alactolyticum... Eubacterium sp... 0 Bifidobacterium sp.... 0 Catenabacterium filamentosuim... Catenabacterium sp... TABLE. usceptibility of anaerobic bacteria to tetracycline tested Cumulative percentages at various concentrations (jug/ml) 0. 0..6. 6.. Bacteroides fragilis... 9 8 6 9 8 90 B. incommunis... 0 0 0 70 90 B. variabiliṡ... B. oralis... B. terebrans... 0 B. melaninogenicus 9 8 6 76 79 8 9 Bacteroides Fl, F, F 8 7 6 9 Fusobacterium fusiforme.... 8 9 78 8 89 Fusobacterium sp... Clostridium perfringens... 6 70 76 8 8 9 Clostridium sp... 7 9 6 88 9 Peptococcus sp... 9 6 9 6 7 89 Peptostreptococcus sp.... 7 8 6 6 7 77 8 Veillonella sp... 69 76 8 Propionibacterium acnes... 6 6 9 7 Eubacterium lentum... 7 7 6 7 8 E. alactolyticum... Eubacterium sp.... 0 Bifidobacterium sp... Catenabacterium filamentosum... Catenabacterium sp... Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest
VOL., N VTRO ANTMCROBAL UCEPTBLTY TABLE. usceptibility of anaerobic bacteria to chloramphenicol tested Cumulative percentages at various concentrations (,ug/mi) 0. 0..6. 6.. Bacteroides fragilis... B. incommunis... B. variabilis... B. oralis... B. terebrans... B. melaninogenicus... Bacteroides Fl, F, F... Fusobacterium fusiforme... Fusobacterium sp... Clostridium perfringens... Clostridium sp... Peptococcus sp... Peptostreptococcus sp... Veillonella sp... Propionibacterium acnes... Eubacterium lentum... E. alactolyticum... Eubacterium sp... Bifidobacterium sp... Catenabacterium filamentosum... Catenabacterium sp... 9 0 9 8 7 7 6 0 7 6 7 6 9 9 8 0 8 7 6 0 0 9 6 6 67 6 8 9 8 TABLE. usceptibility of anaerobic bacteria to erythromycin ted 89 88 7 98 98 Cumulative percentages at various concentrations (pg/ml) 0. 0..6. 6.. Bacteroides fragilis... 9 6 6 9 66 9 9 B. incommunis... 0 0 0 B. variabilis... B. oralis... B. terebrans... B. melaninogenicus... 9 7 79 9 Bacteroides Fl, F, F...... 6 8 9 Fusobacterium fusiforme... 8 6 7 89 Fusobacterium sp... Clostridium perfringens... 6 Clostridium sp... 7 9 9 Peptococcus sp... 9 0 6 8 79 86 87 Peptostreptococcus sp... 7 7 9 6 6 7 88 9 99 Veillonella sp... 8 6 8 69 77 Propionibacterium acnes... 6 88 9 Eubacterium lentum... 7 8 9 E. alactolyticum... Eubacterium sp... 0 Bifidobacterium sp... Catenabacterium filamentosum...... Catenabacterium sp... 99 Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest
MARTN, GARDNER, AND WAHNGTON ANTMCROB. AG. CHEMOTHER. TABLE 6. usceptibility of anaerobic bacteria to linicomycini. Cumulative percentages at various concentrations (ug/ml) trans 0. 0..6. 6.. Bacteroides fragilis... 9 6 7 8 9 99 B. incommunis....... 0 0 0 70 90 B. variabilis B. oralis... B. terebranṣ... 0 B. melaniinogenicus 9 89 Bacteroides Fl, F, F... 6 7 9 Fusobacterium fusiforme... 8 9 6 67 8 9 Fusobacterium sp..... Clostridium perfringeits...... 9 8 76 Clostridium sp... 7 9 76 88 Peptococcus sp... 9 69 9 9 Peptostreptococctus sp... 7 9 8 7 8 Veilloneela sp... 6 77 9 Propiontibacterium acues... 6 8 88 9 Eubacterium lentum... 8 7 9 E. alactolyticum Eubacterium sp Bifidobacterium sp Catenabacterium filamentosum... 66 Caten7abacterium sp... TABLE 7. uiseeptibility of aniaerobic bacteria to clinidaniyciui Cumulative percentages at various concentrations (,ug/ml) Or tested 0. 0..6. 6.. Bacteroides fragilis... 9 67 7 8 89 B. incommunis... 0 70 90 B. variabilis... B. oralis... B. terebrans... B. melaninogenicus... 9 89 Bacteroides Fl, F, F... Fusobacterium fusiforme... 8 67 89 9 Fusobacterium sp... Clostridium perfringens 6 79 9 Clostridium sp... 7 7 9 76 88 9 6 76 87 9 9 Peptococcus sṗ... Peptostreptococcus sp... 7 8 8 90 98 Veillonella sp... Propionibacterium acnes 6 88 Eubacterium lentum... 78 8 E. alactolyticum... Eubacterium sp... Bifidobacteriumn sp... Catenabacterium filamentosum 66 Catenabacterium sp... Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest
VOL., N VTRO ANTMCROBAL UCEPTBLTY TABLE 8. usceptibility of anaerobic bacteria to kanamycin tested Cumulative percentages at various concentrations (ug/ml) 0. 0..6. 6.. Bacteroides fragilis... B. incommunis... B. variabilis... B. oralis... B. terebrans... B. melaninogenicus... Bacteroides Fl, F, F Fusobacterium fusiforme... Fusobacterium sp... Clostridium perfringens... Clostridium sp...... Peptococcus sp... Peptostreptococcus sp... Veillonella sp Propionibacterium acnes... Eubacterium lentum... E. alactolyticum... Eubacterium sp Bifidobacterium sp... Catenabacterium filamentosum... Catenabacterium sp... TABLE 9. 9 0 9 8 7 7 6 7 6 8 0 7 9. 8 6 8 usceptibility of anaerobic bacteria to gentamicin 7 8 9 6 0 0 6 6 6 78 0 Cumulative percentages at various concentrations (jug/ml) tested-_ 0. 0..6. 6.. Bacteroides fragilis... 9 6 B. incommunis... 0 0 B. variabilis... B. oralis... B. terebrans... B. melaninogenicus... 9 9 76 Bacteroides Fl, F, F... 7 6 7 Fusobacterium fusiforme... 8 6 Fusobacterium sp... Clostridium perfringens.... 6 Clostridium sp........ 7 6 8 Peptococcus sp... 7 0 6 9 Peptostreptococcus sp...... 7 9 8 0 8 78 Veillonella sp... 8 6 8 Propionibacterium acnes... 6 6 7 8 Eubacterium lentum... 7 7 7 8 9 E. alactolyticum... Eubacterium sp... 0 Bifidobacterium sp... 0 Catenabacterium filamentosum... 66 Catenabacterium sp... Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest
MARTN, GARDNER, AND WAHNGTON ANTMCROB. AG. CHEMOTHER. TABLE 0. usceptibility of anaerobic bacteria to rifampint tested Cumulative percentages at various concentrations (jug/ml) 0. 0..6. 6.. Bacteroides fragilis... B. incommunis... B. variabilis... B. oralis... B. terebrans... B. melaninogenicus... Bacteroides Fl, F, F... Fusobacterium fusiforme... Fusobacterium sp... Clostridium perfringens... Clostridium sp... Peptococcus sp... Peptostreptococcus sp... Veillonella sp... Propionibacterium acnies... Eubacterium lentum... E. alactolyticum... Eubacterium sp... Bifidobacterium sp... Catenabacterium filamentosum... Catenabacterium sp... 9 0 9 8 7 7 6 C. filamentosum were not inhibited by as much as,ug/ml. n most instances, the results obtained with lincomycin resembled those obtained with erythromycin (Table 6). Clindamycin, on the other hand, exhibited a high degree of activity against all anaerobes at.6,ug/ml or less (Table 7). n general, the MC of lincomycin exceeded those of clindamycin by fourfold. Nearly all strains in this study were resistant to kanamycin and gentamicin, although both of these drugs showed some activity against the anaerobic cocci, the nonsporeforming grampositive bacilli, and strains of B. melaninogenicus and Fusobacterium fusiforme (Tables 8 and 9). With rifampin, virtually all strains were inhibited at.,ug/ml or less, with the exception of some strains in the genus Eubacterium (Table 0). The MBC of penicillin G (Table ) and tetracycline (Table ) against strains of B. fragilis isolated from blood were generally four to eight times the MC. The bactericidal concentration of chloramphenicol (Table ) was eight or more times the bacteriostatic concentration, whereas with lincomycin (Table ), clindamycin (Table ), and erythromycin (Table 6), the MBC generally exceeded the MC by at least 6- fold. 9 0 0 86 7 7 8 7 68 9 78 0 9 8 6 86 70 9 67 6 8 9 78 88 76 7 89 9 98 99 DCUON n contrast to the voluminous literature on in vitro susceptibility testing of clinically significant aerobic and facultatively anaerobic bacteria, only a few references exist with regard to the anaerobes, and most of these are concerned primarily with the nonsporeforming gram-negative bacilli (, 9, 0, ). n these studies involving anaerobic bacteria, several different techniques were used, thereby making comparisons difficult. Moreover, only a few antibiotics were studied. n some of these studies, species differences were not taken into account. Recently, in vitro studies by Finegold and colleagues (-7, 7; Finegold et al., Bacteriol. Proc., p. 6; 7, p. ), Thornton and Cramer (9), and ngham and associates (, ), among others, have developed meaningful data without the aforementioned shortcomings. With few exceptions, the data reported here agree closely with those reported by these authors. ndeed, the MC in this study for many of the nonsporeforming gram-negative bacilli, the Peptostreptococcus sp., and the Bifidobacterium sp. agreed well with those published by Finegold and associates (, 6, 7; Finegold et al., Bacteriol. Proc., p. 6; 7, p. ). Moreover, the MC of cephalothin against Clostridium perfringens showed excellent agreement with those recently reported by Traub (0). One particularly Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest
VOL., N VTRO ANTMCROBAL UCEPTBLTY TABLE. Minimal bactericidal concentrations (MBC) against Bacteroides fragilis: penicillin G MBC, Ag/ml (no. of strains)a MC (pg/ml) >. 6...6 0. 0. a a. 6...6 0. 0. >, Not bactericidal at 0OAg/ml or less; no concentrations greater than l,g/ml were tested. TABLE. Minimal bactericidal concentrations (MBC) against Bacteroides fragilis: tetracycline MC (Ag/ml). 6...6 0. 0. >. 6. MBC, pg/ml (no. of strains)"..6 0. 0. >, Not bactericidal at loo,ug/ml or less; no concentrations greater than lg/ml were tested. TABLE. MC (pg/ml). 6...6 0. 0. Minimal bactericidal concentrations (MBC) against Bacteroides fragilis: chloramphenicol > 7. MBC, pg/ml (no. of strains)a 6...6 0. 0. Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest a >, Not bactericidal at,ug/ml or less; no concentrations greater than /Ag/ml were tested.
6 MARTN, GARDNER, AND WAHNGTON ANTMCROB. AG. CHEM OTHER TABLE. Miniimal bactericidal concenitrations (MBC) againist Bacteroides fragilis: lincomycin MC (ug/ml) > MBC, pag/ml (no. of strains)a. 6...6 0. 0. a >, Not bactericidal at lig/ml or less; no concentrations greater than loo,g/ml were tested. TABLE. Minimal bactericidal conicenitrationis (AMBC) agailst Bacteroides fragilis: clilndamycin MC (pg/mi). 6...6 0. 0.. 6...6 0. 0. MBC, pg/ml (no. of strains)a.6 0. a >, Not bactericidal at Ag/ml or less; no concentrations greater than /g/ml were tested. TABLE 6. MC (pg/ml). 6...6 0. 0. Minimal bactericidal concentrations (MBC) againtst Bacteroides fragilis: erythromycin > MBC, pg/ml (no. of strains)'. 6...6 0. 0.. 0. Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest a >, Not bactericidal at lg/ml or less; no concentrations greater than 0 Ag/ml were tested.
VOL., N VTRO ANTMCROBAL UCEPTBLTY 7 noteworthy area of disagreement in this study is the activity of tetracycline against B. fragilis. everal of the aforementioned investigators reported that B. fragilis was sensitive to tetracycline. For example, with the agar-dilution technique, ngham et al. () found that all 7 strains tested were inhibited at,ug/ml or less, whereas Finegold and Hewitt (7) found that 90% of their strains of B. fragilis were sensitive to tetracycline at concentrations of.6,ug/ml or less. n our study, this drug inhibited only 9% of strains of B. fragilis at 6.,ug/ml or less. ome of the differences can be attributed to differences in procedure; however, it is conceivable that B. fragilis is becoming more resistant to tetracycline. Recent in vitro studies by Finegold and associates (personal communication), as well as by others (,, 9), suggest that many of their recent isolates are noted to be resistant to this drug. The MC of penicillin G against the 9 strains of B. melaninogenicus in this study are of interest in that 8% of these were inhibited at concentrations of. j,g/ml or less. Finegold et al. (6) reported in 7 that all 9 of their strains were completely inhibited at concentrations of,ug/ ml or less. t is difficult to reconcile this fourfold difference, since the data on the MC of lincomycin and erythromycin against this species appear to be in close agreement. Our data showing the antibacterial effect of both clindamycin and rifampin against strains of B. fragilis are in good agreement with the MC reported by ngham et al. (). The effect of CO on the susceptibility of i0 strains of B. fragilis to four antibiotics in vitro was recently reported by ngham et al. (). They found that the MC of erythromycin and lincomycin were to times higher when grown in hydrogen plus 0% CO than when grown in pure hydrogen. Clindamycin and rifampin, to which their strains of B. fragilis were uniformly sensitive, were not affected by additional CO. Although none of our strains were incubated in pure hydrogen, the activities of erythromycin and lincomycin against our strains of B. fragilis were in general agreement with those in antimicrobial susceptibility tests performed with incubation in an environment containing to 0% CO (6, 9-). This observation is not surprising since the GasPak (BBL) system used in this study for anaerobic incubation (8) provides an atmosphere containing 8 to 0% CO (the remainder being hydrogen gas) once the generator envelope is activated by the addition of water (D. A. Power, BBL, personal communication). The efficacy of both lincomycin and erythromycin in the treatment of infections caused by Bacteroides sp., despite the CO present in the body, has been reported (). More than half of the strains of B. fragilis tested failed to be killed at concentrations of each of six antibiotics attainable in serum at their normally recommended dosages. Bactericidal activity of these antibiotics tended to be inconsistent. These results are in disagreement with those obtained by ngham et al. () using a replica-plating technique with velvet pads; however, it is likely that ngham et al. used a smaller inoculuni of bacteria in the inhibitory phase of their test than we did. Moreover, their definition of significant growth was 0 or more colonies in subcultures of plates with no growth or with growth of not more than 9 colonies. Our MBC was defined by the absence of any growth on subculture of broth containing no or barely visible growth. These differences in results emphasize the desirability of standardization of the techniques and interpretations of bactericidal tests. Although tetracycline has been considered to be the agent of choice in the treatment of infections due to penicillin-resistant strains of Bacteroides (,, ), our data and those of others (,, 9) demonstrating substantial resistance of these organisms to this antibiotic and its inconsistent bactericidal activity raise serious questions about this recommendation. The efficacy of chloramphenicol in the treatment of Bacteroides sepsis, however, has also been questioned recently by Kagnoff and Armstrong (). The need for a well-controlled prospective clinical study of antibiotic efficacy in bacteremia due to anaerobic bacteria is clear. The antimicrobial susceptibility data accumulated from these clinical isolates of anaerobic bacteria indicate certain definite patterns that should be helpful in the selection of appropriate antibacterial therapy. With the possible exception of blood culture isolates, we do not think at this time that routine antibiotic susceptibility testing can be performed with the same facility and frequency as can be performed on the aerobic bacteria. Periodic testing, however, probably should be carried out to detect any significant changes in patterns of resistance that may develop. Data correlating results of disc-diffusion susceptibility testing with MC would be helpful in simplifying the routine susceptibility testing of anaerobic bacteria. ACKNOWLEDGEMENT We thank A. G. Karlson for providing the antibiotic, rifampin, and Fred E. Day and Charmaine A. Flen for excellent technical assistance, Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest
8 MARTN, GARDNER, AND WAHNGTON ANTMCROB. AG. CHEMOTHER. LTERATURE CTED. Bodner,. J., M. G. Koenig, and J.. Goodman. 0. Bacteremic bacteroides infections. Ann. ntern. Med. 7:7-.. Dowell, V. R., Jr., and T. M. Hawkins. 8. Laboratory methods in anaerobic bacteriology. Center for Disease Control, Atlanta.. Ericsson, H. M., and J. C. herris.. Antibiotic sensitivity testing: report of an international collaborative study. Acta. Pathol. Microbiol. cand. B uppl. 7:-90.. Finegold,. M., A. Davis, and L. G. Miller, 7. Comparative effect of broad-spectrum antibiotics on nonsporeforming anaerobes and normal bowel flora. Ann. N.Y. Acad. ci. :68-8.. Finegold,. M., N. E. Harada. and L. G. Miller. 6. Lincomycin: activity against anaerobes and effect on normal human fecal flora. Antimicrob. Ag. Chemother., p. 69-667 6. Finegold,. M., N. E. Harada, and L. G. Miller. 7. Antibiotic susceptibility patterns as aids in classification and characterization of gram-negative anaerobic bacilli. J. Bacteriol. 9:-. 7. Finegold,. M., and W. L. Hewitt.. Antibiotic sensitivity pattern of Bacteroides species, p. 79-. n H. Welch and F. Marti-banez (ed.), Antibiotics annual, 9-. Medical Encyclopedia, nc., New York. 8. Gardner, M., and W. J. Martin.. implified method of anaerobic incubation. Appl. Microbiol. :09. 9. Garrod, L. P. 9. ensitivity of four species of Bacteroides to antibiotics. Brit. Med. J. :9-. 0. Gillespie, W. A., and J. Guy.. Bacteroides in intra-abdominal sepsis: Their sensitivity to antibiotics. Lancet : 09-0.. Hoogendijk, J. L.. Resistance of some strains of Bacteroides to ampicillin, methicillin, and cloxacillin. Antonie van Leeuwenhoek J. Microbiol. erol. :8-8.. ngham, H. R., J. B. elkon, A. A. Codd, and J. H. Hale. 8. A study in vitro of the sensitivity to antibiotics of Bacteroides fragilis. J. Clin. Pathol. :-6.. ngham, H. R., J. B. elkon, A. A. Codd, and J. H. Hale. 0. The effect of carbon dioxide on the sensitivity of Bacteroides fragilis to certain antibiotics in vitro. J. Clin. Pathol. : -8.. Keusch, G. T., and C. J. O'Connell. 6. The stusceptibility of Bacteroides to the penicillins and cephalothin. Amer. J. Med. ci. :8-.. Kagnoff, M. F., and D. Armstrong.. Antibiotics for Bacteroides sepsis (letters to the editor). Ann. ntern. Med. 7:6-7. 6. Martin, W. J.. Practical method for isolation of anaerobic bacteria in the clinical laboratory. Appl. Microbiol. :68-7. 7. Miller, L. G., and. M. Finegold. 7. Antibacterial sensitivity of Bifidobacterium (Lactobacillus bifidus). J. Bacteriol. 9:-0. 8. teers, E., E. L. Foltz, and B.. Graves. 99. An inocular replicating apparatus for routine testing of bacterial susceptibility to antibiotics. Antibiot. Chemother. 9:07-. 9. Thornton, G. F., and J. A. Cramer.. Antibiotic susceptibility of Bacteroides species. Antimicrob. Ag. Chemother. 0, p. 9-. 0. Traub, W. H.. The susceptibility of Clostridium perfringens Type A to cephalosporin C antibiotics in vitro. Chemotherapy 6:-7. Downloaded from http://aac.asm.org/ on eptember 0, 08 by guest