Journal of Infection (I99 o) zo, I29-I33
CASE R E P O R T
M e t r o n i d a z o l e resistant Bacteroidesfragilis i n f e c t i o n o f a p r o s t h e t i c hip joint M. M. H i c k e y , * U. M. D a v i e s , ~ J. D a v e , * M. V o g l e r * a n d R. A. Wall*
* Department of Microbiology, Northwick Park Hospital, Watford Road, Harrow, Middlesex H A I 3 UJ and t Division of Rheumatology, Clinical Research Centre, Warlord Road, Harrow, Middlesex H A I 3 UJ, U.K. Accepted for publication 25 October 1989 Summary A case of infection involving a prosthetic joint in a patient with adult Still's Disease is described. The causative organism was a strain of Bacteroides fragilis which was resistant to metronidazole. The rarity of this occurrence is emphasised. Diagnostic difficulties which arose are described and the problems encountered with therapy discussed.
Introduction T h e isolation of metronidazole resistant Bacteroides species f r o m clinical material is a rare event, a fact that has led m a n y laboratories routinely to screen cultures for the presence of anaerobic micro-organisms with the use of metronidazole 5 #g discs. Since the first report in 1978 by I n g h a m et al., of metronidazole resistance in a strain of B. fragilis isolated f r o m a clinical specimen 1 there has been only one other i n d e p e n d e n t l y confirmed report of stable metronidazole resistance in a B. fragilis strain 2 and a few u n c o n f i r m e d reports of reduced metronidazole sensitivity in B. fragilis strains 3-a and in other Bacteroides species. 6-9 A n u m b e r of these strains appear to have caused significant clinical problems, being isolated f r o m such sites as faecal fistulae in a patient with C r o h n ' s Disease 1, brain abscess 2' 7 and blood cultures. '~ Some of these patients had been receiving metronidazole therapy for extended periods of time (e.g. 17 days, 7 two years, 6 and 3 Years1) prior to the isolation of the resistant organisms. We report a case of infection of a hip joint prosthesis due to a metronidazole resistant ( M I C 8 # g / m l ) strain of B. fragilis which had severe consequences for the patient.
Case report A 3o-year-old m a n was a d m i t t e d with septic infection of a right hip joint prosthesis following gastroenteritis contracted while on holiday in Spain. Bilateral total hip and knee prostheses had previously been inserted because of progression of adult Still's Disease which had developed at the age of 21 years. T r e a t m e n t at the time of admission had consisted of a combination of Gold, Prednisolone and I n d o m e t h a c i n . Bacteroidesfragilis sensitive to metronidazole (5 #g disc) was isolated f r o m blood cultures and from pus aspirated from the 0163-4453/90/020129+05 $02.00/0
© I990 The British Society for the Study of Infection 6-2
I3O
M. M. H I C K E Y
ET
AL.
right hip joint. Metronidazole was administered intravenously for 3 days then continued orally in a dose of 4oo mg 8 hourly. Good clinical response was achieved. After 7 weeks of therapy a peripheral neuropathy developed necessitating withdrawal of metronidazole. Augmentin, to which the organism had documented in-vitro susceptibility, was substituted in a dose of 5oo mg orally 8 hourly. Antibiotic therapy was continued for a total of 6 months. After this he was well apart from occasional twinges of pain from the right hip joint which eventually became frequent and severe prompting readmission 6 months later. At this time there was no clinical evidence of infection but radiologically the prosthesis had loosened and was removed. Culture of tissue taken from the hip at operation failed to yield any organisms after 7 days of incubation. However, prolonged culture of this tissue was not carried out. T w o weeks after removal of the prosthesis another right total hip prosthesis was inserted. Within 3 weeks of its insertion a discharge of pus occurred from the wound. Culture was initially negative but volatile fatty acids (VFA) with a profile consistent with B. fragilis were detected in the pus by gas liquid chromatography (GLC). He was therefore commenced on oral Augmentin (amoxycillin + clavulanic acid). After 5 weeks incubation a Gram-negative anaerobic organism was isolated from this specimen of pus. T h e organism, which was identified as B. fragilis, was found to be resistant to metronidazole (no zone obtained with a 5 #g metronidazole disc) but sensitive to Augmentin, Timentin (ticarcillin+ clavulanic acid), clindamycin, and rifampicin by disc testing. Metronidazole resistance was confirmed by demonstrating that the M I C was 8 #g/ml. At this stage therapy was changed to a combination of intravenous clindamycin 6oo mg 6 hourly plus oral rifampicin 3oo mg Iz hourly. After 5 weeks of this therapy he developed diarrhoea, abdominal pain, tenderness and distension. Although Clostridium difficile was not isolated from stools and toxin not detected, the severity of these symptoms required that clindamycin be discontinued. A combination of Augmentin and rifampicin was substituted and he was discharged home on this treatment. He was reviewed regularly and complied well with therapy. Despite this, after 3 months, he was readmitted with a large abscess over the upper third of his right femur. At operation pus was found originating from the femoral shaft and extending through the posterior cortex into the hamstrings. This was drained and the prosthesis was removed. Treatment with intravenous Timentin 3"2 g 6 hourly was commenced perioperatively and continued. Bacteroides fragilis resistant to metronidazole was again isolated from the joint. T h e wound continued to discharge pus for several months but eventually healed. Intravenous Timentin via a Hickman line was continued for a total of 7 months. This therapy was complicated by an episode of Staphylococcus aureus septicaemia arising from infection at the Hickman line site. T h e septicaemia was successfully treated but removal of the line was necessary. Oral Augmentin 5oo mg 8 hourly plus Probenecid was continued. T h e patient remains well on this therapy x8 months after removal of the prosthesis.
Metronidazole resistant B. fragilis in hip joint
131
Table I Minimum inhibitory concentrations of control and test strains
Minimum inhibitory concentration (#g/ml)
Strain NCTC 9343 NCTC II295 Test strain
0"5 #g/ml 32 #g/ml 8 #g/ml
Laboratory m e t h o d s
Initially, culture of the pus samples obtained from the wound following revision of the prosthesis failed to yield growth of an organism. However, G L C performed directly on a sample of the pus revealed a volatile fatty acid profile consistent with B. fragilis. Some of the pus was inoculated into Robertson's cooked meat medium for prolonged incubation. Five weeks later it was subcultured on to blood agar plates on which minute colonies appeared after lO days of anaerobic incubation. This organism was identified as B. fragilis by standard biochemical techniques 1° and by its VFA profile obtained with GLC. T h e identification was independently confirmed by the Microbiology Department, St. Thomas' Hospital, London, and by the Anaerobe Reference Unit, Public Health Laboratory, Luton. Antibiotic disc susceptibility testing was carried out using standard methodology 1~ on Isosensitest agar (Oxoid) supplemented with fresh horse blood. T h e antibiotics tested included metronidazole (5 #g disc), Augmentin (3o#g), Timentin (85 #g), rifampicin (5 #g), clindamycin (2 #g) and cefoxitin (3o#g). T h e organism was found to be resistant to metronidazole (no zone obtained around the 5 #g disc) but sensitive to the other antibiotics. M i n i m u m inhibitory concentrations were performed on Isosensitest agar and on Columbia agar, both supplemented with fresh horse blood, and containing a range of metronidazole concentrations from 6 4 # g / m l to o'oo7 #g/ml. T h e sensitive control organism used was B. fragilis N C T C 9343 and a resistant control organism B.fragilis N C T C 11295 (H. R. Ingham) 1 was tested simultaneously. An inoculum of lO 6 organisms per ml was used. Plates were incubated anaerobically at 37 C for 48 h. Weekly subcultures of the strain were made and the M I C repeated at I, 3 and 6 month intervals to determine the stability of the resistance. T h e results of the M I C determinations are shown in Table I. T h e r e was no difference in the M I C obtained after weekly subculture for 6 months. T h e M I C (8 #g/ml) was confirmed by the Microbiology Department, St. Thomas' Hospital, London. Discussion
It is well recognised that patients with prosthetic devices are at risk of infection involving the prosthesis following even transient bacteraemic episodes. Our
I32
M. M. H I C K E Y
ET AL.
patient, perhaps because of immunosuppressive theory, may have experienced bacteraemia at the time of his gastroenteritis, the consequence of which was seeding of B. fragilis in one of his prosthetic joints. Unfortunately the original metronidazole-sensitive B. fragilis strain isolated from this patient is no longer available. It is therefore impossible to establish that the second metronidazole-resistant isolate is indeed the same organism which has acquired resistance determinants against metronidazole. It seems likely that this was the case and that continued low grade infection persisted in the joint despite 6 months of continuous antimicrobial chemotherapy, more than 4 months of this being with Augmentin to which the strain remained sensitive. Our patient received a total of 7 weeks of metronidazole therapy. Previously reported metronidazole-resistant Bacteroides species have been isolated from patients who had received it for periods ranging from I7 days 7 to 3 Years-1 We are not told whether the patient described by Eme et al., 2 had perioperative metronidazole 3 months before presenting with a subphrenic abscess. Treatment of the latter included 7 days of oral Ornidazole. Two days later a metronidazole-resistant B. fragilis species was isolated from pus drained from a cerebral abscess. However, Rotimi et al., 6 reported a strain of B. distasonis, resistant to metronidazole, from a peritoneal swab from a 9-yearold boy with a perforated appendix who had never received metronidazole. T h e mechanism of metronidazole resistance is still not fully understood but it is thought that there are at least two m e c h a n i s m s - decreased uptake and decreased nitro reduction. 1~ Despite widespread use of metronidazole, often for prolonged periods, resistance amongst anaerobes remains exceedingly rare. Other effective agents are available for treating such infections but the choice of agent may be limited by other factors. For example, clindamycin may cause pseudomembranous colitis, while some patients are allergic to B lactam antibiotics such as Augmentin and Timentin. T h e optimal duration of therapy is difficult to determine. In our patient the initial 6 months duration of antibiotic therapy proved ineffective. He remains on antibiotics I8 months after the final removal of his prothesis because of concern that persistent low grade infection may pose a risk of infection to his three other prosthetic joints. Detection of such persistent infection is extremely difficult, as this case illustrates, and thus it may be almost impossible to decide with confidence about the timing of insertion of a further prosthesis at the site of a previous infection. It is clear that prolonged antibiotic therapy in sufficient doses is mandatory, but this is not without its hazards. Our patient's therapy was complicated by S. aureus septicaemia relating to a Hickman line required for antibiotic administration. This type of nosocomial infection may be just as detrimental to a patient with joint prostheses as the original infection for which the therapy is being given. Finally, it must be stressed that material obtained from joints suspected of being infected should have prolonged incubation in enrichment media for several weeks under both aerobic and anaerobic conditions to ensure that fastidious organisms are not missed. Gas liquid chromatography is an extremely useful adjunct to culture in the diagnosis of infection in such specimens.
M e t r o n i d a z o l e resistant B . fragilis in hip j o i n t
I33
( W e w i s h to t h a n k D r B a r b a r a A n s e l l , H e a d o f t h e D i v i s i o n o f R h e u m a t o l o g y , C l i n i c a l R e s e a r c h C e n t r e , W a t f o r d R o a d , H a r r o w , M i d d l e s e x , for a l l o w i n g us to r e p o r t this case a n d t h e M i c r o b i o l o g y D e p a r t m e n t , St. T h o m a s ' H o s p i t a l , L o n d o n a n d t h e P u b l i c H e a l t h L a b o r a t o r y , L u t o n for t h e i r assistance.)
References I. I n g h a m H R , Eaton S, V e n a b l e s C W , Adams PC. Bacteroides fragilis resistant to metronidazole after long-term therapy. Lancet I978 ; i: 214. 2. Eme Me A, Acar JF, Goldstein FW. Bacteroides fragilis resistant to metronidazole. J Antimicrob Chemo I983; 12:523-524 . 3. Tabaqchali S, Pantosti A, Oldfield S. Pyruvate dehydrogenase activity and metronidazole susceptibility in Bacteroides fragilis. J Antimicrob Chemother 1983 ; H : 393-4oo. 4. Dublanchet A, Caillon J, Emond JP, Chandon H, Drugeon HB. Isolation of Bacteroides strains with reduced sensitivity to 5 - n i t r o i m i d a z o l e s . Eur J Clin Microbiol 1986; 5: 346-347, 5. Borobio MV, Pascual A, Perea EJ. Increasing resistance of Bacteroides fragilis group strains to metronidazole in Spain between 1977 and I982. E u r J Clin Mierobiol I984; 3 (2) : I53-I55. 6. Rotimi VO, Duerden BI, Ede V, Mackinnon AE. Metronidazole resistant Bacteroides from untreated patient. Lancet I979; i: 833. 7. Sprott MS, Ingham HR, Hickman JE, Sisson PR. Metronidazole resistant anaerobes. Lancet 1983; i: 122o. 8. McWalter PW, Baird DR. Metronidazole resistant anaerobes. Lancet I983; i: I22o. 9- Sprott MS, Kearns AM. Metronidazole-resistant Bacteroides melaninogenicus. J Antimicrob Chemother 1988; 22: 951-954. lO. Holdeman LV, Cato EP, Moore W E C (Eds) Anaerobe laboratory manual. 4th ed. Virginia Polytechnic Institute and State University Anaerobe Laboratory, Blackbury, Virginia, I977 : 30044 • zI. Brown D, Blowers R. Disc methods of sensitivity testing and other semiquantitative methods. In: Reeves PS, Phillips I, Williams JD~ Wise, R, Eds. Laboratory methods in antimicrobial chemotherapy. Edinburgh: Churchill, I978: 18-27. 12. Tally FP, Cuchural GJ Jr, Malamy MH. Mechanisms of resistance and resistance transfer in anaerobic bacteria: Factors influencing antimicrobial therapy. Rev Infect Dis 1984; 6 (Suppl. I): $26o-$269.
CASE R E P O R T
M e t r o n i d a z o l e resistant Bacteroidesfragilis i n f e c t i o n o f a p r o s t h e t i c hip joint M. M. H i c k e y , * U. M. D a v i e s , ~ J. D a v e , * M. V o g l e r * a n d R. A. Wall*
* Department of Microbiology, Northwick Park Hospital, Watford Road, Harrow, Middlesex H A I 3 UJ and t Division of Rheumatology, Clinical Research Centre, Warlord Road, Harrow, Middlesex H A I 3 UJ, U.K. Accepted for publication 25 October 1989 Summary A case of infection involving a prosthetic joint in a patient with adult Still's Disease is described. The causative organism was a strain of Bacteroides fragilis which was resistant to metronidazole. The rarity of this occurrence is emphasised. Diagnostic difficulties which arose are described and the problems encountered with therapy discussed.
Introduction T h e isolation of metronidazole resistant Bacteroides species f r o m clinical material is a rare event, a fact that has led m a n y laboratories routinely to screen cultures for the presence of anaerobic micro-organisms with the use of metronidazole 5 #g discs. Since the first report in 1978 by I n g h a m et al., of metronidazole resistance in a strain of B. fragilis isolated f r o m a clinical specimen 1 there has been only one other i n d e p e n d e n t l y confirmed report of stable metronidazole resistance in a B. fragilis strain 2 and a few u n c o n f i r m e d reports of reduced metronidazole sensitivity in B. fragilis strains 3-a and in other Bacteroides species. 6-9 A n u m b e r of these strains appear to have caused significant clinical problems, being isolated f r o m such sites as faecal fistulae in a patient with C r o h n ' s Disease 1, brain abscess 2' 7 and blood cultures. '~ Some of these patients had been receiving metronidazole therapy for extended periods of time (e.g. 17 days, 7 two years, 6 and 3 Years1) prior to the isolation of the resistant organisms. We report a case of infection of a hip joint prosthesis due to a metronidazole resistant ( M I C 8 # g / m l ) strain of B. fragilis which had severe consequences for the patient.
Case report A 3o-year-old m a n was a d m i t t e d with septic infection of a right hip joint prosthesis following gastroenteritis contracted while on holiday in Spain. Bilateral total hip and knee prostheses had previously been inserted because of progression of adult Still's Disease which had developed at the age of 21 years. T r e a t m e n t at the time of admission had consisted of a combination of Gold, Prednisolone and I n d o m e t h a c i n . Bacteroidesfragilis sensitive to metronidazole (5 #g disc) was isolated f r o m blood cultures and from pus aspirated from the 0163-4453/90/020129+05 $02.00/0
© I990 The British Society for the Study of Infection 6-2
I3O
M. M. H I C K E Y
ET
AL.
right hip joint. Metronidazole was administered intravenously for 3 days then continued orally in a dose of 4oo mg 8 hourly. Good clinical response was achieved. After 7 weeks of therapy a peripheral neuropathy developed necessitating withdrawal of metronidazole. Augmentin, to which the organism had documented in-vitro susceptibility, was substituted in a dose of 5oo mg orally 8 hourly. Antibiotic therapy was continued for a total of 6 months. After this he was well apart from occasional twinges of pain from the right hip joint which eventually became frequent and severe prompting readmission 6 months later. At this time there was no clinical evidence of infection but radiologically the prosthesis had loosened and was removed. Culture of tissue taken from the hip at operation failed to yield any organisms after 7 days of incubation. However, prolonged culture of this tissue was not carried out. T w o weeks after removal of the prosthesis another right total hip prosthesis was inserted. Within 3 weeks of its insertion a discharge of pus occurred from the wound. Culture was initially negative but volatile fatty acids (VFA) with a profile consistent with B. fragilis were detected in the pus by gas liquid chromatography (GLC). He was therefore commenced on oral Augmentin (amoxycillin + clavulanic acid). After 5 weeks incubation a Gram-negative anaerobic organism was isolated from this specimen of pus. T h e organism, which was identified as B. fragilis, was found to be resistant to metronidazole (no zone obtained with a 5 #g metronidazole disc) but sensitive to Augmentin, Timentin (ticarcillin+ clavulanic acid), clindamycin, and rifampicin by disc testing. Metronidazole resistance was confirmed by demonstrating that the M I C was 8 #g/ml. At this stage therapy was changed to a combination of intravenous clindamycin 6oo mg 6 hourly plus oral rifampicin 3oo mg Iz hourly. After 5 weeks of this therapy he developed diarrhoea, abdominal pain, tenderness and distension. Although Clostridium difficile was not isolated from stools and toxin not detected, the severity of these symptoms required that clindamycin be discontinued. A combination of Augmentin and rifampicin was substituted and he was discharged home on this treatment. He was reviewed regularly and complied well with therapy. Despite this, after 3 months, he was readmitted with a large abscess over the upper third of his right femur. At operation pus was found originating from the femoral shaft and extending through the posterior cortex into the hamstrings. This was drained and the prosthesis was removed. Treatment with intravenous Timentin 3"2 g 6 hourly was commenced perioperatively and continued. Bacteroides fragilis resistant to metronidazole was again isolated from the joint. T h e wound continued to discharge pus for several months but eventually healed. Intravenous Timentin via a Hickman line was continued for a total of 7 months. This therapy was complicated by an episode of Staphylococcus aureus septicaemia arising from infection at the Hickman line site. T h e septicaemia was successfully treated but removal of the line was necessary. Oral Augmentin 5oo mg 8 hourly plus Probenecid was continued. T h e patient remains well on this therapy x8 months after removal of the prosthesis.
Metronidazole resistant B. fragilis in hip joint
131
Table I Minimum inhibitory concentrations of control and test strains
Minimum inhibitory concentration (#g/ml)
Strain NCTC 9343 NCTC II295 Test strain
0"5 #g/ml 32 #g/ml 8 #g/ml
Laboratory m e t h o d s
Initially, culture of the pus samples obtained from the wound following revision of the prosthesis failed to yield growth of an organism. However, G L C performed directly on a sample of the pus revealed a volatile fatty acid profile consistent with B. fragilis. Some of the pus was inoculated into Robertson's cooked meat medium for prolonged incubation. Five weeks later it was subcultured on to blood agar plates on which minute colonies appeared after lO days of anaerobic incubation. This organism was identified as B. fragilis by standard biochemical techniques 1° and by its VFA profile obtained with GLC. T h e identification was independently confirmed by the Microbiology Department, St. Thomas' Hospital, London, and by the Anaerobe Reference Unit, Public Health Laboratory, Luton. Antibiotic disc susceptibility testing was carried out using standard methodology 1~ on Isosensitest agar (Oxoid) supplemented with fresh horse blood. T h e antibiotics tested included metronidazole (5 #g disc), Augmentin (3o#g), Timentin (85 #g), rifampicin (5 #g), clindamycin (2 #g) and cefoxitin (3o#g). T h e organism was found to be resistant to metronidazole (no zone obtained around the 5 #g disc) but sensitive to the other antibiotics. M i n i m u m inhibitory concentrations were performed on Isosensitest agar and on Columbia agar, both supplemented with fresh horse blood, and containing a range of metronidazole concentrations from 6 4 # g / m l to o'oo7 #g/ml. T h e sensitive control organism used was B. fragilis N C T C 9343 and a resistant control organism B.fragilis N C T C 11295 (H. R. Ingham) 1 was tested simultaneously. An inoculum of lO 6 organisms per ml was used. Plates were incubated anaerobically at 37 C for 48 h. Weekly subcultures of the strain were made and the M I C repeated at I, 3 and 6 month intervals to determine the stability of the resistance. T h e results of the M I C determinations are shown in Table I. T h e r e was no difference in the M I C obtained after weekly subculture for 6 months. T h e M I C (8 #g/ml) was confirmed by the Microbiology Department, St. Thomas' Hospital, London. Discussion
It is well recognised that patients with prosthetic devices are at risk of infection involving the prosthesis following even transient bacteraemic episodes. Our
I32
M. M. H I C K E Y
ET AL.
patient, perhaps because of immunosuppressive theory, may have experienced bacteraemia at the time of his gastroenteritis, the consequence of which was seeding of B. fragilis in one of his prosthetic joints. Unfortunately the original metronidazole-sensitive B. fragilis strain isolated from this patient is no longer available. It is therefore impossible to establish that the second metronidazole-resistant isolate is indeed the same organism which has acquired resistance determinants against metronidazole. It seems likely that this was the case and that continued low grade infection persisted in the joint despite 6 months of continuous antimicrobial chemotherapy, more than 4 months of this being with Augmentin to which the strain remained sensitive. Our patient received a total of 7 weeks of metronidazole therapy. Previously reported metronidazole-resistant Bacteroides species have been isolated from patients who had received it for periods ranging from I7 days 7 to 3 Years-1 We are not told whether the patient described by Eme et al., 2 had perioperative metronidazole 3 months before presenting with a subphrenic abscess. Treatment of the latter included 7 days of oral Ornidazole. Two days later a metronidazole-resistant B. fragilis species was isolated from pus drained from a cerebral abscess. However, Rotimi et al., 6 reported a strain of B. distasonis, resistant to metronidazole, from a peritoneal swab from a 9-yearold boy with a perforated appendix who had never received metronidazole. T h e mechanism of metronidazole resistance is still not fully understood but it is thought that there are at least two m e c h a n i s m s - decreased uptake and decreased nitro reduction. 1~ Despite widespread use of metronidazole, often for prolonged periods, resistance amongst anaerobes remains exceedingly rare. Other effective agents are available for treating such infections but the choice of agent may be limited by other factors. For example, clindamycin may cause pseudomembranous colitis, while some patients are allergic to B lactam antibiotics such as Augmentin and Timentin. T h e optimal duration of therapy is difficult to determine. In our patient the initial 6 months duration of antibiotic therapy proved ineffective. He remains on antibiotics I8 months after the final removal of his prothesis because of concern that persistent low grade infection may pose a risk of infection to his three other prosthetic joints. Detection of such persistent infection is extremely difficult, as this case illustrates, and thus it may be almost impossible to decide with confidence about the timing of insertion of a further prosthesis at the site of a previous infection. It is clear that prolonged antibiotic therapy in sufficient doses is mandatory, but this is not without its hazards. Our patient's therapy was complicated by S. aureus septicaemia relating to a Hickman line required for antibiotic administration. This type of nosocomial infection may be just as detrimental to a patient with joint prostheses as the original infection for which the therapy is being given. Finally, it must be stressed that material obtained from joints suspected of being infected should have prolonged incubation in enrichment media for several weeks under both aerobic and anaerobic conditions to ensure that fastidious organisms are not missed. Gas liquid chromatography is an extremely useful adjunct to culture in the diagnosis of infection in such specimens.
M e t r o n i d a z o l e resistant B . fragilis in hip j o i n t
I33
( W e w i s h to t h a n k D r B a r b a r a A n s e l l , H e a d o f t h e D i v i s i o n o f R h e u m a t o l o g y , C l i n i c a l R e s e a r c h C e n t r e , W a t f o r d R o a d , H a r r o w , M i d d l e s e x , for a l l o w i n g us to r e p o r t this case a n d t h e M i c r o b i o l o g y D e p a r t m e n t , St. T h o m a s ' H o s p i t a l , L o n d o n a n d t h e P u b l i c H e a l t h L a b o r a t o r y , L u t o n for t h e i r assistance.)
References I. I n g h a m H R , Eaton S, V e n a b l e s C W , Adams PC. Bacteroides fragilis resistant to metronidazole after long-term therapy. Lancet I978 ; i: 214. 2. Eme Me A, Acar JF, Goldstein FW. Bacteroides fragilis resistant to metronidazole. J Antimicrob Chemo I983; 12:523-524 . 3. Tabaqchali S, Pantosti A, Oldfield S. Pyruvate dehydrogenase activity and metronidazole susceptibility in Bacteroides fragilis. J Antimicrob Chemother 1983 ; H : 393-4oo. 4. Dublanchet A, Caillon J, Emond JP, Chandon H, Drugeon HB. Isolation of Bacteroides strains with reduced sensitivity to 5 - n i t r o i m i d a z o l e s . Eur J Clin Microbiol 1986; 5: 346-347, 5. Borobio MV, Pascual A, Perea EJ. Increasing resistance of Bacteroides fragilis group strains to metronidazole in Spain between 1977 and I982. E u r J Clin Mierobiol I984; 3 (2) : I53-I55. 6. Rotimi VO, Duerden BI, Ede V, Mackinnon AE. Metronidazole resistant Bacteroides from untreated patient. Lancet I979; i: 833. 7. Sprott MS, Ingham HR, Hickman JE, Sisson PR. Metronidazole resistant anaerobes. Lancet 1983; i: 122o. 8. McWalter PW, Baird DR. Metronidazole resistant anaerobes. Lancet I983; i: I22o. 9- Sprott MS, Kearns AM. Metronidazole-resistant Bacteroides melaninogenicus. J Antimicrob Chemother 1988; 22: 951-954. lO. Holdeman LV, Cato EP, Moore W E C (Eds) Anaerobe laboratory manual. 4th ed. Virginia Polytechnic Institute and State University Anaerobe Laboratory, Blackbury, Virginia, I977 : 30044 • zI. Brown D, Blowers R. Disc methods of sensitivity testing and other semiquantitative methods. In: Reeves PS, Phillips I, Williams JD~ Wise, R, Eds. Laboratory methods in antimicrobial chemotherapy. Edinburgh: Churchill, I978: 18-27. 12. Tally FP, Cuchural GJ Jr, Malamy MH. Mechanisms of resistance and resistance transfer in anaerobic bacteria: Factors influencing antimicrobial therapy. Rev Infect Dis 1984; 6 (Suppl. I): $26o-$269.
