Taurine Levels in Human Aqueous Humour MEDICAL SCIENCES (2000), 2, 25−31 © 2000 SULTAN QABOOS UNIVERSITY Department of Microbiology, College of Medicine, Sultan Qaboos University, P.O.Box: 35, Postal Code: 123, Muscat, Sultanate of Oman 25 In-vitro activity of synercid and related drugs against Streptococcus oralis isolated from septicaemia and endocarditis cases * Rafay A M فاعلية عقار السنرسيد وأمثاله ضد المكورات السبحية الفمية المعزولة من )ن الدم وعفونتهانتا( حاالت التهاب بطانة القلب واألنتانية رافع. أ تمت معمليًا :الطريقة. ا موجبة الصبغة وشدة خطورة التهاب بطانة القلب أصبح من الضرورة النظر الى طرق بديلة للعالج لبكيتري مع زيادة المقاومة ل :الهدف: الملخص القلب البكتيري، وأثنين من مرضى تسمم الدم ، واثنين من أفواه أشخاص أصحاء ، ثم دراسة منحنى اإلبادة لســتة من المكورات السبحية تم عزلها من مرضى التهاب بطانة آانت الفاعلية التثبيطية الصغرى للسنرسيد :النتائج. مقارنة فاعلية السنرسيد مع البنسلين، األموآسسلين، التيكوبالنين، الفنكومايسين، الكليندمايسين واإلرثرومايسين في المختبر 0.5 (الفاعلية التثبيطية الكبرىو) لتر/ملغ0.25 (الفاعلية التثبيطية الصغرى وقد وجد فرق بسيط بين . لتر/ملغ0.25وآانت قيمة القراءتين لتر/ ملغ 0.5-0.06بين ضيقة وتتراوح بكل من البنسلينن، آليندمايسين، ارثرومايسين وبالرغم من أن الفاعلية الصغرى للسنرسيد ضد المكورات السبحية من نوع أوراليس آانت نسبيًا أعلى مقارنة ). لتر/ملغ لتر لمعظم المعزوالت ماعدا /ملغ4وجد أن الترآيزات القاتلة للسنرسيد مساوية أو أدنى من . وتيكوبالنين إال أن مقدرة السنرسيد على إبادة الباآتريا في المختبر آانت أآبر بكثير أظهر السنرسيد فاعلية إبادة عالية متفوقًا على آل من البنسلين والفانكومايسين، بالنسبة لكل المعزوالت :الخالصة. لتر/ملغ 64لتر واألخرى أآبر من /ملغ16إثنتين واحدة آانت .خالل ستة ساعات من المالمسة% 99.9العشرة من المكورات السبحية بنسبة ABSTRACT: ��������� – The increase in resistance to gram positive organisms and seriousness of infective endocarditis, makes it necessary to look for an alternate treatment. �� �� – In-vitro activity of synercid was compared with penicillin, amoxycillin, teicoplanin, vancomycin, clindamycin and erythromycin. ������ – Synercid showed minimum inhibitory concentrations (MIC) within the narrow range of 0.06 – 0.5 mg/l. MIC50 and mode values were both 0.25 mg/l. There was just two-fold difference between the MIC50 (0.25 mg/l) and the MIC90, (0.5 mg/l). Although the MICs of synercid for S. oralis were relatively high compared to penicillin, clindamycin, erythromycin and teicoplanin, the in-vitro bactericidal activity of synercid was much greater. Synercid MBC values were < 4 mg/l for most of the isolates, except for one of 16 mg/l and the other >64 mg/l. Killing curve was performed on six isolates of S. oralis from infective endocarditis, two from septicaemia patients and two from the oral flora of normal individuals. ���������� – Synercid showed superior bactericidal activity when compared to penicillin and vancomycin against all ten isolates of S. oralis tested. Synercid was bactericidal (99.9% kill) against all ten isolates of S. oralis within six hours of contact. KEY WORDS: streptococcus oralis, synercid, penicillin, amoxycillin, erythromycin, vancomycin, teicoplanin, clindamycin iridans streptococci are among the com- monest causes of infective endocarditis, except in intravenous drug abusers where Staphylococcus epidermidis is frequently isolated.1 Bayliss found that streptococci or enterococci were the causative organisms in 63% of infective endocarditis cases and that 48% of these cases were viridans streptococci.2 These findings were also supported by Young.3 With newer identification methods viridans streptococci have been further classified to its species level and it has been shown that S. oralis, S. sanguis, and S. gordonii are the most frequently isolated species in patients with infective endocarditis.4,5 Owing to an increasing resistance to β-lactam antibiotics, the treat- ment of infective endocarditis has become more complicated.6 Keeping these in mind, a range of anti- biotics was considered, where antibiotic sensitivity, bact- ericidal kill and killing curve were tested to estimate their potential for the treatment of infective endocarditis caused by S. oralis. Synercid (RP59500), like pristina- mycin, is a streptogramin antibiotic. It is a semi-synth- etic modification of the two major constituents of pristinamycin: pristinamycin IA and pristinamycin IIA. Synercid consists of a quinuclidinylthiomethyl pristina- mycin IA derivative and a diethlyaminoethyl-sulphonyl pristinamycin IIA derivative in a ratio of 30:70 weight for weight.7 Its several novel properties have excited the interest of infectious diseases researchers.7,8,9 One of these is the activity of synercid against a number of resistant Gram-positive pathogens.10 Because of its V 25 R A F A Y 26 bactericidal activity against oral streptococci, its role in the treatment of infective endocarditis is indicated. METHOD A total of sixty clinical isolates of S. oralis were collected from patients either with endocarditis, neutropenia and from the normal oral flora of healthy individuals. Strains from blood culture were primarily isolated using Bactec NR850 and identified using API 20 Strep (bio Merieux, La Balme les Grottes, France), and were further identified using laboratory-devised method.11 DETERMINATION OF MIC The isolates were tested for their susceptibility to penicillin (Glaxo), amoxycillin (Sigma), erythromycin (Abbot), vancomycin (Sigma), teicoplanin (Merrel Dow), clindamycin (Upjohn) and synercid, a new injectable streptogramin. Isolates grown on columbia agar (CA) were used to inoculate 10 ml of iso-sensitest broth (Oxoid CM473) supplemented with 2% horse serum (Wellcome No. 5) and incubated for 4 hours at 37°C in air. Broth suspensions were adjusted by making a standard dilution in iso-sensitest broth in order to obtain a final inoculum on antibiotic containing agar plates of approximately 104 colony-forming units (cfu). Doubling dilutions of the antibiotics were prepared in 0.1M phosphate buffer of pH 7 to provide final concen- trations in iso-sensitest agar (Oxoid CM471) over the range 0.003–128 mg/l. A multipoint inoculator (Denley Instruments Ltd) was used to inoculate the isolates, which were then incubated aerobically at 37°C for 18 hours. The MIC was defined as the lowest antibiotic concentration that completely suppressed visible growth (one colony being ignored). Standard strain of S. oralis (A6) was inoculated with each batch of susceptibility tests to serve as control (MIC 0.12 mg/l for penicillin). DETERMINATION OF MINIMUM BACTERICIDAL CONCENTRATIONS (MBC) A total of 15 clinical isolates of S. oralis were used. Isolates AR3, AR12, AR13, AR19, AR40 were from patients with endocarditis, 92C17, 93C87, T8-2-12 from patients with neutropenia, 23, 24, A26, N4-1-4 from those with normal oral flora and A6, A10, A 9 from those with septicaemia. MIC/MBC values were deter- mined for synercid, penicillin, vancomycin, clindamycin, erythromycin and teicoplanin against 15 strains of S. oralis using a microtitre method, with antibiotic concentrations ranging from 0.003–64 mg/ml. Doubl- ing dilutions of antibiotics were prepared in iso-sensitest broth and these were inoculated with 5 hour broth cultures, diluted to give a final concentration of 104 cfu/mL. After 18 hours of incubation at 37°C, MBCs were determined by subculture of all wells with no visible growth. MIC was recorded as the highest antibiotic dilution showing no turbidity. MBCs were determined by transferring 100µl from wells showing no growth to CA plates. The inoculum was allowed to dry before spreading and incubated for 18 hours at 37°C in air. The MBC was taken as the lowest antibiotic concentrations of antimicrobial that reduced the number of viable organisms by 99.9% kill after 18 hours incubation. TIME KILL CURVES. The in-vitro bactericidal activities of penicillin, vancomycin and synercid were compared against ten isolates of S. oralis. Organisms were grown in brain heart infusion (BHI) for 18 hours at 37°C in air and 100 µl added to 100 ml of freshly prepared pre-warmed BHI. After one hour incubation at 37°C on an aerobic shaker, solutions of antibiotics were added to the culture to provide final concentrations of 4 times the previously determined MICs for S. oralis under investi- gation and an antibiotic-free growth control. Viable counts were performed at one, two, four, six and twenty-four hours by the Miles and Misra12 method. The counts were converted to log10 and the mean of the duplicate determination calculated. The counts did not differ by more than 10% and the majority of the counts differed by less than 5%. RESULTS Table 1 demonstrates the relative activities of peni- cillin, amoxycillin, erythromycin, clindamycin, vanco- mycin, teicoplanin and synercid against 60 isolates of S. oralis isolated from infective endocarditis, neutropneic and normal oral flora patients. Table 2 shows the MIC50, MIC90 and mode MIC values for each of the antibiotics tested. Synercid was the most active of all the agents tested, except with clindamycin and for some strains with erythromycin. One distinct population of isolates could be distinguished with synercid, all of which were inhibited within a narrow 0.06–0.5 mg/l range. The MIC50 and mode values were both at 0.25 mg/l, with two-fold difference between the MIC50 and MIC90, at 0.25 mg/l and 0.5 mg/l respectively. Synercid was four fold more active compared with penicillin and amoxycillin. MICs for penicillin and amoxycillin were similar, with a range of 0.015–16.0 mg/l. The mode and MIC50 values for penicillin and amoxycillin were 0.03 mg/l and 0.125 mg/l respectively, while MIC90 values were 2 and 8 mg/l, respectively. The distribution of isolates according to their susceptibility to erythromycin showed one population with an MIC range of 0.015 – 2 mg/l, in an approximate normal distribution with 6% strains requiring MIC 8 mg/l and 2% requiring 64 mg/l. I N - V I T R O A C T I V I T Y O F S Y N E R C I D Two very distinct populations of isolates could distinguished for clindamycin with no isolates showin intermediate susceptibility. Clindamycin was the mo active of the antibiotics tested against these isolates wi MIC50 value of 0.00375 mg/l, with a sensitive pop lation in MIC range of < 0.00375 – 0.06 mg/l. T majority of isolates were clustered within this narro band at 0.00375 – 0.06 mg/l and 14% isolates showed higher range of MICs of 2–8 mg/l. The distribution isolates according to their susceptibility to teicoplan was uni-modal with MICs range of 0.06–1 mg/l, show Percentage of S. oralis (n=60) isolate erythromycin, , teicoplanin Antibiotics 0.0037 0.0075 0.015 0.03 0.06 Penicillin - - 3 21 14 Amoxycillin - - 3 24 14 Clindamycin 43 14 13 13 3 Erythromycin - - 2 24 8 Teicoplanin - - - - 14 Vancomycin - - - - - Synercid - - - - 5 MIC (mg/l) of the 7 antibiotic against 6 Antibiotic Mode Penicillin 0.03 Amoxycillin 0.03 Clindamycin 0.00375 Erythromycin 0.03 Teicoplanin 0.125 Vancomycin 0.5 Syncercid 0.125 TABLE 1. s susceptible to penicillin, amoxycillin, clindamycin, , vancomycin, Synercid, (MIC, mg/l). 0.12 0.25 0.50 1 2 4 8 16 32 64 20 14 5 11 3 6 3 - - - 9 18 3 13 3 - 5 8 - - - - - - 2 7 5 - - - 14 14 10 14 6 - 6 - - 2 40 41 2 2 - 1 - - - - - 2 60 36 2 - - - - - 25 52 18 - - - - - - - be g st th u- he w a of in - ing a normal distribution curve, and only 1% strain with an MIC of 4 mg/l fell outside this range. Vancomycin showed narrow MIC range of 0.25–2 mg/l, in an ap- proximate normal distribution curve. For teicoplanin, the values for MIC50, mode and MIC90 were generally two fold lower than those for vancomycin. Synercid was four fold more active than vancomycin. IN-VITRO MBCS WITH SIX ANTIBIOTICS TO S. ORALIS. Table 3 shows the comparative in-vitro bactericidal activity of synercid, penicillin, vancomycin, clindamycin, erythromycin and teicoplanin against fifteen isolates of . oralis, using a microdilution broth technique. hree strains showed moderate penicillin esistance (>0.25 mg/l), but all fifteen isolates ere inhibited by < 2 mg/L penicillin. Seven of hese were penicillin tolerant (MIC/MBC ratio 1:8) and required >2 mg/l of penicillin for a 9.9% kill. The MIC's for teicoplanin (range .03–0.5 mg/l) against these isolates were lower han those of vancomycin (range 0.5–2 mg/l); he bactericidal activity of teicoplanin was also ower than that of vancomycin recorded over he 24 hour period. An MBC range of 16– >32 g/l teicoplanin was needed for 14 strains; the BC for one isolate was 4 mg/l. All isolates howed a high tolerance to teicoplanin with IC/MBC ratio of >32. With vancomycin, BC values for ten of the fifteen isolates anged from 16 to 128 mg/l and from 1 to 4 g/l for four isolates. The majority (10/14) of he isolates showed a high tolerance to ancomycin with an MIC/MBC ratio >8. ynercid achieved a >99.9% kill against ten of S T r w t > 9 0 t t l t m M s M M r m t v S TABLE 2 s tested exhibiting mode, MIC50 and MIC90 0 isolates of S.oralis MIC50 MIC90 % of strains sensitive % of strains outside normal range 0.125 2 72 28 0.125 8 84 16 0.0075 4 86 14 0.25 2 92 8 0.125 0.25 99 1 0.5 0.5 100 0 0.125 0.125 100 0 27 R A F A Y the fifteen isolates at a concentration of < 2 mg/l. Of the five remaining isolates, three required 4 mg/l, one 16 mg/l and the remaining one 64 mg/l of synercid for a 99.9% kill. The MBC 99.9% values for synercid were within the 1–4 times MIC range for all but two of the isolates. The majority of the isolates showed a relatively low tolerance to synercid (87% MIC/MBC ratio of < 4). Although the isolates were inhibited by lower concentrations of erythromycin than of synercid erythromycin showed much lower bactericidal activity than synercid. Clindamycin also demonstrated lower MIC values than those for synercid, but the MBC values for ten of the fifteen isolates were between 1–4 mg/l of clindamycin, for a 99.9% kill, five isolates required >4 mg/l. All isolates showed a relatively high tolerance to clindamycin with 12/15 MIC/MBC ratio of > 8. Two Comparative MIC/MBC values (mg/l) for synercid, penicill Strains Syncercid Penicillin Erythromycin MIC MBC MIC MBC MIC MBC AR3 0.5 >64 0.12 0.12 0.06 >16 AR12 1 1 0.12 16 0.06 4 AR13 1 2 0.12 0.12 0.12 >16 AR19 1 4 0.25 2 0.5 >16 AR40 0.5 16 1 >16 0.5 >16 23 1 2 0.25 >16 0.25 >16 N4-1-4 1 1 0.25 0.25 2 4 A9 1 1 0.25 0.5 0.03 >16 24 1 4 0.06 <0.06 0.25 >16 26 1 1 0.06 8 0.12 1 A6 1 2 0.06 <0.06 0.12 0.12 A10 0.5 0.5 2 >2 0.12 0.5 92C17 1 2 0.06 4 0.12 >16 93C87 1 2 0.5 0.5 0.12 0.5 T8-2-12 1 4 0.25 >8 0.12 0.5 strains were tolerant to synercid show tolerance to all TABLE 3 in, erythromycin, teicoplanin, vanomycin and clindamycin against S.oralis Vanomycin Teicoplanin Clindamycin MIC MBC MIC MBC MIC MBC 0.5 64 0.03 32 0.12 >4 2 >64 0.06 32 0.12 >4 2 16 0.12 4 0.12 >4 2 16 0.25 >32 0.25 4 2 >64 0.03 >32 0.12 >4 4 >64 0 >32 0.25 >4 2 1 0.03 >32 0.25 2 2 >128 0.06 >16 0.06 >1 1 4 0.12 >16 0.12 >1 2 32 0.12 >16 0.06 0.25 2 - 0.5 >16 0.12 0.12 2 >128 0.25 >16 0.06 0.5 2 4 0.5 >16 0.12 >1 2 2 0.25 >16 0.12 >1 2 >128 0.5 >16 0.12 >1 28 , the antibiotics as well. KILLING CURVE Killing curve was performed on ten isolates from endocarditis, neutropenic and normal oral flora strains. The pattern of kill was similar within these different sources of strains. Figures 1 and 2 show the comparative bactericidal activity at 4x MIC of synercid, vancomycin and penicillin against S. oralis (AR12 & AR13) from a patient with endocarditis. A three-log reduction in viable count was achieved within two hours of the organism coming into contact with synercid. Figure 3 shows the comparative bactericidal activity at 4x MIC of synercid, vancomycin and penicillin against an isolate of S. Oralis (23) from the I N - V I T R O A C T I V I T Y O F S Y N E R C I D 29 1 2 3 4 5 6 7 8 9 10 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (hour) Lo g1 0 cf u Control Vancomycin Synercid Penicillin 1 2 3 4 5 6 7 8 9 10 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (hour) Lo g1 0 cf u Control Vancomycin Synercid Penicillin 1 2 3 4 5 6 7 8 9 10 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (hour) Lo g1 0 cf u Control Vancomycin Synercid Penicillin FIGURE 1. Bacterial activity of synercid (RP 595,00), vancomycin and penicillin at 4 x MIC against S.Oralis from endocarditis patient. FIGURE 2. Bacterial activity of synercid (RP 595,00), vancomycin and penicillin at 4xMIC against S.oralis from endocaridtis patient. FIGURE 3. Bacterial activity of synercid (RP 595,00), vancomycin and penicillin at 4xMIC against S.oralis from normal oral flora. R A F A Y 30 normal oral flora. Synercid reduced the viable count of this isolate by three-log10 after 1.5 hour's exposure; a five-log10 reduction was achieved within six hours. DISCUSSION Susceptibility studies demonstrated that both peni- cillin and amoxycillin exerted similar activities against 60 isolates of S. oralis. These strains showed a wide range of susceptibilities but the MIC50 and the mode MIC values for both antibiotics were 0.125 mg/l and 0.03 mg/l respectively. Synercid, a streptogramin, demonstrated a relatively high MIC50 against S. oralis when compared with the macrolides and clindamycin. Similar findings were observed in a study reported by Williams.13 The result of this study regarding synercid activity against S. oralis correlates well with the observations of Fass14 who tested 30 viridans streptococci and found MIC50 of synercid to be 1 mg/l. MIC90 against these isolates was 2 mg/l and all isolates were inhibited by < 4 mg/l synercid. These findings were also supported by sepa- rate studies.14-16 There was a two-fold difference bet- ween the MIC50 of 0.25 mg/l and the MIC90 of 0.5 mg/l, compared to MIC90 values for clindamycin and erythromycin between 2–4 mg/l. These findings corre- late well with other studies.17-19 However, 14 % isolates required >2 mg/l clindamycin for inhibition and 28% isolates required >1 mg/l erythromycin for inhibition. Maskell20,21 performed in-vitro susceptibility testing on 50 isolates of oral streptococci and obtained similar results for pristinamycin: all isolates were inhibited by < 1 mg/l pristinamycin. Susceptibility testing showed that teico- planin demonstrated greater in-vitro activity than vanco- mycin, although it is not used as frequently as the latter. MICs of Synercid for S. oralis were relatively high compared to all antibiotics tested; MBC values were < 4 mg/l for most of the isolates, except for one at 16 mg/l and the other at > 64 mg/l. From these findings it was clear that Synercid has superior bactericidal activity against S. oralis compared to penicillin, erythromycin, vancomycin, teicoplanin and clindamycin. None of the S. oralis strains tested was tolerant to synercid. Similar findings have been demonstrated elsewhere.16, 19 Synercid was bactericidal (99.9% kill) against all ten isolates of S. oralis within six hours of contact. This correlates with the previous killing curve studies per- formed using Synercid against oral streptococci.19-20 Interestingly, in this study, 99.9% kill was achieved with nine out of the ten isolates within four hours of contact. The isolates from infective endocarditis cases required two to six hours of contact with synercid for 99.9% kill, whereas for isolates from neutropenic cases and the normal oral flora, 2.5 and 1.5 hours respectively were sufficient. These results also showed that none of the ten isolates tested were tolerant to synercid. This finding correlates well with the other studies.15,16,18 With peni- cillin, only four of the six infective endocarditis isolates showed a three-log10 reduction in viable colony count within 6 –24 hours. Vanomycin achieved a three-log10 reduction with only three out of the ten isolates. CONCLUSION There is concern about the increasing prevalence of methicillin resistant S. aureus (MRSA) S. epidermidis21-23 and reduced vancomycin susceptibility.24 There is great need for an agent with excellent activity against macro- lide resistant strains of gram-positive organisms and the recently reported strains of Enterococcus faecium which are resistant to both vancomycin and gentamicin.25 Thus synercid offers a potentially new agent for use in the treatment of infections caused by MRSA and other gram-positive bacteria.15 Synercid might be useful against most viridans streptococci for the treatment of complicated cases of infective endocarditis. REFERENCES 1. Skehan, JD, Murray, M, Mills PG. Infective endo- carditis: incidence and mortality in the North Thames Region. Brit Heart J 1988, 59, 62–68. 2. Bayliss R, Clarke C, Oakley CM, Somerville W, Young JE. The microbiology and pathogenesis of endocarditis. Br Heart J 1983, 50, 513–519. 3. Young JE, Susan. Aetiology and epidemiology of in- fective endocarditis in England and Wales. J Antimicrob Chemother 1987, 20, 7–14. 4. Bouvet A, Durand A, Devine C, Etienne J, Leport C, and the Group D'enquete Sur L'endocardite en France En 1990–1991. In vitro susceptibility to antibiotics of 200 strains of streptococci and enterococci isolated during infective endocarditis. Lancer Publication St.Petersburg, Russia 1994,72–3. 5. Douglas CWI, Heath J, Hampton KK, Preston FE. Identity of viridans streptococci isolated from cases of infective endocarditis. J Med Microbiol 1993, 39, 179–82. 6. Parker MT, Ball LC. Streptococci and aerococci associated with systemic infections in man. J Med Microbiol 1976, 9, 275–302. 7. Barriere JC, Bouanchaud DH, Harris NV, Paris JM, Rolin O, Smith C. The design synthesis and properties of RP59500 and related semi-synthetic streptogramin antibiotics. In: Program and abstract of the 30th Conference on Antimicrobial Agents and Chemotherapy. Atlanta. American Society for Microbiology, Washington, DC, 1990, 768A. 8. Barriere JC, Bouanchaud DH, Paris JM, Rolin O, Harris NV, Smith C. Antimicrobial activity against Staphylococcus aureus of semi synthetic injectable streptogramin: RP 59500 and related compounds. J Antimicrob Chemother 1992, 30, 1–8. 9. Aumercier M, Bouhallab S, Capmau M, Goffic FL. RP 59500: a proposed mechanism for its bacterial activity. J Antimicrob Chemother 1992, 30, 9–14. I N - V I T R O A C T I V I T Y O F S Y N E R C I D 31 10. Baquero F Gram-positive resistance: a challenge for the development of new antibiotics. 19th ICC Montreal, 1995. 11. Beighton D, Hardie JM, Whiley RA. A scheme for the identification of viridans streptococci. J Med Microbiol 1991, 35, 367–72. 12. Miles AA, Misra SSK, Irwin JO. The estimation of the bactericidal power of the blood. J Hygiene 1938, 38, 732– 49. 13. Williams JD, Maskell JP, Shain H, Chrysos G, Sefton AM, Fraser HY, Hardie JM. Comparative in– vitro activity of azithromycin, macrolides (erythromycin, clarithromycin and spiramycin) and streptogramin RP 59500 against oral organisms. J Antimicrob Chemother 1992, 30, 27–37. 14. Fass RJ. In vitro activity of RP59500, a semi-synthetic injectable prestinamycin, against staphylococci, strepto- cocci and enterococci. Antimicrob Agents Chemother 1991, 35, 553–9. 15. Verbist L, Verhaegen J. Comparative in-vitro activity of RP59500. J Antimicrob Chemother 1992, 30, 39–44. 16. Neu C Harold Chin, Nai-Xun, Gu, Jain-Wei. The in- vitro activity of new streptogramin, RP 59500, RP 57667 and RP 54476, alone and in combination. J Antimicrob Chemother 1992, 30, 83–94. 17. Soussy CJ, Acar JF, Cluzel R, Courvalin P, Duval J, Fleurette J, Megraoud F, Meryaan M, Thabaut A. A collaborative study of the in-vitro sensitivity to RP 59500 of bacteria isolated in seven hospitals in France. J Antimicrob Chemother 1992, 30, 53–8. 18. Pankuch GA, Jacobs MR, Appelbaum PC. Study of comparative anti pneumococcal activities of penicillin G, RP59500, erythromycin, sparfloxacin, ciprofloxacin and vancomycin by using the time-kill methodology. Antimicrob Agents Chemother 1994, 38, 2065–72. 19. Pechere JC. In-vitro activity of RP 59500, a semi synthetic streptogramin, against staphylococci and streptococci. J Antimicrob Chemother 1992, 30, 15–18. 20. Maskell JP, Willams JD. In-vitro susceptibility of oral streptococci to pristinamycin. J Antimicrob Chemother 1987, 19, 585–90. 21. Hoban DJ, Weshnoweski B, Palatnick L. In–vitro activity of RP59500, a new semi-synthetic streptogramin antibiotic against Staphylococcus species. In program an Abstract of the Thirteenth International conference on Antimicrobial agents and Chemotherapy, Atlanta, Georgia. American Society for Microbiology, Washington, DC 1990, 770, 214. 22. Boyce JM. Methicillin resistant Staphylococcus aureus. Detection, epidemiology and control measures. Infect Dis Clin North Am 1989, 3, 901–13. 23. Nafziger DJ, Wenzel RP. Coagulase-negative staphylo- cocci epidimiology evaluation and therapy. Infect Dis Clin North Am 1989, 3, 915–29. 24. Hiramatsu K, Hanaki H, Ino T, Yabutta K, Oguri T, Tenover FC. Methicillin-resistant Staphylococcus aureus clinical strains with reduced vancomycin suscepti- bility. J Antimicrob Chemother 1997, 40, 135–6 25. Cassewell MW, Seyed-Akhavani M, Wade J. In vitro activity of RP 59500 against vancomycin resistant Enterococcus faecium also resistant to >512 mg/l of gentamicin. 33rd ICAAC, New Orleans 1993, Poster presentation. In-vitro activity of synercid and related drugs �against Streptococcus oralis isolated from �septicaemia and endocarditis cases Intro METHOD Determination of MIC Determination of minimum bactericidal �concen˜trations (MBC) Time kill curves. RESULTS In-vitro MBCs with six antibiotics to S. oralis. killing curve DISCUSSION CONCLUSION REFERENCES