Journal of Antimicrobial Chemotherapy (1992) 30, Suppl. A, 45-51
Comparative in-vitro activity of RP 59500 against clinical bacterial isolates Matsnhisa Iroue", Ryokhi Okamoto*, Toyoji Okubo*, Kunlo Inoaer and Sasamn Mitsuhashlr
The activity of RP 59500 against Gram-positive cocci was determined by an agar dilution method and compared with that of erythromycin, cefotaxime and ampicillin. Of the 344 clinical isolates tested, none was resistant to RP 59500; this compound was active both against methicillin-resistant Staphylococcus aureus and against macrolidc-resistant Gram-positive cocci. The bactericidal activity of RP 59500 was confirmed by killing curve determinations.
Introduction Resistance to /J-lactam and macrolide antibiotics has been reported in many clinical isolates, including methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA). MRSA is generally considered to be resistant to all the /Mactam antibiotics, aminoglycosides such as gentamicin, tobramycin and amikacin, as well as to macrolides (Inoue el al., 1980; Smith, 1986). They are usually susceptible to vancomycin, rifampicin, some newer antimicrobial agents, such as teicoplanin (Greenwood, 1988; Van Laethem et al., 1988), coumermycin and the fluoroquinolones. RP 59500 is a combination of semisynthetic derivatives of pristinamycin IA and IIB. The purpose of this study was to compare the activity of RP 59500 with that of other antibiotics against clinical bacterial isolates, including MSSA and MRSA.
Materials and methods Microorganisms The organisms used in this study were fresh clinical isolates collected from hospitals over the period of 1986 to 1990. These were stored in 50% glycerol solution at -80°C and maintained at Gunma University. S. aureus Smith, Staphylococcus epidermidis IID 866, Enterococcus faecalis ATCC 19433 and Streptococcus pyogenes E771 were used as reference strains. 'Corresponding author Professor M. Inoue, Department of Microbiology, Kitasato Univenity School of Mediant, 1-33-1 Kitasato Sagaraihara, Kanagawa, Japan 228. 03O5-7453/92/3OAO45+07 $03.00/0
45 © 1992 The British Society for Antimicrobial Chemotherapy
Downloaded from http://jac.oxfordjournals.org/ at University of Sussex on August 21, 2015
'Department of Microbiology, Kitasato University School of Medicine; bLaboratory of Drug Resistance in Bacteria, Gunma University School of Medicine; 'Episome Institute, Japan
46
M. Ioone et aL
Antibiotics Reference powders of the different antibiotics of known potency were obtained as follows: RP 59500 (Rhone-Poulenc Rorer Japan, Inc., Tokyo), ampicillin (Toyama Chemical Co., Tokyo), cefotaxime (Hochst Japan, Co., Tokyo), minocycline (Lederle Japan, Tokyo), and gentamicin and tobramycin (Shionogi Pharmaceutical Co., Osaka); all were dissolved in distilled water. Norfloxacin (Kyorin Pharmaceutical Co., Tokyo) was dissolved in 01 N NaOH and then diluted in distilled water. Erythromycin (Shionogi Pharmaceutical Co., Osaka) was prepared in 100% ethanol and diluted further in water. MIC determinations
Bactericidal activity Killing curves were obtained by sampling each culture at appropriate time intervals over 24 h. Additional killing curves were obtained by starting with inocula of about 5 x 103 cfu/mL in flasks containing Sensitivity Disk Broth (Nissui, Tokyo) and the antibiotic to be tested. Samples were incubated aerobically at 37CC, then diluted and subcultured on to agar plates to determine viable counts. Results Changes in antibiotic susceptibility Table I summarizes the changing pattern of drug resistance in S. aureus in 1986 and 1989. In both years, MRSA resistant to erythromycin, gentamicin, tobramycin, minocycline and norfloxacin were isolated more frequently than MSSA strains resistant to these antibiotics. However, although fewer erythromycin-resistant MSSA were isolated in 1989 than in 1986, 15-5% of MSSA strains were found to be resistant to gentamicin
Table I. Changes in antibiotic resistance among S. aureus between 1986 and 1989 Type of S. aureus
No. of strains tested
1986
MSSA MRSA
187 67
1989
MSSA MRSA
124 164
Year
EM
GM
48 64 14 155
28 54 13 148
No. resistant to TOB MINO NFLX
29 55 13 159
1 6 0 19
3 14 8 91
EM, Erythromycin; GM, gentamicin, TOB, tobramycin; MINO, minocydinc; NFLX, norfloxacin; MSSA, methicillin-jusceptible 5. aureus, and MRSA, methicillin-retistint S. aureus.
Downloaded from http://jac.oxfordjournals.org/ at University of Sussex on August 21, 2015
MICs were determined in Sensitivity Disk Agar N (Nissui, Tokyo) by agar dilution with an inoculum of 3 x 104 cfu/spot delivered by a Microplanter inoculator (Sakuma Seisaku, Tokyo). The medium used for Haemophilus influenzae consisted of haemin 100 mg/L, /7-nicotinamide adenine dinucleotide 20 mg/L in 10 mL of Brain Heart Infusion agar. The break-points of each drug were as follows: RP 59500, 156 mg/L; erythromycin, 0-39 mg/L; gentamicin, 0-78 mg/L; tobramycin, 0-78 mg/L; minocycline, 0-78 mg/L; and norfloxacin, 6-25 mg/L.
47
In-ritro activity of RP 59500
Table IL Antibacterial activity of RP 59500 against Gram-positive and Gram-negative bacteria as determined by the agar dilution method Cmoculum, 10* cfu/spot) ^/rganism (no. of strains)
Antibiotic
range
MIC (mg/L) MIC J0
MIC, 0
RP 59500 erythromycin cefotaxime ampicillin
0-39-0-78 0-l->100 313->100 1-56-50
039 >100 100 50
078 >100 >100 50
MethicUlin-resistant S. aureus' (74)
RP 59500 erythromycin cefotaxime ampicillin
0-39-1-56 0-20-> 100 12-5->100 6-25-100
0-78 >100 >100 50
1-56 >100 >100 50
Methknllin-susceptible S. aweus (50)
RP 59500 erythromycin cefotaxime ampicillin
0-39-0-78 0-l->100 1-56-25 0-10-25
039 01 313 078
039 313 6-25 313
Methiciuin-susceptible S. aureus" (97)
RP 59500 erythromycin cefotaxime ampicillin
100 100 50
078 >100 >100 50
S. epidermidis (54)
RP 59500 erythromycin cefotaxime ampicillin
0-2-313 0-2-> 100 0-39-> 100 005-100
039 02 313 078
078 >100 6-25 313
S. pyogenes (50)
RP 59500 erythromycin cefotaxime ampicillin
0-2-0-39 0013-005
Comparative in-vitro activity of RP 59500 against clinical bacterial isolates Matsnhisa Iroue", Ryokhi Okamoto*, Toyoji Okubo*, Kunlo Inoaer and Sasamn Mitsuhashlr
The activity of RP 59500 against Gram-positive cocci was determined by an agar dilution method and compared with that of erythromycin, cefotaxime and ampicillin. Of the 344 clinical isolates tested, none was resistant to RP 59500; this compound was active both against methicillin-resistant Staphylococcus aureus and against macrolidc-resistant Gram-positive cocci. The bactericidal activity of RP 59500 was confirmed by killing curve determinations.
Introduction Resistance to /J-lactam and macrolide antibiotics has been reported in many clinical isolates, including methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA). MRSA is generally considered to be resistant to all the /Mactam antibiotics, aminoglycosides such as gentamicin, tobramycin and amikacin, as well as to macrolides (Inoue el al., 1980; Smith, 1986). They are usually susceptible to vancomycin, rifampicin, some newer antimicrobial agents, such as teicoplanin (Greenwood, 1988; Van Laethem et al., 1988), coumermycin and the fluoroquinolones. RP 59500 is a combination of semisynthetic derivatives of pristinamycin IA and IIB. The purpose of this study was to compare the activity of RP 59500 with that of other antibiotics against clinical bacterial isolates, including MSSA and MRSA.
Materials and methods Microorganisms The organisms used in this study were fresh clinical isolates collected from hospitals over the period of 1986 to 1990. These were stored in 50% glycerol solution at -80°C and maintained at Gunma University. S. aureus Smith, Staphylococcus epidermidis IID 866, Enterococcus faecalis ATCC 19433 and Streptococcus pyogenes E771 were used as reference strains. 'Corresponding author Professor M. Inoue, Department of Microbiology, Kitasato Univenity School of Mediant, 1-33-1 Kitasato Sagaraihara, Kanagawa, Japan 228. 03O5-7453/92/3OAO45+07 $03.00/0
45 © 1992 The British Society for Antimicrobial Chemotherapy
Downloaded from http://jac.oxfordjournals.org/ at University of Sussex on August 21, 2015
'Department of Microbiology, Kitasato University School of Medicine; bLaboratory of Drug Resistance in Bacteria, Gunma University School of Medicine; 'Episome Institute, Japan
46
M. Ioone et aL
Antibiotics Reference powders of the different antibiotics of known potency were obtained as follows: RP 59500 (Rhone-Poulenc Rorer Japan, Inc., Tokyo), ampicillin (Toyama Chemical Co., Tokyo), cefotaxime (Hochst Japan, Co., Tokyo), minocycline (Lederle Japan, Tokyo), and gentamicin and tobramycin (Shionogi Pharmaceutical Co., Osaka); all were dissolved in distilled water. Norfloxacin (Kyorin Pharmaceutical Co., Tokyo) was dissolved in 01 N NaOH and then diluted in distilled water. Erythromycin (Shionogi Pharmaceutical Co., Osaka) was prepared in 100% ethanol and diluted further in water. MIC determinations
Bactericidal activity Killing curves were obtained by sampling each culture at appropriate time intervals over 24 h. Additional killing curves were obtained by starting with inocula of about 5 x 103 cfu/mL in flasks containing Sensitivity Disk Broth (Nissui, Tokyo) and the antibiotic to be tested. Samples were incubated aerobically at 37CC, then diluted and subcultured on to agar plates to determine viable counts. Results Changes in antibiotic susceptibility Table I summarizes the changing pattern of drug resistance in S. aureus in 1986 and 1989. In both years, MRSA resistant to erythromycin, gentamicin, tobramycin, minocycline and norfloxacin were isolated more frequently than MSSA strains resistant to these antibiotics. However, although fewer erythromycin-resistant MSSA were isolated in 1989 than in 1986, 15-5% of MSSA strains were found to be resistant to gentamicin
Table I. Changes in antibiotic resistance among S. aureus between 1986 and 1989 Type of S. aureus
No. of strains tested
1986
MSSA MRSA
187 67
1989
MSSA MRSA
124 164
Year
EM
GM
48 64 14 155
28 54 13 148
No. resistant to TOB MINO NFLX
29 55 13 159
1 6 0 19
3 14 8 91
EM, Erythromycin; GM, gentamicin, TOB, tobramycin; MINO, minocydinc; NFLX, norfloxacin; MSSA, methicillin-jusceptible 5. aureus, and MRSA, methicillin-retistint S. aureus.
Downloaded from http://jac.oxfordjournals.org/ at University of Sussex on August 21, 2015
MICs were determined in Sensitivity Disk Agar N (Nissui, Tokyo) by agar dilution with an inoculum of 3 x 104 cfu/spot delivered by a Microplanter inoculator (Sakuma Seisaku, Tokyo). The medium used for Haemophilus influenzae consisted of haemin 100 mg/L, /7-nicotinamide adenine dinucleotide 20 mg/L in 10 mL of Brain Heart Infusion agar. The break-points of each drug were as follows: RP 59500, 156 mg/L; erythromycin, 0-39 mg/L; gentamicin, 0-78 mg/L; tobramycin, 0-78 mg/L; minocycline, 0-78 mg/L; and norfloxacin, 6-25 mg/L.
47
In-ritro activity of RP 59500
Table IL Antibacterial activity of RP 59500 against Gram-positive and Gram-negative bacteria as determined by the agar dilution method Cmoculum, 10* cfu/spot) ^/rganism (no. of strains)
Antibiotic
range
MIC (mg/L) MIC J0
MIC, 0
RP 59500 erythromycin cefotaxime ampicillin
0-39-0-78 0-l->100 313->100 1-56-50
039 >100 100 50
078 >100 >100 50
MethicUlin-resistant S. aureus' (74)
RP 59500 erythromycin cefotaxime ampicillin
0-39-1-56 0-20-> 100 12-5->100 6-25-100
0-78 >100 >100 50
1-56 >100 >100 50
Methknllin-susceptible S. aweus (50)
RP 59500 erythromycin cefotaxime ampicillin
0-39-0-78 0-l->100 1-56-25 0-10-25
039 01 313 078
039 313 6-25 313
Methiciuin-susceptible S. aureus" (97)
RP 59500 erythromycin cefotaxime ampicillin
100 100 50
078 >100 >100 50
S. epidermidis (54)
RP 59500 erythromycin cefotaxime ampicillin
0-2-313 0-2-> 100 0-39-> 100 005-100
039 02 313 078
078 >100 6-25 313
S. pyogenes (50)
RP 59500 erythromycin cefotaxime ampicillin
0-2-0-39 0013-005
