- Email: [email protected]
Changes in susceptibilities to teicoplanin, vancomycin and other antibiotics among Staphylococcus aureus isolates in a tertiary-care University hospital
I\I~H\\ll,l\\l
IO, “\\I
Ob
,4ntimicrobial Agents ELSEVIER
International Journal of Antimicrobial Agents 7 (1996)93-96
Changes in susceptibilities to teicoplanin, vancomycin and other antibiotics among Staphylococcus aurem isolates in a tertiary-care University hospital Pia Baiocchi, Alessandro Capone, Paolo Carfagna, Claudio Santini, Mario Venditti* Dipartimento
di Medicina Clinica, Policlinico Umberto I, 00161 Rome, Italy
Accepted 21 February 1996
AlJhlCt
Changes in antibiotics susceptibilities were evaluated among 374 nosocomial clinical isolates of Stu~Ir~fococcus aureus collected from 1986 to 1994 in a tertiary-care University hospital where methicillin-resistant S. aureus (MRSA) is an increasing cause of infection. Significant increases in resistance to ciprofloxacin, clindamycin and rifampicin were observed among MRSA isolates in recent years. No resistance to glycopeptides was observed. However, during the last 2 years a significant trend towards a decreasing susceptibility to teicoplanin was observed among MRSA isolates. Keywords: Teicoplanin; Vancomycin; Staphylococcus aureur; Antibiotic resistance; Methicillin resistance
1. Introduction Staphylococcus aureus represents an increasing cause of infection among our lhospitalised patients. A recent review of our routine clinical laboratory records disclosed more than a fourfold increase in clinically significant isolations of this micro-organism since 1992 [ 141. More importantly, a parallel increase in antibiotic resistance was also observed. During the first 6 months of 1983 the methicillin resistance rate: among S. aureus isolates from our patients was 22% [ 1381;in contrast, the annual rates during the 1990-1993 period ranged from 62 to 68% [14]. Obviously, this particular epidemiologic situation has led to a widespread use of antistaphylococcal drugs. We therefore investigated. possible changes in antimicrobial susceptibilities among S. aureus isolates from our hospitalised patients. 2. Materials and methods Strains (one per patient) of patients with nosocomial S. aureus infections, and who were observed by one of
us as consulting infectiologist, were collected since 1986.
l
Corresponding author. Fax: +39 6 4940421.
As shown in Table 1, they were categorised by period of collection, source of isolation, and susceptibility to methicillin. For the purpose of this study oxacillin, instead of methicillin, was used for in vitro studies, according to standard guidelines [5]. Oxacillin (methicillin) susceptibility was evaluated by means of the standard disk diffusion test [9] and agar screen method [ 121. Minimal inhibitory concentrations of clindamycin (Upjohn Co., Kalamazoo, MI), vancomycin (Ely Lilly, Sesto Fiorentino, Italy), teicoplanin and rifampicin @petit Research Center, Gerenzano, Italy), netilmicin (Schering Cot-p, Bloomfield, NY), ciprofloxacin (Bayer Italia SPA, Milan, Italyj, trimethoprim-sulfamethoxazole (Roche Italia, Milan, Italy) were determined by a microdilution procedure in cation supplemented Mueller Hinton broth using a final inoculum of approximately 5 x 10’ organisms per ml [lo]. The MIC was defined as the lowest concentration of antibiotic that completely inhibited growth after 24-h incubation at 35°C. Resistance to the evaluated agents was defined by the following MICs [lo]: clindamycin, rifampicin and ciprofloxacin ~4 &ml; vancomycin, teicoplanin and netihnicin 2 32 &ml; trimethoprim-sulfamethoxazole ~2.7/13.3 &ml. Statistical evaluation of the data was carried out by means of Chi square test, Student’s t-test and Bonferroni t-test as appropriate [l].
0924-8579/96/$15.000 1996 IElsevier Science Ireland Ltd. All rights reserved PII: 0924-8579(96)00301-9
P. Baiocchi et al. /International Journal of Antimicrobial Agents 7 (19%)
94
93-96
Table 1
Sourceof clinical isolates of Sraphylococcus aureus
source
No. isolates (% methicillin resistance)
Wound Blood Respiratory secretions Foreign
1986-1989
1990-1992
1993-1994
Total
46 (33) 25 (36) 7 (42)
45 (46) 26 (65) 5 (80)
99 (52) 25 (52) 31 (48)
190 (38) 76 (51) 43 (51)
7 (42)
5 (60)
10 (50)
22 (50)
5 (20)
2 (50) 6 (66)
9 (55) 12 (20)
lI(54) 23 (26)
body
CSF Miscellaneous
-
resistant S. aureus (MRSA) isolates to clindamycin, rifampicin, ciprofloxacin and netihnicin. MSSA also showed somewhat lower MI& and MIC& values for cotrimoxazole; however, the rates of resistance to this
3. Results
As shown in Table 2, methicillin-susceptible S. aure~ (MSSA) isolates were more susceptible than methicillin-
Table 2 In vitro activity of various antibiotics against 50 and 90% of methicillin susceptible (MSSA) and resistant (MRSA) S. aureus isolates: comparison of three different
periods
MRSA (n = 31)
MSSA (n = 5%)
MICw, 1986-1989* Clindamycin Ciprofloxacin Rifampicin Netihnicin Trimethoprim/ Sulfamethoxaz. Teicoplanin Vancomycin
MIC,,,,
0.06 0.25 0.01 0.5 0.08/ 0.42 0.12 0.5
0.5
0.03 0.12 0.01
0.25 0.25 0.06
0.5 0.041 0.21 0.12 0.5
0.161 0.84 0.25
1 0.03 2 0.32l 1.68 0.25 1
%Resist.
3.4s 1.6 6.7d 0 0 0 0
MIC,
MIC,
%RESIST.
0.5 0.5 0.03
45A 29D 22.5G OL
0.081 0.42 0.25 0.5
16 8 16 8 0.64 3.36 0.5 1
0.25 8 32 16 0.161 0.84 0.25 0.5
32 32 32 32 1.4J 6.6 0.5 I
32B 72E 84’ 28M
32 16 32 4 0.32/
32
7oc
32 32 16 2.71 13.3 4
88F 72n 6.6N
1
0 0 0
1990-1992t
Clindamycin Ciprofloxacin Rifampicin Netihnicin Trimethopriti Sulfametoxaz. Teicoplanin
1993-1994$ Clindamycin Ciprofloxacin Rifampicin Netihnicin Trimethoprim/ Sulfamethoxaa. Teicoulanin
0.25 0.25 0.01 0.25 0.161 0.84 0.12 0.5
1
0.5
32
1 32 4 0.3u 1.68 0.5
I
Ob
7.7 5.le 0 0 0 0
12.6c 7 17f
1 4.2 0 0
1.68 1 0.5
1
4 0 0
8.8 0
0
*MSSA, n = 59; MRSA, n = 31. TMSSA, n = 39; MRSA, n = 50. $MSSA, n = 95; MRSA, n = 91. Superscripts denote significance as follows: a + b vs. c, P = 0.011; b vs. c, P = 0.046; d + e vs. f, P = 0.063; A + B vs. C, and B vs. C, P < 0.0001; D vs. E, P = 0.01; D vs. E + F, G vs. H, and G vs. H + K, P < O.OO@l;L vs. M and L vs. N, P = 0.03 according to Chi-square test.
P. Baiocchi et al. /International Journal of Antimicrobial Agents 7 (19%)
compound were negligible for both groups. Teicoplanin showed similar activities against MSSA and MRSA isolated in the study periods 1986-1989 and 1990-1992; however, when the last study period, 1992-1994, was considered, MI& and MI&, against MRSA were eightfold and fourfold higher, respectively, than MI& and MU&, values against MSSA. In contrast, vancomycin showed similar activity against MSSA and MRSA isolates of each study period. Table 2 also shows thlat the activities of antibiotics against MSSA isolates did not change consistently through the years. The exceptions were clindamycin, with a 12.6% resistance rate during the study period 1993- 1994 that was significantly higher than the 0% rate observed during 1990-1992 (P = 0.046) and, to a lesser extent, rifampicin with a 17% resistance rate during 1993-1994 vs. 5.1-6.70//o during the previous study periods (P = 0.063). The evolution of antibiotic resistance among MRSA isolates was more consistent. When the earlier study period was compared with the period 1990-1992, significant increases in resistance rates to ciprofloxacin (29% vs. 79%, P = 0.01) and to rifampicin (22% vs. 84%, P < 0.0001) were observed. High resistance rates to these antibiotics were also maintained during the last period of study (1993-1994). The resistance rates of clindamycin was 70% during 1993-1994 versus 45% during 1986- 1989 (P= 0.021) and 32”/0during 1990-1992 (P c 0.0001). The resistance to netihnicin achieved a peak of 28% during 1990-1992, but fortunately declined to 6.6% during 1993- 1994. No significant variations in resistance to cotrimoxazole, teicoplanin and vancomycin were observed during the three study periods. No isolates resistant to the latter two compounds were ever observed. Table 3 shows the changes of susceptibility to glycopeptides among our MRSA isolates in terms of mean MIC and number of strains inhibited by MICs of 2-4 &ml that we arbitrarily defined as ‘moderately susceptible’. Isolates w:ith MICs of 2-4 &ml to teicoplanin were very rare during the first two periods,
93-96
95
accounting for only five (6%) of 81 MRSA isolates; on the contrary, of 91 isolates representative of the last study period as many as 25 (27S”/,) were inhibited by an MIC of 2 &ml and nine (10%) by an MIC of 4 @g/ml of teicoplanin. Isolates inhibited by an MIC of 2 &ml of vancomycin remained rare during all three study periods and no isolate ever required a concentration 14 &ml for inhibition. The mean MIC values of teicoplanin against MRSA isolates of the first two study periods were significantly lower than the value of the last period (0.33 &ml during 1986- 1989 and 0.43 &ml during 1990-1992 vs. 1.18 &ml during 1993-1994, P < 0.0001, according to Bonferroni ?-test). As far as vancomycin is concerned, the mean MIC values of the first two study periods were also lower than the value of the last period; however, the difference did not achieve statistical significance even when results of the earlier period where compared with those of the last period (P > 0.5,according to Bonferroni t-test). When vancomycin was compared to teicoplanin, a significantly lower number of isolates inhibited by an MIC of 2 &ml (P= 0.0001) or by an MIC of 4 &ml (P= 0.03) was found during the last study period. Based on data of mean MIC values, teicoplanin was more active than vancomycin against MRSA during the periods 1986-1989 (P= 0.018) and 1990-1992 (P= 0.033) but was less active than vancomycin during the 1993-1994 period (P < 0.0001). Among MSSA strains, only three isolated in the 1993- 1994 period had a moderate susceptibility to glycopeptides: two were inhibited by an MIC of 2 &ml of teicoplanin and one by an MIC of 2 &ml of vancomycin. 4. Discussion Since the present study is based on non-consecutive clinical isolates, the results may not strictly define the true epidemiology of antibiotic resistances among our MRSA. However, despite this limitation the available data seem to provide evidence of a trend towards
Table 3 Changes in susceptibility to glycopeptides among clinical isolates of methicillin-resistant Staphylococcus aureus from hospitalized patients during three study periods PCtiod
:No. isolates with the indicated MIC (&nl)/total
isolates and mean MIC MIC to vancomycin
IMICto teicoplanin
1986-1989 1990-1992 1993-1994
.2
4
Mean f SD.
2
4
Mean
1/31a 4/50b :25/91c
o/31* O/SOB 9l91C
0.33 l o.34c 0.43 + 0.51’ 1.18 * 1.17s
l/31 2l50 2f91d
o/31 o/50 0l91o
0.54 f 0.34h 0.63 f 0.41’ 0.70 l 0.35’
l
S.D.
Superscriptsdenote significance as follows: a vs. c, b vs. c, A + B vs. C, P = 0.01; B vs. C, P = 0.053; c vs. d, P C 0.0001; C VS. D, P = 0.006, according to Cbi-square test. e ‘vs.g, f vs. g, P < O.ooOl,according to Bonferroni r-test. e vs. h, P = 0.018; f vs. k, P = 0.033; g VS. J, P < 0.0001, according to Student’s J-test.
P. Baiocchi et al. /International Journal of Antimicrobial Agents 7 (1996) 93-96
96
increased antibiotic resistance among our nosocomial S. aureus. Based on previous reports [4,17], it is not surprising to document high rate of resistance to ciprofloxacin, rifampicin and clindamycin among MRSA isolates in a setting where these organisms are prevalent pathogens. Nevertheless, it was disappointing that most of MRSA isolates from our hospitalised patients are nowadays resistant to all three the above antibiotics. Potential advantages of combinations of these agents with glycopeptides for the treatment of serious or slowly responding infections seem obviously negated by such a wide spectrum of antibiotics resistance [3,5,8,11,15,16]. More importantly, our data show the emergence of ORSA isolates with a decreased susceptibility to glycopeptides, and in particular to teicoplanin. Of interest, teicoplanin concentrations of 2-4 &ml were very rarely required for inhibition of S. aureus before 1986- 1989 and for the 2 years after (1990- 1992) this drug became available in Italy. Decreased susceptibility to teicoplanin became apparent only after 1992, as a probable consequence of the increased usage of glycopeptides, in particular teicoplanin, for the high frequency of MRSA infections. In fact, during 1994 approximately 6000 vials of vancomycin and 18 000 vials of teicoplanin were administered in our hospital. Resistance to teicoplanin, but not to vancomycin, has been readily induced ‘in vitro’ in S. aureus isolates [18]. Emergence of teicoplanin resistance during therapy of a serious S. aureus infection has been also described [7] and MRSA isolates with MICs of 8- 16 &ml have been observed in other hospital settings [2,6]. It is therefore likely that, under the pressure of glycopeptide usage, the introduction of poorly susceptible MRSA strains in our hospital may provide a setting for development of full resistance in future. To conclude, the present study provides some data on the evolution of antibiotics resistances in a hospital where MRSA has emerged as a prevalent pathogen. The most interesting finding was a trend towards decreased susceptibility to teicoplanin documented among MRSA isolates. Whether this phenomenon arose from multiple instances of coincidental infection or from sequential transmission of a single strain remains to be elucidated, Further study is also required to understand the clinical significance of such reduced susceptibility to teicoplanin. Nevertheless, on the basis of our data we recommend strict adoption of infection control measures, including monitoring of susceptibility to glycopeptides, and a prudent use of teicoplanin in hospital settings where MRSA is a frequent cause of nosocomial infection. References [I] Annitage P. Statistical methods in medical research, 1st ed. Oxford: Blackwell Scientific Publications, 1971.
121Brunet F, Vedel G, Dreyfus F et al. Failure to teicopianin therapy in two neutropenic patients with staphylococcal septicemia who recovered after administration of vancomycin. Eur J Clin Microbial Infect Dis 1990$145-147. I31 Chuard C, Hermann M, Vandaux P, Waldvogel FA, Lew DP. Successful treatment of methicillin-resistant Staphyfococcus aureus by antimicrobial combination. Antimicrob Agents Chemother 1991;35:261l-2616. 141 Dawn TE, Schaberg DR, Terpenning MS, Sottile WS, Kaufmann CA. Increasing resistance of Staphylococcus aureus to ciprofloxacin. Antimicrobial Agents Chemother 1990,34: 1862-1863. 151 Faville RJ Jr, Zaske DE, Kaplan EL, Crossley K, Sabath LD, Anie PG. Staphylococcus aureus endocarditis. Combined therapy with vancomycin and rifampin. J Am Med Assoc 1978;240:1963-1965. M Goering RW, Fey PD, Goldstein FW. Usefulness of pulse-field gel electroforesis in the epidemiological analysis of Staphylococcus aureus isolates with decreased susceptibility to teicoplanin. Eur J Clin Microbial Infect Dis 1995;14(Suppl 1):3-5. [71 KaatzGW, Seo SM. Dorman NJ, Lemer SA. Emergence of teicoplanin resistance during therapy of Staphylococcus aureus endocarditis. J Infect Dis 1990,162:103-108. 181 Levine DP, Fromm BS, Reddy BR. Slow response to vancomycin or vancomycin plus rifampin in methicillin-resistant Staphylococm aureus endocarditis. Ann Intern Med 1991;115:674-680. [91 National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial disk susceptibility test, 4 th ed. Approved standard M2-A4. Villanova, PA: National Committee for Clinical Laboratory Standards, 1990. 1101 National Committee for Clinical Laboratory Standards. Methods for dilution antimicrobial susceptibility test for bacteria that grow aerobically, 2nd ed. Approved standard M7-A2. Villanova, PA: National Committee for Clinical Laboratory Standards, 1990. Small PM, Chambers HF. Vancomycin for Staphylococcus aureus endocarditis in intravenous drug users. Antimicrob Agents Chemother 1990,34:1227-1231. WI Thornsberry C, MC Dougal LK. Successful use of broth microdilution in susceptibility tests for methicillin-resistant (heteroresistant) staphylococci. J Clin Microbial 1983;18: 1084-1091. iI31 Varaldo PE, Cipriani P, Foci A et al. Identification, clinical distribution and susceptibility to methicillin and 18 additional antibioticsof clinical Staphylococcus isolates: nationwide investigation in Italy. J Clin Microbial 1984;19:833-843. 1141 Venditti M, Baiocchi P, Brandimarte C et al. High rate of oxacillin resistant Staphylococcus aureus isolates in an italian university hospital. J Chemother 1994;6:25-28. 1151 Venditti M, Baiocchi P, Santini C et al. Potential of clindamycin in addition to vancomycin for the treatment of oxacillinresistant Staphylococcus aureus septicemia persisting under vancomycin therapy. Int J Antimicrob Agents 1995;5:123-128. [IfA Voss A, Milatovic D, Wallranch-Schwatz C, Rosdhal VT, Braveny 1. Methicillin-resistant Staphylococcus aureus in Europe. Eur J Clin Microbial Infect Dis 1994;13:50-55. iI71 Watanakunakom C. Clindamycin therapy of Staphylococcus aureus endocarditis. Am J Med 1976;60:419-425. U81 Watanakunakom C. In vitro selection of resistance of Staphylococw aurew to teicoplanin and vancomycin. J Antimicrob Chemother 1990;25:69-72.
IO, “\\I
Ob
,4ntimicrobial Agents ELSEVIER
International Journal of Antimicrobial Agents 7 (1996)93-96
Changes in susceptibilities to teicoplanin, vancomycin and other antibiotics among Staphylococcus aurem isolates in a tertiary-care University hospital Pia Baiocchi, Alessandro Capone, Paolo Carfagna, Claudio Santini, Mario Venditti* Dipartimento
di Medicina Clinica, Policlinico Umberto I, 00161 Rome, Italy
Accepted 21 February 1996
AlJhlCt
Changes in antibiotics susceptibilities were evaluated among 374 nosocomial clinical isolates of Stu~Ir~fococcus aureus collected from 1986 to 1994 in a tertiary-care University hospital where methicillin-resistant S. aureus (MRSA) is an increasing cause of infection. Significant increases in resistance to ciprofloxacin, clindamycin and rifampicin were observed among MRSA isolates in recent years. No resistance to glycopeptides was observed. However, during the last 2 years a significant trend towards a decreasing susceptibility to teicoplanin was observed among MRSA isolates. Keywords: Teicoplanin; Vancomycin; Staphylococcus aureur; Antibiotic resistance; Methicillin resistance
1. Introduction Staphylococcus aureus represents an increasing cause of infection among our lhospitalised patients. A recent review of our routine clinical laboratory records disclosed more than a fourfold increase in clinically significant isolations of this micro-organism since 1992 [ 141. More importantly, a parallel increase in antibiotic resistance was also observed. During the first 6 months of 1983 the methicillin resistance rate: among S. aureus isolates from our patients was 22% [ 1381;in contrast, the annual rates during the 1990-1993 period ranged from 62 to 68% [14]. Obviously, this particular epidemiologic situation has led to a widespread use of antistaphylococcal drugs. We therefore investigated. possible changes in antimicrobial susceptibilities among S. aureus isolates from our hospitalised patients. 2. Materials and methods Strains (one per patient) of patients with nosocomial S. aureus infections, and who were observed by one of
us as consulting infectiologist, were collected since 1986.
l
Corresponding author. Fax: +39 6 4940421.
As shown in Table 1, they were categorised by period of collection, source of isolation, and susceptibility to methicillin. For the purpose of this study oxacillin, instead of methicillin, was used for in vitro studies, according to standard guidelines [5]. Oxacillin (methicillin) susceptibility was evaluated by means of the standard disk diffusion test [9] and agar screen method [ 121. Minimal inhibitory concentrations of clindamycin (Upjohn Co., Kalamazoo, MI), vancomycin (Ely Lilly, Sesto Fiorentino, Italy), teicoplanin and rifampicin @petit Research Center, Gerenzano, Italy), netilmicin (Schering Cot-p, Bloomfield, NY), ciprofloxacin (Bayer Italia SPA, Milan, Italyj, trimethoprim-sulfamethoxazole (Roche Italia, Milan, Italy) were determined by a microdilution procedure in cation supplemented Mueller Hinton broth using a final inoculum of approximately 5 x 10’ organisms per ml [lo]. The MIC was defined as the lowest concentration of antibiotic that completely inhibited growth after 24-h incubation at 35°C. Resistance to the evaluated agents was defined by the following MICs [lo]: clindamycin, rifampicin and ciprofloxacin ~4 &ml; vancomycin, teicoplanin and netihnicin 2 32 &ml; trimethoprim-sulfamethoxazole ~2.7/13.3 &ml. Statistical evaluation of the data was carried out by means of Chi square test, Student’s t-test and Bonferroni t-test as appropriate [l].
0924-8579/96/$15.000 1996 IElsevier Science Ireland Ltd. All rights reserved PII: 0924-8579(96)00301-9
P. Baiocchi et al. /International Journal of Antimicrobial Agents 7 (19%)
94
93-96
Table 1
Sourceof clinical isolates of Sraphylococcus aureus
source
No. isolates (% methicillin resistance)
Wound Blood Respiratory secretions Foreign
1986-1989
1990-1992
1993-1994
Total
46 (33) 25 (36) 7 (42)
45 (46) 26 (65) 5 (80)
99 (52) 25 (52) 31 (48)
190 (38) 76 (51) 43 (51)
7 (42)
5 (60)
10 (50)
22 (50)
5 (20)
2 (50) 6 (66)
9 (55) 12 (20)
lI(54) 23 (26)
body
CSF Miscellaneous
-
resistant S. aureus (MRSA) isolates to clindamycin, rifampicin, ciprofloxacin and netihnicin. MSSA also showed somewhat lower MI& and MIC& values for cotrimoxazole; however, the rates of resistance to this
3. Results
As shown in Table 2, methicillin-susceptible S. aure~ (MSSA) isolates were more susceptible than methicillin-
Table 2 In vitro activity of various antibiotics against 50 and 90% of methicillin susceptible (MSSA) and resistant (MRSA) S. aureus isolates: comparison of three different
periods
MRSA (n = 31)
MSSA (n = 5%)
MICw, 1986-1989* Clindamycin Ciprofloxacin Rifampicin Netihnicin Trimethoprim/ Sulfamethoxaz. Teicoplanin Vancomycin
MIC,,,,
0.06 0.25 0.01 0.5 0.08/ 0.42 0.12 0.5
0.5
0.03 0.12 0.01
0.25 0.25 0.06
0.5 0.041 0.21 0.12 0.5
0.161 0.84 0.25
1 0.03 2 0.32l 1.68 0.25 1
%Resist.
3.4s 1.6 6.7d 0 0 0 0
MIC,
MIC,
%RESIST.
0.5 0.5 0.03
45A 29D 22.5G OL
0.081 0.42 0.25 0.5
16 8 16 8 0.64 3.36 0.5 1
0.25 8 32 16 0.161 0.84 0.25 0.5
32 32 32 32 1.4J 6.6 0.5 I
32B 72E 84’ 28M
32 16 32 4 0.32/
32
7oc
32 32 16 2.71 13.3 4
88F 72n 6.6N
1
0 0 0
1990-1992t
Clindamycin Ciprofloxacin Rifampicin Netihnicin Trimethopriti Sulfametoxaz. Teicoplanin
1993-1994$ Clindamycin Ciprofloxacin Rifampicin Netihnicin Trimethoprim/ Sulfamethoxaa. Teicoulanin
0.25 0.25 0.01 0.25 0.161 0.84 0.12 0.5
1
0.5
32
1 32 4 0.3u 1.68 0.5
I
Ob
7.7 5.le 0 0 0 0
12.6c 7 17f
1 4.2 0 0
1.68 1 0.5
1
4 0 0
8.8 0
0
*MSSA, n = 59; MRSA, n = 31. TMSSA, n = 39; MRSA, n = 50. $MSSA, n = 95; MRSA, n = 91. Superscripts denote significance as follows: a + b vs. c, P = 0.011; b vs. c, P = 0.046; d + e vs. f, P = 0.063; A + B vs. C, and B vs. C, P < 0.0001; D vs. E, P = 0.01; D vs. E + F, G vs. H, and G vs. H + K, P < O.OO@l;L vs. M and L vs. N, P = 0.03 according to Chi-square test.
P. Baiocchi et al. /International Journal of Antimicrobial Agents 7 (19%)
compound were negligible for both groups. Teicoplanin showed similar activities against MSSA and MRSA isolated in the study periods 1986-1989 and 1990-1992; however, when the last study period, 1992-1994, was considered, MI& and MI&, against MRSA were eightfold and fourfold higher, respectively, than MI& and MU&, values against MSSA. In contrast, vancomycin showed similar activity against MSSA and MRSA isolates of each study period. Table 2 also shows thlat the activities of antibiotics against MSSA isolates did not change consistently through the years. The exceptions were clindamycin, with a 12.6% resistance rate during the study period 1993- 1994 that was significantly higher than the 0% rate observed during 1990-1992 (P = 0.046) and, to a lesser extent, rifampicin with a 17% resistance rate during 1993-1994 vs. 5.1-6.70//o during the previous study periods (P = 0.063). The evolution of antibiotic resistance among MRSA isolates was more consistent. When the earlier study period was compared with the period 1990-1992, significant increases in resistance rates to ciprofloxacin (29% vs. 79%, P = 0.01) and to rifampicin (22% vs. 84%, P < 0.0001) were observed. High resistance rates to these antibiotics were also maintained during the last period of study (1993-1994). The resistance rates of clindamycin was 70% during 1993-1994 versus 45% during 1986- 1989 (P= 0.021) and 32”/0during 1990-1992 (P c 0.0001). The resistance to netihnicin achieved a peak of 28% during 1990-1992, but fortunately declined to 6.6% during 1993- 1994. No significant variations in resistance to cotrimoxazole, teicoplanin and vancomycin were observed during the three study periods. No isolates resistant to the latter two compounds were ever observed. Table 3 shows the changes of susceptibility to glycopeptides among our MRSA isolates in terms of mean MIC and number of strains inhibited by MICs of 2-4 &ml that we arbitrarily defined as ‘moderately susceptible’. Isolates w:ith MICs of 2-4 &ml to teicoplanin were very rare during the first two periods,
93-96
95
accounting for only five (6%) of 81 MRSA isolates; on the contrary, of 91 isolates representative of the last study period as many as 25 (27S”/,) were inhibited by an MIC of 2 &ml and nine (10%) by an MIC of 4 @g/ml of teicoplanin. Isolates inhibited by an MIC of 2 &ml of vancomycin remained rare during all three study periods and no isolate ever required a concentration 14 &ml for inhibition. The mean MIC values of teicoplanin against MRSA isolates of the first two study periods were significantly lower than the value of the last period (0.33 &ml during 1986- 1989 and 0.43 &ml during 1990-1992 vs. 1.18 &ml during 1993-1994, P < 0.0001, according to Bonferroni ?-test). As far as vancomycin is concerned, the mean MIC values of the first two study periods were also lower than the value of the last period; however, the difference did not achieve statistical significance even when results of the earlier period where compared with those of the last period (P > 0.5,according to Bonferroni t-test). When vancomycin was compared to teicoplanin, a significantly lower number of isolates inhibited by an MIC of 2 &ml (P= 0.0001) or by an MIC of 4 &ml (P= 0.03) was found during the last study period. Based on data of mean MIC values, teicoplanin was more active than vancomycin against MRSA during the periods 1986-1989 (P= 0.018) and 1990-1992 (P= 0.033) but was less active than vancomycin during the 1993-1994 period (P < 0.0001). Among MSSA strains, only three isolated in the 1993- 1994 period had a moderate susceptibility to glycopeptides: two were inhibited by an MIC of 2 &ml of teicoplanin and one by an MIC of 2 &ml of vancomycin. 4. Discussion Since the present study is based on non-consecutive clinical isolates, the results may not strictly define the true epidemiology of antibiotic resistances among our MRSA. However, despite this limitation the available data seem to provide evidence of a trend towards
Table 3 Changes in susceptibility to glycopeptides among clinical isolates of methicillin-resistant Staphylococcus aureus from hospitalized patients during three study periods PCtiod
:No. isolates with the indicated MIC (&nl)/total
isolates and mean MIC MIC to vancomycin
IMICto teicoplanin
1986-1989 1990-1992 1993-1994
.2
4
Mean f SD.
2
4
Mean
1/31a 4/50b :25/91c
o/31* O/SOB 9l91C
0.33 l o.34c 0.43 + 0.51’ 1.18 * 1.17s
l/31 2l50 2f91d
o/31 o/50 0l91o
0.54 f 0.34h 0.63 f 0.41’ 0.70 l 0.35’
l
S.D.
Superscriptsdenote significance as follows: a vs. c, b vs. c, A + B vs. C, P = 0.01; B vs. C, P = 0.053; c vs. d, P C 0.0001; C VS. D, P = 0.006, according to Cbi-square test. e ‘vs.g, f vs. g, P < O.ooOl,according to Bonferroni r-test. e vs. h, P = 0.018; f vs. k, P = 0.033; g VS. J, P < 0.0001, according to Student’s J-test.
P. Baiocchi et al. /International Journal of Antimicrobial Agents 7 (1996) 93-96
96
increased antibiotic resistance among our nosocomial S. aureus. Based on previous reports [4,17], it is not surprising to document high rate of resistance to ciprofloxacin, rifampicin and clindamycin among MRSA isolates in a setting where these organisms are prevalent pathogens. Nevertheless, it was disappointing that most of MRSA isolates from our hospitalised patients are nowadays resistant to all three the above antibiotics. Potential advantages of combinations of these agents with glycopeptides for the treatment of serious or slowly responding infections seem obviously negated by such a wide spectrum of antibiotics resistance [3,5,8,11,15,16]. More importantly, our data show the emergence of ORSA isolates with a decreased susceptibility to glycopeptides, and in particular to teicoplanin. Of interest, teicoplanin concentrations of 2-4 &ml were very rarely required for inhibition of S. aureus before 1986- 1989 and for the 2 years after (1990- 1992) this drug became available in Italy. Decreased susceptibility to teicoplanin became apparent only after 1992, as a probable consequence of the increased usage of glycopeptides, in particular teicoplanin, for the high frequency of MRSA infections. In fact, during 1994 approximately 6000 vials of vancomycin and 18 000 vials of teicoplanin were administered in our hospital. Resistance to teicoplanin, but not to vancomycin, has been readily induced ‘in vitro’ in S. aureus isolates [18]. Emergence of teicoplanin resistance during therapy of a serious S. aureus infection has been also described [7] and MRSA isolates with MICs of 8- 16 &ml have been observed in other hospital settings [2,6]. It is therefore likely that, under the pressure of glycopeptide usage, the introduction of poorly susceptible MRSA strains in our hospital may provide a setting for development of full resistance in future. To conclude, the present study provides some data on the evolution of antibiotics resistances in a hospital where MRSA has emerged as a prevalent pathogen. The most interesting finding was a trend towards decreased susceptibility to teicoplanin documented among MRSA isolates. Whether this phenomenon arose from multiple instances of coincidental infection or from sequential transmission of a single strain remains to be elucidated, Further study is also required to understand the clinical significance of such reduced susceptibility to teicoplanin. Nevertheless, on the basis of our data we recommend strict adoption of infection control measures, including monitoring of susceptibility to glycopeptides, and a prudent use of teicoplanin in hospital settings where MRSA is a frequent cause of nosocomial infection. References [I] Annitage P. Statistical methods in medical research, 1st ed. Oxford: Blackwell Scientific Publications, 1971.
121Brunet F, Vedel G, Dreyfus F et al. Failure to teicopianin therapy in two neutropenic patients with staphylococcal septicemia who recovered after administration of vancomycin. Eur J Clin Microbial Infect Dis 1990$145-147. I31 Chuard C, Hermann M, Vandaux P, Waldvogel FA, Lew DP. Successful treatment of methicillin-resistant Staphyfococcus aureus by antimicrobial combination. Antimicrob Agents Chemother 1991;35:261l-2616. 141 Dawn TE, Schaberg DR, Terpenning MS, Sottile WS, Kaufmann CA. Increasing resistance of Staphylococcus aureus to ciprofloxacin. Antimicrobial Agents Chemother 1990,34: 1862-1863. 151 Faville RJ Jr, Zaske DE, Kaplan EL, Crossley K, Sabath LD, Anie PG. Staphylococcus aureus endocarditis. Combined therapy with vancomycin and rifampin. J Am Med Assoc 1978;240:1963-1965. M Goering RW, Fey PD, Goldstein FW. Usefulness of pulse-field gel electroforesis in the epidemiological analysis of Staphylococcus aureus isolates with decreased susceptibility to teicoplanin. Eur J Clin Microbial Infect Dis 1995;14(Suppl 1):3-5. [71 KaatzGW, Seo SM. Dorman NJ, Lemer SA. Emergence of teicoplanin resistance during therapy of Staphylococcus aureus endocarditis. J Infect Dis 1990,162:103-108. 181 Levine DP, Fromm BS, Reddy BR. Slow response to vancomycin or vancomycin plus rifampin in methicillin-resistant Staphylococm aureus endocarditis. Ann Intern Med 1991;115:674-680. [91 National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial disk susceptibility test, 4 th ed. Approved standard M2-A4. Villanova, PA: National Committee for Clinical Laboratory Standards, 1990. 1101 National Committee for Clinical Laboratory Standards. Methods for dilution antimicrobial susceptibility test for bacteria that grow aerobically, 2nd ed. Approved standard M7-A2. Villanova, PA: National Committee for Clinical Laboratory Standards, 1990. Small PM, Chambers HF. Vancomycin for Staphylococcus aureus endocarditis in intravenous drug users. Antimicrob Agents Chemother 1990,34:1227-1231. WI Thornsberry C, MC Dougal LK. Successful use of broth microdilution in susceptibility tests for methicillin-resistant (heteroresistant) staphylococci. J Clin Microbial 1983;18: 1084-1091. iI31 Varaldo PE, Cipriani P, Foci A et al. Identification, clinical distribution and susceptibility to methicillin and 18 additional antibioticsof clinical Staphylococcus isolates: nationwide investigation in Italy. J Clin Microbial 1984;19:833-843. 1141 Venditti M, Baiocchi P, Brandimarte C et al. High rate of oxacillin resistant Staphylococcus aureus isolates in an italian university hospital. J Chemother 1994;6:25-28. 1151 Venditti M, Baiocchi P, Santini C et al. Potential of clindamycin in addition to vancomycin for the treatment of oxacillinresistant Staphylococcus aureus septicemia persisting under vancomycin therapy. Int J Antimicrob Agents 1995;5:123-128. [IfA Voss A, Milatovic D, Wallranch-Schwatz C, Rosdhal VT, Braveny 1. Methicillin-resistant Staphylococcus aureus in Europe. Eur J Clin Microbial Infect Dis 1994;13:50-55. iI71 Watanakunakom C. Clindamycin therapy of Staphylococcus aureus endocarditis. Am J Med 1976;60:419-425. U81 Watanakunakom C. In vitro selection of resistance of Staphylococw aurew to teicoplanin and vancomycin. J Antimicrob Chemother 1990;25:69-72.