A Comparative In Vitro Surveillance Study of Gemifloxacin Activities against 2,632 Recent Streptococcus pneumoniae Isolates from across Europe, North America, and South America

Abstract

From 1997 to 1999, 94 study centers in 15 European, 3 North American, and 2 South American countries contributed 2,632 isolates of Streptococcus pneumoniae to an international antimicrobial susceptibility testing study. Only 62.0% of isolates were susceptible to penicillin, while 22.3% were penicillin intermediate and 15.6% were penicillin resistant. Resistance to trimethoprim-sulfamethoxazole (24.4%), azithromycin (26.0%), and clarithromycin (27.1%) was also highly prevalent. For the penicillin-resistant isolates (n = 411), the MICs at which 90% of isolates are inhibited (MIC₉₀s) for gemifloxacin, levofloxacin, ofloxacin, clarithromycin, and azithromycin were 0.03, 1, 2, >16, and >64 μg/ml, respectively. Similarly, for isolates resistant to both azithromycin and clarithromycin (n = 649), gemifloxacin, levofloxacin, ofloxacin, and penicillin MIC₉₀s were 0.03, 1, 2, and 4 μg/ml, respectively. Overall rates of resistance to trovafloxacin (0.3%), levofloxacin (0.3%), grepafloxacin (0.6%), and ofloxacin (0.7%) were low. For ofloxacin-intermediate and -resistant isolates (n = 142), gemifloxacin had the lowest MIC₉₀ (0.12 μg/ml) compared to the MIC₉₀s of trovafloxacin (0.5 μg/ml), grepafloxacin (1 μg/ml), and levofloxacin (2 μg/ml). For all S. pneumoniae isolates tested, gemifloxacin MICs were ≤0.5 μg/ml, suggesting that gemifloxacin has the potential to be used as a treatment for pneumococcal infections, including those arising from isolates resistant to β-lactams and macrolides.

Streptococcus pneumoniae is an important bacterial pathogen in upper and lower respiratory tract infections such as community-acquired pneumonia, meningitis, otitis media, and sinusitis. The rapid emergence of penicillin, macrolide, and multidrug resistance among isolates of S. pneumoniae during the 1990s (8) has encouraged the development, testing, and marketing of new antimicrobial agents such as quinolones with increased activity against respiratory pathogens. It has also resulted in new recommendations for the treatment of community-acquired pneumonia (3) and has necessitated antibiotic resistance surveillance studies to ensure continued efficacious, empiric therapy for patients (1, 2). Newer quinolones are now recommended for the treatment of respiratory tract infections due to S. pneumoniae, particularly for isolates resistant to β-lactam antibiotics (3).

Gemifloxacin (SB 265805) has been reported to possess excellent in vitro activity against S. pneumoniae, albeit against limited collections of isolates (<500 isolates) that were typically components of regional or national studies (5, 6, 10, 15, 16). The preceding investigations demonstrated that gemifloxacin possessed more potent activity than currently available quinolones against clinically significant gram-positive cocci, including S. pneumoniae (5, 6, 10, 15, 16). In addition, gemifloxacin also retained excellent activity against gram-negative bacilli and modest potency against nonfermentative gram-negative bacilli and anaerobes (5, 10, 15, 16). Gemifloxacin MICs have also been shown to be less affected in strains of S. pneumoniae harboring target site mutations (GyrA, GyrB, ParC, ParE) that resulted in significantly elevated MICs of other currently marketed quinolones, most noticeably, ciprofloxacin (4, 6, 9). The current study extends previous reports and presents comparative gemifloxacin susceptibility data by using a large collection of 2,632 recent international isolates of S. pneumoniae, including 141 ofloxacin-intermediate and -resistant isolates.

MATERIALS AND METHODS

S. pneumoniae isolates.

Between September 1997 and August 1999, 94 study sites in 20 countries each prospectively collected up to 50 isolates of S. pneumoniae. An isolate was accepted, one per patient, from a variety of specimen sources. Isolate inclusion was independent of medical history, patient age, or gender. Each isolate was identified as S. pneumoniae and was deemed to be a significant pathogen by using local laboratory criteria. The S. pneumoniae isolates described here are a component of a larger prospective international surveillance study of the activity of gemifloxacin against selected aerobic gram-positive and gram-negative pathogens. The demographic information available was limited to patient age.

One study center in each of the following countries participated in the study: Denmark, Finland, Poland, Spain, Sweden, and Switzerland. For Austria, Belgium, France, Germany, Greece, Italy, Luxembourg, The Netherlands, and the United Kingdom, 7, 6, 5, 6, 8, 3, 2, 16, and 2 study centers participated, respectively. In North America, 12 Canadian, 7 Mexican, and 3 U.S. study centers were used. In South America, there were five study centers in Argentina and six study centers in Brazil.

Antimicrobial susceptibility testing.

MICs were determined by the National Committee for Clinical Laboratory Standards (NCCLS)-recommended broth microdilution testing method (13). The dried microdilution panels used in this study, MicroScan (Dade Behring Inc., Sacramento, Calif.) and Sensititre (Trek Diagnostics Inc., West Sussex, United Kingdom), were purchased from two companies and used identical antibiotic dilution configurations. Gemifloxacin was supplied by SmithKline Beecham (Collegeville, Pa.), and the 10 comparative antimicrobials were supplied by their respective manufacturers or the panel manufacturer. Appropriate broth medium was also provided directly by the panel manufacturers. MICs were determined in each participating country at one or more designated testing laboratories. Each designated testing laboratory performed daily quality control testing that included S. pneumoniae ATCC 49619 (13). Test isolate results were accepted into the final analysis only if the MIC for the quality control isolate tested was within the acceptable range defined by NCCLS guidelines (13).

RESULTS

A total of 2,632 isolates of S. pneumoniae were tested for their susceptibilities to gemifloxacin and comparative antimicrobials (Table 1). The European study centers provided 76.1% (n = 2,002) of the isolates, with the study centers in North America (16.5%; n = 435) and South America (7.4%; n = 195) supplying the remaining organisms. The overall rates of resistance to penicillin (15.6%), cefuroxime (20.5%), azithromycin (26.0%), clarithromycin (27.1%), and trimethoprim-sulfamethoxazole (24.4%) were considerable and were a contrast to the low rates of resistance to trovafloxacin (0.3%), levofloxacin (0.3%), grepafloxacin (0.6%), and ofloxacin (0.7%) (14). Ofloxacin-intermediate (MIC, 4 μg/ml) isolates were prevalent (4.7%; n = 123), but most (>90%) retained their susceptibilities to the other quinolones tested. The activity of gemifloxacin against the 2,632 isolates was notably more potent than those of the other quinolones tested, with the MICs for all isolates being ≤0.5 μg/ml and with 99.7% of isolates being susceptible to gemifloxacin at ≤0.25 μg/ml. On the basis of comparisons of the MICs at which 90% of isolates are inhibited (MIC₉₀s) for the quinolones, gemifloxacin was 8-fold more potent than trovafloxacin and grepafloxacin, 32-fold more potent than levofloxacin, and 64-fold more potent than ciprofloxacin and ofloxacin (Table 1).

TABLE 1.

In vitro activities of gemifloxacin and 10 comparative antimicrobial agents against 2,632 isolates of S. pneumoniae collected from across Europe, North America, and South America

Antimicrobial agent	MIC (μg/ml)			Percenta
	50%	90%	Range	S	I	R
Penicillin	0.03	2	0.015–>16	62.0	22.3	15.6
Cefuroxime	0.06	4	0.06–>64	75.4	4.1	20.5
Azithromycin	0.06	>64	0.06–>64	72.0	2.1	26.0
Clarithromycin	0.03	>16	0.015–>16	71.2	1.7	27.1
SXTb	0.25	8	0.06–>64	64.3	11.4	24.4
Ciprofloxacin	1	2	0.015–>16	—c	—	—
Grepafloxacin	0.12	0.25	0.015–16	99.2	0.2	0.6
Levofloxacin	1	1	0.015–16	99.5	0.2	0.3
Ofloxacin	2	2	0.06–64	94.6	4.7	0.7
Trovafloxacin	0.12	0.25	0.015–>16	99.6	0.1	0.3
Gemifloxacin	0.015	0.03	0.001–0.5	—	—	—

^aNCCLS-recommended breakpoints were used to group isolates into the susceptible (S), intermediate (I), and resistant (R) categories (14). Breakpoints for ciprofloxacin and gemifloxacin susceptibility, intermediate, and resistance have not been published by NCCLS (14) for S. pneumoniae. 

^bSXT, trimethoprim-sulfamethoxazole at a ratio of 1:19. 

^c—, breakpoints have not been published by NCCLS (14) for S. pneumoniae. 

Table 2 depicts the in vitro activities of gemifloxacin and the 10 comparative antibiotics against penicillin-resistant, macrolide-resistant, and ofloxacin-intermediate and -resistant isolates of S. pneumoniae. Macrolide-resistant isolates were defined as isolates resistant to both azithromycin and clarithromycin (14). Rates of resistance to grepafloxacin, levofloxacin, ofloxacin, and trovafloxacin were low (<2%) for penicillin-resistant and macrolide-resistant isolates. Among the 142 ofloxacin-intermediate and -resistant isolates identified, 12.0, 9.8, and 4.9% were also nonsusceptible to grepafloxacin, levofloxacin, and trovafloxacin, respectively. On the basis of MIC₉₀ comparisons, gemifloxacin was 4-, 8-, 16-, 32-, and 64-fold more potent than trovafloxacin, grepafloxacin, levofloxacin, ciprofloxacin, and ofloxacin, respectively, against ofloxacin-intermediate and -resistant isolates (Table 2).

TABLE 2.

In vitro activities of gemifloxacin and 10 comparative antimicrobial agents against penicillin-resistant, macrolide-resistant, and ofloxacin-intermediate and -resistant isolates of S. pneumoniae

Phenotype (no. of isolates)	Antimicrobial agent	MIC (μg/ml)			Percenta
		50%	90%	Range	S	I	R
Penicillin resistant (411)	Penicillin	2	8	2–>16			100
	Cefuroxime	4	8	0.06–>64	3.4	6.3	90.2
	Azithromycin	16	>64	0.06–>64	31.0	4.6	64.4
	Clarithromycin	8	>16	0.015–>16	31.2	1.7	67.1
	SXTb	4	8	0.06–>64	12.2	13.6	74.2
	Ciprofloxacin	1	2	0.015–>16
	Grepafloxacin	0.12	0.25	0.015–16	98.3	0	1.7
	Levofloxacin	1	1	0.015–16	99.0	0.7	0.2
	Ofloxacin	2	2	0.06–32	91.4	6.1	1.7
	Trovafloxacin	0.12	0.25	0.015–>16	99.0	0.2	0.7
	Gemifloxacin	0.015	0.03	0.002–0.5
Macrolide resistantc (649)	Penicillin	1	4	0.015–>16	24.8	35.6	39.6
	Cefuroxime	4	8	0.06–>64	41.8	7.9	50.4
	Azithromycin	>64	>64	2–>64			100
	Clarithromycin	>16	>16	1–>16			100
	SXT	2	8	0.06–>64	36.1	14.5	49.5
	Ciprofloxacin	1	2	0.015–>16
	Grepafloxacin	0.12	0.25	0.015–16	98.5	0.2	1.4
	Levofloxacin	0.5	1	0.015–16	98.5	0.6	0.9
	Ofloxacin	2	2	0.06–64	92.0	6.6	1.4
	Trovafloxacin	0.12	0.25	0.015–>16	98.9	0.2	0.9
	Gemifloxacin	0.015	0.03	0.001–0.5
Ofloxacin intermediate + ofloxacin resistant (142)	Penicillin	0.12	4	0.015–>16	39.4	38.0	22.5
	Cefuroxime	0.12	8	0.06–>64	69.0	5.6	25.4
	Azithromycin	0.25	>64	0.06–>64	59.2	2.1	38.7
	Clarithromycin	0.06	>16	0.015–>16	55.6	4.2	40.1
	SXT	0.5	8	0.06–>64	54.9	14.1	31.0
	Ciprofloxacin	2	4	0.015–>16
	Grepafloxacin	0.25	1	0.03–16	87.9	2.1	9.9
	Levofloxacin	1	2	0.015–16	90.1	3.5	6.3
	Ofloxacin	4	8	4–64		86.6	13.4
	Trovafloxacin	0.25	0.5	0.015–>16	95.1	0	4.9
	Gemifloxacin	0.06	0.12	0.004–0.5

^aThe Breakpoints used to define the susceptible (S), intermediate (I), and resistant (R) categories are those recommended by NCCLS (14). 

^bSXT, trimethoprim-sulfamethoxazole at a ratio of 1:19. 

^cOnly isolates resistant to azithromycin and clarithromycin were included. 

All isolates for which ofloxacin MICs were ≥16 μg/ml (n = 9) were uniformly resistant to grepafloxacin, with seven of nine (77.8%) isolates resistant to trovafloxacin and six of nine (66.7%) isolates resistant to levofloxacin. For seven of the nine isolates for which ofloxacin MICs were ≥16 μg/ml, ciprofloxacin MICs were also ≥16 μg/ml. For isolates for which ofloxacin MICs were ≥16 μg/ml, gemifloxacin MICs ranged from 0.015 to 0.5 μg/ml (Table 2).

Ofloxacin-intermediate and -resistant isolates were primarily from European (5.8%; 117 of 2,002) and North American (5.1%; 22 of 435) study centers and were less prevalent among isolates from South America (1.5%; 3 of 195). Age data were provided for 2,491 of the 2,632 patients. Patients ≤16 years of age accounted for 43.5% (n = 1,083) of the isolates, while 33.2% (n = 828) and 23.3% (n = 580) of the patients were aged 17 to 64 and ≥65 years, respectively. Of the ofloxacin-intermediate and -resistant S. pneumoniae isolates, 5.1% (55 of 1,083) were isolated from patients ≤16 years of age, 5.7% (47 of 828) were isolated from patients 17 to 64 years of age, and 6.9% (40 of 580) were isolated from patients ≥65 years of age. In comparison, penicillin-resistant S. pneumoniae isolates were isolated from 18.7% (202 of 1,083) of patients ≤16 years of age, 12.3% (102 of 828) of patients 17 to 64 years of age, and 11.5% (67 of 580) of patients ≥65 years of age. Macrolide-resistant S. pneumoniae isolates were isolated from 23.5% (255 of 1,083) of patients ≤16 years of age, 22.8% (189 of 828) of patients 17 to 64 years of age, and 24.5% (142 of 580) of patients ≥65 years of age.

DISCUSSION

The 2,632 global isolates of S. pneumoniae tested in this study demonstrated high levels of penicillin (37.9%), trimethoprim-sulfamethoxazole (35.8%), clarithromycin (28.8%), and azithromycin (28.1%) nonsusceptibility. These data concur with those from other recent studies in which it was concluded that for patients with penicillin-resistant S. pneumoniae infections, one can assume almost complete cross-resistance to oral cephalosporins such as cefuroxime and a high likelihood (approximately 40%) of additional cross-resistance to macrolides, tetracycline, and/or trimethoprim-sulfamethoxazole (8, 17). The rapid increase in the rate of isolation of penicillin-intermediate, penicillin-resistant, and multidrug-resistant S. pneumoniae isolates will continue to alter empiric treatment guidelines for both community-acquired respiratory infections such as pneumonia, acute exacerbations of chronic bronchitis, sinusitis, and otitis media, as well as the treatment of hospitalized patients (3, 17).

In the present study, gemifloxacin was the most potent antibiotic tested against S. pneumoniae, an important respiratory tract pathogen. The potent activity of gemifloxacin against pneumococci resistant to penicillin, azithromycin, clarithromycin, and ofloxacin supports similar findings by other investigators (5, 6, 10, 15, 16). Most recently, Davies and coworkers (6) reported that gemifloxacin demonstrated similar activity against pneumococci irrespective of penicillin susceptibility, with MIC₉₀s of 0.03 to 0.06 μg/ml (range, 0.03 to 0.25 μg/ml). In addition, those investigators (6) reported that gemifloxacin retained potent activity against 28 isolates for which ciprofloxacin MICs were ≥8 μg/ml and that possessed defined GyrA and ParC mutations and efflux resistance mechanisms. The gemifloxacin MIC₉₀ for this collection was 0.5 μg/ml (range, 0.03 to 1 μg/ml) and demonstrated that gemifloxacin was 8- to >64-fold more potent than levofloxacin, sparfloxacin, grepafloxacin, and trovafloxacin against the same isolates (6). Others have shown similarly potent activity for gemifloxacin against strains for which ciprofloxacin (9, 11, 15) and levofloxacin (12) MICs are elevated. Investigators have also reported that the antipneumococcal potency of gemifloxacin is two- to fourfold greater than that of clinafloxacin (12), fourfold greater than that of moxifloxacin (11), and eightfold greater than that of sparfloxacin (11).

Prior to the recent introduction of quinolones specific for respiratory tract infections into clinical use, quinolones were generally not recommended for the treatment of S. pneumoniae infections. Irrespective of this, low levels of resistance (<1%) to grepafloxacin, levofloxacin, sparfloxacin, and trovafloxacin have been reported, with higher levels (approximately 1.7%) of S. pneumoniae isolates demonstrating decreased susceptibility to ciprofloxacin (4). For all 2,632 isolates of S. pneumoniae tested in the present study gemifloxacin MICs were ≤0.5 μg/ml, despite concurrent resistance to grepafloxacin, levofloxacin, ofloxacin and trovafloxacin among some isolates, and for 3.4% (n = 89) of isolates ciprofloxacin MICs were ≥4 μg/ml.

Appendix

The participating centers or contact investigators in Europe were Institute für Hygeine, Innsbruck, Austria; B. Sixl, Graz, Austria; Bundesst. Bakteriologie-Serologie Untersuchangsanstalt, Salzburg, Austria; Bundesst. Bakteriologie-Serologie, Klagenfurt, Austria; Institute für Pathologie, Steyr, Austria; Pathologie Institute, Neustadt, Austria; Universität-Klinik für Innere Medizin, Vienna, Austria; Laboratorium Micro UZ St. Rafael, Lueven, Belgium; Medisch Centrum Huisartsen, Leuven, Belgium; Lab. Cliniques Université U.C.L. De Mont-Godinne, Yvoir, Belgium; Eeinheid Antibiotica-Onderzoek Pasteurinstitut, Brussels, Belgium; Lab. De Micro Hopital Université Erasme, Brussels, Belgium; La Microbiologia UZ Antwerpen, Edegern, Belgium; Aarhus University Hospital, Aarhus, Denmark; Haartman Institute, Helsinki, Finland; R. Leclercq, Chucote de Nacre, France; M. Chomarat, Centre Hospitalier Lyon-SUD, Lyon, France; Faculte De Medecine, Strasbourg, France; Hospital Calmette, Lille, France; Hospital Central, Nancy, France; Pharmazeutische Mikrobiologie, Bonn, Germany; Zentrum für Hygiene, Freiburg, Germany; Institut für Medizinische Mikrobiologie, Cologne, Germany; Institut für Medizinische Mikrobiologie, Frankfurt, Germany; MEDQM, Berlin, Germany; Institut für Medizinische Mikrobiologie, Aachen, Germany; LAIKON General Hospital, Athens, Greece; Ippokrateion Hospital, Thessaloniki, Greece; Geniko Nomarhiako Mitilinis Hospital, Mitilini, Greece; Geniko Nomarhiako Kerkyras Hospital “Agia Eirini,” Kerkyra, Greece; Geniko Nomarhiako Rethimnou Hospital, Rethimno, Greece; AHEPA Hospital, Thessaloniki, Greece; Geniko Kratiko Periferiako Patras Hospital “Agios Andreas,” Patra, Greece; National and Capodistrian University of Athens, Athens, Greece; Universita degli studi di Genova, Genoa, Italy; Laboratorio Analisi Presidio Ospedaliero Macedon, Milan, Italy; Laboratorio Analisi Chimicocliniche Microbiologia, Sondalo, Italy; Streeklaboratorium Siunt Elisabeth Ziekenhuis, Tilburg, The Netherlands; Medische Microbiologie Diaconessenhuis, Utrecht, The Netherlands; Medische Microbiologie Ziekenhuis De Heel, Zaandam, The Netherlands; Streeklaboratorium Zeeland, Terneuzen, The Netherlands; Eijkman-Winkler Institute, Utrecht, The Netherlands; St. P.A.M.M., Veldhoven, The Netherlands; Academisch Ziekenhuis Maastricht, Maastricht, The Netherlands; Medische Microbiologie Vrije Universiteit AZVU, Amsterdam, The Netherlands; Streeklaboratorium GG & GD, Amsterdam, The Netherlands; Laborator. Medische Microbiologie D. C. SSDZ, Delft, The Netherlands; Medische Microbiologie, Groot Ziekengasthuis, Den Bosch, The Netherlands; Medische Microbiologie Westende Ziekenhuis, Den Haag, The Netherlands; Streeklaboratorium vd Volsgezondheid, Enschede, The Netherlands; Streeklaboratorium Zeeland, Goes, The Netherlands; Streeklaboratorium vd Volksgezondheid, Groningen, The Netherlands; Streeklaboratorium vd Volksgezondheid, Haarlem, The Netherlands; C.B.S.L., Hilversum, The Netherlands; Streeklaboratorium vd Volksgezondheid, Leeuwarden, The Netherlands; Regionaal Med. Microbiologisch Lab. Zuiderzieknhuis, Rotterdam, The Netherlands; Central Sera and Vaccines Laboratory, Warsaw, Poland; Hospital Gregorio Maranon, Madrid, Spain; Lund University Hospital, Lund, Sweden; Universitaire Vaudois Hospitalier, Lausanne, Switzerland; St. Thomas Hospital, London, United Kingdom; and The North Middlesex Hospital, London, United Kingdom.

The participating centers in North America were Mount Sinai Hospital, Toronto, Ontario, Canada; Health Sciences Centre, Winnipeg, Manitoba, Canada; Calgary Laboratory Services, Calgary, Alberta, Canada; Victoria General Hospital, Victoria, British Columbia, Canada; St. Joseph's Health Centre, London, Ontario, Canada; General Hospital, St. John's Newfoundland, Canada; Hospital Maisonneuve-Rosemont, Montreal, Quebec, Canada; The Moncton Hospital, Moncton, New Brunswick, Canada; QE II Health Services Centre, Halifax, Nova Scotia, Canada; Ottawa Hospital, Ottawa, Ontario, Canada; Princess Margaret Hospital, Toronto, Ontario, Canada; The Toronto Hospital, Toronto, Ontario, Canada; Hospital General de Durango; Durango, Mexico; Instituto Nacional de la Nutricion “Salvador Zubiran,” Mexico City, Mexico; Departamento de Infectologia Instituto Nacional de Enfermedades Respiratorias, Mexico City, Mexico; Instituto Mex. del Seguro Social, Monterrey, Mexico; Asesores Especializadores en Lab., Puebla, Mexico; Lab. de Bacteriologia 3er Piso, Instituto Nacional Ped., San Jose Insurgentes, Mexico; Hospital Infantil de Mexico, Mexico City, Mexico; Stanford University Hospital, Stanford, Calif.; The Bryn Mawr Hospital, Bryn Mawr, Pa.; and Evanston Northwestern Healthcare, Evanston, Ill.

The participating centers in South America were FUNCEI Centro de Estudios Infectologicos, Buenos Aires, Argentina; Hospital Medico Policial Churruca-Visca, Buenos Aires, Argentina; Centro de Infectologia, Buenos Aires, Argentina; Hospital Britanico de Buenos Aires, Buenos Aires, Argentina; Centro de Estudios Microbiologicos, Buenos Aires, Argentina; Instituto de Infectologia Emilio Ribas, Sao Paulo, Brazil; Silo Controle de Qualidade em Alimentos E Productos Ltda., Rio de Janeiro, Brazil; Laboratorio do Hospital Santa Helena, Sao Paulo, Brazil; Laboratorio Medico Santa Luzia, Florianopolis, Brazil; Laboratorio Fleury, Sao Paulo, Brazil; and Laboratorio da Faculdade de Ciencias Farmaceuticas, Sao Paulo, Brazil.