Title: Resistance of Streptococcus pneumoniae to penicillin, erythromycin and third-generation cephalosporins in Seville, Southern Spain
Abstract: Clin Microbiol Infect 1997; 3: 382-385 Resistance of Streptococcus pneumoniae to penicillin and third-generation cephalosporins is increasing in many countries, particularly in Spain, where some of the highest incidences of resistance to penicillin and other antimicrobial agents have been described [1Baquero F Pneumococcal resistance to β-lactam antibiotics: a global geographical overview.Microb Drug Resist. 1995; 1: 115-120Crossref PubMed Scopus (158) Google Scholar]. Both penicillin-resistant (PRP) and -intermediate strains are less susceptible to other β-lactams than penicillin-susceptible strains [2Liñares J Alonso T Pérez JL et al.Decreased susceptibility of penicillin-resistant pneumococci to twenty-four β-lactams.J Antimicrob Chemother. 1992; 30: 279-288Crossref PubMed Scopus (143) Google Scholar]. Third-generation cephalosporins have been considered to be an alternative for the treatment of infections caused by PRP. Nevertheless, strains resistant to third-generation cephalosporins have been described and, in some cases, therapeutic failures have been observed when these agents were used [3John CC Treatment failure with use of a third-generation cephalosporin for penicillin- resistant pneumococcal meningitis: case report and review.Clin Infect Dis. 1994; 18: 188-193Crossref PubMed Scopus (186) Google Scholar, 4Catalán MJ Fernández JM Vázquez A Varela de Seijas E Suárez A Bernaldo de Quirós C Failure of cefotaxime in the treatment of meningitis due to relatively resistant Streptococcus pneumoniae.Clin Infect Dis. 1994; 18: 766-769Crossref PubMed Scopus (91) Google Scholar]. In this study, the activities of penicillin, cefotaxime, ceftriaxone, erythromycin and vancomycin against clinical isolates of S. pneumoniae were determined. The incidence of resistance to these agents in our area and the relationship between resistance to third-generation cephalosporins and other agents were also evaluated. Two hundred and twelve S. pneumoniae strains, consecutively isolated from different patients between January 1993 and December 1995 at the University Hospital V. Macarena, Seville, Spain, were studied. The sources of the strains were sputum (84, 39.6%), blood culture (53, 25.0%), bronchial aspirate (23, 10.8%), ocular exudate (19, 9.0%), pleural effusion (9, 4.2%), cerebrospinal fluid (CSF) (4, 1.9%), and others (20, 9.4%). Isolates were identified by standard methods [5Ruoff KL Streptococcus.in: Murray PR Baron EJ Pfaller MA Tenover FC Yolken RH Manual of clinical microbiology, 6th edn. American Society for Microbiology, Washington1995: 299-307Google Scholar]. S. pneumoniae ATCC 49619 and Staphylococcus aureus ATCC 29213 were used as control strains. Penicillin G (Sigma, USA), cefotaxime (Hoechst, Germany), ceftriaxone (Sigma, USA), erythromycin (Sigma, USA) and vancomycin (Lilly, USA) were used as standard powders of known potency. A microdilution assay using cation-adjusted Mueller-Hinton broth (Difco, USA), supplemented with 5% lysed horse blood (Difco, USA), was used, with incubation at 35°C for 24 h in air. The antimicrobial concentrations evaluated ranged from 0.03 to 64 μg/mL. Strains were classified as susceptible, intermediate or resistant to penicillin when MIC values were ≤0.06, 0.125-1, or ≥2 μg/mL, respectively [6National Committee for Clinical Laboratory Standards. Methods for dilution antimicrobial susceptibility test for bacteria that grow aerobically, 3rd edn. NCCLS publication M7-A3. Villanova, Pa: NCCLS.Google Scholar]. Strains with MICs of cefotaxime or ceftriaxone of 1 μg/mL were considered intermediate, and those with MICs of ≥2 μg/mL resistant to these agents [7National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial susceptibility testing: Fifth International Supplement. NCCLS Document M100-S5. Villanova, Pa: NCCLS.Google Scholar]. Susceptibility categories for erythromycin and vancomycin were established according to the NCCLS guidelines [6National Committee for Clinical Laboratory Standards. Methods for dilution antimicrobial susceptibility test for bacteria that grow aerobically, 3rd edn. NCCLS publication M7-A3. Villanova, Pa: NCCLS.Google Scholar]. Range, MIC50, MIC90 values and percentages of intermediate and resistant strains to the antimicrobial agents evaluated are presented in Table 1. Considering penicillin G, 39.2% were intermediate and 12.3% were resistant, while 4.2% were resistant to cefotaxime and 4.2% to ceftriaxone. Resistance to erythromycin was observed in 27.4% of the strains. No resistance to vancomycin was observed.Table 1Range, MIC50 and MIC90 values (μg/mL) of five antimicrobial agents against S. pneumoniae (212 strains)RangeMIC50MIC90% Intermediate% ResistancePenicillin≤0.03-40.125239.212.3Cefotaxime≤0.03-40.0618.44.2Ceftriaxone≤0.03-20.0619.84.2Erythromycin≤0.03->64≤0.03>644.227.4Vancomycin≤0.03-10.250.250.00.0 Open table in a new tab The relationship between resistance to third-generation cephalosporins and penicillin resistance is shown in Table 2. All strains resistant to cefotaxime and/or ceftriaxone (10, 4.7%) were also penicillin resistant. Resistant strains always had an MIC of third-generation cephalosporins of 2 μg/mL, except for one strain, for which the MIC of cefotaxime was 4 μg/mL. One strain was resistant to ceftriaxone (MIC 2 μg/mL) but susceptible to cefotaxime (MIC 0.5 μg/mL). Another one was resistant to cefotaxime (MIC 2 μg/mL) but susceptible to ceftriaxone (MIC 0.5 μg/mL). Eighteen (8.4%) strains were intermediate to cefotaxime and 21 (9.8%) to ceftriaxone. All of them were also intermediate or resistant to penicillin. Of penicillin-resistant and penicillin-intermediate strains, 57.7% and 43.4%, respectively, were resistant to erythromycin. Similarly, 45.5% and 56.5% of cefotaxime-ceftriaxone-resistant and -intermediate strains, respectively, were resistant to erythromycin.Table 2Relationship between susceptibility to penicillin and to cefotaxime-ceftriaxone among 212 isolates of S. pneumoniaeCefotaximeCeftriaxoneIntermediate (%)Resistant (%)Intermediate (%)Resistant (%)PenicillinSusceptible0.00.00.00.0Intermediate4.20.05.60.0Resistant4.24.24.24.2 Open table in a new tab Among the 57 strains isolated from either blood or CSF, 18 (31.6%) and eight (14%), respectively, were intermediate or resistant to penicillin G, and seven (12.3%) and two (3.5%), respectively, were intermediate or resistant to third-generation cephalosporins. These values are similar to those obtained for the total strain population studied (see Table 1). There are many studies on the resistance of S. pneumoniae to antimicrobial agents. The different results in those reports led to the recommendation that each community should develop its own surveillance system to determine the local epidemiology of this problem. For this reason, we have studied the resistance of S. pneumoniae to five antimicrobial agents in our area, located in southern Spain. In this study, 12.3% of pneumococci were resistant to penicillin. In other areas of Spain, the current prevalence of PRP (MIC of penicillin >1 μg/mL) ranges from 10% to 20%, depending on the age of the patients, the geographic area and the origin of the isolates [8Liñares J Tubau F Meningitis neumocócica y cefalosporinas de tercera generación.Enf Infect Microb Clin. 1996; 14: 1-6PubMed Google Scholar]. In other regions of Europe, the prevalence of PRP varies significantly from 0-5% (in Germany, Switzerland and Italy) to 11-17% (in France) to around 50% (in Hungary and Romania) [1Baquero F Pneumococcal resistance to β-lactam antibiotics: a global geographical overview.Microb Drug Resist. 1995; 1: 115-120Crossref PubMed Scopus (158) Google Scholar]. Similar variations have been reported in the USA. In one large multicenter study, an overall incidence of 6.6% was reported [9Greiman RF Butler JC Tenover FC Elliot JA Facklam RP Emergence of drug resistant pneumococcal infections in the United States.JAMA. 1994; 271: 1831-1835Crossref PubMed Scopus (559) Google Scholar], but the incidence was 61% in Kentucky among isolates from the nasopharynx of children from day-care centers [10Morbid Mortal Wkly Rep. Update: Drug-resistant S.P.Kentucky and Tennessee. 1994; 43: 23-25Google Scholar]. The emergence of S. pneumoniae strains intermediate or resistant to third-generation cephalosporins has been recognized in several countries. Considering only resistant strains (MIC ≥2 μg/mL), data range from 0% (Germany) to 2.5% (UK) to 4% (USA) [1Baquero F Pneumococcal resistance to β-lactam antibiotics: a global geographical overview.Microb Drug Resist. 1995; 1: 115-120Crossref PubMed Scopus (158) Google Scholar]. Pérez-Trallero et al reported a prevalence of 5.2% in northern Spain [11Pérez-Trallero E García-Arenzana JM Montes M López-Lopategui C Cilia G Incremento de la resistencia a cefotaxima en Streptococcus pneumoniae en Guipúzcoa. Estudio de 14 años.VI Reunión Nacional de Enfermedades Infecciosas y Microbiología Clínica Sitges, Barcelona. 1995; (Resumen 7.9.)Google Scholar], a figure similar to that presented in this study (Table 1). The vast majority of our S. pneumoniae strains intermediate/resistant to third-generations cephalosporins were not susceptible to penicillin as has been previously reported. Resistance to cefotaxime and susceptibility to penicillin has also been described [12Coffey TJ Daniels M McDougal K Dowson CG Tenover FC Spratt BF Genetic analysis of clinical isolates of Streptococcus pneumoniae with high-level resistance to expanded-spectrum cephalosporins.Antimicrob Agents Chemother. 1995; 39: 1306-1313Crossref PubMed Scopus (143) Google Scholar], but was not found among our strains. In Spain, Moreno et al reported an increasing resistance to erythromycin from 7.6% in 1988 to 15.2% in 1992, particularly in children under 5 years and hospitalized patients [13Moreno S García-Leoni ME Cercenado E Díaz MD Bernaldo de Quirós JCL Bouza E Infections caused by erythromycin-resistant Streptococcus pneumoniae: incidence, risk-factors, and response to therapy in a prospective study.Clin Infect Dis. 1995; 20: 1195-1200Crossref PubMed Scopus (98) Google Scholar]. Similar trends have been observed in other European countries and the USA [14Geslin P Buu-Hoi A Frémaux A Acar JF Antimicrobial resistance in Streptococcus pneumoniae: an epidemiological survey in France, 1970-1990.Clin Infect Dis. 1992; 15: 95-98Crossref PubMed Scopus (166) Google Scholar, 15Tarpay MM Welch DF Salari H Marks MI In vitro activity of antibiotics commonly used in the treatment of otitis media against Streptococcus pneumoniae isolates with different susceptibilities to penicillin.Antimicrob Agents Chemother. 1982; 22: 145-147Crossref PubMed Scopus (16) Google Scholar]. In Barcelona (Spain), 13-24% of S. pneumoniae isolates were resistant to erythromycin [8Liñares J Tubau F Meningitis neumocócica y cefalosporinas de tercera generación.Enf Infect Microb Clin. 1996; 14: 1-6PubMed Google Scholar]. In our study, the resistance to this antimicrobial agent was even higher (27.4%). About one-quarter (25.8%) of erythromycin- resistant S. pneumoniae isolates were also resistant to penicillin, and 8.6% of them were also resistant to third-generation cephalosporins. As has been documented in all published reports, we found no strain resistant to vancomycin. The authors thank P. Hidalgo and J. Dawson for preparing the manuscript. These data were partially presented at the 7th European Congress of Clinical Microbiology and Infectious Diseases, held in Vienna from 26 March to 30th March 1995.