Susceptibility of group A beta-hemolytic streptococci in the lower St Lawrence region, Quebec

A DesRosiers, P Dolcé, P Jutras, LP Jetté. Susceptibility of group A beta-hemolytic streptococci in the lower St Lawrence region, Quebec, Canada. Can J Infect Dis 1999;10(4):279-285. OBJECTIVE: To determine the susceptibility of group A beta-hemolytic streptococci (GABHS) in the lower St Lawrence region, Quebec to different antibiotics, particularly macrolides, and to compare different antibiogram methods (disk diffusion, E-test and microdilution) and incubation atmospheres (ambient air and 5% carbon dioxide). METHODS: A total of 384 strains of GABHS isolated from 377 patients (throat 335; other sites 49) from three hospitals in the lower St Lawrence region were analyzed for their susceptibility to erythromycin, clarithromycin, azithromycin, penicillin, clindamycin, cephalothin, rifampin and vancomycin by disk diffusion on Mueller-Hinton (MH) agar supplemented with 5% defibrinated sheep blood (MHB) at 35ºC in 5% carbon dioxide. Strains that were found to be intermediately resistant or resistant to one of the antibiotics by disc diffusion, strains from sites other than throat, and a sample of 97 pharyngeal strains were evaluated by E-test on MHB (35ºC, 5% carbon dioxide) for their susceptibility to the antibiotics erythromycin, clarithromycin, azithromycin, penicillin, clindamycin and ceftriaxone. In addition, minimum inhibitory concentrations (MICs) were determined for erythromycin and azithromycin by broth microdilution using MH broth supplemented with 2.5 % of lysed horse blood (35ºC, ambient air) on strains that were resistant or intermediately resistant to the macrolides (erythromycin, clarithromycin, azithromycin). An evaluation was also carried out on these strains to determine the influence of the incubating atmosphere (ambient air versus 5% carbon dioxide) on susceptibility results obtained by disk diffusion (erythromycin, clarithromycin and azithromycin) and E-test (erythromycin and azithromycin) methods. RESULTS: Nine strains (2%) from nine patients (throat eight, pus one) were resistant to all macrolides as tested by three different techniques (disk diffusion, E-test and microdilution). All strains were susceptible to all the other antibiotics tested. For the strains intermediately resistant or resistant to macrolides, incubation in a 5% carbon dioxide atmosphere was associated with a reduction in the diameter of inhibition determined by disk diffusion (P<0.001) with frequent minor variations in interpretation, and with an increase in the MIC by E-test (P<0.001), which had no impact on interpretation. CONCLUSIONS: Resistance of GABHS to macrolides was not common (2%) in the lower St Lawrence Region. GABHS susceptibility to erythromycin seemed to predict the susceptibility to the other macrolides. Significant variation in antibiogram results (disk diffusion and E-test) of GABHS susceptibility to macrolides was related to the incubation atmosphere and may have an impact on the interpretation of disk diffusion results. I n the past few years with the resurgence of invasive infections, group A beta-hemolytic streptococci (GABHS) have become a public health threat (1-8). Surveillance programs have been implemented in many countries. In Canada, in the province of Quebec, GABHS invasive infections became a notifiable disease in 1995 (unpublished data). In 1995, 11 cases of invasive GABHS infections occurred in the lower St Lawrence region (LSLR) of Quebec. This region, with a population of approximately 215,000 people, had an incidence rate of 5.1/100 000 cases/year, the highest in the province of Quebec. The overall incidence rate in Quebec was 1.4/100,000 cases/year (unpublished data). Pharyngitis is the most frequent clinical manifestation of GABHS infections, and it is believed that pharyngitis usually precedes invasive infections. Penicillin is the antibiotic of choice in the treatment of pharyngitis. Erythromycin is recommended as an alternative for patients allergic to penicillin (9,110). Recently, increasing resistance of GABHS to erythromycin and its derivatives has been observed in several countries. In Japan, the frequency of GABHS erythromycin resistance rose from 2% in 1971 to 50% to 70% in the 1990s (11-13). A resistance of nearly 40% was reported in certain areas of Finland in 1990 (14-16) and was associated with the level of regional erythromycin consumption. Erythromycin resistance dropped to 8.6% after a successful nationwide information and education program to reduce erythromycin consumption (17). Such high levels of resistance have not been reported in North America. For instance, the rate of erythromycin resistance is low in the United States: 5% and less, for studies published between 1968 and 1997 (11,18,19). Very few Canadian studies have addressed the issue of GABHS resistance to macrolides. In 1992, Knowles et al (20) found 2% erythromycin resistance among 492 GABHS isolates from clinical specimens gathered from in a children's hospital in Montreal. They also reported that, in comparison with ambient air, incubation under a 5% carbon dioxide atmosphere was associated with a significant increase in minimal inhibition concentration (MIC) for GABHS isolates to erythromycin and clarithromycin. A similar effect of incubation atmosphere was described by Brorson and Larsson (21). The aim of the present study was to determine the susceptibility level of GABHS to different antibiotics, particularly macrolides, in the LSLR. In addition, the study compared different antibiogram methods (disk diffusion, E-test and microdilution) and two incubation atmospheres (ambient air and 5% carbon dioxide) in a subset of isolates. MATERIALS AND METHODS GABHS strains: GABHS isolates were collected between March 1995 and February 1996 from three hospitals in the LSLR: the Centre Hospitalier Régional de Rimouski, the Centre Hospitalier d'Amqui and the Centre Hospitalier du Grand Portage. A maximum of two strains per patient were admissible: one strain from the throat and the other from a normally sterile site. 280 Can J Infect Dis Vol 10 No 4 July/August 1999 MÉTHODES : En tout, on a analysé 384 isolats de SBHGA provenant de 377 patients (gorge, 335; autres foyers, 49) de trois hôpitaux du Bas Saint-Laurent pour vérifier leur sensibilité à l'érythromycine, à la clarithromycine, à l'azithromycine, à la pénicilline, à la clindamicyne, à la céphalothine, au rifampim et à la vancomycine, par diffusion en gélose de Mueller-Hinton (MH) enrichie de sang de mouton à 5 % défibriné (SMD), à 35°C, dans du dioxyde de carbone à 5 %. Les souches qui se sont révélées résistantes ou moyennement résistantes à l'un des antibiotiques par la méthode de diffusion en gélose, les souches provenant d'autres foyers que la gorge et un échantillon de 97 isolats pharyngés ont été éva-lués par test E sur SMD (35°C, dioxyde de carbone à 5 %) pour en mesurer la sensibilité à l'endroit des antibiotiques érythromycine, clarithromycine, azithromycine, pénicilline, clindamycine et ceftriaxone. De plus, les concentrations minimales inhibitrices (CMI) ont été calculées pour l'érythromycine et l'azithromycine par microdilution sur bouillon de culture, à l'aide de solutions MH auxquelles a été ajouté du sang de cheval à 2,5 % lysé (35°C, air ambiant), sur des souches qui se sont révélées résistantes ou moyennement résistantes à l'endroit des macrolides (érythromycine, clarithromycine, azithromycine). Une évaluation a en outre été effectuée sur ces souches afin de déterminer l'influence de l'atmosphère d'incubation (air ambiant vs dioxyde de carbone à 5 %) sur les résultats d'antibiogrammes obtenus par diffusion en gélose (érythromycine, clarithromycine et azithromycine) et test E (érythromycine et azithromycine). RÉSULTATS : Neuf souches (2 %) provenant de neuf patients (8 prélèvements de gorge, 1 spécimen de pus) se sont révé-lées résistantes à tous les macrolides testés au moyen des trois techniques (diffusion en gélose, test E et microdilution). La totalité des souches se sont révélées sensibles à tous les autres antibiotiques testés. Pour les souches résistantes ou moyennement résistantes aux macrolides, l'incubation dans une atmosphère de dioxyde de carbone à 5 % a été associée à une réduction du diamètre d'inhibition, déterminée par la méthode de diffusion en gélose (p < 0,001), avec fréquentes variations mineures des interprétations et augmentation de la CMI selon le test E (p < 0,001), qui n'ont eu aucun impact sur l'interprétation de ces résultats. CONCLUSIONS : La résistance des SBHGA à l'endroit des macrolides n'a pas été fréquente (2 %) dans le Bas Saint-Laurent. Leur sensibilité à l'érythromycine a semblé être un facteur de prévisibilité de leur sensibilité aux autres macrolides. La variabilité significative des résultats d'antibiogrammes (diffusion en gélose et test E), du degré de sensibilité des SBHGA à l'endroit des macrolides a été jugée en lien avec l'atmosphère d'incubation et pourrait exercer un impact sur l'interprétation des résultats obtenus au moyen de la technique par diffusion en gélose. Statistical analysis: Data were analyzed on EPI INFO, version 6.0 (Atlanta, Georgia). The influence of the incubation atmosphere (ambient air versus carbon dioxide) was determined by ANOVA with a significance level of P<0.05 using SYSTAT software, version 5.02 (Systat Inc, Evanston, Illinois). Conservation and reidentification: Review of the medical files: The medical files of patients with strains resistant or intermediately resistant to macrolides were reviewed to obtain any pertinent clinical data. RESULTS A total of 384 GABHS strains isolated from 377 patients (throat 335 [87%], other sites 49 [13%]) were examined (Table 1). Seven patients had two isolates: one from the throat and the second from another site (wound four, fascia two, joint liquid one). Fifteen of the 49 nonpharyngeal strains were isolated in patients with invasive infections. The re-identification of all 384 strains confirmed them to be S pyogenes. Only six isolates yielded unexpected results; all exhibited trimethoprim/sulphamethoxazole susceptibility. In these cases, seroagglutination with group A antigen gave positive results

Susceptibility of Group A Beta-Hemolytic Streptococci in the Lower St Lawrence Region, Quebec

OBJECTIVE: To determine the susceptibility of group A beta-hemolytic streptococci (GABHS) in the lower St Lawrence region, Quebec to different antibiotics, particularly macrolides, and to compare different antibiogram methods (disk diffusion, E-test and microdilution) and incubation atmospheres (ambient air and 5% carbon dioxide)

Coxiella burnetii seroprevalence of shepherds and their flocks in the lower Saint-Lawrence River region of Quebec, Canada

OBECTIVE: To determine the seroprevalence of Coxiella burnetii among the shepherds and their sheep in the lower Saint-Lawrence River region (LSLRR) of Quebec, Canada