Antimicrobial susceptibilities of 1,684 Streptococcus pneumoniae and 2,039 Streptococcus pyogenes isolates and their ecological relationships: results of a 1-year (1998-1999) multicenter surveillance study in Spain

Gaps in the wall: understanding cell wall biology to tackle amoxicillin resistance in Streptococcus pneumoniae

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia, and one of the main pathogens responsible for otitis media infections in children. Amoxicillin (AMX) is a broad-spectrum β-lactam antibiotic, used frequently for the treatment of bacterial respiratory tract infections. Here, we discuss the pneumococcal response to AMX, including the mode of action of AMX, the effects on autolysin regulation, and the evolution of resistance through natural transformation. We discuss current knowledge gaps in the synthesis and translocation of peptidoglycan and teichoic acids, major constituents of the pneumococcal cell wall and critical to AMX activity. Furthermore, an outlook of AMX resistance research is presented, including the development of natural competence inhibitors to block evolution via horizontal gene transfer, and the use of high-throughput essentiality screens for the discovery of novel cotherapeutics.

Endolysins as emerging alternative therapeutic agents to counter drug-resistant infections

Endolysins are the lytic products of bacteriophages which play a specific role in the release of phage progeny by degrading the peptidoglycan of the host bacterium. In the light of antibiotic resistance, endolysins are being considered as alternative therapeutic agents because of their exceptional ability to target bacterial cells when applied externally. Endolysins have been studied against a number of drug-resistant pathogens to assess their therapeutic ability. This review focuses on the structure of endolysins in terms of cell binding and catalytic domains, lytic ability, resistance, safety, immunogenicity and future applications. It primarily reviews recent advancements made in evaluation of the therapeutic potential of endolysins, including their origin, host range, applications, and synergy with conventional and non-conventional antimicrobial agents.

Antimicrobial Resistance in Streptococcus spp

The genus Streptococcus includes Gram-positive organisms shaped in cocci and organized in chains. They are commensals, pathogens, and opportunistic pathogens for humans and animals. Most Streptococcus species of veterinary relevance have a specific ecological niche, such as S. uberis, which is almost exclusively an environmental pathogen causing bovine mastitis. In contrast, S. suis can be considered as a true zoonotic pathogen, causing specific diseases in humans after contact with infected animals or derived food products. Finally, Streptococcus species such as S. agalactiae can be sporadically zoonotic, even though they are pathogens of both humans and animals independently. For clarification, a short taxonomical overview will be given here to highlight the diversity of streptococci that infect animals. Several families of antibiotics are used to treat animals for streptococcal infections. First-line treatments are penicillins (alone or in combination with aminoglycosides), macrolides and lincosamides, fluoroquinolones, and tetracyclines. Because of the selecting role of antibiotics, resistance phenotypes have been reported in streptococci isolated from animals worldwide. Globally, the dynamic of resistance acquisition in streptococci is slower than what is experienced in Enterobacteriaceae, probably due to the much more limited horizontal spread of resistance genes. Nonetheless, transposons or integrative and conjugative elements can disseminate resistance determinants among streptococci. Besides providing key elements on the prevalence of resistance in streptococci from animals, this article will also largely consider the mechanisms and molecular epidemiology of the major types of resistance to antimicrobials encountered in the most important streptococcal species in veterinary medicine.

Results from the Survey of Antibiotic Resistance (SOAR) 2011-13 in Turkey

OBJECTIVES

Data are presented from the Survey of Antibiotic Resistance (SOAR) for respiratory tract infection pathogens collected in 2011-13 from Turkey.

METHODS

MICs were determined using Etest(®). Susceptibility was assessed using CLSI, EUCAST and pharmacokinetic/pharmacodynamic (PK/PD) interpretive criteria.

RESULTS

Rates of antibiotic susceptibility were very low among 333 isolates of Streptococcus pneumoniae tested: penicillin 38% using CLSI (oral) and EUCAST breakpoints; erythromycin 51% using CLSI and EUCAST criteria; and cefuroxime 64.6% using CLSI and PK/PD and 46.9% using EUCAST. Of the isolates, >90% were susceptible to amoxicillin/clavulanic acid, ceftriaxone (except using EUCAST criteria: 76%), levofloxacin and high-dose intravenous penicillin. Among 339 Haemophilus influenzae isolates, 6.8% were β-lactamase positive while 9.1% were β-lactamase negative but ampicillin resistant (BLNAR) by CLSI (14.7% by EUCAST) criteria. Amoxicillin/clavulanic acid susceptibility was ∼90% by CLSI (with or without BLNAR adjustment, EUCAST and high-dose PK/PD) but lower, at 82.9%, by EUCAST with BLNAR adjustment. Levofloxacin susceptibility was 96% using all three breakpoints. Dramatic differences in rates of susceptibility, depending on the breakpoints used, were seen for cefaclor [94% by CLSI (86.4% BLNAR adjusted), 23% by PK/PD] and cefuroxime [97% by CLSI (89.1% BLNAR adjusted), 85% by PK/PD, 15% by EUCAST (13.0% BLNAR adjusted)]. Streptococcus pyogenes (n = 222) and Moraxella catarrhalis (n = 40) isolates remained highly susceptible to amoxicillin/clavulanic acid, cephalosporins and levofloxacin, with only erythromycin susceptibility dropping below 95% for S. pyogenes.

CONCLUSIONS

Overall, amoxicillin/clavulanic acid and levofloxacin were the most active antibiotics based on all three breakpoints against these pathogens. Although susceptibility was not universally low in Turkey, high resistance rates were found in S. pneumoniae and, when using PK/PD and EUCAST breakpoints, in other respiratory pathogens.

Efficacy and Tolerability of Eight Antimicrobial Regimens in the Outpatient Treatment of Exacerbations of Chronic Obstructive Pulmonary Disease

BACKGROUND: Bacterial infections are considered as the most important cause of exacerbations in patients with chronic obstructive pulmonary disease.AIM: To compare the efficacy and tolerability of eight antibiotics empirically administered for outpatient treatment of exacerbations of COPD.METHODS: We performed an observational study including 343 COPD patients with probable bacterial exacerbation (Group A and Group B COPD patients) managed in an outpatient setting. Eight antibiotic regimens each used 10 days were evaluated: amoxicillin/clavulonic acid, doxycycline, cefuroxime, cefixime, clarithromycin, roxithromycin, ciprofloxacin, and moxifloxacin. All patients were followed up for 30 days, with an intermediate visits at 5, 7 and 10 days at which the duration of symptoms and the side-effects of the drug were evaluated.RESULTS: The clinical success rate varied from 69.8% with doxycycline to 80.9% with moxifloxacin. The mean time to relief of symptoms varied from 5.6 days with moxifloxacin to 6.3 days with amoxicillin/clavulonic acid. Significant increase of the post-treatment FEV1value was registered in all treatment groups. Relapse within the first 20 days was registered in the group receiving doxycycline, clarithromycin, and ciprofloxacin. The prevalence of the adverse events was low varying from 6.7% with cefuroxime to 11.3% with ciprofloxacin.CONCLUSION: Our findings suggest high clinical success rate and high safety of all studied regimens.

Serotyping, Antibiotic Susceptibility and Related Risk Factors Aspects of Nasopharyngeal Carriage of Streptococcus pneumoniae in Healthy School Students

BACKGROUND

Streptococcus pneumoniae is an important problem worldwide and nasopharyngeal colonization plays significant role in pneumococcal infections. The aims of this study were to determine the nasopharyngeal colonization rate, serotyping, antibiotics susceptibility and study the risk factors for nasopharyngeal colonization with S. pneumoniae in students in Kashan, Iran.

METHODS

A cross-sectional study was conducted on children aged 7 to 19 years from December 2011 to November 2012. Nasopharyngeal swabs were plated onto brain heart infusion agar plates with 5% sheep blood and 4µg/ml of gentamycin. Antimicrobial susceptibility profiles were determined on Mueller-Hinton agar in accordance with CLSI. S. pneumoniae strains were investigated for the presence of the most common pneumococcal serotypes using a multiplex polymerase chain reaction.

RESULTS

13.9% were found to be carriers. The most prevalent serogroups were 19F (30%), 6A/B (18.9%), 15A (16.5%), 11 (11.3%), 23F (8.2%), 1 (6.2%), 19A (3.4%), and 35B (2.4%). Nine strains (3.1%) were non-typeable. The carrier rate was significantly higher in 12 to15 year old age group. Upper respiratory tract infections within the last month (OR=1.5, P<0.011), previous hospitalization (OR=1.6, P<0.001), previous antibiotic usage last two weeks (OR=1.89, P<0.001), rhinorea (OR=1.9 P<0.001), male sex (OR=3.5 P< 0.001) and passive smoking (OR=1.56, P< 0.001) have been determined to be risk factors for S. pneumoniae carriage. The highest pneumococcal resistance was to tetracycline (25.4%). All strains were susceptible to linezolid and levofloxacin.

CONCLUSION

Our information leads to an important source to screen the future impact of pneumococcal vaccination on bacterial colonization.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Molecular resistance mechanisms of macrolide-resistant invasive Streptococcus pneumoniae isolates from Alaska, 1986 to 2010

The rapid emergence of antibiotic-resistant pneumococcal strains has reduced treatment options. The aim of this study was to determine antimicrobial susceptibilities, serotype distributions, and molecular resistance mechanisms among macrolide-resistant invasive pneumococcal isolates in Alaska from 1986 to 2010. We identified cases of invasive pneumococcal disease in Alaska from 1986 to 2010 through statewide population-based laboratory surveillance. All invasive pneumococcal isolates submitted to the Arctic Investigations Program laboratory were confirmed by standard microbiological methods and serotyped by slide agglutination and the Quellung reaction. MICs were determined by the broth microdilution method, and macrolide-resistant genotypes were determined by multiplex PCR. Among 2,923 invasive pneumococcal isolates recovered from 1986 to 2010, 270 (9.2%) were nonsusceptible to erythromycin; 177 (66%) erythromycin-nonsusceptible isolates demonstrated coresistance to penicillin, and 167 (62%) were multidrug resistant. The most frequent serotypes among the macrolide-resistant isolates were serotypes 6B (23.3%), 14 (20.7%), 19A (16.7%), 9V (8.9%), 19F (6.3%), 6A (5.6%), and 23F (4.8%). mef and erm(B) genes were detected in 207 (77%) and 32 (12%) of the isolates, respectively. Nineteen (7%) of the erythromycin-nonsusceptible isolates contained both mef and erm(B) genotypes; 15 were of serotype 19A. There was significant year-to-year variation in the proportion of isolates that were nonsusceptible to erythromycin (P < 0.001). Macrolide resistance among pneumococcal isolates from Alaska is mediated predominantly by mef genes, and this has not changed significantly over time. However, there was a statistically significant increase in the proportion of isolates that possess both erm(B) and mef, primarily due to serotype 19A isolates.

Global fluoroquinolone resistance epidemiology and implictions for clinical use

This paper on the fluoroquinolone resistance epidemiology stratifies the data according to the different prescription patterns by either primary or tertiary caregivers and by indication. Global surveillance studies demonstrate that fluoroquinolone resistance rates increased in the past years in almost all bacterial species except S. pneumoniae and H. influenzae, causing community-acquired respiratory tract infections. However, 10 to 30% of these isolates harbored first-step mutations conferring low level fluoroquinolone resistance. Fluoroquinolone resistance increased in Enterobacteriaceae causing community acquired or healthcare associated urinary tract infections and intraabdominal infections, exceeding 50% in some parts of the world, particularly in Asia. One to two-thirds of Enterobacteriaceae producing extended spectrum β-lactamases were fluoroquinolone resistant too. Furthermore, fluoroquinolones select for methicillin resistance in Staphylococci. Neisseria gonorrhoeae acquired fluoroquinolone resistance rapidly; actual resistance rates are highly variable and can be as high as almost 100%, particularly in Asia, whereas resistance rates in Europe and North America range from <10% in rural areas to >30% in established sexual networks. In general, the continued increase in fluoroquinolone resistance affects patient management and necessitates changes in some guidelines, for example, treatment of urinary tract, intra-abdominal, skin and skin structure infections, and traveller's diarrhea, or even precludes the use in indications like sexually transmitted diseases and enteric fever.

Resistance surveillance studies: a multifaceted problem--the fluoroquinolone example

INTRODUCTION

This review summarizes data on the fluoroquinolone resistance epidemiology published in the previous 5 years.

MATERIALS AND METHODS

The data reviewed are stratified according to the different prescription patterns by either primary- or tertiary-care givers and by indication. Global surveillance studies demonstrate that fluoroquinolone- resistance rates increased in the past several years in almost all bacterial species except Staphylococcus pneumoniae and Haemophilus influenzae causing community-acquired respiratory tract infections (CARTIs), as well as Enterobacteriaceae causing community-acquired urinary tract infections. Geographically and quantitatively varying fluoroquinolone resistance rates were recorded among Gram-positive and Gram-negative pathogens causing healthcare-associated respiratory tract infections. One- to two-thirds of Enterobacteriaceae producing extended-spectrum β-lactamases (ESBLs) were fluoroquinolone resistant too, thus, limiting the fluoroquinolone use in the treatment of community- as well as healthcare-acquired urinary tract and intra-abdominal infections. The remaining ESBL-producing or plasmid-mediated quinolone resistance mechanisms harboring Enterobacteriaceae were low-level quinolone resistant. Furthermore, 10-30 % of H. influenzae and S. pneumoniae causing CARTIs harbored first-step quinolone resistance determining region (QRDR) mutations. These mutants pass susceptibility testing unnoticed and are primed to acquire high-level fluoroquinolone resistance rapidly, thus, putting the patient at risk. The continued increase in fluoroquinolone resistance affects patient management and necessitates changes in some current guidelines for the treatment of intra-abdominal infections or even precludes the use of fluoroquinolones in certain indications like gonorrhea and pelvic inflammatory diseases in those geographic areas in which fluoroquinolone resistance rates and/or ESBL production is high. Fluoroquinolone resistance has been selected among the commensal flora colonizing the gut, nose, oropharynx, and skin, so that horizontal gene transfer between the commensal flora and the offending pathogen as well as inter- and intraspecies recombinations contribute to the emergence and spread of fluoroquinolone resistance among pathogenic streptococci. Although interspecies recombinations are not yet the major cause for the emergence of fluoroquinolone resistance, its existence indicates that a large reservoir of fluoroquinolone resistance exists. Thus, a scenario resembling that of a worldwide spread of β-lactam resistance in pneumococci is conceivable. However, many resistance surveillance studies suffer from inaccuracies like the sampling of a selected patient population, restricted geographical sampling, and undefined requirements of the user, so that the results are biased. The number of national centers is most often limited with one to two participating laboratories, so that such studies are point prevalence but not surveillance studies. Selected samples are analyzed predominantly as either hospitalized patients or patients at risk or those in whom therapy failed are sampled; however, fluoroquinolones are most frequently prescribed by the general practitioner. Selected sampling results in a significant over-estimation of fluoroquinolone resistance in outpatients. Furthermore, the requirements of the users are often not met; the prescribing physician, the microbiologist, the infection control specialist, public health and regulatory authorities, and the pharmaceutical industry have diverse interests, which, however, are not addressed by different designs of a surveillance study. Tools should be developed to provide customer-specific datasets.

CONCLUSION

Consequently, most surveillance studies suffer from well recognized but uncorrected biases or inaccuracies. Nevertheless, they provide important information that allows the identification of trends in pathogen incidence and antimicrobial resistance.

Evaluation of short-term clinical efficacy of 3-day therapy with azithromycin in comparison with 5-day cefcapene-pivoxyl for acute streptococcal tonsillopharyngitis in primary care

Group A streptococcal (GAS) tonsillopharyngitis is one of the few conditions for which antibiotics are advocated among common upper respiratory infections. Although a 3-day course of azithromycin is attracting attention as a treatment of choice for the condition, it is not clear if the efficacy of the treatment is comparable with that of treatment with cephalosporins. A prospective, randomized, comparative multicenter study was conducted to compare the efficacy of azithromycin (AZM) given once daily for 3 days with that of cefcapene-pivoxyl (CFPN-PI) divided into three daily doses for 5 days. 88 patients (male: 38, mean age: 16.5) were treated with AZM and 69 (male: 34, mean age: 16.9) with CFPN-PI. The symptoms of all but 5 (2 for AZM and 3 for CFPN-PI) of the patients were resolved by the 8th day of the treatment. By the 4th day of the treatment, criteria for clinical efficacy were fulfilled in 71 (80.7%) subjects who were treated with AZM and in 48 (67.6%) of those treated with CFPN-PI (p = 0.07). The same figures on the 8th day of the treatment were 86 (97.7%) and 68 (95.8%), respectively (p = 0.66), confirming there was no significant difference in clinical efficacy between the two treatments. Mild adverse reactions were reported by two patients treated with AZM and by none treated with CFPN-PI. The clinical efficacy of a 3-day course with AZM was comparable with that of a 5-day course of CFPN-PI for GAS tonsillopharyngitis.

Drug resistance in community-acquired respiratory tract infections: role for an emerging antibacterial

The nasopharynx is the ecological niche where evolution towards resistance occurs in respiratory tract isolates. Dynamics of different bacterial populations in antibiotic-free multibacterial niches are the baseline that antibiotic treatments can alter by shifting the competitive balance in favor of resistant populations. For this reason, antibiotic resistance is increasingly being considered to be an ecological problem. Traditionally, resistance has implied the need for development of new antibiotics for which basic efficacy and safety data are required prior to licensing. Antibiotic development is mainly focused on demonstrating clinical efficacy and setting susceptibility breakpoints for efficacy prediction. However, additional information on pharmacodynamic data predicting absence of selection of resistance and of resistant subpopulations, and specific surveillance on resistance to core antibiotics (to detect emerging resistances and its link with antibiotic consumption in the community) are valuable data in defining the role of a new antibiotic, not only from the perspective of its therapeutic potential but also from the ecologic perspective (countering resistances to core antibiotics in the community). The documented information on cefditoren gleaned from published studies in recent years is an example of the role for an emerging oral antibacterial facing current antibiotic resistance in community-acquired respiratory tract infections.

Antimicrobial resistance among respiratory pathogens in Spain: latest data and changes over 11 years (1996-1997 to 2006-2007)

A nationwide multicenter susceptibility surveillance study (Susceptibility to the Antimicrobials Used in the Community in España [SAUCE] project), SAUCE-4, including 2,559 Streptococcus pneumoniae, 2,287 Streptococcus pyogenes, and 2,736 Haemophilus influenzae isolates was carried out from May 2006 to June 2007 in 34 Spanish hospitals. Then, the results from SAUCE-4 were compared to those from all three previous SAUCE studies carried out in 1996-1997, 1998-1999, and 2001-2002 to assess the temporal trends in resistance and the phenotypes of resistance over the 11-year period. In SAUCE-4, on the basis of the CLSI breakpoints, penicillin (parenteral, nonmeningitis breakpoint) and cefotaxime were the antimicrobials that were the most active against S. pneumoniae (99.8% and 99.6%, respectively). Only 0.9% of isolates had a penicillin MIC of > or = 2 microg/ml. In S. pyogenes, nonsusceptibility to erythromycin was observed in 19.4% of isolates. Among the H. influenzae isolates, a beta-lactamase-positive prevalence of 15.7% was found. A statistically significant temporal decreasing trend over the 11-year period was observed for nonsusceptibility (from 60.0% to 22.9%) and resistance (from 36.5% to 0.9%) to penicillin and for the proportion of erythromycin-resistant isolates of S. pneumoniae of the macrolide-lincosamide-streptogramin B (MLS(B)) phenotype (from 98.4% to 81.3%). A similar trend was observed for the prevalence of ampicillin resistance (from 37.6% to 16.1%), beta-lactamase production (from 25.7% to 15.7%), and beta-lactamase-negative ampicillin resistance (BLNAR) in H. influenzae (from 13.5% to 0.7%). Among erythromycin-resistant isolates of S. pyogenes, a significant increasing trend in the prevalence of MLS(B) was observed (from 7.0% to 35.5%). SAUCE-4 confirms a generalized decline in the resistance of the main respiratory pathogens to the antimicrobials as well as a shift in their resistance phenotypes.

Penicillin-binding protein gene alterations in Streptococcus uberis isolates presenting decreased susceptibility to penicillin

Streptococcus uberis is an environmental pathogen commonly causing bovine mastitis, an infection that is generally treated with penicillin G. No field case of true penicillin-resistant S. uberis (MIC > 16 mg/liter) has been described yet, but isolates presenting decreased susceptibility (MIC of 0.25 to 0.5 mg/liter) to this drug are regularly reported to our laboratory. In this study, we demonstrated that S. uberis can readily develop penicillin resistance in laboratory-evolved mutants. The molecular mechanism of resistance (acquisition of mutations in penicillin-binding protein 1A [PBP1A], PBP2B, and PBP2X) was generally similar to that of all other penicillin-resistant streptococci described so far. In addition, it was also specific to S. uberis in that independent resistant mutants carried a unique set of seven consensus mutations, of which only one (Q(554)E in PBP2X) was commonly found in other streptococci. In parallel, independent isolates from bovine mastitis with different geographical origins (France, Holland, and Switzerland) and presenting a decreased susceptibility to penicillin were characterized. No mosaic PBPs were detected, but they all presented mutations identical to the one found in the laboratory-evolved mutants. This indicates that penicillin resistance development in S. uberis might follow a stringent pathway that would explain, in addition to the ecological niche of this pathogen, why naturally occurring resistances are still rare. In addition, this study shows that there is a reservoir of mutated PBPs in animals, which might be exchanged with other streptococci, such as Streptococcus agalactiae, that could potentially be transmitted to humans.

In vitro activity of CEM-101 against Streptococcus pneumoniae and Streptococcus pyogenes with defined macrolide resistance mechanisms

CEM-101 had MIC ranges of 0.002 to 0.016 microg/ml against macrolide-susceptible pneumococci and 0.004 to 1 microg/ml against macrolide-resistant phenotypes. Only 3 strains with erm(B), with or without mef(A), had CEM-101 MICs of 1 microg/ml, and 218/221 strains had CEM-101 MICs of 64 microg/ml, while 17/19 strains had telithromycin MICs of 4 to 16 microg/ml; CEM-101 MICs were 0.015 to 1 microg/ml. By comparison, erm(A) and mef(A) strains had CEM-101 MICs of 0.015 to 0.5 microg/ml, clindamycin and telithromycin MICs of 64 microg/ml. Pneumococcal multistep resistance studies showed that although CEM-101 yielded clones with higher MICs for all eight strains tested, seven of eight strains had clones with CEM-101 MICs that rose from 0.004 to 0.03 microg/ml (parental strains) to 0.06 to 0.5 microg/ml (resistant clones); for only one erm(B) mef(A) strain with a parental MIC of 1 microg/ml was there a resistant clone with a MIC of 32 microg/ml, with no detectable mutations in the L4, L22, or 23S rRNA sequence. Among two of five S. pyogenes strains tested, CEM-101 MICs rose from 0.03 to 0.25 microg/ml, and only for the one strain with erm(B) did CEM-101 MICs rise from 1 to 8 microg/ml, with no changes occurring in any macrolide resistance determinant. CEM-101 had low MICs as well as low potential for the selection of resistant mutants, independent of bacterial species or resistance phenotypes in pneumococci and S. pyogenes.

Prevalence and clonal characterization of Streptococcus pyogenes clinical isolates with reduced fluoroquinolone susceptibility in Spain

The aim of this study was to determine the prevalence and characteristics of non-fluoroquinolone (FQ)-susceptible Streptococcus pyogenes isolates and to study their mechanisms of resistance. We performed a prospective prevalence study with 468 isolates collected from 2005 to 2007 and a retrospective study that was based on the examination of existing data collected from 1999 to 2008. The retrospective study included data for isolates with high-level resistance (HR) to ciprofloxacin (MIC >or= 32 microg/ml) (HR isolates) and isolates with the same emm types as those reported in the literature with low-level resistance (LR) to ciprofloxacin (MICs, 2 to 8 microg/ml) (LR isolates, n = 205). Genetic characterization of the isolates was performed by means of emm typing and multilocus sequence typing. The prevalence of LR ranged from 1.9% in 2005 to 30.8% in 2007. This increase was mainly due to the circulation of an emm6 subtype (emm6.4) that represented 77.1% of the LR isolates in 2007. Notably, another emm6 subtype, also detected in 2007 (emm6.37), showed coresistance to 14- and 15-membered macrolides mediated by the mefA gene. Only three HR isolates were detected (isolates emm68.1/ST247/T3,13,B3264, emm77/ST399/T28, and emm28/ST52/T28), and all were identified in the retrospective study. Overall, the 673 isolates represented 25 emm types. All LR isolates were clustered into two emm types: emm6 (six emm6 subtypes) and emm75. All the 156 emm6 isolates had LR, harbored the Ser79/Ala mutation in the parC gene product, and had the same sequence type (ST), ST382. Most (21/33) of the emm75 isolates had LR, showed the Ser79/Phe plus Asp91/Asn double mutation in the parC gene product, and were ST150. The Asp91/Asn mutation by itself did not confer resistance to FQs.

Prevalence and mechanisms of macrolide resistance inStreptococcus pyogenesin Ankara, Turkey

From 2002 to 2003, a total of 381 consecutive S. pyogenes isolates were obtained from throat swabs (n = 337) and samples of pus (n = 31), sputum (n=10) and blood (n = 3) at Hacettepe University Hospital. The susceptibility of the isolates to erythromycin was tested by the agar dilution method. Erythromycin resistant strains were then tested for their MICs to azithromycin, clindamycin, and penicillin, their phenotype of resistance to macrolides-lincosamides-streptogramin B (MLSB) and for the presence of macrolide resistance genes. The rate of resistance to erythromycin was 6.8%. Constitutive (cMLSB), inducible (iMLSB), and M phenotypes of resistance were detected in 7.7, 30.8, and 57.7% of resistant strains, respectively. One strain had both cMLSB and iMLSB phenotypes. All M phenotypes carried the mefA gene, all iMLSB phenotype carried the ermTR gene, 1 isolate with cMLSB phenotype harboured the ermB gene, and 1 isolate with cMLSB phenotype carried both the ermB and mefA genes. One strain which showed cMLSB and iMLSB phenotypes harboured the ermB gene.

Population biology of the human restricted pathogen, Streptococcus pyogenes

Streptococcus pyogenes, also referred to as beta-hemolytic group A streptococci, are strictly human pathogens with a global distribution and high prevalence of infection. The organisms are characterized by high levels of genetic recombination, extensive strain diversity, and a narrow habitat. This review highlights many key features of the population genetics and molecular epidemiology of this biologically diverse bacterial species, with special emphasis on ecological subdivisions and tissue-specific infections, strain diversity and population dynamics in communities, selection pressures arising from the specific host immune response and antibiotic exposure, and within-host selection during the course of invasive disease.

Population biology of the human restricted pathogen, Streptococcus pyogenes

Streptococcus pyogenes, also referred to as beta-hemolytic group A streptococci, are strictly human pathogens with a global distribution and high prevalence of infection. The organisms are characterized by high levels of genetic recombination, extensive strain diversity, and a narrow habitat. This review highlights many key features of the population genetics and molecular epidemiology of this biologically diverse bacterial species, with special emphasis on ecological subdivisions and tissue-specific infections, strain diversity and population dynamics in communities, selection pressures arising from the specific host immune response and antibiotic exposure, and within-host selection during the course of invasive disease.

Antimicrobial susceptibility of Streptococcus pyogenes in Central, Eastern, and Baltic European Countries, 2005 to 2006: the cefditoren surveillance program

The in vitro activity of penicillin, ampicillin, cefditoren, cefotaxime, erythromycin, clarithromycin, and levofloxacin against 763 clinical isolates of Streptococcus pyogenes was determined. Clinically significant isolates collected from November 2005 to December 2006 in the Czech Republic, Slovakia, Hungary, Poland, Romania, Estonia, Latvia, and Lithuania (the latter 3 analyzed as Baltic countries) were studied. No resistance to beta-lactams and levofloxacin was found. The rate of erythromycin resistance in S. pyogenes varied among countries, being low (<10%) in Romania and Baltic countries, intermediate (10-20%) in Poland and Czech Republic, and high (>25%) in Hungary and Slovakia. The predominant (75.0%) erythromycin-resistant phenotype among S. pyogenes isolates was MLS(B). The identification of the prevalence of erythromycin resistance mechanism could have impact on the choice of empiric antibiotic therapy for the clinicians in such countries.

Antibiotic Resistance of Non-Pneumococcal Streptococci and Its Clinical Impact

Viridans streptococci (VGS) form a phylogenetically heterogeneous group of species belonging to the genus Streptococcus (1). However, they have some common phenotypic properties. They are alfa- or non-haemolytic. They can be differentiated from S. pneumoniae by resistance to optochin and the lack of bile solubility (2). They can be differentiated from the Enterococcus species by their inability to grow in a medium containing 6.5% sodium chloride (2). Earlier, so-called nutritionally variant streptococci were included in the VGS but based on the molecular data they have now been removed to a new genus Abiotrophia (3) and are not included in the discussion below. VGS belong to the normal microbiota of the oral cavities and upper respiratory tracts of humans and animals. They can also be isolated from the female genital tract and all regions of the gastrointestinal tract (2, 3). Several species are included in VGS and are listed elsewhere (2, 3). Clinically the most important species belonging to the VGS are S. mitis, S. sanguis and S. oralis.

Breakthrough in penicillin resistance? Streptococcus pneumoniae isolates with penicillin/cefotaxime MICs of 16 mg/L and their genotypic and geographical relatedness

OBJECTIVES

To phenotypically and genotypically characterize 11 strains (isolated in four different centres) exhibiting penicillin MIC of 8-32 mg/L among isolates of the SPICE project. Nine isolates were from Romania (9/162; 5.56%) and two from Poland (2/305; 0.66%).

METHODS

In vitro susceptibility was determined in triplicate by microdilution (CLSI guidelines), and additionally, MICs of penicillin, cefotaxime and amoxicillin were confirmed in triplicate by agar dilution. Multilocus sequence typing (MLST), PFGE and gene amplification and sequencing were performed.

RESULTS

For the nine Romanian isolates, MICs were >/=16 mg/L for penicillin, cefotaxime and amoxicillin, >/=32 mg/L for cefuroxime and cefpodoxime, 4-8 mg/L for cefditoren and >/=128 mg/L for erythromycin and gentamicin. All isolates were non-susceptible to imipenem (MIC = 0.5-1 mg/L) and susceptible to levofloxacin (MIC = 0.5-1 mg/L) and vancomycin (MIC = 0.25-0.5 mg/L). These Romanian strains presented a new cluster in the 595-600 region of PBP2X (YSGIQL-->LSTPWF) conferring 98% homology with Streptococcus mitis PBP2X, with a new MurM allele (seven strains) with eight amino acid changes versus R6. PBP nucleotide sequences were highly conserved suggesting a common origin. Allelic profiles of two strains gave sequence type 321, three strains exhibited a single- and four a double-locus variance. MLST-predicted serotype was 23F in all but one strain (19F), but three strains were 19A by Quellung.

CONCLUSIONS

The multidrug high resistance (precluding adequate oral therapy in children), its origin, the prevalence found in Romania and the presence of non-vaccine (7-valent) serotypes should worry the medical community because of a possible clonal diffusion that would limit therapeutic alternatives.

Superiority of D-zone Testing Method over Standard Method to detect Rnducible Resistance in Gram Positive Bacteria: a Prospective Surveillance from a Teaching Hospital in Saudi Arabia

OBJECTIVE

In this prospective study, we determined phenotypic resistance to erythromycin among gram positive bacteria.

METHODS

BACTERIAL ISOLATES WERE IDENTIFIED BY CONVENTIONAL METHODS AND BY THE MICROSCAN: D-test zone was performed according to the Clinical and Laboratory Standards institutes (CLSI) recommendations to determine inducible resistance to clindamycin on gram positive bacteria isolated from different clinical specimens. Bacterial isolates included : group A streptococci (GAS), group B streptococci (GBS), viridans streptococci, S.pneumoniae, Staphylococcus aureus (S.aureus) (both methicillin susceptible (MSSA) and methicillin resistant (MRSA).

RESULTS

A total of 1072 gram positive bacterial isolates were tested. The majority was from swabs collected from outpatient clinics. Erythromycin resistance was 8/23 (35%) for S. pneumoniae, 12/91(13%) for GAS and 17/300(5.7%) for GBS. All GAS and viridans streptococci possessed the efflux phenotype only, 8(8.8% and 1(20%), respectively. For GBS, cMLS(B) was 11(3.7%), 3 (1%) iMLS(B) and 2(0.33%) were of efflux phenotype. All S.pneumoniae strains possessed cMLS(B) phenotype. Seventy five isolates (16.3%) of MSSA were resistant to erythromycin compared to 160(83%) of MRSA. The majority of MSSA, 31/460 (6.7%) had an efflux phenotype while 26/460(5.6%) were of cMLS(B) and 19/460(4%) iMLS(B) phenotypes. Constitutive MLS(B) was the most predominant resistant phenotype, 152/193(78.8%) among MRSA.

CONCLUSION

D-test zone should be considered for routine testing to detect inducible clindamycin resistance among significant gram positive bacteria.

An intrinsic pattern of reduced susceptibility to fluoroquinolones in pediatric isolates of Streptococcus pyogenes

A total of 116 clinical isolates collected in 2003 from a tertiary pediatric hospital and a primary pediatric department in Chicago, IL, were screened for reduced susceptibility to selected fluoroquinolones by disc diffusion. Correlation between reduced susceptibility and point mutations in the quinolone resistance-determining region of parC and gyrA genes was evaluated, and point mutations were compared with other reports of isolates derived from adult or mixed patient populations. Nine percent of isolates had reduced susceptibility to 1 or more of these fluoroquinolones by Etest: ciprofloxacin, levofloxacin, and moxifloxacin. A single point mutation (Ser-79) in parC seemed responsible for the reduced susceptibility. Resistant Streptococcus pyogenes isolates were compared using M/emm type, repetitive sequence-based PCR (rep-PCR), and pulsed-field gel electrophoresis (PFGE). Rep-PCR provided no more separation of strains than M/emm typing, and PFGE results with SgrAI were more discriminatory than with SmaI. The majority of these isolates were M/emm type 6. PFGE analysis using SgrAI demonstrated 2 different resistant strains among the M/emm type 6 isolates. The findings suggest that a population of S. pyogenes with an intrinsic reduced susceptibility to fluoroquinolones exists in pediatric clinical isolates. Monitoring of amino acid changes in both parC and gyrA will assist in the prediction of emergence of high-level fluoroquinolone resistance.

Antistreptococcal activity of AR-709 compared to that of other agents

Against 300 strains of pneumococci and 100 group A streptococci of differing beta-lactam, macrolide, and quinolone resistance phenotypes, AR-709 was very active, with all MICs being < or =2 microg/ml. Furthermore, AR-709 was active against strains that were both susceptible and resistant to trimethoprim-sulfamethoxazole.

Dual-targeting properties of the 3-aminopyrrolidyl quinolones, DC-159a and sitafloxacin, against DNA gyrase and topoisomerase IV: contribution to reducing in vitro emergence of quinolone-resistant Streptococcus pneumoniae

OBJECTIVES

DC-159a (a novel quinolone) and sitafloxacin (DU-6859a) are structurally related quinolones, bearing a 3-aminopyrrolidyl substitution. We investigated the relationship between the target preferences of these 3-aminopyrrolidyl quinolones, in vitro potencies and emergence of quinolone-resistant mutants in Streptococcus pneumoniae, compared with other quinolones.

METHODS

MICs, resistance frequencies and mutant prevention concentrations (MPCs) were determined using quinolone-susceptible strains and first-step parC mutant strains of S. pneumoniae. Target preferences were tested by the following two methods: antibacterial activities against gyrA or parC mutants and in vitro enzyme assays for the determination of 50% inhibition (IC(50)) values.

RESULTS

DC-159a and sitafloxacin exhibited potent antibacterial activities, low frequencies of mutant selection, low MPCs and narrow mutant selection windows against both quinolone-susceptible strains and first-step parC mutants of S. pneumoniae, compared with gatifloxacin, moxifloxacin and other quinolones tested. DC-159a and sitafloxacin showed relatively low MIC ratios against single gyrA or parC mutants relative to the wild-type strain and low IC(50) ratios against DNA gyrase and topoisomerase IV.

CONCLUSIONS

DC-159a and sitafloxacin demonstrated a more balanced dual-targeting activity than gatifloxacin, moxifloxacin and other quinolones tested. In addition, DC-159a and sitafloxacin have a lower propensity for selecting first- and second-step resistant mutants.

Fatal levofloxacin failure in treatment of a bacteremic patient infected with Streptococcus pneumoniae with a preexisting parC mutation

The fatal outcome of levofloxacin treatment in a patient with bacteremic pneumonia caused by Streptococcus pneumoniae with a preexisting parC mutation is reported. Failure was due to the emergence of a gyrA mutation after 4 days of therapy. Problems encountered in detecting first-step mutation isolates are discussed.

Antibiotic resistant beta-hemolytic streptococci

OBJECTIVE

An antibiotic-sensitivity study was conducted on 117 strains of group A streptococcus (GAS), 60 strains of group G streptococcus (GGS) and 20 strains of group C streptococcus (GCS) in order to understand current resistance trends.

METHODS

All strains were tested by the Kirby Bauer disc diffusion method to 15 antibiotics. Resistant strains were confirmed by testing the minimum inhibitory concentration (MIC) of antibiotics by broth dilution technique.

RESULTS

Among GAS, highest resistance was observed to tetracycline (27.4%) and erythromycin (16.2%). The GGS and GCS tested, showed similar resistance patterns.

CONCLUSION

All beta-hemolytic streptococci were susceptible to penicillin, amoxycillin, cephalosporins and linezolid. Resistance to erythromycin, tetracycline, clindamycin, chloramphenicol, and quinolones is emerging.

Influence of penicillin/amoxicillin non-susceptibility on the activity of third-generation cephalosporins against Streptococcus pneumoniae

To study the influence of penicillin/amoxicillin non-susceptibility on the activity of third-generation cephalosporins, 430 consecutive penicillin non-susceptible Streptococcus pneumoniae 2007 isolates received in the Spanish Reference Pneumococcal Laboratory were tested. For comparative purposes, 625 penicillin-susceptible 2007 isolates were also tested. Susceptibility was determined by agar dilution using Mueller-Hinton agar supplemented with 5% sheep blood. Penicillin-susceptible strains were susceptible to amoxicillin, cefotaxime and ceftriaxone, 99.8% to cefpodoxime and 99.5% to cefdinir, and were inhibited by 0.12 microg/ml of cefditoren and 4 microg/ml of cefixime. Penicillin-intermediate strains were susceptible to cefotaxime and ceftriaxone, with <50% susceptibility to cefdinir and cefpodoxime. The MIC(50) and MIC(90) values of cefditoren were 0.25 microg/ml and 0.5 microg/ml, respectively, whereas cefixime exhibited only marginal activity (MIC(90)=16 microg/ml). Penicillin-resistant strains were resistant to cefdinir and cefpodoxime, with 74.8% and 94.1% susceptibility to cefotaxime and ceftriaxone, respectively. Cefditoren MIC(50)/MIC(90) (0.5/1 microg/ml) were lower than cefotaxime and ceftriaxone. Among amoxicillin non-susceptible strains, susceptibility to cefdinir and cefpodoxime was <10%, and susceptibility to cefotaxime decreased from 87.9% in the intermediate category to 63.0% in the resistant group. Cefditoren MIC(50)/MIC(90) (0.5/1 microg/ml) were lower than cefotaxime. In conclusion, the activity of cefixime, cefdinir and cefpodoxime was highly affected by penicillin/amoxicillin non-susceptibility, while parenteral third-generation cephalosporins exhibited higher intrinsic activity (MIC(90)=1 microg/ml for penicillin-resistant and 2 microg/ml for amoxicillin-resistant strains). Cefditoren exhibited one-dilution lower MIC(90) values for these strains, even against those of the most troublesome serotypes.

Antimicrobial susceptibilities of amoxycillin-non-susceptible and susceptible isolates among penicillin-non-susceptible Streptococcus pneumoniae

Antimicrobial susceptibilities of 244 amoxycillin-non-susceptible and 81 amoxycillin-susceptible pneumococcal isolates from 15 Spanish hospitals were determined and clonal relationships were investigated by pulsed-field gel electrophoresis after SmaI restriction. Amoxycillin-non-susceptible isolates exhibited higher rates of resistance to cefuroxime, cefixime, cefpodoxime and clarithromycin, but not to levofloxacin and cefotaxime. Cefditoren exhibited MIC(90) values one dilution lower than those of cefotaxime. Higher numbers of the Spain(14)-5 and Spain(6B)-2 clones, but not the Spain(9V)-3 and Spain(23F)-1 clones, were found among amoxycillin-non-susceptible isolates. Spain(14)-5 was the most problematic clone in terms of antibiotic resistance.

Characterisation of levofloxacin-resistant clinical isolates of Streptococcus pyogenes in Bilbao, Spain

The resistance mechanisms and clonal relationship were determined for two Streptococcus pyogenes isolates with high-level resistance to levofloxacin as well as to other fluoroquinolones. DNA amplification and sequencing revealed a serine-81-->phenylalanine substitution in GyrA and a double substitution in ParC of serine-79-->phenylalanine and aspartic acid-91-->asparagine. Pulsed-field gel electrophoresis analysis and emm typing determined that both isolates were emm type 28 and were genetically indistinguishable.

Impact of amoxicillin, associated or not with clavulanic acid, on pharyngeal colonization and selection of Streptococcus pneumoniae resistance in children under 5 years of age

Among young children, pneumococcal nasopharyngeal colonization (NPC) rates of >90% have been described. The aim of our study was to assess the effect of amoxicillin exposure on the NPC. From Dec 2001 to Feb 2004, less than 5 years old children with respiratory symptoms and fever who were prescribed amoxicillin were eligible. Three nasopharyngeal swabs were taken: at the time of the initial visit (IV), 60 hours after amoxicillin discontinuation (end of treatment visit, ETV), and 4 weeks later (follow-up visit, FUV). One hundred and thirty four children were included. NPC was detected in 58.5%, 42.9% and 51% of <1, 1-2 and >2 years-old children respectively (NS). Vaccine serotypes (VS) or vaccine-related serotypes (VRS) were identified in 80%, 40% and 55% of <1-year-old, 1-2 year-old and >2-year-old children respectively (NS). The proportion of PNSSP was 60% in <1-year-old children, 43% in 1-2 year-old children and 40% in >2-year-old children (NS). 49 out of 134 (36.5%) children completed the three study visits. 51%, 22.4% and 46.9% of those were colonized at IV, ETV and FUV, respectively (p=0.007). The percentage of resistant SP was 28%, 45.5% and 8.7% (p=0.05) for penicillin. In children <1 year of age, a higher proportion of SP colonization, presence of VS and PNSSP was found. A downfall of NPC at the end of therapy was observed. NPC returned to baseline levels thanks to "de novo" colonization in half of the cases, a few weeks after.

Microbiologic Workload and Clinical Significance ofStreptococcus pneumoniaeIsolated during One Week in Spain

Most studies reporting Streptococcus pneumoniae (Sp) infections select either specific populations/diseases, or refer to a single or a low number of institutions. A nationwide point-prevalence study including 147 hospitals from which we collected all the isolates of Sp reported in a single week (February 16-22, 2004). Workload and clinical data were studied, and susceptibility testing and serotyping of all isolates were performed. The participating institutions had an estimated catchment population of 37,534,750 inhabitants. During the study week, microbiology laboratories received 224,956 samples of which 34,647 were positive and 360 had S. pneumoniae. Overall, 69% of the isolates were from adults (> or = 15 years). Most of the isolates (89%) were considered clinically significant. Infection was community-acquired in 88% of infections and monomicrobial in 79%. We calculated that S. pneumoniae was isolated 38 times per 100,000 inhabitants/year and it was present in 1% of all samples with one or more bacterial isolates. We also calculated that pneumococcal disease (invasive and noninvasive) was present in 34 patients per 100,000 inhabitants/year. Penicillin resistance (I+R) was 42%, and erythromycin resistance was 35%. The most frequent serotypes were 3, 19F, and 19A. Considering only invasive isolates, the estimated coverage of the 7-valent vaccine was 61% in children and 41% in adults, and the estimated coverage of the 23-valent vaccine in adults was 79%. A nationwide point-prevalence study is an efficient tool for surveying pneumococcal infection in a large population.

Changing trends in antimicrobial-resistant pneumococci: it's not all bad news

In the early 1990s, we witnessed a dramatic and relentless increase in multidrug-resistant pneumococci worldwide. However, there is now evidence of decreasing resistance to some antimicrobials in some regions of the world. This may well be a result of several initiatives to promote the judicious use of antimicrobials, as well as the introduction of the pneumococcal conjugate vaccine, suggesting that the fight against resistance is maybe not futile.

Mutations in penicillin-binding protein (PBP) genes and in non-PBP genes during selection of penicillin-resistant Streptococcus gordonii

Penicillin resistance in Streptococcus spp. involves multiple mutations in both penicillin-binding proteins (PBPs) and non-PBP genes. Here, we studied the development of penicillin resistance in the oral commensal Streptococcus gordonii. Cyclic exposure of bacteria to twofold-increasing penicillin concentrations selected for a progressive 250- to 500-fold MIC increase (from 0.008 to between 2 and 4 microg/ml). The major MIC increase (> or = 35-fold) was related to non-PBP mutations, whereas PBP mutations accounted only for a 4- to 8-fold additional increase. PBP mutations occurred in class B PBPs 2X and 2B, which carry a transpeptidase domain, but not in class A PBP 1A, 1B, or 2A, which carry an additional transglycosylase domain. Therefore, we tested whether inactivation of class A PBPs affected resistance development in spite of the absence of mutations. Deletion of PBP 1A or 2A profoundly slowed down resistance development but only moderately affected resistance in already highly resistant mutants (MIC = 2 to 4 microg/ml). Thus, class A PBPs might facilitate early development of resistance by stabilizing penicillin-altered peptidoglycan via transglycosylation, whereas they might be less indispensable in highly resistant mutants which have reestablished a penicillin-insensitive cell wall-building machinery. The contribution of PBP and non-PBP mutations alone could be individualized in DNA transformation. Both PBP and non-PBP mutations conferred some level of intrinsic resistance, but combining the mutations synergized them to ensure high-level resistance (> or = 2 microg/ml). The results underline the complexity of penicillin resistance development and suggest that inhibition of transglycosylase might be an as yet underestimated way to interfere with early resistance development.

Vigilancia de resistencias a los antimicrobianos: estudio VIRA 2006

INTRODUCTION

The objective of this study was to determine the current antimicrobial susceptibility patterns of the most frequent multi-resistant bacteria and to analyze any possible changes with respect to the two VIRA studies carried out in 2001 and 2004.

METHODS

In February 2006, the 40 participating hospitals sent the following microorganisms: non-penicillin-susceptible Streptococcus pneumoniae (92), methicillin-resistant Staphylococcus aureus (MRSA) (290), clinically significant coagulase-negative staphylococci (136), ampicillin-resistant Enterococcus faecium (89), ampicillin-resistant Haemophilus influenzae (67), ciprofloxacin-resistant Escherichia coli (365), Pseudomonas aeruginosa (181), and Acinetobacter baumannii (92). The hospitals provided epidemiological data on these microorganisms. Susceptibility was determined with a broth microdilution method.

RESULTS

Among the non-penicillin-susceptible S. pneumoniae isolates, the proportion of those ones resistant to this antibiotic showed a significant (p < 0.001) decrease (59.8% in 2001, 30.2% in 2004 and 14.3% in 2006). Among MRSA, we detected one isolate nonsusceptible to linezolid, four resistant to quinupristin-dalfopristin and one strain with a vancomycin MIC of 4 microg/mL. The prevalence of extended-spectrum beta-lactamase-producing E. coli was 12.1%. Resistance of A. baumannii to imipenem varied from 27% in the 2001-2004 period to 47.8% in 2006 (p < 0.005).

CONCLUSION

These results again emphasize that resistance surveillance systems are an important tool for preventing the emergence and spread of multi-resistant pathogens.