Macrolide resistance among middle ear isolates of Streptococcus pneumoniae observed at eight United States pediatric centers: prevalence of M and MLSB phenotypes

Characterization of macrolide-resistant non-invasive pneumococci in the pre-vaccine era in Serbia

Numerous reports have confirmed that increased macrolide use in the treatment of respiratory tract infection has contributed to the emergence of antibiotic resistance worldwide. Studies have also shown that pneumococcal vaccine can reduce pneumococcal resistance. The aim of this study was to determine the prevalence of co-resistance to penicillin and other antibiotics in macrolide-resistant (MR) non-invasive pneumococcal isolates and to evaluate serotype distribution in resistant strains in the pre-vaccine era in Serbia. About 80% of MR isolates expressed the MLS phenotype with very high resistance to both erythromycin and clindamycin. A total of 132 (84.1%) MR isolates were multiresistant, i.e., they were resistant to erythromycin, penicillin, tetracycline, and trimethoprim-sulfamethoxazole. Among 157 MR pneumococci, 11 different serotypes were found. Four serotypes, 19F, 14, 6B, and 23F, accounted for 77.7% of all MR pneumococcal isolates. Among isolates with the cMLS phenotype, serotypes 19F and 14 were predominant, whereas serotype 6A was the most common among those with the M phenotype, followed by 14. In conclusion, co-resistance to macrolides and penicillin in our non-invasive pneumococcal isolates is high. The majority of tested strains (∼80%) belonged to the four serotypes (19F, 14, 6B, and 23F) that are included in all conjugate vaccine formulations.

Patterns of Macrolide Resistance Determinants among S. pyogenes and S. pneumoniae Isolates in Saudi Arabia

In the study we characterized the macrolide sensitivity of recent clinical isolates of Streptococcus pyogenes and S. pneumoniae collected from major Saudi Arabian hospitals. Susceptibility testing was performed using standard National Committee for Clinical Laboratory Standards methodology on 335 S. pyogenes and 350 S. pneumoniae isolates. Macrolide resistance mechanism phenotypes were identified using double-disk diffusion. All S. pyogenes were penicillin sensitive, while 6.3% were macrolide resistant, the main mechanism of which was of M phenotype (96%). Approximately 51% of S. pneumoniae were penicillin non-susceptible. Macrolide resistance in S. pneumoniae accounted for 18.8%, the majority of which were M phenotype (91%). Low-level resistance mediated by mef-bearing strains predominated. Newer macrolides, including azithromycin, are still considered drugs of choice for empirical treatment of respiratory infection in such circumstances.

Interaction of antibacterial compounds with RND efflux pumps in Pseudomonas aeruginosa

Pseudomonas aeruginosa infections are becoming increasingly difficult to treat due to intrinsic antibiotic resistance and the propensity of this pathogen to accumulate diverse resistance mechanisms. Hyperexpression of efflux pumps of the Resistance-Nodulation-Cell Division (RND)-type multidrug efflux pumps (e.g., MexAB-OprM), chromosomally encoded by mexAB-oprM, mexCD-oprJ, mexEF-oprN, and mexXY (-oprA) is often detected in clinical isolates and contributes to worrying multi-drug resistance phenotypes. Not all antibiotics are affected to the same extent by the aforementioned RND efflux pumps. The impact of efflux on antibiotic activity varies not only between different classes of antibiotics but also between members of the same family of antibiotics. Subtle differences in physicochemical features of compound-pump and compound-solvent interactions largely determine how compounds are affected by efflux activity. The combination of different high-resolution techniques helps to gain insight into the functioning of these molecular machineries. This review discusses substrate recognition patterns based on experimental evidence and computer simulations with a focus on MexB, the pump subunit of the main RND transporter in P. aeruginosa.

Osteomyelitis in children

Osteomyelitis is one of the more common invasive bacterial infections in children leading to hospitalization and prolonged antibiotic administration. Over the past decade, increasing microbial virulence, diminishing antibiotic susceptibility, and advances in diagnostic molecular microbiology and imaging techniques have led to changes in the clinical management of children with suspected osteomyelitis, which are reviewed in this article.

Estudo fenotípico e genotípico da resistência aos macrolídeos de "Streptococcus pneumoniae" isolados em hospitais de Porto Alegre - RS

OBJETIVO: O objetivo deste estudo foi determinar a prevalência do S. pneumoniae resistente aos macrolídeos e identificar suas características fenotípicas e genotípicas. MÉTODOS: Amostras de S. pneumoniae isoladas entre maio de 2002 e agosto de 2004, em Porto Alegre (RS), a partir de materiais clínicos coletados de diferentes sítios anatômicos foram analisadas. Para o teste de difusão em ágar foram utilizados discos de eritromicina, claritromicina, azitromicina e clindamicina. As concentrações inibitórias mínimas de eritromicina foram determinadas nos isolados resistentes aos macrolídeos pelo método de diluição em ágar. Os fenótipos dos isolados resistentes aos macrolídeos foram investigados pelo teste de difusão em ágar e a genotipagem pela reação em cadeia da polimerase. RESULTADOS: Foram avaliados 229 isolados de pneumococos, e 12 mostraram-se resistentes aos macrolídeos (5,2%). Entre estes, 9 apresentaram o fenótipo MLSB (75%) e 3 o fenótipo M (25%). A reação em cadeia da polimerase indicou que 8 isolados com o fenótipo MLSB portavam apenas o gene ermB, enquanto que o gene mefE estava presente em todos os 3 isolados com o fenótipo M. Um isolado com o fenótipo MLSB apresentou ambos os genes. CONCLUSÃO: A resistência aos macrolídeos do S. pneumoniae em Porto Alegre permanece baixa, sendo devida principalmente à presença do gene ermB, com expressão do fenótipo MLSB.

Macrolide resistance in Streptococci and Haemophilus influenzae

Antimicrobial resistance is a growing problem among pathogens from respiratory tract infections. b-Lactam resistance rates are escalating among Streptococcus pneumoniae and Haemophilus influenzae. Macrolides are increasingly used for the treatment of respiratory tract infections, but their utility is compromised by intrinsic and acquired resistance. This article analyses macrolide-resistance mechanisms and their worldwide distributions in S pneumoniae, S pyogenes, and H influenzae.

Single dose azithromycin for the treatment of uncomplicated otitis media

Three clinical trials have examined the efficacy and safety of single dose azithromycin (30 mg/kg) in children with uncomplicated acute otitis media (AOM). In the first trial, a small pilot study, the clinical and microbiologic efficacy of single dose azithromycin was comparable with that of 3-day azithromycin or single dose ceftriaxone. A second, non-comparative trial confirmed the clinical and microbiologic efficacy of the single dose regimen. The third study, a large double blind, double dummy trial, demonstrated comparable clinical success rates between single dose azithromycin and 10-day standard amoxicillin/clavulanate. The incidence of drug-related adverse events in patients treated with single dose azithromycin was low in all three trials and similar to rates that have been reported for other antimicrobial agents used for the treatment of patients with AOM. In the amoxicillin/clavulanate trial, compliance with single dose azithromycin was significantly better than with the amoxicillin/clavulanate regimen (P < 0.001). We conclude that a single dose of azithromycin (30 mg/kg) is safe and effective for the treatment of uncomplicated AOM in children.

Management of recurrent and persistent acute otitis media: new options with familiar antibiotics

Recurrent and persistent acute otitis media (AOM) is a common problem, affecting close to 20% of children in their first years of life. It presents a therapeutic challenge to physicians, particularly as beta-lactamase-producing Haemophilus influenzae, as well as penicillin- and, more recently, macrolide-resistant Streptococcus pneumoniae are often responsible for AOM in these patients. Intramuscular ceftriaxone (50 mg/kg, once daily for 3 days) has been shown to be effective in treating nonresponsive AOM, but there have been relatively few clinical trials exploring oral antibiotic regimens. Higher doses of commonly used antibiotics (amoxicillin-clavulanate ratio, 14:1 ratio and azithromycin 60 mg/kg divided into three equal once daily doses) have demonstrated high rates of clinical success. These studies will be discussed together with a review of the clinical and microbiologic characteristics of this disease. We will also address the impact that the pneumococcal conjugate vaccine may have on the microbiology of recurrent and persistent AOM.