Laura Bonofiglio

Dissemination of an Erythromycin-Resistant Penicillin-Nonsusceptible Streptococcus pneumoniae Poland6B-20 Clone in Argentina

Prevalence of serotype 6B penicillin (PEN)-nonsusceptible Streptococcus pneumoniae significantly increased from 15.8% (1993-1997) to 67.3% (1998-2002) (p<0.001) in Argentina. Serogroup 6 ranks fourth among different capsular types within invasive isolates from Argentinean patients <6 years of age. To evaluate whether the increase in PEN resistance in serotype 6B pneumococci was due to the dissemination of one or more clones, the genetic diversity of 93 S. pneumoniae serotype 6B isolates was analyzed. Five BOX-polymerase chain reaction types were obtained (65.5% isolates) and a group of 15 isolates, representing 41.6% of those having a decreased susceptibility to PEN, were further characterized. The antibiotype of these isolates showed their multiresistance, with 100% of the isolates being resistant to erythromycin, 80% to tetracycline, and 73.3% to trimethoprim-sulfamethoxazole. Of the 15 isolates, 13 belonged to the same pulsed-field gel electrophoresis type and galU cluster and were members of the same clone. The identity of the clone was confirmed in four isolates by multilocus sequence typing. The sequence type found (ST315) corresponds to the Poland(6B)-20 clone. In summary, BOX-polymerase chain reaction, pulsed-field gel electrophoresis, and galU polymorphism were useful tools to detect the presence of a clone whose identity was confirmed by multilocus sequence typing. The isolates belonging to Poland(6B)-20 found in this work are described for the first time in Latin America.

Antimicrobial susceptibility of clinical isolates of Actinomyces and related genera reveals an unusual clindamycin resistance among Actinomyces urogenitalis strains

OBJECTIVES Patterns of antimicrobial susceptibility in Actinomyces and related genera are very limited in the literature. Data of predominant susceptibility profiles could contribute to the establishment of an accurate empirical treatment. METHODS A total of 113 isolates from clinical samples were included in this study. Each isolate was identified using phenotypic methods and MALDI-TOF/MS. When discrepancies were observed, 16S rRNA gene sequencing was performed. The minimum inhibitory concentrations (MICs) of nine antimicrobial agents (penicillin, ceftriaxone, linezolid, tetracycline, clindamycin, erythromycin, ciprofloxacin, levofloxacin and vancomycin) were tested against the species Actinotignum schaalii (n=23), Actinomyces turicensis (n=18), Actinomyces europaeus (n=13), Actinomyces naeslundii/Actinomyces viscosus group (n=12), Actinomyces urogenitalis (n=11), Actinomyces radingae (n=11), Actinomyces neuii (n=9), Actinomyces odontolyticus (n=8), Bifidobacterium scardovii (n=3), Actinomyces graevenitzii (n=2), Alloscardovia omnicolens (n=2) and Varibaculum cambriense (n=1). RESULTS All of the isolates were susceptible to penicillin, ceftriaxone, vancomycin and linezolid. Almost all of the A. urogenitalis isolates (8/11) were resistant to clindamycin and showed susceptibility to erythromycin, suggesting an L-phenotype, however no determinants of clindamycin resistance (lnu and lsa genes) were detected by PCR. High MIC values to quinolones were observed in 54/113 isolates (47.8%). All of the A. urogenitalis isolates were highly resistant to ciprofloxacin and levofloxacin. CONCLUSIONS These data highlight the importance of ongoing surveillance to provide relevant information for empirical management of infections caused by these organisms.

The galU gene expression in Streptococcus pneumoniae

The polysaccharide capsule of Streptococcus pneumoniae is the main virulence factor making the bacterium resistant to phagocytosis. The galU gene of S. pneumoniae encodes a UDP-glucose pyrophosphorylase absolutely required for capsule biosynthesis. In silico analyses indicated that the galU gene is co-transcribed with the gpdA gene, and four putative promoter regions located upstream of gpdA were predicted. One of them behaved as a functional promoter in a promoter reporter system. It is conceivable that the sequence responsible for initiating transcription of gpdA-galU operon is an extended -10 site TATGATA(T/G)AAT. Semi-quantitative real-time reverse transcription PCR experiments indicated that galU was expressed mainly in the exponential phase of growth.

Susceptibility to β-lactams in β-hemolytic streptococci

Group A (GAS), B (GBS), C (GCS) and G (GGS) β-hemolytic streptococci are important human pathogens. They cause infections of different severity and frequency. Nowadays, after 70 years of use, penicillin is still universally active against GAS, GCS and GGS. However, therapeutic failures have been recorded in 2-28% of pharyngitis cases (median: 12%) attributable to different causes. By contrast, some GBS with reduced susceptibility to penicillin have been described, especially in Japan. In this group of bacteria, it is important to highlight that confirmation by reference methods is mandatory when decreased susceptibility to penicillin is suspected as well as checked for the detection of the mechanisms involved.

Resistance to β-lactams in enterococci

Enterococci are intrinsically resistant to several antimicrobial classes and show a great ability to acquire new mechanisms of resistance. Resistance to β-lactam antibiotics is a major concern because these drugs either alone or in combination are commonly used for the treatment of enterococcal infections. Ampicillin resistance, which is rare in Enterococcus faecalis, occurs in most of the hospital-associated Enterococcus faecium isolates. High-level resistance to ampicillin in E. faecium is mainly due to the enhanced production of PBP5 and/or by polymorphisms in the beta subunit of this protein. The dissemination of high-level ampicillin resistance can be the result of both clonal spread of strains with mutated pbp5 genes and horizontal gene transfer.

Group B streptococcal necrotizing pneumonia in a diabetic adult patient

The aim of this report is to describe a rare case of necrotizing pneumonia due to group B Streptococcus serotype III in a relatively young male adult (48 years old) suffering from diabetes. The organism was isolated from his pleural fluid and was only resistant to tetracycline. The patient first received ceftazidime (2g/8h i.v.)+clindamycin (300mg/8h) for 18 days and then he was discharged home and orally treated with amoxicillin clavulanic acid (1g/12h) for 23 days with an uneventful evolution. As in the cases of invasive infection by Streptococcus pyogenes, clindamycin could prevent streptococcal toxic shock syndrome.

Application of Molecular Typing Methods to the Study of Medically Relevant Gram-Positive Cocci

Strain typing is an integral part of epidemiological investigations of bacterial infections. Typing methods fall into two broad categories: phenotypic and genotypic methods. Phenotypic methods are those that characterize the products of gene expression in order to differentiate strains. Properties such as biochemical profiles, antimicrobial susceptibility profiles, bacteriophage types, and antigens present on the cell surface are examples of phenotypic methods that can be used for typing isolates. Since they involve gene expressions, these properties have a tendency to vary, based on changes in growth conditions and growth phase, being often difficult to detect.