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1.  Genotypes and serotype distribution of macrolide resistant invasive and non- invasive Streptococcus pneumoniae isolates from Lebanon 
Background
This study determined macrolide resistance genotypes in clinical isolates of Streptococcus pneumoniae from multiple medical centers in Lebanon and assessed the serotype distribution in relation to these mechanism(s) of resistance and the source of isolate recovery.
Methods
Forty four macrolide resistant and 21 macrolide susceptible S. pneumoniae clinical isolates were tested for antimicrobial susceptibility according to CLSI guidelines (2008) and underwent molecular characterization. Serotyping of these isolates was performed by Multiplex PCR-based serotype deduction using CDC protocols. PCR amplification of macrolide resistant erm (encoding methylase) and mef (encoding macrolide efflux pump protein) genes was carried out.
Results
Among 44 isolates resistant to erythromycin, 35 were resistant to penicillin and 18 to ceftriaxone. Examination of 44 macrolide resistant isolates by PCR showed that 16 isolates harbored the erm(B) gene, 8 isolates harbored the mef gene, and 14 isolates harbored both the erm(B) and mef genes. There was no amplification by PCR of the erm(B) or mef genes in 6 isolates. Seven different capsular serotypes 2, 9V/9A,12F, 14,19A, 19F, and 23, were detected by multiplex PCR serotype deduction in 35 of 44 macrolide resistant isolates, with 19F being the most prevalent serotype. With the exception of serotype 2, all serotypes were invasive. Isolates belonging to the invasive serotypes 14 and 19F harbored both erm(B) and mef genes. Nine of the 44 macrolide resistant isolates were non-serotypable by our protocols.
Conclusion
Macrolide resistance in S. pneumoniae in Lebanon is mainly through target site modification but is also mediated through efflux pumps, with serotype 19F having dual resistance and being the most prevalent and invasive.
doi:10.1186/1476-0711-11-2
PMCID: PMC3371826  PMID: 22248318
Antimicrobials; Macrolides; Resistance; Genes; Serotyping
2.  Decrease in Shiga toxin expression using a minimal inhibitory concentration of rifampicin followed by bactericidal gentamicin treatment enhances survival of Escherichia coli O157:H7-infected BALB/c mice 
Background
Treatment of Escherichia coli O157:H7 infections with antimicrobial agents is controversial due to an association with potentially fatal sequelae. The production of Shiga toxins is believed to be central to the pathogenesis of this organism. Therefore, decreasing the expression of these toxins prior to bacterial eradication may provide a safer course of therapy.
Methods
The utility of decreasing Shiga toxin gene expression in E. coli O157:H7 with rifampicin prior to bacterial eradication with gentamicin was evaluated in vitro using real-time reverse-transcription polymerase chain reaction. Toxin release from treated bacterial cells was assayed for with reverse passive latex agglutination. The effect of this treatment on the survival of E. coli O157:H7-infected BALB/c mice was also monitored.
Results
Transcription of Shiga toxin-encoding genes was considerably decreased as an effect of treating E. coli O157:H7 in vitro with the minimum inhibitory concentration (MIC) of rifampicin followed by the minimum bactericidal concentration (MBC) of gentamicin (> 99% decrease) compared to treatment with gentamicin alone (50-75% decrease). The release of Shiga toxins from E. coli O157:H7 incubated with the MIC of rifampicin followed by addition of the MBC of gentamicin was decreased as well. On the other hand, the highest survival rate in BALB/c mice infected with E. coli O157:H7 was observed in those treated with the in vivo MIC equivalent dose of rifampicin followed by the in vivo MBC equivalent dose of gentamicin compared to mice treated with gentamicin or rifampicin alone.
Conclusions
The use of non-lethal expression-inhibitory doses of antimicrobial agents prior to bactericidal ones in treating E. coli O157:H7 infection is effective and may be potentially useful in human infections with this agent in addition to other Shiga toxin producing E. coli strains.
doi:10.1186/1476-0711-10-34
PMCID: PMC3180354  PMID: 21906403
Escherichia coli O157:H7; rifampicin; gentamicin; Shiga toxins
3.  Frequency of conjugative transfer of plasmid-encoded ISEcp1 - blaCTX-M-15 and aac(6')-lb-cr genes in Enterobacteriaceae at a tertiary care center in Lebanon - role of transferases 
Background
The frequency of transfer of genes encoding resistance to antimicrobial agents was determined by conjugation in ESBL-producing and/or fluoroquinolone or aminoglycoside resistant Enterobacteriaceae clinical isolates at a tertiary care center in Lebanon. In addition, the role of tra genes encoding transferases in mediating conjugation was assessed.
Methods
Conjugation experiments were done on 53 ESBL-producing and/or fluoroquinolone resistant E. coli and K. pneumoniae and ESBL-producing S. sonnei isolates. Antimicrobial susceptibility testing on parent and transconjugant isolates, and PCR amplifications on plasmid extracts of the resistance-encoding genes: blaCTX-M-15 with the ISEcp1 insertion sequence, the aac(6')-lb-cr and qnrS genes, as well as tra encoding transferases genes were done. Random amplified polymorphic DNA (RAPD) analysis was performed to demonstrate whether conjugative isolates are clonal and whether they are linked epidemiologically to a particular source.
Results
Antimicrobial susceptibility testing on transconjugants revealed that 26 out of 53 (49%) ESBL-producing Enterobacteriaceae were able to transfer antimicrobial resistance to the recipients. Transfer of high-level resistance to the transconjugants encoded by the blaCTX-M-15 gene downstream the ISEcp1 insertion sequence against 3rd generation cephalosporins, and of low-level resistance against ciprofloxacin, and variable levels of resistance against aminoglycosides encoded by aac(6')-lb-cr gene, were observed in transconjugants. tra encoding transferase genes were detected exclusively in conjugative isolates.
Conclusion
In conclusion, the frequency of transfer of antimicrobial resistance in non clonal Enterobacteriaceae at the tertiary care center by conjugation was 49%. Conjugation occurred in isolates expressing the tra encoding transferase genes. Multiple conjugative strains harboring the plasmid encoded antimicrobial resistant genes were circulating in the medical center. Molecular epidemiology analysis showed that conjugative isolates are neither clonal nor linked to a particular site and transfer of antimicrobial resistance is by horizontal transfer of plasmids.
doi:10.1186/1476-0711-9-19
PMCID: PMC2919444  PMID: 20646305

Results 1-3 (3)