Antibiotic resistance and identification of uncommon Gram-negative bacteria isolated from sputum of adult patients with cystic fibrosis

Ralstonia species - do these bacteria matter in cystic fibrosis?

Ralstonia species, often regarded as an environmental organism of low pathogenicity, can cause significant disease in certain at-risk patient groups, including those with cystic fibrosis. Difficulties with its identification in the clinical laboratory mean that it may be misidentified and therefore under recognised as a cause of disease. A number of outbreaks have been associated with the use of devices for inhaled respiratory therapy, putting those with chronic respiratory conditions at risk. Antimicrobial treatment of infection is challenging and limited due to frequent antimicrobial resistance. This review highlights issues regarding the identification, treatment and prevention of infection due to Ralstonia spp. in children with cystic fibrosis.

Amoxicillin-clavulanic acid resistance in fecal Enterobacteriaceae from patients with cystic fibrosis and healthy siblings

BACKGROUND

The present study set out to detect and identify amoxicillin-clavulanic acid (AMC)-resistant Enterobacteriaceae in fecal samples of two patients with cystic fibrosis (CF) and their respective siblings.

METHODS

Fecal Enterobacteriaceae were enumerated onto EMB agar containing amoxicillin (AMX). A total of 173 CF isolates and 41 sibling isolates were grouped into seven Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) clusters and identified through 16S rRNA and rpoB sequence analysis.

RESULTS

The fecal microbiota of patients with CF revealed a higher prevalence of AMX resistant Enterobacteriaceae compared to that of their healthy siblings. Whereas all selected isolates of healthy siblings were assigned to Escherichia coli, isolates of patients with CF belonged to Klebsiella oxytoca (58.4%), E. coli (28.3%), Klebsiella variicola (7.5%) or Citrobacter sp. (5.8%). All tested CF isolates showed a high resistance rate to AMX, and a lower level of resistance to the combination with clavulanic acid. In contrast, all tested sibling isolates were susceptible for both AMX and AMC.

CONCLUSION

The higher abundance of AMX resistance in the investigated patients with CF suggests that frequent AMC administration may be one of the major contributing factors in the proliferation of Enterobacteriaceae and the development of resistant strains in the gastrointestinal tract.

Rational design of engineered cationic antimicrobial peptides consisting exclusively of arginine and tryptophan, and their activity against multidrug-resistant pathogens

The emergence of multidrug-resistant (MDR) pathogens underscores the need for new antimicrobial agents to overcome the resistance mechanisms of these organisms. Cationic antimicrobial peptides (CAPs) provide a potential source of new antimicrobial therapeutics. We previously characterized a lytic base unit (LBU) series of engineered CAPs (eCAPs) of 12 to 48 residues demonstrating maximum antibacterial selectivity at 24 residues. Further, Trp substitution in LBU sequences increased activity against both P. aeruginosa and S. aureus under challenging conditions (e.g., saline, divalent cations, and serum). Based on these findings, we hypothesized that the optimal length and, therefore, the cost for maximum eCAP activity under physiologically relevant conditions could be significantly reduced using only Arg and Trp arranged to form idealized amphipathic helices. Hence, we developed a novel peptide series, composed only of Arg and Trp, in a sequence predicted and verified by circular dichroism to fold into optimized amphipathic helices. The most effective antimicrobial activity was achieved at 12 residues in length (WR12) against a panel of both Gram-negative and Gram-positive clinical isolates, including extensively drug-resistant strains, in saline and broth culture and at various pH values. The results demonstrate that the rational design of CAPs can lead to a significant reduction in the length and the number of amino acids used in peptide design to achieve optimal potency and selectivity against specific pathogens.

Isolation of Burkholderia cenocepacia and Burkholderia vietnamiensis from human sewage

Fresh human sewage was examined from a sewage treatment plant for the presence of members of the Burkholderia cepacia complex (BCC) of bacterial organisms and confirmed the presence of viable B. cenocepacia and B. vietnamiensis, by a combination of cultural, phenotypic and genotypic techniques. Both these organisms are important respiratory pathogens for patients with cystic fibrosis (CF). Presently, the survival dynamics of these organisms in sewage effluent and sludge is, as yet, unknown. Therefore, as this study represents the first report of these CF pathogens in sewage and until such survival data is available, careful risk assessment needs to be undertaken in relation to the end use application of potentially contaminated sewage and where such material comes into association with non-colonised patients with cystic fibrosis, so that any potential transmission of these pathogens from sewage to patient is assessed and minimised/eliminated.