An \u3cem\u3eEscherichia coli\u3c/em\u3e Nissle 1917 Missense Mutant Colonizes the Streptomycin-Treated Mouse Intestine Better than the Wild Type but Is Not a Better Probiotic

Previously we reported that the streptomycin-treated mouse intestine selected for two different Escherichia coli MG1655 mutants with improved colonizing ability: nonmotile E. coli MG1655 flhDC deletion mutants that grew 15% faster in vitro in mouse cecal mucus and motile E. coli MG1655 envZ missense mutants that grew slower in vitro in mouse cecal mucus yet were able to cocolonize with the faster-growing flhDC mutants. The E. coli MG1655 envZ gene encodes a histidine kinase that is a member of the envZ-ompR two-component signal transduction system, which regulates outer membrane protein profiles. In the present investigation, the envZ P41L gene was transferred from the intestinally selected E. coli MG1655 mutant to E. coli Nissle 1917, a human probiotic strain used to treat gastrointestinal infections. Both the E. coli MG1655 and E. coli Nissle 1917 strains containing envZ P41L produced more phosphorylated OmpR than their parents. The E. coli Nissle 1917 strain containing envZ P41L also became more resistant to bile salts and colicin V and grew 50% slower in vitro in mucus and 15% to 30% slower on several sugars present in mucus, yet it was a 10-fold better colonizer than E. coli Nissle 1917. However, E. coli Nissle 1917 envZ P41L was not better at preventing colonization by enterohemorrhagic E. coli EDL933. The data can be explained according to our “restaurant” hypothesis for commensal E. coli strains, i.e., that they colonize the intestine as sessile members of mixed biofilms, obtaining the sugars they need for growth locally, but compete for sugars with invading E. coli pathogens planktonically

The importance of clonal complex 258 and IncFK2-like plasmids among a global collection of Klebsiella pneumoniae with blaKPCs

Please read abstract in the article.The Calgary Laboratory Services (#10015169)http://aac.asm.org2017-10-30hb2017Medical Microbiolog

When fluids are not allowed: how can we decontaminate surfaces with emphasis on spores?

Kazmierczak K, Petersson LP, Albrecht U-V, Vonberg R-P. When fluids are not allowed: how can we decontaminate surfaces with emphasis on spores? Presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID 2013), Berlin, Germany

Instability of ackA (Acetate Kinase) Mutations and Their Effects on Acetyl Phosphate and ATP Amounts in Streptococcus pneumoniae D39▿ †

Acetyl phosphate (AcP) is a small-molecule metabolite that can act as a phosphoryl group donor for response regulators of two-component systems (TCSs). The serious human respiratory pathogen Streptococcus pneumoniae (pneumococcus) synthesizes AcP by the conventional pathway involving phosphotransacetylase and acetate kinase, encoded by pta and ackA, respectively. In addition, pneumococcus synthesizes copious amounts of AcP and hydrogen peroxide (H2O2) by pyruvate oxidase, which is encoded by spxB. To assess possible roles of AcP in pneumococcal TCS regulation and metabolism, we constructed strains with combinations of spxB, pta, and ackA mutations and determined their effects on ATP, AcP, and H2O2 production. Unexpectedly, ΔackA mutants were unstable and readily accumulated primary suppressor mutations in spxB or its positive regulator, spxR, thereby reducing H2O2 and AcP levels, and secondary capsule mutations in cps2E or cps2C. ΔackA ΔspxB mutants contained half the cellular amount of ATP as a ΔspxB or spxB+ strain. Acetate addition and anaerobic growth experiments suggested decreased ATP, rather than increased AcP, as a reason that ΔackA mutants accumulated spxB or spxR suppressors, although experimental manipulation of the AcP amount was limited. This finding and other considerations suggest that coping with endogenously produced H2O2 may require energy. Starting with a ΔspxB mutant, we constructed Δpta, ΔackA, and Δpta ΔackA mutants. Epistasis and microarray experiment results were consistent with a role for the SpxB-Pta-AckA pathway in expression of the regulons controlled by the WalRKSpn, CiaRHSpn, and LiaSRSpn TCSs involved in sensing cell wall status. However, AcP likely does not play a physiological role in TCS sensing in S. pneumoniae

Transcriptional Regulation and Signature Patterns Revealed by Microarray Analyses of Streptococcus pneumoniae R6 Challenged with Sublethal Concentrations of Translation Inhibitors

The effects of sublethal concentrations of four different classes of translation inhibitors (puromycin, tetracycline, chloramphenicol, and erythromycin) on global transcription patterns of Streptococcus pneumoniae R6 were determined by microarray analyses. Consistent with the general mode of action of these inhibitors, relative transcript levels of genes that encode ribosomal proteins and translation factors or that mediate tRNA charging and amino acid biosynthesis increased or decreased, respectively. Transcription of the heat shock regulon was induced only by puromycin or streptomycin treatment, which lead to truncation or mistranslation, respectively, but not by other antibiotics that block translation, transcription, or amino acid charging of tRNA. In contrast, relative transcript amounts of certain genes involved in transport, cellular processes, energy metabolism, and purine nucleotide (pur) biosynthesis were changed by different translation inhibitors. In particular, transcript amounts from a pur gene cluster and from purine uptake and salvage genes were significantly elevated by several translation inhibitors, but not by antibiotics that target other cellular processes. Northern blotting confirmed increased transcript amounts from part of the pur gene cluster in cells challenged by translation inhibitors and revealed the presence of a 10-kb transcript. Purine metabolism genes were negatively regulated by a homologue of the PurR regulatory protein, and full derepression in a ΔpurR mutant depended on optimal translation. Unexpectedly, hierarchical clustering of the microarray data distinguished among the global transcription patterns caused by antibiotics that inhibit different steps in the translation cycle. Together, these results show that there is extensive control of transcript amounts by translation in S. pneumoniae, especially for de novo purine nucleotide biosynthesis. In addition, these global transcription patterns form a signature that can be used to classify the mode of action and potential mechanism of new translation inhibitors

Prevalence of mcr-type genes among colistin-resistant Enterobacteriaceae collected in 2014-2016 as part of the INFORM global surveillance program.

A set of 908 clinically derived colistin-resistant Enterobacteriaeae isolates collected worldwide in 2014-2016 were screened for the presence of the plasmid-borne mcr-1, mcr-2, mcr-3, mcr-4 and mcr-5 genes. In total 3.2% (29/908) of the collection were positive for mcr, including 27 Escherichia coli, 1 Klebsiella pneumoniae and 1 Enterobacter cloacae. Twenty-four isolates possessed genes from the mcr-1 family, including the original mcr-1 (n = 22), as well as mcr-1.2 (n = 1) and mcr-1.5 (n = 1), which each differ from mcr-1 by encoding single amino acid variations. Genes from the mcr-3 family were found in isolates from Thailand, including mcr-3.1 (n = 3) and mcr-3.2 (n = 1). An E. coli isolated from a patient with a urinary tract infection in Colombia contained the recently discovered mcr-5. The full colistin-resistant collection was tested against a panel of antimicrobial agents with ceftazidime-avibactam and tigecycline exhibiting the highest activity

<i>In vitro</i> activity of selected antimicrobials against 908 colistin-resistant <i>Enterobacteriaceae</i> collected worldwide during 2014–2016.

<p><i>In vitro</i> activity of selected antimicrobials against 908 colistin-resistant <i>Enterobacteriaceae</i> collected worldwide during 2014–2016.</p