Our results highlight the distribution of carbapenem- and colistin-resistance in Gram-negative bacteria isolated from the Tamil Nadu region in South India.
The nonthermotolerant Campylobacter species C. fetus, C. hyointestinalis, C. iguaniorum, and C. lanienae form a distinct phylogenetic cluster within the genus. These species are primarily isolated from foraging (swine) or grazing (e.g., cattle, sheep) animals and cause sporadic and infrequent human illness. Previous typing studies identified three putative novel C. lanienae-related taxa, based on either MLST or atpA sequence data. To further characterize these putative novel taxa and the C. fetus group as a whole, 76 genomes were sequenced, either to completion or to draft level. These genomes represent 26 C. lanienae strains and 50 strains of the three novel taxa. C. fetus, C. hyointestinalis and C. iguaniorum genomes were previously sequenced to completion; therefore, a comparative genomic analysis across the entire C. fetus group was conducted (including average nucleotide identity analysis) that supports the initial identification of these three novel Campylobacter species. Furthermore, C. lanienae and the three putative novel species form a discrete clade within the C. fetus group, which we have termed the C. lanienae clade. This clade is distinguished from other members of the C. fetus group by a reduced genome size and distinct CRISPR/Cas systems. Moreover, there are two signature characteristics of the C. lanienae clade. C. lanienae clade genomes carry four to ten unlinked and similar, but nonidentical, flagellin genes. Additionally, all 76 C. lanienae clade genomes sequenced demonstrate a complete absence of genes related to selenium metabolism, including genes encoding the selenocysteine insertion machinery, selenoproteins, and the selenocysteinyl tRNA.
BackgroundPhage therapy is the therapeutic use of bacteriophages to treat highly drug resistant bacterial infections. The current surge in bacteriophage therapy is motivated mainly because of the emergence of antibiotic-resistant bacteria in clinics. This study evaluated the therapeutic potential of three bacteriophages isolated against Escherichia coli ec311, Klebsiella pneumoniae kp235 and Enterobacter cloacae el140 strains using Galleria mellonella. The in vitro activity of three different phages belonging to Podoviridae and Myoviridae families was studied by the double agar overlay method against multi-drug resistant strains. Larval survivability studies were performed to evaluate the potential of phages against infection using G. mellonella.ResultsAll the three phages were found to have potential to infect the host bacterial strains. For in vivo studies it was observed that E. coli and E. cloacae infected larvae, should be treated with three phage doses (20 μL, 104 PFU/mL) at 6 h interval to achieve 100% survival rate. But in the case of K. pneumoniae, a single phage dose treatment showed promising outcome. When mixed bacterial infections (all three bacterial cultures at 108 CFU/mL) were tested, minimum of four doses of phage cocktail (three phages) at 6 h interval was necessary to recover the larvae. All the results were confirmed by enumerating bacteria from the larvae.ConclusionOur data shows that although in vitro studies showed high infectivity of phages, for in vivo models multiple phage doses were required for effective treatment.Electronic supplementary materialThe online version of this article (10.1186/s12866-018-1234-4) contains supplementary material, which is available to authorized users.
Genetic variation in an infectious disease pathogen can be driven by ecological niche dissimilarities arising from different host species and different geographical locations. Whole genome sequencing was used to compare E. coli O157 isolates from host reservoirs (cattle and sheep) from Scotland and to compare genetic variation of isolates (human, animal, environmental/food) obtained from Scotland, New Zealand, Netherlands, Canada and the USA. Nei’s genetic distance calculated from core genome single nucleotide polymorphisms (SNPs) demonstrated that the animal isolates were from the same population. Investigation of the Shiga toxin bacteriophage and their insertion sites (SBI typing) revealed that cattle and sheep isolates had statistically indistinguishable rarefaction profiles, diversity and genotypes. In contrast, isolates from different countries exhibited significant differences in Nei’s genetic distance and SBI typing. Hence, after successful international transmission, which has occurred on multiple occasions, local genetic variation occurs, resulting in a global patchwork of continental and trans-continental phylogeographic clades. These findings are important for three reasons: first, understanding transmission and evolution of infectious diseases associated with multiple host reservoirs and multi-geographic locations; second, highlighting the relevance of the sheep reservoir when considering farm based interventions; and third, improving our understanding of why human disease incidence varies across the world.
Acinetobacter baumannii is a multi-resistant opportunistic nosocomial pathogen responsible for several outbreaks worldwide. It can cause several infections at various sites of the body. One of the main infections caused by this bacterium is ventilator-associated pneumonia in patients in intensive care units. Treating these infections is becoming difficult because of the high resistance to antimicrobial agents. This study compared the expression of the chromosomally encoded bla ADC gene in isolates having ISAba1, ISAba125 and no insertion upstream of the bla ADC gene in A. baumannii clinical isolates. It showed that the expression of bla ADC was six times greater when ISAba125 was present upstream of the gene in comparison with the constitutively expressed bla ADC gene with no insertion present upstream. The study indicated that ISAba125 has better promoters than ISAba1 and this is responsible for the overexpression of the bla ADC gene as they share considerable homology to the well-established Escherichia coli promoters. The "10 box of ISAba125 formed a fusion promoter with the "35 box of the bla ADC gene causing the bla ADC gene to be significantly overexpressed. The ability to upregulate the expression of bla ADC with the assistance of different insertion elements such as ISAba1 and ISAba125 has become an important factor in A. baumannii resistance to cephalosporins. INTRODUCTIONThe predominant mechanism of b-lactam resistance in Gram-negative bacteria is the synthesis of b-lactamases (Philippon et al., 2002). Following the introduction of highly stable cephalosporins, the carbapenems and monobactams, resistance initially appeared in organisms such as Enterobacter cloacae, Citrobacter freundii, Serratia marcescens and Pseudomonas aeruginosa, where mutations in the chromosome lead to the overproduction of the AmpC blactamase. This confers resistance to oxyimino-and 7-alphamethoxy-cephalosporins and monobactams (Sanders, 1987). Class C b-lactamases produced by Gram-negative bacteria can hydrolyse many b-lactam antibiotics including the cephamycins and oxyimino-cephalosporins (Philippon et al., 2002;Sanders, 1987;Caroff et al., 2000). These enzymes can also hydrolyse monobactams, such as aztreonam, to a lesser extent (Bush et al., 1995;Mammeri & Nordmann, 2007). Acinetobacter baumannii is a Gramnegative, non-fermenting coccobacillus, which is associated with serious nosocomial infections (Cisneros & Rodríguez-Baño, 2002;Levin et al., 2003). Antimicrobial treatment of such infections is difficult due to their multidrug resistance profile (Corvec et al., 2003). The AmpC enzyme from multiresistant A. baumannii was first sequenced from a Spanish isolate (Bou & Martínez-Beltrán, 2000). This constitutively expressed AmpC enzyme shares low similarity with Enterobacteriaceae AmpC cephalosporinases (Corvec et al., 2003). High-level expression of AmpC b-lactamase is a mechanism of chromosomally mediated resistance to cephalosporins in A. baumannii (Bou & Martínez-Beltrán, 2000). Transposable elements are important motors...
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