Antibiotic resistance in Campylobacter jejuni and Campylobacter coli isolated from poultry in the South-East Queensland region

Objectives: The aim of this study was to determine the antimicrobial resistance patterns of 125 Campylobacter jejuni and 27 Campylobacter coli isolates from 39 Queensland broiler farms. Methods: Two methods, a disc diffusion assay and an agar-based MIC assay, were used. The disc diffusion was performed and interpreted as previously described (Huysmans MB, Turnidge JD. Disc susceptibility testing for thermophilic campylobacters. Pathology 1997; 29: 209–16), whereas the MIC assay was performed according to CLSI (formerly NCCLS) methods and interpreted using DANMAP criteria. Results: In both assays, no C. jejuni or C. coli isolates were resistant to ciprofloxacin or chloramphenicol, no C. coli were resistant to nalidixic acid, and no C. jejuni were resistant to erythromycin. In the MIC assay, no C. jejuni isolate was resistant to nalidixic acid, whereas three isolates (2.4%) were resistant in the disc assay. The highest levels of resistance of the C. jejuni isolates were recorded for tetracycline (19.2% by MIC and 18.4% by disc) and ampicillin (19.2% by MIC and 17.6% by disc). The C. coli isolates gave very similar results (tetracycline resistance 14.8% by both MIC and disc; ampicillin resistance 7.4% by MIC and 14.8% by disc). Conclusions: This work has shown that the majority of C. jejuni and C. coli isolates were susceptible to the six antibiotics tested by both disc diffusion and MIC methods. Disc diffusion represents a suitable alternative methodology to agar-based MIC methods for poultry Campylobacter isolates.

The persistence of biofilm-associated antibiotic resistance of Staphylococcus aureus isolated from clinical bovine mastitis cases in Australia

The aim of this investigation was to determine the persistence of biofilm-associated antibiotic resistance developed by methicillin-sensitive Staphylococcus aureus (MSSA), of different capsular types, during biofilm formation. Because of superiority of the tissue culture plate (TCP) over the Congo Red Agar (CRA) method for measuring biofilm formation, it was used to determine the persistence of the antibiotic resistance developed by the isolates in biofilms. The antibiotic resistance was found to persist for 3-4 wk post-propagation as planktonic subcultures. Interestingly, some strains even developed resistance to vancomycin and/or teicoplanin. However, no association of either biofilm formation or persistent antibiotic resistance with the major capsular phenotype was observed. These observations highlight the potential significance of (a) determining the antibiograms of S. aureus subcultured from biofilms developed in vitro using the TCP method as well as from planktonic cultures for formulation of an optimal therapeutic strategy, and (b) continuing to identify predominant non-capsular antigens contributing to biofilm formation, regardless of the capsular phenotype for the development of an effective potentially broad-spectrum vaccine for prevention of bovine mastitis caused by S. aureus.

Reply to Bonten and Mevius : Less Evidence for an Important Role of Food-Producing Animals as Source of Antibiotic Resistance in Humans

To the Editor—We thank Bonten and Mevius for their interest in our systematic review [1]. In their letter, they disagree with our finding that whole-bacterium transmission (WBT) of expanded-spectrum cephalosporin-resistant (ESCR) Escherichia coli between food-producing animals and humans likely contributes to the burden of human extraintestinal infections. We respectfully argue against 2 assumptions that underlie their assertion.

QTL mapping of multiple foliar disease and root-lesion nematode resistances in wheat.

A genetic linkage map, based on a cross between the synthetic hexaploid CPI133872 and the bread wheat cultivar Janz, was established using 111 F1-derived doubled haploid lines. The population was phenotyped in multiple years and/or locations for seven disease resistance traits, namely, Septoria tritici blotch (Mycosphaeralla graminicola), yellow leaf spot also known as tan spot (Pyrenophora tritici-repentis), stripe rust (Puccinia striiformis f. sp. tritici), leaf rust (Puccinia triticina), stem rust (Puccinia graminis f. sp. tritici) and two species of root-lesion nematode (Pratylenchyus thornei and P. neglectus). The DH population was also scored for coleoptile colour and the presence of the seedling leaf rust resistance gene Lr24. Implementation of a multiple-QTL model identified a tightly linked cluster of foliar disease resistance QTL in chromosome 3DL. Major QTL each for resistance to Septoria tritici blotch and yellow leaf spot were contributed by the synthetic hexaploid parent CPI133872 and linked in repulsion with the coincident Lr24Sr24/ locus carried by parent Janz. This is the first report of linked QTL for Septoria tritici blotch and yellow leaf spot contributed by the same parent. Additional QTL for yellow leaf spot were detected in 5AS and 5BL. Consistent QTL for stripe rust resistance were identified in chromosomes 1BL, 4BL and 7DS, with the QTL in 7DS corresponding to the Yr18Lr34/ region. Three major QTL for P. thornei resistance (2BS, 6DS, 6DL) and two for P. neglectus resistance (2BS, 6DS) were detected. The recombinants combining resistance to Septoria tritici blotch, yellow leaf spot, rust diseases and root-lesion nematodes from parents CPI133872 and Janz constitute valuable germplasm for the transfer of multiple disease resistance into new wheat cultivars.

Trends in therapeutic and prevention strategies for management of Bovine Mastitis: An overview

Mastitis is one of the most economically significant diseases for the dairy industry for backyard farmers in developing countries and high producing herds worldwide. Two of the major factors impeding reduction in the incidence of this disease is [a] the lack of availability of an effective vaccine capable of protecting against multiple etiological agents and [b] propensity of some of the etiological agents to develop persistent antibiotic resistance in biofilms. This is further complicated by the continuing revolving shift in the predominant etiological agents of mastitis, depending upon a multitude of factors such as variability in hygienic practices on farms, easy access leading to overuse of appropriate or inappropriate antibiotics at suboptimal concentrations, particularly in developing countries, and lack of compliance with the recommended treatment schedules. Regardless, Staphylococcus aureus and Streptococcus uberis followed by Escherichia coli, Streptococcus agalactiae has become the predominant etiological agents of bovine mastitis followed Streptococcus agalactiae, Streptococcus dysagalactiae, Klebsiella pneumonia and the newly emerging Mycoplasma bovis. Current approaches being pursued to reduce the negative economic impact of this disease are through early diagnosis of infection, immediate treatment with an antibiotic found to either inhibit or kill the pathogen(s) in vitro using planktonic cultures and the use of the currently marketed vaccines regardless of their demonstrated effectiveness. Given the limitations of breeding programs, including genetic selection to improve resistance against infectious diseases including mastitis, it is imperative to have the availability of an effective broad-spectrum, preferably cross-protective, vaccine capable of protecting against bovine mastitis for reduction in the incidence of bovine mastitis, as well as interrupting the potential cross-species transmission to humans. This overview highlights the major etiological agents, factors affecting susceptibility to mastitis, and the current status of antibiotic-based therapies and prototype vaccine candidates or commercially available vaccines against bovine mastitis as potential preventative strategies. © 2013 Tiwari JG, et al.

The plasticity of NBS resistance genes in sorghum is driven by multiple evolutionary processes

Background Increased disease resistance is a key target of cereal breeding programs, with disease outbreaks continuing to threaten global food production, particularly in Africa. Of the disease resistance gene families, the nucleotide-binding site plus leucine-rich repeat (NBS-LRR) family is the most prevalent and ancient and is also one of the largest gene families known in plants. The sequence diversity in NBS-encoding genes was explored in sorghum, a critical food staple in Africa, with comparisons to rice and maize and with comparisons to fungal pathogen resistance QTL. Results In sorghum, NBS-encoding genes had significantly higher diversity in comparison to non NBS-encoding genes and were significantly enriched in regions of the genome under purifying and balancing selection, both through domestication and improvement. Ancestral genes, pre-dating species divergence, were more abundant in regions with signatures of selection than in regions not under selection. Sorghum NBS-encoding genes were also significantly enriched in the regions of the genome containing fungal pathogen disease resistance QTL; with the diversity of the NBS-encoding genes influenced by the type of co-locating biotic stress resistance QTL. Conclusions NBS-encoding genes are under strong selection pressure in sorghum, through the contrasting evolutionary processes of purifying and balancing selection. Such contrasting evolutionary processes have impacted ancestral genes more than species-specific genes. Fungal disease resistance hot-spots in the genome, with resistance against multiple pathogens, provides further insight into the mechanisms that cereals use in the “arms race” with rapidly evolving pathogens in addition to providing plant breeders with selection targets for fast-tracking the development of high performing varieties with more durable pathogen resistance.

Homologues of the maize rust resistance gene Rp1-D are genetically associated with a major rust resistance QTL in sorghum

As part of a comparative mapping study between sugarcane and sorghum, a sugarcane cDNA clone with homology to the maize Rp1-D rust resistance gene was mapped in sorghum. The cDNA probe hybridised to multiple loci, including one on sorghum linkage group (LG) E in a region where a major rust resistance QTL had been previously mapped. Partial sorghum Rp1-D homologues were isolated from genomic DNA of rust-resistant and -susceptible progeny selected from a sorghum mapping population. Sequencing of the Rp1-D homologues revealed five discrete sequence classes: three from resistant progeny and two from susceptible progeny. PCR primers specific to each sequence class were used to amplify products from the progeny and confirmed that the five sequence classes mapped to the same locus on LG E. Cluster analysis of these sorghum sequences and available sugarcane, maize and sorghum Rp1-D homologue sequences showed that the maize Rp1-D sequence and the partial sugarcane Rp1-D homologue were clustered with one of the sorghum resistant progeny sequence classes, while previously published sorghum Rp1-D homologue sequences clustered with the susceptible progeny sequence classes. Full-length sequence information was obtained for one member of a resistant progeny sequence class ( Rp1-SO) and compared with the maize Rp1-D sequence and a previously identified sorghum Rp1 homologue ( Rph1-2). There was considerable similarity between the two sorghum sequences and less similarity between the sorghum and maize sequences. These results suggest a conservation of function and gene sequence homology at the Rp1 loci of maize and sorghum and provide a basis for convenient PCR-based screening tools for putative rust resistance alleles in sorghum.

Antibiotic Sensitivity Testing

Respiratory bacterial pathogens in pigs are currently treated with antibiotics. Intervet - Schering Plough markets an antibiotic called Nurflor (Florfenicol) targeting respiratory pathogens. This project tests the effectiveness of this antibiotic against a series of respiratory pathogens. 6 isolates will be tested per serovar/strain and the isolates will be from 4 different farms using MIC testing. The sensitivity of Florfenicol will be compared to sensitivity of the organisms to Tilmicosin and Amoxicillin. Development of resistance to certain antibiotics have been reported, so it is important to have alternative antibiotics available to treat the respiratory pathogens on farms.

Association mapping of resistance to Puccinia hordei in Australian barley breeding germplasm

Key message “To find stable resistance using association mapping tools, QTL with major and minor effects on leaf rust reactions were identified in barley breeding lines by assessing seedlings and adult plants.” Abstract Three hundred and sixty (360) elite barley (Hordeum vulgare L.) breeding lines from the Northern Region Barley Breeding Program in Australia were genotyped with 3,244 polymorphic diversity arrays technology markers and the results used to map quantitative trait loci (QTL) conferring a reaction to leaf rust (Puccinia hordei Otth). The F3:5 (Stage 2) lines were derived or sourced from different geographic origins or hubs of international barley breeding ventures representing two breeding cycles (2009 and 2011 trials) and were evaluated across eight environments for infection type at both seedling and adult plant stages. Association mapping was performed using mean scores for disease reaction, accounting for family effects using the eigenvalues from a matrix of genotype correlations. In this study, 15 QTL were detected; 5 QTL co-located with catalogued leaf rust resistance genes (Rph1, Rph3/19, Rph8/14/15, Rph20, Rph21), 6 QTL aligned with previously reported genomic regions and 4 QTL (3 on chromosome 1H and 1 on 7H) were novel. The adult plant resistance gene Rph20 was identified across the majority of environments and pathotypes. The QTL detected in this study offer opportunities for breeding for more durable resistance to leaf rust through pyramiding multiple genomic regions via marker-assisted selection.

Spot form of net blotch resistance in barley is under complex genetic control

Key message: Evaluation of resistance toPyrenophora teresf.maculatain barley breeding populations via association mapping revealed a complex genetic architecture comprising a mixture of major and minor effect genes. Abstract: In the search for stable resistance to spot form of net blotch (Pyrenophora teres f. maculata, SFNB), association mapping was conducted on four independent barley (Hordeum vulgare L.) breeding populations comprising a total of 898 unique elite breeding lines from the Northern Region Barley Breeding Program in Australia for discovery of quantitative trait loci (QTL) influencing resistance at seedling and adult plant growth stages. A total of 29 significant QTL were validated across multiple breeding populations, with 22 conferring resistance at both seedling and adult plant growth stages. The remaining 7 QTL conferred resistance at either seedling (2 QTL) or adult plant (5 QTL) growth stages only. These 29 QTL represented 24 unique genomic regions, of which five were found to co-locate with previously identified QTL for SFNB. The results indicated that SFNB resistance is controlled by a large number of QTL varying in effect size with large effects QTL on chromosome 7H. A large proportion of the QTL acted in the same direction for both seedling and adult responses, suggesting that phenotypic selection for SFNB resistance performed at either growth stage could achieve adequate levels of resistance. However, the accumulation of specific resistance alleles on several chromosomes must be considered in molecular breeding selection strategies.

Inheritance and Characterization of Strong Resistance to Phosphine in Sitophilus oryzae(L.)

Sitophilus oryzae (Linnaeus) is a major pest of stored grain across Southeast Asia and is of increasing concern in other regions due to the advent of strong resistance to phosphine, the fumigant used to protect stored grain from pest insects. We investigated the inheritance of genes controlling resistance to phosphine in a strongly resistant S. oryzae strain (NNSO7525) collected in Australia and find that the trait is autosomally inherited and incompletely recessive with a degree of dominance of -0.66. The strongly resistant strain has an LC50 52 times greater than a susceptible reference strain (LS2) and 9 times greater than a weakly resistant strain (QSO335). Analysis of F2 and backcross progeny indicates that two or more genes are responsible for strong resistance, and that one of these genes, designated Sorph1, not only contributes to strong resistance, but is also responsible for the weak resistance phenotype of strain QSO335. These results demonstrate that the genetic mechanism of phosphine resistance in Soryzae is similar to that of other stored product insect pests. A unique observation is that a subset of the progeny of an F1 backcross generation are more strongly resistant to phosphine than the parental strongly resistant strain, which may be caused by multiple alleles of one of the resistance genes.