Antimicrobial Resistance in Chlamydiales, Rickettsia, Coxiella, and Other Intracellular Pathogens

Antibiotic resistance in tick-borne bacteria: A One Health approach perspective

The emergence and re-emergence of tick-borne bacteria (TBB) as a public health problem raises the uncertainty of antibiotic resistance in these pathogens, which could be dispersed to other pathogens. The impact of global warming has led to the emergence of pathogenic TBB in areas where they were not previously present and is another risk that must be taken into account under the One Health guides. This review aimed to analyze the existing information regarding antibiotic-resistant TBB and antibiotic-resistance genes (ARG) present in the tick microbiome, considering the potential to be transmitted to pathogenic microorganisms. Several Ehrlichia species have been reported to exhibit natural resistance to fluoroquinolones and typhus group Rickettsiae are naturally susceptible to erythromycin. TBB have a lower risk of acquiring ARG due to their natural habitat, but there is still a probability of acquiring them; furthermore, studies of these pathogens are limited. Pathogenic and commensal bacteria coexist within the tick microbiome along with ARGs for antibiotic deactivation, cellular protection, and efflux pumps; these ARGs confer resistance to antibiotics such as aminoglycosides, beta-lactamase, diaminopyrimidines, fluoroquinolones, glycopeptides, sulfonamides, and tetracyclines. Although with low probability, TBB can be a reservoir of ARGs.

Nanobiotics against antimicrobial resistance: harnessing the power of nanoscale materials and technologies

Given the spasmodic increment in antimicrobial resistance (AMR), world is on the verge of “post-antibiotic era”. It is anticipated that current SARS-CoV2 pandemic would worsen the situation in future, mainly due to the lack of new/next generation of antimicrobials. In this context, nanoscale materials with antimicrobial potential have a great promise to treat deadly pathogens. These functional materials are uniquely positioned to effectively interfere with the bacterial systems and augment biofilm penetration. Most importantly, the core substance, surface chemistry, shape, and size of nanomaterials define their efficacy while avoiding the development of AMR. Here, we review the mechanisms of AMR and emerging applications of nanoscale functional materials as an excellent substitute for conventional antibiotics. We discuss the potential, promises, challenges and prospects of nanobiotics to combat AMR.

An Update on the Laboratory Diagnosis of Rickettsia spp. Infection

Rickettsia species causing human illness are present globally and can cause significant disease. Diagnosis and identification of this intracellular bacteria are challenging with many available diagnostic modalities suffering from several shortcomings. Detection of antibodies directed against Rickettsia spp. via serological methods remains widely used with a broad range of sensitivity and specificity values reported depending on the assay. Molecular methods, including polymerase chain reaction (PCR) testing, enables species-specific identification with a fast turnaround time; however, due to resource requirements, use in some endemic settings is limited. Reports on the use of next-generation sequencing (NGS) and metagenomics to diagnose Rickettsia spp. infection have been increasing. Despite offering several potential advantages in the diagnosis and surveillance of disease, genomic approaches are currently only limited to reference and research laboratories. Continued development of Rickettsia spp. diagnostics is required to improve disease detection and epidemiological surveillance, and to better understand transmission dynamics.

Generation of Tetracycline and Rifamycin Resistant Chlamydia Suis Recombinants

The Chlamydiaceae are a family of obligate intracellular, gram-negative bacteria known to readily exchange DNA by homologous recombination upon co-culture in vitro, allowing the transfer of antibiotic resistance residing on the chlamydial chromosome. Among all the obligate intracellular bacteria, only Chlamydia (C.) suis naturally integrated a tetracycline resistance gene into its chromosome. Therefore, in order to further investigate the readiness of Chlamydia to exchange DNA and especially antibiotic resistance, C. suis is an excellent model to advance existing co-culture protocols allowing the identification of factors crucial to promote homologous recombination in vitro. With this strategy, we co-cultured tetracycline-resistant with rifamycin group-resistant C. suis, which resulted in an allover recombination efficiency of 28%. We found that simultaneous selection is crucial to increase the number of recombinants, that sub-inhibitory concentrations of tetracycline inhibit rather than promote the selection of double-resistant recombinants, and identified a recombination-deficient C. suis field isolate, strain SWA-110 (1-28b). While tetracycline resistance was detected in field isolates, rifampicin/rifamycin resistance (RifR) had to be induced in vitro. Here, we describe the protocol with which RifR C. suis strains were generated and confirmed. Subsequent whole-genome sequencing then revealed that G530E and D461A mutations in rpoB, a gene encoding for the β-subunit of the bacterial RNA polymerase (RNAP), was likely responsible for rifampicin and rifamycin resistance, respectively. Finally, whole-genome sequencing of recombinants obtained by co-culture revealed that recombinants picked from the same plate may be sibling clones and confirmed C. suis genome plasticity by revealing variable, apparently non-specific areas of recombination.

A Robust Symbiotic Relationship Between the Ciliate Paramecium multimicronucleatum and the Bacterium Ca. Trichorickettsia Mobilis

Close reciprocal interactions in symbiotic systems have suggested the holobiont concept, in which the host and its microbiota are considered as a single entity. Ciliates are known for their ability to form symbiotic associations with prokaryotes. Relationships between the partners in such systems vary from mutualism to parasitism and differ significantly in their robustness. We assessed the viability of the ciliate Paramecium multimicronucleatum and its ability to maintain its intranuclear endosymbiont Ca. Trichorickettsia mobilis (Rickettsiaceae) after treatment with antibiotics characterized by different mode of action, such as ampicillin, streptomycin, chloramphenicol, tetracycline. The presence of endosymbionts in the host cell was determined by means of living cell observations made using differential interference contrast or fluorescence in situ hybridization with the species-specific oligonucleotide probe (FISH). Administration of antibiotics traditionally used in treatments of rickettsioses, tetracycline and chloramphenicol, depending on the concentration used and the ciliate strain treated, either caused death of both, infected and control cells, or did not affect the ability of the host to maintain the intranuclear endosymbiont. The surviving cells always manifested motile bacteria in the macronucleus. Streptomycin treatment never led to the loss of endosymbionts in any of the four infected strains, and nearly all ciliates remained viable. Ampicillin treatment never caused host cell death, but resulted in formation of filamentous and immobile oval bacterial forms. Under repeated ampicillin treatments, a part of endosymbionts was registered in the host cytoplasm, as evidenced both by FISH and transmission electron microscopy. Endosymbionts located in the host cytoplasm were enclosed in vacuoles, apparently, corresponding to autophagosomes. Nevertheless, the bacteria seemed to persist in this compartment and might cause relapse of the infection. Although the antibiotic sensitivity profile of Trichorickettsia seems to resemble that of other representatives of Rickettsiaceae, causative agents of severe diseases in humans, neither of the antibiotic treatments used in this study resulted in an aposymbiotic cell line, apparently, due to the protists’ sensitivity to tetracyclines, the drugs of preference in rickettsiosis treatment. The observed robustness of this symbiotic system makes it a good model for further elaboration of the holobiont concept.

New Real-Time PCRs to Differentiate Rickettsia spp. and Rickettsia conorii

Rickettsia species are an important cause of emerging infectious diseases in people and animals, and rickettsiosis is one of the oldest known vector-borne diseases. Laboratory diagnosis of Rickettsia is complex and time-consuming. This study was aimed at developing two quantitative real-time PCRs targeting ompB and ompA genes for the detection, respectively, of Rickettsia spp. and R. conorii DNA. Primers were designed following an analysis of Rickettsia gene sequences. The assays were optimized using SYBR Green and TaqMan methods and tested for sensitivity and specificity. This study allowed the development of powerful diagnostic methods, able to detect and quantify Rickettsia spp. DNA and differentiate R. conorii species.

Water Filtered Infrared A and Visible Light (wIRA/VIS) Irradiation Reduces Chlamydia trachomatis Infectivity Independent of Targeted Cytokine Inhibition

Chlamydia trachomatis is the major cause of infectious blindness and represents the most common bacterial sexually transmitted infection worldwide. Considering the potential side effects of antibiotic therapy and increasing threat of antibiotic resistance, alternative therapeutic strategies are needed. Previous studies showed that water filtered infrared A alone (wIRA) or in combination with visible light (wIRA/VIS) reduced C. trachomatis infectivity. Furthermore, wIRA/VIS irradiation led to secretion of pro-inflammatory cytokines similar to that observed upon C. trachomatis infection. We confirmed the results of previous studies, namely that cytokine secretion (IL-6, IL-8, and RANTES/CCL5) upon wIRA/VIS treatment, and the subsequent reduction of chlamydial infectivity, are independent of the addition of cycloheximide, a host protein synthesis inhibitor. Reproducible cytokine release upon irradiation indicated that cytokines might be involved in the anti-chlamydial mechanism of wIRA/VIS. This hypothesis was tested by inhibiting IL-6, IL-8, and RANTES secretion in C. trachomatis or mock-infected cells by gene silencing or pharmaceutical inhibition. Celastrol, a substance derived from Trypterygium wilfordii, used in traditional Chinese medicine and known for anti-cancer and anti-inflammatory effects, was used for IL-6 and IL-8 inhibition, while Maraviroc, a competitive CCR5 antagonist and anti-HIV drug, served as a RANTES/CCL5 inhibitor. HeLa cell cytotoxicity and impact on chlamydial morphology, size and inclusion number was evaluated upon increasing inhibitor concentration, and concentrations of 0.1 and 1 μM Celastrol and 10 and 20 μM Maraviroc were subsequently selected for irradiation experiments. Celastrol at any concentration reduced chlamydial infectivity, an effect only observed for 20 μM Maraviroc. Triple dose irradiation (24, 36, 40 hpi) significantly reduced chlamydial infectivity regardless of IL-6, IL-8, or RANTES/CCL5 gene silencing, Celastrol or Maraviroc treatment. Neither gene silencing nor pharmaceutical cytokine inhibition provoked the chlamydial stress response. The anti-chlamydial effect of wIRA/VIS is independent of cytokine inhibition under all conditions evaluated. Thus, factors other than host cell cytokines must be involved in the working mechanism of wIRA/VIS. This study gives a first insight into the working mechanism of wIRA/VIS in relation to an integral component of the host immune system and supports the potential of wIRA/VIS as a promising new tool for treatment in trachoma.