Plasmid-mediated streptomycin and sulfamethoxazole resistance in Shigella flexneri 3a

Shigella flexneri: an emerging pathogen

Shigella flexneri is a leading etiologic agent of diarrhea in low socioeconomic countries. Notably, various serotypes in S. flexneri are reported from different regions of the world. The precise approximations of illness and death owing to shigellosis are missing in low socioeconomic countries, although it is widespread in different regions. The inadequate statistics available reveal S. flexneri to be a significant food and waterborne pathogen. All over the world, different antibiotic-resistant strains of S. flexneri serotypes have been emerged especially multidrug-resistant strains. Recently, increased resistance was observed in cephalosporins (3rd generation), azithromycin, and fluoroquinolones. There is a need for a continuous surveillance study on antibiotic resistance that will be helpful in the update of the antibiogram. The shigellosis burden can be reduced by adopting preventive measures like delivery of safe drinking water, suitable sanitation, and development of an effective and inexpensive multivalent vaccine. This review attempts to provide the recent findings of S. flexneri related to epidemiology and the emergence of multidrug resistance.

Shigella: Antibiotic-Resistance Mechanisms And New Horizons For Treatment

Shigella spp. are a common cause of diarrheal disease and have remained an important pathogen responsible for increased rates of morbidity and mortality caused by dysentery each year around the globe. Antibiotic treatment of Shigella infections plays an essential role in reducing prevalence and death rates of the disease. However, treatment of these infections remains a challenge, due to the global rise in broad-spectrum resistance to many antibiotics. Drug resistance in Shigella spp. can result from many mechanisms, such as decrease in cellular permeability, extrusion of drugs by active efflux pumps, and overexpression of drug-modifying and -inactivating enzymes or target modification by mutation. Therefore, there is an increasing need for identification and evolution of alternative therapeutic strategies presenting innovative avenues against Shigella infections, as well as paying further attention to this infection. The current review focuses on various antibiotic-resistance mechanisms of Shigella spp. with a particular emphasis on epidemiology and new mechanisms of resistance and their acquisition, and also discusses the status of novel strategies for treatment of Shigella infection and vaccine candidates currently under evaluation in preclinical or clinical phases.

The Complete Genome and Physiological Analysis of the Eurythermal Firmicute Exiguobacterium chiriqhucha Strain RW2 Isolated From a Freshwater Microbialite, Widely Adaptable to Broad Thermal, pH, and Salinity Ranges

Members of the genus Exiguobacterium are found in diverse environments from marine, freshwaters, permafrost to hot springs. Exiguobacterium can grow in a wide range of temperature, pH, salinity, and heavy-metal concentrations. We characterized Exiguobacterium chiriqhucha strain RW2 isolated from a permanently cold freshwater microbialite in Pavilion Lake, British Columbia using metabolic assays, genomics, comparative genomics, phylogenetics, and fatty acid composition. Strain RW2 has the most extensive growth range for temperature (4–50°C) and pH (5–11) of known Exiguobacterium isolates. Strain RW2 genome predicts pathways for wide differential thermal, cold and osmotic stress using cold and heat shock cascades (e.g., csp and dnaK), choline and betaine uptake/biosynthesis (e.g., opu and proU), antiporters (e.g., arcD and nhaC Na⁺/K⁺), membrane fatty acid unsaturation and saturation. Here, we provide the first complete genome from Exiguobacterium chiriqhucha strain RW2, which was isolated from a freshwater microbialite. Its genome consists of a single 3,019,018 bp circular chromosome encoding over 3,000 predicted proteins, with a GC% content of 52.1%, and no plasmids. In addition to growing at a wide range of temperatures and salinities, our findings indicate that RW2 is resistant to sulfisoxazole and has the genomic potential for detoxification of heavy metals (via mercuric reductases, arsenic resistance pumps, chromate transporters, and cadmium-cobalt-zinc resistance genes), which may contribute to the metabolic potential of Pavilion Lake microbialites. Strain RW2 could also contribute to microbialite formation, as it is a robust biofilm former and encodes genes involved in the deamination of amino acids to ammonia (i.e., L-asparaginase/urease), which could potentially boost carbonate precipitation by lowering the local pH and increasing alkalinity. We also used comparative genomic analysis to predict the pathway for orange pigmentation that is conserved across the entire Exiguobacterium genus, specifically, a C₃₀ carotenoid biosynthesis pathway is predicted to yield diaponeurosporene-4-oic acid as its final product. Carotenoids have been found to protect against ultraviolet radiation by quenching reactive oxygen, releasing excessive light energy, radical scavenging, and sunscreening. Together these results provide further insight into the potential of Exiguobacterium to exploit a wide range of environmental conditions, its potential roles in ecosystems (e.g., microbialites/microbial mats), and a blueprint model for diverse metabolic processes.

Characterization of a plasmid carrying cat, ermB and tetS genes in a foodborne Listeria monocytogenes strain and uptake of the plasmid by cariogenic Streptococcus mutans

A multi-drug resistant (MDR) Listeria monocytogenes isolate (serotype 1/2c) was recovered from a quick-frozen rice flour product collected from Langfang city in northern China. PCR screening identified the presence of cat, ermB and tetS genes. The plasmid profile of the strain showed the presence of an approximately 22.4-kb plasmid. Curing of this plasmid resulted in the loss of cat, ermB and tetS genes and increased susceptibility to several antibiotics, suggesting the involvement of the plasmid in multiple antibiotic resistances. Moreover, the plasmid was able to be uptaken by human oral pathogen Streptococcus mutans by natural transformation and resulted in the acquiring of multiple resistances in the transconjugants. This study contributes to our knowledge on acquired multi-drug resistance in foodborne pathogenic L.monocytogenes, which will add to a better understanding of effective clinical management of listeriosis.

Circulating Gut-Homing (α4β7+) Plasmablast Responses against Shigella Surface Protein Antigens among Hospitalized Patients with Diarrhea

Developing countries are burdened with Shigella diarrhea. Understanding mucosal immune responses associated with natural Shigella infection is important to identify potential correlates of protection and, as such, to design effective vaccines. We performed a comparative analysis of circulating mucosal plasmablasts producing specific antibodies against highly conserved invasive plasmid antigens (IpaC, IpaD20, and IpaD120) and two recently identified surface protein antigens, pan-Shigella surface protein antigen 1 (PSSP1) and PSSP2, common to all virulent Shigella strains. We examined blood and stool specimens from 37 diarrheal patients admitted to the Infectious Diseases & Beliaghata General Hospital, Kolkata, India. The etiological agent of diarrhea was investigated in stool specimens by microbiological methods and real-time PCR. Gut-homing (α4β7 (+)) antibody-secreting cells (ASCs) were isolated from patient blood by means of combined magnetic cell sorting and two-color enzyme-linked immunosorbent spot (ELISPOT) assay. Overall, 57% (21 of 37) and 65% (24 of 37) of the patients were positive for Shigella infection by microbiological and real-time PCR assays, respectively. The frequency of α4β7 (+) IgG ASC responders against Ipas was higher than that observed against PSSP1 or PSSP2, regardless of the Shigella serotype isolated from these patients. Thus, α4β7 (+) ASC responses to Ipas may be considered an indirect marker of Shigella infection. The apparent weakness of ASC responses to PSSP1 is consistent with the lack of cross-protection induced by natural Shigella infection. The finding that ASC responses to IpaD develop in patients with recent-onset shigellosis indicates that such responses may not be protective or may wane too rapidly and/or be of insufficient magnitude.

Outbreak of plasmid-mediated NDM-1-producing Klebsiella pneumoniae ST105 among neonatal patients in Yunnan, China

Background

In the past decade, the carbapenemase-producing Enterobacteriaceae (CPE) have been reported worldwide. Emergence of carbapenemase-producing strains among Enterobacteriaceae has been a challenge for treatment of clinical infection. The present study was undertaken to investigate the characteristics of carbapenem-resistant Klebsiella pneumoniae recovered from an outbreak that affected 17 neonatal patients in neonatal intensive care unit (NICU) of Kunming City Maternal and Child health Hospital, which is located in the Kunming city in far southwest of China.

Methods

Minimum inhibitory concentrations (MICs) for antimicrobial agents were determined according to the guidelines of the Clinical and Laboratory Standards Institute (CLSI); Modified Hodge test and Carba-NP test were preformed to identified the phenotypes of carbapenemases producing; To determine whether carbapenem resistance was transferable, a conjugation experiment was carried out in mixed broth cultures; Resistant genes were detected by using PCR and sequencing; Plasmids were typed by PCR-based replicon typing method; Clone relationships were analyzed by using multilocus-sequence typing (MLST) and pulsed field gel electrophoresis (PFGE).

Results

Eighteen highly carbapenem-resistant Klebsiella pneumoniae were isolated from patients in NICU and one carbapenem-resistant K. pneumoniae isolate was detected in incubator water. All these isolates harbored bla_NDM-1. Moreover, other resistance genes, viz., bla_IMP-4, bla_SHV-1, bla_TEM-1, bla_CTX-M-15, qnrS1, qnrB4, and aacA4 were detected. The bla_NDM-1 gene was located on a ca. 50 kb IncFI type plasmid. PFGE analysis showed that NDM-1-producing K. pneumoniae were clonally related and MLST assigned them to sequence type 105.

Conclusions

NDM-1 producing strains present in the hospital environment pose a potential risk and the incubator water may act as a diffusion reservoir of NDM-1- producing bacteria. Nosocomial surveillance system should play a more important role in the infection control to limit the spread of these pathogens.

Occurrence and Antibiotic Resistance of Vibrio parahaemolyticus from Shellfish in Selangor, Malaysia

High consumer demand for shellfish has led to the need for large-scale, reliable shellfish supply through aquaculture or shellfish farming. However, bacterial infections which can spread rapidly among shellfish poses a major threat to this industry. Shellfish farmers therefore often resort to extensive use of antibiotics, both prophylactically and therapeutically, in order to protect their stocks. The extensive use of antibiotics in aquaculture has been postulated to represent a major contributing factor in the rising incidence of antimicrobial resistant pathogenic bacteria in shellfish. This study aimed to investigate the incidence of pathogenic Vibrio parahaemolyticus and determine the antibiotic resistance profile as well as to perform plasmid curing in order to determine the antibiotic resistance mediation. Based on colony morphology, all 450 samples tested were positive for Vibrio sp; however, tox-R assay showed that only 44.4% (200/450) of these were V. parahaemolyticus. Out of these 200 samples, 6.5% (13/200) were trh-positive while none were tdh-positive. Antibiotic resistance was determined for all V. parahaemolyticus identified against 14 commonly used antibiotics and the multiple antibiotic resistance index (MAR) was calculated. The isolates demonstrated high resistance to several antibiotics tested- including second and third-line antibiotics- with 88% resistant to ampicillin, 81% to amikacin,70.5% to kanamycin, 73% to cefotaxime, and 51.5% to ceftazidime. The MAR index ranged from 0.00 to 0.79 with the majority of samples having an index of 0.36 (resistant to five antibiotics). Among the 13 trh-positive strains, almost 70% (9/13) demonstrated resistance to 4 or more antibiotics. Plasmid profiling for all V. parahaemolyticus isolates revealed that 86.5% (173/200) contained plasmids - ranging from 1 to 7 plasmids with DNA band sizes ranging from 1.2 kb to greater than 10 kb. 6/13 of the pathogenic V. pathogenic strains contained plasmid. After plasmid curing, the plasmid containing pathogenic strains isolated in our study have chromosomally mediated ampicillin resistance while the remaining resistance phenotypes are plasmid mediated. Overall, our results indicate that while the incidence of pathogenic V. parahaemolyticus in shellfish in Selangor still appears to be at relatively reassuring levels, antibiotic resistance is a real concern and warrants ongoing surveillance.

An insight of traditional plasmid curing in Vibrio species

As the causative agent of foodborne related illness, Vibrio species causes a huge impact on the public health and management. Vibrio species is often associated with seafood as the latter plays a role as a vehicle to transmit bacterial infections. Hence, antibiotics are used not to promote growth but rather to prevent and treat bacterial infections. The extensive use of antibiotics in the aquaculture industry and environment has led to the emerging of antibiotic resistant strains. This phenomenon has triggered an alarming public health concern due to the increase number of pathogenic Vibrio strains that are resistant to clinically used antibiotics and is found in the environment. Antibiotic resistance and the genes location in the strains can be detected through plasmid curing assay. The results derived from plasmid curing assay is fast, cost effective, sufficient in providing insights, and influence the antibiotic management policies in the aquaculture industry. This presentation aims in discussing and providing insights on various curing agents in Vibrio species. To our best of knowledge, this is a first review written discussing on plasmid curing in Vibrio species.

Antibiotic-resistant vibrios in farmed shrimp

Antimicrobial susceptibility pattern was determined in 100 strains of Vibrio isolated from the Litopenaeus vannamei shrimp and identified phenotypically. A high antibiotic-resistance index (75%) was observed, with the following phenotypic profiles: monoresistance (n = 42), cross-resistance to β-lactams (n = 20) and multiple resistance (n = 13). Plasmid resistance was characterized for penicillin (n = 11), penicillin + ampicillin (n = 1), penicillin + aztreonam (n = 1), and ampicillin (n = 1). Resistance to antimicrobial drugs by the other strains (n = 86) was possibly mediated by chromosomal genes. The findings of this study support the conclusion that the cultured shrimps can be vehicles of vibrios resistant to β-lactam and tetracycline.

Plasmid-mediated sulfamethoxazole resistance encoded by the sul2 gene in the multidrug-resistant Shigella flexneri 2a isolated from patients with acute diarrhea in Dhaka, Bangladesh

In this study, mechanisms of plasmid-mediated sulfamethoxazole resistances in the clinical strains of multi-drug resistant (MDR) Shigella flexneri 2a were elucidated for the first time in Bangladesh. From 2006 to 2011, a total of 200 S. flexneri 2a strains were randomly selected from the stock of the Enteric and Food Microbiology Laboratory of icddr,b. Antimicrobial susceptibility of the strains showed 73%, 98%, 93%, 58%, 98%, 64% and 4% resistance to trimethoprim-sulfamethoxazole, nalidixic acid, ampicillin, erythromycin, tetracycline, ciprofloxacin and ceftriaxone respectively. Plasmid profiling revealed heterogeneous patterns and interestingly, all the trimethoprim-sulfamethoxazole resistant (SXT(R)) strains yielded a distinct 4.3 MDa plasmid compared to that of the trimethoprim-sulfamethoxazole susceptible (SXT(S)) strains. Curing of this 4.3 MDa plasmid resulted in the susceptibility to sulfamethoxazole alone suggesting the involvement of this plasmid in the resistance of sulfamethoxazole. Moreover, PCR analysis showed the presence of sul2 gene in SXT(R) strains which is absent in SXT(S) strains as well as in the 4.3 MDa plasmid-cured derivatives, confirming the involvement of sul2 in the resistance of sulfamethoxazole. Furthermore, pulsed-field gel electrophoresis (PFGE) analysis revealed that both the SXT(R) and SXT(S) strains were clonal. This study will significantly contributes to the knowledge on acquired drug resistance of the mostly prevalent S. flexneri 2a and further warrants continuous monitoring of the prevalence and correlation of this resistance determinants amongst the clinical isolates of Shigella and other enteric pathogens around the world to provide effective clinical management of the disease.

Bacterial resistance mechanism: what proteomics can elucidate

Antibiotics are important therapeutic agents commonly used for the control of bacterial infectious diseases; however, resistance to antibiotics has become a global public health problem. Therefore, effective therapy in the treatment of resistant bacteria is necessary and, to achieve this, a detailed understanding of mechanisms that underlie drug resistance must be sought. To fill the multiple gaps that remain in understanding bacterial resistance, proteomic tools have been used to study bacterial physiology in response to antibiotic stress. In general, the global analysis of changes in the protein composition of bacterial cells in response to treatment with antibiotic agents has made it possible to construct a database of proteins involved in the process of resistance to drugs with similar mechanisms of action. In the past few years, progress in using proteomic tools has provided the most realistic picture of the infective process, since these tools detect the end products of gene biosynthetic pathways, which may eventually determine a biological phenotype. In most bacterial species, alterations occur in energy and nitrogen metabolism regulation; glucan biosynthesis is up-regulated; amino acid, protein, and nucleotide synthesis is affected; and various proteins show a stress response after exposing these microorganisms to antibiotics. These issues have been useful in identifying targets for the development of novel antibiotics and also in understanding, at the molecular level, how bacteria resist antibiotics.

Comparison of the prevalence and changing resistance to nalidixic acid and ciprofloxacin of Shigella between Europe-America and Asia-Africa from 1998 to 2009

Shigella is becoming an increasing public health problem due to development of multiple antimicrobial resistance, frequently resulting in treatment failure. A systematic review was conducted based on a literature search of computerised databases. Random or fixed-effects models were used, based on the P-value considering the possibility of heterogeneity between studies, for meta-analysis. Statistical analyses were performed using STATA 10.0. In the area of Asia-Africa, resistance rates to nalidixic acid and ciprofloxacin were 33.6% [95% confidence interval (CI) 21.8-46.6%] and 5.0% (95% CI 2.8-7.8%), respectively, 10.5 and 16.7 times those of Europe-America. Moreover, resistance to nalidixic acid and ciprofloxacin in Asia-Africa progressively increased each year, reaching 64.5% (95% CI 13.8-99.3%) and 29.1% (95% CI 0.9-74.8%), respectively, in 2007-2009, whilst isolates in Europe-America remained at low levels of resistance (<5.0% and <1.0%, respectively). All Shigella flexneri strains showed higher resistance than Shigella sonnei in Europe-America: overall, 3.5% (95% CI 1.4-6.4%) vs. 2.6% (95% CI 1.0-5.0%) resistant to nalidixic acid and 1.0% (95% CI 0.3-2.2%) vs. 0.1% (95% CI 0.0-0.3%) resistant to ciprofloxacin. In Asia-Africa, a similar trend was found for ciprofloxacin [3.0% (95% CI 1.4-5.3%) vs. 0.5% (95% CI 0.2-0.8%)], whereas the trend was reversed for nalidixic acid [32.6% (95% CI 14.5-53.9%) vs. 44.3% (95% CI 26.9-62.5%). In conclusion, quinolone resistance in Shigella has increased at an alarming speed, reinforcing the importance of continuous monitoring of antimicrobial resistance in Shigella.

Zoonotic diseases of primates

A zoonotic disease is transmissible from vertebrate animals to humans. This article focuses on pertinent zoonotic diseases that have to be taken into consideration when working with nonhuman primate (NHP) species. Many factors may influence the occurrence of these diseases. Human and NHPs share many similarities, not only anatomically but also physiologically. NHP are valuable models for many human infectious diseases; therefore, staff can be exposed to many potential pathogens. In general, the disease state of a primate can range from asymptomatic carrier to death from infection.