Outbreak of infections caused by Shigella sonnei with reduced susceptibility to azithromycin in the United States

Bioactivity and efficacy of a hyperimmune bovine colostrum product- Travelan, against shigellosis in a non-Human primate model (Macaca mulatta)

Infectious diarrhea is a World Health Organization public health priority area due to the lack of effective vaccines and an accelerating global antimicrobial resistance crisis. New strategies are urgently needed such as immunoprophylactic for prevention of diarrheal diseases. Hyperimmune bovine colostrum (HBC) is an established and effective prophylactic for infectious diarrhea. The commercial HBC product, Travelan® (Immuron Ltd, Australia) targets multiple strains of enterotoxigenic Escherichia coli (ETEC) is highly effective in preventing diarrhea in human clinical studies. Although Travelan® targets ETEC, preliminary studies suggested cross-reactivity with other Gram-negative enteric pathogens including Shigella and Salmonella species. For this study we selected an invasive diarrheal/dysentery-causing enteric pathogen, Shigella, to evaluate the effectiveness of Travelan®, both in vitro and in vivo. Here we demonstrate broad cross-reactivity of Travelan® with all four Shigella spp. (S. flexneri, S. sonnei, S. dysenteriae and S. boydii) and important virulence factor Shigella antigens. Naïve juvenile rhesus macaques (NJRM) were randomized, 8 dosed with Travelan® and 4 with a placebo intragastrically twice daily over 6 days. All NJRM were challenged with S. flexneri 2a strain 2457T on the 4th day of treatment and monitored for diarrheal symptoms. All placebo-treated NJRM displayed acute dysentery symptoms within 24-36 hours of challenge. Two Travelan®-treated NJRM displayed dysentery symptoms and six animals remained healthy and symptom-free post challenge; resulting in 75% efficacy of prevention of shigellosis (p = 0.014). These results strongly indicate that Travelan® is functionally cross-reactive and an effective prophylactic for shigellosis. This has positive implications for the prophylactic use of Travelan® for protection against both ETEC and Shigella spp. diarrheal infections. Future refinement and expansion of pathogens recognized by HBC including Travelan® could revolutionize current management of gastrointestinal infections and outbreaks in travelers' including military, peacekeepers, humanitarian workers and in populations living in endemic regions of the world.

Evaluation of antimicrobial, anticancer potential and Flippase induced leakage in model membrane of Centella asiatica fabricated MgONPs

The use of chemically synthesized nanoparticles and crude plant extracts as antimicrobial -anticancer agents have many limitations. In this study, we have used Centella asiatica extract (CaE) having relatively less explored but tremendous medicinal properties, as reducing and stabilizing agents to green synthesize magnesium oxide nanoparticles (MgONPs) using magnesium nitrate. In comparison to the bulk material, capabilities of Ca-MgONPs as an improved antibacterial, antifungal, and anticancer agent in human prostatic carcinoma cells (PC3), as well as membranolytic capability in model cell membrane, were studied. The phyto-functionalized Ca-MgONPs were characterized using UV-Visible spectroscopy (UV-Vis), Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray Spectroscopy (EDX), X-ray Diffraction (XRD), Fourier Transform Infra-Red Spectroscopy (FT-IR) and Atomic Force Microscopy (AFM). Observation of characteristic peaks by spectroscopic and microscopic analysis confirmed the synthesis of Ca-MgONPs. The Ca-MgONPs showed broad spectrum of bactericidal activity against both gram-positive and gram-negative bacteria and fungicidal activity against two species of the Candida fungus. The Ca-MgONPs also exhibited dose-dependent and selective inhibition of proliferating PC3 cells with IC₅₀ of 123.65 ± 4.82 μg/mL at 24 h, however, without having any cytotoxicity toward non-cancerous HEK293 cells. Further studies aimed at understanding the probable mechanism of toxicity of Ca-MgONPs in PC3 cells, the results indicated a significant reduction in cell migration capacities, increment in cytosolic ROS, loss of mitochondrial transmembrane potential, DNA damage and S-phase cell cycle arrest. Ca-MgONPs also induced pore formation in a synthetic large unilamellar vesicle. Thus, Ca-MgONPs might be useful in the effective management of several human pathogens of concern and some more cancer types.

Antimicrobial-Resistant Shigella spp. in San Diego, California, USA, 2017-2020

Annually, Shigella spp. cause ≈188 million cases of diarrheal disease globally, including 500,000 cases in the United States; rates of antimicrobial resistance are increasing. To determine antimicrobial resistance and risk factors in San Diego, California, USA, we retrospectively reviewed cases of diarrheal disease caused by Shigella flexneri and S. sonnei diagnosed during 2017-2020. Of 128 evaluable cases, S. flexneri was slightly more common than S. sonnei; most cases were in persons who were gay or bisexual cisgender men, were living with HIV, were unhoused, or used methamphetamines. Overall, rates of resistance to azithromycin, fluoroquinolones, ampicillin, and trimethoprim/sulfamethoxazole (TMP/SMX) were comparable to the most recent national data reported from the Centers for Disease Control and Prevention; 55% of isolates were resistant to azithromycin, 23% to fluoroquinolones, 70% to ampicillin, and 83% to TMP/SMX. The rates that we found for TMP/SMX were slightly higher than those in national data.

Mechanism of action, resistance, synergism, and clinical implications of azithromycin

Background

Azithromycin (AZM), sold under the name Zithromax, is classified as a macrolide. It has many benefits due to its immunomodulatory, anti‐inflammatory, and antibacterial effects. This review aims to study different clinical and biochemisterial aspects and properties of this drug which has a priority based on literature published worldwide.

Methods

Several databases including Web of Science, Google Scholar, PubMed, and Scopus were searched to obtain the relevant studies.

Results

AZM mechanism of action including the inhibition of bacterial protein synthesis, inhibition of proinflammatory cytokine production, inhibition of neutrophil infestation, and macrophage polarization alteration, gives it the ability to act against a wide range of microorganisms. Resistant organisms are spreading and being developed because of the irrational use of the drug in the case of dose and duration. AZM shows synergistic effects with other drugs against a variety of organisms. This macrolide is considered a valuable antimicrobial agent because of its use as a treatment for a vast range of diseases such as asthma, bronchiolitis, COPD, cystic fibrosis, enteric infections, STIs, and periodontal infections.

Conclusions

Our study shows an increasing global prevalence of AZM resistance. Thus, synergistic combinations are recommended to treat different pathogens. Moreover, continuous monitoring of AZM resistance by registry centers and the development of more rapid diagnostic assays are urgently needed.

Decreased Susceptibility to Azithromycin in Clinical Shigella Isolates Associated with HIV and Sexually Transmitted Bacterial Diseases, Minnesota, USA, 2012-2015

Shigellosis outbreaks caused by Shigella with decreased susceptibility to azithromycin (DSA-Shigella) among men who have sex with men (MSM) have been reported worldwide. We describe sexual health indicators and antimicrobial drug resistance for shigellosis cases in Minnesota, USA. We analyzed a sample of isolates received during 2012-2015 and cross-referenced cases with the Minnesota Department of Health Sexually Transmitted Disease Database to ascertain patients' HIV status and recent chlamydia, gonorrhea, and syphilis infections. Of 691 Shigella isolates, 46 (7%) were DSA-Shigella; 91% of DSA-Shigella patients were men, of whom 60% were living with HIV. Among men, those with DSA-Shigella infection had greater odds of living with HIV, identifying as MSM, or having a recent diagnosis of a sexually transmitted disease. DSA-Shigella was associated with MSM, HIV infection, and recent sexually transmitted disease. To decrease spread of DSA-Shigella, interventions targeted at communities at high risk are needed.

Intranasal Immunization of Mice with Multiepitope Chimeric Vaccine Candidate Based on Conserved Autotransporters SigA, Pic and Sap, Confers Protection against Shigella flexneri

Shigellosis is a diarrheal disease and the World Health Organization prompts the development of a vaccine against Shigella flexneri. The autotransporters SigA, Pic and Sap are conserved among Shigella spp. We previously designed an in silico vaccine with immunodominat epitopes from those autotransporters, and the GroEL protein of S. typhi as an adjuvant. Here, we evaluated the immunogenicity and protective efficacy of the chimeric multiepitope protein, named rMESF, in mice against lethal infection with S. flexneri. rMESF was administered to mice alone through the intranasal (i.n.) route or accompanied with Complete Freund’s adjuvant (CFA) intradermically (i.d.), subcutaneously (s.c.), and intramuscular (i.m.), as well as with Imject alum (i.m.). All immunized mice increased IgG, IgG1, IgG2a, IgA and fecal IgA titers compared to PBS+CFA and PBS+alum control groups. Furthermore, i.n. immunization of mice with rMESF alone presented the highest titers of serum and fecal IgA. Cytokine levels (IFN-γ, TNF-α, IL-4, and IL-17) and lymphocyte proliferation increased in all experimental groups, with the highest lymphoproliferative response in i.n. mice immunized with rMESF alone, which presented 100% protection against S. flexneri. In summary, this vaccine vests protective immunity and highlights the importance of mucosal immunity activation for the elimination of S. flexneri.

Prevalence of Plasmid-Mediated Determinants With Decreased Susceptibility to Azithromycin Among Shigella Isolates in Anhui, China

Objective

The aims of this study were to describe azithromycin (AZM) susceptibility patterns among Shigella isolates in Anhui, China and identify predictors of resistance with mobile element-mediated genes.

Methods

A total of 517 non-duplicate Shigella isolates (449 S. flexneri and 68 S. sonnei) were collected in the Anhui Province of China from September 2011–September 2015, and screened for the plasmid-mediated genes of decreased susceptibility to AZM (DSA), using polymerase chain reaction amplification and sequencing. Conjugation experiments and pulsed-field gel electrophoresis were conducted for all mphA-positive DSA isolates.

Results

The DSA rate for 449 S. flexneri isolates was 33.6%, compared with 39.7% for 68 S. sonnei isolates. Among 161 DSA S. flexneri isolates, 93 (57.8%) carried the mphA gene. Among 27 DSA S. sonnei isolates, 11 (40.7%) carried the mphA gene. However, other plasmid-mediated DSA genes were not found in these isolates. A total of 89 transconjugants (95.7%) were obtained from 93 mphA-positive S. flexneri isolates through conjugation, and 10 transconjugants (90.9%) were obtained from 11 mphA-positive S. sonnei isolates. Furthermore, the minimum inhibitory concentrations (MICs) of AZM among 89 S. flexneri transconjugants ranged from 4 to 128 μg/mL, with an MIC₅₀ of 8 μg/mL and MIC₉₀ of 32 μg/mL. The MICs of AZM among 10 S. sonnei transconjugants ranged from 4 to 256 μg/mL, with an MIC₅₀ of 8 μg/mL and MIC₉₀ of 64 μg/mL. Thirteen clusters were found for mphA-positive S. flexneri, and five clusters were found for mphA-positive S. sonnei. Furthermore, 10 homologous isolates among 13 mphA-positive S. flexneri isolates with high-level DSA were from Sixian county and were multidrug-resistant strains. Of the 10 homologous S. flexneri isolates, eight were from children (≤5 years old), and two from the elderly (>60 years old).

Conclusion

Our study demonstrates that the DSA for Shigella isolates was severe, and the plasmid-mediated mphA gene was the most common macrolide resistance gene detected in Shigella isolates collected in Anhui, China. The mphA-positive S. flexneri isolates with high-level DSA facilitated clonal spread in children and the elderly. This finding is noteworthy and warrants further study.

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.

Evaluation of Shigella Species Azithromycin CLSI Epidemiological Cutoff Values and Macrolide Resistance Genes

Azithromycin (AZM) has been recommended by the American Academy of Pediatrics for the treatment of shigellosis in children. In this study, 502 Shigella species isolated between 2004 and 2014 were tested for AZM epidemiological cutoff values (ECV) by disk diffusion. AZM MICs and the presence of the macrolide resistance genes [erm(A), erm(B), erm(C), ere(A), ere(B), mph(A), mph(B), mph(D), mef(A), and msr(A)] were determined for all 56 (11.1%) isolates with an AZM disk diffusion zone diameter of ≤15 mm. The distribution of AZM ECV MICs was also determined for 186 Shigella isolates with a disk zone diameter of ≥16 mm. Finally, pulsed-field gel electrophoresis (PFGE) was performed on 15 Shigella flexneri isolates with an AZM disk zone diameter of <16 mm from different years and geographic locations. Serotyping the 502 Shigella species isolates revealed that 373 (74%) were S. sonnei, 119 (24%) were S. flexneri, and 10 (2%) were S. boydii Of the 119 Shigella flexneri isolates, 48 (42%) isolates had an AZM disk diffusion zone diameter of ≤15 mm and a MIC of ≥16 µg/ml. With the exception of one isolate, all were positive for the macrolide resistance gene mph(A). S. flexneri PFGE showed four distinct patterns, with patterns I and II presenting with 92.3% genetic similarity. On the other hand, 2 (0.5%) of the 373 S. sonnei isolates had the AZM non-wild-type (NWT) ECV phenotype (those with acquired or mutational resistance), as the AZM MICs were ≥32 µg/ml and the isolates were positive for the mph(A) gene. Overall, our S. flexneri results are in concordance with the CLSI AZM ECV, but isolates with an AZM disk diffusion zone diameter between 14 and 15 mm should be carefully evaluated, as the S. flexneri AZM MIC for NWT isolates may need adjustment to 32 µg/ml. Our data on S. sonnei support that the AZM NWT ECV should be 11 mm for the disk diffusion zone diameter and ≥32 µg/ml for the MICs.

Evaluation of the impact of shigellosis exclusion policies in childcare settings upon detection of a shigellosis outbreak

Background

In the event of a shigellosis outbreak in a childcare setting, exclusion policies are typically applied to afflicted children to limit shigellosis transmission. However, there is scarce evidence of their impact.

Methods

We evaluated five exclusion policies: Children return to childcare after: i) two consecutive laboratory tests (either PCR or culture) do not detect Shigella, ii) a single negative laboratory test (PCR or culture) does not detect Shigella, iii) seven days after beginning antimicrobial treatment, iv) after being symptom-free for 24 h, or v) 14 days after symptom onset. We also included four treatments to assess the policy options: i) immediate, effective treatment; ii) effective treatment after laboratory diagnosis; iii) no treatment; iv) ineffective treatment. Relying on published data, we calculated the likelihood that a child reentering childcare would be infectious, and the number of childcare-days lost per policy.

Results

Requiring two consecutive negative PCR tests yielded a probability of onward transmission of < 1%, with up to 17 childcare-days lost for children receiving effective treatment, and 53 days lost for those receiving ineffective treatment.

Conclusions

Of the policies analyzed, requiring negative PCR testing before returning to childcare was the most effective to reduce the risk of shigellosis transmission, with one PCR test being the most effective for the least childcare-days lost.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-3796-7) contains supplementary material, which is available to authorized users.

A case of multi-drug resistant ESBL-producing Shigella sonnei acute acalculous cholecystitis and gastroenteritis in a returned traveller

The first case of Shigella-associated acalculous cholecystitis is described. A 27-year-old woman presented to hospital with diarrhoea and acute acalculous cholecystitis one day after return to Australia from Vietnam. Her feces culture grew multi-drug resistant ESBL-producing Shigella sonnei and she improved with antimicrobial therapy and intravenous fluids.

In silico analysis to identify vaccine candidates common to multiple serotypes of Shigella and evaluation of their immunogenicity

Shigellosis or bacillary dysentery is an important cause of diarrhea, with the majority of the cases occurring in developing countries. Considering the high disease burden, increasing antibiotic resistance, serotype-specific immunity and the post-infectious sequelae associated with shigellosis, there is a pressing need of an effective vaccine against multiple serotypes of the pathogen. In the present study, we used bio-informatics approach to identify antigens shared among multiple serotypes of Shigella spp. This approach led to the identification of many immunogenic peptides. The five most promising peptides based on MHC binding efficiency were a putative lipoprotein (EL PGI I), a putative heat shock protein (EL PGI II), Spa32 (EL PGI III), IcsB (EL PGI IV) and a hypothetical protein (EL PGI V). These peptides were synthesized and the immunogenicity was evaluated in BALB/c mice by ELISA and cytokine assays. The putative heat shock protein (HSP) and the hypothetical protein elicited good humoral response, whereas putative lipoprotein, Spa32 and IcsB elicited good T-cell response as revealed by increased IFN-γ and TNF-α cytokine levels. The patient sera from confirmed cases of shigellosis were also evaluated for the presence of peptide specific antibodies with significant IgG and IgA antibodies against the HSP and the hypothetical protein, bestowing them as potential future vaccine candidates. The antigens reported in this study are novel and have not been tested as vaccine candidates against Shigella. This study offers time and cost-effective way of identifying unprecedented immunogenic antigens to be used as potential vaccine candidates. Moreover, this approach should easily be extendable to find new potential vaccine candidates for other pathogenic bacteria.

In Vitro Resistance Selection in Shigella flexneri by Azithromycin, Ceftriaxone, Ciprofloxacin, Levofloxacin, and Moxifloxacin

Shigella flexneri continues to be a major cause of diarrhea-associated illness, and increasing resistance to first-line antimicrobials complicates the treatment of infections caused by this pathogen. We investigated the pharmacodynamics of current antimicrobial treatments for shigellosis to determine the likelihood of resistance promotion with continued global antimicrobial use. The mutant prevention concentration (MPC) and mutant selection window (MSW) were determined for azithromycin, ceftriaxone, ciprofloxacin, levofloxacin, and moxifloxacin against a wild-type strain of S. flexneri (ATCC 12022) and an isogenic gyrA mutant (m-12022). Time-kill assays were performed to determine antimicrobial killing. Concentrations of approved doses of ciprofloxacin, levofloxacin, and moxifloxacin are predicted to surpass the MPC for a majority of the dosage interval against ATCC 12022. However, against m-12022, concentrations of all fluoroquinolones are predicted to fall below the MPC and remain in the MSW for a majority of the dosage interval. Concentrations of ceftriaxone fall within the MSW for the majority of the dosage interval for both strains. All agents other than azithromycin displayed bactericidal activity in time-kill assays. Results of pharmacodynamic analyses suggest that all tested fluoroquinolones would achieve a favorable area under the concentration-time curve (AUC)/MPC ratio for ATCC 12022 and would restrict selective enrichment of mutants but that mutant selection in m-12022 would be likely if ciprofloxacin were used. Based on pharmacodynamic analyses, azithromycin and ceftriaxone are predicted to promote mutant selection in both strains. Confirmation of these findings and examination of novel treatment regimens using in vivo studies are warranted.

Decreased Susceptibility to Azithromycin Among Clinical Shigella Isolates from China

The aim of this study was to detect the decreased susceptibility to azithromycin (DSA) and associated mechanisms in Shigella from China. Three hundred and ninety-two Shigella isolates, including 134 Shigella flexneri and 258 Shigella sonnei isolates, were examined for minimum inhibitory concentrations (MICs) and zone sizes to azithromycin by broth microdilution and disk diffusion methods, respectively. The MICs were compared with corresponding zone diameters to find whether there was uniformity between both tests. Twelve macrolide-resistant genes located on mobile elements were determined for the DSA isolates by PCR, and chromosomal efflux pump activity was analyzed using Phe-Arg-β-naphthylamide inhibition test and quantitative real-time PCR. Shigella isolates displayed MICs of 0.125-512 μg/ml and zone sizes of 6-26 mm against azithromycin. There were 80 (20.4%) isolates to be DSA. No significant difference was found between the DSA rates of S. flexneri and S. sonnei isolates (p = 0.052). There was an intimate relativity between MICs and zone diameters (p < 0.001). Only the plasmid-borne mphA conferring high-level DSA was detected in 55.0% (44/80) DSA-Shigella isolates. This study highlighted the prevalence of DSA-Shigella and mphA in the region studied. Clinical laboratories and clinicians should pay attention to the elevated azithromycin MICs in Shigella spp.

Recent Outbreaks of Shigellosis in California Caused by Two Distinct Populations of Shigella sonnei with either Increased Virulence or Fluoroquinolone Resistance

Shigella sonnei has caused unusually large outbreaks of shigellosis in California in 2014 and 2015. Preliminary data indicated the involvement of two distinct bacterial populations, one from San Diego and San Joaquin (SDi/SJo) and one from the San Francisco (SFr) Bay area. Whole-genome analysis and antibiotic susceptibility testing of 68 outbreak and archival isolates of S. sonnei were performed to investigate the microbiological factors related to these outbreaks. Both SDi/SJo and SFr populations, as well as almost all of the archival S. sonnei isolates belonged to sequence type 152 (ST152). Genome-wide single nucleotide polymorphism (SNP) analysis clustered the majority of California (CA) isolates to an earlier described lineage III. Isolates in the SDi/SJo population had a novel lambdoid bacteriophage carrying genes encoding Shiga toxin (STX) that were most closely related to that found in Escherichia coli O104:H4. However, the STX genes (stx1A and stx1B) from this novel phage had sequences most similar to the phages from Shigella flexneri and S. dysenteriae. The isolates in the SFr population were resistant to ciprofloxacin due to point mutations in gyrA and parC genes and were related to the fluoroquinolone-resistant S. sonnei clade within lineage III that originated in South Asia. The emergence of a highly virulent S. sonnei strain and introduction of a fluoroquinolone-resistant strain reflect the changing traits of this pathogen in California. An enhanced monitoring is advocated for early detection of future outbreaks caused by such strains. IMPORTANCE Shigellosis is an acute diarrheal disease causing nearly half a million infections, 6,000 hospitalizations, and 70 deaths annually in the United States. S. sonnei caused two unusually large outbreaks in 2014 and 2015 in California. We used whole-genome sequencing to understand the pathogenic potential of bacteria involved in these outbreaks. Our results suggest the persistence of a local S. sonnei SDi/SJo clone in California since at least 2008. Recently, a derivative of the original clone acquired the ability to produce Shiga toxin (STX) via exchanges of bacteriophages with other bacteria. STX production is connected with more severe disease, including bloody diarrhea. A second population of S. sonnei that caused an outbreak in the San Francisco area was resistant to fluoroquinolones and showed evidence of connection to a fluoroquinolone-resistant lineage from South Asia. These emerging trends in S. sonnei populations in California must be monitored for future risks of the spread of increasingly virulent and resistant clones.

The First Report of a Fully Sequenced Resistance Plasmid from Shigella boydii

The purpose of this study was to characterize mechanisms of plasmid-mediated antimicrobial resistance in Shigella boydii. S. boydii strain 2246 with resistance to ciprofloxacin, ceftriaxone and azithromycin was isolated from a human case of watery diarrhea in a Chinese public hospital. Resistance in strain 2246 to ceftriaxone and azithromycin was attributable to the presence of blaCTX-M-14, and erm(B) and mph(A), respectively, which were co-located on a multidrug-resistant (MDR) plasmid p2246-CTXM. p2246-CTXM represented a novel IncFII-type MDR plasmid with a very complex chimera structure. Its master backbone was genetically closely related to the R100 plasmid, but p2246-CTXM had evolved to integrate additional R100-unrelated backbone regions as well as massive exogenous mobile elements that carried multiple resistance determinants. In p2246-CTXM, erm(B) together with its leading peptide gene erm(C), mph(A) together with its regulatory genes mrx and mphR(A), and blaCTX-M-14 were captured by three different mobile elements Tn6295, the IS26-mph(A)-mrx-mphR(A)-IS6100 unit, and a truncated ISEcp1-blaCTX-M-14-IS903D-iroN transposition unit, respectively, all of which were harbored in a large Tn3-family transposon Tn6285. p2246-CTXM still carried additional resistance determinants mer (mercury resistance), aacA4 (aminoglycoside resistance), cmlA1 (chloramphenicol resistance), and qacED1 (quaternary ammonium compound resistance). This is the first report of identifying a clinical S. boydii strain simultaneously resistant to ciprofloxacin, ceftriaxone, and azithromycin, and determining the complete sequence of a resistance plasmid from S. boydii.

The importance of integrons for development and propagation of resistance in Shigella: the case of Latin America

In Latin America, the disease burden of shigellosis is found to coexist with the rapid and rampant spread of resistance to commonly used antibiotics. The molecular basis of antibiotic resistance lies within genetic elements such as plasmids, transposons, integrons, genomic islands, etc., which are found in the bacterial genome. Integrons are known to acquire, exchange, and express genes within gene cassettes and it is hypothesized that they play a significant role in the transmission of multidrug resistance genes in several Gram-negative bacteria including Shigella. A few studies have described antibiotic resistance genes and integrons among multidrug resistant Shigella isolates found in Latin America. For example, in Brazil, Bolivia, Chile, Costa Rica and Peru, class 1 and class 2 integrons have been detected among multidrug resistant strains of Shigella; this phenomenon is more frequently observed in S. flexneri isolates that are resistant to trimethoprim, sulfamethoxazole, streptomycin, ampicillin, chloramphenicol, and tetracycline. The gene cassette sul2, which is frequently detected in Shigella strains resistant to the sulfonamides, suggests that the sulfonamide-resistant phenotype can be explained by the presence of the sul2 genes independent of the integron class detected. It is to be noted that sul3 was negative in all isolates analyzed in these studies. The high frequency of sulfonamide (as encoded by sul2) and trimethoprim resistance is likely to be a result of the recurrent use of trimethoprim sulfamethoxazole as a popular regimen for the treatment of shigellosis. The observed resistance profiles of Shigella strains confirm that ampicillin and trimethoprim-sulfamethoxazole are ineffective as therapeutic options. In-depth information regarding antibiotic resistance mechanism in this pathogen is needed in order to develop suitable intervention strategies. There is a pressing need for regional and local antimicrobial resistance profiling of Shigella to be included as a part of the public health strategy.

ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults

Acute diarrheal infections are a common health problem globally and among both individuals in the United States and traveling to developing world countries. Multiple modalities including antibiotic and non-antibiotic therapies have been used to address these common infections. Information on treatment, prevention, diagnostics, and the consequences of acute diarrhea infection has emerged and helps to inform clinical management. In this ACG Clinical Guideline, the authors present an evidence-based approach to diagnosis, prevention, and treatment of acute diarrhea infection in both US-based and travel settings.

The Many Faces of IpaB

The type III secretion system (T3SS) is Shigella's most important virulence factor. The T3SS apparatus (T3SA) is comprised of an envelope-spanning basal body and an external needle topped by a tip complex protein called IpaD. This nanomachine is used to deliver effector proteins into host cells to promote pathogen entry. A key component of the matured T3SS needle tip complex is the translocator protein IpaB. IpaB can exist in multiple states when prepared as a recombinant protein, however, it has also been described as having additional roles in Shigella pathogenesis. This mini-review will briefly describe some of the features of IpaB as a T3SS needle tip protein, as a pore-forming translocator protein and as an effector protein. Reflection on the potential importance of the different in vitro states of IpaB on its function and importance in serotype-independent vaccines is also provided.

Triple-targeting Gram-negative selective antimicrobial peptides capable of disrupting the cell membrane and lipid A biosynthesis

A potent Gram-negative selective triple-targeting antimicrobial peptide was developed that attacks the membrane and inhibits two enzymes involved in early lipid A biosynthesis.

Shigellosis in Subjects with Traveler's Diarrhea Versus Domestically Acquired Diarrhea: Implications for Antimicrobial Therapy and Human Immunodeficiency Virus Surveillance

An increase of sexually transmitted shigellosis is currently being reported in developed countries. In addition, travel-related shigellosis can introduce resistant strains that could be disseminated within this new scenario. Epidemiological features and antimicrobial susceptibility of shigellosis depending on where infection was acquired were investigated. From 2008 to 2013, subjects with shigellosis were studied. Patients were classified according to acquisition of Shigella as traveler's diarrhea (TD) or domestically acquired diarrhea (DAD). Ninety cases of shigellosis were identified: 76 corresponding to the TD group and 14 to the DAD group. In the DAD group, most of patients were human immunodeficiency virus (HIV)-positive men who have sex with men (MSM), being shigellosis associated to male sex (P = 0.007) and HIV infection (P < 0.0001). S. sonnei (47.8%) and S. flexneri (42.2%) were the predominant species. The highest resistance was detected for trimethoprim/sulfamethoxazole (SXT) (81.8%), followed by ampicillin (AMP) (37.8%) and ciprofloxacin (CIP) (23.3%). Resistant Shigella strains were more frequent in subjects with TD than those with DAD, although only for CIP the difference was significant (P = 0.034). Continuous monitoring of patients with shigellosis is necessary to control the spread of resistant Shigella strains and for effective therapy. Men with shigellosis who have not traveled to an endemic area should be screened for HIV infection.

Shigellosis Outbreak in Al Batinah South Governorate, Oman: Case-control study

OBJECTIVES

An outbreak of acute gastroenteritis due to Shigella flexneri occurred in August 2012 in the catchment area of the Wadi Sahtan Health Center in Rustaq, Al Batinah South Governorate, Oman. The aim of this study was to discover possible causes of this outbreak in the villages of Fassa, Rogh and Amk and to measure the risk of exposure among cases and controls.

METHODS

A case-control study was conducted in September 2012 in Fassa, Rogh and Amk. All households in the three villages were interviewed. Case and control households were compared to determine possible exposure avenues, including place of residence, source of drinking water, hand hygiene levels and practices related to drinking water, food preparation and environmental sanitation.

RESULTS

Residing in Fassa (P <0.0001; odds ratio [OR] = 4.86, 95% confidence interval [CI] = 2.22-10.63) and average hand hygiene practices (P = 0.008; OR = 13.97, 95% CI = 1.58-123.36) were associated with an increased risk of contracting shigellosis. No significant differences were found with regards to the other exposure avenues.

CONCLUSION

This was the first study conducted in Oman regarding an outbreak of shigellosis in a community setting. The only variables that significantly impacted the risk of acute gastroenteritis were residing in Fassa and average hand hygiene practices. The source of the outbreak could not be identified. However, septic tank sanitation and water and food consumption practices were not satisfactory in the studied villages. These need to be addressed to prevent similar outbreaks of acute gastroenteritis in this region in the future.

Enteropathogens and antibiotics

Infectious gastroenteritis remains a public health problem. The most severe cases are of bacterial origin. In Spain, Campylobacter and Salmonella are the most prevalent bacterial genus, while Yersinia and Shigella are much less frequent. Most cases are usually self-limiting and antibiotic therapy is not generally indicated, unless patients have risk factors for severe infection and shigellosis. Ciprofloxacin, third generation cephalosporins, azithromycin, ampicillin, cotrimoxazole and doxycycline are the most recommended drugs. The susceptibility pattern of the different bacteria determines the choice of the most appropriate treatment. The aim of this review is to analyse the current situation, developments, and evolution of resistance and multidrug resistance in these 4 enteric pathogens.

Diarrhoea and smoking: an analysis of decades of observational data from Bangladesh

BACKGROUND

Although cigarette smoking affects all biological systems of the human body including the gastrointestinal tract, there is a lack of evidence regarding its effect on the severity of diarrhoeal disease and whether a dose-response relationship exists. We therefore tested for the presence of specific causative pathogens for infectious diarrhoea, assessed the independent effect of smoking on its severity and tested whether any dose-response relationship existed while controlling for subjects' age, sociodemographic characteristics and presence of causative pathogens in an urban setting in Bangladesh.

METHODS

A total of 20,757 patients aged 15 years and above with diarrhoea were enrolled into the Diarrhoeal Disease Surveillance System, managed by the International Centre for Diarrhoeal Disease Research, Bangladesh, from 1993 to 2012. We collected data on individuals' current daily consumption of cigarettes and bidis (traditional hand-rolled cigarettes) and conducted an ordered logistic regression to determine the effect of smoking on diarrhoeal disease severity and whether a dose-response relationship exists.

RESULTS

We identified 19 % of patients with diarrhoea as smokers, of whom 52 % smoked 1-9 cigarettes per day. While 97 % of smokers were male, 41 % were aged 15-30 years of age. Smokers were found to have a significantly lower severity of diarrhoeal disease (OR: 0.92, 95 % CI: 0.85-0.99, p = 0.025) after adjusting for age, wealth quintile, illiteracy and the presence of specific causative pathogens (Vibrio cholerae and Shigella). We observed no dose-response relationship between the number of cigarettes smoked per day and disease severity when adjusting for the same covariates. Smokers were more frequently infected with Shigella (7 vs. 6 %, p < 0.001) and less often with Vibrio cholerae (22 vs. 26 %, p < 0.001) than their non-smoking counterparts.

CONCLUSIONS

The aetiology and severity of diarrhoeal disease differed between smokers and non-smokers in our sample. However, we found no dose-response relationship between disease severity and the number of cigarettes smoked per day.

Virulence factors and mechanisms of antimicrobial resistance in Shigella strains from periurban areas of Lima (Peru)

The study was aimed to describe the serotype, mechanisms of antimicrobial resistance, and virulence determinants in Shigella spp. isolated from Peruvian children. Eighty three Shigella spp. were serogrouped and serotyped being established the antibiotic susceptibility. The presence of 12 virulence factors (VF) and integrase 1 and 2, along with commonly found antibiotic resistance genes was established by PCR. S. flexneri was the most relevant serogroup (55 isolates, 66%), with serotype 2a most frequently detected (27 of 55, 49%), followed by S. boydii and S. sonnei at 12 isolates each (14%) and S. dysenteriae (four isolates, 5%). Fifty isolates (60%) were multi-drug resistant (MDR) including 100% of S. sonnei and 64% of S. flexneri. Resistance levels were high to trimethoprim-sulfamethoxazole (86%), tetracycline (74%), ampicillin (67%), and chloramphenicol (65%). Six isolates showed decreased azithromycin susceptibility. No isolate was resistant to nalidixic acid, ciprofloxacin, nitrofurantoin, or ceftriaxone. The most frequent resistance genes were sul2 (95%), tet(B) (92%), cat (80%), dfrA1 (47%), blaOXA-1like (40%), with intl1 and intl2 detected in 51 and 52% of the isolates, respectively. Thirty-one different VF profiles were observed, being the ipaH (100%), sen (77%), virA and icsA (75%) genes the most frequently found. Differences in the prevalence of VF were observed between species with S. flexneri isolates, particularly serotype 2a, possessing high numbers of VF. In conclusion, this study highlights the high heterogeneity of Shigella VF and resistance genes, and prevalence of MDR organisms within this geographic region.

Antimicrobial susceptibility testing of bacteria that cause gastroenteritis

Gastroenteritis due to enteric pathogens is generally a self-limiting disease for which antimicrobial treatment is not required. However, treatment should be considered for cases of severe or prolonged diarrhea, extraintestinal isolation of bacteria, or diarrhea in immunocompromised hosts, the elderly, and infants. Various resistance trends and current issues concerning antimicrobial susceptibility testing of enteric pathogens are reviewed in this article, including Campylobacter, Salmonella, Shigella, Vibrio, Aeromonas, Plesiomonas, and Clostridium difficile. Updated interpretive criteria from breakpoint-setting organizations are reviewed, along with explanations for recent changes in antimicrobial breakpoints.

Shigella spp. with reduced azithromycin susceptibility, Quebec, Canada, 2012-2013

During 2012-2013 in Montreal, Canada, 4 locally acquired Shigella spp. pulse types with the mph(A) gene and reduced susceptibility to azithromycin were identified from 9 men who have sex with men, 7 of whom were HIV infected. Counseling about prevention of enteric sexually transmitted infections might help slow transmission of these organisms.

Microbial sequencing analyses suggest the presence of a fecal veneer on indoor climbing wall holds

Artificial climbing walls represent a unique indoor environment in which humans interact closely with a variety of surface types. Climbing wall holds may mediate transmission of organisms between individuals, and yet there are no studies that identify microorganisms present on these surfaces. In the current study, the microorganisms found on climbing wall holds were characterized by analysis of amplified SSU rRNA gene sequences. In contrast to many other studies of built environments, the majority of microorganisms on holds were most closely related to microbes annotated as being recovered from environmental sources, such as soil, with human skin also representing an important source. Regional patterns were evident as rRNA gene sequences from the marine cyanobacterium Prochlorococcus were abundant in gyms found within 16 km of the ocean. Enterobacteriaceae were present on 100 % of holds surveyed, and the members detected are commonly associated with fecal matter.

Notes from the field: Shigella with decreased susceptibility to azithromycin among men who have sex with men - United States, 2002-2013

Bacteria of the genus Shigella cause approximately 500,000 illnesses each year in the United States. Diarrhea (sometimes bloody), fever, and stomach cramps typically start 1-2 days after exposure and usually resolve in 5-7 days. For patients with severe disease, bloody diarrhea, or compromised immune systems, antibiotic treatment is recommended, but resistance to traditional first-line antibiotics (e.g., ampicillin and trimethoprim-sulfamethoxazole) is common. For multidrugresistant cases, azithromycin, the most frequently prescribed antibiotic in the United States, is recommended for both children and adults. However, not all Shigellae are susceptible to azithromycin. Nonsusceptible isolates exist but are not usually identified because there are no clinical laboratory guidelines for azithromycin susceptibility testing. However, to monitor susceptibility of Shigellae in the United States, CDC's National Antimicrobial Resistance Monitoring System (NARMS) has, since 2011, routinely measured the azithromycin minimum inhibitory concentration (MIC) for every 20th Shigella isolate submitted from public health laboratories to CDC, as well as outbreak-associated isolates. All known U.S. Shigella isolates with decreased susceptibility to azithromycin (DSA-Shigella), and the illnesses caused by them, are described in this report.

Emerging infectious colitis

PURPOSE OF REVIEW

The present review will highlight recent advances in the knowledge of emerging pathogens causing infectious colitis and provide a description of the most important food-borne outbreaks.

RECENT FINDINGS

Outbreaks of enteric disease caused by Salmonella spp., Campylobacter spp., and Shiga toxin-producing Escherichia coli (STEC) continue to surprise with new epidemiological findings or changing virulence characteristics. These pathogens evolve to exploit novel opportunities for spread and transmission, such as fresh produce within the food chain, and generate new public health challenges. Organic sprouts were recently considered as the source responsible for a large German disease outbreak comprising 3842 patients. The outbreak strain was identified as an enteroaggregative STEC O104:H4 (EAggC), a rare hybrid pathogen that harbours the phage encoded Shiga toxin gene and antibiotic resistance in an EAggEC background. Clostridium difficile PCR ribotype 078 is emerging across Europe, causing severe disease outside healthcare facilities as well as disease in farm animals, indicating that the species border has been crossed. Although the global impact of cryptosporidiosis is less pronounced, these organisms have been responsible for large outbreaks of infectious diarrhoea, often not reported. Invasive listeriosis is a serious food-borne illness and was found recently in 28 US states affecting 147 patients, associated with eating contaminated cantaloupe. Outbreaks of gastroenteritis caused by Listeria monocytogenes are most likely severely underestimated. Centralized surveillance of food-borne enteropathogens is essential for the early detection of disease outbreaks and for the organization of an immediate and appropriate response.

SUMMARY

An improved understanding of the pathogenesis, pathology and epidemiology of emerging enteropathogens causing infectious colitis will provide new approaches for disease prevention and control.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Notes from the field: Outbreak of infections caused by Shigella sonnei with decreased susceptibility to azithromycin--Los Angeles, California, 2012

In May 2012, the Los Angeles County Department of Public Health's Acute Communicable Disease Control Unit and Environmental Health, Food, and Milk Program investigated an outbreak of shigellosis associated with a private bridge club. This investigation documented the first known transmission of Shigella sonnei with decreased susceptibility to azithromycin in the United States.