Characterization of the first extended-spectrum beta-lactamase-producing nontyphoidal Salmonella strains isolated in Tehran, Iran

Deciphering the genetic network and programmed regulation of antimicrobial resistance in bacterial pathogens

Antimicrobial resistance (AMR) in bacteria is an important global health problem affecting humans, animals, and the environment. AMR is considered as one of the major components in the "global one health". Misuse/overuse of antibiotics in any one of the segments can impact the integrity of the others. In the presence of antibiotic selective pressure, bacteria tend to develop several defense mechanisms, which include structural changes of the bacterial outer membrane, enzymatic processes, gene upregulation, mutations, adaptive resistance, and biofilm formation. Several components of mobile genetic elements (MGEs) play an important role in the dissemination of AMR. Each one of these components has a specific function that lasts long, irrespective of any antibiotic pressure. Integrative and conjugative elements (ICEs), insertion sequence elements (ISs), and transposons carry the antimicrobial resistance genes (ARGs) on different genetic backbones. Successful transfer of ARGs depends on the class of plasmids, regulons, ISs proximity, and type of recombination systems. Additionally, phage-bacterial networks play a major role in the transmission of ARGs, especially in bacteria from the environment and foods of animal origin. Several other functional attributes of bacteria also get successfully modified to acquire ARGs. These include efflux pumps, toxin-antitoxin systems, regulatory small RNAs, guanosine pentaphosphate signaling, quorum sensing, two-component system, and clustered regularly interspaced short palindromic repeats (CRISPR) systems. The metabolic and virulence state of bacteria is also associated with a range of genetic and phenotypic resistance mechanisms. In spite of the availability of a considerable information on AMR, the network associations between selection pressures and several of the components mentioned above are poorly understood. Understanding how a pathogen resists and regulates the ARGs in response to antimicrobials can help in controlling the development of resistance. Here, we provide an overview of the importance of genetic network and regulation of AMR in bacterial pathogens.

Structural Comparisons of Cefotaximase (CTX-M-ase) Sub Family 1

The cefotaximase or CTX-M, family of serine-β-lactamases represents a significant clinical concern due to the ability for these enzymes to confer resistance to a broad array of β-lactam antibiotics an inhibitors. This behavior lends CTX-M-ases to be classified as extended spectrum β-lactamases (ESBL). Across the family of CTX-M-ases most closely related to CTX-M-1, the structures of CTX-M-15 with a library of different ligands have been solved and serve as the basis of comparison within this review. Herein we focus on the structural changes apparent in structures of CTX-M-15 in complex with diazabicyclooctane (DABCO) and boronic acid transition state analog inhibitors. Interactions between a positive surface patch near the active site and complementary functional groups of the bound inhibitor play key roles in the dictating the conformations of active site residues. The insights provided by analyzing structures of CTX-M-15 in complex with DABCO and boronic acid transition state analog inhibitors and analyzing existing structures of CTX-M-64 offer opportunities to move closer to making predictions as to how CTX-M-ases may interact with potential drug candidates, setting the stage for the further development of new antibiotics and β-lactamase inhibitors.

Prevalence of Extended-Spectrum β-Lactamase-Producing Enterobacteriaceae in Ethiopia: A Systematic Review and Meta-Analysis

Background

Antimicrobial resistance especially caused by extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-PE) has become a global public health concern. Globally, these isolates have remained the most important causes of several infections and associated mortality. Their rapid spread in Ethiopia is associated with a lack of regular surveillance and antibiotic stewardship programs. Isolates of ESBL-PE from different regions of Ethiopia were searched exhaustively. However, published data regarding the pooled estimate of ESBL-PE are not conducted in Ethiopia. For this reason, we systematically reviewed laboratory-based studies to summarize the overall pooled prevalence of the isolates recovered from various human specimens.

Methods

An exhaustive literature search was carried out using the major electronic databases including PubMed, Web of Science, MEDLINE, EMBASE, CINAHL, Google Scholar, Cochrane Library, Scopus, and Wiley Online Library to identify potentially relevant studies without date restriction. Original articles which address the research question were identified, screened, and included using the PRISMA follow diagram. Data extraction form was prepared in Microsoft Excel, and data quality was assessed by using 9-point Joanna Briggs Institute critical appraisal tools. Then, data were exported to STATA 16.0 software for analyses of pooled estimation of outcome measures. Estimation of outcome measures at 95% confidence interval was performed using Der-Simonian-Laird's random-effects model. Finally, results were presented via text, figures, and tables.

Results

A comprehensive electronic database literature search has yielded a total of 86 articles. Among the total, 68 original articles were excluded after the review process. A total of 18 studies with 1191 bacterial isolates recovered from 7919 various clinical samples sizes were included for systematic review and meta-analysis. In this study, the pooled prevalence of ESBL-PE was 18% (95% CI: 9–26). Nine out of the total (50%) reviewed articles were studied using the combination disk test. Likewise, E. coli and K. pneumoniae (50% both) were the predominant isolates of ESBL-PE in addition to other isolates such as Salmonella spp. and Shigella spp.

Conclusion

This meta-analysis has shown a low pooled estimate of ESBL-PE in Ethiopia.

Geographical distribution of Typhoid using Geographic Information System (GIS) during 2009-2014 in Iran

Background: Salmonella induced infections remain one of the most important health problems worldwide. The purpose of this study is to investigate the incidence and geographical distribution of typhoid using GIS and to predict its incidence in Iran in 2021.

Methods: This study is a descriptive analytical study. Information on pertussis was obtained from the Center for Communicable Diseases Control during 2009-2015. In the next step, ArcGIS 9.3 was used to prepare geographic maps of the disease incidence and frequency Therefore, using the Raster Calculator tool, the disease prediction map was drawn.

Results: The results showed that the highest incidence of typhoid during 2009-2014 was in Kermanshah, Lorestan, Hamadan, Kurdistan, and Ilam provinces. The incidence of typhoid in Iran increased during 2009-2010. The annual incidence of typhoid decreased from 0.85 per 100,000 in 2010 to 0.5 in 2014. Based on the modeling results for Iran, Kermanshah, Lorestan, Kurdistan, Ilam and Hamadan provinces with 92.17%, 46.56%, 31.74%, 25.62% and 22.96% of their areas (Km2) are at high risk for typhoid in the coming years, respectively.

Conclusion: Considering that the provinces of Kermanshah, Lorestan, Kurdistan, Ilam, and Hamadan are at risk of typhoid incidence in the coming years in Iran, and given that salmonella infections have a direct relationship with the individual’s health status and individual’s environmental health and socioeconomic status, improving the health status and disease control in carriers as well as improving the socio-economic status of the population living in these areas can prevent the disease in the years to come.

Extended spectrum beta-lactamase and fluoroquinolone resistance genes among Escherichia coli and Salmonella isolates from children with diarrhea, Burkina Faso

BACKGROUND

The emergence and spread of multidrug-resistant gram-negative bacteria (MDR) has become a major public health concern worldwide. This resistance is caused by enzymes-mediated genes (i.e., extended spectrum beta-lactamases) that are common in certain Enterobacterioceae species. However, the distribution of these genes is poorly documented in Burkina Faso. This study aims to determine the prevalence and distribution of the resistant genes coding for broad spectrum beta-lactamases and quinolones in rural Burkina Faso.

METHODS

Multiplex PCR assays were carried out to detect ESBL-encoding genes, including bla_OXA, bla_TEM, bla_CTX-M, bla_SHV. The assays also assessed the presence of quinolone resistance gene namely qnrA, qnrB and qnrS in the quinolone-resistance DEC and Salmonella strains.

RESULTS

The Extended-Spectrum Beta-Lactamases (ESBL) resistance phenotype was reported in all the E. coli isolates (5/5). Cross-resistance phenotype to quinolones (CRQ) was shown by one Salmonella strain (1/9) and three E. coli (3/5). Cross-resistance phenotypes to fluoroquinolones (CRFQ) were harboured by one Salmonella (1/9) and carbapenemase phenotypes were detected in two E. coli strains (2/5). Whilst the bla_OXA genes were detected in 100% (5/5) of E. coli isolates and in 33.33% (3/9) Salmonella isolates. One strain of E. coli (1/5) harbored the bla_CTX-M gene and the qnrB gene simultaneously.

CONCLUSIONS

This study identified β-lactam (bla) and quinolone resistance (qnr) genes in multidrug-resistant E. coli and Salmonella spp. in rural Burkina Faso. Our finding which highlighted the enterobacteriaceae strains resistance to β-lactams and quinolones are of high interest for adequate management of antimicrobial resistant genes outbreak in Burkina Faso.

The Frequency of Antibiotic Resistance and ESBLs Among Clinically Acinetobacter baumannii Strains Isolated from Patients in a Major Hospital in Tehran, Iran

Background:

Bacterial resistance to antibiotics limits treatment options, increases morbidity and mortality, and raises the risk of antibiotic-associated adverse events. Antibacterial resistance emerges rapidly following an increase in the consumption of antibiotics against infectious diseases. The spread of ESBL producing strains has a limiting factor based on antibiotic function for the treatment of infections particularly caused by Acinetobacter baumannii (A. baumannii).

Objective:

This study was conducted to evaluate the prevalence of antimicrobial resistance and distribution of bla_TEM, bla_CTX, and bla_SHV genes among A. baumannii strains isolated from clinical samples at a major hospital in Teheran, Iran.

Methods:

A. baumannii strains were isolated and identified using standard microbiological methods. The disc diffusion and combined discs methods were used for testing antimicrobial susceptibility and to identify the strains producing Extended-Spectrum Beta-Lactamases (ESBL), respectively. DNA extraction was done by boiling method. Finally, the frequency of resistant genes including bla_TEM, bla_CTX, and bla_SHV in ESBL producing isolates was studied by PCR.

Results:

Gender distribution in this study was 53 (53%) samples for men and 47 (47%) for women. Totally, one hundred A. baumannii strains were isolated. More than 93% of the isolates were multi drug resistant. The highest to lowest antibiotic resistance was observed against amoxicillin/clavulanic acid (98%), ceftriaxone (96%), cefotaxime (94%), and ceftazidime (93%), respectively. The frequency of positive phenotypic test of ESBL was 19% and 16% for CAZ-C and CTX-C, respectively. The frequency of bla_TEM, bla_CTX, and bla_SHV genes was 52.1, 43.4, and 21.7, respectively.

Conclusion:

A. baumannii isolates exhibited an extremely worrying level of antibiotic resistance, and a high percentage of the isolates showed MDR in this study. This is a serious warning because ESBLs are a major threat to the effectiveness of antibiotics that are currently available for medical uses. The frequency of genes encoded ESBL isolates of A. baumannii may be due to overuse and misuse of antibiotics.

Genetic Investigation of Beta-Lactam Associated Antibiotic Resistance Among Escherichia Coli Strains Isolated from Water Sources

Background:

Antimicrobial resistance is an important factor threatening human health. It is widely accepted that antibiotic resistant bacteria such as Escherichia coli (E. coli) released from humans and animals into the water sources, can introduce their resistance genes into the natural bacterial community.

Objective:

The aim of this study was to investigate the prevalence of bla_TEM, bla_CTX, bla_SHV, bla_OXA and bla_VEB associated-antibiotic resistance among E. coli bacteria isolated from different water resources in Iran.

Methods:

The study contained all E. coli strains segregated from different surface water sources. The Kirby-Bauer method and combined discs method was determined in this study for testing antimicrobial susceptibility and strains that produced Extended-Spectrum Beta Lactamases (ESBL), respectively. DNA extraction kit was applied for genomic and plasmid DNA derivation. Finally the frequency of resistant genes including bla_TEM, bla_CTX, bla_SHV, bla_OXA and bla_VEB in ESBL producing isolates were studied by PCR.

Results:

One hundred E. coli strains were isolated and entered in the study. The highest antibiotic resistance was observed on clindamycin (96%). Moreover, 38.5% isolates were ESBL producers. The frequency of different ESBLs genes were 37%, 27%, 27%, and 25% for bla_TEM, bla_CTX, bla_SHV, and bla_OXA, respectively. The bla_VEB wasn’t found in any isolates.

Conclusion:

The study revealed a high prevalence of CTX-M, TEM, SHV and OXA genes among E. coli strains in surface water resources. In conclusion, these results raised a concern regarding the presence and distribution of these threatening factors in surface water sources and its subsequent outcomes.

The Molecular Study of Antibiotic Resistance to Quinolones in Salmonella enterica Strains Isolated in Tehran, Iran

Introduction:

Salmonella is known as one of the most important causes of gastrointestinal disease in the world. Quinolones and fluoroquinolones are used successfully in the treatment of salmonellosis particularly for infections that have become resistant to several antibiotics. But non-susceptible isolates to quinolones have been reported in several countries. The data are limited about the prevalence of quinolone-resistant isolates in our country. Therefore, this study investigated the plasmid-mediated quinolone resistance genes in Salmonella enterica isolated in Children's Medical Center in Tehran during 2014-2015.

Methods and Materials:

Salmonella isolates were isolated and identified using standard microbiological methods. Antibiotic susceptibility testing and screening of Salmonella strains resistant to quinolones were performed according to the CLSI guidelines. The molecular investigation was done using specific primers for detection of qnr genes including: qnrA, qnrB and qnrS, by polymerase chain reaction.

Results:

Overall, 92 (66.6%) strains were resistant to nalidixic acid. None of the strains showed resistance to ciprofloxacin. Out of the 92 nalidixic acid resistant strains, 52 (56.52%) harbored qnrS genes, 15 strains (16.30%) had both qnrA and qnrS genes. Two (1.1%) isolates were positive for qnrB gene. Twenty four (26.08%) nalidixic acid resistant isolates did not have any qnr qens.

Conclusion:

The results of this study show high prevalence of resistance to nalidixic and qnr genes in Salmonella isolates. Plasmid nature of this type of resistance poses an increased risk of dissemination of quinolone resistance between Salmonella and non-Salmonella isolates circulating in hospitals environments.

Multilocus Sequence Typing of the Clinical Isolates of Salmonella Enterica Serovar Typhimurium in Tehran Hospitals

BACKGROUND

Salmonella enterica serovar Typhimurium is one of the most important serovars of Salmonella enterica and is associated with human salmonellosis worldwide. Many epidemiological studies have focused on the characteristics of Salmonella Typhimurium in many countries as well as in Asia. This study was conducted to investigate the genetic characteristics of Salmonella Typhimurium using multilocus sequence typing (MLST).

METHODS

Clinical samples (urine, blood, and stool) were collected from patients, who were admitted to 2 hospitals in Tehran between April and September, 2015. Salmonella Typhimurium strains were identified by conventional standard biochemical and serological testing. The antibiotic susceptibility patterns of the Salmonella Typhimurium isolates against 16 antibiotics was determined using the disk diffusion assay. The clonal relationship between the strains of Salmonella Typhimurium was analyzed using MLST.

RESULTS

Among the 68 Salmonella isolates, 31% (n=21) were Salmonella Typhimurium. Of the total 21 Salmonella Typhimurium isolates, 76% (n=16) were multidrug-resistant and showed resistance to 3 or more antibiotic families. The Salmonella Typhimurium isolates were assigned to 2 sequence types: ST19 and ST328. ST19 was more common (86%). Both sequence types were further assigned to 1 eBURST group.

CONCLUSION

This is the first study of its kind in Iran to determine the sequence types of the clinical isolates of Salmonella Typhimurium in Tehran hospitals using MLST. ST19 was detected as the major sequence type of Salmonella Typhimurium.

Evaluation of Antioxidant Activity and Growth Control Properties of Nonoscale Structure Produced from Aloe vera var. littoralis Extract on Clinical Isolates of Salmonella

The aim of the study was to examine antibacterial properties of microemulsion structure produced from Aloe vera var. littoralis extract as a new tool of nanoscale drug-like materials. Aloe vera var. littoralis (A. littoralis) extract was prepared by distillation method. A nonocarrier structure in the microemulsion system was prepared from the extract. Serial concentrations were prepared from 8 mg/mL extract and the nonocarrier containing 0.1 mg/mL pure extract and were evaluated by a disk diffusion method for 35 Salmonella clinical isolates. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by microbroth dilution assay using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method by an enzyme-linked immunosorbent assay(ELISA) Microplate Reader apparatus. Antioxidant activity of the extract was determined by measuring the ferric reducing ability of plasma (FRAP) assay. From 35 clinical isolates of Salmonella, 17 isolates-including resistant isolates of S.E.1103 and S.E.49-had a zone of inhibition (ZI) of 7 to 32 mm in 0.007 mg/mL of the extract. S.E.76 isolate exposed to 30 µg/mL ceftazidime disk had a ZI of 12 mm but had 10 mm in 7µg/mL of A. littoralis extract. The inhibitory effect of a nanocarrier at a concentration of 25 µg/mL by 20 mm ZI was comparable by the ceftazidime (30 µg/mL) effect. MIC50 was 0.25 mg/mL and MBC50 was 0.5 mg/mL by MTT method for the extract. It was shown that A.littoralis extract had antioxidant activity of 31.67 µM/mg that could be increased based on concentration. It was concluded that the nanocarrier had a significant effect on the studied isolates in comparison with ordinary antibiotics and had potential for use as a natural antioxidant and antimicrobial material in complementary medicine.

The Prevalence of CTX-M-15 Extended-spectrum β-Lactamases Among Salmonella spp. and Shigella spp. Isolated from three Iranian Hospitals

Bacterial antimicrobial resistance mediated by the production of extended-spectrum β-lactamases (ESBLs) is considered a major threat for treatment of Salmonella and Shigella infections. This study aimed to investigate antibiotic resistance patterns of Salmonella and Shigella spp. and presence of CTX-M from three teaching hospitals in Iran. In the present study, 58 clinical Shigella and 91 Salmonella isolates were recovered between 2009 and 2013 from 3 teaching hospitals in Iran. After culture and antimicrobial susceptibility testing, ESBL-positive isolates were subjected to further investigations. These included polymerase chain reaction (PCR) amplification and DNA sequencing of bla_CTX-M-15 encoding plasmid. In both genera, high sensitivity to gentamicin and amikacin, but high resistance to ampicillin, tetracycline, and trimethoprim-sulfamethoxazole, was found. Molecular investigation showed that 31.8% isolates of Salmonella spp. and 34.48% isolates of Shigella spp. were CTX-M positive and all of them were also positive for ISEcpI. Protein translation, comparing with reference sequences, showed that all CTX-M isolates belong to CTX-M-15. The present study suggests that the resistance of ESBLs-producing Salmonella and Shigella spp. in Iran hospitals is very serious. Therefore, strategies to minimize the spread of ESBL-producing isolates should be implemented.

Multiple-locus variable-number tandem repeat analysis (MLVA) for genotyping of Salmonella enterica subspecies enterica serotype Infantis isolated from human sources

Salmonella is an important cause of food-borne infection worldwide. Detection of outbreaks caused by Salmonella spp. relies on suitable and robust methods for genotyping. Little is known about the genetic diversity of the Salmonella enterica subspecies enterica serotype Infantis strains isolated from human sources in Iran. In this study, 40 isolates of S. Infantis, which were previously recovered from patients with gastroenteritis or diarrhea in Tehran between years 2007 and 2009, were subjected to multiple-locus variable-number of tandem repeat (VNTR) analysis (MLVA), pulsed-field gel electrophoresis (PFGE), and ERIC-PCR. Using MLVA method, 31 types were identified. The MLVA clustering of the isolates by the unweighted pair group method with arithmetic mean (UPGMA) revealed the presence of two major clusters. The discriminatory power of MLVA was superior to that of PFGE and ERIC-PCR. Overall, our data showed that MLVA assay could effectively differentiate closely related strains. It is technically simple and inexpensive to perform. Furthermore, MLVA can be used as a helpful method for epidemiological investigations.

Molecular characterization of Salmonella enterica serotype Enteritidis isolates from food and human samples by serotyping, antimicrobial resistance, plasmid profiling, (GTG)5-PCR and ERIC-PCR

In recent years, Salmonella enterica serovar Enteritidis has been a primary cause of human salmonellosis in many countries. The major objective of this study was to investigate genetic diversity among Salmonella Enteritidis strains from different origins (food and human) by Enterobacterial Repetitive Intergenic Consensus (ERIC) -PCR, as well as to assess their plasmid profiling and antimicrobial resistance. A total of 30 Salmonella Enteritidis isolates, 15 from food samples (chicken, lamb, beef and duck meats) and 15 from clinical samples were collected in Tehran. Identification of isolates as Salmonella was confirmed by using conventional standard biochemical and serological tests. Multiplex-PCR was used for serotyping of isolates to identify Salmonella Enteritidis. Antimicrobial susceptibility testing to 16 agents founds drug resistance patterns among Salmonella Enteritidis isolates. No resistance was observed to cephalexin, ceftriaxone, ceftazidime and cefotaxime, ciprofloxacin, imipenem or meropenem, chloramphenicol and gentamicin. The highest resistance (96.7%) was observed to nitrofurantoin. Seven plasmid profiles (P1-P7) were detected, and a 68-kb plasmid was found in all isolates. Two different primers; ERIC and (GTG)5 were used for genotyping, which each produced four profiles. The majority of clinical and food isolates fell into two separate common types (CTs) with a similar percentage of 95% by ERIC-PCR. Using primer (GTG)5, 29 isolates incorporated in three CTs with 70% of isolates showing a single banding pattern. Limited genetic diversity among human and food isolates of Salmonella Enteritidis may indicate that contaminated foods were possibly the source of human salmonellosis. These results confirmed that ERIC-PCR genotyping has limited discriminatory power for Salmonella Enteritidis of different origin.

Evaluation the antibacterial effects of Echinophora platyloba extracts against some Salmonella species

INTRODUCTION

Salmonellosis, which is caused by nontyphoid salmonella bacteria, is one of the most common foodborne diseases, and it causes gastrointestinal infections worldwide, most of which are limited gastroenteritis that requires antimicrobial treatment. The aim of this study was to investigate the effects of echinophora platyloba extract on inhibiting the growth of Salmonella typhi, Salmonella enteritidis, and salmonella choleraesuis.

METHODS

Echinophora Platyloba extract was collected in the East Azarbaijan Province in Iran in June 2015. Weeds, infected plants, and dried roots were separated and removed. After drying and grinding the plant, 100 grams of powder were weighed, and the extraction of the plant was carried out by percolation. This study tested the Minimum Inhibitory Concentration (MIC) by the broth micro dilution method and Minimum Bactericidal Concentration (MBC). All of the data were analyzed by SPSS statistical software, version 22.0. One-Way ANOVA and the Duncan test were used to compare the effect of various concentrations of the extract on each type of bacteria.

RESULTS

Our results indicated that, in 250 mg/ml of extracts discs, the largest growth inhibition zones were formed, and they were 26.11 ± 1.16, 21.23 ± 0.89, and 19.65 ± 0.60 in S. enteritidis, S. typhi, and S. choleraesuis groups, respectively. The statistical results indicated that, in each type of bacteria, there was a statistical difference (p < 0.01) between the various concentrations of the extracts and the chloramphenicol discs. Also, it was indicated that this extract at a concentration of 150 mg/ml had a germicidal effect on S. enteritidis and S. typhi bacteria and that 250 mg/ml had a bactericidal effect on S. choleraesuis.

CONCLUSION

The results of this study indicated that E. platyloba extract has potential effects as antimicrobial agents.

Association of Three Plasmid-Encoded spv Genes Among Different Salmonella Serotypes Isolated from Different Origins

The virulence plasmid associated Salmonella plasmid virulence (spv) locus is strongly concomitant with strains that cause non typhoid bacteremia. The spv region contains three genes required for the virulence, the positive transcriptional regulator spvR and two structural genes spvB and spvC. The purpose of this study was to investigate the presence of these three genes among salmonella serotypes isolated from different sources. A collection of 60 salmonella serotypes from different sources were used. Polymerase chain reaction was carried out for the presence of these genes using specific primers. The prevalence of spvB, spvC, and spvR genes were 26 (43.3 %), 44 (73.3 %), and 28 (46.6 %), respectively. The findings revealed that the distribution of these genes was dissimilar among these serotypes. Many of the human pathogenic salmonella strains which can be transmitted by animals may have these genes and can be very injurious for public health.

The Study of Genetic Relationship Among Third Generation Cephalosporin-resistant Salmonella enterica Strains by ERIC-PCR

Background and Objectives:

Salmonella is an important food-borne pathogen responsible for disease in humans and animals. The aim of this study was to investigate the genetic relationship among third generation cephalosporin-resistant Salmonella enterica strains by Enterobacterial Repetitive Intergenic Consensus (ERIC)-PCR.

Methods:

The study included all Salmonella isolates obtained from clinical cases in a pediatric hospital in Tehran, Iran during 2006 to 2009. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute. The genetic relationship between third generation cephalosporins-resistant Salmonella enterica strains was determined using ERIC-PCR.

Results:

Of 136 Salmonella enterica isolates recovered from pediatric patients, six isolates including four Salmonella enterica serotype Infantis and two Salmonella enterica serotype Enteritidis showed an extended-spectrum cephalosporins resistant phenotype. ERIC-PCR differentiated Salmonella enterica serotypes Infantis and Enteritidis into 2 distinct clusters arbitrarily named as E1 and E2. Profile E1 was found in two Salmonella enterica serotype Enteritidis isolates, and profile E2 was found in four Salmonella enterica serotype Infantis isolates.

Conclusion:

Extended-spectrum cephalosporins resistant Salmonella could be attributed to a few predominant serotypes including Enteritidis and Infantis in this study. Genetic analysis using ERIC-PCR showed that closely related clones are responsible for the occurrence of extended-spectrum cephalosporins resistant Salmonella infection in Tehran.

Epidemiology and genetics of CTX-M extended-spectrum β-lactamases in Gram-negative bacteria

CTX-M enzymes, the plasmid-mediated cefotaximases, constitute a rapidly growing family of extended-spectrum β-lactamases (ESBLs) with significant clinical impact. CTX-Ms are found in at least 26 bacterial species, particularly in Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis. At least 109 members in CTX-M family are identified and can be divided into seven clusters based on their phylogeny. CTX-M-15 and CTX-M-14 are the most dominant variants. Chromosome-encoded intrinsic cefotaximases in Kluyvera spp. are proposed to be the progenitors of CTX-Ms, while ISEcp1, ISCR1 and plasmid are closely associated with their mobilization and dissemination.

Characterization of class I integrons among Salmonella enterica serovar Enteritidis isolated from humans and poultry

A total of 84 Salmonella enterica serovar Enteritidis (S. Enteritidis) isolates, 42 of human and 42 of poultry origin, were characterized for antimicrobial resistance patterns and class I integrons. Among them, 58 (69%) S. Enteritidis were multidrug-resistant (MDR) and showed resistance to two or more antibiotic classes. By PCR assays and DNA sequencing, 50 (59.5%) S. Enteritidis isolates were found to carry class I integrons. Amplification of internal variable regions of class I integrons revealed five different arrays (0.75 kb only, 1 kb only, 1.3 kb only, both 1 and 1.2 kb, and both 1 and 1.3 kb). The integrons were further sequenced and the dfrA25 (0.75 kb), aadA1 (1 kb), aadA2 (1 kb), bla(PSE1) (1.2 kb) aadA6-orfD (1.3 kb) gene cassette arrays were identified. Ciprofloxacin minimum inhibitory concentration (MIC) values for the three isolates that showed resistance or reduced susceptibility via the disc diffusion method were 0.5-4 μg mL(-1), although only three isolates exhibited resistance to cefteriaxone (MIC: 128-256 μg mL(-1)) and four isolates were resistant to florfenicol (MIC: 32-128 μg mL(-1)). In conclusion, the high rates of multidrug-resistance and class I integrons found among S. Enteritidis isolates in humans and poultry in Tehran suggest that efforts are needed to confine the prevalence of MDR Salmonella isolates.

Serotypes, antibiotic resistance, and class 1 integrons in Salmonella isolates from pediatric cases of enteritis in Tehran, Iran

The present study was conducted to investigate serotype distribution, antimicrobial resistance patterns, carriage of class 1 integron, and clonality of Salmonella strains isolated from patients aged 0-12 years in Tehran, Iran, during 2007-2008. A total of 139 Salmonella isolates were studied. Salmonella serotypes Enteritidis, Infantis, and Typhimurium included 84.9% of isolates, Enteritidis accounting for 41.7%. The most prevalent resistances were to doxycycline (64.7%), nalidixic acid (61.2%), tetracycline (51.8%), and streptomycin (42.8%). Fifty-three (38.1%) isolates contained class 1 integron. Eight different gene cassettes were identified, aadA1 being the most frequently encountered. Pulsed-field gel electrophoresis showed that integron-positive Salmonella strains belonging to serotypes Infantis, Enteritidis, and Typhimurium were attributed to two, three, and five different pulsotypes, respectively. The findings indicated that the distribution and drug resistance pattern of most prevalent Salmonella serotypes were broadly similar to that reported globally from human isolates. Presence of class 1 integrons was common among Salmonella serotypes in Tehran, Iran. Concurrent clonal expansion and horizontal transmission events seem to contribute to increase in drug resistance prevalence among Salmonella serotypes.