Ceftriaxone resistance of nontyphoidal Salmonella enterica isolates in Northern Taiwan attributable to production of CTX-M-14 and CMY-2 beta-lactamases

Molecular characterization of extended-spectrum cephalosporin and fluoroquinolone resistance genes in Salmonella and Shigella isolated from clinical specimens in Thailand

Antimicrobial resistance of Salmonella and Shigella has become a major clinical and public health problem. The incident of co-resistance to third generation cephalosporins and fluoroquinolone is a serious therapeutic issue in Thailand. The present study aimed to investigate the antimicrobial resistance and molecular character of clinical Shigella and Salmonella isolates. A total of 33 Salmonella and 53 Shigella cefotaxime-resistant isolates were collected from human clinical cases in Thailand during the period from 2011-2018. The antimicrobial susceptibility of Salmonella and Shigella was determined by the disk diffusion method, and extended-spectrum beta-lactamase (ESBL) production was characterized by the double-disk synergy test. Genotype characterization was performed by PCR and DNA sequencing. Thirty-two (97.0%) and fifty-two (98.1%) isolates of cefotaxime-resistant Salmonella and Shigella, respectively, were identified as ESBL producers. Shigella sonnei (4 isolates), Salmonella serovar 4,5,12:i:- (6 isolates), Salmonella serovar Agona (2 isolates) and Salmonella serovar Rissen (2 isolates) showed co-resistance to ciprofloxacin and cefotaxime or ceftriaxone. The combination of bla _CTX-M-15 plus other ESBL and/or AmpC β-lactamase genes was the most dominant of the genotype patterns in ESBL-producing isolates. The plasmid harbouring the aac(6')-Ib-cr gene and mutations of gyrA (S83F, D87Y or D87G) and parC (T57S) genes was found in 2 ESBL-producing Salmonella isolates. Three Shigella sonnei isolates harboured mutations in gyrA (S83L, D87Y or D87G), and only one Shigella sonnei phase I isolate showed mutations in both gyrA (S83L and D87G) and parC (S80I) genes. Among these clinical Shigella sonnei isolates, qnrS determinants were identified. Production of ESBLs is an important mechanism for resistance to extended-spectrum cephalosporins in Salmonella and Shigella. The emergence of a decreased susceptibility to extended-spectrum cephalosporins and fluoroquinolone in ESBL-producing isolates has important clinical and therapeutic implications.

Factors Associated with Multi-Drug-Resistant Non-Typhoidal Salmonella in the Invasive Disease, Thailand

PURPOSE

Invasive non-typhoidal Salmonella disease, iNTS is a major global health concern, especially multi-drug resistant non-typhoidal Salmonella, MDR-NTS. Information about risk factors of MDR-NTS in the invasive disease patient group was limited. This study aimed to identify those risk factors.

METHODS

This retrospective study examined data from patients who had non-typhoidal Salmonella, NTS infection, from 10 hospitals between June 2011 and June 2020. The multivariate regression analysis included demographic data, clinical data, culture reports, and antimicrobial susceptibility.

RESULTS

A total of 166 patients were invasive salmonellosis. where the median age was 8.3 years (IQR 1.8-79). 52% were the under-15-years-old group. Most of the patient data, 64.5% (107/166), was from a tertiary hospital. The majority of cases were bacteremia 95.7% (159/166). Serogroup C was the most common serogroup (39%). MDR-NTS was present in 68.8% (95% CI 7.17-11.06) of patients. Univariate analysis showed that onset of illness >3 days PTA (p=0.11), age over 60 years old (0.014), diabetic (p=0.002), or serogroup C infection (p=0.43) were significant factors for MDR-NTS infection. Multivariate analysis showed that the onset of symptoms more than 3 days before admission (p=0.001), and age over 60 years were significant factors. The patient who had white blood cells >15,000 cells/uL (p<0.001), a peak of fever ≥39 C° (p=001), and illness for more than 3 days before admission (p=0.035) were significantly related to invasive infection by multivariate analyses.

CONCLUSION

The iNTS patients who were over 60 years old or had onset of illness more than 3 days before admission were associated with MDR-NTS infection. Therefore, the choice of antimicrobials selected must be appropriate for the local prevalence and epidemiology of MDR-NTS including clinical correlation.

Prevalence and Trends in Antimicrobial Susceptibility Patterns of Multi-Drug-Resistance Non-Typhoidal Salmonella in Central Thailand, 2012–2019

Purpose

Multi-drug resistance of non-typhoidal Salmonella (MDR-NTS) is an increasing threat worldwide. In Thailand, data for the past decade is limited. This research is to determine the prevalence and trends of nonsusceptibility patterns of the bacteria, especially to ciprofloxacin and ceftriaxone.

Methods

This retrospective study was extracted data of patients who had non-typhoidal Salmonella (NTS) infection, from 10 hospitals between June 2011 and June 2020. Demographic data, culture reports, and antimicrobial susceptibility were included in the analysis.

Results

A total of 433 patients were identified. The most common age group was less than 15 years old (53.6%), with a median age of 12 years (IQR 57–4). Of these people, 61.1% had gastroenteritis and 36.7% had bacteremia. The most prevalent serogroups was C (28.6%). MDR-NTS rate was 52.8% (95% CI 39–44). The resistant rates were 43%, 32.8%, 22.8%, 6.7%, 4%, 0.45%, 0.45% for sulfamethoxazole/trimethoprim, amoxicillin-clavulanic acid, cefotaxime, ampicillin/sulbactam, piperacillin/tazobactam, imipenem and meropenem retrospectively. Resistant rates have been increasing, especially for ciprofloxacin (30%), which rose from 16.6% in 2011–2015 to 39.5% in 2016–2020 (prevalence rate ratio (PRR) 2.4,95% CI 1.51–3.72) and for ceftriaxone 25.4% which rose from 16.1% to 32% (PRR 2 95% CI 1.24–3.16). Ampicillin, norfloxacin, tetracycline, amikacin, gentamicin, and ceftazidime remained static at 62.3%, 49.5%, 33.2%, 15.2%, 8.8%, 2.8%, respectively.

Conclusion

The prevalence of MDR-NTS has been increasing over the past decade, particularly those strains which demonstrate resistance to ciprofloxacin and ceftriaxone. Finding successful treatment requires a comprehensive selection of proper antimicrobials as well as close monitoring, especially in cases with severe infection.

Molecular Characterization of Cephalosporin and Fluoroquinolone Resistant Salmonella Choleraesuis Isolated from Patients with Systemic Salmonellosis in Thailand

The antimicrobial resistance of nontyphoidal Salmonella has become a major clinical and public health problem. Southeast Asia has a high level of multidrug-resistant Salmonella and isolates resistant to both fluoroquinolone and third-generation cephalosporins. The incidence of co-resistance to both drug classes is a serious therapeutic problem in Thailand. The aim of this study was to determine the antimicrobial resistance patterns, antimicrobial resistance genes and genotypic relatedness of third-generation cephalosporins and/or fluoroquinolone-resistant Salmonella Choleraesuis isolated from patients with systemic salmonellosis in Thailand. Antimicrobial susceptibility testing was performed using the agar disk diffusion method, and ESBL production was detected by the combination disc method. A molecular evaluation of S. Choleraesuis isolates was performed using PCR and DNA sequencing. Then, a genotypic relatedness study of S. Choleraesuis was performed by pulse field gel electrophoresis. All 62 cefotaxime-resistant S. Choleraesuis isolates obtained from 61 clinical specimens were multidrug resistant. Forty-four isolates (44/62, 71.0%) were positive for ESBL phenotypes. Based on the PCR sequencing, 21, 1, 13, 23, 20 and 6 ESBL-producing isolates harboured the ESBL genes bla_CTX-M-14, bla_CTX-M-15, bla_CTX-M-55, bla_CMY-2, bla_ACC-1 and bla_TEM-1, respectively. This study also found that nine (9/62, 14.5%) isolates exhibited co-resistance to ciprofloxacin and cefotaxime. All of the co-resistant isolates harboured at least one PMQR gene. The qnr genes and the aac(6')-Ib-cr gene were the most prevalent genes detected. The QRDR mutation, including the gyrA (D87Y and D87G) and parC (T57S) genes, was also detected. PFGE patterns revealed a high degree of clonal diversity among the ESBL-producing isolates.

Correlation Between Pathogenic Determinants Associated with Clinically Isolated Non-Typhoidal Salmonella

Non-typhoidal and Typhoidal Salmonella are bacterial pathogens source of worldwide and major disease burden. Virulent determinants of specific serovars belonging to non-typhoidal Salmonella have been extensively studied in different models, yet the pathogenesis of this group of bacteria and the development of clinical symptoms globally remains underexplored. Herein, we implemented microbiological and molecular procedures to investigate isolate virulence traits and molecular diversity, likely in association with disease severity. Our results show that selected clinical isolates from a tertiary referring hospital, depending on the richness of the environment and isolate serotypes, exhibited different, and sometimes controversial, virulence properties. The tested strains were susceptible to Ceftriaxone (90%) with decreasing reactivity to Trimethoprim–Sulfamethoxazole (72%), Chloramphenicol (64%), Ampicillin (48%), Gentamicin (44%), and Ciprofloxacin (2%). Disc susceptibility results partially correlated with minimum inhibitory concentration (MIC); however, special attention must be given to antimicrobial treatment, as a rise in multi-resistant isolates to Trimethoprim–Sulfamethoxazole (2/38 µg/mL), Minocycline (8 µg/mL) and Ampicillin (16 µg/mL) has been noticed, with two isolates resistant to Ceftazidime (16 µg/mL). By comparison to previous molecular epidemiology studies, the variation in the gene profiles of endemic pathogens supports the need for continuous and up-to-date microbiological and molecular reports.

Genetic analysis and plasmid-mediated blaCMY-2 in Salmonella and Shigella and the Ceftriaxone Susceptibility regulated by the ISEcp-1 tnpA-blaCMY-2-blc-sugE

BACKGROUND

Nontyphoid Salmonella and Shigella can cause gastroenteritis in humans. Ceftriaxone (CRO) has been used to treat their infection, however, development of CRO resistance are often associated with plasmid-mediated bla_CMY. Here, we investigated the presence of plasmid-mediated ISEcp-1 tnpA-bla_CMY-2-blc-sugE and the role of these genes in regulation of CRO susceptibility in different hosts.

METHODS

194 strains of Salmonella serovars and Shigella were tested for CRO susceptibility. Non-susceptibility strains were examined for plasmid-mediated ISEcp-1 tnpA-bla_CMY-2-blc-sugE by PCR amplification, Southern blot, and DNA sequencing. The plasmid profiles were determined by HindIII-digested restriction fragment length polymorphism (RFLP). Four recombinant plasmids with different genes from ISEcp-1 tnpA-bla_CMY-2-blc-sugE were constructed and then were transferred into Escherichia coli and different Salmonella serovars to evaluate the CRO susceptibility.

RESULTS

Among 20 CRO-nonsusceptible isolates of Salmonella Choleraesuis (5), S. Typhimurium (4), S. Mons (1), S. Stanley (2) and Shigella sonnei (8) with plasmid-mediated bla_CMY-2, 19 isolates carried the ISEcp-1 tnpA-bla_CMY-2-blc-sugE and only one isolate with tnpA-bla_CMY-2. Transformation of these plasmids into E. coli pir116 produced multidrug resistance. Furthermore, PCR-RFLP analysis determined 5 different plasmid profiles and identical RFLP pattern between S. Typhimurium and S. sonnei. Transformation of the recombinant plasmids into E. coli and different Salmonella serovars resulted in phenotypes ranging from susceptible to resistant (especially inducible resistance) to CRO that were dependent on the genes, and host.

CONCLUSION

The CRO susceptibility associated with the ISEcp-1 tnpA-bla_CMY-2-blc-sugE element is regulated positively by ISEcp-1 tnpA and SugE and negatively regulated by Blc and unknown species-dependent host factor(s).

Salmonella enterica Serovar Typhi in Bangladesh: Exploration of Genomic Diversity and Antimicrobial Resistance

Typhoid fever, caused by Salmonella enterica serovar Typhi, is a global public health concern due to increasing antimicrobial resistance (AMR). Characterization of S Typhi genomes for AMR and the evolution of different lineages, especially in countries where typhoid fever is endemic such as Bangladesh, will help public health professionals to better design and implement appropriate preventive measures. We studied whole-genome sequences (WGS) of 536 S Typhi isolates collected in Bangladesh during 1999 to 2013 and compared those sequences with data from a recent outbreak in Pakistan reported previously by E. J. Klemm, S. Shakoor, A. J. Page, F. N. Qamar, et al. (mBio 9:e00105-18, 2018, https://doi.org/10.1128/mBio.00105-18), and a laboratory surveillance in Nepal reported previously by C. D. Britto, Z. A. Dyson, S. Duchene, M. J. Carter, et al. [PLoS Negl. Trop. Dis. 12(4):e0006408, 2018, https://doi.org/10.1371/journal.pntd.0006408]. WGS had high sensitivity and specificity for prediction of ampicillin, chloramphenicol, co-trimoxazole, and ceftriaxone AMR phenotypes but needs further improvement for prediction of ciprofloxacin resistance. We detected a new local lineage of genotype 4.3.1 (named lineage Bd) which recently diverged into a sublineage (named Bdq) containing qnr genes associated with high-level ciprofloxacin resistance. We found a ceftriaxone-resistant isolate with the bla _CTX-M-15 gene and a genotype distinct from the genotypes of extensively drug-resistant (XDR) isolates from Pakistan. This result suggests a different source and geographical origin of AMR. Genotype 4.3.1 was dominant in all three countries but formed country-specific clusters in the maximum likelihood phylogenetic tree. Thus, multiple independent genetic events leading to ciprofloxacin and ceftriaxone resistance took place in these neighboring regions of Pakistan, Nepal, and Bangladesh. These independent mutational events may enhance the risk of global spread of these highly resistant clones. A short-term global intervention plan is urgently needed.IMPORTANCE Typhoid fever, caused by Salmonella enterica serovar Typhi, is responsible for an estimated burden of approximately 17 million new episodes per year worldwide. Adequate and timely antimicrobial treatment invariably cures typhoid fever. The increasing antimicrobial resistance (AMR) of S Typhi severely limits the treatment options. We studied whole-genome sequences (WGS) of 536 S Typhi isolates collected in Bangladesh between 1999 and 2013 and compared those sequences with data from a recent outbreak in Pakistan and a laboratory surveillance in Nepal. The analysis suggests that multiple ancestral origins of resistance against ciprofloxacin and ceftriaxone are present in three countries. Such independent genetic events and subsequent dissemination could enhance the risk of a rapid global spread of these highly resistant clones. Given the current treatment challenges, vaccination seems to be the most appropriate short-term intervention to reduce the disease burden of typhoid fever at a time of increasing AMR.

Investigation into a community outbreak of Salmonella Typhi in Bengaluru, India

Background & objectives:

Outbreaks of infection due to Salmonella enterica servovar Typhi (S. Typhi) are a great threat to public health. A rapid molecular typing method to characterize strains implicated in an outbreak is critical in implementing appropriate control measures. This study was done to demonstrate the power of a PCR-based method to provide rapid insights into the genetic relatedness amongst the Salmonella isolates implicated in a suspected typhoid fever outbreak.

Methods:

Forty two S. Typhi isolates originating from three geographically distinct areas, with one area suspected to have a single-source outbreak were included in the study. The genetic fingerprint of all isolates was generated using enterobacterial repetitive intergenic consensus sequence based-PCR (ERIC-PCR). The antimicrobial susceptibility profiles were also evaluated.

Results:

ERIC-PCR was found to be rapid and reproducible with a discriminatory index of 0.766. The dendrogram constructed based on ERIC-PCR fingerprinting revealed the existence of 12 distinct genotypes. The location suspected to have an outbreak displayed two genotypes amongst the 24 isolates. The other two locations (18 isolates) displayed genetic heterogeneity. The clonality of the outbreak isolates from the time-matched control isolates was established. The observed antimicrobial susceptibility profiles did not have any discriminatory power to subtype the isolates compared to the genetic fingerprints.

Interpretation & conclusions:

Our study demonstrated the discriminatory power and value of ERIC-PCR in the typing of S. Typhi isolates and providing valuable epidemiological insights.

Extended-spectrum β-lactamases producing multidrug resistance Escherichia coli, Salmonella and Klebsiella pneumoniae in pig population of Assam and Meghalaya, India

Aim

The present study was conducted to record the prevalence of extended spectrum β-lactamases (ESBLs) producing Escherichia coli, Salmonella spp., and Klebsiella pneumoniae from pig population of Assam and Meghalaya and to record the ability of the resistant bacteria to transfer the resistance genes horizontally.

Materials and Methods

Fecal samples (n=228), collected from pigs of Assam (n=99) and Meghalaya (n=129), were processed for isolation and identification of E. coli and Salmonella spp. All the isolates were tested for ESBLs production by double disc synergy test (DDST) followed by screening for ESBLs producing genes (bla_TEM, bla_SHV, bla_CTX-M, and bla_CMY) by polymerase chain reaction (PCR). Possible transfer of resistance encoding genes between enteric bacterial species was carried out by in vitro and in vivo horizontal gene transfer (HGT) method.

Results

A total of 897 enteric bacteria (867 E. coli and 30 Salmonella) were isolated and identified. Altogether 25.41% isolates were confirmed as ESBL producers by DDST method. Majority of the isolates were E. coli followed by Salmonella. By PCR, 9.03% isolates were found positive for at least one of the target resistance genes. bla_SHV was absent in all the isolates. bla_CMY was the most prevalent gene. All the E. coli isolates from Assam were negative for bla_TEM. A total of 2.76% isolates were positive for bla_TEM + bla_CMY. On the other hand, 0.67% isolates were positive for bla_CTX-M + bla_CMY genes. Only 0.33% isolates carried all the three genes. Altogether, 4.68% bacteria carried the resistance encoding genes in their plasmids. bla_TEM gene could be successfully transferred from Salmonella (donor) to E. coli (recipient) by in vitro (5.5-5.7×10^-5) and in vivo (6.5×10^-5 to 8.8×10^-4) methods. In vivo method was more effective than in vitro in the transfer of resistance genes.

Conclusion

The pig population of Assam and Meghalaya are carrying multidrug resistance and ESBLs producing E. coli and Salmonella. The isolates are also capable to transfer their resistance trait to other bacterial species by HGT. The present finding could be considered as a serious public health concern as similar trait can also be transmitted to the human commensal bacteria as well as pathogens.

High prevalence of ceftriaxone resistance among invasive Salmonella enterica serotype Choleraesuis isolates in Thailand: The emergence and increase of CTX-M-55 in ciprofloxacin-resistant S. Choleraesuis isolates

S. Choleraesuis is a highly invasive zoonotic pathogen that causes a serious systemic infection in humans. The emergence and increase of resistance to ceftriaxone and ciprofloxacin among S. Choleraesuis has become a serious therapeutic problem. The present study demonstrated high frequency of antimicrobial resistance in Salmonella Choleraesuis among 414 nontyphoidal Salmonella isolates from bacteremic patients in Thailand. High rates of ceftriaxone (58.3%) and ciprofloxacin (19.6%) resistances were observed in S. Choleraesuis isolates. The dissemination of the self-transferable bla_CTX-M-14-carrying IncFII_s, IncFII, and IncI1 plasmids and bla_CMY-2-carrying IncA/C plasmid along with the clonal spread of bla_CMY-2-harbouring S. Choleraesuis isolates contributed to the high frequency of resistance to extended-spectrum cephalosporins (ESCs; third- and fourth-generation cephalosporins) during 2005-2007. We reported the first occurrence of ceftazidime-hydrolysing CTX-M-55 in S. Choleraesuis isolates which dramatically increased and became the most abundant CTX-M variant among ESC-resistant S. Choleraesuis isolates during 2012-2016. The spread of clone pulsotype B3 was due to the dissemination of IncA/C plasmids carrying both bla_CTX-M-55 and qnrS1 among ciprofloxacin-resistant S. Choleraesuis isolates harbouring D87G in GyrA. These isolates were apparently responsible for the high rates of co-resistance to ESCs and ciprofloxacin (51.3%) during 2012-2016. This study emphasizes the importance to have an action plan to control the dissemination of antimicrobial resistance in S. Choleraesuis since this poses a threat to global health due to travel and trade in animal food products.

Detection and characterization of extended-spectrum β-lactamases (blaCTX-M-1 and blaSHV ) producing Escherichia coli, Salmonella spp. and Klebsiella pneumoniae isolated from humans in Mizoram

Aim:

The present study was conducted to isolate and characterize the extended spectrum β-lactamases (ESBLs) producing enteric bacteria in human beings in Mizoram, India.

Materials and Methods:

Fecal samples were collected from human beings with or without the history of diarrhea from different hospitals of Mizoram. Samples were processed for isolation and identification of Escherichia coli, Salmonella and Klebsiella pneumoniae. All the isolates were subjected to antibiotic sensitivity assays. Phenotypically, ESBLs production ability was determined by double discs synergy test (DDST) method. ESBLs producing isolates were subjected to polymerase chain reaction (PCR) for detection of ESBLs genes. Plasmids were cured by acridine orange. Transfer of resistance from a donor to recipient strains was done by in vitro horizontal method.

Results:

A total of 414 enteric bacteria were isolated from 180 fecal samples (113 were from diarrheic patients and 67 were from non-diarrheic patients), of which 333 (80.44%), 52 (12.56%), and 29 (7.00%) were E. coli, K. pneumoniae and Salmonella spp., respectively. Double discs synergy test (DDST) exhibited 72 (21.62%) E. coli, 12 (23.08%) K. pneumoniae and 4 (13.79%) Salmonella spp. were ESBLs producers. Altogether, 24 (13.04%) isolates were found to be positive for at least one resistance genes under this study. A total of 36 (8.70%) E. coli, 4 (0.97%) K. pneumoniae and 2 (0.48%) Salmonella spp. were found to be positive for bla_CTX-M-1 gene by PCR. Similarly, 5 (1.21%) E. coli and 4 (0.97%) K. pneumoniae isolates were found to be positive for bla_SHV gene. A total of 3 (0.72%) K. pneumoniae isolates were recorded as positive for both bla_CTX-M-1 and bla_SHV genes. All the isolates were carrying plasmids ranging between 0.9 kb and ~30 kb. The resistance plasmid could not be transferred to a recipient by in vitro horizontal gene transfer method.

Conclusion:

ESBLs producing enteric bacteria are circulating in human population in North Eastern Region of India. Indiscriminate use of antibiotics should be avoided to control the menace of multidrug resistance bacteria in the environment, animals, and human beings.

Characterization of Salmonella food isolates with concurrent resistance to ceftriaxone and ciprofloxacin

Foodborne salmonellosis is an important public health problem worldwide. Most human Salmonella infections occur through the consumption of contaminated food of animal origin. The study reported the first isolation of two Salmonella enterica serovar Oranienburg strains from pork in China with concurrent resistance to ciprofloxacin and ceftriaxone. Both isolates also showed resistance to norfloxacin, trimethoprim-sulfamethoxazole, and chloramphenicol, and an elevated minimal inhibitory concentraton of azithromycin; one strain was also resistant to amikacin, gentamicin, tetracycline, and amoxicillin-clavulanic acid. Salmonella ceftriaxone resistance was due to the production of IncN plasmidborne CTX-M-14 ESBL, and their ciprofloxacin resistance was mediated by target mutations and efflux pump activity. This is the first time that ceftriaxone- and ciprofloxacin-resistant Salmonella was reported in meat products, which may be due to the uses of antibiotics in animal production. The study warrants the continuous surveillance of multidrug-resistant Salmonella in meat products and cautious use of antibiotics in food animals.

Serotype profile and molecular characterization of antimicrobial resistance in non-typhoidal Salmonella isolated from gastroenteritis cases over nine years

Resistance to third-generation cephalosporins in non-typhoidal Salmonella (NTS) is emerging worldwide. We report the occurrence of extended-spectrum beta-lactamase (ESBL) phenotypes in 53.4 % of NTS isolated over a period of nine years from gastroenteritis cases. ESBL and AmpC co-production was observed in 21 % of the isolates. Occurrence of blaCTX-M-15 and blaCMY-2 resistance genes was observed in 11.6 % and 37 % of the isolates respectively. Overall, Salmonella enterica serovar Senftenberg was the predominant serovar carrying blaCTX-M-15 and blaCMY-2 resistance genes. We report for the first time from India, one isolate each of S. enterica serovar Thompson, S. enterica serovar Infantis and S. enterica serovar Newport, carrying the blaCTX-M-15 gene. We also report for the first time from India, a case of gastroenteritis due to S. enterica serovar Thompson.

Pathogens resistant to antibacterial agents

Resistance to antimicrobial drugs is increasing at an alarming rate among both gram-positive and gram-negative bacteria. Traditionally, bacteria resistant to multiple antimicrobial agents have been restricted to the nosocomial environment. A disturbing trend has been the recent emergence and spread of resistant pathogens in nursing homes, in the community, and in the hospital. This article reviews the epidemiology, molecular mechanisms of resistance, and treatment options for pathogens resistant to antimicrobial drugs.

High prevalence of extended-spectrum beta lactamases among Salmonella enterica Typhimurium isolates from pediatric patients with diarrhea in China

We investigated the extended-spectrum beta lactamases among 62 Salmonella enterica Typhimurium isolates recovered from children with diarrhea in a Chinese pediatric hospital. A large proportion of S. enterica Typhimurium isolates were resistant to multiple antimicrobial agents, including ampicillin (90.3%), tetracycline (80.6%), trimethoprim/sulfamethoxazole (74.2%), chloramphenicol (66.1%), cefotaxime (27.4%). Forty-nine (79.0%) of S. enterica Typhimurium isolates were positive for bla_TEM-1b and resistant to ampicillin. Thirteen S. enterica Typhimurium isolates (21.0%) were positive for bla_{CTX-M-1-group} and bla_{CTX-M-9-group}, and all isolates harboring bla_CTX-M genes were positive for ISEcp1. Two main clones (PFGE type A and D) accounted for nearly 70% of S. enterica Typhimurium isolates, and 7 CTX-M-producing isolates belonged to PFGE type D. Collectively, our data reveal multi-drug resistance and a high prevalence of extended spectrum beta lactamases among S. enterica Typhimurium isolates from children in China. In addition, we report the first identification of bla_CTX-M-55 within Salmonella spp. Our data also suggest that clonal spread is responsible for the dissemination of S. enterica Typhimurium isolates.

Increase in isolation of extended spectrum beta lactamase producing multidrug resistant non typhoidal Salmonellae in Pakistan

Background

Increasing resistance to quinolones and ceftriaxone in non typhoidal Salmonellae is a global concern. Resistance to quinolone and 3^rd generation cephalosporin amongst non typhoidal Salmonellae (NTS) from Pakistan has been reported in this study.

Methods

Retrospective analysis of laboratory data was conducted (1990-2006). NTS were isolated and identified from clinical samples using standard microbiological techniques. Antimicrobial susceptibility testing was performed by Kirby Bauer. Extended spectrum beta lactamase production (ESBL) was detected using combined disc method. Ciprofloxacin sensitivity was detected by nalidixic acid screening method. Minimum inhibitory concentration (MIC) of ciprofloxacin was determined by agar dilution method. Statistical analysis was performed using SPSS version 13.

Results

Analysis of 1967 NTS isolates showed a significant increase in ciprofloxacin resistance from 23% in 2002 to 50.5% in 2006, with increased mean MIC values from 0.6 to 1.3 ug/mL. Ceftriaxone resistant NTS also increased and ESBL production was seen in 98.7% isolates. These isolates exhibited high resistance against amoxicillin clavulanic acid (57%), gentamicin (69%), amikacin (44%) and piperacillin tazobactam (30%). No resistance to carbapenem was seen. Ceftriaxone resistance was significantly higher in children <1 year, in invasive isolates and in Salmonella Typhimurium.

Conclusions

Increase in quinolone and ceftriaxone NTS is a serious threat to public health requiring continuous surveillance and use of appropriate screening tests for laboratory detection.

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

The infections caused by Salmonella remain a significant public health problem throughout the world. beta-Lactams and fluoroquinolones are generally used to treat invasive Salmonella infections, but emergence and spread of antibiotic-resistant strains are being increasingly notified in many countries. In particular, detection of extended-spectrum beta-lactamases (ESBLs) in Salmonella spp. is a newly emerging threat worldwide. This study was carried out to characterize beta-lactamase-producing Salmonella strains identified in Tehran, Iran. Over the 2-year period from 2007 to 2008, 6 of 136 Salmonella isolates recovered from pediatrics patients, including three Salmonella enterica serotypes Enteritidis (S. Enteritidis) and three S. Infantis, showed an ESBL-positive phenotype. Polymerase chain reaction and sequencing were used to identify the genetic determinants responsible for ESBL phenotypes. The Salmonella isolates were also compared by pulsed-field gel electrophoresis. All ESBL-producing strains, but one, carried the bla(CTX-M-15) gene. Moreover, three of four strains that proved to be positive for a bla(TEM) gene were producing a TEM-1 beta-lactamase. Two strains of S. Infantis tested positive for a previously unidentified CTX-M and TEM ESBL, respectively. All ESBL-producing strains carried the insertion sequence ISEcp1 gene. Except for one strain of serotype Infantis, all strains were able to transfer the ESBL determinants by conjugation. Distinct, but closely related, pulsed-field gel electrophoresis patterns were observed among the strains belonging to both serotypes. This study reports for the first time the emergence and characterization of ESBL-producing S. Enteritidis and Infantis strains in Iran.

Genetic context of plasmid-carried blaCMY-2-like genes in Enterobacteriaceae

Analysis of 15 European clinical Enterobacteriaceae isolates showed that differences in the genetic context of blaCMY-2-like genes reflected the replicon type, usually IncA/C or IncI1. These blaCMY-2 loci may originate from the same ISEcp1-mediated mobilization from the Citrobacter freundii chromosome as structures described in earlier studies.

Emergence of CTX-M-15 type extended-spectrum beta-lactamase-producing Salmonella spp. in Kuwait and the United Arab Emirates

Cephalosporins are major antimicrobials used to treat serious Salmonella infections. However, their effectiveness is being compromised by the emergence of extended-spectrum beta-lactamases (ESBLs). The genetic determinants encoding ESBL in Salmonella spp. isolated from patients in Kuwait and United Arab Emirates (UAE) were studied over a 2 year period. Out of a total of 407 isolates, 116 isolates possessed the resistance phenotypes consistent with possible ESBL production. Of these, 69 (59.5 %) were ESBL positive. PCR and sequencing were used to determine the genetic determinant(s) responsible for ESBL phenotypes. A total of 14 (12.1 %) and 29 (24.6 %) isolates were CTX-M-15 ESBL producers and TEM producers, respectively. Ten CTX-M-15 producers carried the insertion sequence ISEcpI gene. PFGE analysis revealed identical profiles in 4 of the 13 Kuwaiti strains. This study reports the presence of the bla(CTX-M-15) gene in Salmonella spp. and Salmonella enterica serotype Typhi from Kuwait and UAE for what is believed to be the first time. This is of great concern as the gene is also found in association with the ISEcpI gene, which may easily facilitate its spread. These isolates originated mostly from non-Kuwaiti Arabs rather than from people of Asian origin.

Characterization of extended-spectrum beta-lactamases in Salmonella spp. at a tertiary hospital in Durban, South Africa

Extended-spectrum beta-lactamases (ESBLs) were characterized in 41 Salmonella spp. isolates from patients admitted to a pediatric ward of a tertiary hospital in Durban, South Africa. The most common (17/ 41) serotype was Salmonella enterica serotype Typhimurium, followed by S. enterica serotype Isangi (16/41), S. enterica serotype Saint-paul (2/41), S. enterica serotype Kissi (2/41), S. enterica serotype Kivu (2/41), and S. enterica serotype Reading (1/41). All isolates were resistant to ampicillin, amoxicillin-clavulanate, piperacillin, ceftazidime, and aztreonam but susceptible to meropenem. SHV-12 found in 39% of the isolates was the most common ESBL. TEM-63 was produced in 29% and TEM-116 in 10% of the isolates, and TEM-131 was found in 1 isolate. Other ESBLs that were identified included SHV-2 (n = 2), CTX-M-3 (n = 1), CTX-M-15 (n = 2), and CTX-M-37 (n = 5). In addition, CMY-2 (n = 3) and the OXA-1(n = 1) beta-lactamase were also detected. The diversity of ESBLs suggests that its incidence in Salmonellae needs to be monitored.

Cefotaxime-resistant Citrobacter freundii in isolates from blood in a tertiary teaching hospital in Northern Taiwan

From January 2002 to December 2003, 12 patients in a tertiary teaching hospital in northern Taiwan had bloodstream infections caused by Citrobacter freundii. Seven of the 12 isolates were resistant to cefotaxime. Using polymerase chain reaction and DNA sequencing, 3 of the 7 cefotaxime-resistant C. freundii isolates were found to carry extended-spectrum beta-lactamase (ESBL). AmpC beta-lactamase genes were also detected in all strains of C. freundii. All strains of C. freundii with MICs >or=4 mg/L for cefepime were positive for ESBL. Rather than performing PCR on all cefotaxime-resistant C. freundii isolates, assessment of the MIC for cefepime might be a practical way to choose between treatment with cefepime or with carbapenems.

Antimicrobial resistance in nontyphoidal Salmonella from food sources in Colombia: evidence for an unusual plasmid-localized class 1 integron in serotypes Typhimurium and Anatum

Seventy-two isolates representing 18 serotypes recovered from various food samples collected in Colombia were tested for antimicrobial susceptibilities. The collection was further characterized for extended-spectrum cephalosporin, aminoglycoside, and tetracycline resistance markers. Multidrug resistant (MDR) isolates were further investigated for class 1 integrons and were evaluated for the presence of conjugative plasmids along with a determination of the incompatibility group by polymerase chain reaction (PCR). Antibiogram analysis showed that the incidence rate of ceftiofur resistance was moderately high (15%). A similar level of resistance to neomycin and oxytetracycline (11% and 10%, respectively) was also observed. There was a high prevalence of gene cassettes as part of one or more class 1 integrons (61%), many of which contained determinants that contributed to the resistance profile. Class 1 integrons identified in MDR Salmonella enterica serotypes Typhimurium and Anatum isolates were characterized. Sequencing identified several incomplete open reading frames (ORFs) as part of a gene cassette (bla-( imp-13 ), dfr7, blr1088, and aac8) along with a complete gene cassette (bla-(oxa2)) in each case. A mosaic of gene cassettes was identical in the two Salmonella serotypes. These integrons were located to a conjugative replicon. Plasmid profiling and incompatibility typing identified three plasmids belonging to Inc groups A/C, P, and W. Our study highlights the role of integrons, contributing to a MDR phenotype that is capable of dissemination to other bacteria.

Salmonella resistant to extended-spectrum cephalosporins: prevalence and epidemiology

Salmonella resistant to extended-spectrum cephalosporins (ESCs) have emerged worldwide since 1988. By 2004, 43 countries had reported this public health problem. Resistance was mediated by classical extended-spectrum beta-lactamases, plasmid-mediated cephalosporinases, and recently a class A carbapenemase. Of these, CMY-2 is the most widely disseminated enzyme. Salmonella enterica serotype Typhimurium and S. enterica serotype Enteritidis are the most common serovars associated with ESC resistance in human infections. Many outbreaks in humans have been reported, most often among children and neonates. ESC-resistant Salmonella is frequently recovered from animals and food, with poultry as primary food source, suggesting that humans are often infected by these routes.

Genes and mutations conferring antimicrobial resistance in Salmonella: an update

Resistance to various classes of antimicrobial agents has been encountered in many bacteria of medical and veterinary relevance. Particular attention has been paid to zoonotic bacteria such as Salmonella. Over the years, various studies have reported the presence of genes and mutations conferring resistance to antimicrobial agents in Salmonella isolates. This review is intended to provide an update on what is currently known about the genetic basis of antimicrobial resistance in Salmonella.

Resistance in gram-negative bacteria: Enterobacteriaceae

The emergence and spread of resistance in Enterobacteriaceae are complicating the treatment of serious nosocomial infections and threatening to create species resistant to all currently available agents. Approximately 20% of Klebsiella pneumoniae infections and 31% of Enterobacter spp infections in intensive care units in the United States now involve strains not susceptible to third-generation cephalosporins. Such resistance in K pneumoniae to third-generation cephalosporins is typically caused by the acquisition of plasmids containing genes that encode for extended-spectrum beta-lactamases (ESBLs), and these plasmids often carry other resistance genes as well. ESBL-producing K pneumoniae and Escherichia coli are now relatively common in healthcare settings and often exhibit multidrug resistance. ESBL-producing Enterobacteriaceae have now emerged in the community as well. Salmonella and other Enterobacteriaceae that cause gastroenteritis may also be ESBL producers, which is of relevance when children require treatment for invasive infections. Resistance of Enterobacter spp to third-generation cephalosporins is most typically caused by overproduction of AmpC beta-lactamases, and treatment with third-generation cephalosporins may select for AmpC-overproducing mutants. Some Enterobacter cloacae strains are now ESBL and AmpC producers, conferring resistance to both third- and fourth-generation cephalosporins. Quinolone resistance in Enterobacteriaceae is usually the result of chromosomal mutations leading to alterations in target enzymes or drug accumulation. More recently, however, plasmid-mediated quinolone resistance has been reported in K pneumoniae and E coli, associated with acquisition of the qnr gene. The vast majority of Enterobacteriaceae, including ESBL producers, remain susceptible to carbapenems, and these agents are considered preferred empiric therapy for serious Enterobacteriaceae infections. Carbapenem resistance, although rare, appears to be increasing. Particularly troublesome is the emergence of KPC-type carbapenemases in New York City. Better antibiotic stewardship and infection control are needed to prevent further spread of ESBLs and other forms of resistance in Enterobacteriaceae throughout the world.

Resistance in gram-negative bacteria: enterobacteriaceae

The emergence and spread of resistance in Enterobacteriaceae are complicating the treatment of serious nosocomial infections and threatening to create species resistant to all currently available agents. Approximately 20% of Klebsiella pneumoniae infections and 31% of Enterobacter spp infections in intensive care units in the United States now involve strains not susceptible to third-generation cephalosporins. Such resistance in K pneumoniae to third-generation cephalosporins is typically caused by the acquisition of plasmids containing genes that encode for extended-spectrum beta-lactamases (ESBLs), and these plasmids often carry other resistance genes as well. ESBL-producing K pneumoniae and Escherichia coli are now relatively common in healthcare settings and often exhibit multidrug resistance. ESBL-producing Enterobacteriaceae have now emerged in the community as well. Salmonella and other Enterobacteriaceae that cause gastroenteritis may also be ESBL producers, which is of relevance when children require treatment for invasive infections. Resistance of Enterobacter spp to third-generation cephalosporins is most typically caused by overproduction of AmpC beta-lactamases, and treatment with third-generation cephalosporins may select for AmpC-overproducing mutants. Some Enterobacter cloacae strains are now ESBL and AmpC producers, conferring resistance to both third- and fourth-generation cephalosporins. Quinolone resistance in Enterobacteriaceae is usually the result of chromosomal mutations leading to alterations in target enzymes or drug accumulation. More recently, however, plasmid-mediated quinolone resistance has been reported in K pneumoniae and E coli, associated with acquisition of the qnr gene. The vast majority of Enterobacteriaceae, including ESBL producers, remain susceptible to carbapenems, and these agents are considered preferred empiric therapy for serious Enterobacteriaceae infections. Carbapenem resistance, although rare, appears to be increasing. Particularly troublesome is the emergence of KPC-type carbapenemases in New York City. Better antibiotic stewardship and infection control are needed to prevent further spread of ESBLs and other forms of resistance in Enterobacteriaceae throughout the world.