[Identification of Lactobacillus and Streptococcus thermophilus by PCR amplification and sequence analysis of 16S rRNA]

OBJECTIVE

To develop a PCR method for identifying the 16S rRNA of Lactobacillus and Streptococcus thermophilus at the species level.

METHODS

Optimizing the method for DNA extraction and the conditions for PCR amplification. Joining the PCR amplification products from 16S rRNA to plasmid puc18-T and detecting the sequence.

RESULTS

All 50 isolates recovered from yoghourt products were characterized by 16S rRNA sequence analysis and 7 groups were identified as L. bulgaricus (24 strains), S. thermophilus (12 strains), L. acidophilus (7 strains), L. casei (3 strains), L. delbrueckii (2 strains), L. fermentum (1 strain) and S. lutetiensis (1 strain).

CONCLUSION

16S rRNA PCR method developed in this research is a sensitive and reliable method for the identification of both Lactobacillus and Streptococcus thermophilus.

Dissemination of cefotaxime-M-producing Escherichia coli isolates in poultry farms, but not swine farms, in China

The objective of this study was to investigate the distribution of extended spectrum β-lactamase (ESBL)-producing Escherichia coli isolates in swine and poultry farms in China. Rectal or cloaca swabs of swine and chicken were collected from four province-level regions of China, and E. coli isolates were recovered and tested for antimicrobial susceptibility. The isolates producing ESBLs were further characterized by pulsed-field gel electrophoresis (PFGE) and sequence analysis of genes encoding β -lactamases and class I integrons. In total, 156 and 224 E. coli isolates were recovered from rectal swabs of four swine farms and cloaca swabs of six chicken farms, respectively. Prevalence of resistant isolates was higher in chicken than in swine. Fifty-six isolates producing ESBLs were identified from chicken samples, but no ESBL-producing isolates were identified from swine samples. Of 56 ESBL-producing isolates, 54 isolates contained cefotaxime (CTX)-M type β-lactamases, including bla(CTX-M-14) (n = 24), bla(CTX-M-65) (n = 13), bla(CTX-M-55) (n = 10), bla(CTX-M-24) (n = 3), bla(CTX-M-3) (n = 2), bla(CTX-M-15) (n = 1), and bla(CTX-M-64) (n = 1). Among 54 E. coli isolates containing bla(CTX-M), 11 PFGE clusters and 42 PFGE patterns were identified. More importantly, more than three-fourth of the ESBL-producing isolates in chicken were also resistant to ciprofloxacin. Our data demonstrated that chicken had become an important reservoir of bla(CTX-M) in China. Detailed molecular comparison of plasmids and genomes of isolates from various sources will help to better define the transmission dynamics of bla(CTX-M) between humans and food-producing animals.

[Antimicrobial susceptibility and related genes of Salmonella serovars from retail food in Shaanxi province]

OBJECTIVE

Salmonella isolates from retail food were examined for antimicrobial susceptibility and further characterized to better understand the development and dissemination of antimicrobial resistance among foodborne Salmonella in China.

METHODS

Antimicrobial susceptibility of 359 Salmonella isolates was determined by using agar dilution methods recommended by the Clinical and Laboratory Standards Institute. Antimicrobial resistance integrons and resistance genes were identified using PCR. Mutations in gyrase and Topoisomerase genes related to fluoroquinolones resistance were also determined using PCR and gene sequencing analysis.

RESULTS

Among the 359 Salmonellae isolates, 67% were resistant to Sulfamethoxazole, followed by resistant to trimethoprim/Sulfamethoxazole (58%), tetracycline (56%), kanamycin (37%), nalidixic acid (35%), ampicillin (33%), amoxicillin/clavulanic acid (32%), streptomycin (29%), chloramphenicol and gentamicin (26%), ciprofloxacin (21%), ceftriaxone (16%), cefoxitin (9%) and cefoperazone (8%). Among the 284 resistant isolates, 79% were resistant to at least one antimicrobial, 25.9% to 10 or more than 10 antimicrobials, and 2.5% to 14 antibiotic agents. Integrons were detected in some of sulfamethoxazole-ressitant Salmonella, and the most common integron was 1.4 kb, Antimicrobial resistance genes carried by integrons included aadA1, aadA2, aadA5, tetR, blaPSE1, blaDHA1, blaVEB-1, dhfr I, dhfr V, dhfrVl and dhfr17. The blaTEM gene was also detected in 51.6% of 62 ceftriaxone and/or cefoperazone resistant isolates, and blacMY-2 was detected in 56.5% of the isolates. 13.6% of the Salmonella isolates carried Salmonella Gene Island. Sixty-eight point mutations were detected in gyrA, parC and parE of 35 fluoroquinolone-resistant Salmonella isolates. The common mutations in gyrA gene were Ser83Phe, Ser83Tyr, Asp87Gly and Asp87Asn, whereas ser80Arg was detected in parC. Mutations including Lys441 Ile, Lys428Gln, Asp494Asn, Lys428Gln and Gly442Ser were detected in parE, which was first reported in Salmonella.

CONCLUSION

Antimicrobial resistance of Salmonella recovered from food in Shaanxi province was common. Several genetic elements including integron, Salmonella Gene Island, beta-lactamase genes and mutations in gyrase and topoisomerase genes played an important role in antimicrobial resistance of Salmonella.

Prevalence and characterization of Salmonella serovars in retail meats of marketplace in Shaanxi, China

A total of 764 retail meat including 515 chicken, 91 pork, 78 beef and 80 lamb samples were collected in Shaanxi Province of China in 2007-2008 to determine the prevalence of Salmonella. The isolates were characterized using serotyping, antimicrobial susceptibility testing, and the presence of bla(CMY-2) and bla(TEM) and class I integrons. Selective serovars were further subtyped using PFGE. Approximately 54% (276) of chicken, 31% (28) of pork, 17% (13) of beef and 20% (16) of lamb samples were positive of Salmonella. Among 24 serovars identified, Enteritidis (31.5%) was most common, followed by Typhimurium (13.4%), Shubra (10.0%), Indiana (9.7%), Derby (9.5%) and Djugu (7.0%). Nearly 80% of the isolates (283) were resistant to at least one antimicrobial, and 53% (191) to more than three antimicrobials. Resistance was most frequently observed to sulfamethoxazole (67%), to trimethoprim/sulfamethoxazole (58%) and to tetracycline (56%). Furthermore, many isolates were resistant to nalidixic acid (35%), ciprofloxacin (21%) and ceftriaxone (16%). Most isolates of Shubra (89%) and Indiana (88%) were resistant to > or = 9 antimicrobials, compared to only 11% of Enteritidis and 9% of Infantis that showed similar resistance. Class I integrons were detected in 10% of the isolates, and contained aadA, tetR, dhfr, bla(PSE-1), bla(DHA-1) and bla(VEB-1) gene cassettes alone or various combinations. Ceftriaxone- and/or cefoperazone-resistant isolates (n=62) carried bla(TEM) (51.6%) and/or bla(CMY-2) (56.5%). A total of 116 PFGE patterns were generated among 210 selected isolates. Our findings indicated that Salmonella contamination was common in retail meats, and that the Salmonella isolates were phenotypically and genetically diverse. Additionally, many Salmonella isolates were resistant to multiple antimicrobials.

Isolation and characterization of methicillin-resistant Staphylococcus aureus from swine and workers in China

OBJECTIVES

The objectives of this study were to determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization in livestock and related workers in four Chinese provinces and the characteristics of these isolates.

METHODS

Nasal swabs were collected from animals and farm workers in four Chinese provinces. MRSA isolates were recovered and characterized by PFGE, Panton-Valentine leucocidin PCR, staphylococcal chromosomal cassette (SCC) mec typing, spa typing, multilocus sequence typing, antimicrobial susceptibility testing and testing for inducible clindamycin resistance.

RESULTS

A total of 60 MRSA isolates were recovered from swine and swine workers. Two predominant multidrug resistance profiles were identified: ciprofloxacin/clindamycin/erythromycin/cefoxitin/gentamicin/tetracycline/chloramphenicol and ciprofloxacin/clindamycin/erythromycin/cefoxitin/gentamicin/tetracycline. All isolates were determined to be spa type t899, contained the group III SCCmec element and were Panton-Valentine leucocidin negative. Multilocus sequence type ST9 (n = 46) was identified as the dominant sequence type. One dominant PFGE cluster and a dominant strain type were identified.

CONCLUSIONS

MRSA from Chinese pigs and farm workers (ST9) differed from the European pig-associated clone (ST398) with regard to clonal type, SCCmec content and resistance profile.

Identification of site(s) of insulin nitration by peroxynitrite and characterization of its structural change

Insulin nitration mediated by peroxynitrite (ONOO(-)) has been implicated in diabetes and diabetic cardiovascular complications. In this study, we identified the nitration sites of porcine insulin by infusion of ONOO(-) and quantified its secondary structural change. Insulin was cleaved with V8 protease to six peptides (four of them contained each tyrosine residue), then analyzed by HPLC-MS and further confirmed the nitration sites by HPLC-MS/MS. At low accumulated doses of peroxynitrite, the main products were two different mono-nitrated insulin species at Tyr-A19 and Tyr-B26 with Tyr-A19 being predominant as shown by peptide mapping. Also, the content of alpha-helix structure of insulin reduced to 22.9 % and random-coil structure increased to 30.2 % (compare with native insulin of 41.7 % and 13.7 %, respectively) as determined by FTIR spectra.

Characterization of Salmonella enterica isolates from infants and toddlers in Wuhan, China

BACKGROUND

Extended-spectrum cephalosporins and fluoroquinolones are important antimicrobials for treating invasive salmonellosis, and emerging resistance to these antimicrobials is of paramount concern. This study reports on the antimicrobial susceptibility and molecular characterization of Salmonella enterica isolates recovered in 2006 from 0- to 3-year-old outpatients in China.

METHODS

The isolates were subjected to serotyping, antimicrobial susceptibility testing, screening for beta-lactamase genes, mutations in the quinolone resistance determining regions (QRDRs), qnr alleles and aac-(6')-Ib-cr by PCR followed by DNA sequence analysis. All Salmonella Typhimurium isolates and 43 selected non-Typhimurium isolates were further characterized by PFGE to determine the genetic relatedness.

RESULTS

From 3746 paediatric outpatient stool samples, 221 (5.9%) S. enterica isolates of 29 distinct serotypes were recovered. The antimicrobial resistance profiles differed among serotypes. Ciprofloxacin-resistant isolates were concentrated in serotype Typhimurium that were resistant to at least four additional non-quinolone antimicrobials. Nineteen out of 22 ciprofloxacin-resistant Salmonella Typhimurium isolates were grouped into one PFGE cluster. Plasmid-mediated quinolone resistance determinant aac-(6')-Ib-cr was detected in 18 S. enterica isolates and 4 isolates also carried qnr alleles. Plasmid-mediated blaCTX-M-14-like genes were found in seven ceftriaxone-resistant isolates, and two isolates also exhibited reduced susceptibility to ciprofloxacin.

CONCLUSIONS

Based on these results, fluoroquinolones should not be used to treat the invasive Salmonella Typhimurium infections in this local community. The monitoring programme should stay vigilant for ceftriaxone-resistant S. enterica isolates with reduced fluoroquinolone susceptibility.

[Study on detection and identification of Salmonella species by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry]

OBJECTIVE

To detect and type Salmonella species by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS).

METHODS

With the optimized experimental conditions, a total of 88 Salmonella strains isolated from feces of patients suffered from diarrhea were applied onto MALDI-TOF-MS and the results were compared with those obtained from serotype profiles, drug-resistance profiles and PFGE profiles.

RESULTS

The results illustrated that all strains tested were divided into 15 types by MALDI-TOF-MS at the distance level of 100. Eighty-eight strains were further break into 44 subtypes, based on the results of MALDI-TOF-MS combined with those of drug-resistance profiles. All strains were classified as 46 subtypes and 64 subtypes in combination MALDI-TOF-MS with serotype profiles and PFGE profiles, respectively. These reveal that MALDI-TOF-MS is a good method in Salmonella species typing.

CONCLUSION

The detection and identification of foodborne pathogenic bacteria by MALDI-TOF-MS is of good characteristics of stability and reproducibility. It is a powerful tool in detecting and identifying foodborne pathogenic bacteria.

Ciprofloxacin-resistant Salmonella enterica serotype Typhimurium, China

We characterized 44 Salmonella enterica serotype Typhimurium isolates from Tongji Hospital outpatients in Wuhan, China, May 2002–October 2005. All 31 ciprofloxacin-resistant isolates were also resistant to >8 other antimicrobial drugs and carried >2 mutations in GyrA and 1 mutation in ParC. Class 1 integrons were identified in 37 isolates.

Novel immunocontraceptive targets in mammals: uterine secretions and the conceptus; a marsupial approach

We report the first immunocontraceptive trial in mammals using a uterine-secreted protein, the marsupial shell coat protein 4 (CP4). The marsupial shell coat, which surrounds the conceptus for 60–80% of gestation, is secreted by the uterine epithelium. Following immunization against glutathione S-transferase (GST)-CP4, the fertility of female common brushtail possums (n=6) was significantly reduced (P=0.000), and this reduction in fertility was positively correlated with the maximum GST-CP4 humoral immune response (P=0.025). Ultrastructural examination of the reproductive tract indicated that the cell-mediated immune response against GST-CP4 targeted the shell coat, the shell-free conceptus and the uterine glandular epithelium, thus preventing normal conceptus development and uterine secretion of shell coat proteins and nutrients. These results show that uterine-secreted proteins are promising immunocontraceptive targets, especially in pest mammal species, e.g. possum, rabbit and horse, that have uterine-secreted additions to embryonic coats, or that have late implantation requiring uterine nutrient provisioning from secretions.