Serotype Distribution, Antimicrobial Susceptibility, Multilocus Sequencing Type and Virulence of Invasive Streptococcus pneumoniae in China: A Six-Year Multicenter Study

Background:Streptococcus pneumoniae is an important human pathogen that can cause severe invasive pneumococcal diseases (IPDs). The aim of this multicenter study was to investigate the serotype and sequence type (ST) distribution, antimicrobial susceptibility, and virulence of S. pneumoniae strains causing IPD in China.Methods: A total of 300 invasive S. pneumoniae isolates were included in this study. The serotype, ST, and antimicrobial susceptibility of the strains, were determined by the Quellung reaction, multi-locus sequence typing (MLST) and broth microdilution method, respectively. The virulence level of the strains in the most prevalent serotypes was evaluated by a mouse sepsis model, and the expression level of well-known virulence genes was measured by RT-PCR.Results: The most common serotypes in this study were 23F, 19A, 19F, 3, and 14. The serotype coverages of PCV7, PCV10, PCV13, and PPV23 vaccines on the strain collection were 42.3, 45.3, 73.3 and 79.3%, respectively. The most common STs were ST320, ST81, ST271, ST876, and ST3173. All strains were susceptible to ertapenem, levofloxacin, moxifloxacin, linezolid, and vancomycin, but a very high proportion (>95%) was resistant to macrolides and clindamycin. Based on the oral, meningitis and non-meningitis breakpoints, penicillin non-susceptible Streptococcus pneumoniae (PNSP) accounted for 67.7, 67.7 and 4.3% of the isolates, respectively. Serotype 3 strains were characterized by high virulence levels and low antimicrobial-resistance rates, while strains of serotypes 23F, 19F, 19A, and 14, exhibited low virulence and high resistance rates to antibiotics. Capsular polysaccharide and non-capsular virulence factors were collectively responsible for the virulence diversity of S. pneumoniae strains.Conclusion: Our study provides a comprehensive insight into the epidemiology and virulence diversity of S. pneumoniae strains causing IPD in China.

Distribution of Puccinia striiformis f. sp. tritici races and virulence in wheat growing regions of Kenya from 1970 TO 2014

Stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst), is a major threat to wheat (Triticum spp.) production worldwide. The objective of this study was to determine the virulence of Pst races prevalent in the main wheat growing regions of Kenya, which includes Mt. Kenya, Eastern Kenya, and the Rift Valley (Central, Southern, and Northern Rift). Fifty Pst isolates collected from 1970 to 1992 and from 2009 to 2014 were virulence phenotyped using stripe rust differential sets, and 45 isolates were genotyped with sequence characterized amplified region (SCAR) markers to differentiate among the isolates and identify aggressive strains PstS1 and PstS2. Virulence corresponding to stripe rust resistance genes Yr1, Yr2, Yr3, Yr6, Yr7, Yr8, Yr9, Yr17, Yr25, Yr27 and the seedling resistance in genotype Avocet S were detected. Ten races were detected in the Pst samples obtained from 1970 to 1992, and three additional races were detected from 2009 to 2014, with a single race being detected in both periods. The SCAR markers detected both Pst1 and Pst2 strains in the collection. Increasing Pst virulence was found in the Kenyan Pst population, and that diverse Pst race groups dominated different wheat growing regions. Moreover, recent Pst races in east Africa indicated possible migration of some race groups into Kenya from other regions. This study is important in understanding Pst evolution and virulence diversity and useful in breeding wheat cultivars with effective resistance to stripe rust. Keywords: pathogenicity, Puccinia f. sp. tritici stripe (yellow) rust, Triticum aestivum

Virulence diversity of Phakopsora pachyrhizi in Mexico

Asian soybean rust (ASR), caused by the pathogen Phakopsora pachyrhizi, is the main disease of soybean in Mexico and worldwide, threatening its production. Knowledge about the virulence of Mexican rust populations (MRPs) is crucial in order to develop or introduce soybean cultivars with resistance to this disease. This study investigated the geographic variation on the virulence of 19 MRPs collected in two states of Mexico: Tamaulipas and Chiapas, using a set of 12 differential soybean varieties. The inoculation of MRPs showed that there was no large difference in virulence to differentials carrying Rpp4 or Rpp5 between MRPs from the two states. However, a contrasting phenotype was observed on Rpp1, Rpp1-b, Rpp2, and Rpp3. In the comparative analysis of virulence profiles with 157 and 20 P. pachyrhizi samples from South America and Asia, respectively, the MRPs from Chiapas form an isolated cluster, including the Tamaulipas state. The MRPs from Tamaulipas clustered with South American samples because of common characteristics, such as virulence to Rpp1 and avirulence to Rpp1-b. However, opposite reactions on Rpp1 and Rpp1-b that have been reported in major USA pathogen were also observed in Chiapas samples. A common trend between Chiapas and major USA pathogen was also observed in Rpp3. As the main conclusion of the present study, the 1,000 km distance between these two states in Mexico makes a big difference in the virulence of ASR.

Virulence and race structure of Puccinia graminis f. sp. tritici in Kazakhstan

Severe epidemics of wheat stem rust caused by Puccinia graminis f. sp. tritici (Pgt) have been observed in recent years in major spring wheat producing regions in Kazakhstan. However, information on the virulence structure and race composition of Pgt is currently not available. Stem rust samples were collected in 2015–2018 in three regions of Kazakhstan to determine the virulence diversity and race distribution in the Pgt populations. A total of 203 single-pustule isolates were derived and evaluated on the stem rust differential and supplemental lines and 38 races were identified. Among them, the races QHHSF and THMTF were found in all the regions and in all the years. The races RFRTF, RHMRF, TKRPF and MHCTC were the most common races in the Akmola and Kostanay regions, and the races LHCSF, QKCSF and LKCSF were only widely distributed in East Kazakhstan. The virulence complexity (i.e., number of Sr genes on which the races were virulent) ranged from 5 to 16, with about 40% of the races having 14 or more virulence. The stem rust resistance genes Sr11, Sr13, Sr22, Sr26, Sr31, Sr33 and Sr35 were found to confer resistance to all the races identified during the study period. Hence, these genes can be used as sources of resistance in wheat breeding programmes in Kazakhstan.