Different antibiotic susceptibility between antrum and corpus of the stomach,a possible reason for treatment failure of Helicobacter pylori infection

AIM:To assess whether antibiotic resistance varies between the antrum and corpus of the stomach of patients that are either Helicobacter pylori(H.pylori)therapy-naive or pre-treated.METHODS:H.pylori strains were isolated from antrum and corpus biopsies from 66 patients that received a diagnostic gastroduodenoscopy for variant clinical indications.Antimicrobial susceptibility to amoxicillin,clarithromycin,tetracycline,metronidazole,levofloxacin and rifabutin was tested with the E-test method on IsoSensitest agar with 10 vol%defibrinated horse blood.In patients with a different antibiotic susceptibility pattern between the isolates from the antrum and corpus,DNA fingerprinting via random amplified polymorphic DNA analysis was performed to detect differences among DNA patterns of H.pylori isolates.RESULTS:Primary,secondary and tertiary resistance to clarithromycin was 6.9%,53.8%and 83.3%,retrospectively.Metronidazole and levofloxacin resistance also increased according to the number of previous treatments(17.2%,69.2%,83.3%;13.8%,23.1%,33.3%).Tertiary resistance to rifabutin was detected in12.5%of patients.In none of the 66 patients a resistance against amoxicillin or tetracycline was detectable.Discordant antibiotic susceptibility between antrum and corpus isolates for different antibiotics was seen in 15.2%(10/66)of the patients.Two out of those ten patients were naive to any H.pylori antibiotic treatment.The remaining eight patients previously received at least one eradication therapy.DNA fingerprinting analysis revealed no substantial differences among DNA patterns between antrum and corpus isolates in the majority of patients suggesting an infection with a single H.pylori strain.CONCLUSION:Different antibiotic susceptibility between antrum and corpus biopsies is a common phenomenon and a possible explanation for treatment failure.Resistant H.pylori strains may be missed if just one biopsy from one anatomic site of the stomach is taken for H.pylori susceptibility testing.     

Molecular epidemiology and antimicrobial susceptibility of Campylobacter coli clinical isolates

Introduction

Campylobacter spp. is a major cause of acute bacterial diarrhea in humans worldwide, and C. coli is responsible for 10% of the cases.

Materials and methods

A study was made of the antimicrobial susceptibility using the E-test^®, and the clonal relationship using PCR-RFLP, of the flaA gene, as well as PFGE techniques on 43 C. coli clinical isolates.

Results

Only 49% and 2% of the isolates were susceptible to erythromycin and ciprofloxacin, respectively. Imipenem and clindamyicn, with 100% and 84% of the strains, respectively, being susceptible, were the most active antimicrobials. The PCR-RFLP of flaA gene technique grouped fourteen isolates into six clusters, while the PFGE technique grouped eleven isolates into five clusters.

Conclusion

Ciprofloxacin and erythromycin are not suitable for the treatment of C. coli infections. Clindamycin could be considered as a therapeutic alternative in cases of enteritis, while imipenem is the best alternative for extra-intestinal infections. Both PFGE and PCR-RFLP can be useful to detect clones.     

Potential consequences of essential drug shortages in Canada: Brain abscess due to Nocardia farcinica associated with dapsone prophylaxis for Pneumocystis jirovecii pneumonia

In 2012, Canadian pharmacies experienced a shortage of trimethoprim-sulfamethoxazole tablets. Drug shortages may result in unintended clinical consequences such as infection with pathogens against which the alternative medication is ineffective. This is highlighted in the present article, which describes a case of brain abscess due to Nocardia species that developed while receiving dapsone as an alternative for prophylaxis against Pneumocystis jirovecii pneumonia in a highly immune-suppressed patient. Clinicians should be cognizant of these issues when prescribing alternative agents.     

Antimicrobial susceptibility testing for Helicobacter pylori in times of increasing antibiotic resistance

The gram-negative bacterium Helicobacter pylori(H.pylori)causes chronic gastritis,gastric and duodenal ulcers,gastric cancer and mucosa-associated lymphoid tissue lymphoma.Treatment is recommended in all symptomatic patients.The current treatment options for H.pylori infection are outlined in this review in light of the recent challenges in eradication success,largely due to the rapid emergence of antibiotic resistant strains of H.pylori.Antibiotic resistance is a constantly evolving process and numerous studies have shown that the prevalence of H.pylori antibiotic resistance varies significantly from country to country,and even between regions within the same country.In addition,recent data has shown that previous antibiotic use is associated with harbouring antibiotic resistant H.pylori.Local surveillance of antibiotic resistance is warranted to guide clinicians in their choice of therapy.Antimicrobial resistance is assessed by H.pylori culture and antimicrobial susceptibility testing.Recently developed molecular tests offer an attractive alternative to culture and allow for the rapid molecular genetic identification of H.pylori and resistance-associated mutations directly from biopsy samples or bacterial culture material.Accumulating evidence indicates that surveillance of antimicrobial resistance by susceptibility testing is feasible and necessary to inform clinicians in their choice of therapy for management of H.pylori infection.     

Pasteurella species peritoneal dialysis-associated peritonitis: Household pets as a risk factor

BACKGROUND:

Pasteurella species are Gram-negative coccobacilli that are a part of the normal oropharyngeal flora of numerous domestic animals. They have been recognized as a rare but significant cause of peritonitis in patients undergoing peritoneal dialysis (PD). A consensus about management strategies for PD-associated peritonitis caused by Pasteurella species currently does not exist.

METHODS:

The microbiological database serving the Manitoba Renal Program was searched from 1997 to 2013 for cases of Pasteurella species PD-associated peritonitis, and charts were reviewed. PubMed was searched for case reports and data were abstracted.

RESULTS:

Seven new local cases and 30 previously reported cases were analyzed. This infection is clinically similar to other forms of PD peritonitis, with household pet exposure appearing to be the strongest risk factor. Cats are the most commonly implicated pet. Direct contact between the pet and the equipment was commonly reported (25 of 37 patients) but was not necessary for infection to develop. The mean duration of treatment was 15 days. Complication rates were low, with only 11% of patients requiring PD catheter removal. There was no mortality reported.

CONCLUSION:

Pasteurella species are a rare cause of PD-associated peritonitis that can be successfully treated with a two-week course of intraperitoneal antibiotics with a high likelihood of catheter salvage.     

Ethnicity association of Helicobacter pylori virulence genotype and metronidazole susceptibility

AIM:To characterise the cag pathogenicity island in Helicobacter pylori(H.pylori) isolates by analysing the strains’ vacA alleles and metronidazole susceptibilities in light of patient ethnicity and clinical outcome.METHODS:Ninety-five H.pylori clinical isolates obtained from patients with dyspepsia living in Malaysia were analysed in this study.Six genes in the cagPAI region(cagE,cagM,cagT,cag13,cag10 and cag67) andvacA alleles of theH.pylori isolates were identified by polymerase chain reaction.The isolates’ metronidazole susceptibility was also determined using the E-test method,and the resistant gene was characterised by sequencing.RESULTS:More than 90% of the tested isolates had at least one gene in the cagPAI region,and cag67 was predominantly detected in the strains isolated from the Chinese patients,compared with the Malay and Indian patients(P < 0.0001).The majority of the isolates(88%) exhibited partial deletion(rearrangement) in the cagPAI region,with nineteen different patterns observed.Strains with intact or deleted cagPAI regions were detected in 3.2% and 8.4% of isolates,respectively.The prevalence of vacA s1m1 was significantly higher in the Malay and Indian isolates,whereas the isolates from the Chinese patients were predominantly genotyped as vacA s1m2(P = 0.018).Additionally,the isolates from the Chinese patients were more sensitive to metronidazole than the isolates from the Malay and Indian patients(P = 0.047).Although we attempted to relate the cagPAI genotypes,vacA alleles and metronidazole susceptibilities to disease outcome,no association was observed.The vacA alleles were distributed evenly among the strains with intact,partially deleted or deleted cagPAI regions.Interestingly,the strains exhibiting an intact cagPAI region were sensitive to metronidazole,whereas the strains with a deleted cagPAI were more resistant.CONCLUSION:Successful colonisation by different H.pylori genotypes is dependent on the host’s genetic makeup and may play an important role in the clinical outcome.     

Molecular detection of Helicobacter pylori antibiotic resistance in stool vs biopsy samples

AIMTo compare (1) demographics in urea breath test (UBT) vs endoscopy patients; and (2) the molecular detection of antibiotic resistance in stool vs biopsy samples.METHODSSix hundred and sixteen adult patients undergoing endoscopy or a UBT were prospectively recruited to the study. The GenoType HelicoDR assay was used to detect Helicobacter pylori (H. pylori) and antibiotic resistance using biopsy and/or stool samples from CLO-positive endoscopy patients and stool samples from UBT-positive patients.RESULTSInfection rates were significantly higher in patients referred for a UBT than endoscopy (overall rates: 33% vs 19%; treatment-naïve patients: 33% vs 14.7%, respectively). H. pylori-infected UBT patients were younger than H. pylori-infected endoscopy patients (41.4 vs 48.4 years, respectively, P < 0.005), with a higher percentage of H. pylori-infected males in the endoscopy-compared to the UBT-cohort (52.6% vs 33.3%, P = 0.03). The GenoType HelicoDR assay was more accurate at detecting H. pylori infection using biopsy samples than stool samples [98.2% (n = 54/55) vs 80.3% (n =53/66), P < 0.005]. Subset analysis using stool and biopsy samples from CLO-positive endoscopy patients revealed a higher detection rate of resistance-associated mutations using stool samples compared to biopsies. The concordance rates between stool and biopsy samples for the detection of H. pylori DNA, clarithromycin and fluoroquinolone resistance were just 85%, 53% and 35%, respectively.CONCLUSIONDifferences between endoscopy and UBT patients provide a rationale for non-invasive detection of H. pylori antibiotic resistance. However, the GenoType HelicoDR assay is an unsuitable approach.     

Culture-guided treatment approach for Helicobacter pylori infection:Review of the literature

The progressive loss of efficacy of standard eradication therapies has made the treatment of Helicobacter pylori(H.pylori)more challenging than ever.Endoscopicguided antibiotic susceptibility testing had previously been suggested to guide treatment after failure of second-line therapies.However,its role has expanded over the years,in accordance with the current Maastricht Guidelines.Several authors have dealt with this topic,developing both efficacy trials and cost-effectiveness trials against resistant H.pylori infections as well as infections in nave patients.However,results are not homogeneous enough to provide definite advice,because antibiotic resistance is not the only reason for treatment failure.Moreover,the culture-guided approach is surrounded by many practical issues,such as the availability of both endoscopy units and microbiology laboratories,and the need for a standard of quality that cannot be satisfied everywhere.Finally,pre-treatment susceptibility testing should be partand not the only weapon-of a targeted,personalized strategy to overcome H.pylori infection.     

Molecular epidemiology of Brazilian Biomphalaria: A review of the identification of species and the detection of infected snails

The three vector species of Schistosoma mansoni in Brazil, Biomphalaria glabrata, B. tenagophila and B. straminea show different susceptibility levels to the trematode besides a wide geographical distribution. The identification of such molluscs is important to further understand the disease epidemiology. Considering the fact that morphological identification may become difficult or even impossible under particular circumstances, the use of molecular-based methods have permitted the generation of more consistent information concerning the population structure of Biomphalaria furthering knowledge on taxonomy and diagnosis of infection. We have developed methodologies in order to provide simultaneous species identification of the intermediate host and diagnosis of infection with S. mansoni.     

Bleaching susceptibility and mortality of corals are determined by fine-scale differences in symbiont type

Coral bleaching has been identified as one of the major contributors to coral reef decline, and the occurrence of different symbionts determined by broad genetic groupings (clades A–H) is commonly used to explain thermal responses of reef-building corals. By using Stylophora pistillata as a model, we monitored individual tagged colonies in situ over a two-year period and show that fine level genetic variability within clade C is correlated to differences in bleaching susceptibility. Based on denaturing gradient gel electrophoresis of the internal transcribed spacer region 2, visual bleaching assessments, symbiont densities, host protein, and pulse amplitude modulated fluorometry, we show that subcladal types C78 and C8/a are more thermally tolerant than C79 and C35/a, which suffered significant bleaching and postbleaching mortality. Although additional symbiont types were detected during bleaching in colonies harboring types C79 and C35/a, all colonies reverted back to their original symbionts postbleaching. Most importantly, the data propose that the differential mortality of hosts harboring thermally sensitive versus resistant symbionts rather than symbiont shuffling/switching within a single host is responsible for the observed symbiont composition changes of coral communities after bleaching. This study therefore highlights that the use of broad cladal designations may not be suitable to describe differences in bleaching susceptibility, and that differential mortality results in a loss of both symbiont and host genetic diversity and therefore represents an important mechanism in explaining how coral reef communities may respond to changing conditions.     

Antibiotic resistance and cagA gene correlation: a looming crisis of Helicobacter pylori

AIM: To determine antibiotic resistance of Helicobacter pylori (H. pylori) in Pakistan and its correlation with host and pathogen associated factors.METHODS: A total of 178 strains of H. pylori were isolated from gastric biopsies of dyspeptic patients. Susceptibility patterns against first and second-line antibiotics were determined and trends of resistance were analyzed in relation to the sampling period, gastric conditions and cagA gene carriage. The effect of cagA gene on the acquisition of resistance was investigated by mutant selection assay.RESULTS: The observations showed that monoresistant strains were prevalent with rates of 89% for metronidazole, 36% for clarithromycin, 37% for amoxicillin, 18.5% for ofloxacin and 12% for tetracycline. Furthermore, clarithromycin resistance was on the rise from 2005 to 2008 (32% vs 38%, P = 0.004) and it is significantly observed in non ulcerative dyspeptic patients compared to gastritis, gastric ulcer and duodenal ulcer cases (53% vs 20%, 18% and 19%, P = 0.000). On the contrary, metronidazole and ofloxacin resistance were more common in gastritis and gastric ulcer cases. Distribution analysis and frequencies of resistant mutants in vitro correlated with the absence of cagA gene with metronidazole and ofloxacin resistance.CONCLUSION: The study confirms the alarming levels of antibiotic resistance associated with the degree of gastric inflammation and cagA gene carriage in H. pylori strains.     

Achromobacter species endocarditis: A case report and literature review

Endocarditis due to Achromobacter species is a rare, yet serious, endovascular infection. Achromobacter species infective endocarditis is associated with underlying immunodeficiencies or prosthetic heart valves and devices. A case of prosthetic pulmonary valve endocarditis secondary to Achromobacter xylosoxidans subspecies denitrificans is described in the present report. This life-threatening infection was successfully treated with combined valve replacement and prolonged antibiotic therapy. A Medline/PubMed literature review of Achromobacter endocarditis was also performed. Achromobacter species are an uncommon, yet important, cause of nosocomial endocarditis. Given the significant associated morbidity and mortality, along with a high degree of intrinsic antibiotic resistance, Achromobacter species infective endocarditis remains a clinical treatment challenge.     

Edwardsiella tarda bacteremia. A rare but fatal water- and foodborne infection: Review of the literature and clinical cases from a single centre

BACKGROUND:Edwardsiella tarda bacteremia (ETB) can be a fatal disease in humans.OBJECTIVES:To determine the significant risk factors associated with death caused by ETB, and to examine the geographical, seasonal, environmental and dietary factors of the disease.METHODS:A retrospective, observational, case control study was performed. The PubMed MEDLINE and Japanese Medical Abstract Society (www.jamas.or.jp) databases were searched for ETB case reports and meeting abstracts. In additon, retrospective chart reviews of patients with ETB at the Tokyo Women’s Medical University Hospital (Tokyo, Japan) were conducted to evaluate the risk factors associated with death using multivariate analyses.RESULTS:The literature search yielded 46 publications, comprising 72 cases from the English (n=30), French (n=1), Spanish (n=1) and Japanese (n=14) literature. Five cases at the Tokyo Women’s Medical University Hospital were also included. Of the included 77 cases, the mean age was 61 years and 39% of patients were female; 77.2% of the cases occurred between June and November, and 45.5% were reported in Japan. Dietary factors (raw fish/meat exposure) were reported for 10.4% of patients and 12.9% reported environmental (ie, brackish water) exposure. The overall mortality rate was 44.6%; however, this rate increased to 61.1% for ETB patients with soft tissue infections. Liver cirrhosis was determined to be an independent risk factor associated with death (OR 12.0 [95% CI 2.46 to 58.6]; P=0.00213) using multivariate analyses.DISCUSSION:To our knowledge, the present analysis was the first and largest multi-language review of ETB. Clinical characteristics of ETB resemble those of Aeromonas, typhoid fever and Vibrio vulnificus infections, in addition to sharing similar risk factors.CONCLUSION:ETB should be categorized as a severe food- and waterborne infection, which results in high mortality for patients with liver cirrhosis.     

Anaerobic Bacteria as a Cause of Mycotic Aneurysm of the Aorta: Microbiology and Antimicrobial Therapy

This review summarizes the microbiology, and antimicrobial management of mycotic aneurysm of the aorta (MAA) due to anaerobic bacteria. Anaerobic bacteria are an uncommon but important cause of MAA. Most cases of anaerobic MAA are caused anaerobic gram-negative bacilli (mostly B. fragilis group), Clostridium spp. (mostly Clostridium septicum, and Propionobacterium spp. (mostly P. acnes). Clostridial infection is frequently associated with gastrointestinal or hematologic malignancy. A review of all the reported cases is presented. Treatment of MAA involving anaerobic bacteria includes the use of antimicrobial effective against these organisms.     

Surveillance of infection status of drug resistant Staphylococcus aureus in an Indian teaching hospital

Objective

To access nosocomial and community accounts of multidrug resistant strains of Staphylococcus aureus (S. aureus) isolated by surveillance in a teaching hospital, over a period of 30 months.

Methods

Clinical samples from nosocomial sources, i.e., wards and cabins, intensive care unit (ICU) and neonatal intensive care unit (NICU) sources, as well as community or outpatient department (OPD) sources of a hospital were used for isolating strains of S. aureus resistant to methicillin/oxacillin and vancomycin, over a period, November 2009-April 2012.

Results

Of a total of 1 507 S. aureus isolates, 485 strains from community and 1 022 isolates were from nosocomial sources; Out of 485 (100%) OPD S. aureus isolates, 390 (80.41%) were MRSA strains. Similarly, from wards and cabins of 564 (100%) isolates, 461 (81.73%) strains were MRSA; whereas of 458 (100%) isolates obtained from ICU and NICU, 363 (79.25%) strains were MRSA. It was ascertained with χ²-tests of independence that MRSA strains were equally distributed in “community” or “wards and cabins” or “ICU and NICU” sources, alike rest other drug-resistant S. aureus strains. Antibiotic sensitivity patterns of isolated strains with 16 antibiotics were ascertained. Out of 390 (100%) MRSA strains isolated from OPD, 80 (20.51%) were vancomycin resistant (VRSA) and 173 (44.35%) strains were moderately sensitive to vancomycin or called, vancomycin intermediate strains (VISA). Similarly, from nosocomial sources, out of 461 (100%) MRSA isolates obtained from wards and cabins, 110 (23.86%) strains were VRSA and 208 (45.11%) were VISA strains, whereas out of 363 MRSA isolates obtained from ICU and NICU, 61 (16.8%) VRSA strains and 164 (45.17%) VISA strains were found. A progressive increase of percent values of drug resistance to 16 antibiotics used for antibiotic profiling revealed its subtle infection dynamics.

Conclusions

This study revealed the appalling state of occurrence of MRSA and VRSA in a resource-limited setting. A progressive increase of percent values of drug resistance to 16 antibiotics used revealed its subtle infection dynamics.     

Unilateral incompatibility gene ui1.1 encodes an S-locus F-box protein expressed in pollen of Solanum species

Unilateral interspecific incompatibility (UI) is a postpollination, prezygotic reproductive barrier that prevents hybridization between related species when the female parent is self-incompatible (SI) and the male parent is self-compatible (SC). In tomato and related Solanum species, two genes, ui1.1 and ui6.1, are required for pollen compatibility on pistils of SI species or hybrids. We previously showed that ui6.1 encodes a Cullin1 (CUL1) protein. Here we report that ui1.1 encodes an S-locus F-box (SLF) protein. The ui1.1 gene was mapped to a 0.43-cM, 43.2-Mbp interval at the S-locus on chromosome 1, but positional cloning was hampered by low recombination frequency. We hypothesized that ui1.1 encodes an SLF protein(s) that interacts with CUL1 and Skp1 proteins to form an SCF-type (Skp1, Cullin1, F-box) ubiquitin E3 ligase complex. We identified 23 SLF genes in the S. pennellii genome, of which 19 were also represented in cultivated tomato (S. lycopersicum). Data from recombination events, expression analysis, and sequence annotation highlighted 11 S. pennellii genes as candidates. Genetic transformations demonstrated that one of these, SpSLF-23, is sufficient for ui1.1 function. A survey of cultivated and wild tomato species identified SLF-23 orthologs in each of the SI species, but not in the SC species S. lycopersicum, S. cheesmaniae, and S. galapagense, pollen of which lacks ui1.1 function. These results demonstrate that pollen compatibility in UI is mediated by protein degradation through the ubiquitin–proteasome pathway, a mechanism related to that which controls pollen recognition in SI.Self-incompatibility (SI) in Solanum and other Solanaceae is the S-RNase–based, gametophytic type, in which S-specificity is determined by S-RNases in the pistil (1) and S-locus F-box proteins (SLFs) in pollen (2). F-box proteins, together with Skp1 and Cullin1 proteins, are components of SCF-type (Skp1, Cullin1, F-box) ubiquitin E3 ligases that mark target proteins for degradation by the 26S proteasome (3, 4). The ubiquitin–proteasome pathway controls the pollen compatibility phenotype in SI (5). In the “collaborative non–self-recognition” model (6), the S-locus encodes multiple SLF proteins that together recognize different sets of S-RNases. In a compatible pollination, the SLF/S-RNase interaction leads to protection of pollen tubes against cytotoxic S-RNase, whereas in incompatible pollinations, a failure to recognize self–S-RNase results in pollen tube arrest. In addition, modifier genes, such as those encoding HT-B, NaStEP, and 120-kDa proteins in the pistil, and CUL1 and SSK1 proteins in pollen, are required for SI function but do not confer S-specificity (7–11).Unilateral incompatibility (UI) is a reproductive barrier related to SI in which pollen from one species or population is rejected on pistils of a related species or population, whereas in the reciprocal crosses, no pollen rejection occurs. Pollen of SC species or populations is almost always rejected on pistils of related SI species or populations, whereas in the reciprocal crosses (SC pollinated by SI), pollen rejection rarely occurs. This unidirectional pattern of pollen rejection is referred to as the “SI × SC rule” (12). Although the mechanisms of pollen recognition and rejection by UI are complex (13), several SI factors, including S-RNase, CUL1, and HT, also function in UI (8, 14, 15).Cultivated and wild tomatoes provide a powerful model system to study the mechanisms of reproductive barriers in the Solanaceae (16). They display wide variation in mating systems, both between and within species (17). Cultivated tomato, S. lycopersicum, is SC and accepts pollen of its SI or SC wild relatives; conversely, pollen of S. lycopersicum is rejected by pistils of the SI species. Three other red- or orange-fruited species, S. cheesmaniae, S. galapagense, and S. pimpinellifolium, are bilaterally cross-compatible with each other and with S. lycopersicum. There are notable exceptions to SI × SC rule in the tomato clade (18). One is that pollen of all of the red/orange-fruited species (SC) are rejected on pistils of the SC green-fruited species. Another exception is that pollen of some SC biotypes of SI species are compatible on pistils of conspecific SI populations. Therefore, pollen rejection is complex and likely involves more than one mechanism (13). The ability to reject tomato pollen is dominant in interspecific F₁ hybrids between cultivated tomato and related wild SI species (i.e., SC × SI hybrids), although pollen tube arrest occurs lower in the style of hybrids, suggesting that expression of the pistil side barrier is weakened (19). Allotriploid hybrids comprised of two genomes from S. lycopersicum (SC) and one genome from S. lycopersicoides (SI) reject tomato pollen tubes lower in the style than corresponding diploid hybrids (19).We previously reported that two pollen factors from S. pennellii, ui1.1 and ui6.1, are required and sufficient to overcome the UI barrier on allotriploid S. lycopersicum × S. lycopersicoides hybrids (19, 20). These two factors are not sufficient for compatibility on diploid S. lycopersicum × S. lycopersicoides hybrids (19). The ui6.1 locus encodes a pollen specific Cullin1 (CUL1) protein (21) that functions in pollen recognition by UI and SI (8). Pollen lacking ui6.1 are incompatible on pistils expressing active S-RNases, but compatible on pistils expressing a mutant S-RNase lacking RNase activity (8). This observation suggested that ui6.1—and by extension, ui1.1—is required for pollen resistance to S-RNase–based rejection in the pistil. Interestingly, neither ui6.1 nor ui1.1 is required for resistance to S-RNase itself, because tomato pollen is fully compatible on pistils expressing active S-RNase in the absence of a functional HT protein (15, 22). Thus, both SI and UI require multiple pollen and pistil factors. The ui1.1 locus is located at or near the S locus region on the short arm of chromosome 1, suggesting it might encode one or more SLF proteins. The goal of the present research was to isolate ui1.1 from S. pennellii to elucidate the nature of pollen rejection by UI and its relationship to SI.