Proteomic assessment of resistance to the fumigant phosphine in the lesser grain borer, Rhyzopertha dominica (F.)

A previous publication compared a strain of the stored-grain pest beetle, Rhyzopertha dominica, resistant to the fumigant phosphine, with a susceptible strain using two-dimensional polyacrylamide gel electrophoresis. Certain proteins appeared to differ and the authors proposed that arginine kinase in particular might be used as a marker for the rapid monitoring of resistance in this species and other pests of stored grain. Here an expanded set of susceptible and resistant strains is surveyed using the two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) system. Of hundreds of spots only two showed a significant difference between the resistant and susceptible strains and the magnitudes of those differences were less than three-fold. Arginine kinase spots were identified but they did not differ significantly. The proposal that certain abundant proteins of R. dominica might be used as markers of phosphine resistance was not supported by the present study.     

Phosphine resistance in immature stages of a laboratory selected strain of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Responses to phosphine of immature stages of an adult-selected, phosphine-resistant strain of Tribolium castaneum (Herbst) were studied and compared with those of a phosphine-susceptible strain. Larvae (15 and 20-day old) pre-pupae and pupae (early-, mid- and late-) were examined and found resistant to phosphine. The highest resistances were present in early- and mid-pupae at levels much higher than those selected in the adults. Latent toxic effects were observed following treatment of all stages except 15-day larvae and were most pronounced with 20-day larvae.Respiration rates in a normal atmosphere were similar in the two strains on a body-weight basis and differed in terms of oxygen consumption per individual in accordance with the weight differences between the two strains. Normal respiration rates did not account for, or contribute towards, the observed tolerance differences between the two strains. The oxygen consumption of all examined stages of the resistant strain was reduced less by phosphine than that of the corresponding stages of the susceptible strain but the significance of this in terms of phosphine uptake is not known.     

Response of mixed-age cultures of phosphine-resistant and susceptible strains of lesser grain borer, Rhyzopertha dominica, to phosphine at a range of concentrations and exposure periods

Mixed-age cultures, containing all life stages, of a highly resistant strain (Strong-R) of lesser grain borer, Rhyzopertha dominica (F.), were exposed to a series of fixed concentrations of phosphine at a range of exposure periods at 25 °C. A susceptible strain and a less-resistant strain (Weak-R) were also tested. The aim was to characterise the resistant strain and determine if it could be controlled with phosphine. Times to population extinction (TPE) were recorded and lethal time (LT_99.9) values calculated. The relationship between exposure period t and phosphine concentration C for the resistant strains were: for Strong-R LT_99.9C^0.5457t=3.852 and TPE C^0.6105t=4.0404 and for Weak-R LT_99.9C^0.3553t=3.6521 and TPE C^0.4507t=3.4833. The results were used to define a range of minimum exposure period ×concentration protocols for control of the Strong-R populations. For example, at 1.0, 0.3, and 0.2 mg l⁻¹ complete control can be expected in 5, 10 and 14 days, respectively. This information will be used to recommend phosphine rates for field trial and eventual registration.     

Effect of diet on phosphine toxicity,rate of development and reproduction of the rice weevil Sitophilus oryzae (Linnaeus)

One of the loci responsible for strong phosphine resistance encodes dihydrolipoamide dehydrogenase (DLD). The strong co-incidence of enzyme complexes that contain DLD, and enzymes that require thiamine as a cofactor, motivated us to test whether the thiamine deficiency of polished white rice could influence the efficacy of phosphine fumigation against insect pests of stored grain. Three strains of Sitophilus oryzae (susceptible, weak and strong resistance) were cultured on white rice (thiamine deficient), brown rice or whole wheat. As thiamine is an essential nutrient, we firstly evaluated the effect of white rice on developmental rate and fecundity and found that both were detrimentally affected by this diet. The mean time to reach adult stage for the three strains ranged from 40 to 43 days on brown rice and 50–52 days on white rice. The mean number of offspring for the three strains ranged from 7.7 to 10.3 per female over a three day period on brown rice and 2.1 to 2.6 on white rice. Growth and reproduction on wheat was similar to that on brown rice except that the strongly resistant strain showed a tendency toward reduced fecundity on wheat. The susceptible strain exhibited a modest increase in tolerance to phosphine on white rice as expected if thiamine deficiency could mimic the effect of the dld resistance mutation at the rph2 locus. The strongly resistant strain did not respond to thiamine deficiency, but this was expected as these insects are already strongly resistant. We failed, however, to observe the expected synergistic increase in resistance due to combining thiamine deficiency with the weakly resistant strain. The lack of interaction between thiamine content of the diet and the resistance genotype in determining the phosphine resistance phenotype suggests that the mode of inhibition of the complexes is a critical determinant of resistance.     

Active exclusion of phosphine as a mechanism of resistance in Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)

A strain of Rhyzopertha dominica which is resistant to the fumigant phosphine, was found to absorb less radioactive phosphine than a susceptible strain. The non-absorption of phosphine was enhanced by increased temperature and carbon dioxide. Living resistant insects absorbed less toxin than dead insects, and metabolic detoxication did not appear to contribute to resistance. Since respiratory activity in the presence of the gas is known to be unaffected in the resistant insects, a resistance mechanism based on exclusion of toxic gas is proposed.     

The effect of diurnally interrupted doses of phosphine over four days on egg mortality of susceptible and resistant strains of Sitophilus oryzae (L.)

Phosphine concentrations in stored grain are uneven and can undergo cyclic fluctuations caused by diurnal changes in solar heat exchange and wind. Experiments were conducted to investigate the influence of daily concentration variations on insect mortality. Values of LT₅₀ and LT_99.9 are presented for Sitophilus oryzae eggs in response to a range of diurnally interrupted phosphine treatments over four days. Egg mortality was determined for three insect strains that varied in susceptibility to the fumigant, at concentrations that ranged from 0.75 mg/L to 3 mg/L for 32-8 h respectively, giving the same Ct product for all treatment combinations. Effects on mortality were analyzed in terms of accumulated phosphine exposure over 4 days of treatment, and in terms of the total elapsed time of treatment. Results were compared to those obtained from continuous treatments having equivalent Ct combinations. Treatments that were interrupted daily extend the total elapsed time required for a given level of mortality and that time increased as concentration increased and daily treatment time decreased. Values of LT_99.9 for a susceptible strain were 67.6 h and 103.6 h, and for a resistant strain were 133.6 h and 179.5 h at concentrations of 1 mg/L and 3 mg/L respectively. However, diurnal treatments were more efficacious than continuous treatments when only dosage time was measured. Values of LT_99.9 for the susceptible strain were 21.0 h compared with 33.8 h and 11.0 h compared with 17.7 h, and for the resistant strain were 35.2 h compared with 57.4 h and 22.2 h compared with 44.3 h at 1 mg/L and 3 mg/L respectively. The findings show that the level of mortality during interrupted treatment is mainly due to the additional time that the fumigant is absent and not a combined affect including insect recovery during the intervening periods. In fact, the dosage time is reduced by an apparent increase in phosphine toxicity.     

Mobility parameters of Tribolium castaneum and Rhyzopertha dominica populations with different susceptibility to phosphine

Phosphine (PH₃) is the most commonly used fumigant to protect stored products from arthropod infestations worldwide. Our knowledge about the behavioral differences between phosphine-resistant and -susceptible stored product pest populations is limited. This study evaluated differences in mobility and behavior of populations of two major stored product insects, Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.), which have different susceptibility to phosphine. In this regard, laboratory bioassays in Petri dish arenas were designed to determine if phosphine resistance has an impact on the walking and mobility behavior of adult beetles of both species. Results indicated that there were significant differences between resistant and susceptible populations for both species. Regarding velocity, R. dominica susceptible individuals moved faster than resistant ones. However, the resistant population showed reduced activity for several parameters tested compared to the susceptible population. Similar trends were also noted for T. castaneum. Knowledge of these parameters should be further utilized in management tactics, as resistant populations may behave in a different way in key management indicators such as trapping and sampling, as compared with susceptible ones.     

Fitness in a malathion resistant Tribolium castaneum strain; feeding,growth and digestion

Extensive historical use of malathion in grain stores has led to the universal development of resistant strains of the red flour beetle, Tribolium castaneum Herbst. Adaptation to insecticide stress often reduces general fitness. To investigate non-defensive attributes physiological and biochemical properties (that may underlie fitness) of a field-derived malathion-resistant strain (larval resistance factor of 490) were measured against those of a susceptible strain and also with susceptible T. confusum. Further inhibition in vitro of gut proteolysis was determined for the resistant and susceptible strains of T. castaneum.The weights of whole gut tracts of the susceptible T. castaneum strain and T. confusum were similar but the resistant strain had significantly lower weight and width of whole gut tract. The gut of the resistant strain had more, and more intense, electrophoretic protein staining bands. Food consumed through the life cycle was significantly less for the resistant strain. Inhibitors for cysteine proteases had less effect in vitro in the resistant strain than in the susceptible strain. An inhibitor for serine proteases had almost no effect on proteolysis in the resistant strain.The reduced gut dimensions and food consumed, together with lower larval protein, appear to indicate a fitness cost that may be associated with malathion resistance. However, this may be offset by enhanced gut proteins and a relative greater protein content of the adult stage. The latter may be related to the reported increased reproductive capacity of the resistant adult and consequent superior fitness, compared to the susceptible. The lowered response of the resistant strain to cysteine and serine protease inhibitors may interact with adaptations to dietary inhibition in cases where resistant strains need managing, if this result is confirmed to be widespread.     

Influence of malathion resistance status on survival and growth of Tribolium castaneum (Coleoptera: Tenebrionidae), when fed on flour from insect-resistant and susceptible grain rice cultivars

The effect of insecticide resistance on the potential for control of stored product insect pests based on plant resistance was evaluated. Flours made from three rice cultivars (cvs.) that showed resistance or susceptibility to feeding by Tribolium castaneum were studied, using two strains, resistant and susceptible to the organophosphate insecticide, malathion. Flours made from rough, brown and milled rice were used to help identify the locus of any cultivar resistance mechanisms. The insect-resistant (Dawn) and moderately resistant (Lebonnet) cvs. had fewer eggs laid and caused greater mortality of the insects than the susceptible cultivar (cv.) (IR8). For all cvs., flour from brown rice was the most suitable for insect survival, whereas the highest larval weights were found in milled and the lowest in rough rice flours. On the other hand, the highest mortality of the susceptible strain occurred in milled rice flours. The larvae resistant to malathion survived significantly better than those of the susceptible strain, when fed on flour from the insect-resistant cv. (Dawn). The cause of this positive interaction between the insecticide resistance status of T. castaneum and the grain resistance is not known. The mechanism of malathion resistance occurring in this strain is enhanced malathion-specific carboxylesterase activity but it is not known how this can confer survival benefits, when the insect feeds on flour from the resistant cv. These results could have practical implications for the efficacy of stored product pest control using varietal resistance in situations where insecticide resistance is prevalent.     

Effect of low temperatures on the rate of respiration and uptake of phosphine in different life stages of the cigarette beetle Lasioderma serricorne (F.)

Studies were undertaken to establish the effects of low temperatures on the rate of respiration in larvae and adults of a susceptible strain of the cigarette beetle Lasioderma serricorne. The results showed that there was a consistent decrease in the rate of respiration in L. serricorne with a decrease in temperature from 25°C to 5°C. The rate of respiration was slightly affected by circadian rhythm in adult beetles, but not in larvae.The levels of phosphine taken up by different life stages of the beetle were also determined using [³²P]-radiolabelled gas. A comparison between susceptible and phosphine resistant strains showed that the mechanism of resistance in L. serricorne involves a reduced uptake of the fumigant.The uptake of [³²P]-phosphine by different life stages of resistant L. serricorne declined with a decrease in temperature from 25°C to 5°C. Similarly, the uptake by susceptible L. serricorne decreased from 25°C to 10°C, but there was a comparatively higher uptake at 5°C and consequently a higher mortality at the end of the exposure. The significance of the findings in relation to control strategies is discussed.     

Antibiotic susceptibility of members of the Lactobacillus acidophilus group using broth microdilution and molecular identification of their resistance determinants

The range of antibiotic susceptibility to 13 antibiotics in 101 strains of the Lactobacillus acidophilus group was examined using the lactic acid bacteria susceptibility test medium (LSM) and broth microdilution. Additionally, microarray analysis and PCR were applied to identify resistance genes responsible for the displayed resistant phenotypes in a selection of strains. In general, narrow as well as broad unimodal and bimodal MIC distributions were observed for the Lactobacillus acidophilus group and the tested antimicrobial agents. Atypically resistant strains could be determined by visual inspection of the obtained MIC ranges for ampicillin, chloramphenicol, clindamycin, erythromycin, quinupristin/dalfopristin, streptomycin and tetracycline. For most of these atypically resistant strains underlying resistance determinants were found. To our knowledge erm(A) was detected in lactobacilli for the first time within this study. Data derived from this study can be used as a basis for reviewing present microbiological breakpoints for categorization of susceptible and resistant strains within the Lactobacillus acidophilus group to assess the safety of microorganisms intended for use in food and feed applications.     

Variation in the response of Callosobruchus maculatus (F.) to a resistant veriety of cowpea

A Nigerian cultivar of the cowpea has previously been identified as being less suitable than conventional varieties for the development of a local strain of C. maculatus (F.). The survival and duration of development of the immature stages of three strains of C. maculatus in the dried seeds of this cultivar were compared with the performance of the same strains of beetle on a susceptible variety. In all beetle strains, fewer larvae survived to produce adults, and the duration of development was significantly extended, in the resistant cowpea cultivar. A Brazilian strain produced fewest adults and a Nigerian strain had the longest mean development period. Combining all the data, it appeared that a strain from the Yemen Arab Republic was least influenced and that from Brazil most adversely affected by the resistant cowpea. Evidence is presented indicating that factors in both the cowpea seeds and the beetles themselves may contribute to the poorer performance of bruchids in the resistant as compared to the susceptible variety.     

From immobilization to recovery: Towards the development of a rapid diagnostic indicator for phosphine resistance

The aim of this work was to evaluate the insect mobility patterns of phosphine-resistant and -susceptible adults of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) after exposure to phosphine. Exposure bioassays were carried out at two concentrations, 1000 and 3000 ppm, while adults were observed every 15 min, for a total period of 90 min. During this observation interval, adults were visually classified as active (able to walk normally), partially immobilized (not able to walk, but showing a minimal movement), or completely immobilized (no visible movement). After the observation period, all adults were placed in a phosphine-free environment, and they again were classified as active, partially immobilized or completely immobilized. At 1000 ppm, the majority of adults of the susceptible T. castaneum population were quickly immobilized after a 15 min observation period, while in contrast, the majority of adults of the resistant T. castaneum population were still active after the termination of the 90 min interval. At 3000 ppm, the percentage of immobilized susceptible adults was increased at the 15 min observation period, while the majority of resistant adults were immobilized only after 90 min. In the post-exposure period, the vast majority of the susceptible adults were dead. In contrast, most resistant adults recovered, regardless of the concentration that had been exposed. The results of this study delineate major differences in movement in phosphine-resistant and -susceptible T. castaneum strains, and can be applied as a quick diagnostic bioassay for the evaluation of resistance to phosphine in stored product insects.     

Optimising indoor phosphine fumigation of paddy rice bag-stacks under sheeting for control of resistant insects

Three indoor, sheeted bag-stack fumigations of paddy rice using aluminium phosphide were undertaken in Guangdong Province, southern China. We measured the effect of two types of sheeting (polyvinylchloride [PVC] or polyethylene [PE]) and two types of floor sealing (clips or fixing into a slot with a rubber pipe) on phosphine concentration and retention. The aim was to test the feasibility of retaining fumigant at a sufficient concentration for long enough to control known resistant insect pests. Each stack was pressure tested and phosphine concentrations measured daily during the fumigation. Cages of test insects in culture medium, including resistant and susceptible strains, were placed inside each stack and could be observed through the clear sheeting. Highest concentrations for the longest period were obtained in a PVC-covered stack that included a ground sheet and wall sheets sealed to the floor with rubber pipes. A similar PVC-covered stack sealed to the floor with clips instead of pipe did not retain gas as efficiently and required re-dosing. A PE-covered stack, with no ground sheet but also with wall sheets sealed to the floor with pipe, produced an acceptable fumigation. Susceptible Rhyzopertha dominica were controlled in 2 days and the most resistant strain in 15 days. Resistant Cryptolestes ferrugineus survived until day 21. The paddy was still free of insect infestation 7 months later when the bag-stack was opened to mill the rice. Pressure half-lives correlated with gas concentration and retention. Sorption appeared to be a major limiting factor, reducing potential fumigant dosage by about 50%. The trials demonstrated the feasibility of sealing bag-stacks to a standard high enough to control all known resistant strains.     

Characterization of the quinolone resistance mechanism in foodborne Salmonella isolates with high nalidixic acid resistance

Sixteen Salmonella strains resistant to nalidixic acid isolated from kimbab, the most popular ready-to-eat (RTE) food in Korea, and chicken meat were selected for this study. The resistant strains were shown to have high minimal inhibitory concentrations (MICs) against nalidixic acid (512 ~ 4096 μg/mL). Among them, 4 Salmonella enterica serovar Haardt isolates showed multi-drug resistance (MDR) patterns with reduced susceptibility to fluoroquinolone (0.5 μg/mL of ciprofloxacin MICs). The mechanisms of quinolone resistance in the nalidixic acid resistant strains were characterized by PCR and sequence analysis. The presence of plasmid-mediated quinolone resistance (PMQR) genes and amino acid changes in the quinolone resistance determining region (QRDR) were investigated by PCR-based detection and sequencing, and the efflux pump inhibition test was also done using phe-arg-β-naphthylamide (PAβN). Although PMQR genes were not detected in any of the tested strains, the QRDR mutations were found in this study: single mutation in gyrA (Asp87Tyr, Asp87Gly, and Asp87Asn), double mutations in gyrA (Ser83Thr) and parC (Thr57Ser), and single mutation in parC (Thr57Ser). MICs of nalidixic acid were reduced by 2- to 32-folds by the efflux pump inhibitor, PAβN. Pulsed-field gel electrophoresis (PFGE) was carried out to confirm the epidemiological relationship between the nalidixic acid resistant strains. The PFGE patterns were classified into 6 groups at cutoff level of 70 ~ 100% correlation on the dendrogram. Some strains of serotype Haardt and Enteritidis showed several values of genomic identity in accordance with strains, sources, and isolation year. We suggest that point mutation on QRDR and efflux pump systems involved in antimicrobials had independent effects on drug-resistance regardless of bacterial genomic variation.     

Genetic diversity, antimicrobial resistance and toxigenic profiles of Bacillus cereus isolated from food in Brazil over three decades

Bacillus cereus is an ever-present problem. It is widely distributed in several environments such as soil and plants and is commonly isolated from food and additives. In this study we analyzed 97 foodborne B. cereus sensu stricto strains isolated in Brazil in the 1980's, 1990's and 2000's in order to investigate the genetic diversity (assessed by Rep-PCR), antimicrobial resistance and toxigenic profiles (presence of hblA, hblC and hblD; nheA, nheB and nheC as well as cytK, ces and entFM genes) of such strains. The majority of the strains (79, 81.4%) were β-hemolytic. The NHE complex was found in 82 strains (84.5%) and HBL complex was found in 61 (62.9%) strains. All strains were negative to ces. The cytK-2 gene was found in 44 (45.4%) strains. The predominant toxigenic pattern was type I (32, 33%) which included strains positive for all toxin genes but ces. Computer assisted cluster analysis of Rep-PCR profiles showed a high genetic diversity. Seven major clusters comprising two or more strains were found and cluster 1 was predominant (ten strains, nine of them showing 100% similarity). This cluster included strains isolated in the 1980's and the 1990's. Cluster analysis of Rep-PCR profiles based on decade of isolation, source, hemolytic pattern, toxigenic and antibiotic resistance patterns revealed a similar clustering pattern as found in the analysis including all strains. The inability to observe a predominant band pattern when Rep-PCR cluster analysis was based on decade of isolation suggests that this diversity has been maintained over time. All strains were susceptible to gentamicin. We detected resistance to tetracycline (11 strains showing intermediate resistance and nine completely resistant strains), clindamycin (ten intermediate strains) and vancomycin (one strain). Clindamycin resistance showed statistical association with strains isolated in 2000's. The predominant resistance pattern was type A (72, 72.2%) which included strains susceptible to all drugs tested. Our results suggest that the majority of the strains present in several types of food in Brazil pose a potential risk to cause food poisoning due to the high prevalence of toxin genes found in these strains. However, additional studies involving cytotoxicity tests and affiliation of these strains to phylogenetic groups based on molecular data would be useful to better evaluate this potential and could provide a more accurate indication of the risk.     

The cross-resistance spectrum of Sitophilus granarius (L.) (Coleoptera: Curculionidae) heterozygous for pyrethrin resistance

Dose-response data were obtained from the F₁ progeny of crosses between virgin Sitophilus granarius (L.) from pyrethrin-resistant and susceptible strains. These data were compared with data from the parental strains. The insects were tested with pyrethrins, bioresmethrin, malathion, pirimiphos-methyl, lindane, DDT and propoxur. The exposure method was confinement of the insects on filter papers impregnated with insecticide in oil. The pyrethrin-resistant strain showed resistance to all seven insecticides. The probit lines of the heterozygotes fell approximately half-way between those of the resistant and susceptible strains for all the compounds tested. R-strain males responded to lindane more slowly than did the females, whereas there was no significant difference in the rate of response of the sexes of the S-strain.     

Pulsed field gel electrophoresis (PFGE) analysis for multidrug resistant Salmonella enterica serovar Schwarzengrund isolates collected in six years (2000-2005) from retail chicken meat in Taiwan

Salmonella Schwarzengrund is one of the causative agents of human salmonellosis and animal infections. High prevalence of multidrug resistant strains of S. Schwarzengrund from chicken meat has been recently reported in Taiwan. With an attempt to see if such prevalence in chicken meat was due to the recirculation of S. Schwarzengrund strains in traditional marketplaces, a total of 173 S. Schwarzengrund strains isolated between 2000 and 2005 from 417 retail chicken meat samples purchased from Taipei, Taiwan were analyzed using pulsed field gel electrophoresis (PFGE) method. For XbaI and AvrII digested DNA, a total of 23 and 16 PFGE patterns, respectively, were obtained. When these patterns were combined, a total of 47 subtypes were obtained and the major subtypes were X3A2, X1A2 and X2A1. Since it was found that these major subtypes were repeatedly found for multidrug resistant strains collected from 2000 to 2005, we then collected the chicken meat isolates from central and southern Taiwan in 2006. These strains did not show similar major subtypes as those found in Taipei. Such results might also suggest that the repeated appearance of some major subtypes for S. Schwarzengrund strains isolated each year in Taipei was due to the recirculation of these strains in retail marketplace during these years.     

Field validation of phosphine efficacy on the first recorded resistant strains of Sitophilus granarius and Tribolium castaneum from the Czech Republic

This study first estimated the current state of phosphine sensitivity (using a knock-down/KT₁₀₀/Degesch kit) in Sitophilus granarius (23 strains) and Tribolium castaneum (8 strains) in Czech Republic grain stores. The resistance of S. granarius (21.7% resistant strains; coefficient of resistance KT₁₀₀ ranged from 0.5 to 2.3 among strains) was substantially lower and less frequent than that of T. castaneum (87.5% resistant strains; coefficient of resistance KT₁₀₀ ranged from 0.9 to 52.5 among strains). The phosphine efficacy of the laboratory and field (i.e., resistant) pest strains was validated during commercial fumigation when suboptimal tarpaulin sealing resulted in low-concentration phosphine exposure (Ct products ranged from 5.9 to 7.4 g*hr/m³). Although even low-dose fumigation led to 100% adult mortality of both laboratory and field strains of S. granarius and laboratory strains of T. castaneum, the mortality of the field strain of T. castaneum ranged from 47% to 95%. Larval emergence from the fumigated commodity samples with pest eggs was zero or near zero for laboratory strains, while 1.3–6.0 (S. granarius) and 63.7–80.00 (T. castaneum) field-strain larvae emerged per sample (100 g). This study shows that although a high proportion of the tested pest populations were still sensitive, several T. castaneum populations showed an elevated level of resistance that may decrease field fumigation efficacy, especially under suboptimal phosphine dosage conditions.     

Toxin profile, antibiotic resistance, and phenotypic and molecular characterization of Bacillus cereus in Sunsik

Sunsik, a ready-to-eat food in Korea, is comprised of various agricultural and marine products, and has been an important concern in Bacillus cereus food poisoning. The aim of this study was to investigate the toxin profiles, genotypic and phenotypic patterns as well as antibiotic resistance of B. cereus strains isolated from Sunsik. A subtyping method known as automated repetitive sequence-based PCR system (DiversiLab™) was used to assess the intraspecific biodiversity of these isolates. Thirty-five B. cereus strains were isolated from 100 commercial Sunsik samples, all of which harbored at least 1 enterotoxin gene. The detection rates of nheABC, hblCDA, cytK, and entFM enterotoxin gene among all isolates were 97%, 86%, 77%, and 100%, respectively. Most strains also produced corresponding enterotoxins such as HBL (83%) and NHE (94%). One strain (2.9%) carried the emetic toxin genes, including ces and EM1, and was positive for the HEp-2 cell emetic toxin assay. Most strains were positive for various biochemical tests such as salicin hydrolysis (86%), starch fermentation (89%), hemolysis (89%), motility test (100%) and lecithinase hydrolysis (89%). All isolates were susceptible to most antibiotics although they were highly resistant to β-lactam antibiotics. By using the automated rep-PCR system, all isolates were successfully differentiated, indicating the diversity of B. cereus strains present in Sunsik.