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Dieback disease caused by Erwinia mallotivora is a major threat to papaya plantation in Malaysia. The current study was conducted to evaluate the potential of endophytic lactic acid bacteria (LAB) isolated from papaya seeds for disease suppression of papaya dieback. Two hundred and thirty isolates were screened against E. mallotivora BT-MARDI, and the inhibitory activity of the isolates against the pathogen was ranging from 11.7-23.7 mm inhibition zones. The synergistic experiments revealed that combination of W. cibaria PPKSD19 and Lactococcus lactis subsp. lactis PPSSD39 increased antibacterial activity against the pathogen. The antibacterial activity was partially due to the production of bacteriocin-like inhibitory substances (BLIS). The nursery experiment confirmed that the application of bacterial consortium W. cibaria PPKSD19 and L. lactis subsp. lactis PPSSD39 significantly reduced disease severity to 19% and increased biocontrol efficacy to 69% of infected papaya plants after 18 days of treatment. This study showed that W. cibaria PPKSD19 and L. lactis subsp. lactis PPSSD39 are potential candidate as biocontrol agents against papaya dieback disease., Competing Interests: The authors have declared that no competing interests exist.

This study focuses on the potential of Pectobacterium carotovorum subsp. carotovorum (Pcc) strains producing bacteriocin as a tool to control potato soft rot disease. Thirty out of 48 purified bacterial strains were characterized as Pcc using specific PCR and phenotypic tests. The pathogenicity and pectate degrading assays were recorded positive for 13 strains. Bacteriocin typing clustered producers into three groups according to their antimicrobial spectra. Majority of the producers except strains of group II showed antibacterial activity toward relative genus and the role of UV or mitomycin C was inductive. In addition, none of the distant genus was sensitive to Pcc bacteriocins except Rhizobium vitis. Molecular detection of four bacteriocins including carotovoricin, carosin S1, S2 and carosin D was performed. Overall, 54.5% of group I, 47.3 and 70% of groups II and III strains carried carotovoricin and four strains harbored gene corresponding to carosin S1. According to our data divers antimicrobial patterns obtained by Pcc strains and existence of new bateriocines could be possible. Moreover, our findings recommended that direct application of P29 or expression of corresponding genes of Pog22 or P21 in a nonpathogenic strain as a biocontrol agent may improve soft rot disease control., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Biologically active compounds of spore-forming bacteria of Bacillus genus, which have antagonistic effect on opportunistic and pathogenic microorganisms, are characterized in the review. Information about known to date antibiotics and bacteriocins produced by Bacillus species is presented.

All strains of oral streptococci tested and specially those of Streptococcus mutans, Strep. sanguis and Strep. mitior produced more than one distinct bacteriocin-like substance with variable inhibitory activity on 20 indicator staphylococci. Inhibitory activity was comparatively higher on nasal strains of Staph. aureus and Staph. epidermidis than on strains of both species isolated from the mouth. Nineteen of 20 staphylococcal indicators were inhibited by 1-12 of the 12 effector streptococci. Sensitivity of nasal staphylococci to bacteriocins (frequency of positive inhibitory tests and total inhibition zone diameters) was significantly higher (P less than 0.001, chi 2 test and P less than 0.05, t test respectively) than that of oral ones. The sensitivity of nasal over oral Staph. aureus (P less than 0.001 and P less than 0.01) and of oral Staph. epidermidis over oral Staph. aureus (P less than 0.01 and P less than 0.05) was also significantly higher. The evaluation of variability of inhibitory patterns of bacteriocins produced by streptococci (p-typing), of sensitivity patterns of staphylococci to bacteriocins (s-typing) and of the significantly higher sensitivity of nasal over oral staphylococci to bacteriocins from the epidemiological and ecological viewpoints are discussed.

Sensitivity of 84 cultures of L. fermenti, 43 cultures of L. brevis, 13 cultures of L. buchneri and 2 cultures of L. cellobiosus to the effect of 39 types of bacteriocins produced by various species of lactobacilli was studied with the method of delayed antagonism. All the cultures of L. brevis, L. buchneri and L. cellobiosus and 65.5 per cent of the cultures of L. fermenti were sensitive to one or more such bacteriocins. The cultures of L. Fermenti, L. brevis, L. buchneri and L. cellobiosus were sensitive respectively to 37, 19, 16 and 9 types of the bacteriocins out of 39 types tested.

The relationship between 433 V. cholerae strains and 571 enterobacterial strains, isolated from different ecosystems, have been studied by the method of "delayed antagonism". The direct correlation between the virulence of V. cholerae and the width of the spectra of their antagonistic activity towards indicator bacteria was detected. The expediency of studies on the role of the vibriocinogenic factor in the survival of V. cholerae in different ecological systems is substantiated.

Antibacterial activity of 272 Erwinia strains was studied. It was found that 182 or 66.9 per cent of the strains were capable of producing spontaneously antibacterial substances belonging to the class of bacteriocins; 125 bacteriocynogenic strains were divided into 25 groups on the basis of their antibacterial spectrum similarity; 57 bacteriocynogenic strains were not included into any of these groups because of their significant heterogenicity with respect to the feature studied. It was shown that most of the strains inhibited viability of the bacteria of both its own and other species. Investigation of the antagonistic activity of the Erwinia strains with broad antibacterial spectra with respect to E. coli indicative for colicins gave negative results. The study of the Erwinia strains sensitivity to the antibacterial effect of the bacteriocynogenic cultures showed that 210 out of 272 cultures were sensitive to separate bacteriocins.

Capacity for production of bactericin was found in the spheroplasts of the strains of the rodent pseudotuberculosis microbe. The author named it as pseudotuberculocin. The bacteriocin production was not detected in the initial strains of the pseudotuberculosis microbe. Pseudotuberculocin differed in the antibacterial spectrum and morphology of the growth inhibition zones formed on the plates with the indicator strains from the pesticins produced by the strains of the plaque microbe of the marmot and sandword varieties respectively and the cultures of the plaque microbe from the Transcaucasian Upland, as well as from pesticins of the spheroplasts of these strains. Production of a pesticin differing from pesticins of the rod-like forms of these strains by an ability to inhibit the growth of the homologous indicators was shown in the spheroplasts of the plaque microbe of the marmot and sandword varieties. Sensitivity of the plaque microbe strains of the marmot and sandword varieties to the pesticins of the plaque microbe strains and pseudotuberculocin was noted. With an account of the difference in the activity of the tested pesticins and pseudotuberculocin against the strains of the Frederic collection it is recommended to use this property for identifications of pesticins and pseudotuberculocin.

A nutrient medium containing 0.7 per cent of lithium chloride was tested and Yersinia pestis inhibitor was detected in 83.3 per cent of the strains on the growth tufts of 8 indicator strains isolated from a homologous focus. Lowering the lithium chloride concentration in the medium up to 0.6 per cent promoted detection of the inhibitor in a larger number of the tested strains (93.3 per cent). But even on this medium none of the indicator strains formed overall growth tufts. The subcultures of the indicator strains resistant to lithium chloride formed overall growth tufts on agar plates with lithium chloride and were sensitive to the inhibitor of the tested strains from the central Caucasus. However, during storage they lost their sensitivity to the inhibitor which did not permit their use as the test cultures.

The paper describes Bacillus thuringiensis var. galleriae strains possessing a bacteriocin-like factor (factor K) which inhibits the cultures of a number of serotypes of Bac. thuringiensis. The K+ cultures exhibit no antibacterial effect on other gram-positive and gram-negative microorganisms. The maximal level of factor K is found by the 8--9th hour of cultivation. No correlation has been established between the strucutred elements in the preparations of K+ cultures and the antibacterial activity. Apparently, factor K can be transferred to other strains.