Bacteriocinogenic properties of Staphylococci isolated from the oral cavity

Two hundred ninety two staphylococcal strains were isolated out of 130 saliva samples taken from children and adults, among which 116 were coagulase-positive and 176 coagulase negative. Bacteriocinogenic activity against Staphylococcus aureus strain Oxford 209P was found in 13 (4.5%) of the strains only. On the other hand, when a set of 15 sensitive staphylococcal strains selected by cross checking was used for the study 260 (89.0%) strains were found to be bacteriocinogenic. It was found that a higher percentage of coagulase-positive staphylococcal strains is sensitive to staphylococcins than of coagulase-negative strains. However, mean zone of inhibition is smaller in the case of former than of the latter strains. It was shown, that in the case of active strains a positive correlation exists between a percentage of coagulase-positive and negative strains inhibited by them and also between a percentage of all inhibited strains and a mean diameter if the growth inhibition zone. Simultaneous occurrence in saliva of two or more staphylococcal strains was found in 106 persons examined. In 93.4% of those cases coexisting strains did not show antagonistic properties: in remaining 6.6% despite of the number of simultaneously existing strains in oral cavity only one strain showed antagonistic properties against the remaining strains.     

Tests for studying invasive properties of selected Proteus mirabilis strains]

Proteus mirabilis is an important pathogen of the urinary tract infections (UTI). Lipopolysaccharide (LPS, endotoxin) is one of the pathogenic factors of pathogenicity of these bacteria. In this paper we described the invasion of L929 mouse fibroblasts by P. mirabilis strains, classified into the O10, O23, O30, O43 serogroups. The maximal invasiveness was observed between 4-6 hours of incubation of the tested cells with bacteria. The cytotoxic effect slightly increased with the incubation time, probably as a result of the production of HpmA hemolysin. Incubation of L929 fibroblasts with LPS led to decrease of bacterial invasiveness. We observed that with the time of incubation of L929 cells with LPS (2-22 h), the invasiveness decreased (longer incubation time with LPS--weaker penetration).     

Bacteriocinogenic plasmids of Bacillus thuringiensis

When strains of Bacillus thuringiensis v. morrisoni or v. darmstadiensis were plated on solid medium, the appearance of oligosporogenic (Ospo) mutants and bacteriocin non-producing clones (Thc-) was observed. The comparative analysis of the plasmid content of original and mutant strains revealed that the appearance of Ospo and Thc- phenotypes correlated with the loss of certain plasmids.     

Purification and some properties of beta-lactamases from Proteus rettgeri and Proteus inconstans

Two beta-lactamases were isolated from strains of Proteus species and purified, one from a strain of P. rettgeri and the other from a strain of P. inconstans. Each enzyme preparation gave a single protein band on polyacrylamide gel electrophoresis. Molecular weights of P. rettgeri and P. inconstans enzymes were found to be 42,000 and 43,000, and their isoelectric points pH 8.7 and 8.6, respectively. The two enzymes presented typical cephalosporinase profiles. Cefmetazole (CS-1170) and cefoxitin, both cephamycin antibiotics, not only resisted hydrolysis by both of the enzymes, but also inhibited their activities competitively. Rabbit antiserum against purified P. rettgeri enzyme inhibited the activity of both purified and crude enzyme preparations from other strains of P. rettgeri so far tested. None of the beta-lactamases produced by other species of Proteus including P. inconstans was inhibited by the antiserum, thus showing that the purified cephalosporinase was of the species-specific types. The enzymological properties of the preparations were compared with those of beta-lactamases derived from other gram-negative enteric bacteria.     

Bacteriocinogenic properties and in vitro probiotic potential of enterococci from Tunisian dairy products

The aim of this study was to isolate new bacteriocinogenic strains with putative probiotic potential from various Tunisian fermented milks. A total of 44 Gram-positive catalase-negative isolates were colony-purified and screened for antimicrobial activity. Of inhibitory isolates, four were identified as Enterococcus durans and one as Enterococcus faecalis using 16S rRNA gene sequence. The five strains were sensitive to penicillin G, all aminoglycosides tested, to the vancomycin, tetracycline, and chloramphenicol, and E. durans 42G and E. faecalis 61B were resistant to erythromycin. The antimicrobial substances were sensitive to proteolytic enzymes and had good biochemical stability. E. durans 61A showed a good resistance to gastric and small intestinal secretions, but were more sensitive to the duodenal conditions. Considering the safety and the stability under simulated gastrointestinal tract, it appears that the bacteriocinogenic strain E. durans 61A is a good candidate for its application as novel probiotic strain in the food industry.     

The Bacteriocinogenic Potential of Marine Microorganisms

Russian Journal of Marine Biology - One of the modern antibacterial strategies to control various infectious pathogens in agriculture, veterinary medicine, and the food industry is the use of...     

Mechanisms of Proteus resistance to chloramphenicol]

Data on chloramphenicol sensitivity of clinical Proteus strains isolated within 1970--1975 and some mechanisms of their resistance to this antibiotic are presented. It was found that most of the Proteus strains (62.82 +/- 2.15 per cent) were resistant to chloramphenicol. 75 per cent of the isolates had resistance of transmissive character. Resistance of the Proteus cultures to chloramphenicol was not a stable feature and was lost during storage under laboratory conditions. Direct correlation between stability of the antibiotic resistance in the Proteus, the resistance level and the period of the culture storage was found. It was shown that the transmissive resistance to chloramphenicol in the Proteus cultures was due to synthesis of a highly active constituitive chloramphenicol-inactivating enzyme. Direct relation between the Proteus resistance level to chloramphenicol and the rate of the enzyme synthesis was noted. A number of the Proteus strains phenotypically sensitive to this antibiotic was capable of its inactivation. Still, the activity of the enzyme was low. The rate of the enzyme synthesis and the level of the acquired resistance in the chloramphenicol resistant mutants depended on the presence or absence of the enzyme in the cells of the initial sensitive strain. The capacity for chloramphenicol accumulation in a number of the chloramphenicol resistant mutants of the Proteus was decreased.     

Bacteriocinogenic highly antagonistic strains of lactobacilli

Ability to secrete bacteriocines and microcines was studied in 25 cultures of lactobacilli isolated from intestine of healthy children. Sixteen (64%) of them produced microcines with wide spectrum of antagonistic activity. Susceptibility of microcines-secreting cultures to antibacterial preparations, different dilutions of hydrochloric acid and bile was studied along with their acid-producing ability. Five strains without DNA-se, RNA-se, gelatinase, lecitinase and caseinolytic activity were selected from Sixteen microcines-producing cultures. Three of the selected strains carried plasmid DNA and two didn't have plasmids. Bacteria were characterized by tolerance to hydrochloric acid and bile - minimal inhibitory concentrations for them were 1,25 and 10% respectively. Strains without plasmids were susceptible to majority of wide-spectrum antibiotics and resistant to fluorochinolones. Microcines-producing lactobacilli with wide spectrum of antagonistic activity against pathogenic and conditionally pathogenic microorganisms and tolerance to physiological concentrations of hydrochloric acid and bile have a potential to be used in manufacturing of probiotics.     

Regulation of catalase synthesis in Proteus mirabilis]

During the log-phase growth of Proteus mirabilis the specific activity of catalase decreases, while at the beginning of or during the stationary phase an increase takes place which is abolished by inhibitors of nucleic acid or protein synthesis. Glucose in the culture medium has no appreciable effect on the level of enzyme synthesis nor does the passage of bacteria to anaerobiosis bring any noticeable change. Successive additions of hydrogen peroxide up to weak final concentrations (0.2--0.5 mM) stimulate catalase synthesis. Determination of the enzyme in vivo reveals but a weak proportion of the total catalase which can only be titrated after the breakdown of cells. The titrable enzyme in vivo represents, as an order of magnitude, the activity found associated with the cell wall, in an easily released form after the mechanical separation of the inner and outer membranes. Thus, bacteria can act upon exogenous peroxide only through a peripheral catalase while they possess in a masked form an important reserve of cytoplasmic enzyme.     

Beta-lactamase activity of bacteria of the genus Proteus]

beta-Lactamases of Proteus and their role in the mechanism of the microbe resistance to penicillins and ceporin were studied. It was found that the beta-lactamase of Proteus had low activity and were produced by both beta-lactamide resistant and sensitive clinical strains of Proteus. The resistant cultures of Proteus produced enzymes more frequently (3.4--5 times) than the sensitive ones. The synthesis of beta-lactamase in the clinical Proteus strains was inducable. The high induction coefficient was achieved only in the presence of high concentrations of the inductor. No significant dependence of the culture sensitivity level of ampicillin and ceporin on the induction level was observed. The most significant part of the constitutive enzyme in Proteus was intracellular, while that of the inducable enzyme was extracellular. No correlative dependence between the culture resistance levels to penicillins and ceporin and the enzyme activity was noted. The beta-lactamase activity was not found in the transconjugants with the in vitro acquired R-factor controlling the ampicillin and ceporin resistance, as well as in the resistant mutants selected on the media with increasing concentrations of the above antibiotics. Induction of beta-lactamase synthesis was not found in these strains either. The ability of Proteus to synthesize beta-lactamase can be lost on the strain storage under laboratory conditions which was not always accompanied by reduction of the culture sensitivity to ampicillin and ceporin. The enzymatic destruction of beta-lactamides was not the main mechanism of Proteus resistance to the above antibiotics.     

Bacteriocinogenic activity of lactobacilli from fermented sausages

During the screening of the inhibitory activity of 254 strains of lactobacilli isolated from fermented sausages at different times of ripening, 22% of the strains showed inhibition that was not related to acid or hydrogen peroxide, towards one or more indicator strains. Not all the strains were capable of secreting the inhibitory compound in the supernatant fluid. The characterization of the inhibitory compound from three strains showed that they were bacteriocins with a bactericidal mode of action and a molecular weight exceeding 10000 Da. Lactobacillus plantarum CTC 305, CTC 306 and Lact. sake CTC 372 inhibited Listeria monocytogenes. Lactobacillus sake CTC372 was cured of two plasmids of 84.8 kbp and 41.3 kbp, losing the production and the immunity of a bacteriocin as well as the ability to ferment lactose.