فهرست مطالب mohammadreza afradi

Despite advances in oral health and dental industry, tooth decay remains one of the most common oral diseases. One of the new methods to combat dental plaque, which is the main cause of caries, is using specific lytic bacteriophage. This study aimed to investigate the effect of isolated specific lytic phage against growth and biofilm inhibition of Streptococcus mutans and Streptococcus sanguinis isolated from decayed dental plaque samples.

In this descriptive cross-sectional study, dental plaque samples were cultured in MSA-specific medium to isolate S. mutans and S. sanguinis. Suspicious isolates were examined by biochemical tests and finally confirmed molecularly by PCR. The ability to form biofilm was measured by crystal violet colorimetry on a microtiter plate. Lytic bacteriophage was isolated from urban raw sewage using double layer agar method and phage morphology was examined by TEM electron microscopy. The effect of lytic phage on the growth of S. mutans and S. sanguinis was measured by agar spot and well diffusion and its inhibition effect on biofilm was assayed by microtiter plate method.

Out of 150 plaque samples, S. mutans and S. sanguinis strains were isolated from 65 (43.33%) and 40 (26.67%) samples, respectively. S. mutans isolates showed stronger biofilm formation (OD= 0.43). The results of TEM showed lytic bacteriophage belonging to Siphoviridae family with a good inhibitory effect on the growth of S. mutans and S. sanguinis that was able to inhibit biofilm formation up to 96%.

Due to the small size of the phage particles that can have good penetration power to enter the biofilm layers, it can be concluded that the phage has the ability to fight dental plaque.

Dental plaque is a biofilm that is formed on the surface of the tooth. Carious lesions are caused by inappropriate ecological changes in microbial flora of the plaque biofilm. In this study, the effect of Lactobacillus casei bacteriocin, isolated from dairy products, was investigated on Streptococcus salivarius biofilm formation.

In this experimental study, MRS Broth and MRS Agar medium were used to isolate three strains of Lactobacillus casei probiotic from milk samples under microaerophilic conditions. The initial identification of Lactobacillus casei was performed by sugar fermentation and other biochemical tests. Then, 16SrRNA encoding gene was confirmed by PCR and sequenced. At last, Bacteriocin was isolated by ammonium sulfate sedimentation and its molecular weight was measured by SDS-PAGE and the antimicrobial activities were investigated. The Streptococcus salivarius were isolated from dental plaque and phenotypically and biotypically identified. Molecular confirmation of the isolates was performed using gtfK specific gene by PCR. The ability to form Streptococcus salivarius biofilm and the effect of bacteriocin on biofilm formation were measured by microtiter plate.

After partial purification of Lactobacillus casei probiotic from dairy products, two LC3 and LC1 protein samples formed bands (35-40 kDa and about 75 kDa, respectively). The supernatant fluid from the cultivation of Lactobacillus casei and bacteriocins showed antibacterial effects against Streptococcus salivarius isolates from dental plaque and the formation of biofilm by this bacterium.

According to this study, bacteriocin and supernatant fluid from Lactobacillus casei cultures could inhibit the growth of Streptococcus salivarius and also reduced biofilm formation, so, it could be used in oral care products.

Rotational use of antibiotics can decrease antibiotic resistance in Staphylococcus aureus strains. The present study aimed to evaluate the alteration of oxacillin resistance in methicillin-resistant Staphylococcus aureus (MRSA) strain carrying SCCmec III cassette in long-term evolutionary experiments in an antibiotic-free medium.

In a cross-sectional study, 10 MRSA isolates were identified between September to December 2018 by conventional microbiology methods from clinical isolates of a university hospital. Then, SCCmec typing was carried out using Multiplex PCR. One strain was included in the evolutionary experiment as ancestor and was cultivated for up to 900 generations. Minimum inhibitory concentration (MIC) of oxacillin of the evolved strains was evaluated. The selected strains were compared with the ancestral strain in terms of growth characteristics such as generation time and competitive cultivation.

Out of ten MRSA isolates, six and four were found to harbor SCCmec type III and SCCmec type IV, respectively. One strain with SCCmec III was randomly selected as ancestral strain. The ancestor was resistant to oxacillin while the evolved strains were susceptible. Generation times in the evolved strains were 6-8 minutes shorter than those in the ancestral strain. The evolved strains, with the ratio of 1% in competition experiment, accounted for 20-48% of the final population.

Compared to the ancestor, the evolved strains presented higher fitness in the oxacillin-free environment. The current study indicates the powerful effect of antibiotic rotation strategy on reducing methicillin resistant MRSA.