Background: Bacterial resistance to beta-lactam is a major problem in all developed and developing countries. The genera of Klebsiella and Enterobacter are associated with opportunistic and nosocomial infections. All beta-lactamase genes can cause dissemination of resistance to beta-lactams. Objectives: The present study aimed to investigate the phenotypic detection of beta-lactamases in Enterobacter and Klebsiella species isolated from clinical specimens. Materials and Methods:This cross-sectional study was performed on 59 Klebsiella spp. and 49 Enterobacter spp. isolated from clinical samples. They were confirmed using API 20E. These bacteria were evaluated for the production of extended-spectrum beta lactamase (ESBL), metallo-beta-lactamase (MBL) (IMP-1), and the pAmpC and iAmpC enzymes. This was done using the Clinical and Laboratory Standards Institute (CLSI) method, 2-mercaptopropionic acid, the cefoxitin method, and the use of imipenem as an enzyme inducer, respectively. Mask-ESBL production was also identified, using different concentrations of 3-amino-phenyl boronic acid compound. Data were analyzed with SPSS version 22. Results: In total, 38 (64.4%) Klebsiella spp. and 41 (83.7%) Enterobacter spp. produced at least one type of beta-lactamase. AmpCproducing Enterobacter spp. (71.4%), and ESBL-producing Klebsiella spp. (42.4%) had the highest prevalence of beta-lactamase types in each genus. There were two bacteria in both types that were resistant to all antibiotics without producing any type of beta-lactamase. Conclusions: According to our findings, it is necessary to pay special attention to ESBL production in Klebsiella spp., while in Enterobacter spp., it is essential to search for AmpC production (chromosomal and plasmid). In addition, the genotypic evaluation of beta-lactamase variety in these bacteria may be necessary in different geographical areas.

Context: One of the common oral bacterial infectious diseases is dental caries. Control of dental plaque formed by Streptococcus mutans and Streptococcus sobrinus leads to prevention and treatment of caries. Chitosan (1-4, 2-amino-2-deoxy-b-D-glucan), a deacetylated derivative from chitin, is an antimicrobial polysaccharide that exerts broad-spectrum activity against pathogenic bacteria and has been suggested as a preventive and therapeutic material for dental caries. Aim: The aim of this investigation is whether chitosan has effective antimicrobial and antibiofilm properties against common cariogenic microorganisms. Materials and Methods: The effect of 0.019–5 mg/ml of high-molecular-weight (HMW) and low-molecular-weight (LMW) chitosan on S. mutans and S. sobrinus was evaluated, and minimal inhibitory concentration (MIC) and minimal bactericide concentration (MBC) were determined. In addition, the effects of HMW and LMW of chitosan on bacterial adhesion to surfaces and biofilm formation were assayed by tube method. Results: The results showed that chitosan is capable of inhibiting S. mutans and S. sobrinus growth ( P = 0.001). MIC of HMW chitosan for S. mutans and S. sobrinus was 0.62 mg/mL and MIC of LMW chitosan for S. mutans and S. sobrinus was 0.62 mg/mL, 1.25 mg/mL, respectively. MBC of HMW chitosan for S. mutans and S. sobrinus was 1.25 mg/mL, respectively, and MBC of LMW chitosan for S. mutans and S. sobrinus was 1.25 and 2.5 mg/ml, respectively. On the other hand, HMW chitosan was more effective than LMW chitosan. In addition, S. mutans showed equal MIC and MBC values for both MWs chitosan, but S. sobrinus was more resistant to LMW chitosan. Regarding biofilm growth, chitosan inhibited S. mutans and S. sobrinus adhesion and biofilm formation. The results of tube test showed weak adherence and biofilm formation in concentration of 0.312 and 0.625 mg/ml, but 1.25 and 2.5 mg/ml concentrations of both MWs could completely inhibit biofilm formation. Conclusion: These results display the potential of chitosan to be used as an effective antibacterial and antibiofilm agent for oral hygiene and health care.

Infective endocarditis (IE) is an important clinical disease in children with a mortality rate of 11.6%. Prophylaxis with antibiotics is one of the most commonly used methods in children at risk of IE; therefore, the evaluation of antibiotic resistance seems necessary in view of its increasing trend. This study aimed to determine the antibiotic susceptibility pattern of oral viridans group streptococci (VGS) isolated from the dental plaque of children at risk of IE. Fifty-one plaque samples were obtained from children aged 3 to 12 years old in the period from April to July 2018. Samples were obtained with sterile swabs and were transferred to the laboratory in Brain Heart Infusion (BHI) Broth. Samples were immediately cultivated on Columbia blood agar. After identifying VGS, antimicrobial susceptibility test (AST) was performed using Mueller-Hinton agar (MHA) with sheep's blood and E-test strips for selected antibiotics. The minimum inhibitory concentration (MIC) was determined for each isolate and the results were reported as sensitive, intermediate and resistant. Fifty-one VGS bacteria were isolated from children with an average age of 7.3 ± 2.5 years. The highest resistance was observed for azithromycin in 36 (70.6%) isolates and then cefazolin in 35 (68.6%) isolates. The highest susceptibility was observed for amoxicillin in 46 (90.2%) isolates. Based on the findings of this study, amoxicillin is the most effective option for prophylaxis in children. Furthermore, cefazolin should be used with caution because bacteria resistant to this antibiotic can transfer resistance genes to other bacteria.

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Background: Otitis is a general terminology used for inflammation or infection of the ear; Staphylococcus aureus and Pseudomonas spp. are the most common causes of otitis externa. The resistance mechanism against the beta-lactams group is due to the pro-