Sub-minimum inhibitory concentrations (sub-MICs) of colistin on Acinetobacter baumannii biofilm formation potency, adherence, and invasion to epithelial host cells: an experimental study in an Iranian children's referral hospital

Here, we described the efficacy of colistin sub-minimum inhibitory concentrations (sub-MICs) on biofilm-forming activity, host epithelial cell adherence, and invasion capacity of Acinetobacter baumannii strains collected from children admitted to the Children's Medical Center Hospital. Biofilm formation potency of A. baumannii clinical isolates was measured using a 96-well microtiter plate assay. Distribution of biofilm-related genes, including bap, abaI, ompA, csuE, and blaPER-1, was detected by PCR. The mRNA expression level of ompA and csuE was measured by qPCR in the presence of ¼ and ½ MICs of colistin. A. baumannii adhesion and invasion to eukaryotic host cells were phenotypically assayed at sub-MICs of colistin. Eighty percent (56/70) and 35.7% (25/70) of A. baumannii isolates were multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes, respectively. The strong, moderate, and weak biofilm producers of A. baumannii were 37.1% (26/70), 32.8%, (23/70), and 22.8% (16/70), respectively. The frequencies of biofilm-associated genes were 100% for abaI, ompA, and csuE, followed by 22.8% (16/70) and 24.3% (17/70) for bap and blaPER-1, respectively. The downregulation of csuE and ompA expression levels was observed in the sub-MIC of colistin. In vitro cell culture study showed a decreased capability of A. baumannii to adhere to the human epithelial cells at sub-inhibitory doses of colistin; however, none of the isolates could invade HEp-2 cells. Our study showed that the genes encoding biofilm-associated proteins undergo downregulation in expression levels after exposure to sub-MICs of colistin in A. baumannii. Longitudinal in vivo studies are needed to fully understand the clinical aspects of pathogenicity mechanisms and evolutionary dynamics of drug resistance.IMPORTANCESince the toxicity of colistin is dose dependent, there is a focus on strategies that reduce the dose while maintaining the therapeutic effect of the drug. Our findings about sub-inhibitory doses of colistin provide a novel insight into the logical use of colistin to treat and control Acinetobacter baumannii-related infections in clinical practice.

Shigella Flexneri Serotypes: O-antigen Structure, Serotype Conversion, and Serotyping Methods

Shigella flexneri is the most common cause of shigellosis in developing countries. Up to now, 23 serotypes of S. flexneri have been reported. Different serotypes result from the addition of acetyl, glucosyl, or phosphatidylethanolamine groups on the O-antigen backbone and horizontal transfer of mentioned groups can lead to serotype conversion among S. flexneri strains. Serotype conversion causes either a circulation of pre-existing serotypes or is responsible for the emergence of new serotypes. Serotype conversion plays a pivotal role in the protection and evasion of S. flexneri from the host immune response. Furthermore, spreading any new serotype can provide evolutionary advantages. Hence, information about S. flexneri O-antigen structure, serotype conversion, and serotyping methods can be helpful to understand the disease that attributes distinct serotypes in order to apply control or prevention methods in accordance with predominant serotypes over the course of time. Thus, the scope of this review is to give an overview of the serotype structures, factors involved in O-antigen modification, molecular analysis, and epidemiological evidence for the benefits of serotype conversion for S. flexneri serotypes. We are also providing a review of the typing methods.

Alpha-amylase immobilization; methods and challenges

Alpha-amylase is one of the most widely used enzymes in the starch industry. However, industrial application of soluble alpha-amylase is hampered by changes in pH and temperature (adverse effects on enzyme stability) and activity loss, leading to higher costs. Immobilization of alpha-amylase is an efficient strategy to reduce the enzyme losing and subsequently reduces costs in this regard. Alpha-amylases are immobilized by adsorption, entrapment, covalent attachment, and cross-linking. A barrier in alpha-amylase immobilization is the large size of its substrate, namely amylose and amylopectin. Most of these immobilization methods decrease the affinity of the enzyme for its substrate as well as the maximum rate of reaction (Vmax). This review aims to study different aspects of alpha-amylase including enzyme activity, applications, structure, starch, immobilization methods, and immobilization's obstacles to improve alpha-amylase efficiency in the industry and also lowering the costs related to providing this enzyme.

Cloning and expression of Staphylococcus simulans lysostaphin enzyme gene in Bacillus subtilis WB600

Lysostaphin is a glycylglycine endopeptidase, secreted by Staphylococcus simulans, capable of specifically hydrolyzing pentaglycine crosslinks present in the peptidoglycan of the Staphylococcus aureus cell wall. In this paper, we describe the cloning and expression of the lysostaphin enzyme gene in Bacillus subtilis WB600 host using pWB980 expression system. Plasmid pACK1 of S. simulans was extracted using the alkaline lysis method. Lysostaphin gene was isolated by PCR and cloned into pTZ57R/T-Vector, then transformed into Escherichia coli DH5α. The amplified gene fragment and uncloned pWB980 vector were digested using PstI and XbaІ enzymes and purified. The restricted gene fragment was ligated into the pWB980 expression vector by the standard protocols, then the recombinant plasmid was transformed into B. subtilis WB600 using electroporation method. The recombinant protein was evaluated by the SDS-PAGE method and confirmed by western immunoblot. Analysis of the target protein showed a band corresponding to 27-kDa r-lysostaphin. Protein content was estimated 91 mg/L by Bradford assay. The recombinant lysostaphin represented 90% of its maximum activity at 40 °C and displayed good thermostability by keeping about 80% of its maximum activity at 45 °C. Heat residual activity assay of recombinant lysostaphin demonstrated that the enzyme stability was up to 40 °C and showed good stability at 40 °C for 16 h incubation.

Prevalence of β-lactamase-encoding genes and molecular typing of Acinetobacter baumannii isolates carrying carbapenemase OXA-24 in children

Background

β-Lactam antibiotics have been broadly used for the treatment of Acinetobacter baumannii infections, resulting in development of β-lactam inactivating β-lactamases. Here, we described antibiotic resistance rate, prevalence of β-lactamase-encoding genes, and clonal relationships of A. baumannii strains isolated from children referred to Children’s Medical Center in Tehran, Iran, during 2019–2020.

Methods

A total of 60 non-replicate A. baumannii isolates were recovered from clinical specimens of pediatric patients. Antibiotic susceptibility testing was done by the disc diffusion method. Colistin susceptibility of isolates was performed by the broth microdilution method. β-lactamase-encoding genes were characterized by PCR. The presence of ISAba1 element upstream of the several oxacillinase genes was also checked. Genetic relatedness of isolates was determined by using random amplification of polymorphic DNA (RAPD) typing.

Results

The antimicrobial susceptibility tests showed that 83.3% of A. baumannii isolates were MDR, and 40% XDR. Both MDR and XDR A. baumannii isolates were susceptible to colistin. The frequency of bla_OXA-51-like, bla_OXA-23-like, bla_TEM, bla_OXA-24-like, bla_PER, bla_SHV, bla_CTX-M, bla_OXA-58-like, and bla_IMP was 100, 93.33, 60, 36.67, 28.33, 8.33, 5, 3.33, and 1.67%, respectively. Coexistence of ISAba1/bla_OXA-23-like and ISAba1/bla_OXA-51-like was observed in 65% and 85% of isolates, respectively. RAPD analysis revealed 4 common types and 2 single types of A. baumannii isolates.

Conclusions

The multiple clones harboring bla_OXA-23-like, ISAba1-bla_OXA-51-like, and ISAba1-bla_OXA-23-like were responsible for the spread of A. baumannii isolates in our clinical wards. Dissemination of the well-established clones is worrisome and would become therapeutic challenges due to the possible transferring genetic elements associated with resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-021-00480-5.

Genomic pattern analysis of Burkholderia mallei field isolates by pulsed-field gel electrophoresis (PFGE) discriminatory typing

Background and Objectives: Glanders is a serious zoonotic disease caused by Burkholderia mallei. Prevention, control, and treatment strategies of glanders are prerequisites for microbial source tracking. The present study was aimed to analyze the genomic pattern of B. mallei Iranian field isolates by pulsed-field gel electrophoresis (PFGE) typing. Materials and Methods: B. mallei isolates were aerobically cultured in nutrient broth/agar supplemented with glycerol 4% for 48 h at 37°C. API 20NE identification system was used for the biochemical characterization. Genomic DNA of bacterial isolates was extracted using OIE-recommended protocol. Molecular identification of bacterial isolates was done based on amplification of BimA and IS407-flip genes. PFGE was applied to prepare the genomic pattern of B. mallei isolates. The guinea pig was used as a suitable model for studying the histopathological characterization of B. mallei. Results: In both enzymatic digestion patterns by using Af1II and VspI, we found three different clonal types; І) PFGE type of B. mallei Razi 325 strain, ІІ) PFGE type of Tiger, Kordan, and Oshnavieh strains, and ІІІ) PFGE type of Semirom strain. B. mallei Razi 325 was categorized as unrelated strain which was belonged to the different cluster differing more than four bands. Conclusion: PFGE showed more discriminatory power and considerable reproducibility for molecular typing of B. mallei strains in our study. It is standardized the approaches for outbreak detection, pathogen phylogeny, molecular epidemiology, and population studies.

Down-regulation of TGF-β, VEGF, and bFGF in vascular endothelial cells of chicken induced by a brittle star (Ophiocoma erinaceus) extract

Great attention has been focused on the discovery of anti-angiogenic natural and synthetic compounds to be finally used as or at least a part of the treatment of tumors. The marine ecosystems provide diversity in natural chemicals with the potential of being exploited as medicines in the treatment of diseases. Several studies have investigated Ophiuroids as a source of anti-tumor and anti-metastatic organisms. Here, we described the inhibitory effects of an ethanolic crude extract of brittle star (Ophiocoma erinaceus) on angiogenesis and the expression level of TGF-β, VEGF, and bFGF in chicken chorioallantoic membrane (CAM) as an experimental model. To do this 45 embryonated eggs were randomly divided into six groups including the control group, sham, three experimental groups and positive. The number and the length of vessels were calculated using ImageJ® software. The relative mRNA levels of the genes in different groups were evaluated by qRT-PCR method. Our study was suggestive of an anti-angiogenesis effect of brittle star ethanolic crude extract in a CAM model. The extract also showed a pharmacological effect of down-regulation of mRNA related to VEGF, TGF-β, and bFGF genes on chicken vascular endothelial cells. It was also showed that the observed inhibitory effect is with a dose-dependent manner in which the highest inhibitory effect belonged to the highest used dose. We indicated the anti-angiogenesis properties of the Persian Gulf brittle star. Further studies are needed in other aspects of the brittle star extract in the treatment of angiogenesis, hyperplasia, and cancers.

Preliminary survey of extended-spectrum β-lactamases (ESBLs) in nosocomial uropathogen Klebsiella pneumoniae in north-central Iran

Infections caused by extended-spectrum β-lactamases (ESBLs) producing bacteria, including Klebsiella pneumoniae have increasingly subjected to therapeutic limitations and patients with these infections are at high risk for treatment failure, long hospital stays, high health care costs, and high mortality. The aim of this study was to screen the prevalence of the bla_TEM,bla_CTX-M and bla_SHV ESBL genes in K. pneumoniae strains isolated from nosocomial urinary tract infections (UTIs). During the March 2016 to December 2017, one hundred isolates of K. pneumoniae were collected from urine specimens of patients suffering from nosocomial UTI referred to Khatam Al-Anbia hospital in Shahrud, north-central Iran. All isolates were identified by standard bacteriological tests. The pattern of antibiotic susceptibility was determined according to the CLSI guidelines. The presence of the ESBLs was investigated using the double-disc synergy test (DDST). Polymerase chain reaction technique was used to detect the bla_TEM, bla_CTX-M and bla_SHV genes in DDST positive isolates. Most isolates showed remarkable resistance to tested antibiotics with highest rate against nitrofurantoin (75%) and trimethoprim/sulfamethoxazole (65%). The imipenem was the most effective antibiotic against K. pneumoniae isolates. ESBL phenotype was detected in 50 (50%) of isolates. The prevalence of bla_TEM, bla_CTX-M and bla_SHV genes among 50 ESBLs-positive isolates was 25 (50%), 15 (30%) and 35 (70%) respectively. The bla_TEM and bla_SHV genes were seen in 25 isolates (50%) simultaneously. The findings of this study indicated the 50% frequency rate of ESBL-producing K. pneumoniae in our geographic region. Since the treatment of infections caused by this bacterium is associated with many limitations, this high prevalence is a warning sign to adopt new control policies to prevent further spread of this microorganism.

Development of an immunoblotting assay for serodiagnosis of Burkholderia mallei infection: the whole-cell proteome-based paradigm

BACKGROUND AND OBJECTIVES

Burkholderia mallei is the leading cause of glanders, a highly transmittable and an OIE-notifiable disease of equidae. Despite the importance of B. mallei, little is known about serodiagnosis of glanders. The present study aimed to develop an immunoblotting assay based on whole-cell proteome of B. mallei to enable accurate serodiagnosis of glanders.

MATERIALS AND METHODS

Three farm horses were subcutaneously immunized with a crude suspension (10⁶ cfu/ml) of heat-inactivated B. mallei formulated with incomplete Freund's adjuvant (IFA) to achieve a hyperimmune sera panel. The immunization was done for 1, 14 and 28 days with 1 dose of 1 ml antigen containing 10⁶ cfu/ml. The hyperimmunity of sera was confirmed by CFT. B. mallei whole-cell proteome was prepared through sonication and the protein content was visualized by SDS-PAGE and quantified by Western blot using HRP-conjugated rabbit anti-horse IgG. A comprehensive set of positive and negative horse sera validated the test.

RESULTS

A ladder pattern of the B. mallei immunoreactive antigens was seen within the region of 20-90 kDa clearly and the immunoblot was scored positive, while no reaction was seen for the negative sera. The Western blot assay indicated a noticeably higher diagnostic specificity for positive or negative sera of glanders.

CONCLUSION

The whole-cell proteome-based immunoblot proved reliable and straightforward in our study. The prepared antigen was adaptable for application in immunoblotting. We assumed this improved immunoblotting system provides appropriate sensitivity and also specificity expected in serodiagnosis of glanders in endemic areas and typically in less-developed countries.

Comparison of biomarkers between genotypes 1a and 3a in hepatitis C virus patients with control group

Introduction: Three percent of people worldwide are infected with Hepatitis C virus (HCV). A few studies have been performed to evaluate the biochemical markers of the disease. In the current study, biochemical markers were evaluated in HCV patients and the control group. Methods: Two sex- and age-matched healthy individuals (n = 100) and HCV positive patients (n = 100) were included (mean age of 20-75, 26.0% females and 74.0% males). Biochemical markers, including liver enzymes (ALT, AST and ALP), lipid profiles (cholesterol, LDL, and HDL) and triglyceride (TG) were investigated in both groups. HCV genotyping was also performed by Polymerase Chain Reaction (PCR) and OHNO methods. Results: The biochemical markers between HCV patients and controls were compared (cholesterol, ALP, AST, ALT, LDL: p = 0.0001, HDL: p = 0.002, TG: p = 0.003), and statistically significant difference was found between two groups. The biochemical markers between HCV patients and the control group in terms of age was compared and no differences was observed (p = 0.741), however, there was a significant difference in sex between HCV patients and control group (26.0% females, 74.0% males in control group, and x% females and y% males in HCV patients) (p = 0.032). The results of HCV genotyping showed that 39 patients were genotype 1a, and 43 patients were genotype 3a, and 1 patient was genotype 2a. Evaluation of biochemical markers in patients with genotype 1a and 3a showed that there were significant differences in cholesterol (p = 0.001), LDL (p = 0.001) and HDL (p= 0.003) levels, but there were no significant differences in liver enzymes and TG levels in both genotypes. Conclusion: In the present study, we found significant difference in biochemical markers between HCV patients and controls. In HCV patients, the biochemical markers were dependent on HCV genotypes, and their levels in genotype 1a were higher than genotype 3a. In conclusion, biochemical markers are one of the most important factors for the identification of treatment.

Carbapenem-resistant Acinetobacter baumannii isolates carrying blaOXA genes with upstream ISAba1: First report of a novel OXA subclass from Iran

OBJECTIVES

Carbapenem-resistant Acinetobacter baumannii (CRAB) have emerged as a serious threat to public-health worldwide. This study aimed to determine the antimicrobial susceptibility of A. baumannii isolates in Iran and to investigate oxacillinase-encoding determinants and their association with insertion sequence ISAba1 in CRAB isolates.

METHODS

This study was performed on A. baumannii isolates recovered from patients with burn wound infections during 2013. All isolates were evaluated for antimicrobial susceptibility by the disk diffusion method. Minimum inhibitory concentrations (MICs) of five antibiotics (imipenem, meropenem, polymyxin B, colistin and tigecycline) were determined for all CRAB isolates. PCR was performed to determine the distribution of bla_OXA determinants and ISAba1 insertion upstream of each corresponding gene in the CRAB isolates.

RESULTS

A total of 65 A. baumannii isolates were recovered during the 1-year period, with CRAB accounting for 63 (96.9%) of isolates. Polymyxin B, colistin and tigecycline were the most effective agents against CRAB isolates, with susceptibility rates of 100%, 87.3% and 65.1%, respectively. The proportion of CRAB isolates carrying oxacillinase determinants was as follow: bla_OXA-51-like, 100%; bla_OXA-23-like, 74.6%; bla_{OXA-24/40-like}, 47.6%; and bla_OXA-235-like, 12.7%. ISAba1, ISAba1-bla_OXA-23-like and ISAba1-bla_OXA-51-like were detected in 100%, 41.3% and 1.6% of CRAB isolates, respectively. Co-occurrence of bla_OXA determinants or inserted ISAba1 upstream of the corresponding genes was associated with increased carbapenem MICs (≥128μg/mL).

CONCLUSION

The emergence of high-level CRAB with bla_OXA and ISAba1-bla_OXA family in burn patients is a matter of increasing clinical concern, emphasising the need for infection control efforts to limit such problematic bacteria.

Metallo-β-lactamase-mediated resistance among clinical carbapenem-resistant Pseudomonas aeruginosa isolates in northern Iran: A potential threat to clinical therapeutics

Objective:

Carbapenems are effective agents to treat multidrug-resistant (MDR) strains of bacteria, including Pseudomonas aeruginosa. However, there is a potential threat of emergence of carbapenem-resistant P. aeruginosa (CRPA). The aim of this study was to determine antibiotic susceptibility patterns and metallo-beta-lactamase (MBL)-mediated resistance in clinical P. aeruginosa isolates.

Materials and Methods:

Different clinical specimens were subjected to conventional culture-based identification of P. aeruginosa. Antimicrobial susceptibility patterns and MBL production were evaluated using the Kirby-Bauer and combined double-disk synergy test methods, respectively. Multiplex polymerase chain reaction was performed to investigate the presence of the bla_IMP, bla_VIM, bla_NDM, bla_SPM, and bla_SIM genes.

Results:

A total of 71 clinical P. aeruginosa isolates were recovered, of which 28.17% were identified as CRPA. The most active antibiotics were colistin and polymyxin B (92.96% susceptibility to each). A total of 35% and 50% of CRPA isolates were MDR and extensively drug-resistant (XDR), respectively. MBL activity was shown in 20% of CRPA. A total of 90%, 40%, and 5% of CRPA isolates harbored the bla_IMP, bla_VIM, and bla_NDM genes, respectively. No correlation was found between the MBL-encoding genes of P. aeruginosa and patient characteristics.

Conclusion:

Although the prevalence of CRPA in our therapeutic centers was relatively low, this rate of carbapenem resistance reflects a threat limiting treatment choices. A high prevalence of MDR/XDR phenotypes among the MBL-producer isolates suggests the need for continuous assessment of antimicrobial susceptibility and surveillance of antibiotic prescription. In addition, infection control measures are needed to prevent further dissemination of these organisms.