Isolation and Characterization of Antimicrobial Compound from Stem Bark of Traditional Medicinal Plant Sonneratia apetala: Evaluation of their antimicrobial, Cytotoxic and Antioxidant Properties

Sonneratia apetala (S. apetala) (Lythraceae) has been investigated for the isolation and characterization of antimicrobial compounds and evaluation of their biological activities. The chloroform extract of the stem bark and different partitionate of the chloroform extracts i.e. Petroleum ether soluble fraction (PESF), Ethyl acetate soluble fraction(EASF), Methanol soluble fraction(MSF) and aqueous soluble fractions (ASF) were subjected to different chromatographic techniques to isolate secondary metabolites. Successive chromatographic separation and purification yielded a total of two compounds identified and characterized as Taraxerone(1) and 5,8-dihydroxy- 6-methoxy-4,9-dioxo-1,3,4,9-tetrahydronaphthol[2,3-c]furan-1-yl acetate (2) by extensive proton NMR spectrum (1H-NMRspectrum) analysis. The different partitionate like PESF, EASF, MESF and ASF were subjected to screen their antimicrobial properties against some selected Gram positive and Gram negative bacteria and fungi, brine shrimp lethality and antioxidant activities. The maximum zone of inhibition of chloroform extract was found against Pseudomonas sp. (16mm). All fractions showed more activity against Gram negative bacteria then Gram positive bacteria. In the brine shrimp lethality bioassay, among all extracts, the petroleum ether and ethyl acetate soluble fraction showed significant lethality having the LC50 value of 7.72 μg/ml. The antioxidant activity was evaluated in terms of determination of free radical scavenging activity (DPPH assay). Among all the extracts of S. apetala the highest free radical scavenging activity showed by (Methanol soluble fraction) MESF with IC50 value 18.0 μg/ml. Bangladesh J Microbiol, Volume 38, Number 1, June 2021, pp 1-5

Chromium bioremediation potential of indigenous Bacillus pumillus isolated from river water of Bangladesh

Bangladesh has achieved rapid industrialization in recent years. However, many of these industries lack proper effluent treatment plant and discharge untreated effluent laden with different heavy metals into the major rives that surround these industries, affecting the environment as well as human and animal health. Aiming to develop a sustainable effluent treatment plant, a heavy metal tolerant Bacillus pumillus isolated from polluted river water of Bangladesh was studied for its chromium bioremediation potential. Reduction of hexavalent chromium using the Sdiphenylcarbazide (DPC) method showed that whole cells of the Bacillus pumillus reduced 89.5%, 75%, 73% and 45% of 1.0, 2.5, 5 and 10mg/L Cr(VI) to Cr(III), respectively. This bacterium reduced 100% of 20mg/L Cr(VI) to Cr(III) within 8 hours, in a growth associated pattern. A 20kb plasmid was detected in this Bacillus pumillus, and loss of this plasmid did not cause complete impairment of chromium tolerance capacity, though the tolerance efficiency was reduced. The Bacillus pumillus studied in the current study therefore shows its potential to develop a sustainable chromium bioremediation method. Bangladesh J Microbiol, Volume 38, Number 1, June 2021, pp 27-30

Antibacterial activity of ethanol extracts of betel leaf (Piper betle L.) and areca (Areca catechu L.) nuts against food borne and oral pathogens

Antimicrobial activity of ethanol extracts of betel leaf (Piper betle L.) and areca nut (Areca catechu) against six food borne enteric pathogens viz. Staphylococcus aureus (ATCC 25923), Staphylococcus epidermidis (icddr,b), Salmonella typhimurium (AIM-40, icddr,b), Escherichia coli (ATCC 25922), Escherichia coli O157:H7 (ATCC 12079) and Bacillus cereus (ATCC 12079), and four oral pathogens such as isolates 1 & 2 of each of the two bacteria viz. Staphylococcus sp. and Pseudomonas sp. was investigated. Ethanol extract of betel leaf produced highest zone of inhibition (18.0 ± 1.91 mm) against Staphylococcus epidermidis (icddr,b) whereas that of areca nut produced highest zone of inhibition (15.0 ± 0.816 mm) against Staphylococcus aureus (ATCC 25923). But no inhibition was found against Salmonella typhimurium (ATCC AIM-40, icddr,b), Escherichia coli (ATCC 25922), and Escherichia coli O157:H7 (ATCC 12079) by the Ethanol extract of betel leaf. The MIC and MBC values of both ethanol extracts indicated that Gram positive organisms were more susceptible than Gram negative organisms. Highest antimicrobial activity of ethanol extracts of betel leaf was found against the isolate 1 of Staphylococcus sp. (16.5±0.5) and that of areca nut was recorded against the isolate 1 of Staphylococcus sp. (12.0±0.5) and the isolate 2 of Pseudomonas sp. (12.0±0.5). Present study reveals the potentials of both the extracts to inhibit food borne enteric and oral pathogens that could be used as food preservatives to prevent the food borne illness as well as for maintaining the oral and gut health. Bangladesh J Microbiol, Volume 38, Number 1, June 2021, pp 15-19

Antibiotic Sensitivity and Virulence Genes in Staphylococcus aureus Isolates from Surgical Site Infection

Fourteen multi drug resistant Staphylococcus aureus isolates from surgical site infection were analyzed for their antibiotic sensitivity and the presence of nine virulence genes. The isolates showed a high resistance pattern, all being resistant to methicillin, oxacillin, azithromycin, ceftazidime and amoxyclav. Seven of the isolates were sensitive to linezolid; three were sensitive to trimethoprim: sulfamethoxazol and another three were sensitive to ciprofloxacin. Ceftriaxone, gentamicin and amikacin were the drugs of choice as nine (64.3%) isolates were sensitive to ceftriaxone, eleven (78.6%) were sensitive to gentamicin and another eleven (78.6%) to amikacin. The present study focused to identify nine important virulence genes including intrinsic methicillin resistance gene mecA, methicillin resistance assisting gene femA, toxic shock syndrome toxin gene tst, exfoliative toxin A and B genes, eta and etb, Panton Valentine leukocidin gene LukS/F-PVL, along with three enterotoxin genes sec, sed and see. According to the presence of mecA gene and antibiotic resistance profile, two isolates were identified as methicillin resistant Staphylococcus aureus. However, another isolate, despite harbouring both mecA and femA genes, was sensitive to ceftriaxone which excluded it from being considered as an MRSA. Thus, the ratio of MRSA can be considered to be quite high (2/14) among the strains. Interestingly, most of the isolates (10/14) harboured femA gene, the majority of which were mecA negative with an MSSA type antibiotic profile. Although considered as a marker for community acquired MRSA, LukS/F-PV was found in half of these nosocomial isolates. Five, four and two of the isolates harboured etb, tst and sec gene, respectively. However, all the isolates were negative for eta, sed and see genes. Two isolates showed the co-existance of “femA, LukS/F-PV, etb, and tst” genes. Another two virulence gene patterns observed were “femA, mecA, tst, sec” and “femA, LukS/F-PV, etb”. The presence of several virulence genes can be correlated to the highly pathogenic nature of the isolates. Bangladesh J Microbiol, Volume 38, Number 1, June 2021, pp 21-26

Antibacterial and Antibiofilm Activities of Nigella sativa L. Seed Extracts

The emergence of antibiotic-resistant bacteria is a major public health problem. Consequently, the development of new antimicrobials that act on novel bacterial targets and are less susceptible to resistance are of primary importance to researchers in academia and industry alike. The present study was aimed to determine the antimicrobial and antibiofilm activities of Nigella sativa seed extracts. For this, primary (qualitative) and quantitative antibacterial activities of Nigella sativa seed extracts were determined against ten human pathogenic bacteria including four biofilm producing bacterial strains Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus. The antibacterial activities as well as minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extracts were evaluated using disc diffusion and macro-broth dilution methods, respectively. The seed extracts of N. sativa exhibited the highest extract yields (w/v) 23.3% and 21.35% with ethanol and petroleum ether, respectively. The crude extract (essential oil) of petroleum ether exhibited superior antibacterial activity (36 mm in diameter zone of inhibition) against biofilm forming E. coli on a disc diffusion assay at a concentration of 1000 μg/disc when compared to that of ethanolic crude extract. Moreover, the lowest MIC and MBC values were determined as 500 μg/ml and 1500 μg/ml respectively with the same petroleum ether extract against E. coli. However, N. sativa essential oil obtained from petroleum ether extract of seed inhibited 94% biofilm formation of E. coli at 2×MIC concentration. Moreover, at the same concentration (2×MIC), the ethanol extract inhibited 56% biofilm formation of P. aeruginosa. These results consistently revealed that it is possible to isolate novel antimicrobial agents capable of completely eradicating microbial infections including antibiotic resistance. Therefore, bioactive natural products present in plant resources would represent a noteworthy alternative to commercial antibiotics helping treatment of human antibiotic resistant infections. Bangladesh J Microbiol, Volume 38, Number 1, June 2021, pp 7-13

Bacterial Isolates and Antibiotic Sensitivity Pattern from Urinary Tract Infection in a Private Diagnostic Laboratory in Dhaka, Bangladesh

Urinary tract infection (UTI) is a common infection encountered by clinicians and despite the widespread availability of antimicrobial agents, UTI has become difficult to treat because of appearance pathogens with increasing resistance to antimicrobial agents. The objectives of this study were to determine the pathogens causing UTI and to determine the antibiotic sensitivity status among these isolates in a diagnostic laboratory in Dhaka city. A laboratory based cross sectional survey was conducted in a diagnostic Centre in Dhaka Bangladesh from July 2016 to December 2016. A total of 553 urine samples were collected from each patients and processed in microbiology laboratory to isolate pathogens and antibiotic susceptibility test using standard procedure. Among 553 urine samples, 158 (28.57%) samples was found to be culture positive of which 39 (24.70%) were isolated from male patients and 119 (75.30%) from female patients. Escherichia coli (43.67%) were found to be the predominant pathogen followed by Staphylococcus spp. (16.45%), Enterococcus spp. (13.39%), Klebsiella spp. (13.29%), Candida spp. (5.70%), Acinetobacter spp. (4.43%), Pseudomonas spp. (3.80%) and Proteus spp. (1.27%). The carbapenem group antibiotics (imipenem and meropenem) was found to be resistant in 0 to 5.1% of the Gram negative isolates. On the Other hand, most of the Gram positive isolates showed sensitivity to linezolid and vancomycin. This study showed that E. coli isolates were the predominant pathogens and showed resistance to commonly prescribed drugs resulting in a very few options for drug to treat UTIs. Bangladesh J Microbiol, Volume 37 Number 2 December 2020, pp 56-60

Food Safety Knowledge, Attitudes and Behavior of Street Food Vendors and Consumers in Dhaka City

Food safety knowledge, attitudes, and street food suppliers and consumer behaviors of the capital city Dhaka were investigated. A cross-sectional study was conducted using questionnaires based on previous studies. Three main areas addressed in the surveys and statistical analysis are; 1) statistical data including gender, age, education, income, food safety training, and specific elements related to the work experience of suppliers, 2) knowledge of food safety such as the awareness of consumers and suppliers concerning pathogenic microbes that cause food poisoning, food and personal hygiene, proper cleaning procedures and high-risk groups, and 3) list of food handling attitude and behavior of subjects. Results showed food safety knowledge of street vendors in the High-tech Industries Development Zone was the lowest, where education levels are generally relatively low. Food safety attitudes of the youngest consumers were significantly better than those of older age groups. Street vendors were relatively poor in carrying out safe food handling, with only 27.6% using or being fully equipped with hand-washing facilities, although more than 50% of vendors were not wearing clean and tidy clothes and masks. Steps should be taken to improve street food stall operating conditions and facilities, including access of potable water, providing clean protected structures, and efficient waste collection and disposal systems that can promote the plans and strategies to improve street food safety of Dhaka city and Bangladesh as a whole. Bangladesh J Microbiol, Volume 37 Number 2 December 2020, pp 48-51

Clinical Characteristics of Noncritical Patients with Coronavirus Disease 2019 (COVID-19): Lessons from Bangladesh

The scientific literatures on clinical manifestations of coronavirus disease 2019 (COVID-19) patients from South Asian countries including Bangladesh are limited. Documentation of clinical spectrum from various geographic locations is vital for future scientific studies and clinical management. This study is aimed to report the sociodemographic and clinical characteristics of noncritical patients with COVID-19 in Bangladesh. We conducted a cross-sectional study at three dedicated COVID-19 hospitals of Bangladesh. The severity of the COVID-19 cases was assessed based on the WHO interim guidance. Data were collected only from non-critical COVID-19 patients as critical patients required immediate management. A total of 103 real-time polymerase chain reaction (RT-PCR) confirmed noncritical COVID- 19 patients were included. Most of the patients (71.8%) were male. Mild, moderate and severe illness were assessed in 74.76%, 9.71% and 15.53% of patients respectively. Nearly 52.4% patients had a co-morbidity, with hypertension being the most common (34%), followed by diabetes mellitus (21.4%) and ischemic heart disease (9.7%). Fever (78.6%), weakness (68%) and cough (44.7%) were the most common clinical manifestations. Other common symptoms included loss of appetite (37.9%), difficulty in breathing (37.9%), loss of taste or smell (35.0%), headache (32%) and body ache (32%). The median time from onset of the first symptom to attending hospitals was 7 days (interquartile range: 4 - 10). This study will help both the clinicians and epidemiologists to understand the magnitude and clinical spectrum of COVID-19 patients in South Asian perspective including Bangladesh. Bangladesh J Microbiol, Volume 37 Number 2 December 2020, pp 42-46

Comparison of Immunogenicity and Protective Efficacy of the Intranasal and Intraperitoneal Immunization Routes of Escherichia albertii Strain DM104 in Mouse Model

In recent years, our group isolated the Escherichia albertii strain DM104 and characterized it as a vaccine strain against Shigella dysenteriae type 4 in the guinea pig eye model. Protective efficacy of different routes of immunization such as intranasal, oral, and intrarectal routes were also determined and compared by challenging immunized guinea pigs against live S. dysenteriae. In the current study, we compared the intranasal and intraperitoneal routes of immunizations with the DM104 vaccine strain in mice to understand the better route of administration of the DM104 vaccine and its immunogenicity as well as protective efficacy in mouse model. The results indicate that the immune response elicited by the DM104 strain is strongly dependent on the immunization route, with the intranasal route being more effective than the intraperitoneal route following intraperitoneal live S. dysenteriae challenge. Intranasal immunization yielded 80% protective efficacy in immunized mice whereas, intraperitoneal immunization could not provide any protection. Protection generated by intranasal immunization was accompanied by high titre of anti-whole cell lysate IgG and IgA in DM104 immunized sera compared to sera collected from mice of control group. All these data demonstrate the intranasal route of the vaccine DM104 strain in mouse model to be a better immunization route to protect the animals against live S. dysenteriae challenge. Bangladesh J Microbiol, Volume 37 Number 2 December 2020, pp 38-41

Physicochemical Properties of Chitosan Extracted from Pleurotus ostreatus and Improvement of its Antibacterial Activity by Gamma Radiation

This study was carried out to determine the physicochemical characteristics such as intrinsic viscosity (IV), molecular weight (MW), water binding capacity (WBC), and fat binding capacity (FBC) of chitosan extracted Pleurotus ostreatus fruit body. Antibacterial activity of the gamma irradiated chitosan was also determined. The intrinsic viscosity, MW, WBC and FBC of the produced chitosan were 769.69 ml/g, 1.8×105 Da, 408% and 234%, respectively. The fungal chitosan was subjected to different doses (viz., 5, 10, 20, 30 and 40 kGy) of radiation from 60Co gamma source to observe the effect of gamma radiation on its antibacterial activity. After irradiation, antibacterial activity was evaluated and compared with that of non-irradiated chitosan. Non-irradiated chitosan showed moderate antibacterial activity against Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 6538, Escherichia coli ATCC 35150, and Salmonella enteritidis ATCC 13076 whereas chitosan samples treated with 5, 10 and 20 kGy gamma irradiation separately have shown enhanced antibacterial activity than that of non-irradiated chitosan against the above-mentioned bacteria. However, higher doses of gamma irradiation (30 kGy and 40 kGy) caused a gradual decline of the antibacterial activity. Bangladesh J Microbiol, Volume 37 Number 2 December 2020, pp 52-55