Category Archives: Letters in Applied Microbiology

Methanolic extract of Hemidesmus indicus root augments the antibacterial and antibiofilm activity of amoxicillin and clindamycin against methicillin‐resistant Staphylococcus aureus of bovine origin

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Methanolic extract of Hemidesmus indicus root augments the antibacterial and antibiofilm activity of amoxicillin and clindamycin against methicillin-resistant Staphylococcus aureus of bovine origin

Significance and Impact of the Study: The ability of methicillin-resistant Staphylococcus aureus (MRSA) to form biofilms has become a challenge in the treatment of staphylococcal infections in both animals and humans. Antibiotics frequently fail to eradicate MRSA biofilm infections or, at best, only suppress the infection, potentially leading to disease recurrence. In the current study, methanolic extract of Hemidesmus indicus root (MHIR) was used as a natural and safer antibiofilm agent in combination with amoxicillin and clindamycin to treat MRSA infection. MHIR synergizes the antibacterial and antibiofilm activity of both antibiotics, resulting in the eradication of MRSA infection. In combination with MHIR, the effective dose of amoxicillin or clindamycin can also be reduced, avoiding an increased risk of in vivo toxicity.


Abstract

The present study evaluated the antibacterial and antibiofilm activity of methanolic extract of Hemidesmus indicus root (MHIR) in combination with amoxicillin and clindamycin against biofilm-forming methicillin-resistant Staphylococcus aureus (MRSA) isolated from milk samples of mastitic cows. Microdilution susceptibility testing and microtitre plate assays were used to evaluate the in vitro efficacy of MHIR and antibiotic combinations against MRSA (n = 12). Furthermore, in vitro findings were validated in a murine model. Minimum inhibitory concentration and minimum biofilm inhibitory concentration of amoxicillin and clindamycin in combination with MHIR were significantly (P < 0·05) lower than when used alone against MRSA. In terms of antibacterial activity, MHIR showed additive interaction (fractional inhibitory concentrationindex >0·5–4) with amoxicillin and clindamycin against all the MRSA isolates, whereas MHIR synergizes (fractional biofilm inhibitory concentrationindex ≤0·5) the antibiofilm activity of amoxicillin and clindamycin against 58·33% and 83·33% of the MRSA isolates respectively. Amoxicillin/clindamycin in combination with MHIR significantly (P < 0·05) reduced disease activity score, and bacterial load and Gram-positive spots in kidney and liver of MRSA-infected mice. The combined efficacy of MHIR and amoxicillin/clindamycin was comparable to clindamycin alone but superior to amoxicillin alone. Hence, the combination of MHIR with amoxicillin/clindamycin is advocated in the treatment of MRSA-associated infections.

Solid‐state fermentation produces greater stearidonic acid levels in genetically engineered Mucor circinelloides

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Solid-state fermentation produces greater stearidonic acid levels in genetically engineered Mucor circinelloides

Significance and Impact of the Study: Solid-state fermentation is an efficient and economical method for lipid accumulation in the oleaginous microorganism. In this study, engineered strains Mucor circinelloides McD15D with overexpressing the delta15-desaturase were able to accumulate more stearidonic acid (SDA) under solid-state fermentation than submerged fermentation, providing a new strategy for fermentation technology to enhance SDA production by oleaginous microorganisms.


Abstract

Omega-3 (ω-3) polyunsaturated fatty acids (PUFAs) are important dietary components due to their health benefits and preventative role in cardiovascular disease. Fish-based and plant seed oils are rich in stearidonic acid (SDA; 18:4, n-3), which are readily metabolized into ω-3 PUFAs such as eicosapentaenoic acid. However, these natural sources of SDA are generally low yielding and are unlikely to meet global demands, so new sustainable microbial fermentative sources of SDA need to be identified. Expression of delta15-desaturase in the oleaginous filamentous fungus Mucor circinelloides (McD15D) has been used to construct a recombinant SDA-producing McD15D strain that produces 5·0% SDA levels using submerged fermentation conditions. Switching to solid-state fermentation conditions in the same medium with submerged fermentation resulted in this engineered strain producing significantly higher amounts of SDA. A Box–Behnken design of response surface methodology approach has been used to identify optimal glucose and ammonium tartrate concentrations and temperature levels to maximize SDA production. The use of these optimal solid-state fermentation conditions resulted in the spores and mycelium of the recombinant McD15D producing 19·5% (0·64 mg g−1) and 12·2% (1·52 mg g−1) SDA content, respectively, which represents an overall increase in SDA yield of 188·0% compared with SDA yields produced using submerged fermentation conditions.

ERIC‐PCR‐based molecular typing of multidrug‐resistant Escherichia coli isolated from houseflies (Musca domestica) in the environment of milk and meat shops

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ERIC-PCR-based molecular typing of multidrug-resistant Escherichia coli isolated from houseflies (Musca domestica) in the environment of milk and meat shops

Significance and impact of the study: Houseflies (Musca domestica) are endophilic cosmopolitan pests of medical and veterinary importance. These are associated with regions of human activities such as food centres, butcher houses, animal farms and surrounding areas and create an annoyance to people, poultry and domestic farm animals. The present study reports that housefly samples collected from milk and meat outlets were positive for multidrug-resistant (MDR) E. coli and harbour bla CTX-M and bla TEM genes in plasmid along with other resistant genes for tetracyclines and quinolones. The presence of MDR genes in bacteria isolated from housefly samples is of serious concern from public health and food safety points of view. Investigation of genetic determinants of MDR in bacteria would be of great value for formulating and validating suitable control strategies to combat the spread of antimicrobial resistance.


Abstract

The emergence and spread of antimicrobial resistance have become a major global public health concern. A component of this problem is the spread of antibiotic-resistant bacteria. Flies move freely between habitats of food-producing animals and human beings and thus have great potential for dissemination of antimicrobial-resistant bacteria from a contaminated environment to milk and meat markets, posing potential hazards for consumers. During the present study, a total of 150 houseflies were captured from milk and meat shops located in Durg and Raipur city of Chhattisgarh, India. The Escherichia coli were isolated from houseflies and characterized on the basis of cultural and molecular tests. Further, the isolates were subjected to antimicrobial susceptibility testing against frequently used antibiotics using the disk diffusion method. The antibiotic resistance genes and int1 gene were detected using polymerase chain reaction (PCR). A total of 45 E. coli isolates were obtained from the fly samples with an overall prevalence rate of 30·0%. Antibiogram results confirmed that E. coli isolates were resistant to multiple antibiotics. Out of the (45) isolates of E. coli, 17 (37·8%) isolates were extended-spectrum beta-lactamase (ESBL) producer and multi-drug-resistant (MDR). Out of the ESBL and MDR E. coli isolates, bla CTX-M (24·4%), bla TEM (11·1%), tetA (28·8%), tetB (26·7%), gyrA (26·7%), parC (31. 1%) and int1 genes (15·5%) were detected but none of the isolates were found positive for bla SHV gene. Findings of the present study confirm that MDR E. coli are widely distributed in houseflies and play an important role in the transmission of antibiotic-resistant bacteria from contaminated environments to milk and meat shop environment.

Biodeterioration of low‐density polyethylene by mangrove‐associated endolichenic fungi and their enzymatic regimes

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Biodeterioration of low-density polyethylene by mangrove-associated endolichenic fungi and their enzymatic regimes

Significance and Impact of the Study: Endolichenic fungi (ELF) are a unique group of organisms with the ability to sustain under challenging conditions and have rich and versatile metabolite profiles. The present study showed that several ELF, isolated from mangrove ecosystems could grow in low-density polyethylene (LDPE) amended media and showed signatures of LDPE biodeterioration. Qualitative and quantitative enzymatic assays of six extracellular fungal enzymes, having roles in polymer depolymerization were also performed. Results highlighted that six ELF species rich in enzymatic profiles were capable of LDPE biodeterioration.


Abstract

Fungal involvement in the biodeterioration of low-density polyethylene (LDPE) has received great attention in recent years. Among diverse groups of fungi, endolichenic fungi (ELF) are adapted to thrive in resource-limited conditions. The present study was designed to investigate the potential of mangrove-associated ELF, in the biodeterioration of LDPE and to quantify key-depolymerizing enzymes. A total of 31 ELF species, isolated from 22 lichens of mangrove ecosystems in Negombo lagoon, Sri Lanka were identified using DNA barcoding techniques. ELF were inoculated into a mineral salt medium, containing LDPE strips and incubated at 28 ± 2°C, for 21 days, under laboratory conditions. After incubation, biodeterioration was monitored based on percent reductions in weights and tensile properties, increments in the degree of water absorption, changes in peaks of infrared spectra and surface erosions using scanning electron microscopy. Out of 31 species, Chaetomium globosum, Daldinia eschscholtzii, Neofusicoccum occulatum, Phanerochaete chrysosporium, Schizophyllum commune and Xylaria feejeensis showed significant changes. Production of depolymerizing enzymes by these species was assayed qualitatively using plate-based methods and quantitatively by mass-level enzyme production. Among them, Phanerochaete chrysosporium showed the highest enzyme activities as (9·69 ± 0·04) × 10−3, (1·96 ± 0·01) × 10−3, (5·73 ± 0·03) × 10−3, (0·88 ± 0·01), (0·64 ± 0·06), (1·43 ± 0·01) U ml−1 for laccase, lignin peroxidase, manganese peroxidase, amylase, lipase and esterase, respectively.