Current trends of antibiotic resistance in clinical isolates of Staphylococcus aureus

Virulence Potential and Antibiotic Susceptibility of S. aureus Strains Isolated from Food Handlers

Staphylococcus spp. are common members of the normal human flora. However, some Staphylococcus species are recognised as human pathogens due to the production of several virulence factors and enterotoxins that are particularly worrisome in food poisoning. Since many of Staphylococcal food poisoning outbreaks are typically associated with cross-contamination, the detection of S. aureus on food handlers was performed. Hand swabs from 167 food handlers were analysed for the presence of S. aureus. More than 11% of the samples were positive for S. aureus. All S. aureus strains were isolated and analysed for the presence of virulence and enterotoxin genes, namely, sea, seb, sec, sed, seg, sei, tsst-1 and pvl. The same strains were phenotypically characterised in terms of antibiotic susceptibility using the disc diffusion method and antimicrobial agents from 12 different classes. A low prevalence of antibiotic-resistant strains was found, with 55.6% of the strains being sensitive to all of the antimicrobial agents tested. However, a high prevalence of resistance to macrolides was found, with 44.4% of the strains showing resistance to erythromycin. At least one of the virulence or toxin genes was detected in 61.1% of the strains, and seg was the most prevalent toxin gene, being detected in 44.4% of the strains.

Novel Lignin-Capped Silver Nanoparticles against Multidrug-Resistant Bacteria

The emergence of bacteria resistant to antibiotics and the resulting infections are increasingly becoming a public health issue. Multidrug-resistant (MDR) bacteria are responsible for infections leading to increased morbidity and mortality in hospitals, prolonged time of hospitalization, and additional burden to financial costs. Therefore, there is an urgent need for novel antibacterial agents that will both treat MDR infections and outsmart the bacterial evolutionary mechanisms, preventing further resistance development. In this study, a green synthesis employing nontoxic lignin as both reducing and capping agents was adopted to formulate stable and biocompatible silver-lignin nanoparticles (NPs) exhibiting antibacterial activity. The resulting silver-lignin NPs were approximately 20 nm in diameter and did not agglomerate after one year of storage at 4 °C. They were able to inhibit the growth of a panel of MDR clinical isolates, including Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii, at concentrations that did not affect the viability of a monocyte-derived THP-1 human cell line. Furthermore, the exposure of silver-lignin NPs to the THP-1 cells led to a significant increase in the secretion of the anti-inflammatory cytokine IL-10, demonstrating the potential of these particles to act as an antimicrobial and anti-inflammatory agent simultaneously. P. aeruginosa genes linked with efflux, heavy metal resistance, capsular biosynthesis, and quorum sensing were investigated for changes in gene expression upon sublethal exposure to the silver-lignin NPs. Genes encoding for membrane proteins with an efflux function were upregulated. However, all other genes were membrane proteins that did not efflux metals and were downregulated.

Coagulase gene polymorphism, enterotoxigenecity, biofilm production, and antibiotic resistance in Staphylococcus aureus isolated from bovine raw milk in North West India

Background

Staphylococcus aureus is the predominant bacterium responsible for various diseases in animals and humans. Preventive strategies could be better implemented by understanding the prevalence, genetic patterns, and the presence of enterotoxin and biofilm-producing genes along with the antibiotic susceptibility of this organism. This study was conducted in Rajasthan, the northwestern state of India, holding the largest population of cattle that makes it the second largest milk producer in India and no such prior information is available on these aspects.

Methods

A total of 368 individual quarter bovine raw milk samples were collected from 13 districts of Rajasthan, and screened for the presence of S. aureus. Microbiological and molecular approaches were followed for bacterial identification. Genetic diversity was determined by polymerase chain reaction-restriction fragment length polymorphism (PCR–RFLP) of coagulase gene (coa), whereas enterotoxin and biofilm-producing genes were studied by PCR analysis. Antibiotic strips were employed to study the antibiotic resistance among strains.

Results

In all, 73 S. aureus strains were obtained from 368 bovine raw milk samples out of that only 30 showed the presence of coa. Nine types of coa patterns ranging from 730 to 1130 bp were observed among these isolates. PCR–RFLP of coa distinguished the isolates into 15 genotypic patterns, of which patterns I, IV, V, and VI were predominant. Of the isolates, 30% were positive for sec, 10% for sea, and 3.3% for seb; these genes are responsible for enterotoxin production, whereas all isolates were found positive for icaAD and eno. The prevalence rates of other biofilm-producing genes fnbA, clfB, ebpS, sasG, fnbB, sasC, cna, bap, fib and, bbp were 97, 93, 90, 80, 80, 77, 53, 27, 10, and 6.6%, respectively. Twenty-seven (90%) strains were multidrug resistant, of which 15 were methicillin resistant. Maximum sensitivity was reported for kanamycin and it could be considered as a drug of choice for controlling S. aureus mediated cattle infections in the studied regions.

Conclusions

Overall, these strains could cause several diseases to humans, insisting the need for developing a stricter hygiene program for improving milking practices and animal health.

Streptomyces sp. AT37 isolated from a Saharan soil produces a furanone derivative active against multidrug-resistant Staphylococcus aureus

A novel actinobacterium strain, named AT37, showed a strong activity against some multidrug-resistant Staphylococcus aureus, including methicillin-resistant S. aureus MRSA ATCC 43300, other clinical isolates of MRSA and vancomycin resistant S. aureus VRSA S1. The strain AT37 was isolated from a Saharan soil by a dilution agar plating method using chitin-vitamin agar medium supplemented with rifampicin. The morphological and chemical studies indicated that this strain belonged to the genus Streptomyces. Its 16S rRNA gene sequence was determined and a database search indicated that it was closely associated with the type strain of Streptomyces novaecaesareae NBRC 13368^T with 99.6% of similarity. However, the comparison of the morphological and the physiological characteristics of the strain with those of the nearest species showed significant differences. The strain AT37 secreted the antibiotic optimally during mid-stationary phase of growth. One active compound (AT37-1) was extracted from the culture broth with dichloromethane, separated on silica gel plates and purified by HPLC. Based on spectroscopic analysis of UV-Visible, infrared, and ¹H and ¹³C NMR spectra and spectrometric analysis, the chemical structure of the compound AT37-1 was identified as 5-[(5E,7E,11E)-2,10-dihydroxy-9,11-dimethyl-5,7,11-tridecatrien-1-yl]-2-hydroxy-2-(1-hydroxyethyl)-4-methyl-3(2H)-furanone. Minimum inhibitory concentrations and minimum biofilm inhibitory concentration (MBIC₅₀) of this compound showed significant activity against multidrug-resistant S. aureus with 15-30 and 10-15 μg/mL, respectively.