The ESKAPE pathogens (Enterococcus faecium,Staphylococcus aureus,Klebsiella pneumoniae,Acinetobacter baumannii,Pseudomonas aeruginosa, andEnterobacterspecies) are the leading cause of nosocomial infections throughout the world. Most of them are multidrug resistant isolates, which is one of the greatest challenges in clinical practice. Multidrug resistance is amongst the top three threats to global public health and is usually caused by excessive drug usage or prescription, inappropriate use of antimicrobials, and substandard pharmaceuticals. Understanding the resistance mechanisms of these bacteria is crucial for the development of novel antimicrobial agents or other alternative tools to combat these public health challenges. Greater mechanistic understanding would also aid in the prediction of underlying or even unknown mechanisms of resistance, which could be applied to other emerging multidrug resistant pathogens. In this review, we summarize the known antimicrobial resistance mechanisms of ESKAPE pathogens.

A clique of Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. (ESKAPE) bugs is the utmost causative agent responsible for multidrug resistance in hospital settings. These microorganisms employ a type of cell–cell communication termed ‘quorum sensing (QS) system’ to mediate population density and synchronously control the genes that modulate drug resistance and pathogenic behaviors. In this article, we focused on the present understanding of the prevailing QS system in ESKAPE pathogens. Basically, the QS component consisted of an autoinducer synthase, a ligand (e.g., acyl homoserine lactones/peptide hormones), and a transcriptional regulator. QS mediated expression of the bacterial capsule, iron acquisition, adherence factors, synthesis of lipopolysaccharide, poly-N-acetylglucosamine (PNAG) biosynthesis, motility, as well as biofilm development allow bacteria to promote an antimicrobial-resistant population that can escape the action of traditional drugs and endorse a divergent virulence production. The increasing prevalence of these harmful threats to infection control, as well as the urgent need for effective antimicrobial strategies to combat them, serve to highlight the important anti-QS strategies developed to address the difficulty of treating microorganisms.

Subclinical mastitis is a persistent problem in dairy farms worldwide. Environmental Escherichia coli is the bacterium predominantly responsible for this condition. In Thailand, subclinical mastitis in dairy cows is usually treated with various antibiotics, which could lead to antibiotic resistance in bacteria. E. coli is also a reservoir of many antibiotic resistance genes, which can be conveyed to other bacteria. In this study, the presence of E. coli in milk and water samples was reported, among which enteropathogenic E. coli was predominant, followed by enteroaggregative E. coli and enterohemorrhagic E. coli, which was found only in milk samples. Twenty-one patterns of antibiotic resistance were identified in this study. Ampicillin- and carbenicillin-resistant E. coli was the most common among the bacterial isolates from water samples. Meanwhile, resistance to ampicillin, carbenicillin, and sulfamethoxazole-trimethoprim was the pattern found most commonly in the E. coli from milk samples. Notably, only the E. coli from water samples possessed ESBL phenotype and carried antibiotic resistance genes, bla_TEM and bla_CMY-2. This indicates that pathogenic E. coli in dairy farms is also exposed to antibiotics and could potentially transfer these genes to other pathogenic bacteria under certain conditions.

Background: Staphylococcusspp. are major cause of bovine mastitis (BM) worldwide leading to economic damage to dairy farms and public health threat. Recently, a newly emergedStaphylococcus argenteushas been found as a human and animal pathogen. Molecular characteristics, virulence and antibiotic resistant phenotypes of bacteria causing BM in Thailand are rare. This study aimed to investigatedStaphylococcusspp. associated with subclinical bovine mastitis (SCM) in Thailand.Methods: Milk samples were collected from 224 cows of 52 dairy herds in four central and northeast provinces. Total somatic cell counts (SCC) and California mastitis test (CMT) were used to identify SCM cows. Milk samples were cultured forStaphylococcusspp. Coagulase-positive isolates were subjected to pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Organisms suspected asS. argenteuswere verified by detecting nonribosomal peptide synthetase gene. All isolates were checked for antibiograms and the presence of various virulence genes.Results: From the 224 milk samples of 224 cows, 132 (59%) were positive for SCM by SCC and CMT and 229 staphylococcal isolates were recovered. They were 32 coagulase-positive (24S. aureusand eightS. argenteus) and 197 coagulase-negative. PFGE of theS. aureusandS. argenteusrevealed 11 clusters and a non-typeable pattern. MLST of representatives of the 11 PFGE clusters, three PFGE non-typeableS. aureusisolates from different locations andS. argenteusshowed 12 sequence types. The eightS. argenteusisolates belonged to ST1223 (three isolates), ST2250 (two isolates), and ST2793 (two isolates). The antimicrobial tests identified 11 (46%) methicillin-resistantS. aureusand 25 (13%) methicillin-resistant coagulase-negative isolates, while sevenS. argenteuswere methicillin-susceptible and one isolate was methicillin-resistant. All of the 229 isolates were multiply resistant to other antibiotics. The most prevalent virulence genes of the 24S. aureusisolates wereclfA,coaandspa(X and IgG-binding region) (100%),hla(96%),pvl(96%) andsec(79%). SixS. argenteusisolates carried one enterotoxin gene each and other virulence genes includingcoa, clfA, hla/hlb, spa, tsstandpvl, indicating their pathogenic potential.Conclusion and perspective: This is the first report on theS. argenteusfrom cow milk samples with SCM. Data on the molecular characteristics, virulence genes and antibiograms of theStaphylococcusspp. obtained from the present study showed a wide spread and increasing trend of methicillin-resistance and multiple resistance to other antibiotics. This suggests that the “One Health” practice should be nurtured, not only at the dairy farm level, but also at the national or even the international levels through cooperation of different sectors (dairy farmers, veterinarians, medical and public health personnel and scientists) in order to effectively combat and control the spread of these pathogens.

Burkholderia pseudomalleiis a Gram-negative bacterium that causes melioidosis, which can be fatal in humans. Melioidosis is prevalent in the tropical regions of Southeast Asia and Northern Australia. Ecological data have shown that this bacterium can survive as a free-living organism in environmental niches, such as soil and water, as well as a parasite living in host organisms, such as ameba, plants, fungi, and animals. This review provides an overview of the survival and adaptation ofB. pseudomalleito stressful conditions induced by hostile environmental factors, such as salinity, oxidation, and iron levels. The adaptation ofB. pseudomalleiin host cells is also reviewed. The adaptive survival mechanisms of this pathogen mainly involve modulation of gene and protein expression, which could cause alterations in the bacteria’s cell membrane, metabolism, and virulence. Understanding the adaptations of this organism to environmental factors provides important insights into the survival and pathogenesis ofB. pseudomallei, which may lead to the development of novel strategies for the control, prevention, and treatment of melioidosis in the future.

Aim of this study was to compare and assess the screening method, Mannitol fermentation test (Mannitol salt agar [MSA]), and deoxyribonuclease (DNase) test, for S. aureus identification in milk samples