The mecA homolog mecC confers resistance against β-lactams in Staphylococcus aureus irrespective of the genetic strain background

Molecular detection of blaTEM-encoding genes in multidrug-resistant Escherichia coli from cloacal swabs of ducks in Indonesia farms

Background

Globally, there is an increasing frequency of community-acquired illnesses caused by extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. The presence of ESBL-producing E. coli in livestock is a concern, considering its transmission potential to humans, effects on animal health, risks to food safety, and the widespread spread of antibiotic resistance in both human and animal populations.

Aim

This study investigated the prevalence and characterization of ESBL-producing E. coli in cloacal swab samples collected from duck farms in Jombang, Indonesia.

Methods

In total, 125 cloacal swab samples of ducks were collected from farms. Samples were processed and analyzed for E. coli isolation using standard microbiology techniques. Isolated E. coli strains were further subjected to antimicrobial susceptibility testing and ESBL phenotypic detection using disc diffusion and double-disk synergy test techniques, respectively. Identified multidrug-resistant (MDR) E. coli strains were thereafter screened for the detection of blaTEM ESBL gene by PCR.

Results

A total of 94 (52.2%) out of the collected 180 swab samples were positive for E. coli. Twenty-five (39.1%) out of the recovered E. coli isolates were generally noted to exhibit MDR traits. Exactly 24 (96%) out of the 25 MDR E. coli strains that were selected for molecular studies harbored the blaTEM gene.

Conclusion

The detection of MDR E. coli harboring blaTEM ESBL gene in ducks in our study area is a significant public health problem. Therefore, strong and impactful preventive measures, which would curtail the increasing dissemination of MDR bacterial pathogens in agricultural settings, are urgently needed.

Molecular detection of blaTEM-encoding genes in multidrug-resistant Escherichia coli from cloacal swabs of ducks in Indonesia farms

Background

Globally, there is an increasing frequency of community-acquired illnesses caused by extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. The presence of ESBL-producing E. coli in livestock is a concern, considering its transmission potential to humans, effects on animal health, risks to food safety, and the widespread spread of antibiotic resistance in both human and animal populations.

Aim

This study investigated the prevalence and characterization of ESBL-producing E. coli in cloacal swab samples collected from duck farms in Jombang, Indonesia.

Methods

In total, 125 cloacal swab samples of ducks were collected from farms. Samples were processed and analyzed for E. coli isolation using standard microbiology techniques. Isolated E. coli strains were further subjected to antimicrobial susceptibility testing and ESBL phenotypic detection using disc diffusion and double-disk synergy test techniques, respectively. Identified multidrug-resistant (MDR) E. coli strains were thereafter screened for the detection of blaTEM ESBL gene by PCR.

Results

A total of 94 (52.2%) out of the collected 180 swab samples were positive for E. coli. Twenty-five (39.1%) out of the recovered E. coli isolates were generally noted to exhibit MDR traits. Exactly 24 (96%) out of the 25 MDR E. coli strains that were selected for molecular studies harbored the blaTEM gene.

Conclusion

The detection of MDR E. coli harboring blaTEM ESBL gene in ducks in our study area is a significant public health problem. Therefore, strong and impactful preventive measures, which would curtail the increasing dissemination of MDR bacterial pathogens in agricultural settings, are urgently needed.

Antimicrobial resistance, virulence profiling, and drug repurposing analysis of Staphylococcus aureus from camel mastitis

Camel mastitis especially caused by Staphylococcus aureus (S. aureus), is a major risk to animal health and milk production. The current investigation evaluated the antibiotic susceptibility and virulence factors of S. aureus isolates from subclinical mastitis in camels. A total of 384 milk samples were collected and submitted to isolate S. aureus. The S. aureus isolates exhibiting resistance to Penicillin and Cefoxitin disc on Kirby-Bauer disc diffusion method were considered as β-lactam resistant S. aureus (BRSA) and methicillin-resistant S. aureus (MRSA) which were further confirmed by PCR targeting blaZ and mecA genes, respectively. The results showed that S. aureus was found in 57.06% of subclinical (SCM) positive camel milk samples. A high molecular prevalence of BRSA and MRSA were found to be 48.51% and 46.53% respectively depicting that treating these infections is challenging due to their high resistance levels. The phylogenetic analysis revealed a significant resemblance of the study isolates with each other and with already reported sequences from different countries which shows the potential for the spread of pathogen. Virulence profiling of antibiotic resistance strains showed the presence of virulence markers (nuc and coag genes), intercellular adhesion genes (icaA, icaD), Panton-Valentine leukocidin (pvl) gene, and enterotoxin-producing genes including sea, seb, sec, and sed. In-vitro antibiotic susceptibility testing revealed that the most resistant antibiotic group was penicillin followed by aminoglycosides and cephalosporins. Drug repurposing analysis of different non-antibiotics for combination therapies with resistant antibiotics was done to combat the S. aureus isolates harboring the mecA and blaZ genes. The results revealed the synergistic effect of amoxicillin, sulfamethoxazole, gentamicin, and doxycycline with ketoprofen, amikacin with flunixin meglumine, and gentamicin with N-acetylcysteine (NAC) against study isolates. The current investigation provides the status of antibiotic-resistant strains and virulence factors of S. aureus in the udder of dromedary camels. The combinational therapy of resistant antibiotics with non-antibiotics provides a potential therapeutic option for the treatment of resistant strains.

Development of a clinical metagenomics workflow for the diagnosis of wound infections

BACKGROUND

Wound infections are a common complication of injuries negatively impacting the patient's recovery, causing tissue damage, delaying wound healing, and possibly leading to the spread of the infection beyond the wound site. The current gold-standard diagnostic methods based on microbiological testing are not optimal for use in austere medical treatment facilities due to the need for large equipment and the turnaround time. Clinical metagenomics (CMg) has the potential to provide an alternative to current diagnostic tests enabling rapid, untargeted identification of the causative pathogen and the provision of additional clinically relevant information using equipment with a reduced logistical and operative burden.

METHODS

This study presents the development and demonstration of a CMg workflow for wound swab samples. This workflow was applied to samples prospectively collected from patients with a suspected wound infection and the results were compared to routine microbiology and real-time quantitative polymerase chain reaction (qPCR).

RESULTS

Wound swab samples were prepared for nanopore-based DNA sequencing in approximately 4 h and achieved sensitivity and specificity values of 83.82% and 66.64% respectively, when compared to routine microbiology testing and species-specific qPCR. CMg also enabled the provision of additional information including the identification of fungal species, anaerobic bacteria, antimicrobial resistance (AMR) genes and microbial species diversity.

CONCLUSIONS

This study demonstrates that CMg has the potential to provide an alternative diagnostic method for wound infections suitable for use in austere medical treatment facilities. Future optimisation should focus on increased method automation and an improved understanding of the interpretation of CMg outputs, including robust reporting thresholds to confirm the presence of pathogen species and AMR gene identifications.

Genetic Characterization of Methicillin-Resistant Staphylococcus aureus Isolated From Diabetic Foot Ulcers in a Tertiary Care Hospital in Mysuru, South India

Background Diabetic foot ulcers (DFUs) are common complications in diabetes patients, often leading to sepsis and leg amputation. Methicillin-resistant Staphylococcus aureus (MRSA) infections in DFUs pose challenges due to methicillin resistance with mecA and mecC genes. This study aims to assess the prevalence of MRSA in clinical isolates from DFUs, analyze the antibiogram of MRSA isolates, and detect the presence of the mecA and mecC genes among MRSA isolates. Methodology The isolated S. aureus colonies were identified and antimicrobial susceptibility was performed using the Vitek-2 Compact system. Methicillin resistance was also confirmed through the disc diffusion method. Confirmed methicillin-resistant isolates were subjected to real-time polymerase chain reaction (RT-PCR) to detect mecA and mecC genes. Results A total of 474 purulent samples from DFUs yielded 541 distinct isolates, comprising 201 gram-positive and 340 gram-negative organisms. Among the gram-positive organisms, Staphylococcus species predominated, with 79 S. aureus isolates, 34 of which were methicillin-resistant. All MRSA isolates (100%) were sensitive to tetracycline, linezolid, teicoplanin, and vancomycin, and 94% were sensitive to cotrimoxazole but least susceptible to ciprofloxacin and levofloxacin. RT-PCR confirmed the presence of mecA genes in all 34 isolates and mecC genes in three isolates. Conclusions The presence of mecA in all 34 MRSA isolates underscores consistent methicillin resistance. The co-occurrence of mecA and mecC in three isolates hints at genetic diversity. Two MRSA isolates positive for mecC were isolated from rural patients involved in farming and animal husbandry, suggesting an occupational risk. The third patient was from a non-rural area, indicating potential alternative transmission pathways warranting further investigation.

Molecular and epidemiological characterization of Staphylococcus aureus causing bovine mastitis in China

BACKGROUND

Staphylococcus aureus is one of the most prevalent pathogens in bovine mastitis, which leads to substantial financial losses for the dairy industry.

RESULTS

In this study, S. aureus (n = 72) was isolated from 18 dairy farms in 15 provinces across China in 2021. The identification of these isolates at the species level was achieved by employing 16S rRNA sequencing. An isothermal amplification method for auxiliary detection of S. aureus was established, which can be employed not only for laboratory detection but also for point-of-care testing (POCT). Molecular characteristics of S. aureus mastitis in Chinese dairy cows were determined through MLST and spa typing. Finally, methicillin-resistant Staphylococcus aureus (MRSA) and MRSA resistance genes were detected using MIC and PCR amplification techniques. 72 isolates were identified as 12 sequence types (STs) and 7 clonal complexes (CC). ST1/CC1 was the dominant prevalent accounting for 33.3 % of the total, and exhibiting a wide distribution range. In terms of spa types, t114 was the dominant type, accounting for 31.9 % of the total, followed by t529 as the second major type. Four S. aureus strains were classified as MRSA according to their levels of oxacillin resistance (MIC ≥4 μg/mL). Among these four MRSA strains, one of them was found to be mecA positive. However, the presence of drug-resistance genes mecA and mecC was not detected in the remaining three MRSA strains, indicating the possible existence of new resistance genes.

CONCLUSIONS

Our study investigated the prevalence of S. aureus mastitis in dairy cows in China, while also examined the molecular characteristics and MRSA strains. This information will help with the clinical monitoring, prevention, and control of S. aureus mastitis in dairy cattle.

Antimicrobial resistance patterns of Staphylococcus spp. isolated from clinical specimens of companion animals in Northern Portugal, 2021-2023

Staphylococcus spp. are growing pathogens in humans and companion animals. The emergence of multidrug-resistant bacterial infections, such as methicillin-resistant Staphylococcus-associated infections, due to zoonotic transmission, is a major public health concern. Domestic animals, such as dogs and cats, are possible reservoirs of multi-resistant bacterial species, which makes it relevant to monitor them due to their proximity to humans. However, there is a lack of information on the real scenario in Europe, especially in Portugal, particularly for animal infections caused by Staphylococcus spp. Therefore, this study aimed to investigate the antimicrobial resistance profile of Staphylococcus spp. isolated from cats and dogs diagnosed with infection in Northern Portugal. During 2021-2023, 96 Staphylococcus isolates from dogs and cats with symptoms of bacterial infection, including animals being treated in veterinary clinics/hospitals and cadavers submitted for necropsy at INIAV were included in the study collection. Of the 96 isolates, 63 were from dogs and 33 were Staphylococcus spp. from cats, most of which were isolated from ear (57% and 18%, respectively), skin (19 % and 27 %, respectively) and respiratory tract infections (6 % and 27 %, respectively). Among all the isolates, 12 different Staphylococcus spp. were identified, with Staphylococcus pseudintermedius being the most identified (61 % from dogs and 30 % from cats). It is noteworthy that 36 % of the isolates were multi-drug resistant and 25 % of the isolates showed a methicillin-resistant phenotype, with the mecA gene having been identified in all these isolates. This study highlights a high occurrence of multidrug-resistant Staphylococcus spp. in companion animals in Northern Portugal. This underlines the potential for cats and dogs to act as reservoirs of antimicrobial resistance, that can be transmitted to humans, posing a serious threat to public health.

Molecular detection of extended-spectrum β-lactamase-producing Escherichia coli from bat caves on Lombok Island

Background

The discovery of antibiotic-resistant Enterobacteriaceae bacteria in wild animals is an indication of their potential for wildlife as a reservoir. Bats are natural reservoir hosts and a source of infection for several microorganisms and have the potential to become vectors for the spread of zoonotic diseases.

Aim

A study was conducted based on these characteristics to identify and detect the blaTEM gene in Eschericia coli isolated from bat excrements in Tanjung Ringgit Cave, East Lombok.

Methods

Bat fecal samples were firstly inoculated onto eosin methylene blue agar media. Recovered bacterial isolates were further characterized using standard microbiological techniques. Antimicrobial susceptibility testing was done using the Kirby-Bauer disc diffusion method. blaTEM gene detection was carried out using polymerase chain reaction (PCR).

Results

Out of the 150 bat fecal samples obtained from Tanjung Ringgit cave, Lombok Island, Indonesia, 56 (37%) were positive for E. coli. Eight (8) out of the 56 E. coli isolates that underwent antimicrobial susceptibility testing using the disc diffusion method were confirmed to be multidrug-resistant as they exhibited resistance to at least three different classes of antibiotics. Out of the eight (8) multidrug resistance E. coli isolates recovered from fecal samples of bats, 2 (two) harbored the blaTEM gene.

Conclusion

The discovery of the blaTEM gene in bat fecal samples indicates the potential for wild animals, especially bats, to spread ESBL resistance genes to the environment and to humans.

Discrepancies between phenotypic and genotypic identification methods of antibiotic resistant genes harboring Staphylococcusaureus

Antimicrobial resistance is a global issue that limits therapeutic options for infections. S. aureus being a member of the ESKAPE group is capable of "escaping" the biocidal action of antimicrobial agents. There are phenotypic and genotypic methods used for the identification of antibiotic resistant genes harboring S. aureus but these methods do not always show concordant results. To address these discrepancies, a total of 335 equine nasal swab samples from four districts of Punjab were collected using a convenient sampling technique. These samples were first subjected to common microbial techniques to identify S. aureus. The disc diffusion assay was performed for the phenotypic identification of antibiotic resistant S. aureus by using discs of oxacillin, penicillin, vancomycin, gentamycin, and tetracycline. After this, PCR was performed by targeting mecA, blaZ, vanB, aaca-aphd, and tetK genes for genotypic identification of respective antibiotic-resistant S. aureus. Phenotypic discrepancies (number of antibiotic resistant isolates found from disc diffusion who appeared to be negative for the resistant gene), and genotypic discrepancies (number of antibiotic sensitive isolates found from disc diffusion who appeared to be positive for the resistant gene) were calculated. The discrepancy ratio for mecA, blaZ, vanB, aaca-aphd, and tetK genes were 3.09, 1.96, 2.67, 1.93, and 1.67 respectively. These discrepant results indicate that the absence or presence of only one gene is not a true marker of resistant or sensitive isolates. There are multiple resistance determinants and resistance mechanisms. This study also highlighted the phenomenon of silencing of antibiotic resistance determinants.

Molecular Determinants of β-Lactam Resistance in Methicillin-Resistant Staphylococcus aureus (MRSA): An Updated Review

The development of antibiotic resistance in Staphylococcus aureus, particularly in methicillin-resistant S. aureus (MRSA), has become a significant health concern worldwide. The acquired mecA gene encodes penicillin-binding protein 2a (PBP2a), which takes over the activities of endogenous PBPs and, due to its low affinity for β-lactam antibiotics, is the main determinant of MRSA. In addition to PBP2a, other genetic factors that regulate cell wall synthesis, cell signaling pathways, and metabolism are required to develop high-level β-lactam resistance in MRSA. Although several genetic factors that modulate β-lactam resistance have been identified, it remains unclear how they alter PBP2a expression and affect antibiotic resistance. This review describes the molecular determinants of β-lactam resistance in MRSA, with a focus on recent developments in our understanding of the role of mecA-encoded PBP2a and on other genetic factors that modulate the level of β-lactam resistance. Understanding the molecular determinants of β-lactam resistance can aid in developing novel strategies to combat MRSA.

Phenotypic and Genotypic Characterization of Methicillin Resistance in Staphylococci Isolated from an Egyptian University Hospital

Methicillin-resistant in Staphylococci is a serious public health issue. It is mostly encoded by the mecA gene. The mecC gene is a new mecA analog responsible for resistance to methicillin in some Staphylococcal clinical isolates. This mecC gene is still underestimated in Egypt. The aim of the current study was to detect mecA and mecC genes in clinical Staphylococci isolates from a tertiary care university hospital in Egypt compared to the different phenotypic methods. A total of 118 Staphylococcus aureus (S. aureus) and 43 coagulase-negative Staphylococci (CoNS) were identified from various hospital-acquired infections. Methicillin resistance was identified genotypically using the PCR technique and phenotypically using the cefoxitin disc diffusion test, oxacillin broth microdilution and the VITEK2 system in all Staphylococcal isolates. The mecA gene was detected in 82.2% of S. aureus and 95.3% of CoNS isolates, while all of the isolates tested negative for the mecC gene. Interestingly, 30.2% of CoNS isolates showed the unique character of inducible oxacillin resistance, being mecA-positive but oxacillin-susceptible (OS-CoNS). The dual use of genotypic and phenotypic methods is highly recommended to avoid missing any genetically divergent strains.

Invited review: Antimicrobial resistance in bovine mastitis pathogens: A review of genetic determinants and prevalence of resistance in European countries

Antimicrobial resistance is an urgent and growing problem worldwide, both for human and animal health. In the animal health sector actions have been taken as concerns grow regarding the development and spread of antimicrobial resistance. Mastitis is the most common infection in dairy cattle. We aimed to summarize the genetic determinants found in staphylococci, streptococci, and Enterobacteriaceae isolated from mastitic milk samples and provide a comparison of percentage resistance to a variety of antimicrobials in European countries.

Evidence-based identification and characterization of methicillin-resistant Staphylococcusaureus isolated from subclinical mastitis in dairy buffaloes of Pakistan

Background

Methicillin-resistant Staphylococcus aureus (MRSA), affecting livestock and human beings, has become a global public health hazard with economic consequences.

Aims

The current study was designed to investigate the prevailing MRSA-associated subclinical mastitis and associated risk factors in dairy buffaloes. The study also highlighted the genetic variations and in silico-based proteomic differences among MRSA isolates.

Methods

Out of 516 milk samples, 45.93% (237/516) were found positive for subclinical mastitis, while the prevalence of S. aureus was recorded 56.12%. The methicillin resistance in S. aureus isolates was evaluated by oxacillin disc diffusion test and molecular identification of the mecA gene.

Results

The results revealed a phenotypic and molecular prevalence of MRSA at 45.11% and 18.79%, respectively. The risk factor analysis revealed that among various assumed risk factors, parity, milking hygiene, milker care during milking, milk yield, housing system, and floor type were significantly associated with subclinical mastitis in buffaloes. The sequencing and phylogenetic analysis showed no significant genetic variations among study isolates and depicted a high similarity with isolates from Africa, USA, India, Italy, Turkey, and Iran. The in-silico protein analysis showed that all sequences had the same protein motifs resembling penicillin protein 2a except Buff-13, whose protein structure resembles alpha-catenin-like protein hmp-1.

Conclusion

The current study was the first report of the genotypic characterization and in silico protein analysis of MRSA from dairy buffaloes in Pakistan. The result highlighted the importance of antimicrobial resistance (AMR) and development of control strategies against MRSA infections.

Recent Progress in the Diagnosis of Staphylococcus in Clinical Settings

Staphylococci are mainly found on the skin or in the nose. These bacteria are typically friendly, causing no harm to healthy individuals or resulting in only minor issues that can go away on their own. However, under certain circumstances, staphylococcal bacteria could invade the bloodstream, affect the entire body, and lead to life-threatening problems like septic shock. In addition, antibiotic-resistant Staphylococcus is another issue because of its difficulty in the treatment of infections, such as the notorious methicillin-resistant Staphylococcus aureus (MRSA) which is resistant to most of the currently known antibiotics. Therefore, rapid and accurate diagnosis of Staphylococcus and characterization of the antibiotic resistance profiles are essential in clinical settings for efficient prevention, control, and treatment of the bacteria. This chapter highlights recent advances in the diagnosis of Staphylococci in clinical settings with a focus on the advanced technique of surface-enhanced Raman spectroscopy (SERS), which will provide a framework for the real-world applications of novel diagnostic techniques in medical laboratories via bench-top instruments and at the bedside through point-of-care devices.

Detection of Resistant and Enterotoxigenic Strains of Staphylococcus warneri Isolated from Food of Animal Origin

The topic of this work is the detection of antimicrobial resistance to Staphylococcus warneri strains and the genes encoding staphylococcal enterotoxins. It is considered a potential pathogen that can cause various-mostly inflammatory-diseases in immunosuppressed patients. The experimental part of the paper deals with the isolation of individual isolates from meat samples of Oryctolagus cuniculus, Oncorhynchus mykiss, Scomber scombrus, chicken thigh, beef thigh muscle, pork thigh muscle, and bryndza cheese. In total, 45 isolates were obtained and subjected to phenotypic (plasma coagulase activity, nuclease, pigment, hemolysis, lecithinase, and lipase production) and genotypic analyses to confirm the presence of the S. warneri species. The presence of genes encoding staphylococcal enterotoxins A (three isolates) and D (six isolates) was determined by PCR. Using the Miditech system, the minimum inhibitory concentration for various antibiotics or antibiotics combinations was determined, namely for ampicillin; ampicillin + sulbactam; oxacillin; cefoxitin; piperacillin + tazobactam; erythromycin; clindamycin; linezolid; rifampicin; gentamicin; teicoplanin; vancomycin; trimethoprim; chloramphenicol; tigecycline; moxifloxacin; ciprofloxacin; tetracycline; trimethoprim + sulfonamide; and nitrofurantoin. Resistance to ciprofloxacin and tetracycline was most common (73%). At the same time, out of a total of 45 isolates, 22% of the isolates were confirmed as multi-resistant. Isolates that showed phenotypic resistance to β-lactam antibiotics were subjected to mecA gene detection by PCR.

An Interplay of Multiple Positive and Negative Factors Governs Methicillin Resistance in Staphylococcus aureus

The development of resistance to β-lactam antibiotics has made Staphylococcus aureus a clinical burden on a global scale. MRSA (methicillin-resistant S. aureus) is commonly known as a superbug. The ability of MRSA to proliferate in the presence of β-lactams is attributed to the acquisition of mecA, which encodes the alternative penicillin binding protein, PBP2A, which is insensitive to the antibiotics. Most MRSA isolates exhibit low-level β-lactam resistance, whereby additional genetic adjustments are required to develop high-level resistance. Although several genetic factors that potentiate or are required for high-level resistance have been identified, how these interact at the mechanistic level has remained elusive. Here, we discuss the development of resistance and assess the role of the associated components in tailoring physiology to accommodate incoming mecA.

Impact of the Stringent Stress Response on the Expression of Methicillin Resistance in Staphylococcaceae Strains Carrying mecA, mecA1 and mecC

The acquisition of the resistance determinant mecA by Staphylococcus aureus is of major clinical importance, since it confers a resistant phenotype to virtually the entire large family of structurally diverse β-lactam antibiotics. While the common resistance determinant mecA is essential, the optimal expression of the resistance phenotype also requires additional factors. Previous studies showed that the great majority of clinical isolates of methicillin-resistant S. aureus (MRSA) have a heterogeneous resistant phenotype, and we observed that strains carrying methicillin genetic determinants other than mecA also produce similar heterogeneous phenotypes. All these strains were able to express high and homogeneous levels of oxacillin resistance when sub-inhibitory concentrations of mupirocin, an effector of the stringent stress response, were added to growth media. Our studies show that the gene gmk, involved in guanine metabolism, was one of the first genes to exhibit mutations in homoresistant (H*R) derivatives obtained through serial passages (with increasing concentrations of oxacillin) of the prototype mecC-carrying MRSA strain LGA251. All these observations led us to propose that a common molecular mechanism for the establishment of high and homogeneous oxacillin resistance must be present among isolates carrying different methicillin resistance determinants. In this work, we tested this hypothesis using whole-genome sequencing (WGS) to compare isogenic populations differing only in their degrees of oxacillin resistance and carrying various methicillin genetic determinants

Immunofluorescence Targeting PBP2a Protein: A New Potential Methicillin Resistance Screening Test

The indiscriminate use of first-line drugs contributed to the spread of resistant bacteria, a major concern for both human and veterinary medicine. Methicillin resistance is acquired through the mecA gene, which encodes for the PBP2a protein and lends the resistance to β-lactams. Verifying the correspondence between gene harboring and protein expression and accelerating methicillin resistance diagnosis is critical to improve the management of antimicrobial administration and to reduce the spread of drug resistances. We tested the applicability of immunofluorescence targeting PBP2a protein to identify a new potential methicillin resistance screening test, ancillary to conventional culture methods. We collected 26 clinical Staphylococcus pseudintermedius (SP) isolates: 25 from canine pyoderma and 1 from dermatitis in a dog owner. SP is one of the most important etiological agents in canine pyoderma and can harbor the mecA gene. We performed PCR for mecA gene detection, broth microdilution (BMD) for phenotypic methicillin resistance, and immunofluorescence targeting PBP2a protein. Compared to the PCR as the gold standard, immunofluorescence showed an apparent prevalence of 34.6% vs. a true prevalence of 53.8%, with 100% specificity, 64.3% sensitivity, and 80.8% diagnostic accuracy. PBP2a expression showed isolate-dependent variability: in some isolates, most of the bacterial cells showed an intense and clearly membranous pattern, while in others only a few of them could be detected. Performing the assay in duplicate improved the diagnostic accuracy. Since the mecA gene is shared among the members of the Staphylococcus genus, the test can be applied to identify methicillin resistance independently from the staphylococcal species, both in human and animal samples. Being a rapid and easy method and providing the unique possibility to study the expression of PBP2a by directly visualizing the morphology, it could represent a new interesting tool for both research and diagnostics. To accelerate methicillin resistance diagnosis, it would be worth further testing of its performance on cytological samples.

Evaluation of virulence potential of methicillin-sensitive and methicillin-resistant Staphylococcus aureus isolates from a German refugee cohort

BACKGROUND

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) seem to be highly transmissible, often infect otherwise healthy humans and frequently occur in hospital outbreaks.

METHODS

Refugees, living in accommodations in Germany were screened for nasal carriage of S. aureus. The isolates were investigated regarding resistance and virulence, phenotypically and by whole genome data analysis.

RESULTS

5.6% (9/161) of the refugees are carriers of S. aureus. 2.5% (4/161) are MRSA carriers. Among the refugees, spa-types t021, t084, t304, t991 and t4983 were detected, as well as the new spa-types t18794 and t18795. t304 and t991 are assumed to be local spa-types from the middle east. The isolates are less resistant and marginal biofilm formers. Each isolate has a remarkable set of virulence genes, although genes, encoding for proteins strongly associated with invasive S. aureus infections, like Panton-Valentine leucocidin, were not detected.

CONCLUSION

The detection of strains from the middle east, supports the assumption that strains co-travel with the refugees and persist despite a transition of the host's living conditions. Whole genome data analysis does not permit to finally evaluate a germ's virulence. Nevertheless, an impression of the virulence potential of the strains, regarding skills in colonization, resistance, immune evasion, and host cell damaging can be pictured.

Methicillin-Resistant Staphylococcus aureus Proteome Response to Antibiotic Stress Provides Insights for New Therapeutic Strategies

Antimicrobial resistance is a global threat, with methicillin-resistant Staphylococcus aureus (MRSA) being one of the most representative drug-resistant pathogens. MRSA spread is increasing due to its ability to establish new reservoirs. To this end, the clonal complex (CC)-130 is an emerging genetic lineage, generally regarded as animal adapted and carrying the mecC gene, and sporadically found in humans. Although the MRSA antibiotic resistance mechanisms have been described, there are limited data on systems-wide omics responses to antibiotic stress, particularly at the proteome level. In this study, a gel-based quantitative proteomics approach was performed to assess the cellular responses of a mecC-harboring CC130 MRSA strain of human origin to subinhibitory doses of cefoxitin. We focused on the global response of MRSA to antibiotic stress and upon this treatment, 53 proteins were significantly differentially expressed. Most of the latter proteins were mapped to having functions in cellular metabolism while some glycolysis-related proteins showed a decreased expression after cefoxitin stress. On the contrary, pyruvate kinase, a potential antimicrobial drug target, was found upregulated. Also, quorum sensing, genetic information processing, and stress response proteins were found upregulated. Low-affinity penicillin-binding protein (mecC-encoded) was found in cefoxitin-treated samples. In conclusion, these new findings on cefoxitin-induced proteome changes provide important insights and molecular leads for innovation in treatment of MRSA specifically, and omics approaches to address antibiotic resistance generally.

Harnessing Fluorescent Moenomycin A Antibiotics for Bacterial Cell Wall Imaging Studies

The imaging of peptidoglycan (PGN) dynamics in living bacteria facilitates the understanding of PGN biosynthesis and wall-targeting antibiotics. The main tools for imaging bacterial PGN are fluorescent probes, such as the well-known PGN metabolic labeling probes. However, fluorescent small-molecule probes for labeling key PGN-synthesizing enzymes, especially for transglycosylases (TGases), remain to be explored. In this work, the first imaging probe for labeling TGase in bacterial cell wall studies is reported. We synthesized various fluorescent MoeA-based molecules by derivatizing the natural antibiotic moenomycin A (MoeA), and used them to label TGases in living bacteria, monitor bacterial growth and division cycles by time-lapse imaging, and study cell wall growth in the mecA-carrying methicillin-resistant Staphylococcus aureus (MRSA) strains when the β-lactam-based probes were unsuitable.

Detection of Antimicrobial Resistance of Bacteria Staphylococcus chromogenes Isolated from Sheep's Milk and Cheese

Antimicrobial and multidrug resistance is detected in nonaureus staphylococci, including Staphylococcus chromogenes, which commonly causes intramammary infections. Recent clinical studies point to the presence of methicillin-resistant S. chromogenes. Therefore, this study aims to determine the prevalence of this species in samples of sheep's milk and cheeses made from them. Isolates were identified by polymerase chain reaction and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF). A total of 208 staphylococcal isolates were identified. Of these, 18% were identified as S. chromogenes. The antimicrobial resistance of the identified isolates was determined using the agar dilution method against penicillin, ceftaroline, teicoplanin, gentamicin, erythromycin, tetracycline, and ofloxacin. The highest resistance was found to penicillin (95%), tetracycline (86%), and oxacillin (81%). The highest sensitivity was confirmed for gentamicin (55%). The study also confirmed the presence of methicillin resistant staphylococcal isolates (30%) based on the phenotypic manifestation of antimicrobial resistance and detection of the presence of the mecA gene. The study shows that the tested isolates (62%) were multidrug resistant. Resistance to two antibiotics was most often found (39%).

Improved diagnostic prediction of the pathogenicity of bloodstream isolates of Staphylococcus epidermidis

With an estimated 440,000 active cases occurring each year, medical device associated infections pose a significant burden on the US healthcare system, costing about $9.8 billion in 2013. Staphylococcus epidermidis is the most common cause of these device-associated infections, which typically involve isolates that are multi-drug resistant and possess multiple virulence factors. S. epidermidis is also frequently a benign contaminant of otherwise sterile blood cultures. Therefore, tests that distinguish pathogenic from non-pathogenic isolates would improve the accuracy of diagnosis and prevent overuse/misuse of antibiotics. Attempts to use multi-locus sequence typing (MLST) with machine learning for this purpose had poor accuracy (~73%). In this study we sought to improve the diagnostic accuracy of predicting pathogenicity by focusing on phenotypic markers (i.e., antibiotic resistance, growth fitness in human plasma, and biofilm forming capacity) and the presence of specific virulence genes (i.e., mecA, ses1, and sdrF). Commensal isolates from healthy individuals (n = 23), blood culture contaminants (n = 21), and pathogenic isolates considered true bacteremia (n = 54) were used. Multiple machine learning approaches were applied to characterize strains as pathogenic vs non-pathogenic. The combination of phenotypic markers and virulence genes improved the diagnostic accuracy to 82.4% (sensitivity: 84.9% and specificity: 80.9%). Oxacillin resistance was the most important variable followed by growth rate in plasma. This work shows promise for the addition of phenotypic testing in clinical diagnostic applications.

β-Lactams against the Fortress of the Gram-Positive Staphylococcus aureus Bacterium

The biological diversity of the unicellular bacteria-whether assessed by shape, food, metabolism, or ecological niche-surely rivals (if not exceeds) that of the multicellular eukaryotes. The relationship between bacteria whose ecological niche is the eukaryote, and the eukaryote, is often symbiosis or stasis. Some bacteria, however, seek advantage in this relationship. One of the most successful-to the disadvantage of the eukaryote-is the small (less than 1 μm diameter) and nearly spherical Staphylococcus aureus bacterium. For decades, successful clinical control of its infection has been accomplished using β-lactam antibiotics such as the penicillins and the cephalosporins. Over these same decades S. aureus has perfected resistance mechanisms against these antibiotics, which are then countered by new generations of β-lactam structure. This review addresses the current breadth of biochemical and microbiological efforts to preserve the future of the β-lactam antibiotics through a better understanding of how S. aureus protects the enzyme targets of the β-lactams, the penicillin-binding proteins. The penicillin-binding proteins are essential enzyme catalysts for the biosynthesis of the cell wall, and understanding how this cell wall is integrated into the protective cell envelope of the bacterium may identify new antibacterials and new adjuvants that preserve the efficacy of the β-lactams.

Stability Evaluation of Extemporaneously Compounded Vancomycin Ophthalmic Drops: Effect of Solvents and Storage Conditions

Vancomycin is the drug of choice for methicillin-resistant Staphylococcus aureus keratitis and other ocular infections. Vancomycin ophthalmic drops are not commercially available and require compounding. The present study was designed to investigate the stability of vancomycin ophthalmic drops in normal saline, phosphate-buffered saline (PBS), and balanced salt solution (BSS) while stored at room temperature or under refrigeration. Vancomycin ophthalmic drops (50 mg/mL) were aseptically prepared from commercially available intravenous powder using PBS, BSS, and saline. Solutions were stored at room temperature and in a refrigerator for 28 days. The vancomycin stability was tested by a microbiology assay and high-performance liquid chromatography HPLC analysis immediately after formulation and at days 7, 14, and 28 after storage at room temperature or under refrigeration. The pH, turbidity was also tested. Vancomycin formulations in PBS, BSS and normal saline had initial pH of 5; 5.5; 3 respectively. The formulation in PBS developed turbidity and a slight decrease in pH upon storage. Microbiological assay did not show any change in zone of inhibition with any of the formulation upon storage either at room temperature or under refrigeration. HPLC analysis did not detect any decrease in vancomycin concentration or the accumulation of degraded products in any of the formulations upon storage either at room temperature or under refrigeration. Vancomycin ophthalmic drops prepared using PBS, BSS, and normal saline were stable up to the tested time point of 28 days, irrespective of their storage temperature.

Comparative characterisation of human and ovine non-aureus staphylococci isolated in Sardinia (Italy) for antimicrobial susceptibility profiles and resistance genes

We present the comparative characterisation of 195 non-aureus staphylococci (NAS) isolates obtained from sheep (n = 125) and humans (n = 70) in Sardinia, Italy, identified at the species level by gap gene polymerase chain reaction (PCR) followed by restriction fragment length polymorphism analysis with AluI. Isolates were tested phenotypically with a disc diffusion method and genotypically by PCR, for resistance to 11 antimicrobial agents including cationic antiseptic agents. Among the ovine isolates, Staphylococcus epidermidis (n = 57), S. chromogenes (n = 29), S. haemolyticus (n = 17), S. simulans (n = 8) and S. caprae (n = 6) were the most prevalent species, while among human isolates, S. haemolyticus (n = 28) and S. epidermidis (n = 26) were predominant, followed by S. lugdunensis and S. hominis (n = 4). Of the 125 ovine isolates, 79 (63.2%) did not carry any of the resistance genes tested, while the remainder carried resistance genes for at least one antibiotic. The highest resistance rates among ovine isolates were recorded against tetracycline (20.8%), and penicillin (15.2%); none was resistant to methicillin and two exhibited multidrug resistance (MDR); one of which was positive for the antiseptic resistance smr gene. By contrast, most human isolates (59/70, 84.3%) were resistant to ⩾1 antimicrobials, and 41 (58.6%) were MDR. All 52 (74.3%) penicillin-resistant isolates possessed the blaZ gene, and 33 of 70 (47.1%) harboured the mec gene; of these, seven were characterised by the Staphylococcal Chromosomal Cassette (SCCmec) type IV, 6 the type V, 5 of type III and one representative each of type I and type II. The majority (57.1%) was erythromycin-resistant and 17 isolates carried only the efflux msrA gene, 11 the methylase ermC gene and an equal number harboured both of the latter genes. Moreover, 23 (32.8%) were tetracycline-resistant and all but one possessed only the efflux tetK gene. qacA/B and smr genes were detected in 27 (38.6%) and 18 (25.7%) human NAS, respectively. These results underline a marked difference in species distribution and antimicrobial resistance between ovine and human-derived NAS.

First report of a livestock-associated methicillin-resistant Staphylococcus aureus ST126 harbouring the mecC variant in Brazil

Staphylococcus aureus is a versatile and highly adaptable pathogen associated with a wide range of infectious diseases in humans and animals. In the last decades, concern has increased worldwide due to the emergence and spread of methicillin-resistant S. aureus (MRSA) strains shortly after this drug became a therapeutic option. In this study, we report the genomic features of the first mecC-mediated, β-lactam resistant MRSA strain associated with livestock in Brazil and in the American continent. Three clonally related phenotypic MRSA isolates originated from a dairy herd were confirmed by polymerase chain reaction as mecC-harbouring MRSA isolates. Whole-genome sequencing was performed by Illumina Miseq platform. Downstream analyses showed that the strain was identified as the sequence type 126 (ST126) and spa type t605. In silico analysis revealed a mecC homolog gene in the orfX region associated with different penicillin-binding proteins. Moreover, genes encoding for efflux pump systems (arlR, mepR, LmrS, norA and mgrA), and antibiotic inactivation enzymes (blaZ and FosB) were also detected. Virulence analyses revealed that the strain harbours genes encoding for exoenzymes (aur, splA, splB and splE), toxin (hlgA, hlgB, hlgC, lukD and lukE) and enterotoxin (sea). The epidemiologic and genomic information provided by this study will support further epidemiological and evolutionary investigations to understand the origin and dissemination of mecC-MRSA among animals and its impact on public health.

Insufficient repeatability and reproducibility of MALDI-TOF MS-based identification of MRSA

Rapid identification of methicillin-resistant Staphylococcus aureus (MRSA) is essential for proper initial antibiotic therapy and timely set up of hygienic measures. Recently, detection of MRSA using MALDI-TOF mass spectrometer mediated by the peptide-phenol-soluble modulin (PSM-mec)-linked to the class A mec gene complex present in SCCmec cassettes types II, III, and VIII of MRSA strains, has been commercially available. We present here a multicentre study on MALDI-TOF MS detection of MRSA evincing a poor repeatability and reproducibility of the assay. The sensitivity of the assay varies between 50 and 90% in strains carrying psm_MEC and psm_δ genes encoding for PSM-mec and δ-toxin (a member of the PSM peptide family), respectively. No false positive results were found. The very major error calculation was 30% and the major error achieved 0%. Interlaboratory repeatability varies between 0 and 100%. No significant difference was observed with the use of different cultivation media. Our data showed a poor sensitivity of the method excluding it from the use in routine laboratory testing.

The Virulence Potential of Livestock-Associated Methicillin-Resistant Staphylococcus aureus Cultured from the Airways of Cystic Fibrosis Patients

Staphylococcus aureus is one of the most common pathogens that infects the airways of patients with cystic fibrosis (CF) and contributes to respiratory failure. Recently, livestock-associated methicillin-resistant S. aureus (LA-MRSA), usually cultured in farm animals, were detected in CF airways. Although some of these strains are able to establish severe infections in humans, there is limited knowledge about the role of LA-MRSA virulence in CF lung disease. To address this issue, we analyzed LA-MRSA, hospital-associated (HA-) MRSA and methicillin-susceptible S.aureus (MSSA) clinical isolates recovered early in the course of airway infection and several years after persistence in this hostile environment from pulmonary specimens of nine CF patients regarding important virulence traits such as their hemolytic activity, biofilm formation, invasion in airway epithelial cells, cytotoxicity, and antibiotic susceptibility. We detected that CF LA-MRSA isolates were resistant to tetracycline, more hemolytic and cytotoxic than HA-MRSA, and more invasive than MSSA. Despite the residence in the animal host, LA-MRSA still represent a serious threat to humans, as such clones possess a virulence potential similar or even higher than that of HA-MRSA. Furthermore, we confirmed that S. aureus individually adapts to the airways of CF patients, which eventually impedes the success of antistaphylococcal therapy of airway infections in CF.

Penicillin-binding protein PBP2a provides variable levels of protection toward different β-lactams in Staphylococcus aureus RN4220

Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to most β-lactams due to the expression of an extra penicillin-binding protein, PBP2a, with low β-lactam affinity. It has long been known that heterologous expression of the PBP2a-encoding mecA gene in methicillin-sensitive S. aureus (MSSA) provides protection towards β-lactams, however, some reports suggest that the degree of protection can vary between different β-lactams. To test this more systematically, we introduced an IPTG-inducible mecA into the MSSA laboratory strain RN4220. We confirm, by growth assays as well as single-cell microfluidics time-lapse microscopy experiments, that PBP2a expression protects against β-lactams in S. aureus RN4220. By testing a panel of ten different β-lactams, we conclude that there is also a great variation in the level of protection conferred by PBP2a. Expression of PBP2a resulted in an only fourfold increase in minimum inhibitory concentration (MIC) for imipenem, while a 32-fold increase in MIC was observed for cefaclor and cephalexin. Interestingly, in our experimental setup, PBP2a confers the highest protection against cefaclor and cephalexin-two β-lactams that are known to have a high specific affinity toward the transpeptidase PBP3 of S. aureus. Notably, using a single-cell microfluidics setup we demonstrate a considerable phenotypic variation between cells upon β-lactam exposure and show that mecA-expressing S. aureus can survive β-lactam concentrations much higher than the minimal inhibitory concentrations. We discuss possible explanations and implications of these results including important aspects regarding treatment of infection.

Novel strategies for rapid identification and susceptibility testing of MRSA

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) is associated with adverse clinical outcomes and increased morbidity, mortality, length of hospital stay, and health-care costs. Rapid diagnosis of MRSA infections has been associated with positive impact on clinical outcomes.

AREAS COVERED

We searched relevant papers in PubMed for the last 10 years. In major papers, we scanned the bibliographies to ensure that important articles were included. This review describes screening and diagnostic test methods for MRSA and their analytical performances with a focus on rapid molecular-based assays including those that are on the horizon. Future novel technologies will allow more rapid detection of phenotypic resistance. In the case of whole-genome sequencing, detection of mutations may predict resistance, transmission, and virulence.

EXPERT OPINION

Currently there are many diagnostic options for the detection of MRSA in surveillance and clinical samples. In general, these are highly accurate and have resulted in improvements in targeted management and reduction in hospital or intensive care unit length of stay for both MSSA and MRSA. Impact on mortality has been variable. Promising novel technologies will not only accurately identify pathogens and detect their resistance markers but will allow discovery of virulence determinants that might further affect patient management.

First mecC and mecA Positive Livestock-Associated Methicillin Resistant Staphylococcus aureus (mecC MRSA/LA-MRSA) from Dairy Cattle in Malaysia

Livestock associated Methicillin resistant Staphylococcus aureus (S. aureus) (LA-MRSA) was reported to be zoonotic and may transmit to farmers and veterinarians. The objectives of this study were to investigate the occurrence of LA-MRSA from dairy cattle and to evaluate the antimicrobial resistance profiles of the isolates. A total of 63 milk and 32 nasal swab samples were randomly collected from dairy cattle. The samples were processed to isolate S. aureus, MRSA and LA-MRSA using both phenotypic and molecular methods using PCR. The confirmed S. aureus isolates were cultured on oxacillin resistant screening agar base (ORSAB) to detect MRSA and the isolates were further confirmed by PCR targeting the mecA gene. Detection of the novel mecA gene, mecC gene was conducted by PCR amplification. The antimicrobial susceptibility tests were conducted using disc diffusion method. Results revealed 17/95 (17.89%) and 15/95 (15.79%) were positive for mecA and mecC genes respectively. Out of the 15 mecC positive isolates, 12 were positive for both mecA and mecC. The MRSA isolates showed multidrug resistance. The findings showed high prevalence of mecC-positive LA-MRSA in Malaysia and highlight the public health risks to people that may come in contact with the carrier animals or those who may consume unpasteurized milk products from these animals.

A clinical approach to multidrug-resistant urinary tract infection and subclinical bacteriuria in dogs and cats

Multidrug-resistant bacteria are increasingly isolated from the urinary tract of pets, particularly those that suffer from concurrent conditions, have been hospitalised, or were treated with antimicrobials in the recent past. Many of the multidrug-resistant bacteria encountered are resistant to all commonly used oral antibiotics. This poses both a therapeutic dilemma in the individual pet and a threat to public health. This article begins with an overview of multidrug resistance in organisms that are commonly isolated from the urinary tract of pets. This is followed by a proposed clinical approach to managing multidrug-resistant urinary bacteria, which summarises current knowledge regarding appropriate sampling and analysis, reviews the current guidelines regarding appropriate antimicrobial use and discusses treatment options that might be considered. The article highlights several shortcomings of the current knowledge to be considered when planning future clinical research and developing policies.

Antimicrobial Susceptibility Test for the Determination of Resistant and Susceptible S. aureus and Enterococcus spp. Using a Multi-Channel Surface Plasmon Resonance Device

The objective of this study was to investigate the development of a surface plasmon resonance (SPR) sensor platform equipped with multiple channels for the simultaneous determination of methicillin-resistant S. aureus (MRSA), methicillin-susceptible S. aureus (MSSA) and vancomycin-resistant Enterococcus (VRE), and vancomycin-susceptible Enterococcus (VSE). Drug resistance of S. aureus strains against cefoxitin and Enterococcus strains against vancomycin were investigated both using the minimum inhibitory concentration method (MIC) assay and the SPR system equipped with single and multiple channels. The MIC values of MRSA and MSSA ranged from 32 µg/mL to >128 µg/mL and from 1 µg/mL to 4 µg/mL, respectively. The MIC values of VRE and VSE were between 64 to >128 µg/mL and 2-4 µg/mL, respectively. With the multiple-channel system, the angle shifts of MRSA, MSSA, VRE and VSE were found to be -0.030° and -0.260°, -0.010° and -0.090° respectively. The antibiotic-resistant and susceptible strains were distinguished within 3 h for S. aureus strains and within 6 h for Enterococcus strains.

Adaption of an Episomal Antisense Silencing Approach for Investigation of the Phenotype Switch of Staphylococcus aureus Small-Colony Variants

Staphylococcus aureus small-colony variants (SCVs) are associated with chronic, persistent, and relapsing courses of infection and are characterized by slow growth combined with other phenotypic and molecular traits. Although certain mechanisms have been described, the genetic basis of clinical SCVs remains often unknown. Hence, we adapted an episomal tool for rapid identification and investigation of putative SCV phenotype-associated genes via antisense gene silencing based on previously described Tnl0-encoded tet-regulatory elements. Targeting the SCV phenotype-inducing enoyl-acyl-carrier-protein reductase gene (fabI), plasmid pSN1-AS‘fabI’ was generated leading to antisense silencing, which was proven by pronounced growth retardation in liquid cultures, phenotype switch on solid medium, and 200-fold increase of antisense ‘fabI’ expression. A crucial role of TetR repression in effective regulation of the system was demonstrated. Based on the use of anhydrotetracycline as effector, an easy-to-handle one-plasmid setup was set that may be applicable to different S. aureus backgrounds and cell culture studies. However, selection of the appropriate antisense fragment of the target gene remains a critical factor for effectiveness of silencing. This inducible gene expression system may help to identify SCV phenotype-inducing genes, which is prerequisite for the development of new antistaphylococcal agents and future alternative strategies to improve treatment of therapy-refractory SCV-related infections by iatrogenically induced phenotypic switch. Moreover, it can be used as controllable phenotype switcher to examine important aspects of SCV biology in cell culture as well as in vivo.

Recent advances in antibacterial applications of metal nanoparticles (MNPs) and metal nanocomposites (MNCs) against multidrug-resistant (MDR) bacteria

Introduction: In recent years, multidrug resistance (MDR) in bacteria has drastically increased and has posed a great threat to the human health. This problem has generated an urgent need to search alternatives for the treatment of MDR bacteria. It has been proved that metal nanoparticles (MNPs) and metal nanocomposites (MNCs) possess remarkable antimicrobial potential, and hence can be used in alternative therapy. Areas covered: This review is aimed to discuss recent reports on antibacterial activities of MNPs and MNCs against MDR bacteria. Expert opinion: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Serratia marcescens, Streptococcus pneumoniae, and Staphylococcus epidermidis are important pathogenic bacteria which have shown MDR against a wide range of conventional antibiotics. In this context, effects of MNPs and MNCs on these pathogens have demonstrated considerable efficacy. Several mechanisms concerning activity of MNPs and MNCs against pathogenic bacteria which are mainly dependent on type of their precursors and treated bacterium have been investigated. In addition, many studies have been made on antibacterial activities of these nanomaterials with similar and different results.

The Continuing Threat of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus has been an exceptionally successful pathogen, which is still relevant in modern age-medicine due to its adaptability and tenacity. This bacterium may be a causative agent in a plethora of infections, owing to its abundance (in the environment and in the normal flora) and the variety of virulence factors that it possesses. Methicillin-resistant S. aureus (MRSA) strains—first described in 1961—are characterized by an altered penicillin-binding protein (PBP2a/c) and resistance to all penicillins, cephalosporins, and carbapenems, which makes the β-lactam armamentarium clinically ineffective. The acquisition of additional resistance determinants further complicates their eradication; therefore, MRSA can be considered as the first representative of multidrug-resistant bacteria. Based on 230 references, the aim of this review is to recap the history, the emergence, and clinical features of various MRSA infections (hospital-, community-, and livestock-associated), and to summarize the current advances regarding MRSA screening, typing, and therapeutic options (including lipoglycopeptides, oxazolidinones, anti-MRSA cephalosporins, novel pleuromutilin-, tetracycline- and quinolone-derivatives, daptomycin, fusidic acid, in addition to drug candidates in the development phase), both for an audience of clinical microbiologists and infectious disease specialists.

Comparative Metagenomics and Network Analyses Provide Novel Insights Into the Scope and Distribution of β-Lactamase Homologs in the Environment

The β-lactams are the largest group of clinically applied antibiotics, and resistance to these is primarily associated with β-lactamases. There is increasing understanding that these enzymes are ubiquitous in natural environments and henceforth, elucidating the global diversity, distribution, and mobility of β-lactamase-encoding genes is crucial for holistically understanding resistance to these antibiotics. In this study, we screened 232 shotgun metagenomes from ten different environments against a custom-designed β-lactamase database, and subsequently analyzed β-lactamase homologs with a suite of bioinformatic platforms including cluster and network analyses. Three interrelated β-lactamase clusters encompassed all of the human and bovine feces metagenomes, while β-lactamases from soil, freshwater, glacier, marine, and wastewater grouped within a separate "environmental" cluster that displayed high levels of inter-network connectivity. Interestingly, almost no connectivity occurred between the "feces" and "environmental" clusters. We attributed this in part to the divergence in microbial community composition (dominance of Bacteroidetes and Firmicutes vs. Proteobacteria, respectively). The β-lactamase diversity in the "environmental" cluster was significantly higher than in human and bovine feces microbiomes. Several class A, B, C, and D β-lactamase homologs (bla _CTX-M, bla _KPC, bla _GES) were ubiquitous in the "environmental" cluster, whereas bovine and human feces metagenomes were dominated by class A (primarily cfxA) β-lactamases. Collectively, this study highlights the ubiquitous presence and broad diversity of β-lactamase gene precursors in non-clinical environments. Furthermore, it suggests that horizontal transfer of β-lactamases to human-associated bacteria may be more plausible from animals than from terrestrial and aquatic microbes, seemingly due to phylogenetic similarities.

Absence of the mecC gene in methicillin-resistant Staphylococcus aureus isolated from various clinical samples: The first multi-centered study in Turkey

BACKGROUND

mecA is a predefined gene causing methicillin resistance in Staphylococcus aureus (S. aureus) isolates; however, it has been shown that some methicillin-resistant S. aureus (MRSA) strains do not carry this gene. Recently, in isolates found to be MRSA-positive but mecA-negative, a new resistance gene called mecC, which is a homolog of mecA, has been reported. This study aimed to investigate the mecC and mecA genes in MRSA strains isolated from different geographic regions in Turkey.

METHODS

The sample of the study consisted of 494 MRSA strains isolated from seven geographical regions in Turkey between 2013 and 2016. The strains were obtained from 17 centers, comprising 13 university hospitals, three education and research hospitals, and one state hospital. Methicillin resistance in S. aureus strains was determined using the agar disk diffusion method with a cefoxitin disk and the agar dilution method with oxacillin. The mecC and mecA genes in MRSA strains was investigated by Polymerase Chain Reaction (PCR).

RESULTS

Of the MRSA strains investigated, 47.9% were isolated from intensive care units. Concerning sample type, 36.7% were detected in the respiratory tract (tracheal aspirate, sputum, etc.), 24.8% in blood, 18.7% in skin and soft tissues, 9.3% in nasal swabs, 5.4% in urine, 4.1% in ears, and 1% in sterile body fluid. Using PCR, mecC was not identified in any of the S. aureus strains isolated from different clinical microbiology laboratories. mecA gene positivity was found in 315 of the MRSA strains (63.8%). Staphylococcal Cassette Chromosome mec (SCCmec) type was identified in 232 strains (46.9%), of which 136 (58.7%) were type II, 75 (32.4%) were type IV, 12 (5.1%) were type IIIb, six (2.5%) were type I, and three (1.3%) were type III.

CONCLUSION

This is the first multi-centered study to investigate MRSA strains isolated from different regions in Turkey. The mecC gene was not detected in any of the MRSA strains. We believe that this study will constitute an important basis for monitoring possible future changes.

Drug-Resistant Staphylococcus aureus Strains Reveal Distinct Biochemical Features with Raman Microspectroscopy

Staphylococcus aureus ( S. aureus) is a leading cause of hospital-acquired infections, such as bacteremia, pneumonia, and endocarditis. Treatment of these infections can be challenging since strains of S. aureus, such as methicillin-resistant S. aureus (MRSA), have evolved resistance to antimicrobials. Current methods to identify infectious agents in hospital environments often rely on time-consuming, multistep culturing techniques to distinguish problematic strains (i.e., antimicrobial resistant variants) of a particular bacterial species. Therefore, a need exists for a rapid, label-free technique to identify drug-resistant bacterial strains to guide proper antibiotic treatment. Here, our findings demonstrate the ability to characterize and identify microbes at the subspecies level using Raman microspectroscopy, which probes the vibrational modes of molecules to provide a biochemical "fingerprint". This technique can distinguish between different isolates of species such as Streptococcus agalactiae and S. aureus. To determine the ability of this analytical approach to detect drug-resistant bacteria, isogenic variants of S. aureus including the comparison of strains lacking or expressing antibiotic resistance determinants were evaluated. Spectral variations observed may be associated with biochemical components such as amino acids, carotenoids, and lipids. Mutants lacking carotenoid production were distinguished from wild-type S. aureus and other strain variants. Furthermore, spectral biomarkers of S. aureus isogenic bacterial strains were identified. These results demonstrate the feasibility of Raman microspectroscopy for distinguishing between various genetically distinct forms of a single bacterial species in situ. This is important for detecting antibiotic-resistant strains of bacteria and indicates the potential for future identification of other multidrug resistant pathogens with this technique.

The Novel Phage-Derived Antimicrobial Agent HY-133 Is Active against Livestock-Associated Methicillin-Resistant Staphylococcus aureus

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) isolates are increasingly migrating from livestock into human and animal health care settings. Alternative substances are needed to overcome the drawbacks of currently available drugs used for MRSA eradication. The recombinant bacteriophage endolysin HY-133 has proved to be an active agent against S. aureus Here, the in vitro activity of HY-133 was studied against a large collection of genetically diverse LA-MRSA isolates revealing its high activity against mecA-, mecB-, and mecC-positive LA-MRSA.

Emerging discrepancies in conventional and molecular epidemiology of methicillin resistant Staphylococcus aureus isolated from bovine milk

Methicillin resistant Staphylococcus aureus (MRSA) is an emerging public health concern from dairy milk, and its diagnosis by phenotypic methodology is experiencing higher discrepancies. The present study was planned to estimate discrepancies in phenotypic identification of MRSA and MSSA (Methicillin sensitive Staphylococcus aureus) in relation to mecA, and prevalent risk factors from various localities. In-vitro oxacilline antibiotic disks were used for phenotypic identification of MRSA, whereas mecA gene was used as MRSA marker in Staph aureus by PCR. Total of 900 bovine milk samples from private and public farms located in district Faisalabad using convinent sampling technique were collected. Potential risk factors for MRSA prevalence identified by non-parametric statistical tests were compared among different subdistricts. Discrepancy in MRSA was calculated as percentage of mecA negative strains while that of MSSA was determined as percentage of mecA positive strains. Molecular identification presented 17.97% (55/306) of discrepancy in MRSA in terms of negative mecA strains from district Faisalabad while sub-district Faisalabad, sub-district Jaranwala, and sub-district Samundary presented 13.98% (13/93), 18.28% (17/93), and 20.83% (25/120) discrepant results, respectively. On the other hand, 29.1% (55/189) of discrepancy in MSSA in terms of mecA positive strains from MSSA isolates was noted. MSSA results were more discrepant than that of MRSA. Hence discrepancy ratio of MSSA over MRSA was noted to be 1.53, 1.50, and 1.21 from tehsil Faislabad, Samundary, and Jaranwala. Tick infestation, lactation stage, frequency of milking, dirty milker's hands, unhygienic milking procedures, and higher use of beta lactam of antibiotics were risk factors that were prevalent in increasing order from sub-district Faisalabad > Jaranwala > Samundary. The study concluded higher prevalence of MRSA in bovine milk samples, and found remarkable discrepancies in phenotypic and genotypic identification which demand immediate attention to tackle exacerbation in resistance patterns.

Comparison of Different Phenotypic Approaches To Screen and Detect mecC-Harboring Methicillin-Resistant Staphylococcus aureus

Similar to mecA, mecC confers resistance against beta-lactams, leading to the phenotype of methicillin-resistant Staphylococcus aureus (MRSA). However, mecC-harboring MRSA strains pose special difficulties in their detection. The aim of this study was to assess and compare different phenotypic systems for screening, identification, and susceptibility testing of mecC-positive MRSA isolates. A well-characterized collection of mecC-positive S. aureus isolates (n = 111) was used for evaluation. Routinely used approaches were studied to determine their suitability to correctly identify mecC-harboring MRSA, including three (semi)automated antimicrobial susceptibility testing (AST) systems and five selective chromogenic agar plates. Additionally, a cefoxitin disk diffusion test and an oxacillin broth microdilution assay were examined. All mecC-harboring MRSA isolates were able to grow on all chromogenic MRSA screening plates tested. Detection of these isolates in AST systems based on cefoxitin and/or oxacillin testing yielded overall positive agreements with the mecC genotype of 97.3% (MicroScan WalkAway; Siemens), 91.9% (Vitek 2; bioMérieux), and 64.9% (Phoenix, BD). The phenotypic resistance pattern most frequently observed by AST devices was "cefoxitin resistance/oxacillin susceptibility," ranging from 54.1% (Phoenix) and 83.8% (Vitek 2) to 92.8% (WalkAway). The cefoxitin disk diffusion and oxacillin broth microdilution assays categorized 100% and 61.3% of isolates to be MRSA, respectively. The chromogenic media tested confirmed their suitability to reliably screen for mecC-harboring MRSA. The AST systems showed false-negative results with varying numbers, misidentifying mecC-harboring MRSA as methicillin-susceptible S. aureus This study underlines cefoxitin's status as the superior surrogate mecC-positive MRSA marker.

Antimicrobial resistance in coagulase-positive staphylococci isolated from companion animals in Australia: A one year study

Methicillin-resistant coagulase-positive staphylococci (CoPS) have become increasingly recognised as opportunistic pathogens that limit therapeutic options in companion animals. The frequency of methicillin resistance amongst clinical isolates on an Australia-wide level is unknown. This study determined antimicrobial susceptibility patterns for CoPS isolated from clinical infections in companion animals (dogs, cats and horses) as part of the first nation-wide survey on antimicrobial resistance in animal pathogens in Australia for a one-year period (January 2013 to January 2014). Clinical Staphylococcus spp. isolates (n = 888) obtained from 22 veterinary diagnostic laboratories were identified by MALDI-TOF mass spectrometry and subjected to antimicrobial susceptibility testing for 16 antimicrobials, representing 12 antimicrobial classes. Potential risk factors associated with methicillin resistance in Staphylococcus pseudintermedius isolates from dogs were analysed based on demographic factors and clinical history, including gender, age, previous antimicrobial treatment, chronic and/or recurrent diseases and site of infections. The most commonly identified CoPS were S. pseudintermedius (70.8%; dogs n = 616, cats n = 13) and S. aureus (13.2%, horses n = 53, dogs n = 47 and cats n = 17). Overall, the frequency of methicillin resistance among S. pseudintermedius (MRSP) and S. aureus (MRSA) was 11.8% and 12.8%, respectively. MRSP isolates were strongly associated with resistance to fluoroquinolones (OR 287; 95%CI 91.2–1144.8) and clindamycin (OR 105.2, 95%CI 48.5–231.9). MRSA isolates from dogs and cats were also more likely to be resistant to fluoroquinolones (OR 5.4, 95%CI 0.6–252.1), whereas MRSA from horses were more likely to be resistant to rifampicin. In multivariate analysis, MRSP-positive status was significantly associated with particular infection sites, including surgical (OR 8.8; 95%CI 3.74–20.7), and skin and soft tissue (OR 3.9; 95%CI 1.97–7.51). S. pseudintermedius isolated from dogs with surgical site infections were three times more likely to be methicillin-resistant if cases had received prior antimicrobial treatment. Whilst the survey results indicate the proportion of CoPS obtained from Australian companion animals that are methicillin-resistant is currently moderate, the identified risk factors suggest that it could rapidly increase without adequate biosecurity and infection control procedures in veterinary practice.

The recent emergence in hospitals of multidrug-resistant community-associated sequence type 1 and spa type t127 methicillin-resistant Staphylococcus aureus investigated by whole-genome sequencing: Implications for screening

Community-associated spa type t127/t922 methicillin-resistant Staphylococcus aureus (MRSA) prevalence increased from 1%-7% in Ireland between 2010–2015. This study tracked the spread of 89 such isolates from June 2013-June 2016. These included 78 healthcare-associated and 11 community associated-MRSA isolates from a prolonged hospital outbreak (H1) (n = 46), 16 other hospitals (n = 28), four other healthcare facilities (n = 4) and community-associated sources (n = 11). Isolates underwent antimicrobial susceptibility testing, DNA microarray profiling and whole-genome sequencing. Minimum spanning trees were generated following core-genome multilocus sequence typing and pairwise single nucleotide variation (SNV) analysis was performed. All isolates were sequence type 1 MRSA staphylococcal cassette chromosome mec type IV (ST1-MRSA-IV) and 76/89 were multidrug-resistant. Fifty isolates, including 40/46 from H1, were high-level mupirocin-resistant, carrying a conjugative 39 kb iles2-encoding plasmid. Two closely related ST1-MRSA-IV strains (I and II) and multiple sporadic strains were identified. Strain I isolates (57/89), including 43/46 H1 and all high-level mupirocin-resistant isolates, exhibited ≤80 SNVs. Two strain I isolates from separate H1 healthcare workers differed from other H1/strain I isolates by 7–47 and 12–53 SNVs, respectively, indicating healthcare worker involvement in this outbreak. Strain II isolates (19/89), including the remaining H1 isolates, exhibited ≤127 SNVs. For each strain, the pairwise SNVs exhibited by healthcare-associated and community-associated isolates indicated recent transmission of ST1-MRSA-IV within and between multiple hospitals, healthcare facilities and communities in Ireland. Given the interchange between healthcare-associated and community-associated isolates in hospitals, the risk factors that inform screening for MRSA require revision.