Mechanisms of resistance to macrolides and lincosamides: nature of the resistance elements and their clinical implications

Risk factors for fluoroquinolone- and macrolide-resistance among swine Campylobacter coli using multi-layered chain graphs

Campylobacter spp. resistant to fluoroquinolones and macrolides are serious public health threats. Studies aiming to identify risk factors for drug-resistant Campylobacter have narrowly focused on antimicrobial use at the farm level. Using chain graphs, we quantified risk factors for fluoroquinolones- and macrolide-resistance in Campylobacter coli isolated from two distinctive swine production systems, conventional and antibiotic-free (ABF). The chain graphs were learned using genotypic and phenotypic resistance data from 1082 isolates and host exposures obtained through surveys for 18 cohorts of pigs. The gyrA T86I point mutation alone explained at least 58 % of the variance in ciprofloxacin minimum inhibitory concentration (MIC) for ABF and 79 % in conventional farms. For macrolides, genotype and host exposures explained similar variance in azithromycin and erythromycin MIC. Among host exposures, heavy metal exposures were identified as risk factors in both conventional and ABF. Chain graph models can generate insights into the complex epidemiology of antimicrobial resistance by characterizing context-specific risk factors and facilitating causal discovery.

A CRISPR-Cas9 system protecting E. coli against acquisition of antibiotic resistance genes

Antimicrobial resistance (AMR) is an increasing problem worldwide, and new treatment options for bacterial infections are direly needed. Engineered probiotics show strong potential in treating or preventing bacterial infections. However, one concern with the use of live bacteria is the risk of the bacteria acquiring genes encoding for AMR or virulence factors through horizontal gene transfer (HGT), and the transformation of the probiotic into a superbug. Therefore, we developed an engineered CRISPR-Cas9 system that protects bacteria from horizontal gene transfer. We synthesized a CRISPR locus targeting eight AMR genes and cloned this with the Cas9 and transacting tracrRNA on a medium copy plasmid. We next evaluated the efficiency of the system to block HGT through transformation, transduction, and conjugation. Our results show that expression of the CRISPR-Cas9 system successfully protects E. coli MG1655 from acquiring the targeted resistance genes by transformation or transduction with 2-3 logs of protection depending on the system for transfer and the target gene. Furthermore, we show that the system blocks conjugation of a set of clinical plasmids, and that the system is also able to protect the probiotic bacterium E. coli Nissle 1917 from acquiring AMR genes.

Ethical bioprospecting and microbial assessments for sustainable solutions to the AMR crisis

Antimicrobial resistance (AMR) has been declared one of the top 10 global public health challenges of our age by the World Health Organization, and the World Bank describes AMR as a crisis affecting the finance, health, and agriculture sectors and a major threat to the attainment of Sustainable Development Goals. But what is AMR? It is a phenotype that evolves in microbes exposed to antimicrobial molecules and causes dangerous infections. This suggests that scientists and healthcare workers should be on the frontline in the search for sustainable solutions to AMR. Yet AMR is also a societal problem to be understood by everyone. This review aims to explore the need to address the problem of AMR through a coherent, international strategy with buy-in from all sectors of society. As reviewed here, the sustainable solutions to AMR will be driven by better understanding of AMR biology but will require more than this alone to succeed. Some advances on the horizon, such as the use of bacteriophage (phage) to treat AMR infections. However, many of the new technologies and new therapeutics to address AMR require access to biodiversity, where the custodians of that biodiversity-and the traditional knowledge required to access it-are needed as key partners in the scientific, clinical, biotechnological, and international ventures that would treat the problem of AMR and ultimately prevent its further evolution. Many of these advances will be built on microbial assessments to understand the extent of AMR in our environments and bioprospecting to identify microbes that may have beneficial uses. Genuine partnerships for access to this biodiversity and sharing of benefits accrued require a consideration of ethical practice and behavior. Behavior change is needed across all sectors of culturally diverse societies so that rapid deployment of solutions can be implemented for maximum effect against the impacts of AMR.

Characterization of integrative and conjugative elements carrying erm(B) and tet(O) resistance determinants in streptococcus uberis isolates from bovine milk in Chiba prefecture, Japan: CompArative GEne cluster analysis toolbox with ICEfinder

OBJECTIVE

We aimed to characterize integrative and conjugative elements (ICEs) in antimicrobial resistant Streptococcs uberis isolates from bovine milk in Chiba, Japan, based on whole-genome sequence (WGS) data.

RESULTS

Of the 101 isolates, we found the 36 isolates harboring erm(B)-tet(O), showing resistance to macrolides-lincosamides-tetracyclines. The 22 isolates were randomly selected and subject to WGS determination. The genomes measured 1.991-2.517 Mbp, with G + C contents of 35.8-36.9%. We used ResFinder-ICEfinder (web-based applications) to search for the antimicrobial resistant genes and ICEs. ResFinder detected combined erm(B)-tet(O)-ant(6)-Ia at the identical contig in each WGS. ICEfinder detected ICEs belonging to the same contigs, which contained erm(B)-tet(O)-ant(6)-Ia complete or partial sequences. Detection of putative ICEs using comparative genomic analysis was performed with identification of other streptococcal ICE resembling S. uberis ICEs. Using comparative genomic analysis (a reference WGS in NZ01 strain), putative ICE base size in UB37 isolate was 77,386-bp that was identical in other 13 isolates. Another similar streptococcal ICE was S. suis ICEnsui78-tet(O)-erm(B) mobile element. For ICE characterization in S. uberis with WGSs, a comparative genomic analysis is required with use of ICEfinder and other annotation tools.

New avenues of combating antibiotic resistance by targeting cryptic pockets

Antibiotic resistance is a global health concern that is rapidly spreading among human and animal pathogens. Developing novel antibiotics is one of the most significant approaches to surmount antibiotic resistance. Given the difficult in identifying novel targets, cryptic binding sites provide new pockets for compounds design to combat antibiotic resistance. However, there exists a lack of comprehensive analysis and discussion on the successful utilization of cryptic pockets in overcoming antibiotic resistance. Here, we systematically analyze the crucial role of cryptic pockets in neutralizing antibiotic resistance. First, antibiotic resistance development and associated resistance mechanisms are summarized. Then, the advantages and mechanisms of cryptic pockets for overcoming antibiotic resistance were discussed. Specific cryptic pockets in resistant proteins and successful case studies of designed inhibitors are exemplified. This review provides insight into the discovery of cryptic pockets for drug design as an approach to overcome antibiotic resistance.

Regulation of erm(T) MLSB phenotype expression in the emergent emm92 type group A Streptococcus

In the last decade, invasive group A Streptococcus (iGAS) infections have doubled in the US, with equivalent increases in MLSB (macrolide, lincosamide, and streptogramin B)-resistance. The emm92-type isolates carrying the erm(T) gene have been associated with an alarming emergence of iGAS infections in people who inject drugs or experience homelessness. Our goal was to elucidate the mechanisms behind inducible (iMLSB) and constitutive (cMLSB) resistance in emm92 isolates. Sequence analysis identified polymorphisms in the erm(T) regulatory region associated with cMLSB resistance. RT-qPCR and RNAseq revealed increased erm(T) mRNA levels in iMLSB isolates in response to erythromycin exposure, while cMLSB isolates exhibited high erm(T) expression independent from antibiotic exposure. Transcription results were coupled with shifting levels of ribosomal methylation. A homology model of the ErmT enzyme identified structural elements and residues conserved in methyltransferases. Delayed growth of iMLSB isolates cultured with erythromycin and increased clindamycin resistance in cMLSB isolates were observed.

Exposure of gut bacterial isolates to the anthelminthic drugs, ivermectin and moxidectin, leads to antibiotic-like phenotypes of growth inhibition and adaptation

Due to their broad-spectrum activities, ivermectin and moxidectin are widely used anthelminthics in veterinary and human medicine. However, ivermectin has recently been shown to perturbate bacterial growth. Given the macrolide-like structure of both ivermectin and moxidectin, there is a need to characterize the antibiotic spectrum of these anthelminthics and their potential implications in the development of cross-resistance to macrolides and other families of antibiotics. Here, we characterize growth dynamics of 59 bacterial isolates in presence of ivermectin and moxidectin. Further, we assessed the effect of repeated anthelminthic exposure in 5 bacterial isolates on sensitivity to different antibiotics, both via growth dynamics and minimal inhibitory concentration. We found, that anthelminthic growth phenotypes are comparable to a selection of tested antibiotics. Bacterial anthelminthic challenging resulted in decreased anthelminthic sensitivity, and to some extent, decreased antibiotic sensitivity. Hence, potential off-target effects of large-scale administration of ivermectin and moxidectin should be carefully monitored.

Environmental factors influencing the development and spread of resistance in erythromycin-resistant streptococcus pneumoniae

Bacterial drug resistance is becoming increasingly serious, this study aims to investigate the relationship between the resistance rate of erythromycin-resistant Streptococcus pneumoniae (SP) and reasons for the epidemic under complex geographical and climatic factors in China. Data spanning from 2014 to 2021, including drug resistance rates, isolate rates, meteorological variables, and demographic statistics, were collected from the China Antimicrobial Resistance Monitoring System, the China Statistical Yearbook and China Meteorological Website. Our analysis involved nonparametric tests and the construction of multifaceted regression models for rigorous multivariate analysis. Single-factor analysis revealed significant differences in the resistance rate and isolate rate of erythromycin-resistant SP across different regions characterized by Hu Huanyong lines or different climate types. Multivariate regression analysis indicated positive correlations between the drug resistance rate and temperature, Subtropical climate, Gross Domestic Product (GDP), Hu Huanyong line, and the highest temperature in the past period (Tm); the isolate rate showed a positive correlation with regional GDP and a negative correlation with monsoon climate. The model developed in this study provides valuable insights into the resistance rate and potential relationships of erythromycin-resistant SP under complex meteorological conditions in China.

Macrolide resistance outcomes after the Covid-19 pandemic: A one health approach investigation

During the Covid-19 pandemic period, the indiscriminate use of macrolide-class antibiotics was frequent among the Brazilian population due to the lack of knowledge and information with a scientific basis. Thus, the class of drugs that includes azithromycin, clarithromycin, and erythromycin, which alter metabolic reactions in the body and act on the immune system, was widely used without medical prescription. Samples of bacterial strains from hospital environments were obtained during the most extensive spread of Covid-19 and studied in the present article, emphasizing the investigation for macrolide resistance genes (erm and msr) and bacteria of the genus Staphylococcus isolated from urinary tract infections. In addition, the physiological, genetic, immunological, and socio-epidemiological aspects were highlighted with a focus on the One Health approach and implications on the gut-brain axis in this integrative research, revealing that the inappropriate use of antibiotics directly affects entire communities, representing a significant concern for public and environmental health.

Mechanistic Basis for the Translation Inhibition of Cutibacterium acnes by Clindamycin

Inflammation and the Gram-positive anaerobic bacterium Cutibacterium acnes, which is implicated in acne pathogenesis and pilosebaceous-unit inflammation, are the main targets of antibiotic-based therapy against acne vulgaris (acne). The most widely used antibiotics in acne therapy are tetracyclines, macrolides, and lincosamides. Unfortunately, C. acnes bacteria over the past several decades have demonstrated increased resistance to these antibiotics, particularly to clindamycin. The precise knowledge of how antibiotics interact with their clinical target is needed to overcome this problem. Toward this goal, we determined the structure of clindamycin in complex with the ribosome of C. acnes at 2.53 Å resolution using cryogenic electron microscopy. The galactose sugar moiety of clindamycin interacts with nucleotides of the 23S ribosomal RNA directly or through a conserved network of water-mediated interactions. Its propyl pyrrolidinyl group interacts with the 23S ribosomal RNA through van der Waals forces. Clindamycin binding to the C. acnes ribosome interferes with both: proper orientation of the aminoacyl group of the A-site bound transfer RNA that is needed for peptide bond formation and with the extension of the nascent peptide. Our data are important for advancing the understanding of antibiotic resistance and development of narrow-spectrum antibacterial drugs, which is an urgent need for contemporary antibiotic stewardship.

Mechanistic Insights into Clinically Relevant Ribosome-Targeting Antibiotics

Antibiotics targeting the bacterial ribosome are essential to combating bacterial infections. These antibiotics bind to various sites on the ribosome, inhibiting different stages of protein synthesis. This review provides a comprehensive overview of the mechanisms of action of clinically relevant antibiotics that target the bacterial ribosome, including macrolides, lincosamides, oxazolidinones, aminoglycosides, tetracyclines, and chloramphenicol. The structural and functional details of antibiotic interactions with ribosomal RNA, including specific binding sites, interactions with rRNA nucleotides, and their effects on translation processes, are discussed. Focus is placed on the diversity of these mechanisms and their clinical implications in treating bacterial infections, particularly in the context of emerging resistance. Understanding these mechanisms is crucial for developing novel therapeutic agents capable of overcoming bacterial resistance.

Comparative Metabolomics Reveals Changes in the Metabolic Pathways of Ampicillin- and Gentamicin-Resistant Staphylococcus aureus

Antibiotic resistance is a major global challenge requiring new treatments and a better understanding of the bacterial resistance mechanisms. In this study, we compared ampicillin-resistant (R-AMP) and gentamicin-resistant (R-GEN) Staphylococcus aureus strains with a sensitive strain (ATCC6538) using metabolomics. We identified 109 metabolites; 28 or 31 metabolites in R-AMP or R-GEN differed from those in ATCC6538. Moreover, R-AMP and R-GEN were enriched in five and four pathways, respectively. R-AMP showed significantly up-regulated amino acid metabolism and down-regulated energy metabolism, whereas R-GEN exhibited an overall decrease in metabolism, including carbohydrate, energy, and amino acid metabolism. Furthermore, the activities of the metabolism-related enzymes pyruvate dehydrogenase and TCA cycle dehydrogenases were inhibited in antibiotic-resistant bacteria. Significant decreases in NADH and ATP levels were also observed. In addition, the arginine biosynthesis pathway, which is related to nitric oxide (NO) production, was enriched in both antibiotic-resistant strains. Enhanced NO synthase activity in S. aureus promoted NO production, which further reduced reactive oxygen species, mediating the development of bacterial resistance to ampicillin and gentamicin. This study reveals that bacterial resistance affects metabolic profile, and changes in energy metabolism and arginine biosynthesis are important factors leading to drug resistance in S. aureus.

Molecular epidemiology of extended-spectrum beta-lactamase-producing-Klebsiella species in East Tennessee dairy cattle farms

Introduction

The rising prevalence of Extended-Spectrum Beta-Lactamase (ESBL)-producing Klebsiella species (spp.) poses a significant threat to human and animal health and environmental safety. To address this pressing issue, a comprehensive study was undertaken to elucidate the burden and dissemination mechanisms of ESBL-Klebsiella spp. in dairy cattle farms.

Methods

Fifty-seven Klebsiella species were isolated on CHROMagar™ ESBL plates and confirmed with MADLI-TOF MS and whole genome sequenced from 14 dairy farms.

Results and discussion

Six families of beta-lactamase (bla) (bla CTX-M, bla SHV, bla TEM, bla OXY, bla OXA, and bla SED) were detected in ESBL-Klebsiella spp. genomes. Most (73%) of isolates had the first three types of beta-lactamase genes, with bla SHV being the most frequent, followed by bla CTX-M. Most (93%) isolates harbored two or more bla genes. The isolates were genotypically MDR, with 26 distinct types of antibiotic resistance genes (ARGs) and point mutations in gyrA, gyrB, and parC genes. The genomes also harbored 22 different plasmid replicon types, including three novel IncFII. The IncFII and Col440I plasmids were the most frequent and were associated with bla CTXM-27 and qnrB19 genes, respectively. Eighteen distinct sequence types (STs), including eight isolates with novel STs of K. pneumoniae, were detected. The most frequently occurring STs were ST353 (n = 8), ST469 (n = 6), and the novel ST7501 (n = 6). Clusters of ESBL-Klebsiella strains with identical STs, plasmids, and ARGs were detected in multiple farms, suggesting possible clonal expansion. The same ESBL variant was linked to identical plasmids in different Klebsiella STs in some farms, suggesting horizontal spread of the resistance gene. The high burden and dual spread mechanism of ESBL genes in Klebsiella species, combined with the emergence of novel sequence types, could swiftly increase the prevalence of ESBL-Klebsiella spp., posing significant risks to human, animal, and environmental health. Immediate action is needed to implement rigorous surveillance and control measures to mitigate this risk.

Understanding the evolution of macrolides resistance: A mini review

BACKGROUND

Macrolides inhibit the growth of bacterial cells by preventing the elongation of polypeptides during protein biosynthesis and include natural, synthetic, and semi-synthetic products. Elongation prevention occurs by blocking the passage of the polypeptide chain as the macrolides bind at the nascent peptide exit tunnel.

OBJECTIVE

Recent data of ribosome profiling via ribo-seq further proves that, other than blocking the polypeptide chain, macrolides are also able to affect the synthesis of individual proteins. Thus, this shows that the mode of action of macrolides is more complex than we initially thought. Since the discovery of macrolides in the 1950s, they have been widely used in veterinary practice, agriculture, and medicine. Due to misuse and overuse of antibiotics, bacteria have acquired resistance against them. Hence, it is of utmost importance for us to fully understand the mode of action of macrolides as well as the mechanisms of resistance against macrolides in order to mitigate antibiotic-resistance issues.

RESULTS

Chemical modifications can be performed to improve macrolide potency if we have a better understanding of their mode of action. Furthermore, a complete and detailed understanding of the mode of action of macrolides has remained vague, as new findings have challenged theories that are already in existence-due to this obscurity, research into macrolide modes of action continues to this day.

CONCLUSION

In this review, we present an overview of macrolide antibiotics, with an emphasis on the latest knowledge regarding the mode of action of macrolides as well as the mechanisms of resistance employed by bacteria against macrolides.

Molecular Basis of Antimicrobial Resistance in Group B Streptococcus Clinical Isolates from Saudi Arabia

Published data on the molecular mechanisms underlying antimicrobial resistance in Group B Streptococcus (GBS) isolates from Saudi Arabia are lacking. Here, we aimed to determine the genetic basis of resistance to relevant antibiotics in a collection of GBS clinical isolates (n = 204) recovered from colonized adults or infected patients and expressing serotypes Ia, Ib, II, III, V, and VI. Initial susceptibility testing revealed resistance to tetracycline (76.47%, n = 156/204), erythromycin (36.76%, n = 75/204), clindamycin (25.49%, n = 52/204), levofloxacin (6.37%, n = 13/204), and gentamicin (2.45%, n = 5/204). Primers designed for the detection of known resistance determinants in GBS identified the presence of erm(A), erm(B), mef(A), and/or lsa(C) genes at the origin of resistance to macrolides and/or clindamycin. Of these, erm(B) and erm(A) were associated with the cMLSB (n = 46) and iMLSB (n = 28) phenotypes, respectively, while mef(A) was linked to the M phenotype (n = 1) and lsa(C) was present in isolates with the L phenotype (n = 8). Resistance to tetracycline was mainly mediated by tet(M) alone (n = 112) or in combination with tet(O) (n = 10); the remaining isolates carried tet(O) (n = 29), tet(L) (n = 2), or both (n = 3). Isolates resistant to gentamicin (n = 5) carried aac(6')-Ie-aph(2')-Ia, and those exhibiting resistance to levofloxacin (n = 13) had alterations in GyrA and/or ParC. Most isolates with the erm gene (93.24%, n = 69/74) also had the tet gene and were therefore resistant to erythromycin, clindamycin, and tetracycline. Overall, there were no clear associations between serotypes and resistance genotypes except for the presence of erm(B) in serotype Ib isolates. Dissemination of antibiotic resistance genes across different serotypes represents a public health concern that requires further surveillance and appropriate antibiotic use in clinical practice.

Mechanism of antibacterial resistance, strategies and next-generation antimicrobials to contain antimicrobial resistance: a review

Antibacterial drug resistance poses a significant challenge to modern healthcare systems, threatening our ability to effectively treat bacterial infections. This review aims to provide a comprehensive overview of the types and mechanisms of antibacterial drug resistance. To achieve this aim, a thorough literature search was conducted to identify key studies and reviews on antibacterial resistance mechanisms, strategies and next-generation antimicrobials to contain antimicrobial resistance. In this review, types of resistance and major mechanisms of antibacterial resistance with examples including target site modifications, decreased influx, increased efflux pumps, and enzymatic inactivation of antibacterials has been discussed. Moreover, biofilm formation, and horizontal gene transfer methods has also been included. Furthermore, measures (interventions) taken to control antimicrobial resistance and next-generation antimicrobials have been discussed in detail. Overall, this review provides valuable insights into the diverse mechanisms employed by bacteria to resist the effects of antibacterial drugs, with the aim of informing future research and guiding antimicrobial stewardship efforts.

Antibiotic Resistance in Acetic Acid Bacteria Originating from Vinegar

Acetic acid bacteria (AAB) are major contributors to the production of fermented vinegar, offering various cultural, culinary, and health benefits. Although the residual unpasteurized AAB after vinegar production are not pathogens, these are necessary and require safety evaluations, including antibiotic resistance, before use as a starter. In this research, we investigated the antibiotic resistance profiles of 26 AAB strains, including various species of Komagataeibacter and Acetobacter, against 10 different antibiotics using the E-test method. All strains exhibited resistance to aztreonam and clindamycin. Komagataeibacter species demonstrated a 50% resistance rate to ciprofloxacin, analogous to Acetobacter species, but showed twice the resistance rates to chloramphenicol and erythromycin. Genomic analysis of K. saccharivorans CV1 identified intrinsic resistance mechanisms, such as multidrug efflux pumps, thereby enhancing our understanding of antibiotic resistance in acetic acid-producing bacteria. These findings enhance understanding of antibiotic resistance in AAB for food safety and new antimicrobial strategies, suggesting the need for standardized testing methods and molecular genetic study.

Phenotypic and genotypic characterization of commensal staphylococci isolated from young volunteers in Alexandria, Egypt

Nasally colonized staphylococci carry antibiotic resistance genes and may lead to serious opportunistic infections. We are investigating nasal carriage of Staphylococcus aureus and Staphylococci other than S. aureus (SOSA) among young volunteers in Egypt to determine their risk potential. Nasal swabs collected over 1 week in June 2019 from 196 volunteers were cultured for staphylococcus isolation. The participants were interviewed to assess sex, age, general health, hospitalization and personal hygiene habits. Identification was carried out using biochemical tests and VITEK 2 automated system. Disc diffusion and minimum inhibitory concentration tests were performed to determine antibiotic susceptibility. Screening for macrolide resistance genes (ermA, ermB, ermC, ermT and msrA) was performed using polymerase chain reaction. Thirty four S. aureus and 69 SOSA were obtained. Multi-drug resistance (MDR) was detected among most staphylococcal species, ranging from 30.77% among S. hominis to 50% among S. epidermidis. Phenotypic resistance to all tested antibiotics, except for linezolid, was observed. Susceptibility to rifampicin, vancomycin and teicoplanin was highest. ermB showed the highest prevalence among all species (79.41% and 94.2% among S. aureus and SOSA, respectively), and constitutive macrolide-lincosamide-streptogramin B (MLSB) resistance was equally observed in S. aureus and SOSA (11.11% and 16.22%, respectively), whereas inducible MLSB resistance was more often found in S. aureus (77.78% and 43.24%, respectively). The species or resistance level of the carried isolates were not significantly associated with previous hospitalization or underlying diseases. Although over all colonization and carriage of resistance genes are within normal ranges, the increased carriage of MDR S. aureus is alarming. Also, the fact that many macrolide resitance genes were detected should be a warning sign, particularly in case of MLSB inducible phenotype. More in depth analysis using whole genome sequencing would give a better insight into the MDR staphylococci in the community in Egypt.

Recent development and fighting strategies for lincosamide antibiotic resistance

SUMMARYLincosamides constitute an important class of antibiotics used against a wide range of pathogens, including methicillin-resistant Staphylococcus aureus. However, due to the misuse of lincosamide and co-selection pressure, the resistance to lincosamide has become a serious concern. It is urgently needed to carefully understand the phenomenon and mechanism of lincosamide resistance to effectively prevent and control lincosamide resistance. To date, six mobile lincosamide resistance classes, including lnu, cfr, erm, vga, lsa, and sal, have been identified. These lincosamide resistance genes are frequently found on mobile genetic elements (MGEs), such as plasmids, transposons, integrative and conjugative elements, genomic islands, and prophages. Additionally, MGEs harbor the genes that confer resistance not only to antimicrobial agents of other classes but also to metals and biocides. The ultimate purpose of discovering and summarizing bacterial resistance is to prevent, control, and combat resistance effectively. This review highlights four promising strategies, including chemical modification of antibiotics, the development of antimicrobial peptides, the initiation of bacterial self-destruct program, and antimicrobial stewardship, to fight against resistance and safeguard global health.

Major facilitator superfamily efflux pumps in human pathogens: Role in multidrug resistance and beyond

The major facilitator superfamily (MFS) of proteins constitutes a large group of related solute transporters found across all known living taxa of organisms. The transporters of the MFS contain an extremely diverse array of substrates, including ions, molecules of intermediary metabolism, and structurally different antimicrobial agents. First discovered over 30 years ago, the MFS represents an important collection of integral membrane transporters. Bacterial microorganisms expressing multidrug efflux pumps belonging to the MFS are considered serious pathogens, accounting for alarming morbidity and mortality numbers annually. This review article considers recent advances in the structure-function relationships, the transport mechanism, and modulation of MFS multidrug efflux pumps within the context of drug resistance mechanisms of bacterial pathogens of public health concerns.

Suppressed distribution of protein A on the surface of Staphylococcus aureus as a morphological characteristic of erythromycin-resistant strain

To identify a new morphological phenotype of erythromycin (EM)-resistant Staphylococcus aureus (S. aureus) were isolated in vitro from EM-sensitive parent strain, and the distribution of staphylococcus specific protein A (SpA) on the surface of these strains was examined morphologically by using applied immunoelectron microscopy. The isolated EM-resistant strains had thickened cell walls, and the distribution of SpA on the surfaces of these strains was demonstrated to be lower than that of the parent strain. The SpA suppression was confirmed by enzyme-linked immunosorbent assay (ELISA) using fixed EM-resistant cells. Moreover, the spa gene of EM-resistant cells was detected by polymerase chain reaction (PCR) and confirmed by quantitative real-time PCR assay, showing that the expression of SpA was repressed at the transcriptional level in these strains. Furthermore, ELISA assay showed that whole EM-resistant cell SpA content was significantly decreased. Therefore, it was considered that the suppression of surface SpA on the EM-resistant strain was due to regulated SpA production, and not dependent on the conformational change in SpA molecule expression through cell wall thickening. These results strongly suggest that suppressed SpA distribution on the EM-resistant S. aureus is a phenotypical characteristic in these strains.

Genomic insights into the diversity, virulence, and antimicrobial resistance of group B Streptococcus clinical isolates from Saudi Arabia

Introduction

Detailed assessment of the population structure of group B Streptococcus (GBS) among adults is still lacking in Saudi Arabia. Here we characterized a representative collection of isolates from colonized and infected adults.

Methods

GBS isolates (n=89) were sequenced by Illumina and screened for virulence and antimicrobial resistance determinants. Genetic diversity was assessed by single nucleotide polymorphisms and core-genome MLST analyses.

Results

Genome sequences revealed 28 sequence types (STs) and nine distinct serotypes, including uncommon serotypes VII and VIII. Majority of these STs (n=76) belonged to the human-associated clonal complexes (CCs) CC1 (33.71%), CC19 (25.84%), CC17 (11.24%), CC10/CC12 (7.87%), and CC452 (6.74%). Major CCs exhibited intra-lineage serotype diversity, except for the hypervirulent CC17, which exclusively expressed serotype III. Virulence profiling revealed that nearly all isolates (94.38%) carried at least one of the four alpha family protein genes (i.e., alphaC, alp1, alp2/3, and rib), and 92.13% expressed one of the two serine-rich repeat surface proteins Srr1 or Srr2. In addition, most isolates harbored the pilus island (PI)-2a alone (15.73%) or in combination with PI-1 (62.92%), and those carrying PI-2b alone (10.11%) belonged to CC17. Phylogenetic analysis grouped the sequenced isolates according to CCs and further subdivided them along with their serotypes. Overall, isolates across all CC1 phylogenetic clusters expressed Srr1 and carried the PI-1 and PI-2a loci, but differed in genes encoding the alpha-like proteins. CC19 clusters were dominated by the III/rib/srr1/PI-1+PI-2a (43.48%, 10/23) and V/alp1/srr1/PI-1+PI-2a (34.78%, 8/23) lineages, whereas most CC17 isolates (90%, 9/10) had the same III/rib/srr2/P1-2b genetic background. Interestingly, genes encoding the CC17-specific adhesins HvgA and Srr2 were detected in phylogenetically distant isolates belonging to ST1212, suggesting that other highly virulent strains might be circulating within the species. Resistance to macrolides and/or lincosamides across all major CCs (n=48) was associated with the acquisition of erm(B) (62.5%, 30/48), erm(A) (27.1%, 13/48), lsa(C) (8.3%, 4/48), and mef(A) (2.1%, 1/48) genes, whereas resistance to tetracycline was mainly mediated by presence of tet(M) (64.18%, 43/67) and tet(O) (20.9%, 14/67) alone or in combination (13.43%, 9/67).

Discussion

These findings underscore the necessity for more rigorous characterization of GBS isolates causing infections.

Antimicrobial Resistance Profiles of Campylobacter spp. Recovered from Chicken Farms in Two Districts of Bangladesh

The rapid emergence of antimicrobial resistance (AMR) in Campylobacter has reinforced its status as a foodborne pathogen of significant public health concern. Resistant Campylobacter is typically transferred to humans via the consumption of contaminated animal products, particularly poultry. The genes associated with antimicrobial resistance in Campylobacter spp. are poorly understood. To address this knowledge gap, we conducted a prevalence survey of AMR Campylobacter across 84 chicken farms in two districts of Bangladesh. Pooled cloacal swabs were collected from chickens and underwent bacteriological testing for Campylobacter spp. with PCR confirmation. Antimicrobial susceptibility was tested against 14 antibiotics by disk diffusion method, and 12 resistance genes were screened in Campylobacter-positive isolates using multiplex PCR. A total of 34 (40.5%) farms were Campylobacter-positive of which 73.5% of isolates were resistant to at least 10 antibiotics. The antimicrobial susceptibility results indicate a high level of resistance against streptomycin (97.1%), clindamycin (97.1%), ampicillin (94.1%), tetracycline (94.1%), erythromycin (91.2%), ciprofloxacin (88.2%), nalidixic acid (85.3%), and imipenem (82.4%), and comparatively a low frequency of resistance to chloramphenicol (47.1%), ceftazidime (44.1%), and colistin (35.3%). Multidrug-resistant (MDR) and extensively drug-resistant Campylobacter were identified in 97.1%, and 50% of isolates, respectively. Ten resistance genes were identified including blaTEM (in 97.1% of isolates), strA-strB (85.9%), tetA (70.6%), tetB (32.4%), qnrS (23.5%), blaCTX-M-1 (20.6%), qnrB (20.6%), blaSHV (8.8%), aadB (5.9%), and qnrA (2.9%). Our findings demonstrate that resistance to ampicillin, tetracycline, and ceftazidime in Campylobacter isolates was significantly (p ≤ 0.05) associated with the presence of blaTEM, tetA, and blaSHV genes, respectively. The high rates of AMR in Campylobacter isolates from our study are not surprising given the liberal use of antimicrobials and incomplete biosecurity provisions on farms. Of particular concern are resistance rates to those classes of antibiotics that should be reserved for human use (azithromycin, ciprofloxacin, and colistin). AMR was more prevalent in chicken farms that used multiple antibiotics, engaged in prophylactic treatment of the birds, and improperly disposed of antibiotic packages. The high prevalence of MDR in chicken-derived Campylobacter isolates from the different regions of our study reinforces the need for more prudent use of antimicrobial compounds in Bangladeshi chicken farms.

Multidrug-resistant conjugative plasmid carrying mphA confers increased antimicrobial resistance in Shigella

Shigellosis remains a common gastrointestinal disease mostly in children < 5 years of age in developing countries. Azithromycin (AZM), a macrolide, is currently the first-line treatment for shigellosis in Bangladesh; ciprofloxacin (CIP) and ceftriaxone (CRO) are also used frequently. We aimed to evaluate the current epidemiology of antimicrobial resistance (AMR) and mechanism(s) of increasing macrolide resistance in Shigella in Bangladesh. A total of 2407 clinical isolates of Shigella from 2009 to 2016 were studied. Over the study period, Shigella sonnei was gradually increasing and become predominant (55%) over Shigella flexneri (36%) by 2016. We used CLSI-guided epidemiological cut-off value (ECV) for AZM in Shigella to set resistance breakpoints (zone-diameter ≤ 15 mm for S. flexneri and ≤ 11 mm for S. sonnei). Between 2009 and 2016, AZM resistance increased from 22% to approximately 60%, CIP resistance increased by 40%, and CRO resistance increased from zero to 15%. The mphA gene was the key macrolide resistance factor in Shigella; a 63MDa conjugative middle-range plasmid was harboring AZM and CRO resistance factors. Our findings show that, especially after 2014, there has been a rapid increase in resistance to the three most effective antibiotics. The rapid spread of macrolide (AZM) resistance genes among Shigella are driven by horizontal gene transfer rather than direct lineage.

Lincosamide Antibiotics: Structure, Activity, and Biosynthesis

Lincosamides are naturally occurring antibiotics isolated from Streptomyces sp. Currently, lincomycin A and its semisynthetic analogue clindamycin are used as clinical drugs. Due to their unique structures and remarkable biological activities, derivatizations of lincosamides via semi-synthesis and biosynthetic studies have been reported. This review summarizes the structures and biological activities of lincosamides, and the recent studies of lincosamide biosynthetic enzymes.

The pH-responsive SmrR-SmrT system modulates C. difficile antimicrobial resistance, spore formation, and toxin production

Clostridioides difficile is an anaerobic gastrointestinal pathogen that spreads through the environment as dormant spores. To survive, replicate, and sporulate in the host intestine, C. difficile must adapt to a variety of conditions in its environment, including changes in pH, the availability of metabolites, host immune factors, and a diverse array of other species. Prior studies showed that changes in intestinal conditions, such as pH, can affect C. difficile toxin production, spore formation, and cell survival. However, little is understood about the specific genes and pathways that facilitate environmental adaptation and lead to changes in C. difficile cell outcomes. In this study, we investigated two genes, CD2505 and CD2506, that are differentially regulated by pH to determine if they impact C. difficile growth and sporulation. Using deletion mutants, we examined the effects of both genes (herein smrR and smrT) on sporulation frequency, toxin production, and antimicrobial resistance. We determined that SmrR is a repressor of smrRT that responds to pH and suppresses sporulation and toxin production through regulation of the SmrT transporter. Further, we showed that SmrT confers resistance to erythromycin and lincomycin, establishing a connection between the regulation of sporulation and antimicrobial resistance.IMPORTANCEClostridioides difficile is a mammalian pathogen that colonizes the large intestine and produces toxins that lead to severe diarrheal disease. C. difficile is a major threat to public health due to its intrinsic resistance to antimicrobials and its ability to form dormant spores that are easily spread from host to host. In this study, we examined the contribution of two genes, smrR and smrT, on sporulation, toxin production, and antimicrobial resistance. Our results indicate that SmrR represses smrT expression, while production of SmrT increases spore and toxin production, as well as resistance to antibiotics.

Confronting antibiotic-resistant pathogens: Distinctive drug delivery potentials of progressive nanoparticles

Antimicrobial resistance arises over time, usually due to genetic modifications. Global observations of high resistance rates to popular antibiotics used to treat common bacterial diseases, such as diarrhea, STIs, sepsis, and urinary tract infections, indicate that our supply of effective antibiotics is running low. The mechanisms of action of several antibiotic groups are covered in this review. Antimicrobials disrupt the development and metabolism of bacteria, leading to their eventual death. However, in recent years, microorganisms become resistant to the drugs. Bacteria encode resistant genes against antibiotics and inhibit the function of antibiotics by reducing the uptake of drugs, modifying the enzyme's active site, synthesizing enzymes to degrade antibiotics, and changing the structure of ribosomal subunits. Additionally, the methods of action of resistant bacteria against different kinds of antibiotics as well as their modes of action are discussed. Besides, the resistant pathogenic bacteria which get the most priority by World Health Organisation (WHO) for synthesizing new drugs, have also been incorporated. To overcome antimicrobial resistance, nanomaterials are used to increase the efficacy of antimicrobial drugs. Metallic, inorganic, and polymer-based nanoparticles once conjugated with antibacterial drugs, exhibit synergistic effects by increasing the efficacy of the drugs by inhibiting bacterial growth. Nanomaterial's toxic properties are proportional to their concentrations. Higher concentration nanomaterials are more toxic to the cells. In this review, the toxic properties of nanomaterials on lung cells, lymph nodes, and neuronal cells are also summarized.

Genetic diversity of macrolides resistant Staphylococcus aureus clinical isolates and the potential synergistic effect of vitamins, C and K3

BACKGROUND

Macrolide antibiotics have been extensively used for the treatment of Staphylococcus aureus infections. However, the emergence of macrolide-resistant strains of S. aureus has become a major concern for public health. The molecular mechanisms underlying macrolide resistance in S. aureus are complex and diverse, involving both target site modification and efflux pump systems. In this study, we aim to overcome the molecular diversity of macrolide resistance mechanisms in S. aureus by identifying common molecular targets that could be exploited for the development of novel therapeutics.

METHODS

About 300 Staphylococcus aureus different isolates were recovered and purified from 921 clinical specimen including urine (88), blood (156), sputum (264), nasal swabs (168), pus (181) and bone (39) collected from different departments in Tanta University Hospital. Macrolide resistant isolates were detected and tested for Multi Drug Resistant (MDR). Gel electrophoresis was performed after the D test and PCR reaction for erm(A), (B), (C), msr(A), and mph(C) genes. Finally, we tried different combinations of Erythromycin or Azithromycin antibiotics with either vitamin K3 or vitamin C.

RESULTS

Macrolide resistance S. aureus isolates exhibited 7 major resistance patterns according to number of resistance markers and each pattern included sub patterns or subgroups. The PCR amplified products of different erm genes; analysis recorded different phenotypes of the Staphylococcus aureus isolates according to their different genotypes. In addition, our new tested combinations of Erythromycin and vitamin C, Erythromycin, and vitamin K3, Azithromycin and vitamin C and Azithromycin and vitamin K3 showed significant antibacterial effect when using every antibiotic alone. Our findings provide new insights into the molecular mechanisms of macrolide resistance in S. aureus and offer potential strategies for the development of novel protocols to overcome this emerging public health threat.

Baseline azithromycin resistance in the gut microbiota of preterm born infants

BACKGROUND

Macrolides, including azithromycin, are increasingly used in preterm-born infants to treat Ureaplasma infections. The baseline carriage of macrolide resistance genes in the preterm stool microbiota is unknown.

OBJECTIVES

Identify carriage of azithromycin resistant bacteria and the incidence of macrolide resistant genes.

METHODS

Azithromycin resistant bacteria were isolated from serial stool samples obtained from preterm infants (≤32 weeks' gestation) by culturing aerobically/anaerobically, in the presence/absence of azithromycin. Using quantitative PCR, we targeted 6 common macrolide resistance genes (erm(A), erm(B), erm(C), erm(F), mef(A/E), msr(A)) in DNA extracted from selected bacteria resistant to azithromycin.

RESULTS

From 89 stool samples from 37 preterm-born infants, 93.3% showed bacterial growth in aerobic or anaerobic conditions. From the 280 azithromycin resistant isolates that were identified, Staphylococcus (75%) and Enterococcus (15%) species dominated. Macrolide resistance genes were identified in 91% of resistant isolates: commonest were erm(C) (46% of isolates) and msr(A) (40%). Multiple macrolide resistance genes were identified in 18% of isolates.

CONCLUSION

Macrolide resistance is common in the gut microbiota of preterm-born infants early in life, most likely acquired from exposure to the maternal microbiota. It will be important to assess modulation of macrolide resistance, if macrolide treatment becomes routine in the management of preterm infants.

IMPACT STATEMENT

Azithromycin resistance is present in the stool microbiota in the first month of life in preterm infants 91% of azithromycin resistant bacteria carried at least one of 6 common macrolide resistant genes Increasing use of macrolides in the preterm population makes this an important area of study.

Circular intermediate-mediated horizontal transfer of the chromosome-encoded cfr(C) gene in multi-drug resistant Campylobacter coli from swine sources

Campylobacter is a major zoonotic pathogen that causes gastrointestinal and, rarely, immune diseases in humans. The antimicrobial-resistance gene cfr(C) carried by Campylobacter and is a cfr-like gene that targets bacterial 23S rRNA through A2503 methylation. cfr(C) confers cross-resistance to five antimicrobial classes (PhLOPSA), including lincosamide, streptogramin A, and pleuromutilin, which are classified as critically important antimicrobials to human by the World Health Organization. To elucidate the genetic variation and horizontal transfer mechanism of cfr(C), we analyzed the genetic background and horizontal transfer unit of Campylobacter-derived cfr(C) through comparative genomic analysis. We identified nine cfr(C)-positive C. coli strains of 157 strains isolated from swine sources. Three novel cfr(C) gene single nucleotide polymorphism (SNP) sites (19delA, 674C > A, and 890 T > C) were identified from nine cfr(C)-positive strains. Among six identified cfr(C) SNP variant types (SNP-I to -VI), five types of randomly inserted cfr(C)-cassettes on chromosome and one type of plasmid-like element were identified, their gene cassette composition differing depending on the cfr(C) variants. Three of six cfr(C) cassette types contained aminoglycoside-streptothricin resistance cluster "aphA3-sat4-aadE." The cfr(C) gene cassette with pcp gene (GC-1, GC-4, and GC-5) formed a pcp-mediated circular intermediate "pcp-hp-cfr(C)-aphA3," which has not been previously reported. Other two cfr(C) cassette-types with ISChh1 formed circular intermediate "ISChh1-aphA3-cfr(C)-lnu (G)-pnp-ant1-hp-ATPase" and "ISChh1-aphA3-cfr(C)-hp." In conjugation assay, the pcp-mediated circular intermediate was naturally transferred to the plasmid of recipient C. coli wild-type strain from swine source, and comparative genomic analysis revealed that cfr(C) encoded in pcp-mediated circular intermediate was inserted into the plasmid of recipient by homologous recombination with pcp and aphA3. This study revealed that novel multidrug resistance gene cfr(C) carried by C. coli from swine sources can be highly genetically diverse and transferable. Moreover, we suggest that the transferability of chromosomal cfr(C) may contribute to the global spread of multidrug resistance against clinically important antimicrobials.

Antibiotic Resistance Genes, Virulence Factors, and Biofilm Formation in Coagulase-Negative Staphylococcus spp. Isolates from European Hakes (Merluccius merluccius, L.) Caught in the Northeast Atlantic Ocean

The indiscriminate use of antibiotics has contributed to the dissemination of multiresistant bacteria, which represents a public health concern. The aim of this work was to characterize 27 coagulase-negative staphylococci (CoNS) isolated from eight wild Northeast Atlantic hakes (Merluccius merluccius, L.) and taxonomically identified as Staphylococcus epidermidis (n = 16), Staphylococcus saprophyticus (n = 4), Staphylococcus hominis (n = 3), Staphylococcus pasteuri (n = 2), Staphylococcus edaphicus (n = 1), and Staphylococcus capitis (n = 1). Biofilm formation was evaluated with a microtiter assay, antibiotic susceptibility testing was performed using the disk diffusion method, and antibiotic resistance and virulence determinants were detected by PCR. Our results showed that all staphylococci produced biofilms and that 92.6% of the isolates were resistant to at least one antibiotic, mainly penicillin (88.8%), fusidic acid (40.7%), and erythromycin (37%). The penicillin resistance gene (blaZ) was detected in 66.6% (18) of the isolates, of which 10 also carried resistance genes to macrolides and lincosamides (mphC, msr(A/B), lnuA, or vgaA), 4 to fusidic acid (fusB), and 3 to trimethoprim-sulfamethoxazole (dfrA). At least one virulence gene (scn, hla, SCCmecIII, and/or SCCmecV) was detected in 48% of the isolates. This study suggests that wild European hake destined for human consumption could act as a vector of CoNS carrying antibiotic resistance genes and/or virulence factors.

Multimodal learning in clinical proteomics: enhancing antimicrobial resistance prediction models with chemical information

MOTIVATION

Large-scale clinical proteomics datasets of infectious pathogens, combined with antimicrobial resistance outcomes, have recently opened the door for machine learning models which aim to improve clinical treatment by predicting resistance early. However, existing prediction frameworks typically train a separate model for each antimicrobial and species in order to predict a pathogen's resistance outcome, resulting in missed opportunities for chemical knowledge transfer and generalizability.

RESULTS

We demonstrate the effectiveness of multimodal learning over proteomic and chemical features by exploring two clinically relevant tasks for our proposed deep learning models: drug recommendation and generalized resistance prediction. By adopting this multi-view representation of the pathogenic samples and leveraging the scale of the available datasets, our models outperformed the previous single-drug and single-species predictive models by statistically significant margins. We extensively validated the multi-drug setting, highlighting the challenges in generalizing beyond the training data distribution, and quantitatively demonstrate how suitable representations of antimicrobial drugs constitute a crucial tool in the development of clinically relevant predictive models.

AVAILABILITY AND IMPLEMENTATION

The code used to produce the results presented in this article is available at https://github.com/BorgwardtLab/MultimodalAMR.

Metal nanoparticles as inhibitors of enzymes and toxins of multidrug-resistant Staphylococcus aureus

Staphylococcus aureus is an aerobic Gram-positive spherical bacterium known to cause a broad range of infections worldwide. It is a major cause of infective skin and soft infections and severe and life-threatening conditions, such as pneumonia, bloodstream infections, and endocarditis. The emergence of drug-resistant strains of S aureus, particularly methicillin-resistant S aureus (MRSA), has become a significant concern in the healthcare community. Antibiotic-resistant S aureus is commonly acquired in hospitals and long-term care facilities. It often affects patients with weakened immune systems, those undergoing invasive medical procedures, or those who have been hospitalized for extended periods. In the US, S aureus is known to cause potentially fatal illnesses, such as toxic shock syndrome (TSS) and acute-onset toxic shock syndrome (TSS), which are characterized by fever and hypotension. It develops resistance to antibiotics through several mechanisms, such as the production of enzymes that inactivate antibiotics, target site modification, efflux pumps, and plasmid-mediated resistance. Therefore, preventing the spread of drug-resistant S aureus is needed, and there is an urgent need to explore novel approaches in the development of anti-staphylococcal agents. This article reviews the principal infections caused by S aureus, major virulence factors, mechanisms of resistance development, and nanotechnology-based solutions for the control of drug-resistant S aureus.

Microbiological and hematological aspects of canine pyometra and associated risk factors

Canine Pyometra, also known as cystic endometrial hyperplasia complex, is a common reproductive issue in bitches. This study aimed to identify associated risk factors, hematological variation, bacteria involved, and the most potent anti-bacterial against bacterial isolates of canine pyometra. Forty-five bitches of different habitats, breeds, and ages infected with pyometra were included in the study. The samples were cultured to isolate bacteria associated with the pyometra and antibiotic sensitivity was done for each bacterial isolates to get antibiogram. The study findings showed that potential risk factors such as age group, medroxyprogesterone acetate administration, and changes in the white blood cells parameters were significantly associated (P < 0.05) with the type of pyometra. Closed cervix pyometra in dogs showed significantly higher prevalence of clinical signs including depression, vomiting, abdominal enlargement, and fever compared to the open cervix pyometra. Low levels of red blood cells, pack cell volume, and hemoglobin indicated that the pyometra-infected dogs were more likely to have normocytic, normochromic, and non-regenerative anemia. Pyometra was attributed to an increase in AST (Aspertate aminotransferase), ALT (Alanine transaminase), ALP (Alkaline phosphatase), BUN (Blood Urea Nitrogen), and Creatinine while a decrease in serum albumin. Of the all bacterial isolates, E. coli (35.55%) was the most common pathogen isolated from canine pyometra, followed by Pseudomonas spp. (26.66%). E coli and Pseudomonas spp. were susceptible to Imipenem, Amikacin, and Gentamicin while highly resistant to Ampicillin and Erythromycin. Imipenem, Amikacin, and Gentamicin were the most sensitive antibiotics, while Ampicillin and Erythromycin were the most resistant antibiotics for the bacterial strain isolated from canine pyometra. Multidrug resistant was observed in 26 of the isolated bacteria, indicating acquired resistance due to improper and uncontrolled use. Hence early diagnosis and close monitoring of antimicrobial susceptibility before therapeutic intervention is indispensable in preventing the global threat of antimicrobial resistance.

Epidemiology of neonatal sepsis in two neonatal intensive care units in Krakow, Poland in 2016-2017 years

BACKGROUND

Sepsis in low-birth-weight neonates remains one of the most significant causes of neonatal morbidity and mortality. Approximately 3 million newborns suffer from sepsis globally every year. The aim of this study was to compare demographic and clinical features, as well as etiology and antibiotic susceptibility, of the main pathogens related to neonatal sepsis in two neonatal intensive units during a two-year period.

METHODS

We observed early-onset (EO-BSI) and late-onset bloodstream infections (LO-BSI) cases in two high-reference neonatal intensive care units (NICU) over a 24-month period (2016-2017). Samples of patients' blood were tested for the presence of the microorganisms. All bacterial isolates were tested for susceptibility to antibiotics.

RESULTS

The majority of sepsis cases weighed above 1000 g and were born by cesarean section. About 10% of the EO-BSI group died. There were differences in the EO-BSI /LO-BSI ratio in the compared wards due to differences among the admitted children. The most common pathogens isolated from blood were coagulase-negative staphylococci (CoNS) were represented by two dominating species: S. epidermidis and S. haemolyticus, followed by Klebsiella spp. strains and E.coli, which were mostly found in EO-BSI cases. No single S. agalactiae (GBS) strain was isolated. The majority of CoNS strains were resistant to methicillin, half were resistant to aminoglycosides, and one-third were resistant to macrolides and lincosamides. Half of the Gram-negative rods were resistant to beta-lactams.

CONCLUSIONS

The epidemiology of sepsis in two observed NICUs is comparable to data obtained from other studies with a predominance of methicillin-resistant CoNS in LO-BSI and beta-lactam resistant E. coli in EO-BSI. It is of importance that the campaign for controlling GBS carriage in pregnant women in Poland resulted in the disappearance of GBS as a cause of sepsis. Unfortunately, there are no such measures to control E.coli related sepsis.

Comparison of contemporary invasive and non-invasive Streptococcus pneumoniae isolates reveals new insights into circulating anti-microbial resistance determinants

Streptococcus pneumoniae is a major human pathogen with a high burden of disease. Non-invasive isolates (those found in non-sterile sites) are thought to be a key source of invasive isolates (those found in sterile sites) and a reservoir of anti-microbial resistance (AMR) determinants. Despite this, pneumococcal surveillance has almost exclusively focused on invasive isolates. We aimed to compare contemporaneous invasive and non-invasive isolate populations to understand how they interact and identify differences in AMR gene distribution. We used a combination of whole-genome sequencing and phenotypic anti-microbial susceptibility testing and a data set of invasive (n = 1,288) and non-invasive (n = 186) pneumococcal isolates, collected in Victoria, Australia, between 2018 and 2022. The non-invasive population had increased levels of antibiotic resistance to multiple classes of antibiotics including beta-lactam antibiotics penicillin and ceftriaxone. We identified genomic intersections between the invasive and non-invasive populations and no distinct phylogenetic clustering of the two populations. However, this analysis revealed sub-populations overrepresented in each population. The sub-populations that had high levels of AMR were overrepresented in the non-invasive population. We determined that WamR-Pneumo was the most accurate in silico tool for predicting resistance to the antibiotics tested. This tool was then used to assess the allelic diversity of the penicillin-binding protein genes, which acquire mutations leading to beta-lactam antibiotic resistance, and found that they were highly conserved (≥80% shared) between the two populations. These findings show the potential of non-invasive isolates to serve as reservoirs of AMR determinants.

The pH-responsive SmrR-SmrT system modulates C. difficile antimicrobial resistance, spore formation, and toxin production

Clostridioides difficile is an anaerobic gastrointestinal pathogen that spreads through the environment as dormant spores. To survive, replicate, and sporulate in the host intestine, C. difficile must adapt to a variety of conditions in its environment, including changes in pH, the availability of metabolites, host immune factors, and a diverse array of other species. Prior studies showed that changes in intestinal conditions, such as pH, can affect C. difficile toxin production, spore formation, and cell survival. However, little is understood about the specific genes and pathways that facilitate environmental adaptation and lead to changes in C. difficile cell outcomes. In this study, we investigated two genes, CD2505 and CD2506, that are differentially regulated by pH to determine if they impact C. difficile growth and sporulation. Using deletion mutants, we examined the effects of both genes (herein smrR and smrT ) on sporulation frequency, toxin production, and antimicrobial resistance. We determined that SmrR is a repressor of smrRT that responds to pH and suppresses sporulation and toxin production through regulation of the SmrT transporter. Further, we showed that SmrT confers resistance to erythromycin and lincomycin, establishing a connection between the regulation of sporulation and antimicrobial resistance.

IMPORTANCE

C. difficile is a mammalian pathogen that colonizes the large intestine and produces toxins that lead to severe diarrheal disease. C. difficile is a major threat to public health due to its intrinsic resistance to antimicrobials and its ability to form dormant spores that are easily spread from host to host. In this study, we examined the contribution of two genes, smrR and smrT on sporulation, toxin production, and antimicrobial resistance. Our results indicate that SmrR represses smrT expression, while production of SmrT increases spore and toxin production, as well as resistance to antibiotics.

Plasmid-mediated drug resistance in mycobacteria: the tip of the iceberg?

Macrolides, such as clarithromycin, are crucial in the treatment of nontuberculous mycobacteria (NTM). NTM are notoriously innately drug resistant, which has made the dependence on macrolides for their treatment even more important. Not surprisingly, resistance to macrolides has been documented in some NTM, including Mycobacterium avium and Mycobacterium abscessus, which are the two NTM species most often identified in clinical isolates. Resistance is mediated by point mutations in the 23S ribosomal RNA or by methylation of the rRNA by a methylase (encoded by an erm gene). Chromosomally encoded erm genes have been identified in many of the macrolide-resistant isolates, but not in Mycobacterium chelonae. Now, Brown-Elliott et al. (J Clin Microbiol 61:e00428-23, 2023, https://doi.org/10.1128/JCM.00428-23) describe the identification of a new erm variant, erm(55), which was found either on the chromosome or on a plasmid in highly macrolide-resistant clinical isolates of M. chelonae. The chromosomal erm(55) gene appears to be associated with mobile elements; one gene is within a putative transposon and the second is in a large (37 kb) insertion/deletion. The plasmid carrying erm(55) also encodes type IV and type VII secretion systems, which are often linked on large mycobacterial plasmids and are hypothesized to mediate plasmid transfer. While the conjugative transfer of the erm(55)-containing plasmid between NTM has yet to be demonstrated, the inferences are clear, as evidenced by the dissemination of plasmid-mediated drug resistance in other medically important bacteria. Here, we discuss the findings of Brown-Elliott et al., and the potential ramifications on treatment of NTM infections.

The Combination of Antibiotic and Non-Antibiotic Compounds Improves Antibiotic Efficacy against Multidrug-Resistant Bacteria

Bacterial antibiotic resistance, especially the emergence of multidrug-resistant (MDR) strains, urgently requires the development of effective treatment strategies. It is always of interest to delve into the mechanisms of resistance to current antibiotics and target them to promote the efficacy of existing antibiotics. In recent years, non-antibiotic compounds have played an important auxiliary role in improving the efficacy of antibiotics and promoting the treatment of drug-resistant bacteria. The combination of non-antibiotic compounds with antibiotics is considered a promising strategy against MDR bacteria. In this review, we first briefly summarize the main resistance mechanisms of current antibiotics. In addition, we propose several strategies to enhance antibiotic action based on resistance mechanisms. Then, the research progress of non-antibiotic compounds that can promote antibiotic-resistant bacteria through different mechanisms in recent years is also summarized. Finally, the development prospects and challenges of these non-antibiotic compounds in combination with antibiotics are discussed.

Prevalence and antimicrobial susceptibility of Mycoplasma bovis from the upper and lower respiratory tracts of healthy feedlot cattle and those diagnosed with bovine respiratory disease

Mycoplasma bovis is an important respiratory pathogen of cattle. In this study, the prevalence and antimicrobial susceptibility of M. bovis were evaluated from two Cohorts of feedlot cattle spanning an 8-year period. In the first study conducted in 2008-2009, nasopharyngeal swabs from cattle sampled at feedlot entry and after 60 days on feed were collected (Cohort 1). In a second study conducted in 2015-2016, nasopharyngeal and trans-tracheal samples were collected from cattle diagnosed with bovine respiratory disease (BRD) and matching healthy controls (Cohort 2). For Cohort 1, the prevalence of M. bovis was lower in cattle at entry compared to when the same individuals were sampled ≥60 days later (P < 0.05). For Cohort 2, the prevalence of M. bovis was greater in both nasopharyngeal and tracheal samples from cattle diagnosed with BRD, compared to controls (P < 0.05). In both Cohorts, almost all isolates were resistant to tilmicosin. Compared to M. bovis from Cohort 1, isolates of Cohort 2 exhibited increased resistance to clindamycin, enrofloxacin, florfenicol, tylosin, and tulathromycin, with the latter showing resistance levels >90 %. These data suggest that antimicrobials used to prevent and treat BRD selected for resistance in M. bovis over the 8-year period. For macrolides, cross-resistance occurred and M. bovis can retain resistance even when antimicrobial selection pressure is removed. Within 9 years of commercial availability of tulathromycin, the majority of M. bovis displayed resistance. Therefore, longitudinal evaluation of resistance in respiratory pathogens is important to ensure efficacious treatment of BRD.

How Combined Macrolide Nanomaterials are Effective Against Resistant Pathogens? A Comprehensive Review of the Literature

Macrolide drugs are among the broad-spectrum antibiotics that are considered as "miracle drugs" against infectious diseases that lead to higher morbidity and mortality rates. Nevertheless, their effectiveness is currently at risk owing to the presence of devastating, antimicrobial-resistant microbes. In view of this challenge, nanotechnology-driven innovations are currently being anticipated for promising approaches to overcome antimicrobial resistance. Nowadays, various nanostructures are being developed for the delivery of antimicrobials to counter drug-resistant microbial strains through different mechanisms. Metallic nanoparticle-based delivery of macrolides, particularly using silver and gold nanoparticles (AgNPs & AuNPs), demonstrated a promising outcome with worthy stability, oxidation resistance, and biocompatibility. Similarly, macrolide-conjugated magnetic NPs resulted in an augmented antimicrobial activity and reduced bacterial cell viability against resistant microbes. Liposomal delivery of macrolides also showed favorable synergistic antimicrobial activities in vitro against resistant strains. Loading macrolide drugs into various polymeric nanomaterials resulted in an enhanced zone of inhibition. Intercalated nanomaterials also conveyed an outstanding macrolide delivery characteristic with efficient targeting and controlled drug release against infectious microbes. This review abridges several nano-based delivery approaches for macrolide drugs along with their recent achievements, challenges, and future perspectives.

A clindamycin acetylated derivative with reduced antibacterial activity inhibits articular hyperalgesia and edema by attenuating neutrophil recruitment, NF-κB activation and tumor necrosis factor-α production

We recently demonstrated that clindamycin exhibits activities in acute and chronic models of pain and inflammation. In the present study, we investigated the effects of clindamycin and a clindamycin acetylated derivative (CAD) in models of acute joint inflammation and in a microbiological assay. Joint inflammation was induced in mice by intraarticular (i.a.) injection of zymosan or lipopolysaccharide (LPS). Clindamycin or CAD were administered via the intraperitoneal route 1 h before zymosan or LPS. Paw withdrawal threshold, joint diameter, histological changes, neutrophil recruitment, tumor necrosis factor-α (TNF-α) production and phosphorylation of the IκBα and NF-κB/p65 were evaluated. In vitro assays were used to measure the antibacterial activity of clindamycin and CAD and also their effects on zymosan-induced TNF-α production by RAW264.7 macrophages. Clindamycin exhibited activity against Staphylococcus aureus and Salmonella Typhimurium ATCC® strains at much lower concentrations than CAD. Intraarticular injection of zymosan or LPS induced articular hyperalgesia, edema and neutrophil infiltration in the joints. Zymosan also induced histological changes, NF-κB activation and TNF-α production. Responses induced by zymosan and LPS were inhibited by clindamycin (200 and 400 mg/kg) or CAD (436 mg/kg). Both clindamycin and CAD inhibited in vitro TNF-α production by macrophages. In summary, we provided additional insights of the clindamycin immunomodulatory effects, whose mechanism was associated with NF-κB inhibition and reduced TNF-α production. Such effects were extended to a clindamycin derivative with reduced antibacterial activity, indicating that clindamycin derivatives should be investigated as candidates to drugs that could be useful in the management of inflammatory and painful conditions.

Staph wars: the antibiotic pipeline strikes back

Antibiotic chemotherapy is widely regarded as one of the most significant medical advancements in history. However, the continued misuse of antibiotics has contributed to the rapid rise of antimicrobial resistance (AMR) globally. Staphylococcus aureus, a major human pathogen, has become synonymous with multidrug resistance and is a leading antimicrobial-resistant pathogen causing significant morbidity and mortality worldwide. This review focuses on (1) the targets of current anti-staphylococcal antibiotics and the specific mechanisms that confirm resistance; (2) an in-depth analysis of recently licensed antibiotics approved for the treatment of S. aureus infections; and (3) an examination of the pre-clinical pipeline of anti-staphylococcal compounds. In addition, we examine the molecular mechanism of action of novel antimicrobials and derivatives of existing classes of antibiotics, collate data on the emergence of resistance to new compounds and provide an overview of key data from clinical trials evaluating anti-staphylococcal compounds. We present several successful cases in the development of alternative forms of existing antibiotics that have activity against multidrug-resistant S. aureus. Pre-clinical antimicrobials show promise, but more focus and funding are required to develop novel classes of compounds that can curtail the spread of and sustainably control antimicrobial-resistant S. aureus infections.

Review on PLGA Polymer Based Nanoparticles with Antimicrobial Properties and Their Application in Various Medical Conditions or Infections

The rise in the resistance to antibiotics is due to their inappropriate use and the use of a broad spectrum of antibiotics. This has also contributed to the development of multidrug-resistant microorganisms, and due to the unavailability of suitable new drugs for treatments, it is difficult to control. Hence, there is a need for the development of new novel, target-specific antimicrobials. Nanotechnology, involving the synthesis of nanoparticles, may be one of the best options, as it can be manipulated by using physicochemical properties to develop intelligent NPs with desired properties. NPs, because of their unique properties, can deliver drugs to specific targets and release them in a sustained fashion. The chance of developing resistance is very low. Polymeric nanoparticles are solid colloids synthesized using either natural or synthetic polymers. These polymers are used as carriers of drugs to deliver them to the targets. NPs, synthesized using poly-lactic acid (PLA) or the copolymer of lactic and glycolic acid (PLGA), are used in the delivery of controlled drug release, as they are biodegradable, biocompatible and have been approved by the USFDA. In this article, we will be reviewing the synthesis of PLGA-based nanoparticles encapsulated or loaded with antibiotics, natural products, or metal ions and their antibacterial potential in various medical applications.

Whole genome sequence-based analysis of Staphylococcus aureus isolated from bovine mastitis in Thuringia, Germany

Background

Bovine mastitis is a common disease of dairy cattle causing major economic losses due to reduced yield and poor quality of milk worldwide. The current investigation aimed to gain insight into the genetic diversity, antimicrobial resistance profiles and virulence associated factors of Staphylococcus (S.) aureus isolated from clinical bovine mastitis in dairy farms in Thuringia, Germany.

Methods

Forty Staphylococcus aureus isolates collected from clinical bovine mastitis cases from 17 Thuringian dairy farms were phenotyped and genetically characterized using whole genome sequencing.

Results

Out of 40 S. aureus, 30 (75%) were confirmed as methicillin resistant isolates. The isolates showed elevated antimicrobial resistance against penicillin, tetracycline and oxacillin, i.e., 77.5, 77.5, and 75%, respectively. Lower resistance rates were found against moxifloxacin, ciprofloxacin, gentamicin and trimethoprim/sulfamethoxazole, i.e., 35, 35, 30, and 22.5%, respectively. While resistance against clindamycin and erythromycin was rarely found (5 and 2.5%, respectively). All isolates were susceptible to linezolid, teicoplanin, vancomycin, tigecycline, fosfomycin, fusidic acid and rifampicin. These isolates were further allocated into five different sequence types: ST398 (n = 31), ST1074 (n = 4), ST504 (n = 3), ST582 (CC15) (n = 1) and ST479 (n = 1). These isolates were also assigned to seven clusters with up to 100 SNP which has facilitated geographical mapping and epidemiological distribution in Thuringia. Strains belonging to ST398 were classified into clusters 1, 2, 3, 4 and 7. The isolates of ST504 were of cluster 5, those of ST1074 were belonging to cluster 6. Resistance genes blaZ, blaI and blaR associated with penicillin resistance were found in 32 (80%) strains, all except one were belonging to ST398. Methicillin resistance associated mecA was identified in 30 (96.8%) isolates of ST398. All tetracycline and erythromycin resistant isolates were of ST398, and all harbored both tetM and ermA. About 90.3% of tetracycline resistant isolates assigned to ST398 were also carrying tetK gene. The point mutations parC_S80F, gyrA_S84L and parC_S80Y in gyrA and parC associated with quinolone resistance were found in all phenotypically resistant isolates to ciprofloxacin and moxifloxacin (n = 14). Sixty-eight virulence genes were identified among isolates. Both lukD/E and lukM/F-PV-P83 were identified in 22.5% of isolates, all were non-ST398.

Conclusion

In this study, ST398 had the highest potential to cause disease and had a massive prevalence in bovine mastitis cases. Five different sequence types and seven clusters were identified in the federal state of Thuringia. The circulation of some clusters in the same region over several years shows the persistence of cluster-associated infection despite the intensive veterinary care. On the other hand, some regions had different clusters at the same year or in different consecutive years. Different sequence types and associated different clusters of S. aureus were geographically widely distributed among dairy farms in Thuringia. The findings of this study show that various clusters have the potential to spread over a large geographical scale. The detection of LA-MRSA on dairy farms, which is known for cabapility to widely spread among different groups of animals, humans and their environment urges for the implementation of national wide strategic programs. The identification of CA-MRSA among the isolates such as ST398 poses a significant risk for the transmission of such strains between animals and humans on dairy farms.

Novel macrolide-lincosamide-streptogramin B resistance gene erm(56) in Trueperella pyogenes

Whole-genome sequence analysis of a macrolide, lincosamide, streptogramin B (MLSB)-resistant Trueperella pyogenes from a dog revealed a new 23S ribosomal RNA methylase gene erm(56). Expression of the cloned erm(56) confers resistance to MLSB in T. pyogenes and Escherichia coli. The erm(56) gene was flanked by two IS6100 integrated on the chromosome next to a sul1-containing class 1 integron. GenBank query revealed additional erm(56)-containing elements in another T. pyogenes and in Rothia nasimurium from livestock. IMPORTANCE A novel 23S ribosomal RNA methylase gene erm(56) flanked by insertion sequence IS6100 was identified in a Trueperella pyogenes isolated from the abscess of a dog and was also present in another T. pyogenes and in Rothia nasimurium from livestock. It was shown to confer resistance to macrolide, lincosamide, streptogramin B antibiotics in T. pyogenes and E. coli, indicating functionality in both Gram-positive and Gram-negative bacteria. The detection of erm(56) on different elements in unrelated bacteria from different animal sources and geographical origins suggests that it has been independently acquired and likely selected by the use of antibiotics in animals.

Decreased susceptibility to vancomycin and other mechanisms of resistance to antibiotics in Staphylococcus epidermidis as a therapeutic problem in hospital treatment

Multidrug-resistant coagulase-negative staphylococci represent a real therapeutic challenge. The aim of the study was to emphasize the importance of heteroresistance to vancomycin presence in methicillin-resistant strains of S. epidermidis. The research comprised 65 strains of S. epidermidis. Heteroresistance to vancomycin was detected with the use of the agar screening method with Brain Heart Infusion and a population profile analysis (PAP test). In addition, types of cassettes and genes responsible for resistance to antibiotics for 22 multidrug resistant strains were determined. Our investigations showed that 56 of 65 S. epidermidis strains were phenotypically resistant to methicillin. The tested strains were mostly resistant to erythromycin, gentamicin, clindamycin, and ciprofloxacin. Six strains showed decreased susceptibility to vancomycin and their heterogeneous resistance profiles were confirmed with the PAP test. All tested multi-resistant strains exhibited the mecA gene. More than half of them possessed type IV cassettes. ant(4')-Ia and aac(6')/aph(2''), ermC and tetK genes were most commonly found. The described phenomenon of heteroresistance to vancomycin in multidrug resistant bacteria of the Staphylococcus genus effectively inhibits a therapeutic effect of treatment with this antibiotic. That is why it is so important to search for markers that will enable to identify heteroresistance to vancomycin strains under laboratory conditions.

Novel Starter Strain Enterococcus faecium DMEA09 from Traditional Korean Fermented Meju

The Enterococcus faecium strain DMEA09 was previously isolated from traditional Korean fermented meju. The objective of the current study was to investigate the traits of E. faecium strain DMEA09 as a starter candidate, focusing on its safety and technological properties. Regarding its safety, the DMEA09 strain was found to be sensitive to nine antibiotics (ampicillin, chloramphenicol, erythromycin, gentamicin, kanamycin, streptomycin, tetracycline, tylosin, and vancomycin) by showing lower minimum inhibitory concentrations (MICs) than the cut-off values suggested by the European Union Food Safety Authority for these nine antibiotics. However, its MIC value for clindamycin was twice as high as the cut-off value. A genomic analysis revealed that strain DMEA09 did not encode the acquired antibiotic resistance genes, including those for clindamycin. The DMEA09 strain did not show hemolysis as a result of analyzing α- and β-hemolysis. It did not form biofilm either. A genomic analysis revealed that strain DMEA09 did not encode for any virulence factors including hemolysin. Most importantly, multilocus sequence typing revealed that the clonal group of strain DMEA09 was distinguished from clinical isolates. Regarding its technological properties, strain DMEA09 could grow in the presence of 6% salt. It showed protease activity when the salt concentration was 3%. It did not exhibit lipase activity. Its genome possessed 37 putative protease genes and salt-tolerance genes for survivability under salt conditions. Consequently, strain DMEA09 shows safe and technological properties as a new starter candidate. This was confirmed by genome analysis.

Diversity of virulence and antibiotic resistance genes expressed in Class A biosolids and biosolids-amended soil as revealed by metatranscriptomic analysis

Class A biosolids is a treated sewage sludge, commonly applied to agricultural fields, home lawns/gardens, golf courses, forests, and remediation sites around the world. This practice is of public and agricultural concern due to the possibility that biosolids contain antibiotic-resistant bacteria and fungal pathogens that could persist for extended periods in soil. This possibility was determined by metatranscriptomic analysis of virulence, antibiotic resistance, and plasmid conjugation genes, a Class A biosolids, organically managed soil, and biosolids-amended soil under realistic conditions. Biosolids harbored numerous transcriptionally active pathogens, antibiotic resistance genes, and conjugative genes that annotated mostly to Gram-positive pathogens of animal hosts. Biosolids amendment to soil significantly increased the expression of virulence genes by numerous pathogens and antibiotic-resistant genes that were strongly associated with biosolids. Biosolids amendment also significantly increased the expression of virulence genes by native soil fungal pathogens of plant hosts, which suggests higher risks of crop damage by soil fungal pathogens in biosolids-amended soil. Although results are likely to be different in other soils, biosolids, and microbial growth conditions, they provide a more holistic, accurate view of potential health risks associated with biosolids and biosolids-amended soils than has been achievable with more selective cultivation and PCR-based techniques.

Phenotypic and genotypic characterization of erythromycin-resistant Staphylococcus aureus isolated from bovine subclinical mastitis in Egypt

Background and Aim

Subclinical mastitis (SCM) caused by erythromycin-resistant Staphylococcus aureus is a significant disease in lactating animals. Therefore, it is crucial to understand the genetic factors contributing to erythromycin resistance in S. aureus. This study aimed to estimate the prevalence of S. aureus in milk from subclinical mastitic cattle and buffaloes and tank milk samples as identified by probe-based real-time polymerase chain reaction (PCR) and the genotypic assessment of macrolide and erythromycin resistance profiles, as well as to analyze the phylogenetic relatedness of our local isolates of S. aureus.

Materials and Methods

In total, 285 milk samples were analyzed using the California mastitis test to detect SCM. Milk samples were cultured on different specific Staphylococcus media. The presence of S. aureus was confirmed by Gram staining, the catalase and coagulase tests, the detection of hemolytic activity, DNase agar testing, and biofilm activity in Congo red medium. The genotypic identification of S. aureus (nuc) was performed. The determinants of erythromycin (ermA, ermB, ermC, and ermT) and macrolide resistance (msrA) were screened in all isolates. DNA sequencing of our local isolates of S. aureus was used to analyze their phylogenetic relatedness. Moreover, histopathological examination of tissue specimens of mammary gland was performed.

Results

The S. aureus positivity rates were 36.4%, 48.8%, and 63.6% in cattle, buffalo, and bulk tank milk, respectively. Probe-based real-time PCR molecularly confirmed all 62 S. aureus isolates. Thirty-one isolates were subjected to PCR to create profiles of their genotypic erythromycin resistance. ermA, ermB, ermC, and ermT were present in 5 (8%), 26 (41.9%), 18 (29%), and 15 (24.1%) S. aureus isolates, respectively. Moreover, msrA was found in three (4.8%) strains. Eight PCR products were produced using standard PCR for DNA sequencing. Multiple sequence alignment, phylogenetic tree construction, and analysis of nuc in S. aureus revealed a high degree of homology (100%) with S. aureus strains isolated from milk in cases of bovine mastitis in India and Kenya. Histological analysis of udder tissues revealed extensive aggregation of mononuclear inflammatory cells in the interstitial connective tissue, primarily lymphocytes, and macrophages.

Conclusion

This study showed a high prevalence of erythromycin resistance in S. aureus isolates. This information is vital for controlling mastitis and the spread of resistance genes between bacterial strains and hosts. Moreover, the probe-based real-time PCR approach is helpful for the rapid screening of S. aureus isolates and the consequent efficient treatment and control of S. aureus mastitis.