Transcriptomic signature of bacteria exposed to benzalkonium chloride.

The COVID-19 pandemic has highlighted our reliance on biocides, the increasing prevalence of resistance to biocides is a risk to public health. Bacterial exposure to the biocide, benzalkonium chloride (BAC), resulted in a unique transcriptomic profile, characterised by both a short and long-term response. Differential gene expression was observed in four main areas: motility, membrane composition, proteostasis, and the stress response. A metabolism shift to protect the proteome and the stress response were prioritised suggesting these are main resistance mechanisms. Whereas "well-established" mechanisms, such as biofilm formation, were not found to be differentially expressed after exposure to BAC.

The Hormetic Effect Observed for Benzalkonium Chloride and Didecyldimethylammonium Chloride in Serratia sp. HRI.

Hormesis, or the hormetic effect, is a dose- or concentration-dependent response characterised by growth stimulation at low concentrations and inhibition at high concentrations. The impact of sub-lethal levels of disinfectants on the growth of Serratia species is critical to understanding the increasing number of outbreaks caused by this pathogen in healthcare settings. Serratia sp. HRI and Serratia marcescens ATCC 13880 were cultivated in sub-lethal levels of benzalkonium chloride (BAC), Didecyldimethylammonium chloride (DDAC), and VirukillTM. The maximum specific growth rates, doubling times, and cell counts were compared. The results revealed significant increases in maximum specific growth rates and shorter doubling times for Serratia sp. HRI when cultivated in sub-lethal levels of BAC and DDAC. The significant stimulatory effect of sub-lethal levels of these disinfectants for Serratia sp. HRI represents the first time hormesis has been observed in a Gram-negative bacterium for any disinfectant. Furthermore, this study is the first to observe the hormetic effect after treatment with DDAC and the second study to date analysing the impact of sub-lethal levels of disinfectants on the growth of bacterial species.

Genomic Islands Identified in Highly Resistant Serratia sp. HRI: A Pathway to Discover New Disinfectant Resistance Elements.

Molecular insights into the mechanisms of resistance to disinfectants are severely limited, together with the roles of various mobile genetic elements. Genomic islands are a well-characterised molecular resistance element in antibiotic resistance, but it is unknown whether genomic islands play a role in disinfectant resistance. Through whole-genome sequencing and the bioinformatic analysis of Serratia sp. HRI, an isolate with high disinfectant resistance capabilities, nine resistance islands were predicted and annotated within the genome. Resistance genes active against several antimicrobials were annotated in these islands, most of which are multidrug efflux pumps belonging to the MFS, ABC and DMT efflux families. Antibiotic resistance islands containing genes encoding for multidrug resistance proteins ErmB (macrolide and erythromycin resistance) and biclomycin were also found. A metal fitness island harbouring 13 resistance and response genes to copper, silver, lead, cadmium, zinc, and mercury was identified. In the search for disinfectant resistance islands, two genomic islands were identified to harbour smr genes, notorious for conferring disinfectant resistance. This suggests that genomic islands are capable of conferring disinfectant resistance, a phenomenon that has not yet been observed in the study of biocide resistance and tolerance.

Susceptibility Tests and Predictions of Transporter Profile in Serratia Species.

Disinfectants and biosecurity are critically important to control microbial diseases. Resistance to disinfectants compromises sectors such as agriculture and healthcare systems. Currently, efflux pumps are the most common mechanism of antimicrobial resistance. This study aimed to identify the efflux transporters responsible for disinfectant resistance in a multidrug-resistant isolate Serratia sp. HRI compared to a susceptible Serratia sp. type strain. An efflux system profile was generated using the Transporter Automatic Annotation Pipeline (TransAAP) for both isolates. Thereafter, the efflux pump inhibitors, reserpine (RSP) and carbonyl cyanide 3-chlorophenylhydrazone (CCCP) were used to reveal the role of efflux pumps in susceptibility to three disinfectants (Didecyldimethylammonium chloride, HyperCide®, and benzalkonium chloride). Interestingly, the resistant isolate had fewer efflux systems in total compared to the type strain and fewer efflux systems classified as resistance efflux pumps. After the addition of RSP, a significant reduction in resistance capabilities against all three antimicrobials was observed for both isolates. However, CCCP supplementation produced mixed results with some outcomes suggesting the involvement of the Eagle effect. This study provides evidence that efflux pumps are responsible for the disinfectant resistance phenotype of the Serratia species due to the increased susceptibility when efflux pump inhibitors are added.

Investigation into the Metabolism of Quaternary Ammonium Compound Disinfectants by Bacteria.

Since the start of the COVID-19 pandemic, our reliance on disinfectants and sanitizers and the use thereof has grown. While this may protect human health, it may be selecting for antimicrobial-resistant microorganisms, including those that are not only capable of growth in the presence of disinfectants but also thrive using this as an energy source. Furthermore, there is a growing concern in emerging nosocomial pathogens, which have shown resistance to antibiotics and disinfectants. This rise in resistance has led to the investigation of various mechanisms behind resistance, such as biofilms, efflux pumps, and mobile genetic elements. Although many resistance mechanisms have been identified, it was discovered that some potentially pathogenic microbes could metabolize these compounds, which remains an avenue for further investigation. Investigating alternative metabolic pathways in microorganisms capable of growth using disinfectants as their sole carbon and energy source may provide insight into the metabolism of quaternary ammonium compound (QAC)-based antimicrobials. Many of the metabolic reactions proposed include hydroxylation, N-dealkylation, N-demethylation, and ß-oxidation of QACs. If clear metabolic pathways and reactions are elucidated, possible alternative approaches to QACs may be advised. Alternatively, this may provide opportunities for biodegradation of the compounds that adversely affect the environment.

Genome Sequence of Resistant Serratia sp. Strain HRI, Isolated from a Bottle of Didecyldimethylammonium Chloride-Based Disinfectant.

Antimicrobial resistance is a significant issue, and it threatens the prevention and effective treatment of a range of bacterial infections. Here, we report the whole-genome sequence of the multidrug-resistant isolate Serratia sp. strain HRI. A hybrid assembly was created using sequences from a first (MiSeq) and second (PacBio) sequencing run. This work is imperative for understanding antimicrobial resistance and adds to the knowledge base for combating multidrug-resistant bacteria.

Molecular basis of bacterial disinfectant resistance.

Antibiotic resistance could accelerate humanity towards an already fast-approaching post-antibiotic era, where disinfectants and effective biosecurity measures will be critically important to control microbial diseases. Disinfectant resistance has the potential to change our way of life from compromising food security to threatening our medical health systems. Resistance to antimicrobial agents occurs through either intrinsic or acquired resistance mechanisms. Acquired resistance occurs through the efficient transfer of mobile genetic elements, which can carry single, or multiple resistance determinants. Drug resistance genes may form part of integrons, transposons and insertions sequences which are capable of intracellular transfer onto plasmids or gene cassettes. Thereafter, resistance plasmids and gene cassettes mobilize by self-transmission between bacteria, increasing the prevalence of drug resistance determinants in a bacterial population. An accumulation of drug resistance genes through these mechanisms gives rise to multidrug resistant (MDR) bacteria. The study of this mobility is integral to safeguard current antibiotics, disinfectants and other antimicrobials. Literature evidence, however, indicates that knowledge regarding disinfectant resistance is severly limited. Genome engineering such as the CRISPR-Cas system, has identified disinfectant resistance genes, and reversed resistance altogether in certain prokaryotes. Demonstrating that these techniques could prove invaluable in the combat against disinfectant resistance by uncovering the secrets of MDR bacteria.

Detection of virulence factors of South African Lactococcus garvieae isolated from rainbow trout, Oncorhynchus mykiss (Walbaum).

Lactococcus garvieae is a Gram-positive bacterium that causes mortalities in freshwater and marine fish worldwide and therefore results in severe economic losses in the aquaculture industry. Apart from the apparent integral role of the exopolysaccharide (EPS) capsule in pathogenesis, factors associated with virulence of this bacterium are poorly understood. However, recent studies have indicated that the ability of L. garvieae to cause disease does not depend on the presence of the EPS capsule. Lack of knowledge of virulence factors, pathogenesis and serology of L. garvieae is an impediment to the development of effective typing methods and control measures. This study, therefore, aimed to detect the presence of EPS capsules and other putative virulence factors in South African L. garvieae fish pathogenic isolates and a non-virulent isolate, and to identify possible candidates for subunit vaccine development. No indication of the presence of the EPS capsule was detected by negative staining or amplification of the EPS biosynthesis gene cluster in the virulent isolates or the avirulent strain, discrediting the notion that the EPS capsule is the sole determinant of virulence. However, a set of putative virulence factor genes was detected in all isolates, and candidates for subunit vaccine development (enolase, lactate dehydrogenase phosphoenolpyruvate-protein phosphotransferase) were identified by identification of extracellular proteins of virulent strains.

Regulation of chicken immunity-related genes and host response profiles against Avibacterium paragallinarum pathogen challenge.

Infectious coryza (IC) is a well-recognised and commonly encountered upper respiratory tract disease in chickens. The aim of this study was to monitor aspects of the immune response of chickens infected with Avibacterium paragallinarum. Gene expression profiling of 30 genes was carried out for 11 chicken nasal area samples belonging to four groups, including one non-infected control group. For this purpose, 30 biomarker transcripts were selected for comparative gene expression analysis and were analysed by real-time PCR using TaqMan(®) assays. The biomarkers included three reference genes. The reference genes were used to normalise the results in a relative quantification approach. The gene expression changes of the 27 biomarker transcripts (genes of interest) were quantified between all treated groups in six pair-wise comparisons. It was concluded from the data that immune response initiation is via TLR4, which leads to a Th2 dominant type response. Furthermore, TLR4 results in signalling via the MyD88-dependent pathway, resulting in early onset of NF-kß leading to the production of inflammatory cytokines. This work provides an informative outlay of immune response initiation upon infection with this pathogen.

Transcriptional profiling of chicken immunity-related genes during infection with Avibacterium paragallinarum.

Avibacterium paragallinarum is the causative agent of Infectious Coryza (IC), which is an upper respiratory tract disease in chickens. The occurrence of outbreaks has emphasized the significance of the disease globally in the chicken industry. Studies have demonstrated that early immune responses are critical in defining the severity and physiological outcome of an infection. This prompted the need to investigate the regulation of immune functions by the number of genes that are expressed during the chickens' response to A. paragallinarum serovar C3 insult. This study consisted of 15 male leghorn birds that were scored into groups (score 1, 2, 3) according to severity of symptoms after they were challenged. Expression patterns of immunity-related genes were followed as symptoms progressed from a disease score of 1 to 3. The data proposed that initial pathogen recognition was either through Toll-like receptors 2 or 4. Unique expression patterns were observed such as the up-regulation of TLR7 which recognizes viral-like particles. This substantiated the presence of prophages reported in the genome of A. paragallinarum. Significant down-regulation of metabolic pathways was observed, which led us to hypothesize that the host may rely on an oxidative stress response as initial immune response. The data sheds light onto the mechanisms that govern the immune system towards infection and/or towards the initial response to infections with highly virulent A. paragallinarum.

Nanomedicine and infectious diseases.

The First International Conference on Infectious Diseases and Nanomedicine congress facilitated the mixing of researchers in various fields of nanomedicine and infectious diseases, bringing together researchers from the fields of physics and chemistry, on the production of nanoparticles and researchers from various fields of microbiology where these nanoparticles have practical applications. The manufacture and applications of nanoparticles was one of the main themes of the congress, with much emphasis on the use of nanoparticles for the treatment of cancer. The ever increasing problems and concerns around antibiotic resistance also featured prominently in the congress. Various interesting presentations on human viruses were also presented during this congress.

A unique isolate of beak and feather disease virus isolated from budgerigars (Melopsittacus undulatus) in South Africa.

Beak and feather disease virus (BFDV), the causative agent of psittacine beak and feather disease (PBFD) infects psittaciformes worldwide. We provide an annotated sequence record of three full-length unique genomes of BFDV isolates from budgerigars (Melopsittacus undulatus) from a breeding farm in South Africa. The isolates share >99% nucleotide sequence identity with each other and approximately 96% nucleotide sequence identity to two recent isolates (Melopsittacus undulatus) from Thailand but only between 91.6 and 86.6% identity with all other full-length BFDV sequences. Maximum-likelihood analysis and recombination analysis suggest that the South African budgerigar BFDV isolates are unique to budgerigars, are non-recombinant in origin, and represent a new genotype of BFDV.