On the 24 th November 2021 the sequence of a new SARS CoV-2 viral isolate Omicron-B.1.1.529 was announced, containing far more mutations in Spike (S) than previously reported variants. Neutralization titres of Omicron by sera from vaccinees and convalescent subjects infected with early pandemic as well as Alpha, Beta, Gamma, Delta are substantially reduced or fail to neutralize. Titres against Omicron are boosted by third vaccine doses and are high in cases both vaccinated and infected by Delta. Mutations in Omicron knock out or substantially reduce neutralization by most of a large panel of potent monoclonal antibodies and antibodies under commercial development. Omicron S has structural changes from earlier viruses, combining mutations conferring tight binding to ACE2 to unleash evolution driven by immune escape, leading to a large number of mutations in the ACE2 binding site which rebalance receptor affinity to that of early pandemic viruses.

On the 24th November 2021 the sequence of a new SARS CoV-2 viral isolate spreading rapidly in Southern Africa was announced. Omicron contains a total of 30 substitutions plus deletions and an insertion in Spike, far more than any previously reported variant. The mutations include those previously identified by In-vitro evolution to contribute to high-affinity binding to ACE2, including mutations Q498R and N501Y critical in forming additional interactions in the interface. Together with increased charge complementarity between the RBD and ACE2, these substantially increase affinity and potentially virus transmissibility through increased syncytia formation. Further mutations promote immune evasion. We have studied the binding of a large panel of potent monoclonal antibodies generated from early pandemic or Beta infected cases. Mutations in Omicron will likely compromise the binding of many of these and additionally, the binding of antibodies under commercial development, however residual binding should provide protection from severe disease.

Neisseria gonorrhoeae (gonococcus [Ng]) is the causative organism of the sexually transmitted disease gonorrhoea, and the organism is listed by the World Health Organization as a high-priority pathogen for research and development of new control measures, including vaccines. In this study, we demonstrated that the N. gonorrhoeae adhesin complex protein (Ng-ACP) was conserved and expressed by 50 gonococcal strains and that recombinant proteins induced antibodies in mice that killed the bacteria in vitro. We determined the structure of Ng-ACP by X-ray crystallography and investigated structural conservation with Neisseria meningitidis ACP and MliC/PliC proteins from other bacteria which act as inhibitors of the human innate defense molecule lysozyme. These findings are important and suggest that Ng-ACP could provide a potential dual target for tackling gonococcal infections.

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Neisseria gonorrhoeae (gonococcus) causes the human sexually transmitted disease gonorrhea. Studying gonococcal pathogenesis and developing new vaccines and therapies to combat the increasing prevalence of multi-antibiotic resistant bacteria has made use of many ex vivo models based on human cells and tissues, and in vivo vertebrate models, for example, rodent, pig and human. The focus of the current study was to examine the utility of the invertebrate greater wax moth Galleria mellonella as an in vivo model of gonococcal infection. We observed that a threshold of ~10 6 -10 7 gonococci/larva was required to kill >50% of larvae (P < 0.05), and increased toxicity correlated with reduced health index scores and pronounced histopathological changes such as increases in the total lesion grade, melanized nodules, hemocyte reaction, and multifocal adipose body degeneration. Larval death was independent of the expression of pilus or Opa protein or LOS sialylation within a single gonococcal species studied, but the model could demonstrate relative toxicity of different isolates. N. meningitidis, N. lacatamica and gonococci all killed larvae equally, but were significantly less toxic (P > 0.05) than Pseudomonas aeruginosa. Larvae primed with nontoxic doses of gonococci were more susceptible to subsequent challenge with homologous and heterologous bacteria, and larval survival was significantly reduced (P < 0.05) in infected larvae after depletion of their hemocytes with clodronate-liposomes. The model was used to test the anti-gonococcal properties of antibiotics and novel antimicrobials. Ceftriaxone (P < 0.05) protected larvae from infection with different gonococcal isolates, but not azithromycin or monocaprin or ligand-coated silver nanoclusters (P > 0.05).

Gonorrhea is the second most commonly reported notifiable sexually transmitted disease in the world. Neisseria gonorrhoeae causes 78 million cases annually of gonorrhoea worldwide. There are no vaccines and antibiotic-resistant organisms are circulating rapidly. The estradiol-treated female mouse model is the only animal model available for studying the host response against gonococci and biological significance of host-restricted bacterial-host cell interactions observed in vitro. However, mouse models have limitations such as cost, time and ethics. Therefore, there is an urgent need for the development of new alternative in vivo models. The Galleria mellonella larval model is a simple, widely available, cost-effective, and powerful tool for studying microbial infections prior to any vertebrate animal testing. Here we report, for the first time, that G. mellonella can be used as an infection model for Neisseria spp., focusing particularly on N. gonorrhoeae. We demonstrated dose-dependent larval death and recovery of viable gonococci from the host, visualised host-pathogen interactions using histopathology and confirmed the importance of insect haemocytes as an innate immune cell during infection. The model was also used to test the efficacy of antibiotics used to treat gonorrhoea. Our results demonstrate that G. mellonella can be used as a model to study pathogenesis and virulence of gonococcal infection in addition to rapid in vivo testing of antimicrobials.