(1) Background: Health workers (HWs) are at high risk of acquiring SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) infections. Therefore, health authorities further recommend screening strategies for SARS-CoV-2 infection in exposed or high-risk HWs. Nevertheless, to date, the best/optimal method to screen HWs for SARS-CoV-2 infection is still under debate, and data on the prevalence of SARS-CoV-2 infection in HWs are still scarce. The present study aims to assess the SARS-CoV-2 infection rate amongst HWs in a teaching hospital in Central Italy and the diagnostic performance of SARS-CoV-2 serology (index test) in comparison with the SARS-CoV-2 RNA PCR assay (reference standard). (2) Methods: A cross-sectional study on the retrospective data of HWs tested for SARS-CoV-2 by RNA-RT-PCR on nasopharyngeal swabs and by an IgM/IgG serology assay on venous blood samples, irrespective of exposure and/or symptoms, was carried out. (3) Results: A total of 2057 HWs (median age 46, 19–69 years, females 60.2%) were assessed by the RNA RT-PCR assay and 58 (2.7%) tested positive for SARS-CoV-2 infection. Compared with negative HWs, SARS-CoV-2-positives were younger (mean age 41.7 versus 45.2, p < 0.01; 50% versus 31% under or equal to 40 years old, p < 0.002) and had a shorter duration of employment (64 versus 125 months, p = 0.02). Exposure to SARS-CoV-2 was more frequent in positive HWs than in negatives (55.2% versus 27.5%, p < 0.0001). In 44.8% of positive HWs, no exposure was traced. None of the positive HWs had a fatal outcome, none of them had acute respiratory distress syndrome, and only one required hospitalization for mild/moderate pneumonia. In 1084 (51.2%) HWs, nasopharyngeal swabs and an IgM/IgG serology assay were performed. With regard to IgM serology, sensitivity was 0% at a specificity of 98.99% (positive predictive value, PPV 0%, negative predictive value, NPV 99.2%). Concerning IgG serology and irrespective of the time interval between nasopharyngeal swab and serology, sensitivity was 50% at a specificity of 99.1% (PPV 28.6%, NPV 99.6%). IgG serology showed a higher diagnostic performance when performed at least two weeks after testing SARS-CoV-2-positive at the RNA RT-PCR assay by a nasopharyngeal swab. (4) Conclusions: Our experience in Central Italy demonstrated a low prevalence of SARS-CoV-2 infection amongst HWs, but higher than in the general population. Nearly half of the positive HWs reported no previous exposure to SARS-CoV-2-infected subjects and were diagnosed thanks to the proactive screening strategy implemented. IgG serology seems useful when performed at least two weeks after an RNA RT-PCR assay. IgM serology does not seem to be a useful test for the diagnosis of active SARS-CoV-2 infection. High awareness of SARS-CoV-2 infection is mandatory for all people, but especially for HWs, irrespective of symptoms, to safeguard their health and that of patients.

Temporins are naturally occurring peptides with promising features, which could lead to the development of new drugs. Temporin-1Tl (TL) is the strongest antimicrobial peptide, but it is toxic on human erythrocytes and this fact makes the design of synthetic analogues with a higher therapeutic index vital.We studied the structure-activity relationships of a library of TL derivatives focusing on the correlation between the α-helix content of the peptides, the nature of their cationic residues, and their antibacterial/antiyeast/hemolytic activities. We found that the percentage of helicity of TL analogues is directly correlated to their hemolytic activity but not to their antimicrobial activity. In addition, we found that the nature of positively charged residues can affect the biological properties of TL without changing the peptide's helicity. It is noteworthy that a single amino acid substitution can prevent the antimicrobial activity of TL, making it a lytic peptide presumably due to its self-association. Last, we identified a novel analogue with properties that make it an attractive topic for future research.

Antimicrobial peptides constitute one of the main classes of molecular weapons deployed by the innate immune system of all multicellular organisms to resist microbial invasion. A good proportion of all antimicrobial peptides currently known, numbering hundreds of molecules, have been isolated from frog skin. Nevertheless, very little is known about the effect(s) and the mode(s) of action of amphibian antimicrobial peptides on intact bacteria, especially when they are used at subinhibitory concentrations and under conditions closer to those encountered in vivo. Here we show that esculentin-1b(1-18) [Esc(1-18)] (GIFSKLAGKKLKNL-LISG-NH 2 ), a linear peptide encompassing the first 18 residues of the full-length esculentin-1b, rapidly kills Escherichia coli at the minimal inhibitory concentration. The lethal event is concomitant with the permeation of the outer and inner bacterial membranes. This is in contrast to what is found for many host defense peptides, which do not destabilize membranes at their minimal inhibitory concentrations. Importantly, proteomic analysis revealed that Esc(1-18) has a limited ability to modify the bacterium's protein expression profile, at either bactericidal or sublethal concentrations. To the best of our knowledge, this is the first report on the effects of an antimicrobial peptide from frog skin on the proteome of its bacterial target, and underscores the fact that the bacterial membrane is the major target for the killing mechanism of Esc(1-18), rather than intracellular processes.

Mastitis, or inflammation of the mammary gland, is the most common and expensive illness of dairy cows throughout the world. Although stress and physical injuries may give rise to inflammation of the udders, infections by bacteria or other microorganisms remain the major cause, and infusion of antibiotics is the main treatment approach. However, the increased emergence of multidrug-resistant pathogens and the production of milk contaminated with antibiotics has become a serious threat in the livestock. Hence, there is an urgent need for the discovery of new therapeutic agents with a new mode of action. Gene-encoded AMPs, which represent the first line of defence in all living organisms, are considered as promising candidates for the development of new anti-infective agents. This paper reports on the antibacterial activities in vitro and in an animal model, of the frog skin AMP esculentin 1-21 [Esc(1-21)], along with a plausible mode of action. Our data revealed that this peptide (i) is highly potent against the most common mastitis-causing microbes (e.g. Streptococcus agalactiae); and (ii) is active in vivo, causing a visible regression of the clinical stage of mastitis in dairy cows, after 1 week of peptide treatment. Biophysical characterisation revealed that the peptide adopts an alpha-helical structure in microbial mimicking membranes and is able to permeate the membrane of S. agalactiae in a dose-dependent manner. Overall, these data suggest Esc(1-21) as an attractive AMP for the future design of new antibiotics to cure mastitis in cattle.

The frog skin peptide temporin L (TL, 13-residues long) has a wide and potent spectrum of antimicrobial activity, but it is also toxic on mammalian cells at its microbicidal concentrations. Previous studies have indicated that its analogue [Pro(3)]TL has a slightly reduced hemolytic activity and a stable helical conformation along residues 6-13. Here, to expand our knowledge on the relationship between the extent/position of α-helix in TL and its biological activities, we systematically replaced single amino acids within the α-helical domain of [Pro(3)]TL with the corresponding d isomers, known as helix breakers. Structure-activity relationship studies of these analogues, by means of CD and NMR spectroscopy analyses as well as antimicrobial and hemolytic assays were performed. Besides increasing our understanding on the structural elements that are responsible for cell selectivity of TL, this study revealed that a single l to d amino acid substitution can preserve strong anti-Candida activity of [Pro(3)]TL, without giving a toxic effect towards human cells.