A pilot with pain in his leg: thigh abscess caused by Salmonella enterica serotype Brandenburg

Comparative genomic analysis reveals high intra-serovar plasticity within Salmonella Napoli isolated in 2005-2017

BACKGROUND

Salmonella enterica subsp. enterica serovar Napoli (S. Napoli) is among the top serovars causing human infections in Italy, although it is relatively uncommon in other European countries; it is mainly isolated from humans and the environment, but neither the reservoir nor its route of infection are clearly defined. This serovar is characterized by high genomic diversity, and molecular evidences revealed important similarities with typhoidal serovars.

RESULTS

179 S. Napoli genomes as well as 239 genomes of typhoidal and non-typhoidal serovars were analyzed in a comparative genomic study. Phylogenetic analysis and draft genome characterization in terms of Multi Locus Sequence Typing (MLST), plasmid replicons, Salmonella Pathogenicity Islands (SPIs), antimicrobial resistance genes (ARGs), phages, biocide and metal-tolerance genes confirm the high genetic variability of S. Napoli, also revealing a within-serovar phylogenetic structure more complex than previously known. Our work also confirms genomic similarity of S. Napoli to typhoidal serovars (S. Typhi and S. Paratyphi A), with S. Napoli samples clustering primarily according to ST, each being characterized by specific genomic traits. Moreover, two major subclades of S. Napoli can be clearly identified, with ST-474 being biphyletic. All STs span among isolation sources and years of isolation, highlighting the challenge this serovar poses to define its epidemiology and evolution. Altogether, S. Napoli strains carry less SPIs and less ARGs than other non-typhoidal serovars and seldom acquire plasmids. However, we here report the second case of an extended-spectrum β-lactamases (ESBLs) producing S. Napoli strain and the first cases of multidrug resistant (MDR) S. Napoli strains, all isolated from humans.

CONCLUSIONS

Our results provide evidence of genomic plasticity of S. Napoli, highlighting genomic similarity with typhoidal serovars and genomic features typical of non-typhoidal serovars, supporting the possibility of survival in different niches, both enteric and non-enteric. Presence of horizontally acquired ARGs and MDR profiles rises concerns regarding possible selective pressure exerted by human environment on this pathogen.

Extraintestinal Salmonellosis in the Immunocompromised: An Unusual Case of Pyomyositis

Salmonella infection can cause a wide range of presentations, predominantly gastrointestinal but occasionally with cardiovascular or other extraintestinal manifestations. The diagnosis of extraintestinal salmonellosis requires a high degree of clinical suspicion and should be considered in patients with deep-seated abscesses especially if they are immunocompromised. We present a case of salmonella causing gastroenteritis complicated by an intramuscular abscess of the left leg. With prompt recognition and multidisciplinary management, the patient recovered with no serious sequela.

Muscle Abscess due to Salmonella Enterica

Non typhoidal Salmonellae spp. causes clinical symptoms especially in neonates, infants, aged and immunocompromised patients. Hematogenous dissemination may occur in complicated cases whereas the formation of abscess is rare. A 61-year old woman presented to our hospital with pain and a mass in her left arm, without fever and leukocytosis. She was using methotrexate, corticosteroids and quinine for rheumatoid arthritis. She had a history of cervix cancer and was given radiotherapy and chemotherapy 3 years ago. Upon physical examination and magnetic resonance imaging, the mass was considered as an abscess and was surgically drained. Salmonella enterica spp. enterica was yielded in the culture of the drainage material. Ceftriaxon 2g/day was started intramuscularly and continued for 4 weeks. Salmonellosis is usually a self-limited disease, generally restricted to gastrointestinal tract and acquired following food poisoning. Management of Salmonella abscess requires a combination of antibiotherapy, surgical drainage and eradication of primary foci.

Salmonella enterica serovar Typhi has a 4.1 kb genetic island inserted within the sapABCDF operon that causes loss of resistance to the antimicrobial peptide protamine

OBJECTIVES

To investigate the association between the presence of a genetic island inserted within the sapABCDF operon of Salmonella Typhi and the susceptibility to antimicrobial peptides.

METHODS

Genetics and bioinformatics approaches were used to study the genomic organization of the sap operon of Salmonella Typhi and several serovars of Salmonella enterica. PCR was used to confirm the information obtained from these analyses. Deletion of the entire genetic island of Salmonella Typhi was achieved by the red swap method. RT-PCR amplification and antimicrobial peptide susceptibility tests were used to evaluate expression of the sap genes and bacterial resistance to protamine.

RESULTS

Inspection of the genomes of Salmonella Typhi and 10 serovars of Salmonella enterica showed an insertion of a genetic island located between the sapB and sapC genes of the sap operon. This genetic element was referred to as GICT18/1. Unlike Salmonella Typhimurium, the bacterial susceptibility to protamine is increased in Salmonella Typhi wild-type. Deletion of GICT18/1 resulted in protamine susceptibility levels similar to those of Salmonella Typhimurium, suggesting that restoration of the sap operon occurred in the Salmonella Typhi Delta GICT18-1 mutant strain. RT-PCR experiments supported this assumption because an amplicon containing a fragment of sapD-sapF was detected in Salmonella Typhi Delta GICT18/1, whereas it was not detected in Salmonella Typhi wild-type.

CONCLUSIONS

The presence of GICT18/1 seems to be a natural feature of Salmonella Typhi. This genetic island is found only in 10 out of 32 Salmonella enterica serovars included in this study. Removal of GICT18/1 has an impact in the susceptibility of Salmonella Typhi to the antimicrobial peptide protamine.

The Salmonella Typhi hlyE gene plays a role in invasion of cultured epithelial cells and its functional transfer to S. Typhimurium promotes deep organ infection in mice

Comparison of genome sequences of Salmonella enterica serovars Typhi and Typhimurium reveals that S. Typhi has a small 2.3kb genomic island missing in S. Typhimurium, designated Salmonella pathogenicity island 18 (SPI-18), which includes two potential genes. One of these, hlyE, encodes a hemolysin related to the Escherichia coli K12 HlyE hemolysin. PCR assays show that SPI-18 is present in S. Typhi and in many other, but not all, serovars of S. enterica subsp. enterica belonging to the SARB collection. HlyE activity cannot be detected in S. Typhi by means of standard plate assays. Nevertheless, we were able to reveal this activity upon lysis of bacterial cells with phages, in the presence of ampicillin, and in a ompA genetic background, conditions that compromise the integrity of the bacterial envelope. Almost all serovars of the SARB collection shown to cause systemic infections in humans have SPI-18 and hlyE and express an active hemolysin revealed upon bacterial envelope destabilization. S. Typhi hlyE mutants are impaired in invasion of human epithelial cells in vitro, and its heterologous expression in S. Typhimurium improves the colonization of deep organs in mice, demonstrating that the HlyE hemolysin is a new virulence determinant.

Case report: parotid abscess due to Salmonella enterica serovar Enteritidis in an immunocompetent adult

There are reports of increasing incidence of focal extra-intestinal infections from non-typhoidal salmonellae during the past two decades. We present the first case of a parotid abscess caused by Salmonella enterica serovar Enteritidis (S. Enteritidis) in an apparently immunocompetent adult without other abnormality of the parotid glands. A 58-year-old man was admitted to our hospital because of a 3-day history of fever and painful swelling of the right parotid gland. His medical history was unremarkable. A CT scan revealed an abscess of the right parotid. S. Enteritidis was isolated from a sample of fluid aspirated from the parotid abscess under ultrasound guidance. The stool, urine, and blood cultures were negative. The patient was treated with ciprofloxacin 500 mg per os every 12 h for 10 days, with complete remission of symptoms. The infection did not recur during 3 years of follow up. Our case report adds to the literature regarding the extra-intestinal infections with S. Enteritidis, a common non-typhoidal salmonellosis.