Streptococcus suis serotype 9 in Italy: genomic insights into high-risk clones with emerging resistance to penicillin

BACKGROUND

Streptococcus suis is an important pig pathogen and an emerging zoonotic agent. In a previous study, we described a high proportion of penicillin-resistant serotype 9 S. suis (SS9) isolates on pig farms in Italy.

OBJECTIVES

We hypothesized that resistance to penicillin emerged in some SS9 lineages characterized by substitutions at the PBPs, contributing to the successful spread of these lineages in the last 20 years.

METHODS

Sixty-six SS9 isolates from cases of streptococcosis in pigs were investigated for susceptibility to penicillin, ceftiofur and ampicillin. The isolates were characterized for ST, virulence profile, and antimicrobial resistance genes through WGS. Multiple linear regression models were employed to investigate the associations between STs, year of isolation, substitutions at the PBPs and an increase in MIC values to β-lactams.

RESULTS

MIC values to penicillin increased by 4% each year in the study period. Higher MIC values for penicillin were also positively associated with ST123, ST1540 and ST1953 compared with ST16. The PBP sequences presented a mosaic organization of blocks. Within the same ST, substitutions at the PBPs were generally more frequent in recent isolates. Resistance to penicillin was driven by substitutions at PBP2b, including K479T, D512E and K513E, and PBP2x, including T551S, while reduced susceptibility to ceftiofur and ampicillin were largely dependent on substitutions at PBP2x.

CONCLUSIONS

Here, we identify the STs and substitutions at the PBPs responsible for increased resistance of SS9 to penicillin on Italian pig farms. Our data highlight the need for monitoring the evolution of S. suis in the coming years.

A case of pericarditis caused by Mycoplasma hyorhinis in a weaned piglet

BACKGROUND

Mycoplasma hyorhinis (M. hyorhinis) is a bacterium commonly found in the upper respiratory tract of healthy pigs and an agent of polyserositis and polyarthritis. Moreover, it can carry antibiotic resistance genes (Wu et al, Vet. Microbiol. 76: 25-30, 2000). Economic losses caused by M. hyorhinis can be reduced by antibiotic therapy, however, isolation and antimicrobic susceptibility profile are rarely performed.

CASE PRESENTATION

The present report describes a case of pericarditis caused by M. hyorhinis in a weaned piglet with respiratory symptoms and reduced growth performance. At post mortem examination, the main macroscopic finding was a severe fibrinous pericarditis and M. hyorhins was the only agent isolated from the pericardial fluid. In this strain, Minimum Inhibitory Concentration (MIC) determination revealed resistance to various antimicrobial molecules such as erythromycin, tylosin and tilmicosin.

CONCLUSION

This paper highlights the importance of including M. hyorhins in the differential diagnosis of polyserositis in swine. Moreover, due the possible presence of multidrug resistance, the determination of antimicrobial susceptibility pattern should be performed on a regular basis.

Identification of two divergent swine Noroviruses detected at the slaughterhouse in North East Italy

Norovirus (NoV) has emerged as one of the major causative agents of non-bacterial, food- and water-borne gastroenteritis in humans, with the main genogroup involved in human outbreaks (GII), which has been detected worldwide in different animal species including swine. A four-month investigation at the slaughterhouse aiming to examine the presence of NoV in the swine in North-Eastern Italy, enabled the detection of two divergent Noroviruses (NoVs) (GII.P11) in two swine farms. This represents the first study in the swine population of North-Eastern Italy, which has paved the way for future integrated virological and epidemiological investigations on swine NoVs.

Phenotypic features and phylogenetic background of extraintestinal hemolytic Escherichia coli responsible of mortality in puppies

A 10-day-old litter of five puppies of Bracco Italiano dog breed showed weakness and diarrhea and, 2 days later, four of them died. At the same time, the bitch showed high hyperthermia (40 °C) and endometritis. The necropsy of a puppy revealed a severe lobar pneumonia accompanied with a bilateral nephrosis. No gross lesions were detected in other organs. Histopathology of the lung revealed severe multifocal fibrino-suppurative necrotizing bronchiolar-alveolitis associated with rod-shaped bacterial aggregates and diffuse interstitial lymphocytic infiltration. The kidney showed severe multifocal necrosis of the tubular epithelium and diffuse severe congestion of the parenchyma. A pure culture of hemolytic Escherichia coli carrying the Cnf-1 gene was identified, from both the puppy organs and bitch's milk. Moreover, phylo-typing assigned them to the phylogroup B2. Two weeks later, fecal samples from the bitch and the survived puppy were collected for a second microbiological analysis, identifying two hemolytic E. coli strains, Cnf positive and Cdt negative and Cnf and Cdt negative, respectively. Some E. coli pathogenic strains may cause enteric or extraintestinal disease. In dogs and cats, strains of extraintestinal pathogenic E. coli (ExPEC) produce specific virulent factors such as hemolysis and cytotoxin necrotizing factors (Cnf). In this episode, we hypothesize that the bitch's milk could be the main source of ExPEC infection causing high puppies mortality. The role of the bitch as a carrier could not be excluded: stressful conditions, such as pregnancy and delivery, would change the host-pathogen dynamics possibly increasing the release of the infectious burden.

Genetic complexity and multiple infections with more Parvovirus species in naturally infected cats

Parvoviruses of carnivores include three closely related autonomous parvoviruses: canine parvovirus (CPV), feline panleukopenia virus (FPV) and mink enteritis virus (MEV). These viruses cause a variety of serious diseases, especially in young patients, since they have a remarkable predilection for replication in rapidly dividing cells. FPV is not the only parvovirus species which infects cats; in addition to MEV, the new variants of canine parvovirus, CPV-2a, 2b and 2c have also penetrated the feline host-range, and they are able to infect and replicate in cats, causing diseases indistinguishable from feline panleukopenia. Furthermore, as cats are susceptible to both CPV-2 and FPV viruses, superinfection and co-infection with multiple parvovirus strains may occur, potentially facilitating recombination and high genetic heterogeneity. In the light of the importance of cats as a potential source of genetic diversity for parvoviruses and, since feline panleukopenia virus has re-emerged as a major cause of mortality in felines, the present study has explored the molecular characteristics of parvovirus strains circulating in cat populations. The most significant findings reported in this study were (a) the detection of mixed infection FPV/CPV with the presence of one parvovirus variant which is a true intermediate between FPV/CPV and (b) the quasispecies cloud size of one CPV sample variant 2c. In conclusion, this study provides new important results about the evolutionary dynamics of CPV infections in cats, showing that CPV has presumably started a new process of readaptation in feline hosts.