Serotype diversity and antimicrobial susceptibility profiles of Actinobacillus pleuropneumoniae isolated in Italian pig farms from 2015 to 2022

Actinobacillus pleuropneumoniae (APP) is a bacterium frequently associated with porcine pleuropneumonia. The acute form of the disease is highly contagious and often fatal, resulting in significant economic losses for pig farmers. Serotype diversity and antimicrobial resistance (AMR) of APP strains circulating in north Italian farms from 2015 to 2022 were evaluated retrospectively to investigate APP epidemiology in the area. A total of 572 strains isolated from outbreaks occurring in 337 different swine farms were analysed. The majority of isolates belonged to serotypes 9/11 (39.2%) and 2 (28.1%) and serotype diversity increased during the study period, up to nine different serotypes isolated in 2022. The most common resistances were against tetracycline (53% of isolates) and ampicillin (33%), followed by enrofloxacin, florfenicol and trimethoprim/sulfamethoxazole (23% each). Multidrug resistance (MDR) was common, with a third of isolates showing resistance to more than three antimicrobial classes. Resistance to the different classes and MDR varied significantly depending on the serotype. In particular, the widespread serotype 9/11 was strongly associated with florfenicol and enrofloxacin resistance and showed the highest proportion of MDR isolates. Serotype 5, although less common, showed instead a concerning proportion of trimethoprim/sulfamethoxazole resistance. Our results highlight how the typing of circulating serotypes and the analysis of their antimicrobial susceptibility profile are crucial to effectively manage APP infection and improve antimicrobial stewardship.

Complex interplay between PRRSV-1 genetic diversity, coinfections and antimicrobial use influences performance parameters in post-weaning pigs

Porcine reproductive and respiratory syndrome (PRRS) is one of the main diseases of pigs, leading to large economic losses in swine production worldwide. PRRSV high mutation rate and low cross-protection between strains make PRRS control challenging. Through a semi-longitudinal approach, we analysed the relationships among performance parameters, PRRSV-1 genetic diversity, coinfections and antimicrobial use (AMU) in pig nurseries. We collected data over the course of five years in five PRRS-positive nurseries belonging to an Italian multisite operation, for a total of 86 batches and over 200,000 weaners involved. The farm experienced a severe PRRS outbreak in the farrowing unit at the onset of the study, but despite adopting vaccination of all sows, batch-level losses in nurseries in the following years remained constantly high (mean±SE: 11.3 ± 0.5 %). Consistently with previous studies, our phylogenetic analysis of ORF 7 sequences highlighted the peculiarity of strains circulating in Italy. Greater genetic distances between the strain circulating in a weaners' batch and strains from the farrowing unit and the previous batch were associated with increased mortality (p < 0.0001). All the respiratory and enteric coinfections contributed to an increase in losses (all p < 0.026), with secondary infections by Streptococcus suis and enteric bacteria also inducing an increase in AMU (both p < 0.041). Our findings highlight that relying solely on sows' vaccination is insufficient to contain PRRS losses, and the implementation of rigorous biosecurity measures is pivotal to limit PRRSV circulation among pig flows and consequently minimise the risk of exposure to genetically diverse strains that would increase production costs.

Integrated monitoring of AMR and enterotoxins genes of S. aureus isolated in Lombardy

Background

S. aureus is a widespread pathogen responsible for mild to severe human and animals’ infections. The abuse of antimicrobials provides the potential for selection of resistant strains in livestock, which represents a public health concern. S. aureus can carry several virulence factors of which staphylococcal enterotoxins (SEs) play a key role during food poisoning in human populations. The aim of this study is to monitor the prevalence of antimicrobial resistance factors in S. aureus isolates and their ability to produce enterotoxins.

Methods

Within an ongoing monitoring plan for the assessment of antimicrobial resistance in S. aureus strains, a total of 83 isolates collected from food, and swine and dairy farms, between 2020-2022, were characterized using MLST and then screened for the presence of methicillin resistance and SEs genes. The isolates were tested for susceptibility to a panel of 14 antimicrobial agents using the disc agar diffusion method on Mueller-Hinton agar.

Results

Among 83 S. aureus isolates, 53% carried at least one SEs gene. Eighteen isolates were methicillin-resistant of which 17 were no-enterotoxigenic strains belonging to ST398, and one was a food origin ST8 strain and harbored SEs genes. Among the ST398 isolates, only one was a food origin strain, while the others were from swine farms. The antibiogram showed that a few isolates were susceptible to nalidixic acid, and 42% resulted multidrug-resistant.

Conclusions

Our results showed that more than half of S. aureus isolates were enterotoxigenic, the majority belonging to food industries. Numerous tested isolates resulted multidrug-resistant, confirming that antimicrobial resistance is a critical public health threat in a food safety perspective.

Key messages

• The antimicrobial resistance profiles of S. aureus isolates underlines the importance of monitoring plans with a One Health perspective.

• The prevalence of enterotoxins genes in S. aureus strains in Lombardy confirms the relevance of the microorganism as a foodborne pathogen.

Exploring potential risk factors of antimicrobial use in beef cattle

Livestock species are major contributors to the increase of antimicrobial (AM) resistance which is a worldwide concern for both human and animal health. The over-use of AM is widely acknowledged, however, unlike pigs, poultry and dairy cattle, knowledge on potential risk factors affecting AM usage (AMU) in beef industry is limited. Hence, this study aimed to investigate the impact of farm, breed, sex and season of arrival of purchased beef cattle on AMU in Italian beef cattle. Data on 1063 batches were collected from January 2016 to April 2019 from specialised beef fattening farms located in the north of Italy. Information on breed, sex, date of arrival, performance traits and AM agents used on farm was collected, and the treatment incidence 100 (TI100) indexes per batch were calculated using the defined daily dose animal estimated according to Italian summaries of product characteristics. Factors affecting TI100 indexes were investigated using a cross-classified multilevel model. Farms largely differed in terms of AMU. Males had greater AMU than females (P < 0.001), likely due to their higher susceptibility to disease. Statistically significant differences were observed between seasons of arrival with summer and spring having lower TI100 indexes than winter and autumn (P < 0.001). Indeed, winter is commonly linked to an increase in respiratory diseases in beef cattle. Finally, the TI100it indexes tended to be different among breeds with Blonde d'Aquitaine and Limousine having greater AMU compared to the other breeds. Results of this study provided valuable information on potential risk factors of AMU in beef production which may be useful to address its reduction. For instance, the development of tailored management strategies for specific breeds, targeted approaches to improve the health of males as well as greater care towards batches purchased in winter are possible advice to implement on-farm for a more responsible AM stewardship.

African swine fever: A review of cleaning and disinfection procedures in commercial pig holdings

African swine fever (ASF) is one of the most important diseases in pigs. Since there are no effective vaccines against the virus, farm biosecurity and good farming practices are the only effective tools to prevent the spread of the ASF virus (ASFV) in pig holdings. Hence, an important component of farm biosecurity is the Cleaning and Disinfection (C&D) procedure. Precise indications regarding the ideal disinfectant against ASFV are lacking, but every country has approved and/or authorized a list of biocides effective against ASFV. Lipidic solvents, which destroy the envelope of the virus and commercial disinfectants based on iodine and phenolic compounds are effective in inactivating the ASFV. This review describes the C&D protocol to apply in pig holdings with particular reference to ASFV.

Group A Rotavirus Associated with Encephalitis in Red Fox

In 2011, a group A rotavirus was isolated from the brain of a fox with encephalitis and neurologic signs, detected by rabies surveillance in Italy. Intracerebral inoculation of fox brain homogenates into mice was fatal. Genome sequencing revealed a heterologous rotavirus of avian origin, which could provide a model for investigating rotavirus neurovirulence.

Characterization of Brachyspira hyodysenteriae isolates from Italy by multilocus sequence typing and multiple locus variable number tandem repeat analysis

AIMS

To evaluate and compare the capabilities of multilocus sequence typing (MLST) and multiple locus variable number tandem repeat analysis (MLVA) techniques to characterize Brachyspira hyodysenteriae isolates and to investigate the relationship between pleuromutilin resistance and genetic variability.

METHODS AND RESULTS

MLST genotyping was performed on 180 B. hyodysenteriae isolates, and the results were evaluated considering profiles from 108 other strains previously reported in the database. In total, 37 sequence types were obtained. The MLVA approach completely characterized 172 strains and grouped the isolates into 22 different profiles. The combination of MLST and MLVA showed a slight increase in the discriminatory power, identifying 33 joint profiles. An antibiotic resistance analysis showed a reduction in the susceptibility to pleuromutilins over time, and a weak association between susceptibility to valnemulin and inclusion in clonal complex 4.

CONCLUSION

MLST and MLVA are reliable methods for characterizing B. hyodysenteriae strains and they have comparable discriminatory power.

SIGNIFICANCE AND IMPACT OF THE STUDY

The genotyping of B. hyodysenteriae isolates and a database of all the genetic profiles collected during the diagnostic activities could support traditional epidemiological investigations in identifying infection sources and routes of transmission among herds, and in developing more effective control measures.

Clinical-pathological findings of otitis media and media-interna in calves and (clinical) evaluation of a standardized therapeutic protocol

Background

The aims of this field trial were to describe the clinical-pathologic findings in calves with otitis media (OM) and media-interna (OMI), to evaluate, through the development of a scoring system, the effectiveness of a standardized therapeutic protocol, and to identify the causative pathogens and their possible correlation with concurrent respiratory disease. All animals underwent physical and neurological examinations at three experimental time points: at diagnosis/beginning of treatment (T0), 1 week (T1) and 2 weeks (T2) after therapy was started, respectively. Follow-up telephone interviews with animal owners were conducted 1 month later. The therapeutic protocol consisted of tulathromycin (Draxxin®; Zoetis), oxytetracycline hydrochloride (Terramicina 100®; Zoetis), and carprofen (Rimadyl®; Zoetis).

Results

Twenty-two calves were enrolled. Physical and otoscopic examination at T0 revealed monolateral and bilateral otorrhea in 16 and 6 calves, respectively, with peripheral vestibular system involvement in calves presenting with neurological signs (n = 17; 77 %). A significant improvement of clinical and neurological scores was observed in 20 (90 %) calves, a full recovery in only 1 (5 %). One calf worsened between T0 and T1 and it was removed from the study. None of the other animals showed a worsening of clinical conditions and/or required further treatments at one month follow up. Mycoplasma bovis was isolated in 89 % of the affected ears either alone or together with P. multocida (n = 5), Streptococcus spp. (n = 1), Staphylococcus spp. (n = 1), and Pseudomonas spp. (n = 1). M. bovis either alone or together with these bacteria was also isolated from the upper and/or lower respiratory tract in 19 (86 %) calves.

Conclusions

This is the first prospective study to evaluate the effectiveness of a standardized therapeutic protocol for the treatment of OM/OMI in calves. The therapy led to clinical improvement in the majority of the calves. Persistence of mild clinical-neurological signs did not compromise productive performance. The numerical scoring system for clinical and neurological signs permitted objective evaluation of response to therapy. M. bovis was the pathogen most often isolated. This finding should be considered in the treatment of OM/OMI in calves. Moreover, respiratory tract infection should not be underrated, since it is one of the major risk factors for the development of OM/OMI.

Inactivated Salmonella enterica serovar Typhimurium monophasic variant (S. Typhimurium 1,4,[5],12:i-) in sows is effective to control infection in piglets under field condition

The monophasic variant of Salmonella enterica serovar Typhimurium, namely Salmonella 1,4,[5],12:i-, has been increasingly responsible for foodborne human cases of disease and is most frequently detected in pork, since the variant is widely spread in pig farms. The aim of this study was to assess the efficacy of an autologous vaccine in decreasing the prevalence of Salmonella 1,4,[5],12:i-, in pigs. The trial was performed in a multisite pig production system of Northern Italy. The autogenous vaccine was prepared from the Salmonella 1,4,[5],12:i- strain isolated from the clinical case occurring in the Farm. Different immunization protocols were applied, ranging from interventions only in sows or piglets, or both. Microbiological analysis was performed to assess faecal shedding in sows and their offspring from birth till end of the production cycle and organ colonization of slaughtered pigs. Body weight of pigs was recorded at different time-points. Humoral immune response was evaluated in serum samples of sows and piglets. S. Typhimurium 1,4,[5],12:i- determines reduction of animal growth and farm production, furthermore, contamination of carcasses at the slaughterhouse. The load of bacteria entering into the food processing chain is differently influenced by the regimen of administration of inactivated vaccine. In particular, a combined vaccination of sows and their offspring was able to improve the weight gain of growing pigs, to limit Salmonella colonization of organs and to reduce the number of carrier pigs, and hence lowering the risk of introducing Salmonella organisms in the slaughter process.

Sequence types and pleuromutilin susceptibility of Brachyspira hyodysenteriae isolates from Italian pigs with swine dysentery: 2003-2012

Swine dysentery is a mucohaemorrhagic colitis of pigs caused by infection with Brachyspira hyodysenteriae. The disease can be controlled by treatment with antimicrobial agents, with the pleuromutilins tiamulin and valnemulin being widely used. In recent years, the occurrence of B. hyodysenteriae with reduced susceptibility to these drugs has been increasing. The aim of this study was to determine temporal changes in genetic groups and pleuromutilin susceptibility amongst B. hyodysenteriae isolates from Italy. Multilocus sequence typing (MLST) was performed on 108 isolates recovered from 87 farms in different regions of Italy from 2003 to 2012, and their minimum inhibitory concentrations (MICs) for tiamulin and valnemulin were determined. Logistic regression was performed to assess associations between susceptibility to the two antimicrobial agents and genetic group, year and region of isolation. The isolates were allocated to 23 sequence types (STs), with five clonal clusters (Ccs) and seven singletons. More than 50% of isolates were resistant to both pleuromutilins (MIC >2.0 µg/mL for tiamulin and >1.0 µg/mL for valnemulin). All 10 isolates in ST 83 were resistant; these were first isolated in 2011 and came from nine farms, suggesting recent widespread dissemination of a resistant strain. Significant associations were found between the proportion of pleuromutilin susceptible isolates and the genetic group and year of isolation. Although resistant isolates were found in all Ccs, isolates in Ccs 2 and 7 were over five times more likely to be susceptible than those in the other Ccs. A significant trend in the reduction of susceptibility over time also was observed.

Parenteral administration of attenuated Salmonella Typhimurium ΔznuABC is protective against salmonellosis in piglets

A major cause of salmonellosis in humans is the contamination of pork products. Infection in pigs can be controlled using bio-security programs, but they are not sufficient in countries where a high level of infection is recorded. In this context, the use of vaccines can represent a valid supplementary method of control. Recently, we have demonstrated that an attenuated strain of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium ΔznuABC) is protective against systemic and enteric salmonellosis in mouse and pig infection models, candidating this strain as an oral attenuated vaccine. In this study, we compared the efficacy of this attenuated Salmonella Typhimurium strain when administered orally or parenterally. Furthermore, in order to reproduce a pseudo-natural infection model, vaccinated pigs were allocated in the same pen with animals shedding virulent Salmonella Typhimurium. Animals were monitored weekly after vaccination and contact with infected piglets. Diarrhea and ataxia were recorded and Salmonella shedding was tested individually through bacterial culture. After four weeks of cohousing, piglets were euthanized, after which lymph nodes reactivity and gross lesions of the gut sections were scored at necropsy. Organs were submitted to microbiological and histological analyses. The data reported herein show that parenterally vaccinated animals do not shed the attenuated strain, and at the same time the absence of symptoms and decrease in virulent strain shedding in feces from day 6 after challenge demonstrated protection against infection induced by virulent Salmonella Typhimurium. In conclusion, our findings suggest that this is an alternative route of Salmonella Typhimurium ΔznuABC administration, without ignoring the advantages associated with oral vaccination.

Mycoplasma bovis infection in respiratory disease of dairy calves less than one month old

Mycoplasma bovis is an important cause of bovine respiratory disease, especially in young calves where it can also cause arthritis, tenosynovitis and otitis. During 2009 and 2010 a survey was carried out on carcasses of calves less than one month old sent to the Diagnostic Laboratory of the Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna in Brescia, regardless of the presence of lung lesions, to detect this pathogen. PCR tests for Mycoplasma spp. and M. bovis were applied. 83 out of 224 (37%) lung tissue samples examined were positive at PCR test for Mycoplasma spp.; in 64 cases of these we observed typical respiratory lesions (P<0.001). M. bovis was identified in 26 out of 83 (31%) lung tissue samples positive at PCR test for Mycoplasma spp.; in 24 cases of these we observed typical respiratory lesions (P=0.039). Our data demonstrate that presence of Mycoplasma spp. and M. bovis positively correlates with pneumonic lung lesions in young dairy calves.

Salmonella Typhimurium lacking the Znuabc transporter is attenuated and immunogenic in pigs

Meat contamination by Salmonella spp. is emerging as a major cause of human enteric infections in industrialized countries. The attempts to reduce human cases of salmonellosis encompass pre- and post-harvest interventions. In this context, vaccination of pigs may represent an effective instrument in eliminating/reducing Salmonella burden through the food chain. We have previously demonstrated that Salmonella Typhimurium lacking the ZnuABC transporter (S. Typhimurium ΔznuABC) is a promising candidate live vaccine in different mouse models of Salmonella Typhimurium infection. In this study, we confirmed in pigs the attenuation of S. Typhimurium ΔznuABC. Moreover, we evaluated the safety and immunogenicity of S. Typhimurium ΔznuABC administered to pigs by the oral route. We monitored clinical conditions of animals and we conducted a microbiological culture and a quantification of the humoral and cellular immune response, respectively, on fecal and blood samples of pigs. After vaccination with attenuated S. Typhimurium ΔznuABC, pigs showed a modest degree of hyperthermia. In addition, fecal shedding of S. Typhimurium ΔznuABC could not be detected 28 days after the inoculum. Furthermore, vaccination with S. Typhimurium ΔznuABC elicited a distinct production of anti-Salmonella antibodies and IFN-γ. Taken together, these results suggest that S. Typhimurium ΔznuABC is attenuated and immunogenic in pigs. Although the vaccine dosages do not guarantee complete safety there is ample margin to set up better conditions of use, suggesting that S. Typhimurium ΔznuABC could be a promising attenuated strain to be used as live mucosal vaccine for oral delivery.

An outbreak of viral gastroenteritis linked to municipal water supply, Lombardy, Italy, June 2009

We report an outbreak of viral gastroenteritis linked to municipal drinking water in a town in northern Italy in June 2009. Over one month we identified 299 probable cases of whom 30 were confirmed for at least one of the following viruses: norovirus, rotavirus, enterovirus or astrovirus. Water samples and filters from the water system also tested positive for norovirus and enterovirus. Control measures included treating the water system with chlorine dioxide and filters with peracetic acid, while providing temporary alternative sources of drinking water to the population.