Pericarditis caused by Proteus mirabilis in sheep

Abstract

Pericarditis means inflammation in the pericardial sac. Pericarditis is divided into three categories based on morphology, including fibrinous, purulent, and constrictive. In the present study, a 7-month-old male Ghezel breed sheep was examined for low weighting rate for three months. Tachypnea, tachycardia, heart friction sound, absence of fever and normal appetite were recorded in the clinical examination. In the patient's history, there was a history of perforated chest trauma behind the left scapula about three months ago. After the echocardiography examination and bacteriology procedures, purulent pericarditis caused by Proteus mirabilis was diagnosed. The bacterium was analysed using genome sequencing and new strain called Abhar114 was diagnosed. This is the first report of pericarditis caused by Proteus mirabilis in sheep.

INTRODUCTION

Pericardial lesions are classified into three groups. The first group is comprised of congenital lesions of the pericardium, such as pericardial cysts, congenital peritoneopericardial diaphragmatic hernia, partial or complete congenital absence of the pericardial sac and epicardial fibrous fronds. The second group is noninflammatory lesions of the pericardium, which includes hydropericardium, haemopericardium, and serous atrophy of pericardial fat. The third group includes all types of inflammatory lesions in the pericardium (pericarditis) (Asthana et al., 2013; Hsi et al., 2010; Jubb et al., 2016; Shah & Kronzon, 2015; Yong, 2010).

Hydropericardium means excess volume of clear noninflammatory fluid inside the pericardium. This lesion is usually a part of generalised anasarca and is observed in cachectic diseases (perhaps due to hypoalbuminemia) and congestive heart failure (Asthana et al., 2013; Jubb et al., 2016).

Haemopericardium means accumulation of pure blood inside the pericardium. This lesion is caused by cardiac rupture, cardiac puncture, direct trauma, rupture in intrapericardial part of aorta, arterial bleeding in haemangiosarcoma and idiopathic (Hsi et al., 2010; Jubb et al., 2016).

Serous atrophy of pericardial fat is due to progressive mobilisation of subepicardial fat deposits in cachexia and replacement of fat deposits with proteinaceous fluid (Jubb et al., 2016; Yong, 2010).

Pericarditis means inflammation in the structures of the pericardial sac (epicardium, serous fluid inside the sac and pericardium) (Imazio & Gaita, 2015). Pericarditis is divided into three categories based on morphology, including fibrinous, purulent and constrictive.

Fibrinous pericarditis usually occurs as the result of haematogenous microbial infections, but it may be caused by lymphatic infiltration from an inflammatory process in an adjacent tissue (Jubb et al., 2016). In fibrinous pericarditis, there is rarely significant effusion, so distension of the pericardial sac is not expected (Jubb et al., 2016; Vogiatzidis et al., 2015).

Purulent (suppurative) pericarditis most of the time indicates the presence of pyogenic bacteria, either as primary or opportunistic pathogens. TRP (traumatic reticulopericarditis) is an example of purulent pericarditis. In this type of pericarditis, there is a foul-smelling watery to cream-like purulent exudate mixed with fibrin in the pericardial sac (Jubb et al., 2016; Torki et al., 2011).

Constrictive pericarditis is characterised by fibrotic adhesions of the pericardium and epicardium, which leads to impaired diastolic filling and right-sided heart failure. Fibrotic adhesions cannot be broken by blunt dissection and may mineralise. The heart, restricted by scar tissue, may be smaller than normal, or it may be grossly enlarged and become hypertrophic (Jubb et al., 2016; Ramasamy et al., 2018).

Three important etiologic infectious pathogens in sheep pericarditis include Pasteurellosis, Mycoplasma species and Staphylococcus aureus (Constable et al., 2016). This study describes the first report of pericarditis (purulent type) caused by Proteus mirabilis in a sheep.

CASE HISTORY

In July 2022, a 7-month-old male Ghezel breed sheep was examined at Mahmoodi farm in Abhar city (Zanjan, Iran) for low weighting rate. This closed farm was in a desert area and involved 120 fattening sheep and 40 breeding goats. All fattening sheep were fed with hay (30%) and grain materials (70%) as total mixed ration (TMR) twice a day. Daily dry matter intake (DM) was 3%. The affected sheep had increased heart rate (118/min), increased respiratory rate (58/min), pericardial friction rub on heart auscultation, tachypnea, normal temperature (39.4°C) and normal appetite. The history revealed that there was a penetrating trauma at behind the left scapula due to goat's horn two months earlier, which was sutured by the veterinarian.

Echocardiograpgy examination

Two-dimensional imaging (5 MHz, sector probe) was performed from the right parasternal window (3rd and 4th intercostal space), used to pericardial assessment (Pepi & Muratori, 2006).

Bacterial culture

Under the guidance of echocardiography, the pericardial fluid sample was taken under sterile conditions. The collected samples were inoculated on blood agar (Merck, Germany). Then, purified isolated bacteria were identified by differential culture (MacConkey agar, Oxoid), selective culture (Proteeae isolation medium agar, Oxoid), Gram staining, biochemical tests (TSI, Urea, Indole, Methyl red, Voges-Proskauer, Simmon Citrate, Oxidase, and Catalase) and PCR test (Abdollahi et al., 2022). The antibiotic sensitivity test of the isolate was performed.

Extraction and PCR

The amplified products of PCR test were approximately 1500 bp. Sanger dideoxy sequencing method was used to obtain this sequence. The sequence derived from the isolate was analysed using the sequence analysis by Bioedit (version 7) and BLAST search program (http://blast.ncbi.nlm.nih.gov/Blast.cgi), and this sequence was submitted to the Bankit (Zhang et al., 2013; Abdollahi et al., 2022). The accession number is OP967486.

Necropsy

Due to the grave prognosis (Constable et al., 2016) and unaffordability of the treatment, the affected sheep was slaughtered and subjected to necropsy.

Histopathology

After slaughtering the animal, three samples (0/5 × 0/5 cm) were taken from the lung, pericardium and myocardium with a scalpel blade and placed in 10% neutral buffered formalin and sent to the histopathological laboratory. The samples were routinely processed, dehydrated, embedded in paraffin wax, sectioned at 5 μm in thickness using a rotary microtome (RM2 145; Leica, Wetzlar, Germany) and stained with haematoxylin and eosin (H&E) for histopathological evaluation.

Diagnostic results

The right parasternal short axis echocardiogram view show pericardial thickening, pericardial effusion and fibrin accumulation in the pericardial sac (Figure 1a). In echocardiography, purulent pericarditis was confirmed.

Proteus mirabilis was isolated through differential and selective media (Figure 1b), Gram staining (Figure 1c) and biochemical tests, as shown in Table 1 (Zafar et al., 2019; Abdollahi et al., 2022). Antibiotic susceptibility testing showed that the isolate was sensitive to cefixime, streptomycin, gentamicin, sulfadiazine, neomycin, cefepime, florfenicol, ciprofloxacin, enrofloxacin and colistin; and resistant to tetracycline, minocycline, ceftazidime, penicillin, erythromycin and azithromycin antibiotics. Using genome sequencing, a new Proteus mirabilis strain was characterised and termed as Abhar114.

TABLE 1 Biochemical Characterisation of Proteus mirabilis Isolated from sheep pericarditis

	In MacConkey agar	Nonlactose fermenting, large, circular smooth colonies
Cultural	In Proteeae isolation medium (PIM) agar	Dark brown colonies with a zone of clearing in the medium
	Gram staining	–
	Shape	Rods
	Size	Length: 1–3 μm/width: 0.4–0.8 μm
	Motility	+
	Indole	–
	TSI	Alk/A, H2S+
	Urea	+
	Citrate utilisation	+/–
Biochemical	MR	+
	VP	–
	Urease	+
	Catalase	+
	Oxidase	–
	Glucose	+
	Trehalose	+
	Lactose	–
Sugar fermentation	Sucrose	–
	Mannitol	–
	Dulcitol	–
	Sorbitol	–
	Xylose	+
	Inositol	–

At gross pathology, pericardial membrane thickening (Figures 1d and 2), pericardial effusion and adhesion between a small part of the lung and the pericardium were recorded. Other parts of lung and myocardium were normal in gross pathology. Histopathological examination of heart tissue revealed severe oedema in pericardium (Figure 3a). There was infiltration of lymphocytes and plasma cells, leading to multifocal lymphoplasmacytic myocarditis (Figure 3b). Microscopically, in the affected (attached to the pericardium) lung tissue, the lumen of bronchioles and bronchi were filled with mucus admixed with cell debris (Figure 3c). The alveolar septa were thickened by Moderate interstitial infiltration of inflammatory cells (especially lymphocytes and plasma cells) (Figure 3d). Finally, lymphoplasmacytic bronchopneumonia was diagnosed.

DISCUSSION

The present report found that the referred sheep suffered from pericarditis caused by Proteus mirabilis. Bacterial pericarditis usually occurs as a result of haematogenous spread, development of infection from nearby tissues, such as lung and empyema, development from myocarditis and endocarditis, and direct inoculation during traumatic events (Sawaya et al., 2009). In this report, it seems that the injury caused by the horn trauma of the male goat's horn to the intercostal space or suturing the pleura and the intercostal space in nonsterile conditions (farm conditions) have provided suitable conditions for direct or indirect (through pleural lymphatic drainage) spread of the isolated bacteria to the pericardium. The observed pericarditis was classified as purulent. No other reports of the pericarditis caused by Proteus mirabilis in sheep was found in scientific sources. Pasteurella species, Mycoplasma species and Staphylococcus aureus are more common causes of pericarditis in sheep (Constable et al., 2016).

Isolation of Proteus mirabilis from cases of human pericarditis has been reported. Sawaya et al. (2009) studied the occurrence of a cardiac tamponade in a 52-year-old diabetic and hypertensive woman with symptoms of nausea and vomiting. The infectious agents of purulent pericarditis in the studied patient were Citrobacter diversus and Proteus mirabilis. The method of penetration of the mentioned pathogens into the pericardium was not determined. It seems that this study is the first report of the isolation of Proteus mirabilis from pericarditis in human. Simony et al. (2014) studied the occurrence of cardiac tamponade in a 53-year-old man with chest pain symptoms. The infectious agents of pericarditis were Escherichia coli and Proteus species. In the discussion of this study, it has been stated that the mentioned pathogens have probably entered the pericardium through haematogenous spread. De Jong et al. (2018) studied the occurrence of a cardiac tamponade in a 49-year-old man. The infectious agent of pericarditis was Klebsiella pneumoniae and Proteus mirabilis. These pathogens were introduced into the pericardium due to the penetration of the tip of the laparoscopic catheter.

Proteus are abundant in soil and water and are human intestinal flora. Proteus is an opportunistic pathogen. For pathogenicity, Proteus needs to attach the tissue through fimbriae (or pili) and haemagglutinins. This attachment only occurs to certain tissues (Jacobsen et al., 2008). According to this study and the discussed studies, it seems that the pericardial tissue is one of the tissues to which Proteus bacteria can bind and cause disease.

CONCLUSION

This study showed that Proteus mirabilis could cause pericarditis in sheep and it should be considered as a possible cause for pericarditis. The isolated Proteus mirabilis was sequenced for the 16S rRNA genome and registered as a new strain in the NCBI gene bank with the code of OP967486 and Abhar114.

AUTHOR CONTRIBUTIONS

Abolfazl Najd Ghahremani: conception and design (lead), collecting the data (lead), sampling (equal), writing and revising the article (lead). Mostafa Abdollahi: conception (equal), sampling (lead), writing the article (equal). Sara Shokrpoor: assistance in laboratory work (lead). Iraj Ashrafi Tamai: assistance in laboratory work (equal).

ACKNOWLEDGEMENT

Mr Mohammad Mahmoodi, the owner of Mahmoodi farm, is appreciated for her cooperation in this research.

FUNDING

There is no source of fund to declare.

CONFLICT OF INTEREST STATEMENT

The authors declare that there is no conflict of interest.

ETHICS STATEMENT

The authors confirm that the ethical policies of the journal, as noted on the journal's author guidelines page, have been adhered to and the appropriate ethical review committee approval has been received.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available within the manuscript and also are available from the corresponding author upon reasonable request.

PEER REVIEW

The peer review history for this article is available at https://publons.com/publon/10.1002/vms3.1160.