Microbiological and Histopathological Investigation of Necropsy-Confirmed Lobar Pneumonia in Lambs

Abstract

Lobar pneumonia is a significant cause of losses in lamb raising, yet there is limited integrated necropsy-based data linking histopathology with microbiological identification and susceptibility testing.  This study investigated the etiological diversity of lobar pneumonia among 118 lambs submitted for routine necropsy in 2025. Thirty-six lungs with gross lesions consistent with lobar pneumonia were histologically classified as catarrhal purulent bronchopneumonia (n=20), fibrinous pneumonia (n=9), or purulent necrotizing bronchopneumonia (n=7). Fresh tissues were cultured on blood and chocolate agar and incubated at 37°C for 48 hours under both aerobic and 10% CO₂ conditions. Isolates were identified through MALDI-TOF MS, and Mycoplasma spp. DNA was screened using conventional PCR. Antimicrobial susceptibility testing employed the Kirby-Bauer disk diffusion method with a panel of antibiotics including ampicillin, amoxicillin/clavulanic acid, cefotaxime, tetracycline, trimethoprim-sulfamethoxazole, ciprofloxacin, and gentamicin. Bacterial growth was observed in 25 of 36 lungs, yielding 33 isolates, predominantly Escherichia coli (n=10) and Pasteurella multocida (n=6). Mycoplasma spp. DNA was detected in 13 lungs, including two culture-negative samples. Pasteurellaceae were significantly more common in fibrinous/purulent necrotizing bronchopneumonia compared to catarrhal purulent bronchopneumonia (p<0.001). Resistance in E. coli was most frequent to ampicillin and trimethoprim-sulfamethoxazole, while susceptibility to amoxicillin/clavulanic acid and cefotaxime was maintained. Overall, these results illustrate pattern-specific etiological profiles and support the use of integrated necropsy-based investigation for lamb pneumonia.

Keywords

• Antimicrobial susceptibility
• histopathology
• lamb pneumonia
• lobar pneumonia
• MALDI-TOF MS

Ethical Statement

Ethical approval was not required because this study used post-mortem diagnostic material submitted for routine necropsy and did not involve any live animal experimentation. An official exemption was issued by the Fırat University Local Ethics Committee for Animal Experiments (session no: 2026/06-09; decision date: 04 March 2026; document no: 06.03.2026-45727).

Kuzularda Nekropsi ile Doğrulanan Lober Pnömoni Olgularının Mikrobiyolojik ve Histopatolojik İncelenmesi

Abstract

Lober pnömoni, kuzu yetiştiriciliğinde önemli ekonomik kayıplara yol açan başlıca nedenlerden biridir; ancak histopatoloji ile mikrobiyolojik identifikasyon ve duyarlılık profillemesini birlikte ele alan entegre nekropsi temelli veriler sınırlıdır. Bu çalışma, 2025 yılında nekropsi ile doğrulanan kuzu lober pnömonilerinde etiyolojik çeşitliliği araştırmıştır. Lober pnömoni ile uyumlu makroskobik lezyonlar gösteren 36 akciğer örneği histolojik olarak kataral pürülan bronkopnömoni (n=20), fibrinöz pnömoni (n=9) veya pürülan nekrotik bronkopnömoni (n=7) olarak sınıflandırılmıştır. Taze dokular kanlı agar ve çikolata agara ekilerek 37 °C’de 48 saat süreyle aerob ve %10 CO₂ koşullarında inkübe edilmiştir. İzolatlar MALDI-TOF MS ile tanımlanmış ve Mycoplasma spp. DNA’sı konvansiyonel PCR ile taranmıştır. Antimikrobiyal duyarlılık testi Kirby–Bauer disk difüzyon yöntemiyle tek bir panel kullanılarak yapılmıştır (ampisilin, amoksisilin/klavulanik asit, sefotaksim, tetrasiklin, trimetoprim–sulfametoksazol, siprofloksasin, gentamisin). Otuz altı akciğerin 25’inde bakteriyel üreme elde edilmiş ve toplam 33 izolat saptanmıştır; en sık Escherichia coli (n=10) ve Pasteurella multocida (n=6) izole edilmiştir. Mycoplasma spp. DNA’sı, ikisi kültür-negatif olmak üzere 13/36 akciğerde belirlenmiştir. Pasteurellaceae, fibrinöz/pürülan nekrotik bronkopnömonide kataral pürülan bronkopnömoniye kıyasla anlamlı derecede daha sık saptanmıştır (p<0,001). E. coli izolatlarında ampisilin ve trimetoprim–sulfametoksazole direnç daha sık görülürken, amoksisilin/klavulanik asit ve sefotaksime duyarlılık korunmuştur. Genel olarak bu sonuçlar, histopatolojik paterne özgü etiyolojik profilleri ortaya koymakta ve kuzu pnömonilerinin entegre nekropsi temelli yaklaşımla araştırılmasının değerini desteklemektedir.

Keywords

• antimikrobiyal duyarlılık
• histopatoloji
• kuzu pnömonisi
• lober pnömoni
• MALDI-TOF MS

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