Occurrence of haemolytic Mannheimia spp. in apparently healthy sheep in Norway

Antimicrobial susceptibility profiles among commensal Mannheimia haemolytica and Pasteurella multocida isolated from apparently healthy sheep processed in California: Results from a cross-sectional pilot study

Antimicrobial resistance (AMR) is a growing challenge for the successful treatment of bacterial infections in both human and veterinary medicine. Despite the need to mitigate AMR, food-producing animal species lack adequate information on bacterial susceptibility to support antimicrobial stewardship for conditions that drive antimicrobial usage, such as ovine respiratory disease (ORD). In an effort to help address this gap, the upper respiratory tract (URT) from 620 apparently healthy sheep carcasses was sampled at slaughter in California (CA), from April through September 2021, to determine the antimicrobial susceptibility profiles of commensal Mannheimia haemolytica and Pasteurella multocida, two bacteria commonly associated with ORD. Sheep sampled in the study were selected based on origin prior to processing (out-of-state or CA) and marketing status (antibiotic-free or conventional management), two factors hypothesized to influence antimicrobial susceptibility profiles. Of the total 620 carcasses sampled, 343 had at least one isolate of M. haemolytica or P. multocida recovered, for a recovery rate of 55.3 %. The recovery rate among sampled carcasses was 46.8 % (290/620) for M. haemolytica and 15.8 % (98/620) for P. multocida. Utilizing Clinical and Laboratory Standards Institute (CLSI) clinical breakpoints as interpretive criteria, all 98 P. multocida isolates were pansusceptible to the antimicrobials tested that are labeled for use in sheep, with the exception of one isolate that classified as intermediate to tilmicosin. Of the 290 M. haemolytica isolates, the greatest resistance was found to penicillin, with 51.0 % (148) of isolates classified as intermediate and 25.2 % (73) resistant, while nine isolates were resistant to chlortetracycline and oxytetracycline and one isolate was intermediate to spectinomycin. Multidrug resistance (resistance to three or more antimicrobial classes) was not found in any isolate of either target organism. Very low to no AMR was observed across both bacterial species tested, demonstrating that M. haemolytica and P. multocida in this apparently healthy sheep population remain broadly susceptible to the antimicrobials licensed for the treatment of ORD. In addition, antimicrobial susceptibility did not differ based on origin or marketing status, as defined for this study. Sampling at slaughter provides an opportunity to collect baseline information about antimicrobial susceptibility of the commensal flora of the sheep URT that can give rise to ORD, but may not be generalizable to sheep with clinical respiratory disease or to sheep reared by non-commercial producers.

Molecular characterization of Mannheimia haemolytica associated with ovine and caprine pneumonic lung lesions

This study investigated via polymerase chain reaction (PCR) three main serotypes (A1, A2, and A6) and nine virulence-associated genes in 71 ovine and caprine Mannheimia haemolytica isolates obtained from lungs (n = 349) with pneumonic lesions from a slaughterhouse in Iran. The lung specimens were collected from sheep (n = 197) and goats (n = 152) between December 2018 and January 2020. A total of 71 M. haemolytica isolates were identified in sheep (37/197; 18.8%) and goat (34/152; 22.4%) pneumonic lungs. Serotypes A2 (30/71; 42.3%) and A6 (29/71; 40.9%) were the most frequently detected, whereas the A1 serotype was detected with a frequency of less than 10% (7/71; 9.9%) and five isolates remained unknown. The virulence genes lkt, pomA, and nanH were present in all the isolates. The detection rates for the remaining virulence-associated genes were: gcp (95.8%), lpsA (93%), fhaC (90%), irp (70.4%), hf (57.7%), and sodC (21%). The sodC gene was exclusively detected among A2 isolates (50%), while the irp gene was more prevalent among A2 isolates and the hf gene among A1 and A6 isolates. These data may be useful for the typing of isolates in epidemiological studies. This study provides information about the main serotypes and the prevalence of virulence-associated genes among M. haemolytica ovine and caprine isolates in Iran.

Prevalence of Mannheimia haemolytica in Syrian Awassi sheep

The aim of the present study was to evaluate the prevalence of Mannheimia haemolytica in Syrian Awassi sheep. Between 2008 and 2012, 1520 nasal swabs from pneumonic and apparently healthy sheep, and 110 pneumonic lungs samples were collected and subjected to bacteriological, biochemical and PCR assays. A total of 191 isolates (11.7%) were identified as M. haemolytica, 44 (2.7%) were M. ruminalis and 18 (1.1%) were M. glucosida. All 191 isolates of M. haemolytica gave an amplified product of 1146 bp size by PCR when lktaA primer was applied. The highest rate of M. haemolytica isolation was from pneumonic lungs tissue (21.8%) and pneumonic sheep (14.1%), and the lowest was from apparently healthy sheep (8.5%). Geographical and seasonal distribution of M. haemolytica showed that the majority of the isolates originated from sheep reared in the Syrian Desert (30%) and Euphrates basin (26.7%), and a significant increase (P≤0.05) in the rate of positive isolates in summer and winter as compared to spring. These findings indicate that M. haemolytica may play an important role in development of pneumonia in Syrian Awassi sheep, especially in eastern parts of Syria, where drought and shortage of rain hit these zones periodically.

Mannheimia species associated with ovine mastitis

Mannheimia glucosida, M. haemolytica, and M. ruminalis were isolated from cases of acute mastitis in ewes. M. glucosida was found to be a common cause of clinical mastitis in sheep. Selected phenotypic tests in addition to genotyping were needed to definitively identify Mannheimia species causing ovine mastitis.