Finding of coagulase negative staphylococci in the herd with an increased number of somatic cells in milk and their antimicrobial susceptibility

Abstract

Coagulase-negative staphylococci (CNS) are generally considered to be opportunistic pathogens. Controlling CNS mastitis is difficult because the epidemiology is not clear, and the CNS group consists of about 40 different Staphylococcus species. Therefore, the aim of this study was to determine the prevalence of coagulasenegative staphylococci in milk of the cows with subclinical mastitis, as well as to determine different CNS species isolated from quarter milk samples for their susceptibility to antimicrobials used commonly for mastitis therapy. On the farm where there was found an increase of somatic cells in bulk milk, 112 dairy cows were examined by mastitis test. From 52 udder quarters where mastitis test showed an increase of somatic cells, milk samples were taken for bacteriological examination. For isolating the causes of mastitis there was used blood agar. Identification of the causative agents of mastitis was carried out on the basis of colony appearance on blood agar and their physiological characteristics. Coagulasepositive staphylococci sensitivity which cause mastitis was tested by Kirby Bauer method. For susceptibility testing there were used commercially produced discs containing: 10 IU penicillin, amoxicillin/clavulanic acid (20 +10 g), cloxacillin 25 g, 30 g amoxicillin, cephalexin 30 g, ceftiofur 30 g, 15 g lincomycin, gentamicin and tetracycline 30 g. The sensitivity of microorganisms was evaluated on the basis of inhibition zone diameter recommended by the manufacturer and was labeled as sensitive (S) moderately sensitive (I) or resistant (R). Coagulase-negative staphylococci were isolated from 61.53% of samples from cows with subclinical mastitis, making them the most common cause of subclinical mastitis. The highest resistance of coagulase-negative staphylococci was found to penicillin G (58.33% of isolates). Full sensitivity of coagulase-negative staphylococci was found to amoxicillin / clavulanic acid (100% of isolates), a good sensitivity to ceftiofur (83.33% of isolates), cefalexin (70.83% of isolates) and ceftriaxone (41.66% of isolates).

Koagulaza negativne stafilokoke se smatraju oportunistički patogenim mikroorganizmima. Suzbijanje mastitisa izazvanih koagulaza negativnim stafilokokama je teško, zbog toga što epidemiologija bolesti nije jasna, a grupu koagulaza negativnih stafilokoka čini više od oko 40 različitih vrsta stafilokoka. Stoga je cilj ovog rada bio da se ustanovi prevalenca koagulaza negativnih stafilokoka u mleku krava sa subkliničkim mastitisom, kao i da se ispita njihova osetljivost na odabrana antimikrobna sredstva. Mastitis testom je pregledano 112 muznih krava na farmi, gde je utvrđeno povećanje broja somatskih ćelija u zbirnom mleku sa farme. Iz 52 četvrti vimena krava, gde je mastitis testom utvrđeno povećanje broja somatskih ćelija uzeti su uzorci mleka za bakteriološki pregled. Za izolovanje uzročnika mastitisa korišćen je krvni agar. Identifikacija uzročnika mastitisa je urađena na osnovu izgleda kolonija na krvnom agaru i fizioloških osobina. Osetljivost koagulaza negativnih stafilokoka na uzročnike mastitisa je ispitana metodom po Kirbi Baueru. Za ispitivanje osetljivosti upotrebljeni su komercijalno proizvedeni diskovi koji su sadržavali: penicilin (10 IU), amoksicilin/klavulanska kiselina (20+ 10 µg), kloksacilin 25 µg, amoksicilin 30 µg, cefaleksin 30 µg, ceftiofur 30 µg, linkomicin 15 µg, gentamicin 30 µg i tetraciklin 30 µg. Osetljivost mikroorganizama je procenjivana na osnovu prečnika zone inhibicije prema preporuci proizvođača i označavana kao osetljiv (S) umereno osetljiv (I) ili rezistentan (R). Koagulaza negativne stafilokoke su izolovane iz 61,53% uzoraka mleka krava sa subkliničkim mastitisom, što ih čini najčešćim uzročnikom subkliničkih mastitsa. Najveći broj koagulaza negativnih stafilokoka je bio rezistentan na penicilin G (58,33% izolata). Svi izolati koagulaza negativnih stafilokoka su bili osetljivi na amoksicilin/klavulansku kiselinu, 83,33% izolata je bilo osetljivo na ceftiofur, 70,83% izolata je bilo osetljivo na cefaleksin i 41,66% izolata je bilo osetljivo na ceftriakson.