The effect of pre-enrichment on recovery ofStreptococcus agalactiae, Staphylococcus aureusand mycoplasma from bovine milk

Abstract

SUMMARYThe study was conducted to determine whether pre-enrichment would increase sensitivity of detecting Streptococcus (Str.) aqalactiae, Staphylococcus (S.) aureus, and mycoplasma in bovine milk. Two procedures were followed, one involving direct inoculation of milk on bovine blood agar, and the other involving preenrichment in broth followed by inoculation on agar. Logistic regression was used to predict the probability of isolation as a function of culture procedure and two additional covariates, the California Mastitis Test (CMT) score of the milk and the type of sample (indicating sample storage temperature and herd mastitis status). A total of 13 778 milk samples was cultured for each of the three bacteria. By using results of both direct inoculation and pre-enrichment, the probability of isolation compared to use of direct inoculation only and adjusted for effects of other variables was increased 3*6-fold for Str. agalactiae, 1*6-fold for S. aureus and 17-fold for mycoplasma. The probability of isolation for all three bacteria increased as the CMT score increased. For Str. agalactiae, there was a statistical interaction predicting that enrichment improved the odds of isolation more from milk with high CMT scores than from milk with low scores. Results indicate that preenrichment can substantially increase the sensitivity of bacteriological screening of dairy cows for mastitis caused by Str. agalactiae, S. aureus, and mycoplasma.

Mycoplasma bovis Infections—Occurrence, Diagnosis and Control

“…Detection of M. bovis by real-time PCR preceded by culture enrichment of the samples improves detection when DNA is present at low concentrations. Furthermore, a selective broth-enrichment step increases the probability of Mycoplasma recovery when compared to direct plating on agar [ 55 ]. In the real-time PCR assay [ 45 ], milk samples from dairies and lung tissue samples were culture-enriched in PPLO broth for 24 h before analysis.…”

An improved method to culture Staphylococcus aureus from bovine milk

“…Attempts to increase the sensitivity of detecting Staph. aureus have also been made by testing different enrichment procedures before bacteriological culturing with varying results (Thurmond et al, 1989;Sol et al, 2002;Yamagishi et al, 2007). In our study, neither enrichment of samples in nutrition broth nor processing by the Mastistrip method had any effect on the isolation of Staph.…”

Methicillin-resistant Staphylococcus Aureus Nasal Colonization in People Living With HIV and Healthy People in Kathmandu, Nepal

“…The difference in rates of isolation of MRSA in different studies might be due to the variations in sample collection sites and survey time [ 41 ], implementation of the infection control program and use of antibiotics according to hospitals and countries [ 42 ]. The isolation of S. aureus is affected by the site of sample collection, higher rates of S. aureus isolation have been reported from nasal specimens compared with other sites [ 43 , 44 ], this may be because anterior nares are the common ecological niche for S. aureus , besides, the use of pre-enriched media for isolation could influence the isolation rate of S. aureus as observed in other specimens [ 45 ]. Hidron et al [ 39 ] hypothesized that the use of trimethoprim-sulfamethoxazole (also called cotrimoxazole) for prophylaxis of Pneumocystis carinii pneumonia possibly reduces the colonization of MRSA in PLHIV, and this statement is supported by other researchers as well [ 13 , 46 ].…”