Biomedical subjects

Ashish A Sawant

Publications and source records attributed to Ashish A Sawant.

4 recordsLinked to original sources

PubMed2006

Antimicrobial-resistant enteric bacteria from dairy cattle.

A study was conducted to understand the descriptive and molecular epidemiology of antimicrobial-resistant gram-negative enteric bacteria in the feces of healthy lactating dairy cattle. Gram-negative enteric bacteria resistant to ampicillin, florfenicol, spectinomycin, and tetracycline were isolated from the feces of 35, 8, 5, and 42% of 213 lactating cattle on 74, 39, 9, 26, and 82% of 23 farms surveyed, respectively. Antimicrobial-resistant gram-negative bacteria accounted for 5 (florfenicol) to 14% (tetracycline) of total gram-negative enteric microflora. Nine bacterial species were isolated, of which Escherichia coli (87%) was the most predominant species. MICs showing reduced susceptibility to ampicillin, ceftiofur, chloramphenicol, florfenicol, spectinomycin, streptomycin, and tetracycline were observed in E. coli isolates. Isolates exhibited resistance to ampicillin (48%), ceftiofur (11%), chloramphenicol (20%), florfenicol (78%), spectinomycin (18%), and tetracycline (93%). Multidrug resistance (> or =3 to 6 antimicrobials) was seen in 40% of E. coli isolates from healthy lactating cattle. Of 113 tetracycline-resistant E. coli isolates, tet(B) was the predominant resistance determinant and was detected in 93% of isolates, while the remaining 7% isolates carried the tet(A) determinant. DNA-DNA hybridization assays revealed that tet determinants were located on the chromosome. Pulsed-field gel electrophoresis revealed that tetracycline-resistant E. coli isolates (n = 99 isolates) belonged to 60 subtypes, which is suggestive of a highly diverse population of tetracycline-resistant organisms. On most occasions, E. coli subtypes, although shared between cows within the herd, were confined mostly to a dairy herd. The findings of this study suggest that commensal enteric E. coli from healthy lactating cattle can be an important reservoir for tetracycline and perhaps other antimicrobial resistance determinants.

Animals↗

PubMed2006

Prevalence of enterotoxin and toxic shock syndrome toxin genes in Staphylococcus aureus isolated from milk of cows with mastitis.

Staphylococcus aureus isolated from milk of cows with mastitis were evaluated for the prevalence of 16 enterotoxin genes (sea-see and seg-seq) and toxic shock syndrome toxin gene (tsst-1). Of 78 S. aureus examined, 73 (93.6%) were positive for one or more enterotoxin genes and these were divided into 36 groups by the presence of different enterotoxin genes. Enterotoxin genes including sen (84.6%), sem (71.8%), sei (60.3%) and sed (52.6%) were found frequently, while seg (24.4%), seq (16.7%), seo (12.8%), and seb (1.3%) were found at lower frequencies. Toxic shock syndrome toxin (tsst-1) gene was detected in 20 (25.6%) isolates and was always found in combination with other enterotoxin genes. The majority (88.5%) harbored more than one enterotoxin gene in different combinations. Eight S. aureus isolates (10.3%) were positive for sed, sei, sem, and sen; six (7.7%) possessed sed, seg, sei, sem, sen, and tsst-1; five (6.4%) had sei, sem, and sen; and four (5.1%) had sei, and sen. One isolate was positive for seb along with other SE genes including sed, seh, sem, sen, seq, and tsst-1. None of the isolates carried other enterotoxin genes (sea, sec, see, sej, sek, sel, and sep). PFGE profiles revealed 15 distinct pulsotypes among the 78 S. aureus isolates evaluated. PFGE and enterotoxin gene profiles did not match with each other because a single pulsotype carried different combinations of enterotoxin genes. The majority of S. aureus isolated from milk of mastitic cows carried newly described SE genes sem, sen and sei along with classical SE genes, sed and tsst-1. This is the first report describing the high prevalence of newly described enterotoxin genes, sem and sen in S. aureus from bovine mastitis. The high prevalence of enterotoxin genes and tsst-1 in S. aureus may be important as it is relevant to udder pathogenicity and food hygiene.

Animals↗

PubMed2006

Molecular epidemiology of ceftiofur-resistant Escherichia coli isolates from dairy calves.

Healthy calves (n = 96, 1 to 9 weeks old) from a dairy herd in central Pennsylvania were examined each month over a five-month period for fecal shedding of ceftiofur-resistant gram-negative bacteria. Ceftiofur-resistant Escherichia coli isolates (n = 122) were characterized by antimicrobial resistance (disk diffusion and MIC), serotype, pulsed-field gel electrophoresis subtypes, beta-lactamase genes, and virulence genes. Antibiotic disk diffusion assays showed that the isolates were resistant to ampicillin (100%), ceftiofur (100%), chloramphenicol (94%), florfenicol (93%), gentamicin (89%), spectinomycin (72%), tetracycline (98%), ticarcillin (99%), and ticarcillin-clavulanic acid (99%). All isolates were multidrug resistant and displayed elevated MICs. The E. coli isolates belonged to 42 serotypes, of which O8:H25 was the predominant serotype (49.2%). Pulsed-field gel electrophoresis classified the E. coli isolates into 27 profiles. Cluster analysis showed that 77 isolates (63.1%) belonged to one unique group. The prevalence of pathogenic E. coli was low (8%). A total of 117 ceftiofur-resistant E. coli isolates (96%) possessed the bla(CMY2) gene. Based on phenotypic and genotypic characterization, the ceftiofur-resistant E. coli isolates belonged to 59 clonal types. There was no significant relationship between calf age and clonal type. The findings of this study revealed that healthy dairy calves were rapidly colonized by antibiotic-resistant strains of E. coli shortly after birth. The high prevalence of multidrug-resistant nonpathogenic E. coli in calves could be a significant source of resistance genes to other bacteria that share the same environment.

Animals↗

PubMed2002

Evaluation of five selective media for isolation of catalase-negative gram-positive cocci from bulk tank milk.

Five selective media including Edwards modified medium, Edwards modified medium supplemented with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L), Streptococcus selective medium, Streptosel agar, and thallium-crystal violet-toxin-ferric citrate medium were evaluated for the isolation of streptococci and streptococci-like organisms from raw milk. The sensitivity and specificity of these selective media for streptococci and streptococci-like organisms were determined by using American Type Culture Collection reference strains. Under experimental conditions Edwards modified medium with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L) showed the highest sensitivity (100%) and specificity (100%) for streptococci and streptococci-like organisms followed by thallium-crystal violettoxin-ferric citrate medium, Edwards modified medium, Streptococcus selective medium, and Streptosel agar. Edwards modified medium supplemented with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L) allowed growth of all streptococci and streptococci-like organisms, while inhibiting growth of the staphylococci and gram-negative reference strains. Bulk tank milk samples from 114 dairy herds were spiral plated onto Edwards modified medium with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L). A total of 344 isolates (at least three isolates from each sample) were randomly selected and identified to their species. This medium permitted growth of 328 streptococci and streptococci-like organisms belonging to genera Aerococcus, Enterococcus, Gemella, Lactococcus, Streptococcus, and Vagococcus. When Edwards modified medium supplemented with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L) was evaluated using bulk tank milk samples, the sensitivity and specificity of this medium for streptococci and streptococci-like organisms were observed to be 100 and 87.5%, respectively. The positive predictive value for streptococci and streptococci-like organisms was observed to be 99.4%. The results of the study indicate that Edwards modified medium supplemented with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L) can be used as a selective medium for the isolation of streptococci and streptococci-like organisms from bulk tank milk.

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