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Marler Blog Providing Commentary on Food Poisoning Outbreaks & Litigation

The Dairy Industries Dirty Little Antibiotic Salmonella Newport Secret

So, the dairy industry pumps the cows full of antibiotics and then when done with them sends them to slaughter to be fed to us.

Use of antibiotic susceptibility patterns and pulsed-field gel electrophoresis to compare historic and contemporary isolates of multi-drug-resistant Salmonella enterica subsp. enterica serovar Newport, Appl Environ Microbiol. 2004 Jan;70(1):318-23, Berge AC, Adaska JM, Sischo WM, Veterinary Medicine Teaching and Research Center, University of California-Davis, Tulare, California 93274, USA.

Recently, multi-drug-resistant (MDR) Salmonella enterica subspecies enterica serovar Newport reemerged as a public and animal health problem. The antibiotic resistance of 198 isolates and the pulsed-field gel electrophoresis patterns (PFGE) of 139 isolates were determined. Serovar Newport isolates collected between 1988 and 2001 were included in the study. One hundred seventy-eight isolates were collected from the San Joaquin valley in California and came from dairy cattle clinical samples, human clinical samples, bulk tank milk samples, fecal samples from preweaned calves, and waterways. Twenty clinical isolates from humans from various regions of the United States were also included in the study. Resistance to 18 antibiotics was determined using a disk diffusion assay. PFGE patterns were determined using a single enzyme (XbaI). The PFGE and antibiogram patterns were described using cluster analysis. Although the antibiotic resistance patterns of historic (1988 to 1995) and contemporary (1999 to 2001) isolates were similar, the contemporary isolates differed from the historic isolates by being resistant to cephalosporins and florfenicol and in their general sensitivity to kanamycin and neomycin. With few exceptions, the contemporary isolates clustered together and were clearly separated from the historic isolates. One PFGE-antibiogram cluster combination was predominant for the recent isolates, which were taken from human samples from all parts of the United States, as well as in the isolates from California, indicating a rapid dissemination of this phenotypic strain. The data are consistent with the hypothesis that the reemergence of MDR serovar Newport is not simply an acquisition of further antibiotic resistance genes by the historic isolates but reflects a different genetic lineage.

Chloramphenicol-resistant Salmonella newport traced through hamburger to dairy farms. A major persisting source of human salmonellosis in California, New England Journal of Medicine, Volume 316:565-570, March 5, 1987, Number 10, JS Spika, SH Waterman, GW Hoo, ME St Louis, RE Pacer, SM James, ML Bissett, LW Mayer, JY Chiu, B Hall, and et al.

Animal-to-human transmission of drug-resistant salmonella and the role of antimicrobial use in food animals in the emergence of these bacteria are controversial subjects. Investigation of a 4.9-fold increase in Salmonella newport isolations from Californians in 1985 showed that 87 percent of the isolates had an unusual antimicrobial-resistance pattern (including chloramphenicol resistance) and a single, identical plasmid. Interviews of 45 patients and 89 matched controls in Los Angeles County showed that illness was associated with penicillin or tetracycline use during the month before onset (P less than 0.001) and with eating ground beef during the week before onset (P = 0.052). The epidemic strain was isolated from hamburger products eaten by cases, abattoirs where the animals from which the meat came were slaughtered, dairies that sent cows for slaughter on days when culture-positive products were processed, and ill dairy cows. Isolation of salmonella from beef carcasses in abattoirs correlated with the proportion of dead or moribund animals received for slaughter (r = 0.60, P less than 0.05). Isolation of chloramphenicol-resistant salmonella from dairy farms was associated with the use of chloramphenicol at those dairies. We conclude that food animals are a major source of antimicrobial-resistant salmonella infections in humans and that these infections are associated with antimicrobial use on farms.

Multi-Drug-Resistant Salmonella Newport in Northern California, CHEUNG M, MOHLE-BOETANI J, ABBOTT S, WERNER S, VUGIA D; Interscience Conference on Antimicrobial Agents and Chemotherapy (42nd : 2002 : San Diego, Calif.), Abstr Intersci Conf Antimicrob Agents Chemother Intersci Conf Antimicrob Agents Chemother. 2002 Sep 27-30; 42: abstract no. LB-15, California Department of Health Services, Berkeley, CA.

BACKGROUND: In late 2001, the California (CAL) Department of Health Services Microbial Diseases Laboratory noted an increase in Salmonella Newport (SN) isolates. Screening for chloramphenicol (C) resistance (R) revealed a large number with probable multi-drug resistance (pMDR), as CR has been used as a proxy for MDR [ampicillin (A), (C), streptomycin (S), sulfisoxazole (Su), tetracycline (T)].

METHODS: To determine possible risk factors for pMDR-SN infection, we conducted a case-control study of 27 patients from Northern (N) CAL with pMDR-SN from specimens collected in January 2002 and 27 age- and ethnicity-matched controls. We calculated matched odds ratios (mOR) for food exposures. We also tested isolates for R to A, C, S, Su, T, sulfamethoxazole/trimethoprim (SXT), ceftriaxone (CTX), and ciprofloxacin (CIP) and compared isolates by pulsed field gel electrophoresis (PFGE).

RESULTS: 95% of pMDR-SN patients were Hispanic and 61% were children; 37% were hospitalized. Consumption of Mexican-style (MS) cream (mOR 8.0, p=0.05) and MS cheese or cream (mOR 5.0, p=0.04) were significantly associated with illness. Purchasing cheese (mOR 10.0, p=0.02) or cream (mOR 5.0, p=0.04) at a Mexican market was also associated with illness. 100% of isolates had R to C, S, Su, and T. In addition, 85% had R to A, 74% to SXT, 85% to CTX, but 0% to CIP. Twenty of 27 isolates had an identical PFGE pattern; all 20 had R to ACSSuT plus CTX and SXT. Random screening of SN isolates from 2001 revealed 85% of NCAL isolates to be pMDR-SN.

CONCLUSIONS: MDR-SN infections have increased in NCAL, disproportionately affecting Hispanics and children and resulting in substantial hospitalization. Most isolates are resistant to antibiotics previously used to treat serious Salmonella infections. We identified an epidemiological association between MS dairy products and MDR-SN infection. Despite warnings to the public about unpasteurized dairy products, cases of MDR-SN infection continue to occur and addressing this public health problem is challenging.