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U.S. Department of Health and Human Services

Animal & Veterinary

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Resistance in Pathogenic E. coli from Retail Meat by Shaouha Zhao, DVM, MPVM, Ph.D.

DR. ZHAO: Good afternoon. Today I would like to talk about NARMS E. coli in terms of resistance and pathogenic E. coli among those isolates.


Well, previously my colleague, Johnnie Davis, also talked about the sampling scheme --- Enterococci. They had four FoodNet sites participating in the program. There were four types of meat being analyzed. In 2005 we changed our sampling scheme to random sampling.


This table shows the number of the meat sampled had been analyzed for over seven years and for isolated of E. coli. So you can see we have in total analyzed almost 12,000 meat samples.

For the 2007-2008, you can see our number of samples has decreased compared with previous years. That is because Maryland dropped out due to the, you know, resource problem.


This slide shows the prevalence of the E. coli from 2002 to 2008 for four meat commodities. So you can see the most contaminated meat is poultry meat, both chicken and turkey. It can be as high as 92 percent for turkey meat, followed by beef about 60 to 70 percent, and the pork has a little bit lower prevalence compared to the other three meat commodities.


Okay. This is the resistance profile for E. coil over the seven years. You can see the data is very consistent over the seven years. The most resistance drug is tetracycline, followed by streptomycin, sulfamethoxazole, ampicillin, and then gentamicin. 

The rest of the drugs have less than 10 percent. We did not find any single isolate that showed resistance to amikacin, but we have only a few isolates from pork and ground turkey showed Cipro resistance. 


If we look at the source where the E. coli comes from, the different meat commodities showed resistance for each drug is very different. So this is the average over the seven years by source. 

So you can see the most resistance is tetracycline, but if you look at the turkey for tetracycline resistance, it is almost 80 percent, followed by pork at about 50 percent. The chicken is 45 percent. The beef is over 20 percent.

If you look at Streptomycin for both the chicken and turkey it reaches 50 percent. Beef was less than 10 percent.

This has been shown for each drug. Basically poultry meat shows higher resistance than pork or beef isolates. So that probably reflects the selective pressure differently in the farm labor.


Let’s look at the resistance to ceftiofur or ceftriaxone of E. coli from the four meat commodities. So you can see here chicken isolates over the seven years showed the highest rate compared with other meat commodities. It showed resistance to ceftriaxone which can be more than 10 percent.

It is followed by turkey which for 2007 reached about six percent. Both beef and pork incidence is below five percent. So that is resistance look at the E. coli really reflects differently for the different meat commodities where you got the isolates.


Again, we look at the multidrug resistance. We are looking for resistance to three or more and five or more. So you can see the four meat commodities for over the seven years. Turkey meat shows the highest resistance to three or more and five or more antimicrobials.

So resistance to three or more can reach 55 percent for the turkey meat and resistance to five or more can reach almost 80 percent.

Again, you can see the beef isolates shows the lowest MDR.


Okay look at the very important resistance pattern here. This is to ceftiofur or ceftriaxone in combination with fluoroquinolones. This is ACSSuT and this is a typical MDR --- again you can see the E. coli recovered from all four meat commodities have such a pattern, but again chicken and turkey isolates show the highest number of such important MDR patterns.


Okay, now I would like to switch the topic a little bit here. When we isolated the E. coli from NARMS retail meat, we just picked a single E. coli from the meat. We don’t know whether they are pathogenic or nonpathogenic. So we collaborated with the University of Maryland to look at the pathogenic E. coli from all lumps (sic) of retail meat.


Before we talk about the pathogenic E. coli from the meat, I would like to just briefly review how to classify the E. coli. Normally we classify as nonpathogenic E. coli which we call commensal E. coli and the pathogenic E. coli, depending on what disease is caused. We mainly classify in two groups of E. coli called diarrheagenic E. coli and the other group called extraintestinal pathogenic E. coli.

Based on the pathogenicity and the diseases it causes for the pathogen, diarrheagenic E. coli we classified them to the following six groups: enteropathogenic E. coli, enterotoxigenic E. coli,  Shiga-toxin producing E. coli, Enteroinvasive E. coli, Enteraggregative E. coli, and Diffusely adherent E. coli.

For ExPEC, this group depends on the site of the infection.  Normally with many major two classes here. One is Uropathogenic E. coli, and neonatal meningetic E. coli, and also Other ExPEC infections at different sites of the body.


For the Shiga-toxin producing E. coli we used multiplex PCR that going into E. coli recovered from 2002 to 2007. There were over 7,000 E. coli has been screened and also we screened the other diarrheagenic E. coli and the ExPEC. We used the virulence marker for each group of E. coli by PCR. 


This table shows for the over 7,000 E. coli we only detect 17 Shiga-toxin producing E. coli. This is very interesting data, you know, except for the one we got from pork chops, all 16 isolates are from ground beef.

Four of them contain on shiga-toxin I and five of them contain shiga-toxin II. Many of them contain only shiga-toxin II. It is interesting that we do not find any of those isolates of chuA,yjaA gene. Only three of them contain hemolysin A gene which is a very different from E. coli O157.

Also interesting is that if you look at the serotype here, it is not a very common STEC would it have been associated with human outbreak.


Okay. This is a summary of STEC study here. Overall, the presence of the shiga-toxin producing E. coli in the retail meat is low, about 0.2 percent. Ground beef had the highest contamination, about 0.9 percent. No STEC was found in the chicken breast or ground turkey.

11 serotypes have been identified and 15 PFGE profiles were identified among 17 STEC.

All except one STEC isolate exhibited the toxic effects in the Vero cell.

We also had five STEC genes belonging to the Stx2d*, which is associated with high virulence and HUS in humans.


For other diarrheagenic E. coli we have identified 11 EPEC from the 2006 isolates of about 1,200 isolates. It is about 0.9 percent.

Five EPEC were from chicken breast, four were from ground beef, and two from pork chops. No EPEC were found in ground turkey.

No virulence genes were detected for other diarrheagenic E. coli from the 2006 isolates.


We also used multiplex PCR to detect ExPEC pathogenic E. coli based on finding virulence gene here. The definition is detection of two or more such virulence genes that belong to the ExPEC.

So for the 2006 isolates, we have a total identified 200 ExPEC. Most of them are from ground turkey. It is about 23 percent, followed by chicken breast. But we have 8 percent from pork and 3 percent beef. The average is about 16 percent ExPEC in the 2006 E. coli isolates.


We also did an analysis of this 200 ExPEC for phylogenetic group of ExPEC. So we identified the high number of this ExPEC. It belonged to the B group and we have 84 isolates. We also have 49 isolated belonging to D group. These two groups are highly associated with human disease, particularly for uropathogenic E. coli.


We also selected the 21 virulence genes which are commonly associated with uropathogenic E. coli. So a substitute gene and a virulence gene, one is afa and belonged to an adherence gene. Another is hemolysin D gene. We did not detect it but the rest of the 200 isolates carried different range of this virulence gene. I think the range is between 2 to 13, but the B group we said is highly pathogenic for humans. It carries a high number of virulence genes averaging about nine virulence genes for each of those isolates.


Now I would like to summarize our findings. Poultry meats had the highest contamination rates with E. coli, about 82 to 83 percent, followed by beef and pork.

E. coli from poultry shows a greater resistance to antimicrobials than those from beef and pork.  Turkey isolates had the highest number of MDR.

E. coli from chicken displayed the highest resistance to beta-lactam antimicrobials.

The presence of STEC in retail meats was rare, only less than one percent in beef.

EPEC and ExPEC were also present in the retail meats, and most potential virulent ExPEC were recovered from poultry meats.


Finally, I would like to thank the --- assist the agency who --- this NARMS Retail Meet Program. Thank you.


DR. FEDORKA-CLAY: We are just going to move right in to our next presentation. 


DR. FRYE: --major production industry and also consumer group, AHI and IDSA coming up. We are glad that you are all here and we count on prospective from everybody. So I just wanted everybody to know the themes will switch a little bit at this point.

Paula, I can’t keep talking, so --

DR. FEDORKA-CLAY: Okay, okay.

DR. FRYE: I suppose if you are going to be awhile, if you have a few questions --