Infectious Disease Compendium

Escherichia

Microbiology

Gram negative rod; aerobe, it will grow anaerobically so technically it is microaerophilic. There is E. coli, E. albertii, E. blattae, E. fergusonii, E. hermannii, and E. vulneris.

Epidemiologic Risks

Part of the human colonic flora, O157:H7 is found in cattle stool, which coats your food. Also outbreaks with spinach (PubMed),  strawberries contaminated with deer poo and swimming in poo filled lakes (any lake a child swim in) (PubMed).

Now people, for reason that elude me, think raw milk is a good thing. There is an underground raw milk trade that functions like a speakeasy during prohibition. People also treat cows like condos and own a part share so they can get raw milk legally. And the resultant infections as well (CDC).

Shiga producing E. coli is also found in venison (PubMed).

About 40% of community acquired ESBL E. coli are community acquired with no risk factors (PubMed). This will likely only get worse and makes emperic therapy for serious E. coli infections problematic: go straight to a carbapenem (PubMed)? Not yet.

Healthy Chinese medical students will carry ESBL E. coli for over 4 months (PubMed).

Syndromes

1) Focal infections: urologic infections, any intra abdominal infection, sepsis. Pyomyositis in the neutropenic (PubMed).

2) Diarrhea: travelers, O157:H7 and O111 are associated with Hemolytic-Uremic Syndrome (HUS), the former in children, the latter in adults. The 2011 outbreak in Europe was O104:H4. HUS may be preventable with daily intestinal lavage with polyethylene glycol (PubMed).

How long are they potentially infective? Patients with HUS had a shorter shedding duration (median, 13–14 days) compared to non-HUS patients (median, 33–34 days). Antimicrobial treatment also significantly reduced shedding duration (PubMed).

Some E. albertii can be enterohemorrhagic or enteropathogenic and misidentified by the lab as E. coli (PubMed), can cause outbreaks (PubMed), and is almost certainly missed by your lab.

Treatment

Depends on the disease and the local resistance patterns. The most reliable agents are aminoglycosides, carbapenems, quinolones and third generation cephalosporins. As a rule, all forms of penicillin as well as tmp/sulfa have too much resistance to use empirically.

In the US, 25% of urine isolates are resistant to tmp/sulfa, 17% to ciprofloxacin (PubMed). And it will only get worse with time.

And consider cyloserine for resistant E. coli UTI's. Yes, it's a TB drug, but it is effective against gram negative rods (PubMed).

Be wary. ESBL (extended spectrum beta lactamase that hydrolyse most beta-lactams (sparing only cephamycins and carbapenems) carrying E. coli is are increasing in frequency and the only reliable antibiotic are carbapenems, including ertapenem (PubMed). Risks for ESBL include health care, urinary catheters and prior antibiotics and if you choose wrong there is increased mortality (PubMed).  If the MIC for an ESBL to piperacillin/tazobactam is <= 2 the patient will do fine but if higher MICs expect death (PubMed). For bacteremia (or suspected) from an ESBL, carbepenams have less mortality than piperacillin/tazobactam (PubMed). Maybe (PubMed).

If the organism is an ESBL, DO NOT use cefepime even if susceptible. Won't work as well as carbapenems (PubMed) and avoid piperacillin/tazobactam. Remember that sensitive in the lab does not always mean effective in the patient.

A post analysis (PubMed) suggests the beta lactamase inhibitor combinations (if MIC < 2) are better than carbapenems for treating ESBL producing E. coli (PubMed), but, as the Xigris debacle reminds us, post hoc analysis are often crap and not to be believed.

There is also the New Delhi metallo-beta-lactamase, which gets all beta-lactams including carbapenems aka CRE (PubMed); often these are only sensitive to colistin and tigecycline. Cetazadime-avibactam.html has a high failure rate with CRE.

CRE are perhaps more virulent as well as hard to kill(PubMed).

Travelers diarrhea: ciprofloxacin, 750 mg qd for 1–3 days; azithromycin, 1000 mg in a single dose; or rifaximin, 200 mg tid for 3 days.

Notes

Treatment of O157:H7 diarrhea may help precipitate HUS (PubMed). Long term O157:H7 associated with an increased risk for hypertension, renal impairment, and self reported cardiovascular disease (PubMed). About 11% of family members will acquire infection from the index case (PubMed).  Azithromycin will decrease shedding, but whether to treat is uncertain (PubMed).

If you suspect E. coli O157:H7 and its brethren, avoid quinolones as it markedly up regulates toxin in comparison to other antibiotics, including azithromycin with down regulates toxin (PubMed).