Escherichia coli extraintestinal infections are becoming increasingly challenging to manage as resistance emerges widely to first-line antimicrobial agents, including trimethoprim-sulfamethoxazole (TMP-SMZ), fluoroquinolones, and extended-spectrum cephalosporins.1 Contributing to this problem are several expanding E. coli clonal groups, including clonal group A,2 the O15:K52:H1 clonal group,3 and sequence type ST131.4–7 Person-to-person spread could contribute to the dissemination of these antimicrobial-resistant pathogens, as suggested by the within-household sharing observed with other E. coli strains.8–11
A severe osteoarticular infection in an 8-month-old girl due to fluoroquinolone-resistant, cephalosporin-susceptible E. coli prompted us to assess for involvement of these drug-resistant clonal groups, to search for a reservoir of the causative strain within the household, and to screen for within-household sharing of other E. coli.
Subjects and Strains.
A clinical E. coli isolate from a girl with recalcitrant E. coli septic arthritis and osteomyelitis was saved. Fecal swabs, collected from the girl's healthy parents approximately 2 months after her initial hospitalization, were streaked to modified Mueller-Hinton agar with and without ciprofloxacin (4 mg/L). After overnight incubation at 37°C, 5 colonies of E. coli (lactose and indole positive, citrate negative) per plate, as available, were picked. Isolates were stored in glycerol-broth at −80°C.
Susceptibility to 22 antimicrobial agents was assessed by disk diffusion, using CLSI-recommended methods. Agents tested included amikacin, amoxicillin, amoxicillin-clavulanate, aztreonam, cefazolin, cefepime, cefoxitin, ceftazidime, ceftriaxone, chloramphenicol, ciprofloxacin, gentamicin, imipenem, nalidixic acid, nitrofurantoin, piperacillin, piperacillin-tazobactam, streptomycin, sulfisoxazole, TMP-SMZ, tetracycline, and TMP.
Isolates were screened for clonality by using random amplified polymorphic DNA analysis.4 The daughter's initial isolate and 1 representative per random amplified polymorphic DNA type per fecal sample were analyzed by pulsed-field gel electrophoresis (PFGE).4 Profiles were compared against a private ST131 profile library (J.R.J.) using BioNumerics (Applied Maths). Isolates with ≥94% similar profiles were regarded as the same clone.
One representative per PFGE type per host was assessed by PCR for major E. coli phylogenetic group (A, B1, B2, D), 55 ExPEC-associated virulence traits, 13 infection-associated O types (O1, O2, O4, O6, O7, O12, O15, O16, O18, O25a, O25b, O75, and O157), bla CTX -M, and bla CTX -M- 15.4 The H4 fliC (flagellin) variant was detected by restriction analysis of fliC amplicons.9 Selected isolates underwent multilocus sequence typing (MLST) and assignment of sequence types (STs) based on partial sequence analysis of 7 housekeeping genes (Available at: http:/mlst.ucc.ie).4
An 8-month-old previously healthy girl presented after 10 days of knee motion intolerance and failure to weight-bear, without fevers. Examination showed a well-appearing toddler with a knee joint effusion who resisted passive knee extension. Magnetic resonance imaging confirmed the knee effusion and showed a small area of signal enhancement in the distal femoral metaphysis. The erythrocyte sedimentation rate was slightly elevated, the blood leukocyte count and C-reactive protein values were at the upper limits of normal. Immediate knee arthrotomy and irrigation was performed. Synovial fluid was cloudy, but Gram-stained smear and culture were negative. Intravenous vancomycin was given.
The patient was discharged home to receive oral linezolid after several days in hospital, but the next day returned with new fever and increasing pain. The blood leukocyte count, platelet count, and C-reactive protein values were elevated. Blood and urine cultures were negative. Repeat magnetic resonance imaging showed a recurrent knee effusion and a new 1 cm abscess involving the distal femoral metaphysis and epiphysis. The patient underwent immediate repeat arthrotomy (which yielded purulent-appearing synovial fluid) and corticotomy, to drain the abscess. Vancomycin was resumed. Abscess fluid culture yielded fluoroquinolone-resistant E. coli. Antibiotics therapy was changed to ceftriaxone, gentamicin, and rifampin.
Two days postoperatively the corticotomy wound dehisced, pain increased, and knee motion intolerance worsened. Wound irrigation and debridement again yielded fluoroquinolone-resistant E. coli.
Neutropenia and rash prompted discontinuation of ceftriaxone after 7 days. Intravenous gentamicin was then given for 6 weeks, followed by oral TMP-SMZ plus rifampin for an additional 6 weeks, with progressive resolution of all clinical, laboratory, and radiographic abnormalities. An immunodeficiency evaluation was normal. Ten months after the final surgery, the patient had full knee motion, without physeal arrest.
Molecular analysis of the patient's fluoroquinolone-resistant E. coli isolate from the initial corticotomy showed that it derived from phylogenetic group B2 and contained the O25b rfb and H4 fliC variants, consistent with (ST131-associated) serotype O25:H4. ST131 status was confirmed by 7-locus MLST. The isolate's XbaI PFGE profile represented the third most prevalent PFGE type among 157 ST131-associated PFGE types within a private database that includes representatives of this same PFGE type from Chicago, Galveston, Houston, Minneapolis, Omaha, and Seattle (unpublished, J.R.J.). Consistent with its susceptibility to extended-spectrum cephalosporins, the patient's isolate was PCR-negative for bla CTX -M and bla CTX -M- 15.
To identify a possible external source for the patient's fluoroquinolone-resistant E. coli (strain A), both parents' intestinal E. coli population underwent clonal analysis, with and without ciprofloxacin selection. The father exhibited only ciprofloxacin-susceptible E. coli, of 2 different PFGE types (strains B and C), neither representing the daughter's strain. In contrast, the mother exhibited both ciprofloxacin-resistant E. coli (strain A: the daughter's strain) and ciprofloxacin-susceptible E. coli (strain B: one of the father's strains) (Fig. 1).
E. coli ST131 strain A (daughter and mother) exhibited a virulence profile consistent with previously-reported ST131 isolates.4 This included the F10 papA (P fimbriae structural subunit) allele without other pap elements, iha (adhesin-siderophore), fimH (type 1 fimbriae), sat (secreted autotransporter toxin), fyuA (yersiniabactin system), iutA (aerobactin system), kpsM II (group 2 capsule), usp (uropathogenic-specific protein), traT (serum resistance-associated), ompT (outer membrane protease), and malX (pathogenicity island marker) (Table, Supplemental Digital Content 1, http://links.lww.com/INF/A335). In contrast, strains B and C, from phylogenetic group B1, lacked all tested virulence factors except fimH (strains B and C) and fyuA (strain C only). Whereas strain A exhibited resistance to amoxicillin, amoxicillin-clavulanate, cephalothin, ciprofloxacin, and nalidixic acid, plus intermediate susceptibility to streptomycin, strains B and C were susceptible to all 22 agents tested.
This study provides novel evidence of within-household sharing of an ST131 strain between an infected patient and a healthy family member, and adds to the evidence of E. coli ST131 as a fluoroquinolone-resistant but cephalosporin-susceptible pathogen and an invasive extraurinary and pediatric pathogen. This expands our understanding of this important emerging multidrug-resistant E. coli clonal group.
The observed within-household sharing of the index E. coli ST131 strain suggests host-to-host transmission, a possibly important contributor to the as-yet unexplained global dissemination of ST131.4 Within-household sharing of ST131 strains has been documented previously.9,12 It is conceivable that inapparent sharing of E. coli ST131 strains among epidemiologically associated individuals is common. This would be consistent with the extensive within-household strain sharing documented for other E. coli, especially those from group B2 or with multiple extraintestinal virulence traits, as also characterize ST131.8,10,11,13 However, whether in the present instance transmission occurred, and in what direction, remains uncertain.
Most previous reports involving E. coli ST131 have emphasized its association with CTX-M-15.4 However, recent surveys of fluoroquinolone-resistant E. coli from Europe and Canada found that E. coli ST131, although prominent within the study populations, almost always lacked CTX-M-15 and other extended spectrum β-lactamases.4 Since fluoroquinolones are commonly used for treatment of E. coli infections, efforts to control the expansion of ST131 could have broader benefits than simply limiting the emergence of CTX-M-15.
Additional noteworthy findings were the occurrence of invasive disease outside the urinary tract and the patient's young age. Most previously reported ST131 clinical isolates have been from urine or blood.4–7 Our patient had no manifestations suggesting urinary tract infection, and had a sterile urine culture. This implies possible hematogenous dissemination to the site of infection after translocation from the intestinal reservoir or during a transient episode of asymptomatic bacteriuria. This case illustrates the pathogenic versatility of ST131, supporting use of the inclusive designation ExPEC instead of UPEC (uropathogenic E. coli) for ST131 and similar extraintestinal pathogenic lineages. Likewise, although most previously reported ST131 isolates have been from adults, a recent survey identified (antimicrobial-resistant) E. coli ST131 as a prominent cause of neonatal E. coli sepsis (unpublished data, J.R.J.). These findings implicate ST131 as a threatening new drug-resistant pediatric pathogen.
The occurrence of fluoroquinolone-resistant E. coli in children who have not consumed fluoroquinolones had suggested possible acquisition of already-resistant strains from an external source.14 The food supply, which contains fluoroquinolone-resistant E. coli,15 could be the vehicle whereby ST131 strains enter households. Whatever their initial source, the present findings suggest that adult household members may serve as reservoirs of fluoroquinolone-resistant E. coli for acquisition by children within the household, and possibly vice versa.
This material is based upon work supported by Office of Research and Development, Medical Research Service, Department of Veterans Affairs (J.R.J.). Dave Prentiss (VA Medical Center) prepared the figure. The authors thank the study subjects for their participation.
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