The withdrawal of antimicrobial treatment as a mechanism for defeating resistant microorganisms

Neonatal sepsis in rural India: timing, microbiology and antibiotic resistance in a population-based prospective study in the community setting

OBJECTIVE

To examine the timing and microbiology of neonatal sepsis in a population-based surveillance in the Indian community setting.

STUDY DESIGN

All live born infants in 223 villages of Odisha state were followed at home for 60 days. Suspect sepsis cases were referred to study hospitals for further evaluation including blood culture.

RESULTS

Of 12 622 births, 842 were admitted with suspected sepsis of whom 95% were 4 to 60 days old. Culture-confirmed incidence of sepsis was 6.7/1000 births with 51% Gram negatives (Klebsiella predominating) and 26% Gram positives (mostly Staphylococcus aureus). A very high level of resistance to penicillin and ampicillin, moderate resistance to cephalosporins and extremely low resistance to Gentamicin and Amikacin was observed.

CONCLUSION

The bacterial burden of sepsis in the Indian community is not high. Judicious choice of empiric antibiotics, antibiotic stewardship and alternate modalities should be considered for the management or prevention of neonatal sepsis in India.

Genetic mechanisms of antimicrobial resistance identified in Salmonella enterica, Escherichia coli, and Enteroccocus spp. isolated from U.S. food animals

The prevalence of antimicrobial resistance (AR) in bacteria isolated from U.S. food animals has increased over the last several decades as have concerns of AR foodborne zoonotic human infections. Resistance mechanisms identified in U.S. animal isolates of Salmonella enterica included resistance to aminoglycosides (e.g., alleles of aacC, aadA, aadB, ant, aphA, and StrAB), β-lactams (e.g., bla_{CMY−2, TEM−1, PSE−1}), chloramphenicol (e.g., floR, cmlA, cat1, cat2), folate pathway inhibitors (e.g., alleles of sul and dfr), and tetracycline [e.g., alleles of tet(A), (B), (C), (D), (G), and tetR]. In the U.S., multi-drug resistance (MDR) mechanisms in Salmonella animal isolates were associated with integrons, or mobile genetic elements (MGEs) such as IncA/C plasmids which can be transferred among bacteria. It is thought that AR Salmonella originates in food animals and is transmitted through food to humans. However, some AR Salmonella isolated from humans in the U.S. have different AR elements than those isolated from food animals, suggesting a different etiology for some AR human infections. The AR mechanisms identified in isolates from outside the U.S. are also predominantly different. For example the extended spectrum β-lactamases (ESBLs) are found in human and animal isolates globally; however, in the U.S., ESBLs thus far have only been found in human and not food animal isolates. Commensal bacteria in animals including Escherichia coli and Enterococcus spp. may be reservoirs for AR mechanisms. Many of the AR genes and MGEs found in E. coli isolated from U.S. animals are similar to those found in Salmonella. Enterococcus spp. isolated from animals frequently carry MGEs with AR genes, including resistances to aminoglycosides (e.g., alleles of aac, ant, and aph), macrolides [e.g., erm(A), erm(B), and msrC], and tetracyclines [e.g., tet(K), (L), (M), (O), (S)]. Continuing investigations are required to help understand and mitigate the impact of AR bacteria on human and animal health.

Impact of a hospital-wide antibiotic restriction policy program on the resistance rates of nosocomial Gram-negative bacteria

BACKGROUND

To evaluate the impact of an antibiotic restriction policy on antibiotic consumption and Gram-negative resistance rates, in an environment of antibiotic overconsumption and increasing resistance rates for nosocomial pathogens.

METHODS

The study was a 'before and after' trial of 18-month duration; the antibiotic restriction policy program was implemented in 1998-2000 and was based on a government program addressed by the Ministry of Health to public hospitals on a national basis. This included prescribing of all newer antibiotics on an order form, auditing of the order forms and consultation with infectious diseases (ID) specialists, dispensing of treatment and prophylaxis guidelines, feedback, and face-to-face education. Antibiotic consumption and Gram-negative resistance rates were recorded before and after the intervention.

RESULTS

Despite the addition of a new 40-bed ID department in the hospital during the 'after' period, the consumption of restricted antibiotics was significantly reduced by 42% (and their cost by 31%). Gram-negative resistance rates for Pseudomonas, Klebsiella, and Enterobacter, serving as index microorganisms for Gram-negative nosocomial pathogens, were significantly reduced during the 'after' period, even against antibiotics for which there was an increase in consumption.

CONCLUSIONS

Multidisciplinary restriction programs can reduce antibiotic consumption and Gram-negative resistance rates in the hospital setting.

Analysis of risk factors associated with antibiotic-resistant Escherichia coli

Antimicrobial-resistant bacteria represent a major threat to human and animal health. We compared equine fecal samples (n=264) from 138 horses from hospital and nonhospital (livery stable and riding school) premises in North West England to determine the prevalence of Escherichia coli, Salmonella, and Campylobacter and rates of antimicrobial-resistant E. coli strains. Campylobacter jejuni was detected only in hospitalized horses (1.1%), and no Salmonella was identified. Data analysis of the horses' management and veterinary treatments (Tx) identified risk factors associated with shedding of antimicrobial-resistant E. coli. The hospital was the major source of resistant and multi-drug-resistant (MDR) E. coli. Moreover, shedding of antimicrobial-resistant E. coli was associated significantly with hospitalization for a gastrointestinal problem (odds ratio [OR]:±95% confidence intervals=8.50:1.79-40.32), receipt of oral antimicrobial Tx (OR=3.52:1.11-11.10), multiple antimicrobial Tx in hospital (OR/Tx=1.05:1.01-1.09), or geldings (OR=4.62:1.23-17.46). Interestingly, intravenous antimicrobial Tx was negatively associated with shedding of antimicrobial-resistant E. coli (OR=0.18:0.04-0.76). MDR E. coli was associated with hospitalization, antimicrobial Tx in hospital (OR/Tx=3.65:1.54-8.68), and increased age (OR/year=1.11:1.03-1.19). Thus, equine hospitals in this geographic location appear to be an important source of antimicrobial-resistant and MDR E. coli strains, but unlikely reservoirs of Salmonella or Campylobacter. Thus, it is important to moderate antimicrobial Tx given to hospitalized horses to lessen exposure and fecal shedding of resistant pathogens.

Distribution and characterization of ampicillin- and tetracycline-resistant Escherichia coli from feedlot cattle fed subtherapeutic antimicrobials

Background

Feedlot cattle in North America are routinely fed subtherapeutic levels of antimicrobials to prevent disease and improve the efficiency of growth. This practice has been shown to promote antimicrobial resistance (AMR) in subpopulations of intestinal microflora including Escherichia coli. To date, studies of AMR in feedlot production settings have rarely employed selective isolation, therefore yielding too few AMR isolates to enable characterization of the emergence and nature of AMR in E. coli as an indicator bacterium. E. coli isolates (n = 531) were recovered from 140 cattle that were housed (10 animals/pen) in 14 pens and received no dietary antimicrobials (control - 5 pens, CON), or were intermittently administered subtherapeutic levels of chlortetracycline (5 pens-T), chlortetracycline + sulfamethazine (4 pens-TS), or virginiamycin (5 pens-V) for two separate periods over a 9-month feeding period. Phenotype and genotype of the isolates were determined by susceptibility testing and pulsed field gel electrophoresis and distribution of characterized isolates among housed cattle reported. It was hypothesized that the feeding of subtherapeutic antibiotics would increase the isolation of distinct genotypes of AMR E. coli from cattle.

Results

Overall, patterns of antimicrobial resistance expressed by E. coli isolates did not change among diet groups (CON vs. antibiotic treatments), however; isolates obtained on selective plates (i.e., M^A,M^T), exhibited multi-resistance to sulfamethoxazole and chloramphenicol more frequently when obtained from TS-fed steers than from other treatments. Antibiograms and PFGE patterns suggested that AMR E. coli were readily transferred among steers within pens. Most M^T isolates possessed the tet(B) efflux gene (58.2, 53.5, 40.8, and 50.6% of isolates from CON, T, TS, and V steers, respectively) whereas among the M^A (ampicillin-resistant) isolates, the tem1-like determinant was predominant (occurring in 50, 66.7, 80.3, and 100% of isolates from CON, T, TS, and V steers, respectively).

Conclusions

Factors other than, or in addition to subtherapeutic administration of antibiotics influence the establishment and transmission of AMR E. coli among feedlot cattle.

Antimicrobial resistance in beef and dairy cattle production

Observational studies of cattle production systems usually find that cattle from conventional dairies harbor a higher prevalence of antimicrobial resistant (AMR) enteric bacteria compared to organic dairies or beef-cow operations; given that dairies usually use more antimicrobials, this result is not unexpected. Experimental studies have usually verified that application of antimicrobials leads to at least a transient expansion of AMR bacterial populations in treated cattle. Nevertheless, on dairy farms the majority of antibiotics are used to treat mastitis and yet AMR remains relatively low in mastitis pathogens. Other studies have shown no correlation between antimicrobial use and prevalence of AMR bacteria including documented cases where the prevalence of AMR bacteria is non-responsive to antimicrobial applications or remains relatively high in the absence of antimicrobial use or any other obvious selective pressures. Thus, there are multi-factorial events and pressures that influence AMR bacterial populations in cattle production systems. We introduce a heuristic model that illustrates how repeated antimicrobial selection pressure can increase the probability of genetic linkage between AMR genes and niche- or growth-specific fitness traits. This linkage allows persistence of AMR bacteria at the herd level because subpopulations of AMR bacteria are able to reside long-term within the host animals even in the absence of antimicrobial selection pressure. This model highlights the need for multiple approaches to manage herd health so that the total amount of antimicrobials is limited in a manner that meets animal welfare and public health needs while reducing costs for producers and consumers over the long-term.