Background: Antimicrobial resistance is a serious public-health problem throughout the world. Escherichia coli, the most common Gram-negative microorganism, has developed different resistance mechanisms, making treating infections difficult. Colistin is considered a last-resort drug in the treatment of infections caused by E. coli. Plasmid-mediated mobile-colistin-resistant (mcr) genes in E. coli, now disseminated globally, are considered a major public-health threat. Humans, chickens, and pigs are the main reservoirs for E. coli and the sources of antibiotic resistance. Hence, an up-to-date and precise estimate of the global prevalence of mcr resistance genes in these reservoirs is necessary to understand more precisely the worldwide spread and to more effectively implement control and prevention strategies. Methodology: Publications were identified in the PubMed database on the basis of the PRISMA guidelines. English full-text articles were selected from December 2014 to March 2021. Descriptive statistics and a meta-analysis were performed in Excel and R software, respectively. Colistin resistance was defined as the molecular-genetic detection of the mcr genes. The crude and estimated prevalence were calculated for each host and continent. The studies were divided into two groups; community-based when they involved isolates from healthy humans, chickens, or pigs, and clinical studies when they involved only hospital, outpatient, or laboratory isolates. Results: A total of 1278 studies were identified and 218 were included in this systematic review and meta-analysis, divided into community studies (159 studies) and clinical studies (59 studies). The general prevalence of mcr-mediated colistin-resistant E. coli (mcrMCRE) was 6.51% (n = 11,583/177,720), reported in 54 countries and on five continents; Asia with 119 studies followed by Europe with 61 studies registered the most articles. Asia reported the major diversity of mcr-variants (eight of nine, except mcr-2). Worldwide, chickens and pigs proved to be the principal reservoir of mcr with an estimated prevalence of 15.8% and 14.9%, respectively. Healthy humans and clinical isolates showed a lower prevalence with 7.4% and 4.2% respectively. Conclusions: In this systematic review and meta-analysis, the worldwide prevalence of mcr in E. coli isolated from healthy humans, chickens, and pigs was investigated. A wide prevalence and distribution of mcr genes was demonstrated on all continents in E. coli isolates from the selected reservoirs. Understanding the epidemiology and occurrence in the reservoirs of mcr in E. coli on different continents of the world facilitates tracing how mcr genes are transmitted and determining the infection risks for humans. This knowledge can be used to reduce the incidence of zoonotic transmission by implementing the appropriate control programs.

To determine the prevalence of CTX-M β-lactamase-producing Enterobacteriaceae and to study the risk factors associated with faecal carriage in asymptomatic rural Thai people. In all, 417 stool samples were obtained from rural Thai people and screened for extended-spectrum β-lactamases (ESBLs) using MacConkey agar supplemented with 2 mg/L cefotaxime. Results were confirmed using cefotaxime and ceftazidime with and without clavulanic acid. The bla_CTX-M genes were identified and genotyped using PCR with bacterial DNA samples. Multivariate analysis was performed to investigate risk factors associated with the faecal carriage of CTX-M producers. The prevalence of CTX-M-type ESBL-producing Enterobacteriaceae was 65.7%. The CTX-M-9 group (60.6%) was dominant, followed by the CTX-M-1 group (38.7%). Most of the bacteria were Escherichia coli (85.4%) and Klebsiella pneumoniae (4.7%). Of a total of 234 E. coli strains, 48.7% belonged to phylogenetic group A, 28.6% to group B1, 15.8% to group D and 6.8% to group B2. Most CTX-M producers were susceptible to carbapenems and amikacin, but resistant to tetracycline and gentamicin. In a multivariate logistic regression model, better education status (OR 2.245; 95% CI 1.297–3.884), history of hospitalization (OR 1.643; 95% CI 1.036–2.603) and the use of antibiotics within the last 3 months (OR 1.883; 95% CI 1.221–2.903) were independently associated with faecal carriage. Faecal carriage of CTX-M-type ESBL-producing Enterobacteriaceae among asymptomatic individuals in rural Thailand remains alarmingly high, and previous antibiotic use and a history of hospitalization may contribute to its dissemination.

To determine the prevalence of CTX-M β-lactamase-producing Enterobacteriaceae in stool specimens obtained from healthy individuals in a rural area of Thailand. Bacteria in stool specimens were screened for extended-spectrum β-lactamase (ESBL) production on McConkey agar with cefotaxime and confirmed by the double-disc synergy test. Genetic detection and genotyping of CTX-M-type ESBL was performed by PCR with bacterial DNA extracted from isolates. A markedly high number (82 of 141, 58.2%) of the specimens showed the presence of CTX-M β-lactamase-producing Enterobacteriaceae, as confirmed by both phenotypic and genetic examinations. The majority of the CTX-M β-lactamase-producing bacteria were Escherichia coli (85.1%). The study revealed the wide dissemination of CTX-M β-lactamase-producing Enterobacteriaceae in the healthy population.

The prevalence of and risk factors associated with extended-spectrum β-lactamase (ESBL)-producing micro-organisms have not been well studied in healthy individuals. The aim of this study was to determine this in healthy individuals in Thailand. Stool samples and questionnaires obtained from 445 participants from three provinces in Thailand were analysed. The antimicrobial susceptibility of the isolates was assessed using phenotypic and genotypic methods. PCR analysis was performed to detect and group the bla_CTX-M genes. The prevalence of CTX-M-type ESBL-producing Enterobacteriaceae in the three provinces was as follows: 29.3 % in Nan (43/147), 29.9 % in Nakhon Si Thammarat (43/144) and 50.6 % in Kanchanaburi (78/154) (P<0.001). Of the 445 samples, 33 (7.4 %), 1 (0.2 %) and 127 (28.5 %) isolates belonged to the bla_CTX-M gene groups I, III and IV, respectively. Escherichia coli was the predominant member of the Enterobacteriaceae producing CTX-M-type ESBLs (40/43, 39/43 and 70/78 isolates in Nan, Nakhon Si Thammarat and Kanchanaburi, respectively). No statistically significant association was observed between the presence of ESBL-producing bacteria and gender, age, education, food habits or antibiotic usage. However, the provinces that had the highest prevalence of ESBL-producing Enterobacteriaceae also had the highest prevalence of use and purchase of antibiotics without a prescription. Thus, this study revealed that faecal carriage of ESBL-producing Enterobacteriaceae is very high in asymptomatic individuals in Thailand, with some variations among the provinces. This high prevalence may be linked to antibiotic abuse.

Elucidation of the mechanism of the wide dissemination of colistin-resistant bacteria in communities of developing countries is an urgent public health issue. In this study, we investigated the genetic background of the colistin resistance gene mcr in E. coli isolates from the fecal microbiota of healthy human residents living in a community in Vietnam with a high prevalence of colistin-resistant E. coli . Our study revealed for the first time, a surprisingly high percentage (36.8%) of colistin-resistant E. coli carrying chromosomal mcr-1 , the emergence of which may have occurred recently, in the fecal microbiota of the community residents. The mcr-1 transposon on the chromosome may develop into a more stable genotype by the loss of insertion sequences (ISs). Our results are valuable in understanding the mechanism underlying the increasing prevalence of colistin-resistant bacteria within a community.