6
countries has steadily increased over the years, and is more in humans than in animals (Food and Drug Administration 2012). Resistance to these antibiotics is conferred by a specialized class of beta-lactam ring cleaving enzymes called as
extended- spectrum beta lactamases (ESBLs) and AmpC. Both of these genes are
now found to be present on plasmids and are highly mobile through gene horizontal
transfer (European Medicines Agency 2009). Due to its overuse, resistance to these
antibiotics is often observed in human infections caused by common pathogens
such as E. coli, Salmonella spp. and K. pneumoniae.
Another alarming consequence is the co-transfer (due to the proximity in genetic
loci) of other antibiotic resistance genes (for tetracycline, sulfonamides, aminoglycosides, etc.) with the ESBLs or AmpC. This leads to corresponding co-selection
and enrichment of multi-drug resistant pathogens in affected niches, which are even
more difficult to treat. This has led to drastic decrease in choice of antibiotics for
therapy in these infections and many times carbapenems are left as the last option
(Nordmann 2014). Many studies have found relatedness in ESBL containing E. coli
strains isolated from food, animal and human sample (Jakobsen et al. 2009; Rizzo
et al. 2019; Tadesse et al. 2017; Odsbu et al. 2018). Also, the mode of dissemination
of cephalosporin resistance genes between pathogens of humans and animals has
been found to be through plasmids (de Been et al. 2014). The mass usage of these
antibiotic for metaphylaxis frequently ends up in the environment and directly
through food, further exposing humans to antibiotic resistant microbes (Canadian
Integrated Program for Antimicrobial Resistance 2009). Voluntary stopping the use
of the cephalosporins in hatcheries has shown to bring a drastic decrease in prevalence of cephalosporin resistant microbes in the food animals, in Japan, Denmark
and Canada (Bager et al. 2015; Hiki et al. 2015). The same trend has been observed
regarding the usage of fluoroquinolones and fluoroquinolone resistant bacteria in
food animals remain to be rare in countries like Australia, where its use in food
animals was never approved (Nelson et al. 2007).
Due to emergence of many multi-drug resistant pathogens and limited treatment
options, Colistin is nowadays considered as one of the last resort treatments for
humans infected with multi drug resistant pathogens. Among others, these pathogens include carbapenem-resistant P. aeruginosa, A. baumannii and
Enterobacteriaceae which feature in the WHO priority list of pathogens for which
antibiotics are urgently required (Tacconelli et al. 2018). Due to its toxicity, Colistin
was not preferred earlier for human administration. But limited number of antibiotics and its high potency against multi drug resistant pathogens has made it even
more important in contemporary times, as a last resort antibiotic. However, this
antibiotic is also approved for usage in food animals in many countries, for metaphylaxis and is also used for growth promotion. Recent surveillance of colistin resistance in food animals such as turkey, broilers, poultry etc. in Europe showed the
presence of varying percentage of colistin resistant and multi drug resistant pathogens such as Salmonella enterica. Although, this could be intrinsic resistance in the
microbial population, but the presence of these resistant pathogens in food is definitely a potential hazard to humans. Another great concern was the observation of
the mobilization of a colistin resistance gene (mcr-1) through horizontal gene
K. S. Singh et al.
countries has steadily increased over the years, and is more in humans than in animals (Food and Drug Administration 2012). Resistance to these antibiotics is conferred by a specialized class of beta-lactam ring cleaving enzymes called as
extended- spectrum beta lactamases (ESBLs) and AmpC. Both of these genes are
now found to be present on plasmids and are highly mobile through gene horizontal
transfer (European Medicines Agency 2009). Due to its overuse, resistance to these
antibiotics is often observed in human infections caused by common pathogens
such as E. coli, Salmonella spp. and K. pneumoniae.
Another alarming consequence is the co-transfer (due to the proximity in genetic
loci) of other antibiotic resistance genes (for tetracycline, sulfonamides, aminoglycosides, etc.) with the ESBLs or AmpC. This leads to corresponding co-selection
and enrichment of multi-drug resistant pathogens in affected niches, which are even
more difficult to treat. This has led to drastic decrease in choice of antibiotics for
therapy in these infections and many times carbapenems are left as the last option
(Nordmann 2014). Many studies have found relatedness in ESBL containing E. coli
strains isolated from food, animal and human sample (Jakobsen et al. 2009; Rizzo
et al. 2019; Tadesse et al. 2017; Odsbu et al. 2018). Also, the mode of dissemination
of cephalosporin resistance genes between pathogens of humans and animals has
been found to be through plasmids (de Been et al. 2014). The mass usage of these
antibiotic for metaphylaxis frequently ends up in the environment and directly
through food, further exposing humans to antibiotic resistant microbes (Canadian
Integrated Program for Antimicrobial Resistance 2009). Voluntary stopping the use
of the cephalosporins in hatcheries has shown to bring a drastic decrease in prevalence of cephalosporin resistant microbes in the food animals, in Japan, Denmark
and Canada (Bager et al. 2015; Hiki et al. 2015). The same trend has been observed
regarding the usage of fluoroquinolones and fluoroquinolone resistant bacteria in
food animals remain to be rare in countries like Australia, where its use in food
animals was never approved (Nelson et al. 2007).
Due to emergence of many multi-drug resistant pathogens and limited treatment
options, Colistin is nowadays considered as one of the last resort treatments for
humans infected with multi drug resistant pathogens. Among others, these pathogens include carbapenem-resistant P. aeruginosa, A. baumannii and
Enterobacteriaceae which feature in the WHO priority list of pathogens for which
antibiotics are urgently required (Tacconelli et al. 2018). Due to its toxicity, Colistin
was not preferred earlier for human administration. But limited number of antibiotics and its high potency against multi drug resistant pathogens has made it even
more important in contemporary times, as a last resort antibiotic. However, this
antibiotic is also approved for usage in food animals in many countries, for metaphylaxis and is also used for growth promotion. Recent surveillance of colistin resistance in food animals such as turkey, broilers, poultry etc. in Europe showed the
presence of varying percentage of colistin resistant and multi drug resistant pathogens such as Salmonella enterica. Although, this could be intrinsic resistance in the
microbial population, but the presence of these resistant pathogens in food is definitely a potential hazard to humans. Another great concern was the observation of
the mobilization of a colistin resistance gene (mcr-1) through horizontal gene
K. S. Singh et al.