Time taken to travel to work by region of workplace: Great Britain, October to
3. Knowle: South-east Baptist Church 4 Windmill Hill: South-west Baptist Church.
4.4. Approach to sample groups:
4.5.1 Phase 1: Participant Observation
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Infections caused by K. pneumoniae include lobar pneumonia (especially in immunocompromised and other high risk patient groups) 111 and UTIs.112
The vast majority of Klebsiella infections, however, are associated with hospitalization. Klebsiella has been incriminated in 8% of all nosocomial bacterial infections. The most common foci for such infections are the urinary tract, lower respiratory tract, biliary tract, and surgical wound sites, in that order. Invasive devices found in hospitalized patients, particularly urinary catheters, endotracheal tubes, and intravenous catheters, markedly increase the disposition to nosocomial infections, particularly gram-negative rods. Like most gram-negative organisms found in the hospital environment, Klebsiella is characteristically resistant to multiple antibiotics. Klebsiella is naturally resistant to ampicillin and carbenicillin, and increasing acquisition of R plasmids is mediating drug resistance to cephalosporins and aminoglycosides with increased frequency.101 Especially feared are epidemic hospital infections caused by multidrug-resistant strains. Strains that produce ESBLs, which make them resistant to extended-spectrum cephalosporins, have evolved. The hallmark of these strains, resistance to ceftazidime, is observed in both K. pneumoniae and K. oxytoca isolates. 111
antimicrobial-44
resistant pathogens now threatens these advances. Selective pressure favouring resistant strains arises from misuse and overuse of antimicrobials (notably extended-spectrum cephalosporins), increased numbers of immunocompromised hosts, lapses in infection control, increased use of invasive procedures and devices, and the widespread use of antibiotics in agriculture and animal husbandry.
Antimicrobial resistance, the ability of a micro- organism to resist the action of antimicrobial agents at concentrations achievable in the body after normal dosage, has resulted in increased morbidity and mortality as well as higher healthcare costs.
113
Three biological processes contribute to the accumulation of bacterial drug resistance: new selection, gene epidemics and strain epidemics. New resistance emerges by (i) the advantaging of entire species, (ii) by mutation, and (iii) by the escape of resistance genes to mobile DNA. 114 These are expressed in the various mechanisms of resistance to beta-lactam antibiotics seen in enterobacteriaceae.
One mechanism is by destruction of beta-lactam antibiotic either by increased production of lactamase, modification of the structure of resident beta-lactamase or by importation of new beta-beta-lactamase(s) with different spectrum of activity. Another is by decrease in concentration of beta-lactam antibiotic inside cell either by the restriction of entry of the beta lactam antibiotic (loss of porins) or by efflux mechanisms.115
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Resistance to third generation oxyimino- cephalosporins arose via mutations that increase chromosomal beta-lactamase expression. Organisms with this mode of resistance now account for 30 – 40% of initial Enterobacter isolates from clinical specimens. Cephalosporin resistance was slower to accumulate in Escherichia and Klebsiella spp., where single mutations cannot readily cause chromosomal beta-lactamase hyperprodution. Nevertheless mutation of its structural gene has resulted in the emergence of extended-spectrum beta-lactamases in Klebsiella pneumoniae.116
At functional level, most resistance in Enterobacteriaceae involves the interplay of an endogenous or acquired beta-lactamase along with natural or up-regulated impermeability and efflux.116
BETA-LACTAMASES
Since β-lactam antibiotics came into clinical use, β-lactamases have coevolved with them.117 Early events were an increase in their prevalence in organisms in which the enzyme was known but uncommon (such as Staphylococcus aureus) and spread to pathogens that previously lacked β-lactamase (namely, Haemophilus influenzae and Neisseria gonorrhoeae). Beginning about 20 years ago, agents that shared the property of resistance to the then-common β-lactamases were introduced; they included cephamycins, cephalosporins with an oxyimino side chain, carbapenems, and the monobactam aztreonam.118 Emergence of resistance to
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beta -lactam antibiotics began even before the first beta -lactam, penicillin, was developed. The first beta -lactamase was identified in Escherichia coli prior to the release of penicillin for use in medical practice. The age of penicillin saw the rapid emergence of resistance in Staphylococcus aureus due to a plasmid-encoded penicillinase. This beta -lactamase quickly spread to most clinical isolates of S.
aureus as well as other species of Staphylococci.118
Many genera of gram-negative bacteria possess a naturally occurring, chromosomally mediated beta -lactamase. These enzymes are thought to have evolved from penicillin-binding proteins, with which they show some sequence homology. This development was likely due to the selective pressure exerted by beta-lactam-producing soil organisms found in the environment. Beta-lactamases of gram-negative bacteria are encoded either in chromosomes or in plasmids, and they may be constitutive or inducible. The plasmids can be transferred between bacteria by conjugation. These enzymes can hydrolyze penicillins, cephalosporins, or both.119
The first plasmid-mediated beta-lactamase in gram-negatives, TEM-1, was described in the early 1960s. The TEM-1 enzyme was originally found in a single strain of E. coli isolated from a blood culture from a patient named Temoniera in Greece, hence the designation TEM. Being plasmid and transposon mediated has facilitated the spread of TEM-1 to other species of bacteria, with this spread
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occurring first in hospital isolates, and later, in the community. Within a few years after its first isolation, the TEM-1 beta -lactamase spread worldwide and is now found in many different species of members of the family Enterobacteriaceae, Pseudomonas aeruginosa, Haemophilus influenzae, and Neisseria gonorrhoeae.
Another common plasmid-mediated beta -lactamase found in Klebsiella pneumoniae and E. coli is SHV1 (for sulphydryl variable). The SHV1 beta -lactamase is chromosomally encoded in the majority of isolates of K. pneumoniae but is usually plasmid mediated in E. coli.118 However, there is an inconsistent correlation between the susceptibility of an antibiotic to inactivation by beta-lactamase and the ability of that antibiotic to kill the microorganism.
With the development of penicillin-β-lactamase inhibitor combinations, other resistance factors evolved. Acquired resistance to penicillin-β-lactamase inhibitor combinations in enterobacteriaceae may be due to: (i) penicillinase hyperproduction due to the presence of the blaTEM-1 gene in small multi-copy plasmids or strong promoters; (ii) overproduction of constitutive AmpC cephalosporinase; and (iii) OXA-type and inhibitor-resistant TEM (IRT) β-lactamases.120 IRT enzymes emerge via mutational events from TEM-1 or TEM-2 β-lactamases that affect substrate affinity for β-lactamase inhibitors. They are mainly isolated in urinary infections from community patients. Prevalence is
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variable, depending on geographical area, detection methods and potential selection pressure.120
ESBLs have evolved greatly over the last 20 years. To combat TEM and similar beta-lactamases, pharmaceutical companies developed new beta-lactamase stable compounds during the 1970s and 1980s. These included oxyimino third generation cephalosporins such as cefotaxime, ceftriaxone and ceftazidime and also cephamycins and carbapenemes. Along with quinolones the oxyimino-cephalosporins have become the preferred antibiotics in many hospitals worldwide.
Bacteria responded with a plethora of “new” β-lactamases — including extended-spectrum β-lactamases (ESBLs), plasmid-mediated AmpC enzymes, and carbapenem-hydrolyzing β-lactamases (carbapenemases) — that, with variable success, can confer resistance to the latest β-lactam antibiotics.121
These beta-lactamase enzymes have one or more amino acid substitutions resulting in an altered configuration of the active serine site that increases the substrate spectrum. Specifically, these mutations have opened this active serine site to accommodate the large oxyimino side chain.122 Many ESBLs are generated by mutations in genes coding for broad-spectrum enzymes, which have been mobile since at least the 1960s and which have disseminated very widely in populations of pathogenic bacteria. The largest groups are the mutants of TEM and SHV β-lactamases with over 150 representatives. The second large group of ESBLs is the
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CTX-M type. Based on sequence homology, these divide into five sub-groups, with around 40 members in total. At least two and probably all, of these evolved via the escape of chromosomal beta lactamase genes from Kluyvera species, an enterobacterial genus of little clinical importance. Having migrated to mobile DNA, CTX-M β-lactamase genes may evolve further, for example by undergoing mutations that increase activity against ceftazidime.116
Aside from the main TEM, SHV and CTX-M families there is a further scatter of ESBL types, including SFO, BES, BEL, TLA, GES, PER and VEB types each with a handful of representatives distinguished by minor sequence variations.
While several of these latter are rarely identified, or are very localised, others are becoming locally prevalent, or are increasingly isolated worldwide.123 Also the same process of point mutation that confers ESBL activity in TEM and SHV families can also occur among class D enzymes. Thus, OXA-15 is an ESBL mutant of the OXA-2 penicillinase with one or two amino-acid substitution.116
In summary, first described in 1983, ESBLs have now been described in a range of Enterobacteriaceae and Pseudomonadaceae from different parts of the world. They are most often identified in Klebsiella pneumoniae and Escherichia coli. The majority of ESBLs identified in clinical isolates to date, have been SHV or TEM types, which have evolved from narrow-spectrum ß-lactamases such as TEM-1, -2 and SHV-1. The CTX-M enzymes have originated from Kluyvera spp., and
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recently gained prominence in Enterobacteriaceae. More than 300 natural ESBL variants have been identified since the mid-1980s but in-vitro studies suggest that ESBL evolution has certainly not come to an end; they may also help in predicting future developments.124