Author: Brendan Trafford
Antibiotic resistance prevalence in humans, animals and environments around the world:
MRSA prevalence throughout human populations is broken into two major categories. The first one is community-associated MRSA (CA-MRSA) which is MRSA infections from someone who has not been in a hospital or operated in within the last year (New York Dept. of Health, 2007). These types of infections are most commonly seen in athletes, prisoners and people who work/live in crowded settings. On the other hand, Healthcare-associated MRSA (HA-MRSA) is a MRSA infection that occurred in someone who has recently had surgery or someone who frequently visits healthcare facilities. The extremely worrisome aspect of HA-MRSA is it usually has resistance to multiple antibiotics because it has a higher chance of being exposed to sublethal dosages of antibiotics within a healthcare facility (Lindsay, 2013). MRSA infections almost always start out as boils on the skin that have a high amount of puss and are accompanied by a fever. The real danger in MRSA is its ability to move from a skin infection through the blood and then infect other organs (David and Daum, 2010)
On average the 20-30% of people in this world naturally carry Staphylococcus Aureus, but the distressing aspect of this is that MRSA prevalence within this subset of bacteria is increasing. In a study done in Quebec from 1991 to 2005 it was found that MRSA occurrence went from 0% of the population to 0.0074% respectively. Although these numbers seem relatively low, this trend of increasing MRSA occurrence within populations is happening in North America, Asia and almost all parts around the world (Tong et al., 2015). In a study of the United States, it was found that doctor visits for abscesses and cellulitis increased from 17.3 to 32.5 per 100,000 persons from 1997 to 2005, respectively. This increase was largely due to MRSA bacterium which worries scientists because it is going to be more difficult to fight these infections when most antibiotics are ineffective (David and Daum, 2010). Recently, there have been a wave of genomic markers discovered that are associated with CA-MRSA. Majority of CA-MRSA cases obtained from University of Chicago Medical Center include a Panton-Valentine Leukocidin gene and SCCmec type IV/V (David and Daum, 2010). The PVL gene is a gene that codes for an exotoxin that increases virulence and the SCCmec type IV/V are newer forms of the mec gene mentioned above that offer different ways for MRSA to resist antibiotics (Vandenesch et al., 2003). In a report done in 2017 scientists found varying MRSA strains resistant to one or multiple antibiotics (Akanbi et al., 2017). These resistant genes included strains resistant to vancomycin, penicillin, methicillin, chloramphenicol and 12 other antibiotics (Akanbi et al., 2017). With so many strains and resistances in the gene pool finding a consistent and effective treatment for these bacteria seems highly unlikely.
HA-MRSA is MRSA contracted while being treated at a healthcare facility. These forms of MRSA are usually deadlier because of their resistance to multiple antibiotics and people who are at hospitals are more likely to be immunocompromised which can lead to more life-threatening infections. According to a study done by Klein et al. MRSA related hospitalizations doubled from 127,036 to 278,203 in the years 1999 to 2005 (Klein et al., 2007) In more recent studies it has been shown that HA-MRSA infections have grown in the United States to over 2 million cases per year (Fukunaga et al., 2016). These number not only show the increase of MRSA across the United States but, the progression increases in hospitals at a higher rate. A study of dental healthcare facilities in the middle east found 34 out of 863 bacteria isolates on workers or surfaces had antibiotic resistance (Khairalla et al., 2017). Of those 34 isolates 24 of them had resistances to multiple antibiotics. Seeing as many patients could encounter these workers/surfaces during surgical procedures the chances for infection are very high (Khairalla et al.)
Not only are the occurrences of HA-MRSA increasing but so is the genetic variation. In the dental study mentioned above there were multiple forms of the mec gene, a vanA gene, PVL (gene for producing exotoxins) and toxic shock syndrome gene (a localized exotoxin that can spread throughout the body through the bloodstream) (Khairalla et al., 2017) This proves that not only is MRSA finding multiple ways to resist one or more antibiotics but, it has multiple ways to attack the body. Another study showed that variation in MRSA genes depended on the countries; In the United States the CC5-SCCmecII, CC5-SCCmecIV and CC8-SCCmecIV genes were most common but, in the UK CC22-SCCmecIV and CC30-SCCmecII were the most common in healthcare facilities (Lindsay, 2013). This shows that not only are there many variants of the disease but, depending on what antibiotics it is exposed to or what climate the bacteria exists will naturally select for different strains. This will become a prominent issue in the future because we may need many varying cures for different forms of MRSA because they are so genetically different depending on where you are in the world.
MRSA prevalence is not restricted to humans; In recent years many journals have published findings in natural environments and within livestock. In a 2012 report done by the FDA, it was found that 14.7 million kg of antibiotics sold in the United States were for use in food-producing animals (Survey Report…, 2013). Congresswoman Louise Slaughter (D-NY) was able to confirm the amount of antibiotics shown above was 80% of all antibiotics sold that year (Most antibiotic use…, 2011). There are virtually no policies existing in the United States and around the world to control the use of antibiotics in livestock. The effects of this can be seen in a study done by van Belkum et al. in which it was shown that the ST398 MRSA strain derived from pigs can also infect humans (van Belkum et al., 2008). This phenomenon was also seen to happen with bovine forms of the MRSA bacteria; When a MRSA strain’s genome sequenced from the mastitis in a cow it was found to be indistinguishable from the MRSA present in the caretaker of the cow (Juhász-Kaszanyitzky et al., 2007). There are two major takeaways that come from these studies; the first being that MRSA strains can occur in other species of mammals that are constantly exposed to high amounts of unregulated antibiotic use. The second being these zootic MRSA strains that can share genomic material with human forms of MRSA or in other cases mutate to be able to infect humans.
Picture of MRSA skin Infection. Provided by (Methicillin)
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