NOTES ON ANTIBIOTIC RESISTANCE
                        Brenda Rashleigh
                             3/8/95

*  Shortly after development of antibiotics, which occurred about
the time of WWII, doctors found that pathogenic bacteria could
develop mutations that made them resistant to the antibiotic, or
enabled them to destroy the antibiotic.

*  The development of resistance is correlated with the level of
antibiotic use (Cohen, 1992), and overuse of antibiotics has
therefore increased the number of resistance-conferring mutations.
Dr. Jernigan (pers. comm.) describes the major contributors to
increased resistance include prophylactic use (such as before
surgery) and empiric use (when the cause is unknown).

*  In hospitals, particularly, there has been an increased use of
broad spectrum antibiotics which have contributed to the problem of
resistance.

*  A reservoir for the disease, either animate or inanimate, is
important for transmission, and frequently the hospital serves as
the reservoir.

*  The hospital and the community can be considered as separate
systems that interact with eachother in the epidemiology of
antibiotic resistance (Cohen, 1992).

*  A common way the mutation develops is when a patient does not
complete a cycle of antibiotics and does not completely kill the
pathogen, which has been a problem particularly in the treatment of
TB in AIDS patients.

* Attendant-borne transmission in hospitals is a significant source
of transmission.

*  Particular problem areas for transmission in the community
include child day-care facilities, nursing homes, and correctional
facilities.

*  Transmission routes of antibiotic resistance bacteria are the
same as for non-resistant bacteria: fecal-oral transmission,
foodborne transmission, sexual transmission, and respiratory
transmission.

*  Several factors are contributing to increased levels of
transmission in recent years: increased travel, especially
international travel; living conditions in areas such as inner
cities and developing countries becoming increasingly conducive to
disease transmission through overcrowding, poor nutrition, and poor
sanitation.

*  There has been an increase in the number of citizens who tend to
be most susceptible to infection, such as the elderly and the
immuno-compromised (due to HIV, cancer treatment, organ
transplants)-- Wallace (1989) has suggested that these increasingly
large pools of susceptible individuals could possibly serve as an
avenue for pathogens to become more virulent.

*  A problem with control of antibiotic resistance is that bacteria
can exchange genetic material, and resistance can be transferred
among strains and/or between species (Travis, 1994; Davies, 1994).

*  Historically, the way to combat antibiotic resistance in a
patient was to use a different antibiotic, but now we are running
out of new types to try. 

* Two new strategies in combating antibiotic resistance are 1.
fighting the mutations of bacteria (i.e., combination therapy)
(Page, 1994); and 2. "Darwinian reversal," fighting the mutant
pathogen with the unmutated pathogen (Goldhaber, 1994).   

*Most models assume that there is a cost to resistance which would
cause resistance to decline in the absence of antibiotic use. 
However, Holtzman et al. (1980) studied resistant and non resistant
strains of S. aureus and found that they appeared similar in
virulence and that there was no difference in the rate that the two
were acquired.