Correlation between frequency of isolated bacteria and sex
Significant differences in the frequency of isolated bacteria between
various sexes of the horses were not indicated (p>0.05).
Obviously, due to the isolation of each of Listeria
monocytogenes , Actinomyces spp., Mannheimia haemolytica,and Corynebacterium bovis from only one individual horse,
statistical analysis is impossible.
Discussion
The Conjunctiva of the eye is a mucosal surface which is colonized by
different bacteria. Following surgeries, trauma, or other underlying
conditions the normal flora of the conjunctiva may cause some kinds of
infections in the eye including conjunctivitis, keratitis, or
endophthalmitis (Sthapit and Tuladhar, 2014). Staphylococcus,
Streptococcus, Corynebacterium, and Bacillus spp. are the most common
gram-positive bacteria isolated from normal equine eyes(Hampson et al.,
2019). Conjunctiva and cornea have a very strong unique immune system
against infections which consists of tear, phagocytosis, mechanical
barriers, and bacteriostatic functions of lysozyme (Sousa et al., 2011).
Any agents including stress, dysfunctions of the immune system, and
systemic as well as traumatic diseases that cause an imbalance of the
mentioned immune system can put the eye at risk of probable infections
with internal and external origins(Rosa et al., 2003). The primary
objective of this study was to determine the frequency of bacterial
isolates from the eyes of healthy horses and to investigate any
potential correlation between this frequency and the age or sex of the
horses. Additionally, the study aimed to assess the sensitivity of the
bacterial isolates. This study found that Bacillus cereus was the
most frequently isolated bacteria from the conjunctiva of healthy
horses, followed by Micrococcus luteus , Bacillus
licheniformis , Pasteurella multocida , Bacillus mutans ,Staphylococcus spp., and others. Gram-positive bacteria were the
most commonly found. In a study conducted by Zak et al, the majority of
the isolated bacteria consisted of gram-positive bacteria besides the
lack of significant effect of neither age nor sex on the frequency of
the isolated bacteria resulted the same as the current study(Zak et al.,
2018). Several previous studies have indicated that most frequent
bacteria species are gram-positive(Johns et al., 2011, Gemensky-Metzler
et al., 2005). Despite the similarities of the mentioned studies to the
current one, the major isolated species were different from each other.
As an assumption, this difference may be resulted by various climate and
housing conditions, including the ingredient of the feed. However, in a
study conducted by Johns et al, the effects of geographic location and
type of housing (either housing in the field or stable) on bacteria
isolation were not significant(Johns et al., 2011). It was also resulted
from this study that sex and age have no significant effect on the
frequency of bacteria isolation which is similar to the results of the
current study (Johns et al., 2011). One of the reasons for the high
frequency of bacterial flora in horse eyes is the mechanical
transmission of microorganisms by insects contacting eyes which can be
considered an important factor in determining the type of bacterial
population of the conjunctiva. In a study conducted by Butler et al,
isolated Staphylococcus sciuri from horse eyes was isolated from
Musca domestica fly as well. This result proves the correctness of the
aforementioned claim(Butler et al., 2010). Health condition is another
reason for the variety in the bacterial flora of eyes as indicated in
the current study that sensitivity to trimethoprim-sulfamethoxazole was
significantly higher in neutered horses compared with intact mares which
can be due to the better health conditions in housing neutered horses
resulting in the lower bacterial population of neutered horses (total of
22 isolated bacteria) compared with intact ones (total of 26 isolated
bacteria). Therefore, the lower the frequency of the isolated bacteria,
the lower the amount of sensitivity to antibiotics. Araghi-Sooreh et al.
(2013) in 2013 indicated 100% sensitivity of isolated bacteria to
ciprofloxacin and florfenicol as well as 100% sensitivity of
gram-negative bacteria to gentamycin. In the current study, 100% of
isolated bacteria were sensitive to gentamycin and neomycin. In another
study in Brazil, the bacterial flora of 100 healthy horses with no
clinical disorders was assessed. Like the current study, the majority of
isolated bacteria were gram-positive (65.5%). Sensitivity to
antibiotics was also examined and 94%, 85%, 81%, and 68% of isolated
bacteria were sensitive to ciprofloxacin, gentamycin, chloramphenicol,
and tobramycin, respectively(Ferreira et al., 2017). In a study
conducted by Hampson et al, bacteria and fungi of the normal flora of
eyes in 95 horses were evaluated and the most frequent isolated bacteria
were detected as gram-positive. Furthermore, most of the isolated
bacteria were sensitive to neomycin and florfenicol(Hampson et al.,
2019). In a study in Iran, Tamarzadeh et al studied bacterial flora of
the eyes in 50 healthy mules with 5-12 years old of age using swab
sample collection from conjunctiva as well as the sensitivity of the
isolated bacteria to different 12 antibiotics. 85% of the isolated
bacteria were gram-positive and the bacteria were mostly sensitive to
florfenicol (90.82%) followed by flumequine (70.64%) and gentamycin
(67.88%) (Tamarzadeh and Araghi-Sooreh, 2014).
In conclusion, this study aimed to evaluate the frequency of
the bacterial flora in the conjunctiva of horses with different sex and
age groups as well as their sensitivity to various antibiotics in order
to prevent any further bacterial resistance to antibiotics by
administration of antibiotics according to sex and age groups of the
horses in future. Results of the current study indicated that the
frequency of bacterial flora mainly depends on housing and management
conditions while it was not significantly correlated with age and sex.
Among 10 examined antibiotics, only sensitivity to ciprofloxacin and
enrofloxacin was correlated with age which was only significantly
different between age groups of 1-5 and 5-10 as well as 1-5 years old
and older than 10. Sensitivity to ciprofloxacin and enrofloxacin was
increased by age increment as no resistance to antibiotics was shown in
horses older than 10 years of old which may be related to more
administration of these drugs in young ages, and consequently altering
bacterial population which results in resistance of bacteria to the
antibiotics in younger horses. In addition to previous results, the
sensitivity of the isolated bacteria to trimethoprim-sulfamethoxazole in
intact mares was significantly more than in neutered horses which may be
due to the lower number of total isolated bacteria from neutered horses’
eyes (total number of 22) compared with intact mares (total number of
26) probably because of better care and health conditions in neutered
horses. It should be beard in mind that this result may be also related
to the lower number of studied neutered horses (table 1).