Malik et al.
Growth of the isolates, obtained from human diarrheic
Mean generation time of the isolates
cases, at 10°C with pH of 4.5
At 10 ° C, the mean generation time of the isolates at pH
Isolate S 9 : The initial bacterial count of the isolate was 6.3
values of 4.5, 5.5 and 6.5 was 44.23 ± 0.44, 15.51 ± 0.08
× 10 4 CFU/ml. Lag phase was of 4 days duration and log
and 10.23 ± 0.10 hrs, respectively, while at 30 ° C, the mean
phase lasted for 13 days. Maximum bacterial population
generation time of the isolates at pH values of 4.5, 5.5 and
of 9.2 × 10 6 CFU/ml was attained on day 17. Generation
6.5 was 126.10 ± 0.68, 59.96 ± 0.14 and 36.22 ± 0.07 min,
time for S 9 was 45.45 hrs.
respectively.At 4 ° C, none of the isolates grew at any given
pH value. The results are presented in Table. 3.
Isolate S 10 : The initial bacterial count of the isolate was 5.4
× 10 4 CFU/ml. Lag phase was of 4 days duration and log
It is not surprising that the growth and metabolism of
phase lasted for 13 days. Maximum bacterial population
micro-organisms are influenced by pH because acidity
of 9.3 × 10 6 CFU/ml was attained on day 17. Generation
or alkalinity of an environment has a profound effect on
time for S 10 was 43.47 hrs.
the activity and stability of macromolecules (Adams and
Moss, 2008). In our study no growth of the isolates could
Isolate S 11 : It had bacterial count of 6.6 × 10 4 CFU/ml on
day zero and attained maximum population of 9.6 × 10 6
be observed at the temperature of 4 ° C, the findings are
CFU/ml on day 17. The lag phase and log phase lasted for
more or less in corroboration with Serraino et al. (2012)
although they reported a decrease of S. typhimurium count
4 and 13 days respectively. Generation time for S 11 was
45.45 hrs.
in WBMC (Water buffalo mozzarella cheese) stored at
5 °C. The mean generation time of the isolates was 44.07
hrs at 10 0 C with pH of 4.5 while at 30 ° C with pH of 6.5,
Growth of Salmonella isolates at 4 ° C with pH of 6.5
the mean generation time of the isolates was 36 minutes.
None of the isolates showed growth during the stipulated
In a similar study, Ferreira and Lund, (1987) reported that
incubation time.
when S. typhimurium was incubated at 30 °C, growth was
initiated at a minimum pH of 3.8–4.0 in 1 or 2 day, at
Growth of Salmonella isolates at 4°C with pH of 5.5
20°C growth was initiated at a minimum pH of 3.8 – 4.0
in 3-5 d and at 10°C, incubation for >7 d was required
None of the isolates showed growth during the stipulated
before growth was detected. Similarly, Laub et al. ( 1989)
incubation time.
who studied the growth of Salmonella at pH 5.2 and 7.2,
reported significant increase in the generation time of
Growth of Salmonella isolates at 4°C with pH of 4.5
the organism viz., 26 minutes at pH 5.2 to 40 minutes
Growth of the isolates was not detected at the above
at pH 7.2. Lin et al. (1995) evaluated the growth of S.
mentioned temperature and pH.
typhimurium in pH adjusted buffered Luria- Bertani (LB)
broth and reported S. typhimurium to grow at pH 4.0 at
Table 3. Mean generation time of Salmonella at varying
37°C with generation time of about 2.5 hrs.
temperature and pH
The findings of the afore-mentioned workers agree with
Isolates (n=11)
Level of
our findings which show that as the temperature and
10°C
30°C
with varying pH
significance
pH were lowered, there was significant increase in the
44.23 ± 0.44
126.10 ±
pH 4.5 (n = 11)
* *
generation time of the organism.
hrs
0.68 mins
15.51 ± 0.08 59.96 ± 0.14
pH 5.5 (n = 11)
* *
REFERENCES
hrs
mins
10.23 ± 0.10 36.22 ± 0.07
Fehlhaber, K. and Kruger, G. 1998. The study of Salmonella
pH 6.5 (n = 11)
* *
hrs
mins
Enteritidis growth kinetics using rapid automated bacterial
impedence technique. J. Appl. Microbiol. , 84 : 945-949.
** shows significant difference in the generation times of the
Ferreira, M.A.S.S. and Lund, B. M. 1987. The influence of pH
isolates at pH 4.5, 5.5 and 6.5 at temperature of 10°C and 30°C,
and temperature on initiation of growth of Salmonella spp.
at P < 0.01 level of significance.
Lett. Appl. Microbiol. , 5 : 67-70.
92
Journal of Animal Research: v.5 n.1. April 2015