Human immunodeficiency virus (HIV) associated immunosuppression increases the vulnerability of patients to various infections [1]. As a result, Enterobacteriaceae infections are common and more likely to cause invasive conditions in HIV-infected patients than healthy individuals [3].
The overall rate of Enterobacteriaceae isolates from the various specimens in the current study was shown to be 46.15% (48/104) among HIV positive patients versus 27.47% (56/204) in HIV uninfected patients. HIV positive patients were 2.265 times more prone to Enterobacteriaceae infection than HIV-negative ones (OR: 2.265 (1.365-3.655) P=0.0014), highlighting the fact that a compromised immunity resulting from HIV infection hampers the defense against microbes. Our finding is in accordance with previous studies reporting that rates of Gram-negative bacterial enteric infections are at least 10-fold higher among HIV-infected adults than in the general population [4-7].
The tract of infection to be study and the corresponding sample collected also affect the rate of enteric bacterial isolates as it was shown in the present study that 47.91, 31.25, 12.5, 4.16 and 4.16% of these pathogens were isolated respectively from urine, vaginal swab, stool, wound swab and blood samples respectively.
Regarding the rate of Enterobacteriaceae isolates according to the collected specimen and HIV status, our finding showed that urine (47.91 vs 42.85%), vaginal exudates (31.25 vs 23.21%) and blood (4.16 vs 3.57%) samples were the most colonialized specimens among HIV infected persons compared to non-infected ones, suggesting that urogenital tract disorders and bacteraemia related to Enterobacteriaceae are common in HIV individual than gastrointestinal tract. This is true as it is reported that, among opportunistic infections, urinary tract infections accounts for 60% of AIDS defined illness [26].
The presence of bacteraemia among HIV infected individual compared to non-infected ones is not unexpected, since individuals with HIV infections are prone to salmonellosis and shigellosis which develops into bacteremia in more than 40 [27] and 50% [28] of cases respectively. Bloodstream infection (BSI) is a frequent complication found in HIV-infected patients and is usually associated with a poor prognosis, responsible for the immediate cause of death in up to 32% of HIV-infected patients [29].
Concerning gastrointestinal tract infections, Enterobacteriaceae are commensal enteric flora usually not pathogenic in healthy individual. However, in HIV infected individuals, these bacterial are pathogenic because of the immunological response repression at the mucosal level that prevent intestinal idiopathic defense mechanisms [30].
The rate of Enterobacteriaceae isolates in the present study from stool sample of HIV infected individuals was shown to be 12.5%. Previous studies reported similar rates of; 12.6% in southwest Ethiopia [31], 12.5% in Cambodia [32] and 14.5% in Peru [33]. However, rates reported in Uganda (19.2%) [34], in India (29%) [35], in Southwest Ethiopia (Jimma) (16%) [36] and South Africa (43.3%) [37] were higher than our findings. On the other hand, the current rate was higher than the rate of 8.3% reported among HIV-infected individuals from Arba Minch General Hospital, Southern Ethiopia [38]. The observed difference in the rates of Enterobacteriaceae isolated in stool sample could be attributed to differences in risk factors of the various populations. Since the probable source for most enteric infections is ingestion of contaminated food or water [4], factors like hand washing practice, contact with animals, consumption of raw food and others are indicated as potential factors for acquiring enteric bacterial infection [39].
After considering the colony morphology and biochemical characteristics, fourteen Enterobacteriaceae species were identified. Among the isolates, Escherichia coli was the most commonly identified, accounting for over 35.41%, followed by Klebsiella species (14.58%), Proteus and Serratia species (14.58%) among HIV positive patients. Our findings concerning the commonest of Escherichia species among the isolates is similar to previous studies. In fact it reported that Salmonella, Shigella, Campylobacter and Escherichia coli are the most common enteric bacterial pathogens in HIV-infected patients [40] and etiologic agents with potential cause of severe illness among them [30]. Our data also revealed that 4.16% of the overall Enterobacteriaceae isolates were Salmonella spp and that 66.66% of these isolates were from HIV positive patients. Our findings correlated with previous reports that individuals with HIV infections have a 20- to 100-fold higher risk of salmonellosis than healthy individuals [27]. The present rate of Salmonella infection (4.16%) is similar to that reported in Southern Ethiopia (5.1%) [31], but was higher than a finding in Peru (1%) [33], and Southern Ethiopia (2.8%) [38], but rather lower than a result from Uganda (8.1%) [34].
Previous studies reported very low rate of Shigella species in India (1%) [35] and Cambodia (1.3%) [32]. In the current study, no Shigella species was isolated among stool samples although using a specific medium for culture. In immuno-competent individuals, gastroenteritis with Shigella rarely develops into bacteremia, whereas up to 50% of AIDS patients with shigellosis become bacteremic [28]. This may be the reason of the absence of Shigella among our isolates since we did not culture blood in a specific medium for Shigella.
The absence of Campylobacter species or Clostridium difficile among the present enteric bacterial isolates is not unexpected, since we did not used specific culture medium for these species isolation.
The mean value of CD4 count among HIV positive patients with Enterobacteriaceae infection was whereas it was cells/mm3 among non-infected ones. This difference was significant (t= 6.015, p<0.0001).
The distribution of enteric bacterial infection rate in HIV-infected individuals was affected by their immunological status. The mean value of CD4 count among HIV positive patients with Enterobacteraceae infection was 260.3 ± 121.4 whereas it was 473.8 ± 118.4 cells/mm3 among non-infected ones, suggesting that HIV patients with low CD4 count are more prone to Enterobacteraceae infection. Moreover, the rate of Enterobacteraceae isolation according to CD4 range groups was higher in HIV-patients who had low CD4+ T-lymphocyte counts. In fact, 20.83% (10/48), 37.5% (18/48), 35.42% (17/48) and 6.25% (3/48) of Enterobacteriae isolated from HIV positive patients were respectively from patients with CD4 T lymphocyte range above 500, ]300-500], ]100-300] and < 100 cells/mm3. Such observations indicate that the rate of Enterobacteraceae infection among HIV positive patients increase when the CD4 level decrease and highlight the fact that HIV patients with low CD4 count are more prone to Enterobacteriaceae infection than uninfected ones. The present lower Enterobacteriaceae infection rate among CD4 group < 100 cells/mm3 may simply reflect the low number of species isolated from this group of patient since they were not representative in our sample population. Similar high enteric bacterial isolation rate (80%) in patients with CD4 T cell count less than 200 cells/mm3 has been documented [41]. Such results highlight the fact that the progression of HIV infection to AIDS, and that the incidence to opportunistic infections increases while CD4 count decreases [42, 43]. In contrast, no significant difference was noticed in the bacterial isolation rate according to CD4 T cell count among patients in Southern Ethiopia [31]. Also, a study carry out in England reveals that 65.6% of the isolates were recorded in patients with higher CD4 T cell count [30].
Escherichia coli was the species found at all CD4 range group with the highest proportion at CD4 up to 100 cells/mm3. Such observation justified the predominance of Escherichia coli among Enterobateriaceae isolates in HIV positive patients as mentioned above. The presence of Klebsiella pneumonia at CD4 range less than 100 cells/mm3 may explain the highest prevalence of respiratory tract infection among HIV patients at an advanced stage of HIV infection.
Resistant of enteric bacteria to common antibiotics reduce the efficacy of these drugs to treat these infections and increase the frequency of therapeutic failure. The situation can become alarming for the immune-compromised patients as HIV infected individuals, who are at risk of repeated infections. In the present study, resistance rate of 27.72 and 35.49% were detected respectively among isolates from HIV negative and positive patients. Similarly, previous studies revealing higher resistance rate to antimicrobials among enteric bacterial coming from HIV-patients has been documented [44, 45]. Long term exposure to antimicrobials in order to cure or to prevent opportunistic infections in HIV patients may lead to the emergence of multidrug-resistant bacteria [46]. In fact, co-trimoxazole is recommended to HIV adults and children born to HIV-infected women as prophylaxis measures against opportunistic infection [47]. The continuous exposure to this drug has result to the emergence of co-trimoxazole-resistant bacteria in HIV population and the therapeutic failure against bacterial infections.
β-lactam antibiotics such as penicillins, cephalosporins and carbapenems are the most commonly used antibacterial drugs. The predominant drug resistance mechanism against β-lactam antibiotics among Gram-negative bacteria is the production of β-lactamase enzymes. Most important β-lactamase enzymes are extended spectrum β-lactamases (ESBLs), AmpC β- lactamase (AmpC) and Metallo β-lactamase (MBL). In this study, bacterial isolates from HIV infected patients were highly resistant to cephalosporins (cefotaxim, ceftazidim, cefoxitin, cefuroxim) and lowly to cefuroxine/sulfobactam and piperacillin/tazobactam, characteristics which are specific to extended spectrum β-lactam antibiotics producing microorganisms. Few of them were also resistant to imipenem. Thus, the magnitude of extended-spectrum beta-lactamases (ESBLs) and carbapenemase production were evaluated among these isolates according to HIV status of the participants.
Our data showed that 25% (26/104), 21.15% (22/104) and 4.81% (5/104) of the isolated Enterobacteriaceae were found to be ESBL, AmpC and carbapenemase producing bacterial infection independent of the HIV status. The highest frequency of ESBL and AmpC production was observed among E. coli, followed by Enterobacterspp whereas carbapenemase producing Enterobacteriaceae were predominantly E. coli and Klebsiella pneumonia. The overall prevalence of ESBL, AmpC and carbapenemase producing Enterobacteria infection was 16.34, 12.5, and 4.81% respectively among HIV infected patients versus 8.62, 8.65 and 0% among HIV uninfected patients, suggesting that isolates coming from HIV infected patients are more prone to produce β-lactamase enzyme than those from uninfected ones (X2 18.32, p = 0.0055). Moreover, among the Enterobacteriaceae isolates from HIV infected patients, 35.42, 27.08 and 10.42% respectively were ESBL, AmpC and carbapenemase producing enteric bacterial infection. The current findings on the prevalence of extended spectrum β-lactamases producing Enterobacteria among HIV infected patients (35.42%) is comparable with studies from Ethiopia like Jimma (38.4%) [48], and Harar (33.3%) [49]. However this prevalence was higher compared with that documented in studies from others parts of Ethiopia (25%) [50], (21.4%) [51] and Saudi Arabia (22%) [52] and significantly higher with reports in the United States (8.6%) [53] and the United Kingdom (1%) [54]. On the other hand, it was lower than reports from different African countries such as Ghana (49.3%) [55], Addis Ababa (52%) [56] and Uganda (62%) [57]. The variation might be due to the difference in sampling population, the policy of antibiotics prescription, as well as socio-cultural and economic factors.
In Cameroon, few studies on the extent of E-ESBL circulating strains among the general population have been investigated but none among HIV infected patients. A ESBL carriage of 12% and 16% was reported among enteric bacteria isolates respectively in HIV uninfected patients in Yaounde and in the community of Ngaoundéré [59, 58]. Approximately 45% (45.3%) enteric bacteria produced ESBL was isolated from women with urinary tract infections in Yaounde-Cameroon prior to antibiotics use [60]. The higher prevalence of extended spectrum β-lactamases producing Enterobacteria of this study compared with the aforementioned reports may be due to the difference in sampling population. In fact, HIV patients are in high risk for ESBL carriage because they are commonly subjected to infections and hospitalization, and more likely to consume antimicrobial agents than HIV negative persons. This may also justify the present high prevalence of AmpC (27.08%) and carbapenemase (10.42%) producing Enterobacteria infection among HIV-patients compared to uninfected persons. Carbapenems are antibiotics usually used to treat extended-spectrum and AmpC β-lactamases producing pathogens [61]. However, the spread of enzymes that break down these antibiotics has been reported [62]. This situation may further compromise therapeutic alternatives using every beta-lactam antibiotics but also those using non-beta-lactam as a connection with resistance determinants which can easily disseminated, since carbapenemase mediated resistance are usually transposon- and/or integron-encoded determinants [63].